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The economic potential of El-Gedida glauconite deposits, El-Bahariya Oasis, Western Desert, Egypt
Journal of African Earth Sciences 120 (2016) 186e197
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Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci
The economic potential of El-Gedida glauconite deposits, El-Bahariya Oasis, Western Desert, Egypt Galal El-Habaak a, Mohamed Askalany b, Mohamed Faraghaly c, Mahmoud Abdel-Hakeem b, * a b c
Department of Geology, Faculty of Science, Assiut University, Egypt Department of Geology, Faculty of Science, South Valley University, Egypt Department of Mining and Petroleum Engineering, Faculty of Engineering, El-Azhar University, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 December 2015 Received in revised form 19 April 2016 Accepted 7 May 2016 Available online 9 May 2016
The mining work at El-Gedida iron mine, El-Bahariya Oasis, in the Western Desert of Egypt extracts commercial iron ore deposits without attention paid to the large glauconite deposits overlying these iron ore deposits. For this reason, the present paper aims at evaluating and attracting the attention to these glauconite deposits as alternative potassium fertilizers. The study was achieved by investigating mineralogical, physical and chemical properties of the green deposits. Mineralogical and physical properties involved the determination of glauconite pellets content in different grain size fractions relative to impurities and the analysis of the percentage of clay matrix and grain size distribution. Different pre-treatment strategies and methods including comminution, sieving, magnetic separation, and X-ray diffraction were used for investigating those mineralogical and physical properties. On the other hand, chemical analyses included potassium content, heavy metal concentrations, and pH and salinity measurements. The major elements and trace elements were measured using ICP-OES and the pH was measured using a pH conductometer. Moreover, this study investigated the nature of grain boundaries and the effect of sieving on glauconite beneficiation. Results of this study suggest that ElGedida glauconite deposits are mineralogically, physically and chemically suitable for exploitation and can be beneficiated for use as an alternative potassium fertilizer. © 2016 Elsevier Ltd. All rights reserved.
Keywords: El-Gedida iron mine Glauconite deposits Physical properties Chemical properties Potassium fertilizer
1. Introduction Glauconite is defined as a green, iron-potassium-rich micaceous mineral, with 2:1 dioctahedral illite-like structure. It is characterized by inter-stratification of nonexpandable (10 Å) and expandable Fe-smectite layers. Glauconite-smectite (sensu lato) contains more than 50% expanding layers, but glauconite (sensu strict) contains less than 10% expanding layers (McRae, 1972; Odin, 1988). Glauconite deposits have been used as natural potassium fertilizers, especially in forage crops, for over 100 years (Dooley, 2006). The commercial value of glauconite is attributed to its potassium content. Beside, nitrogen and phosphorous, potassium is an important macronutrient essential for osmotic regulation and plant growth (Ryoung et al., 2006). The global demand for potassiumbearing fertilizers continuously increases and is expected to grow
* Corresponding author. E-mail address: [email protected] (M. Abdel-Hakeem). http://dx.doi.org/10.1016/j.jafrearsci.2016.05.007 1464-343X/© 2016 Elsevier Ltd. All rights reserved.
annually at 3% from 2012 to 2017, reaching 37.4 Mt K2O in 2017 (Heffer and Prudhomme, 2013). Glauconite deposits have been studied in many countries for use as an alternative to potassium salt fertilizers. Franzosi et al. (2014) magnetically treated and evaluated green sands from the Salamanca formation, Patagonia, Argentina, as a substitution potassium fertilizer, with potassium contents around 4.05% K2O. The authors found that the fertilization effect of green sands was similar to that of KCl, and they also referred to the low cost of treatment and production of these deposits compared to KCl mining. According to Levchenko et al. (2008), glauconite in Russia has been reported from glauconite-bearing deposits: the Koporskoe and Karinskoe deposits with reserves of about 100 million tons. The most important use of glauconite is as a chemical fertilizer and soil conditioner for agricultural and land reclamation purposes. The application of glauconite as fertilizer owes to its high content of potassium (5e9.5%), phosphorous and micro-nutrients (such as Mn, Cu, Co, Ni, etc.).
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In New Jersey, Delaware, and Maryland Districts (in the USA) the most significant glauconitic green sands lie at the Mid-Atlantic Coastal plains, in the Upper Cretaceous and Early Palaeocene formations. The glauconitic sediments are used for fertilization and soil enhancement (Heckman and Tedrow, 2004). Karimi et al. (2011) tested glauconitic sandstone from Maraveh, northeast Iran as a potassium fertilizer for olive plants. The authors carried out lixiviation tests of the ground deposit (250 mm) in water and various types of 1 M acids (phosphoric and hydrochloric acids) and measured the potassium contents in the extractant solutions. They found that the potassium content extracted in water was 23 mg Kþ kg1 of sandstone powder while that released in acid solutions was 2200 mg Kþ kg1 of sandstone powder. The authors also suggested the possibility of applying green sands, with 2.24 wt % K2O as source of soil soluble potassium for a long time. In Egypt, glauconite deposits have been reported from El-Gedida iron mine, El-Bahariya Oasis, in the Western Desert. These deposits belong to the Bartonian age and occur as a green sands cover overlying the Lutetian iron ore, of about 25 m thickness at the eastern and western wadis of the mining area. The glauconite sediments have been studied by many authors (El-Sharkawi and Khalil, 1977; Mesaed and Surour, 1999; Hassan et al., 2011; Baioumy and Boulis, 2012) in terms of their petrology, mineralogy and geochemistry. The deposits are mined as overburden and are removed to reach the commercial iron ore deposit. The main objective of this paper is to add value to El-Gedida glauconites by performing mineralogical, physical and chemical assessments of the deposits for use as an alternative to potassium salt fertilizers. 2. Geological setting El-Gedida glauconite deposits are located at the eastern and western wadis of El-Gedida mining area as a condensed section that reaches a thickness of up to 25 m above the commercial Middle Eocene ironstone deposit (Hassan and Baioumy, 2007). According to El Aref et al. (1999) and Mesaed and Surour (1999) the glauconite deposits belong to the Upper Eocene Hamra Formation divided into two units. The lower unit consists of highly fossiliferous glauconitic mudstone and sandstone with marl intercalations while the upper unit is composed of well-bedded green sand, glauconitic mudstone and sandstone with intercalations of lateritic iron bands. The glauconite deposits are equivalent to the upper unit of the Upper Eocene Hamra Formation. The studied glauconites are unconformably covered by fluvial deposits of the Qatrani Formation (Oligocene) and overly the carbonates of the Naqb Formation (Middle Eocene). Depending on stratigraphy, mineralogy and geochemistry, El-Habaak et al. (2016) proved that the Upper Eocene glauconites were deposited in a shallow marine environment under regressive conditions at 100 m depth. 3. Materials and methods The rock samples investigated in this study were collected from sandy glauconite deposits at the eastern and western wadis of ElGedida mine, El-Bahariya Oasis, in the Western Desert (Figs. 1 and 2). For the petrographic characterization of the samples, thin sections were prepared and examined using the conventional optical microscope attached to a Leica camera. The acquired images were processed using the Image Analyzer Software for investigating the nature of optical appearance of the glauconite grains. To achieve this, the image processing techniques of linear stretching and edge detection were applied. The bulk mineralogy of these deposits was determined using X-ray diffractometer (X’Pert PROPAN). The contents of glauconite pellets were determined through
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three steps. The first step involved a size reduction of the two representative samples (100 kg per each sample) up to -1 mm by using a jaw crusher and a rod mill in a closed circuit. Secondly, each 100 kg representative sample was subjected to coning and quartering processes. Afterwards, a representative sample (50 g) of the ground ore was beneficiated using a Frantz isodynamic magnetic separator adjusted to a current intensity of 0.7 Am, 20 forward slope, 15 side slope, and feed rate of 10 g/minute. The magnetic and tailing fractions were mineralogically examined using XRD. The principal aim of separation was to investigate the amounts of glauconite pellets compared to that of impurities. The percentage of clay matrix and the grain size of glauconite were determined by a dry sieving of the ground ore, resulting in five size fractions (1þ500, 500 þ 250, 250 þ 125, 125 þ 75 and 75 mm). The glauconite deposits were chemically studied to determine the contents of macronutrients and heavy metals using ICP-OES at Acme laboratory, Canada. The influence of sieving on the beneficiation of glauconite, a representative sample of each size fraction was mineralogically and chemically analysed using XRD and ICPOES, respectively. Measuring the pH of glauconite was performed using multiparameter pH meter (WTW Multi 340i), at the ratio of 1:5 glauconite/water mixture, according to Kalra (1995). For each glauconite sample, a 10 g portion was weighed and dried at 60 C for 1 h. The dried sample was put into a 100 ml beaker and 50 ml of distilled water was added. The mixture was stirred for 1 h and allowed to stand for 30 min. After the calibration of pH meter using two buffer solutions of pH 7 and 4.01, the pH was measured at 25 C. For measuring salinity of the glauconite deposits, another glass electrode was used. The procedure for calibration was performed by immersing the conductometer electrode into a standard solution of 0.01 mol/l KCl. 4. Results and discussion 4.1. Microscopic characterization The studied glauconite deposit is composed mainly of green pellets with minor amounts of quartz, calcite, halloysite and iron oxyhydroxides set in a matrix that consists of a greenish (glauconitic) mud (Fig. 3a). Glauconite occurs as green, brownish green and yellowish green pellets ranging in diameter from 100 to 500 mm, thus these pellets are moderate to well sorted. Originally, the glauconite pellets developed in specific micro-environments such as faecal pellets and/or in bioclasts by increasing the contents of Fe and K during maturation from smectitic glauconite to glauconitic mica, but the alteration and extensive weathering of the pellets result in oxidation of the divalent Fe and depletion of K forming brown pellets that contain nanometric inclusions of Feoxyhydroxides (Pestitschek et al., 2012). The oval, sub-oval, rounded to subrounded glauconite grains detected contain random microcrystalline internal structures that occasionally are fractured (Fig. 3b). The cracks are interpreted as a result of expansion related to the differential mineral growth in the pellets (Odin and Matter, 1981). As illustrated in Fig. 3c some fractured pellets are filled with a greenish glauconitic mud generated by the destabilization of the glauconite pellets (Meunier, 2004). The pellets have experienced three stages of development: (1) initial pellet formation, (2) pellet fracturing and (3) infilling of pellet cracks with a glauconitic mud. Quartz occurs as angular to sub angular detrital grains that are 100e250 mm in diameter, associated with glauconite pellets. White halloysite vienlets cutting through the clayey matrix were detected (Fig. 3d). Botryoidal masses composed of sparry calcite occur as independent aggregates or as vienlets replacing the glauconitic
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Fig. 1. Geological map of the Bahariya Oasis, Western Desert, Egypt, with the location of glauconite sample illustrated by the Google earth image of El-Gedida mine.
Fig. 2. Field photos showing glauconite deposits in the eastern wadi (a) and western wadi (b).
clayey matrix. The replacement reactions widen the vienlets, resulting in non-matching walls and relicts of clayey matrix (Fig. 3e & f). Glauconite grains are also replaced by alunite (white in colour) occurring along fractures and grain boundaries (Fig. 3g & h). Halloysite and alunite are alteration products of the glauconites under humid conditions prevailing at El-Bahariya Oasis during the Late Eocene, as discussed by Hassan and Baioumy (2007). The optical microscope also provides valuable data related to the nature of contacts between various mineral grains, and hence, the extent of liberation of valuables from gangue minerals is expected before the comminution step (Misra et al., 2004). In the El-Gedida glauconites, the grain contacts between glauconite and quartz (the main gangue mineral) are classified as rectilinear and curved
(Fig. 4). Amstutz and Giger (1972) and Petruk (2000) classified the textures of ore minerals depending on the nature of the interlock between mineral grains. They suggested that the straight, rectilinear or curving contacts are characterized by simple locking and easy liberation. The nature of contacts between glauconite and quartz grains has a bearing on the ease of liberation of glauconite from quartz.
4.2. Mineralogical and physical properties The mineralogical analysis of glauconite samples collected from the eastern and western wadis are composed of glauconite with gangue minerals such as quartz, alunite, halloysite, calcite, hematite
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Fig. 3. Oval to sub-oval, green, yellowish green and brownish green glauconite pellets (Gt) in association with few amount of detrital quartz (Qt) set in a greenish glauconitic mud (Gm), as shown in (a). Also, some pellets are highly cracked with empty fractures (b) and filled one by a greenish glauconitic mud (c). Moreover, vienlets of halloysite (d) and calcite (e PPL and f XPL) invade and replace the glauconite grains and clay matrix consisting of illite-smectite mixed layer (IeS). Furthermore, glauconite is replaced by alunite (white spots) along fractures, as exposed in g (PPL) and h (XPL). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
and feldspar (Fig. 5). Quartz is the most predominant gangue
mineral detected by XRD. Calcite, feldspar, hematite and goethite
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Fig. 4. Sequential steps of edge detection between glauconite (green in colour) and quartz (colourless) start with noisy original image (a) transformed into linear stretched image (b) for which the edge detection was performed, resulting in clarifying straight and curved boundaries between the two mineral particles (c). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. XRD patterns of the eastern and western wadis glauconite, (a) and (b) respectively, showing the predominant peaks of glauconite (Gt) with associated gangue minerals including quartz (Qt), hematite (He), alunite (Al), halloysite (Ha), calcite (Ca) and feldspar (Fs).
minerals are the second common detrital constituents after quartz. On the other hand, the presence of alunite, halloysite and hematite minerals is attributed to extensive weathering of the glauconite
deposits. During the Late Eocene, humid conditions prevailed at ElBahariya Oasis under which the glauconite deposits were subjected to chemical weathering, resulting in the liberation of silica,
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aluminium and potassium ions. Under the closed-system conditions the ions reacted to form halloysite and alunite (El-Sharkawi and Khalil, 1977; Baioumy and Hassan, 2004; Hassan and Baioumy, 2007). The mineralogical investigation of the products of magnetic separation indicates that the magnetic fraction consists of glauconite with a trace amount of hematite, while the non-magnetic fraction comprises the other gangue minerals (Fig. 6). Weighing the magnetic and non-magnetic fractions reveals that the percentage of glauconite grains in the studied deposit represents about 97.81 wt % and 98.32 wt % compared to the amount of impurities reported at 2.19 wt % and 1.68 wt % for the eastern and western wadis glauconites, respectively. On the other hand, the clay matrix is included in the pan fraction (75 mm). The pan fraction represents about 2.57 wt % of the representative sample obtained from the eastern wadi glauconite and about 2.20 wt % of the representative sample from the western wadi glauconite. The results of sieving are listed in Tables 1 and 2 and show that the samples are represented by five size fractions (1þ500, 500 þ 250, 250 þ 125, 125 þ 75 and 75 mm) among which the 250 þ 125 mm fraction characterizes 81.74 wt % and 73.94 wt % of deposits in the eastern and western wadis, respectively (Fig. 7a). The fractions are calculated as the retained fractions on a 125 mm
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Table 1 Distributions of wt% and cumulative wt% of the eastern Wadi glauconite. Particle size, mm
Weight, % (retained)
Cumulative weight, % (retained)
1þ500 500þ250 250þ125 125þ75 75
5.02 7.30 81.74 3.37 2.57
5.02 12.32 92.06 97.43 100
Table 2 Distributions of wt% and cumulative wt% of the western Wadi glauconite. Particle size, mm
Weight, % (retained)
Cumulative weight, % (retained)
1þ500 500þ250 250þ125 125þ75 75
3.94 8.80 73.94 11.12 2.20
3.94 12.74 81.68 97.8 100
sieve. In addition, the d50 (coarse fraction) has been determined using the cumulative wt % curve of the sieved glauconite samples at the 250 þ 125 mm fraction (Fig. 7b). In order for the glauconite deposits to be of an economic value
Fig. 6. XRD patterns of magnetic and non-magnetic fractions extracted from glauconite samples. It is clear that the magnetic fractions of the eastern Wadi sample (a) and that of the western Wadi sample (c) are dominated by glauconite (Gt) with a trace amount of hematite (H), on the other hand, the non-magnetic fractions of the eastern Wadi glauconite (b) and that of the western Wadi glauconite (d) are mainly composed of quartz (Qt), alunite (Al), halloysite (Ha), calcite (Ca) and feldspar (F).
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Fig. 7. Distributions of wt % and cumulative wt % of the studied samples showing the majority of wt % is concentrated at þ250125 mm fraction (a) and the d50 of the sieved samples is also located at the same size fraction (b).
for fertilizer purposes, they must contain at least 90% of glauconite pellets at size fraction 250 þ 88 mm, with a percentage of clay matrixes ranging from 2 wt % to 3 wt % of the total weight as suggested by Dooley (2006). According to Dooley’s standard based on the physical properties of glauconites, the El-Gedida glauconite deposits are appropriate to be exploited as a potassium fertilizer. It is known that glauconites outperform K salt fertilizers in enhancing soil texture, porosity and permeability due to their uniform grain size (Indian Minerals Yearbook 2011, 2012). Green sands are characterized by high cation exchange capacity which improves the ability of soil to store exchangeable macro-nutrients (e.g. K, Ca and Mg). The micro pores of glauconite pellets can improve the water retaining and absorbing property of soils (Heckman and Tedrow, 2004). The effect of sieving glauconite for beneficiation and the mineralogical analysis of each sieve fraction (Figs. 8 and 9) shows that most of the gangue minerals (quartz, alunite, halloysite, feldspar, and calcite) are concentrated in the 125 þ 75 mm and 75 mm fractions. The e concentration of quartz, feldspar, and calcite in the finer fractions is ascribed to the size difference among these minerals and glauconite pellets. Because these minerals are harder than glauconite as discussed by Korbel and Novak (2001), the beneficiation of El-Gedida glauconites require only sieving to
obtain the proper size fraction (250 þ 125 mm) containing the appropriate potassium content for fertilizing purposes.
4.3. Chemical properties The major element analysis of El-Gedida glauconite reveals that the eastern wadi glauconites contain 6.75 wt % K2O and 52.10 wt % SiO2, while the western wadi deposit contains 7.30 wt % K2O and 50.89 wt % SiO2. Glauconite deposits must contain at least 2.27 wt % to 4.05 wt % K2O to be an acceptable potassium fertilizer (Franzosi et al., 2014; Heckman and Tedrow, 2004; Karimi et al., 2011). In addition, El-Gedida glauconites show similarities in chemical composition to the commercial New Jersey (USA) glauconite deposits, as shown in Table 3. This suggests that El-Gedida glauconite deposits contain required amounts of potassium for use in land reclamation and cultivation purposes. The chemical analysis of the size fractions are listed in Tables 4 and 5. The potassium contents increase toward the coarser size fraction (þ1000500 mm), with strong positive correlations for the eastern wadi (r ¼ 0.66) and the western wadi (r ¼ 0.75) (Fig. 10a). In contrast, the silica contents decreases toward the coarser fraction (þ1000500 mm), with strong negative correlations for the eastern wadi (r ¼ 0.72) and the western wadi (r ¼ 0.78) (Fig. 10b).
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Fig. 8. XRD patterns of five size fractions (1þ500,500 þ 250, 250 þ 125, 125 þ 75 and 75 mm) ordered as (a, b, c, d, e) obtained from the eastern Wadi glauconite showing the concentration of quartz (Qt), alunite (Al), halloysite (Ha), calcite (Ca) and feldspar (F) in the finer fractions (d & e).
Furthermore, the potassium contents reach up to 6.9 3 wt % K2O for the eastern wadi samples and up to 7.38 wt % K2O for the western wadi samples at the size fraction 250 þ 125 mm. Glauconite deposits have been used for more than 100 years as a source of fine potash owing to high contents of K (up to 8 wt % K2O) that is an essential macronutrient for healthy growth of plants (Indian Minerals Yearbook 2011; 2012). The low reactivity of glauconite with water compared to commercial K salt fertilizers (e.g. KCl and K2SO4). The liberation of K from the glauconite lattice may take a long time to produce sufficient K amounts for plant growth. Martin and Gershuny (1992) showed that the K release is improved by incorporating the glauconite sands with compost.
Majumder et al. (1995) converted the K2O present in a glauconitic sandstone sample into leachable KCl by roasting the sample with CaCl2. The thermal treatment of glauconite was carried out at conditions that included a roasting temperature of 750 Ce850 C, roasting time of 60 min, mixing ratio of (CaCl2 to glauconitic sandstone) 0.8 and size fraction 240 þ 90.5 mm. Although the solubility of chemical fertilizers (e.g. NaNO3, NH4NO3, KCl and K2SO4) is higher than that of glauconite, the prolonged use of these fertilizers results in the deterioration of the soil structure negatively affecting the quality and efficiency of field crop production (Savci, 2012). K-bearing Fe-smectite is more reactive than glauconite (Baldermann et al., 2013), therefore the percentage of Fe-
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Fig. 9. XRD patterns of five size fractions (1þ500, 500 þ 250, 250 þ 125, 125 þ 75 and 75 mm) ordered as (a, b, c, d, e) obtained from the western Wadi glauconite showing the concentration of quartz (Qt), alunite (Al), halloysite (Ha), calcite (Ca) and feldspar (F) in the finer fractions (d & e).
smectite present in the interstratified structure consisting of glauconite-smectite may affect the K availability. The percentage of K-bearing Fe-smectite in El-Gedida deposit was calculated by substituting K2O wt % determined by ICP-OES into the equation of Compton (1989): % Fe-smectite ¼ 7.79*K2O þ 68.7. The results show that glauconites of eastern and western wadis contain 16.11 wt % and 11.83 wt % expendables, respectively. Depending on
K contents, the studied glauconites are classified as high mature and evolved glauconites (Odin and Fullagar, 1989). The maturation and K content of glauconite is inversely correlated with the content of expendables (%) incorporated in the interstratified structure of glauconite (Odin and Matter, 1981). Micronutrients (heavy metals) also have a role in the metabolism activity, protein synthesis and nitrogen fixation for normal
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Table 3 Comparison between the chemical composition of El-Gedida glauconite and that of New Jersey glauconite. Oxides (100%)
Glauconite of eastern Wadi
Glauconite of western Wadi
New Jersey glauconite
SiO2 TiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O MnO P2O5 SO3 L.O.I. Total
52.10 0.13 5.99 22.23 3.75 0.31 0.10 6.75 0.02 0.14 0.21 8.3 99.90
50.89 0.04 5.88 22.99 4.34 0.20 0.05 7.30 0.08 0.07 e 8.3 99.89
51.83 e 6.23 20.08 3.66 0.52 0.76 6.60 e 0.31 e 10.34 100.33
Table 4 Contents potassium and silica of the studied size fractions extracted from the eastern Wadi glauconite illustrating the increase of silica content toward the finer fractions and vice versa for potassium content. Particle size, mm
K2O %
SiO2 %
K2O % (cumulative)
SiO2% (cumulative)
1þ500 500þ250 250þ125 125þ75 75
6.71 7.15 6.93 5.17 4.10
51.10 50.36 51.55 60.69 65.34
6.71 6.97 6.93 6.87 6.8
51.10 50.66 51.43 51.75 52.10
Table 5 Contents potassium and silica of the studied size fractions extracted from the western Wadi glauconite illustrating the increase of silica content toward the finer fractions and vice versa for potassium content. Particle size, mm
K2O %
SiO2 %
K2O % (cumulative)
SiO2% (cumulative)
1þ500 500þ250 250þ125 125þ75 75
7.61 7.78 7.38 6.61 5.98
49.23 48.83 50.59 54.50 56.39
7.61 7.72 7.43 7.33 7.30
49.23 48.95 50.34 50.82 50.94
phyto-sanitary effect on pathogens (Brown, 2007). Molybdenum has a crucial role in nitrogen metabolism of plants because of its involvement in nitrate reduction and transport of N compounds in plants and N2 fixation (Hamlin, 2007). Aside from their contribution to increase the field crop productivity, the concentrations and accumulation of heavy metals in soils can lead to toxic effects on the human food chain. For example, the human consumption of heavy metal-contaminated food can lead to intrauterine growth retardation, a decrease in immunological defences of body and a prevalence of upper gastrointestinal cancer (Falls, 2001; Orisakwe et al., 2012). Chemical fertilizers are implicated in raising the concentration of heavy metals in soils and are a potential source of radionuclides in the food chain (Savci, 2012). The contents of heavy metals in fertilizers must be monitored for consistency with the tolerant levels safe for healthy human food chain. In this respect the concentrations of heavy metals (Mo, Cu, Pb, Zn, Ni, As, Cd, Co and Cr) in El-Gedida glauconites have been considered in this study. By comparing the heavy metal contents of El-Gedida glauconites to standards issued by the Canadian Food Inspection Agency (1997), El-Gedida glauconites contain concentrations of heavy metals lower than the tolerant
Fig. 10. Plot K2O and SiO2 vs. the obtained size fractions showing an increase in the potassium content toward the coarse fraction (a) and vice versa for the silica content (b).
plant growth. For instance, zinc is predominantly absorbed by plants as a divalent cation (Zn2þ) and has a structural and catalytic role in enzyme reactions owing to its strong tendency to form tetrahedral complexes with N-, O- and S-legands (Vallee and Auld, 1990). Nickel contributes to the growth of nitrogen fixing species and enhances plant resistance to disease resistance due to its direct
levels as shown in Table 6. Therefore, exploiting these deposits as fertilizers or agricultural soils will not result in excessive accumulation of heavy metals in soils or food products and thus toxicity problems occurring at high levels of heavy elements are avoided. Changes in the pH value of soil solutions associated with using fertilizers, i.e. KCl, K2SO4, KNO3, can negatively affect the soil
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Table 6 Comparison between the heavy metal contents of El-Gedida glauconite and that reported by the Canadian Food Inspection Agency (CFIA, 1997). Heavy metal content (ppm)
Mo
Cu
Pb
Zn
Ni
As
Cd
Co
Cr
Eastern Wadi glauconite Western Wadi glauconite CFIA
<0.1 <0.1 5
3.7 2.4 400
2.0 0.3 150
86 208 700
15.4 30.7 62
2.4 2.2 13
<0.1 <0.1 3
25.8 28.0 34
110 130 210
Table 7 Ph and salinity degree of glauconite deposits at the eastern and western Wadis. Glauconite sample
Glauconite of eastern Wadi
Glauconite of western Wadi
pH value Salinity value (d S m1)
6.71 0.056
7.59 0.128
fertility and plant growth. The pH controls the availability of nutrients present in soil and soil solutions. The continued use of acidforming nitrogen fertilizers increases soil acidity while high concentrations of Na and K salt fertilizers increase soil pH (Arsova, 1999; Savci, 2012). As illustrated in Table 7, a slightly acidic behaviour is noticed for glauconite deposits from the eastern wadi, while those in the western wadi are characterized by slightly basic behaviour. The pH values of these glauconites are consistent with pH conditions by most plants ranging from a pH of 5.5e7 (Kidd and Proctor, 2001). Some fertilizers can contribute to increase the soil salinization that affects the root growth and photosynthesis of plants (Jouyban, 2012). As shown in Table 7 the salinity measurements of El-Gedida glauconites are lower than that reported by Esmaili et al. (2008) for nitrogen fertilizers. The authors found that applying nitrogen fertilizers can increase the salinity of soils up to 12 ds/m. The degree of salinity increase using El-Gedida glauconites is in accordance with Franzosi et al. (2014) on the advantages of low salinity green sands compared to other chemical potassium fertilizers (e.g. KCl). 5. Conclusions i. El-Gedida glauconite deposits are characterized by rectilinear and curved contacts between glauconite and quartz grains, therefore, the liberation and separation of the green sand grain fraction is expected to be easy during the comminution step. ii. As a potassium fertilizer, El-Gedida glauconite deposits are characterized by 97.81 wt % to 98.32 wt % glauconite pellets and impurities that range from 2.19 wt % to 1.68 wt %. Moreover, the sieve analysis of ground glauconites resulted in five size fractions (þ100e500, þ500e250, þ250e125, þ125e75 and 75 mm) among which the following fraction was suitable as fertilizer (þ250125 mm) representing 81.74 wt % to 73.94 wt % of representative samples obtained from the eastern and western wadis glauconites, respectively. The clay matrix occurs in the 75 mm fraction occupying 2.57 wt % to 2.20 wt % of the studied glauconite samples. iii. Chemically, El-Gedida glauconite deposits are appropriate to be exploited as alternative potassium fertilizers as they have potassium contents ranging from 6.75 wt % to 7.30 wt % K2O at the optimum size fraction (þ250125 mm). iv. Results of sieving glauconite for beneficiation, chemical and mineralogical analysis of each size fraction revealed that the sieving concentrates most impurities into the finer size fractions (þ125e75 & 75 mm). v. The heavy metal contents of El-Gedida glauconites are below the guideline limits issued by the Canadian Food Inspection
Agency (1997) for fertilizers and composites, and hence the toxic effects of these metals in El-Gedida glauconites are negligible. vi. The evaluation of pH and salinity of El-Gedida glauconite deposits indicates that exploiting these deposits for agricultural purposes will protect the cultivated soils from acidification and salinization that affect the availability of nutrients required for plant growth. Acknowledgements Authors are highly grateful to Dr. M. Mansour, the Chairman of El-Bahariya Oasis Sector, Egyptian Iron & Steel Co. and Mr. A. Abbas, the Manager of Laboratories of El-Bahariya Oasis Sector, for their help during the fieldwork. Also, this work would not have been possible without the help of Prof. Vesnica Garasi c, the Head of Department of Mineralogy, Petrology and Mineral Resources, Faculty of Mining, Geology and Petroleum Engineering, Zagreb University, Croatia. The authors acknowledge the reviewers of the Journal of African Earth Sciences for their great efforts in the revision of manuscript to be in the perfect form. References Amstutz, G.C., Giger, H., 1972. Stereological methods applied to mineralogy, petrology, mineral deposits and ceramics. J. Microsc. 95, 145e157. Arsova, A., 1999. Effect of fertilizer application and soil pH on the acidic and sorption properties of maize leaves and stems. Bulg. J. Plant Phsicololgy 21, 52e57. Baioumy, H.M., Boulis, S.N., 2012. Glauconites from the Bahariya Oasis: an evidence for Cenomanian marine transgression in Egypt. J. Afr. Earth Sci. 70, 1e7. Baioumy, H.M., Hassan, M.S., 2004. Authigenic halloysite from El-Gideda iron ore, Bahria Oasis, Egypt: characterization and origin. Clay Miner. 39, 207e217. Baldermann, A., Warr, L.N., Grathoff, G.H., Dietzel, M., 2013. The rate and mechanism of deep-sea glauconite formation at the Ivory Coast-Ghana Marginal Ridge. Clays Clay Minerals 61, 258e276. Brown, P.H., 2007. Nickel. In: Barker, A.V., Pilbeam, D.J. (Eds.), Handbook of Plant Nutrition. Taylor & Francis Group (CRC), New York, pp. 397e400. Canadian Food Inspection Agency Standards for Metals in Fertilizers and Supplements. 1997; Trade MemorandumT-4e93.[2015-09-07]. http://www. inspection.gc.ca/plants/fertilizers/trade-memoranda/t-493/eng/ 1305611387327/1305611547479. Compton, M.S., 1989. Morphology and geochemistry of glauconite from the TeKuiti Group, South Auckland Region, New Zealand. University of Waikato, Hamilton, New Zealand, pp. 64e69 (Master’s thesis). Dooley, J.H., 2006. Glauconite. In: Koger, J., Trivedi, N., Barrer, J., Krukowsky, N. (Eds.), Industrial Minerals and Rocks: Commodities Market and Uses. Society for Mining, Metallurgy and Exploration, Littleton, CO, pp. 493e495. El Aref, M.M., El-Sharkawi, M.A., Khalil, M.A., 1999. Geology and genesis of the stratabound to strataform Cretaceous, Eocene iron ore deposits of El-Bahariya region, Western Desert, Egypt. The 4th International Conference on Geology of the Arab World, pp. 450e475. El-Habaak, G.H., Askalany, M.S., Farghaly, M.G., Abdel-Hakeem, M.S., 2016. Upper Eocene glauconites from the Bahariya depression: an evidence for the marine regression in Egypt. J. Afr. Earth Sci. 117, 1e11. El-Sharkawi, M.A., Khalil, M.A., 1977. Glauconite, a possible source of iron for El Gedida iron ore deposits, Bahariya Oasis, Egypt. Egypt. J. Geol. 21, 116e122.
G. El-Habaak et al. / Journal of African Earth Sciences 120 (2016) 186e197 Esmaili, E., Kapourchal, S.A., Malakouti, M.J., Homaee, M., 2008. Interactive effect of salinity and two nitrogen fertilizers on growth and composition of sorghum. Plant Soil Environ. 12, 537e546. Falls, J.H., 2001. Metals in fertilizers and some pitfalls to avoid. In: The Phosphate Regional Conference in Lakeland, Florida, pp. 50e61. Franzosi, C., Castro, L.N., Celeda, A.M., 2014. Technical evaluation of Glauconies as alternative potassium fertilizer from the Salamanca formation, Patagonia, Southwest Argentina. Nat. Resour. Res. 23, 311e320. Hamlin, R.L., 2007. Molybdenum. In: Barker, A.V., Pilbeam, D.J. (Eds.), Handbook of Plant Nutrition. Taylor & Francis Group (CRC), New York, pp. 376e378. Hassan, M., Baioumy, H., 2007. Characterization and origin of alunite in the ElGedida iron mine (Egypt). Period. Mineral. 76, 11e24. Hassan, M., Sabah, N., Mervat, S., 2011. Occurrences and petrographical variations among the glauconite deposits from Egypt. In: 10th International Congress for Applied Mineralogy (ICAM), Berlin Heidelberg, pp. 39e47. Heffer, P., Prudhomme, M., 2013. Fertilizer outlook 2013e2017. In: 81st IFA Annual Conference, Chicago, U.S.A, pp. 1e6. Heckman, J.R., Tedrow, J.C.F., 2004. Green sand as a soil Amendment. Better Crops 88, 1e17. Indian Minerals Yearbook 2011, 2012. Potash (Advance Release). Government of India, Ministry of Mines, Indian Bureau of Mines, pp. 2e5. Jouyban, Z., 2012. The Effects of Salt stress on plant growth. Tech. J. Eng. Appl. Sci. 2, 7e10. Kalra, Y.P., 1995. Determination of pH of soils by different methods: collaborative study. J. AOAC Int. 78, 310e324. Karimi, E., Abdolzadeh, A., Sadeghipour, H.R., Aminei, A., 2011. The potential of glauconitic sandstone as a potassium fertilizer for olive plants. Archives Agron. Soil Sci. 1, 1e11. Kidd, P.S., Proctor, J., 2001. Why plants grow poorly on very acid soils: are ecologists missing the obvious? J. Exp. Bot. 52, 791e799. Korbel, P., Novak, M., 2001. The complete encyclopedia of minerals. Grange Books PLC, United Kingdom, pp. 87e91. Levchenko, E., Ptyk-kara, N., Levchenko, M., 2008. Glauconite deposits of Russia: perspectives of development. In: International Geological Congress, Oslo [2015-
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09-07]. http://www.cprm.gov.br/publique/?tpl¼home. Majumder, A.K., Govindarajan, B., Sharma, T., Ray, H.S., 1995. An empirical model for chloridising-roasting of potassium in glauconitic sandstone. Int. J. Min. Process 43, 81e89. Martin, D.L., Gershuny, G., 1992. The Rodale book of composting. Rodal Press, Emmaus, Pennsylvania, pp. 74e78. McRae, S.G., 1972. Glauconite. Earth-Science Rev. 8, 39e440. Mesaed, A.A., Surour, A.A., 1999. Mineralogy and geochemistry of the Bartonian stratabound diagenetic and lateritic glauconitic ironstones of El-Gideda mine, Bahariya Oasis, Egypt. In: International Conference on the Geology of the Arab World, Cairo University, Egypt, pp. 540e548. Meunier, A., 2004. Clays. Springer, Berlin, pp. 83e327. Misra, V.N., Reddy, P.S.R., Mohapatra, B.K., 2004. Mineral characterization and processing. Allied Publishers, New Delhi (India), pp. 235e238. Odin, G.S., 1988. Green marine clays. Elsevier, Oxford, pp. 22e441. Odin, G.S., Matter, A., 1981. De glauconiarum origine. Sedimentology 28, 611e641. Odin, G.S., Fullagar, P.D., 1989. Geological significance of the glaucony facies. In: Odin, G.S. (Ed.), Green Marine Clays. Elsevier, Amsterdam, pp. 295e332. Orisakwe, O.E., Nduka, J.K., Amadi, C.N., Dike, D.O., Bede, O., 2012. Heavy metals health risk assessment for population via consumption of food crops and fruits in Owerri, South Eastern, Nigeria. Chem. Central J. 6, 2e7. Pestitschek, B., Gier, S., Essa, M., Kurzwell, H., 2012. Effects of weathering on glauconite: evidence from the Abu Tartur plateau, Egypt. Clays Clay Minerals 60, 76e88. Petruk, W., 2000. Applied Mineralogy in the Mining Industry. Elsevier Science BV, Amsterdam, pp. 83e94. Ryoung, S., Howard, B., Daniel, P.S., 2006. Reactive oxygen species and root hairs in arabidopsis root response to nitrogen, phosphorus and potassium deficiency. J. Plant Cell Physiology 46, 1341e1350. Savci, S., 2012. An agricultural pollutant: chemical fertilizer. Int. J. Environ. Sci. Dev. 3, 77e80. Vallee, B.L., Auld, D.S., 1990. Zinc coordination, function, and structure of zinc enzymes and other protein. Biochemistry 29, 5647e5659.
Contents lists available at ScienceDirect
Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci
The economic potential of El-Gedida glauconite deposits, El-Bahariya Oasis, Western Desert, Egypt Galal El-Habaak a, Mohamed Askalany b, Mohamed Faraghaly c, Mahmoud Abdel-Hakeem b, * a b c
Department of Geology, Faculty of Science, Assiut University, Egypt Department of Geology, Faculty of Science, South Valley University, Egypt Department of Mining and Petroleum Engineering, Faculty of Engineering, El-Azhar University, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 December 2015 Received in revised form 19 April 2016 Accepted 7 May 2016 Available online 9 May 2016
The mining work at El-Gedida iron mine, El-Bahariya Oasis, in the Western Desert of Egypt extracts commercial iron ore deposits without attention paid to the large glauconite deposits overlying these iron ore deposits. For this reason, the present paper aims at evaluating and attracting the attention to these glauconite deposits as alternative potassium fertilizers. The study was achieved by investigating mineralogical, physical and chemical properties of the green deposits. Mineralogical and physical properties involved the determination of glauconite pellets content in different grain size fractions relative to impurities and the analysis of the percentage of clay matrix and grain size distribution. Different pre-treatment strategies and methods including comminution, sieving, magnetic separation, and X-ray diffraction were used for investigating those mineralogical and physical properties. On the other hand, chemical analyses included potassium content, heavy metal concentrations, and pH and salinity measurements. The major elements and trace elements were measured using ICP-OES and the pH was measured using a pH conductometer. Moreover, this study investigated the nature of grain boundaries and the effect of sieving on glauconite beneficiation. Results of this study suggest that ElGedida glauconite deposits are mineralogically, physically and chemically suitable for exploitation and can be beneficiated for use as an alternative potassium fertilizer. © 2016 Elsevier Ltd. All rights reserved.
Keywords: El-Gedida iron mine Glauconite deposits Physical properties Chemical properties Potassium fertilizer
1. Introduction Glauconite is defined as a green, iron-potassium-rich micaceous mineral, with 2:1 dioctahedral illite-like structure. It is characterized by inter-stratification of nonexpandable (10 Å) and expandable Fe-smectite layers. Glauconite-smectite (sensu lato) contains more than 50% expanding layers, but glauconite (sensu strict) contains less than 10% expanding layers (McRae, 1972; Odin, 1988). Glauconite deposits have been used as natural potassium fertilizers, especially in forage crops, for over 100 years (Dooley, 2006). The commercial value of glauconite is attributed to its potassium content. Beside, nitrogen and phosphorous, potassium is an important macronutrient essential for osmotic regulation and plant growth (Ryoung et al., 2006). The global demand for potassiumbearing fertilizers continuously increases and is expected to grow
* Corresponding author. E-mail address: [email protected] (M. Abdel-Hakeem). http://dx.doi.org/10.1016/j.jafrearsci.2016.05.007 1464-343X/© 2016 Elsevier Ltd. All rights reserved.
annually at 3% from 2012 to 2017, reaching 37.4 Mt K2O in 2017 (Heffer and Prudhomme, 2013). Glauconite deposits have been studied in many countries for use as an alternative to potassium salt fertilizers. Franzosi et al. (2014) magnetically treated and evaluated green sands from the Salamanca formation, Patagonia, Argentina, as a substitution potassium fertilizer, with potassium contents around 4.05% K2O. The authors found that the fertilization effect of green sands was similar to that of KCl, and they also referred to the low cost of treatment and production of these deposits compared to KCl mining. According to Levchenko et al. (2008), glauconite in Russia has been reported from glauconite-bearing deposits: the Koporskoe and Karinskoe deposits with reserves of about 100 million tons. The most important use of glauconite is as a chemical fertilizer and soil conditioner for agricultural and land reclamation purposes. The application of glauconite as fertilizer owes to its high content of potassium (5e9.5%), phosphorous and micro-nutrients (such as Mn, Cu, Co, Ni, etc.).
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In New Jersey, Delaware, and Maryland Districts (in the USA) the most significant glauconitic green sands lie at the Mid-Atlantic Coastal plains, in the Upper Cretaceous and Early Palaeocene formations. The glauconitic sediments are used for fertilization and soil enhancement (Heckman and Tedrow, 2004). Karimi et al. (2011) tested glauconitic sandstone from Maraveh, northeast Iran as a potassium fertilizer for olive plants. The authors carried out lixiviation tests of the ground deposit (250 mm) in water and various types of 1 M acids (phosphoric and hydrochloric acids) and measured the potassium contents in the extractant solutions. They found that the potassium content extracted in water was 23 mg Kþ kg1 of sandstone powder while that released in acid solutions was 2200 mg Kþ kg1 of sandstone powder. The authors also suggested the possibility of applying green sands, with 2.24 wt % K2O as source of soil soluble potassium for a long time. In Egypt, glauconite deposits have been reported from El-Gedida iron mine, El-Bahariya Oasis, in the Western Desert. These deposits belong to the Bartonian age and occur as a green sands cover overlying the Lutetian iron ore, of about 25 m thickness at the eastern and western wadis of the mining area. The glauconite sediments have been studied by many authors (El-Sharkawi and Khalil, 1977; Mesaed and Surour, 1999; Hassan et al., 2011; Baioumy and Boulis, 2012) in terms of their petrology, mineralogy and geochemistry. The deposits are mined as overburden and are removed to reach the commercial iron ore deposit. The main objective of this paper is to add value to El-Gedida glauconites by performing mineralogical, physical and chemical assessments of the deposits for use as an alternative to potassium salt fertilizers. 2. Geological setting El-Gedida glauconite deposits are located at the eastern and western wadis of El-Gedida mining area as a condensed section that reaches a thickness of up to 25 m above the commercial Middle Eocene ironstone deposit (Hassan and Baioumy, 2007). According to El Aref et al. (1999) and Mesaed and Surour (1999) the glauconite deposits belong to the Upper Eocene Hamra Formation divided into two units. The lower unit consists of highly fossiliferous glauconitic mudstone and sandstone with marl intercalations while the upper unit is composed of well-bedded green sand, glauconitic mudstone and sandstone with intercalations of lateritic iron bands. The glauconite deposits are equivalent to the upper unit of the Upper Eocene Hamra Formation. The studied glauconites are unconformably covered by fluvial deposits of the Qatrani Formation (Oligocene) and overly the carbonates of the Naqb Formation (Middle Eocene). Depending on stratigraphy, mineralogy and geochemistry, El-Habaak et al. (2016) proved that the Upper Eocene glauconites were deposited in a shallow marine environment under regressive conditions at 100 m depth. 3. Materials and methods The rock samples investigated in this study were collected from sandy glauconite deposits at the eastern and western wadis of ElGedida mine, El-Bahariya Oasis, in the Western Desert (Figs. 1 and 2). For the petrographic characterization of the samples, thin sections were prepared and examined using the conventional optical microscope attached to a Leica camera. The acquired images were processed using the Image Analyzer Software for investigating the nature of optical appearance of the glauconite grains. To achieve this, the image processing techniques of linear stretching and edge detection were applied. The bulk mineralogy of these deposits was determined using X-ray diffractometer (X’Pert PROPAN). The contents of glauconite pellets were determined through
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three steps. The first step involved a size reduction of the two representative samples (100 kg per each sample) up to -1 mm by using a jaw crusher and a rod mill in a closed circuit. Secondly, each 100 kg representative sample was subjected to coning and quartering processes. Afterwards, a representative sample (50 g) of the ground ore was beneficiated using a Frantz isodynamic magnetic separator adjusted to a current intensity of 0.7 Am, 20 forward slope, 15 side slope, and feed rate of 10 g/minute. The magnetic and tailing fractions were mineralogically examined using XRD. The principal aim of separation was to investigate the amounts of glauconite pellets compared to that of impurities. The percentage of clay matrix and the grain size of glauconite were determined by a dry sieving of the ground ore, resulting in five size fractions (1þ500, 500 þ 250, 250 þ 125, 125 þ 75 and 75 mm). The glauconite deposits were chemically studied to determine the contents of macronutrients and heavy metals using ICP-OES at Acme laboratory, Canada. The influence of sieving on the beneficiation of glauconite, a representative sample of each size fraction was mineralogically and chemically analysed using XRD and ICPOES, respectively. Measuring the pH of glauconite was performed using multiparameter pH meter (WTW Multi 340i), at the ratio of 1:5 glauconite/water mixture, according to Kalra (1995). For each glauconite sample, a 10 g portion was weighed and dried at 60 C for 1 h. The dried sample was put into a 100 ml beaker and 50 ml of distilled water was added. The mixture was stirred for 1 h and allowed to stand for 30 min. After the calibration of pH meter using two buffer solutions of pH 7 and 4.01, the pH was measured at 25 C. For measuring salinity of the glauconite deposits, another glass electrode was used. The procedure for calibration was performed by immersing the conductometer electrode into a standard solution of 0.01 mol/l KCl. 4. Results and discussion 4.1. Microscopic characterization The studied glauconite deposit is composed mainly of green pellets with minor amounts of quartz, calcite, halloysite and iron oxyhydroxides set in a matrix that consists of a greenish (glauconitic) mud (Fig. 3a). Glauconite occurs as green, brownish green and yellowish green pellets ranging in diameter from 100 to 500 mm, thus these pellets are moderate to well sorted. Originally, the glauconite pellets developed in specific micro-environments such as faecal pellets and/or in bioclasts by increasing the contents of Fe and K during maturation from smectitic glauconite to glauconitic mica, but the alteration and extensive weathering of the pellets result in oxidation of the divalent Fe and depletion of K forming brown pellets that contain nanometric inclusions of Feoxyhydroxides (Pestitschek et al., 2012). The oval, sub-oval, rounded to subrounded glauconite grains detected contain random microcrystalline internal structures that occasionally are fractured (Fig. 3b). The cracks are interpreted as a result of expansion related to the differential mineral growth in the pellets (Odin and Matter, 1981). As illustrated in Fig. 3c some fractured pellets are filled with a greenish glauconitic mud generated by the destabilization of the glauconite pellets (Meunier, 2004). The pellets have experienced three stages of development: (1) initial pellet formation, (2) pellet fracturing and (3) infilling of pellet cracks with a glauconitic mud. Quartz occurs as angular to sub angular detrital grains that are 100e250 mm in diameter, associated with glauconite pellets. White halloysite vienlets cutting through the clayey matrix were detected (Fig. 3d). Botryoidal masses composed of sparry calcite occur as independent aggregates or as vienlets replacing the glauconitic
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Fig. 1. Geological map of the Bahariya Oasis, Western Desert, Egypt, with the location of glauconite sample illustrated by the Google earth image of El-Gedida mine.
Fig. 2. Field photos showing glauconite deposits in the eastern wadi (a) and western wadi (b).
clayey matrix. The replacement reactions widen the vienlets, resulting in non-matching walls and relicts of clayey matrix (Fig. 3e & f). Glauconite grains are also replaced by alunite (white in colour) occurring along fractures and grain boundaries (Fig. 3g & h). Halloysite and alunite are alteration products of the glauconites under humid conditions prevailing at El-Bahariya Oasis during the Late Eocene, as discussed by Hassan and Baioumy (2007). The optical microscope also provides valuable data related to the nature of contacts between various mineral grains, and hence, the extent of liberation of valuables from gangue minerals is expected before the comminution step (Misra et al., 2004). In the El-Gedida glauconites, the grain contacts between glauconite and quartz (the main gangue mineral) are classified as rectilinear and curved
(Fig. 4). Amstutz and Giger (1972) and Petruk (2000) classified the textures of ore minerals depending on the nature of the interlock between mineral grains. They suggested that the straight, rectilinear or curving contacts are characterized by simple locking and easy liberation. The nature of contacts between glauconite and quartz grains has a bearing on the ease of liberation of glauconite from quartz.
4.2. Mineralogical and physical properties The mineralogical analysis of glauconite samples collected from the eastern and western wadis are composed of glauconite with gangue minerals such as quartz, alunite, halloysite, calcite, hematite
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Fig. 3. Oval to sub-oval, green, yellowish green and brownish green glauconite pellets (Gt) in association with few amount of detrital quartz (Qt) set in a greenish glauconitic mud (Gm), as shown in (a). Also, some pellets are highly cracked with empty fractures (b) and filled one by a greenish glauconitic mud (c). Moreover, vienlets of halloysite (d) and calcite (e PPL and f XPL) invade and replace the glauconite grains and clay matrix consisting of illite-smectite mixed layer (IeS). Furthermore, glauconite is replaced by alunite (white spots) along fractures, as exposed in g (PPL) and h (XPL). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
and feldspar (Fig. 5). Quartz is the most predominant gangue
mineral detected by XRD. Calcite, feldspar, hematite and goethite
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Fig. 4. Sequential steps of edge detection between glauconite (green in colour) and quartz (colourless) start with noisy original image (a) transformed into linear stretched image (b) for which the edge detection was performed, resulting in clarifying straight and curved boundaries between the two mineral particles (c). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. XRD patterns of the eastern and western wadis glauconite, (a) and (b) respectively, showing the predominant peaks of glauconite (Gt) with associated gangue minerals including quartz (Qt), hematite (He), alunite (Al), halloysite (Ha), calcite (Ca) and feldspar (Fs).
minerals are the second common detrital constituents after quartz. On the other hand, the presence of alunite, halloysite and hematite minerals is attributed to extensive weathering of the glauconite
deposits. During the Late Eocene, humid conditions prevailed at ElBahariya Oasis under which the glauconite deposits were subjected to chemical weathering, resulting in the liberation of silica,
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aluminium and potassium ions. Under the closed-system conditions the ions reacted to form halloysite and alunite (El-Sharkawi and Khalil, 1977; Baioumy and Hassan, 2004; Hassan and Baioumy, 2007). The mineralogical investigation of the products of magnetic separation indicates that the magnetic fraction consists of glauconite with a trace amount of hematite, while the non-magnetic fraction comprises the other gangue minerals (Fig. 6). Weighing the magnetic and non-magnetic fractions reveals that the percentage of glauconite grains in the studied deposit represents about 97.81 wt % and 98.32 wt % compared to the amount of impurities reported at 2.19 wt % and 1.68 wt % for the eastern and western wadis glauconites, respectively. On the other hand, the clay matrix is included in the pan fraction (75 mm). The pan fraction represents about 2.57 wt % of the representative sample obtained from the eastern wadi glauconite and about 2.20 wt % of the representative sample from the western wadi glauconite. The results of sieving are listed in Tables 1 and 2 and show that the samples are represented by five size fractions (1þ500, 500 þ 250, 250 þ 125, 125 þ 75 and 75 mm) among which the 250 þ 125 mm fraction characterizes 81.74 wt % and 73.94 wt % of deposits in the eastern and western wadis, respectively (Fig. 7a). The fractions are calculated as the retained fractions on a 125 mm
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Table 1 Distributions of wt% and cumulative wt% of the eastern Wadi glauconite. Particle size, mm
Weight, % (retained)
Cumulative weight, % (retained)
1þ500 500þ250 250þ125 125þ75 75
5.02 7.30 81.74 3.37 2.57
5.02 12.32 92.06 97.43 100
Table 2 Distributions of wt% and cumulative wt% of the western Wadi glauconite. Particle size, mm
Weight, % (retained)
Cumulative weight, % (retained)
1þ500 500þ250 250þ125 125þ75 75
3.94 8.80 73.94 11.12 2.20
3.94 12.74 81.68 97.8 100
sieve. In addition, the d50 (coarse fraction) has been determined using the cumulative wt % curve of the sieved glauconite samples at the 250 þ 125 mm fraction (Fig. 7b). In order for the glauconite deposits to be of an economic value
Fig. 6. XRD patterns of magnetic and non-magnetic fractions extracted from glauconite samples. It is clear that the magnetic fractions of the eastern Wadi sample (a) and that of the western Wadi sample (c) are dominated by glauconite (Gt) with a trace amount of hematite (H), on the other hand, the non-magnetic fractions of the eastern Wadi glauconite (b) and that of the western Wadi glauconite (d) are mainly composed of quartz (Qt), alunite (Al), halloysite (Ha), calcite (Ca) and feldspar (F).
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Fig. 7. Distributions of wt % and cumulative wt % of the studied samples showing the majority of wt % is concentrated at þ250125 mm fraction (a) and the d50 of the sieved samples is also located at the same size fraction (b).
for fertilizer purposes, they must contain at least 90% of glauconite pellets at size fraction 250 þ 88 mm, with a percentage of clay matrixes ranging from 2 wt % to 3 wt % of the total weight as suggested by Dooley (2006). According to Dooley’s standard based on the physical properties of glauconites, the El-Gedida glauconite deposits are appropriate to be exploited as a potassium fertilizer. It is known that glauconites outperform K salt fertilizers in enhancing soil texture, porosity and permeability due to their uniform grain size (Indian Minerals Yearbook 2011, 2012). Green sands are characterized by high cation exchange capacity which improves the ability of soil to store exchangeable macro-nutrients (e.g. K, Ca and Mg). The micro pores of glauconite pellets can improve the water retaining and absorbing property of soils (Heckman and Tedrow, 2004). The effect of sieving glauconite for beneficiation and the mineralogical analysis of each sieve fraction (Figs. 8 and 9) shows that most of the gangue minerals (quartz, alunite, halloysite, feldspar, and calcite) are concentrated in the 125 þ 75 mm and 75 mm fractions. The e concentration of quartz, feldspar, and calcite in the finer fractions is ascribed to the size difference among these minerals and glauconite pellets. Because these minerals are harder than glauconite as discussed by Korbel and Novak (2001), the beneficiation of El-Gedida glauconites require only sieving to
obtain the proper size fraction (250 þ 125 mm) containing the appropriate potassium content for fertilizing purposes.
4.3. Chemical properties The major element analysis of El-Gedida glauconite reveals that the eastern wadi glauconites contain 6.75 wt % K2O and 52.10 wt % SiO2, while the western wadi deposit contains 7.30 wt % K2O and 50.89 wt % SiO2. Glauconite deposits must contain at least 2.27 wt % to 4.05 wt % K2O to be an acceptable potassium fertilizer (Franzosi et al., 2014; Heckman and Tedrow, 2004; Karimi et al., 2011). In addition, El-Gedida glauconites show similarities in chemical composition to the commercial New Jersey (USA) glauconite deposits, as shown in Table 3. This suggests that El-Gedida glauconite deposits contain required amounts of potassium for use in land reclamation and cultivation purposes. The chemical analysis of the size fractions are listed in Tables 4 and 5. The potassium contents increase toward the coarser size fraction (þ1000500 mm), with strong positive correlations for the eastern wadi (r ¼ 0.66) and the western wadi (r ¼ 0.75) (Fig. 10a). In contrast, the silica contents decreases toward the coarser fraction (þ1000500 mm), with strong negative correlations for the eastern wadi (r ¼ 0.72) and the western wadi (r ¼ 0.78) (Fig. 10b).
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Fig. 8. XRD patterns of five size fractions (1þ500,500 þ 250, 250 þ 125, 125 þ 75 and 75 mm) ordered as (a, b, c, d, e) obtained from the eastern Wadi glauconite showing the concentration of quartz (Qt), alunite (Al), halloysite (Ha), calcite (Ca) and feldspar (F) in the finer fractions (d & e).
Furthermore, the potassium contents reach up to 6.9 3 wt % K2O for the eastern wadi samples and up to 7.38 wt % K2O for the western wadi samples at the size fraction 250 þ 125 mm. Glauconite deposits have been used for more than 100 years as a source of fine potash owing to high contents of K (up to 8 wt % K2O) that is an essential macronutrient for healthy growth of plants (Indian Minerals Yearbook 2011; 2012). The low reactivity of glauconite with water compared to commercial K salt fertilizers (e.g. KCl and K2SO4). The liberation of K from the glauconite lattice may take a long time to produce sufficient K amounts for plant growth. Martin and Gershuny (1992) showed that the K release is improved by incorporating the glauconite sands with compost.
Majumder et al. (1995) converted the K2O present in a glauconitic sandstone sample into leachable KCl by roasting the sample with CaCl2. The thermal treatment of glauconite was carried out at conditions that included a roasting temperature of 750 Ce850 C, roasting time of 60 min, mixing ratio of (CaCl2 to glauconitic sandstone) 0.8 and size fraction 240 þ 90.5 mm. Although the solubility of chemical fertilizers (e.g. NaNO3, NH4NO3, KCl and K2SO4) is higher than that of glauconite, the prolonged use of these fertilizers results in the deterioration of the soil structure negatively affecting the quality and efficiency of field crop production (Savci, 2012). K-bearing Fe-smectite is more reactive than glauconite (Baldermann et al., 2013), therefore the percentage of Fe-
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Fig. 9. XRD patterns of five size fractions (1þ500, 500 þ 250, 250 þ 125, 125 þ 75 and 75 mm) ordered as (a, b, c, d, e) obtained from the western Wadi glauconite showing the concentration of quartz (Qt), alunite (Al), halloysite (Ha), calcite (Ca) and feldspar (F) in the finer fractions (d & e).
smectite present in the interstratified structure consisting of glauconite-smectite may affect the K availability. The percentage of K-bearing Fe-smectite in El-Gedida deposit was calculated by substituting K2O wt % determined by ICP-OES into the equation of Compton (1989): % Fe-smectite ¼ 7.79*K2O þ 68.7. The results show that glauconites of eastern and western wadis contain 16.11 wt % and 11.83 wt % expendables, respectively. Depending on
K contents, the studied glauconites are classified as high mature and evolved glauconites (Odin and Fullagar, 1989). The maturation and K content of glauconite is inversely correlated with the content of expendables (%) incorporated in the interstratified structure of glauconite (Odin and Matter, 1981). Micronutrients (heavy metals) also have a role in the metabolism activity, protein synthesis and nitrogen fixation for normal
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Table 3 Comparison between the chemical composition of El-Gedida glauconite and that of New Jersey glauconite. Oxides (100%)
Glauconite of eastern Wadi
Glauconite of western Wadi
New Jersey glauconite
SiO2 TiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O MnO P2O5 SO3 L.O.I. Total
52.10 0.13 5.99 22.23 3.75 0.31 0.10 6.75 0.02 0.14 0.21 8.3 99.90
50.89 0.04 5.88 22.99 4.34 0.20 0.05 7.30 0.08 0.07 e 8.3 99.89
51.83 e 6.23 20.08 3.66 0.52 0.76 6.60 e 0.31 e 10.34 100.33
Table 4 Contents potassium and silica of the studied size fractions extracted from the eastern Wadi glauconite illustrating the increase of silica content toward the finer fractions and vice versa for potassium content. Particle size, mm
K2O %
SiO2 %
K2O % (cumulative)
SiO2% (cumulative)
1þ500 500þ250 250þ125 125þ75 75
6.71 7.15 6.93 5.17 4.10
51.10 50.36 51.55 60.69 65.34
6.71 6.97 6.93 6.87 6.8
51.10 50.66 51.43 51.75 52.10
Table 5 Contents potassium and silica of the studied size fractions extracted from the western Wadi glauconite illustrating the increase of silica content toward the finer fractions and vice versa for potassium content. Particle size, mm
K2O %
SiO2 %
K2O % (cumulative)
SiO2% (cumulative)
1þ500 500þ250 250þ125 125þ75 75
7.61 7.78 7.38 6.61 5.98
49.23 48.83 50.59 54.50 56.39
7.61 7.72 7.43 7.33 7.30
49.23 48.95 50.34 50.82 50.94
phyto-sanitary effect on pathogens (Brown, 2007). Molybdenum has a crucial role in nitrogen metabolism of plants because of its involvement in nitrate reduction and transport of N compounds in plants and N2 fixation (Hamlin, 2007). Aside from their contribution to increase the field crop productivity, the concentrations and accumulation of heavy metals in soils can lead to toxic effects on the human food chain. For example, the human consumption of heavy metal-contaminated food can lead to intrauterine growth retardation, a decrease in immunological defences of body and a prevalence of upper gastrointestinal cancer (Falls, 2001; Orisakwe et al., 2012). Chemical fertilizers are implicated in raising the concentration of heavy metals in soils and are a potential source of radionuclides in the food chain (Savci, 2012). The contents of heavy metals in fertilizers must be monitored for consistency with the tolerant levels safe for healthy human food chain. In this respect the concentrations of heavy metals (Mo, Cu, Pb, Zn, Ni, As, Cd, Co and Cr) in El-Gedida glauconites have been considered in this study. By comparing the heavy metal contents of El-Gedida glauconites to standards issued by the Canadian Food Inspection Agency (1997), El-Gedida glauconites contain concentrations of heavy metals lower than the tolerant
Fig. 10. Plot K2O and SiO2 vs. the obtained size fractions showing an increase in the potassium content toward the coarse fraction (a) and vice versa for the silica content (b).
plant growth. For instance, zinc is predominantly absorbed by plants as a divalent cation (Zn2þ) and has a structural and catalytic role in enzyme reactions owing to its strong tendency to form tetrahedral complexes with N-, O- and S-legands (Vallee and Auld, 1990). Nickel contributes to the growth of nitrogen fixing species and enhances plant resistance to disease resistance due to its direct
levels as shown in Table 6. Therefore, exploiting these deposits as fertilizers or agricultural soils will not result in excessive accumulation of heavy metals in soils or food products and thus toxicity problems occurring at high levels of heavy elements are avoided. Changes in the pH value of soil solutions associated with using fertilizers, i.e. KCl, K2SO4, KNO3, can negatively affect the soil
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Table 6 Comparison between the heavy metal contents of El-Gedida glauconite and that reported by the Canadian Food Inspection Agency (CFIA, 1997). Heavy metal content (ppm)
Mo
Cu
Pb
Zn
Ni
As
Cd
Co
Cr
Eastern Wadi glauconite Western Wadi glauconite CFIA
<0.1 <0.1 5
3.7 2.4 400
2.0 0.3 150
86 208 700
15.4 30.7 62
2.4 2.2 13
<0.1 <0.1 3
25.8 28.0 34
110 130 210
Table 7 Ph and salinity degree of glauconite deposits at the eastern and western Wadis. Glauconite sample
Glauconite of eastern Wadi
Glauconite of western Wadi
pH value Salinity value (d S m1)
6.71 0.056
7.59 0.128
fertility and plant growth. The pH controls the availability of nutrients present in soil and soil solutions. The continued use of acidforming nitrogen fertilizers increases soil acidity while high concentrations of Na and K salt fertilizers increase soil pH (Arsova, 1999; Savci, 2012). As illustrated in Table 7, a slightly acidic behaviour is noticed for glauconite deposits from the eastern wadi, while those in the western wadi are characterized by slightly basic behaviour. The pH values of these glauconites are consistent with pH conditions by most plants ranging from a pH of 5.5e7 (Kidd and Proctor, 2001). Some fertilizers can contribute to increase the soil salinization that affects the root growth and photosynthesis of plants (Jouyban, 2012). As shown in Table 7 the salinity measurements of El-Gedida glauconites are lower than that reported by Esmaili et al. (2008) for nitrogen fertilizers. The authors found that applying nitrogen fertilizers can increase the salinity of soils up to 12 ds/m. The degree of salinity increase using El-Gedida glauconites is in accordance with Franzosi et al. (2014) on the advantages of low salinity green sands compared to other chemical potassium fertilizers (e.g. KCl). 5. Conclusions i. El-Gedida glauconite deposits are characterized by rectilinear and curved contacts between glauconite and quartz grains, therefore, the liberation and separation of the green sand grain fraction is expected to be easy during the comminution step. ii. As a potassium fertilizer, El-Gedida glauconite deposits are characterized by 97.81 wt % to 98.32 wt % glauconite pellets and impurities that range from 2.19 wt % to 1.68 wt %. Moreover, the sieve analysis of ground glauconites resulted in five size fractions (þ100e500, þ500e250, þ250e125, þ125e75 and 75 mm) among which the following fraction was suitable as fertilizer (þ250125 mm) representing 81.74 wt % to 73.94 wt % of representative samples obtained from the eastern and western wadis glauconites, respectively. The clay matrix occurs in the 75 mm fraction occupying 2.57 wt % to 2.20 wt % of the studied glauconite samples. iii. Chemically, El-Gedida glauconite deposits are appropriate to be exploited as alternative potassium fertilizers as they have potassium contents ranging from 6.75 wt % to 7.30 wt % K2O at the optimum size fraction (þ250125 mm). iv. Results of sieving glauconite for beneficiation, chemical and mineralogical analysis of each size fraction revealed that the sieving concentrates most impurities into the finer size fractions (þ125e75 & 75 mm). v. The heavy metal contents of El-Gedida glauconites are below the guideline limits issued by the Canadian Food Inspection
Agency (1997) for fertilizers and composites, and hence the toxic effects of these metals in El-Gedida glauconites are negligible. vi. The evaluation of pH and salinity of El-Gedida glauconite deposits indicates that exploiting these deposits for agricultural purposes will protect the cultivated soils from acidification and salinization that affect the availability of nutrients required for plant growth. Acknowledgements Authors are highly grateful to Dr. M. Mansour, the Chairman of El-Bahariya Oasis Sector, Egyptian Iron & Steel Co. and Mr. A. Abbas, the Manager of Laboratories of El-Bahariya Oasis Sector, for their help during the fieldwork. Also, this work would not have been possible without the help of Prof. Vesnica Garasi c, the Head of Department of Mineralogy, Petrology and Mineral Resources, Faculty of Mining, Geology and Petroleum Engineering, Zagreb University, Croatia. The authors acknowledge the reviewers of the Journal of African Earth Sciences for their great efforts in the revision of manuscript to be in the perfect form. References Amstutz, G.C., Giger, H., 1972. Stereological methods applied to mineralogy, petrology, mineral deposits and ceramics. J. Microsc. 95, 145e157. Arsova, A., 1999. Effect of fertilizer application and soil pH on the acidic and sorption properties of maize leaves and stems. Bulg. J. Plant Phsicololgy 21, 52e57. Baioumy, H.M., Boulis, S.N., 2012. Glauconites from the Bahariya Oasis: an evidence for Cenomanian marine transgression in Egypt. J. Afr. Earth Sci. 70, 1e7. Baioumy, H.M., Hassan, M.S., 2004. Authigenic halloysite from El-Gideda iron ore, Bahria Oasis, Egypt: characterization and origin. Clay Miner. 39, 207e217. Baldermann, A., Warr, L.N., Grathoff, G.H., Dietzel, M., 2013. The rate and mechanism of deep-sea glauconite formation at the Ivory Coast-Ghana Marginal Ridge. Clays Clay Minerals 61, 258e276. Brown, P.H., 2007. Nickel. In: Barker, A.V., Pilbeam, D.J. (Eds.), Handbook of Plant Nutrition. Taylor & Francis Group (CRC), New York, pp. 397e400. Canadian Food Inspection Agency Standards for Metals in Fertilizers and Supplements. 1997; Trade MemorandumT-4e93.[2015-09-07]. http://www. inspection.gc.ca/plants/fertilizers/trade-memoranda/t-493/eng/ 1305611387327/1305611547479. Compton, M.S., 1989. Morphology and geochemistry of glauconite from the TeKuiti Group, South Auckland Region, New Zealand. University of Waikato, Hamilton, New Zealand, pp. 64e69 (Master’s thesis). Dooley, J.H., 2006. Glauconite. In: Koger, J., Trivedi, N., Barrer, J., Krukowsky, N. (Eds.), Industrial Minerals and Rocks: Commodities Market and Uses. Society for Mining, Metallurgy and Exploration, Littleton, CO, pp. 493e495. El Aref, M.M., El-Sharkawi, M.A., Khalil, M.A., 1999. Geology and genesis of the stratabound to strataform Cretaceous, Eocene iron ore deposits of El-Bahariya region, Western Desert, Egypt. The 4th International Conference on Geology of the Arab World, pp. 450e475. El-Habaak, G.H., Askalany, M.S., Farghaly, M.G., Abdel-Hakeem, M.S., 2016. Upper Eocene glauconites from the Bahariya depression: an evidence for the marine regression in Egypt. J. Afr. Earth Sci. 117, 1e11. El-Sharkawi, M.A., Khalil, M.A., 1977. Glauconite, a possible source of iron for El Gedida iron ore deposits, Bahariya Oasis, Egypt. Egypt. J. Geol. 21, 116e122.
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