Flotation recovery of rare earth oxides from hematite–quartz mixture using sodium oleate as a collector

Minerals Engineering 141 (2019) 105847

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Flotation recovery of rare earth oxides from hematite–quartz mixture using sodium oleate as a collector

T

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George Blankson Abaka-Wooda, , Shadrach Fosub, Jonas Addai-Mensaha,c, William Skinnera a

Future Industries Institute, University of South Australia, Mawson Lakes Campus, Adelaide, Australia University of Mines and Technology, Tarkwa, Ghana c Department of Mining and Process Engineering, Namibia University of Science and Technology, Windhoek, Namibia b

A R T I C LE I N FO

A B S T R A C T

Keywords: Flotation Hematite Monazite Quartz Sodium oleate Sodium silicate Starch

Froth flotation plays a significant role in the beneficiation of rare earth elements (REE) minerals from differing ores. Monazite has been identified as one of the principal REE minerals in most iron oxide silicate rich tailings generated in Australia from the extraction of primary commodities such as copper and gold. These tailings generally contain hematite and quartz as the major gangue minerals. A previous investigation has identified almost identical flotation response between monazite and hematite in the presence of anionic collectors. Therefore, it is necessary to investigate the feasibility of selective flotation of rare earth oxides (REO) in monazite from hematite–quartz mixtures, to identify cost-effective processing methods. The flotation conditions for selective REO separation from model minerals mixtures were tested in a 1.2 L Denver flotation cell using sodium oleate as a collector. Sodium silicate and starch were tested as depressants for hematite and quartz. Results from the flotation tests revealed that the increased dosage of sodium oleate led to an increase in REO recovery with a corresponding decrease in upgrade, and increased hematite (Fe2O3) and quartz (SiO2) recoveries. In the absence of depressants, the separation of REO from a low grade mixture (0.83% REO feed grade) was unselective, where 3000 g/t sodium oleate recovered 98% REO at a grade of 1.31% (enrichment ratio, E = 1.58) along with 77% Fe2O3 and 37% SiO2 recoveries. However, the depressants reduced the flotation recovery of Fe2O3 and SiO2, which was shown by an improvement in REO grade. The flotation recovery of REO decreased to 84% with a corresponding increase in grade to 4.13% when 1000 g/t sodium silicate was used in the presence of 3000 g/t sodium oleate. Furthermore, 1000 g/t starch in the presence of 3000 g/t sodium oleate increased REO concentrate grade to 5.56% although the recovery decreased to 65%. Subsequently, a rougher–scavenger flotation test conducted with the mixed depressants (sodium silicate: starch, 1:1) produced a final concentrate recovering 61% REO at a grade of 6.25%. This study has shown that REO can be separated selectively from hematite–quartz rich mixtures by flotation when using sodium oleate as the collector and sodium silicate and starch as depressants.

1. Introduction Data published by Geoscience-Australia (2014) has suggested that more than 53 Mt of REE are lost to tailings generated from the extraction of primary commodities such as copper, gold, uranium, and silver in Australia. The REE contained in such tailings have a wide range of technological applications in energy production and storage, catalysis, medicine, electronics/magnets, and advanced glasses and ceramics (Geoscience-Australia, 2012; Geoscience-Australia, 2014). Currently, the local mining industry has not devised an economically viable processing method for recovering the REE, which is long overdue. However, investigations have identified bastnäsite and

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monazite as the major REE-bearing minerals, in complex associations with iron oxides (mainly hematite) and silicates (quartz) (Ehrig et al., 2012; Geoscience-Australia, 2012; Geoscience-Australia, 2014). The beneficiation of the tailings would normally involve physical preconcentration separation (e.g., magnetic, gravity, and electrostatic) and froth flotation. As part of an ongoing project to research and develop cost-effective processing methods for recovering and upgrading REE minerals from such tailings and low-grade ores of complex mineralogy in South Australia, different separation methods (magnetic, gravity, electrostatic, and froth flotation) are being tested. An integral part of this project is the use of model minerals to help identify and provide a benchmark for elucidating the separation possibilities of REE

Corresponding author at: Future Industries Institute, University of South Australia, Mawson Lakes Campus, SA 5095 Adelaide, Australia. E-mail address: [email protected] (G.B. Abaka-Wood).

https://doi.org/10.1016/j.mineng.2019.105847 Received 26 December 2018; Received in revised form 19 April 2019; Accepted 4 June 2019 Available online 22 June 2019 0892-6875/ © 2019 Elsevier Ltd. All rights reserved.

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using starch has been well documented and the reader is referred to a number of classic references and reviews (Araujo et al., 2004; Filippov et al., 2014; Kar et al., 2013; Montes-Sotomayor et al., 1998; Pavlovic and Brandao, 2003; Peres and Correa, 1996). Sodium silicate has also been studied as depressant for iron oxides (Araujo et al., 2004; Satur et al., 2016).

minerals from the key gangue minerals. Pure monazite mineral sample was selected as the model REE mineral, because it was readily available. Hematite and quartz were selected as the model gangue minerals, as they have been reported to occupy the bulk of typical REE-bearing tailings generated in South Australia. Froth flotation, which is one of the most important beneficiation processes, has been the most effective and efficient method for recovering and upgrading REE minerals. The process of flotation exploits the differences in the physicochemical properties of minerals to effect separation (Wills and Finch, 2015). Typically, collectors are used during this process to enhance surface hydrophobicity, whereas depressants are used to promote hydrophilicity on some unwanted minerals (Bulatovic, 2007; Wills and Finch, 2015). In direct froth flotation process, the hydrophobic minerals (usually minerals of interest) get selectively attached to air bubbles and are usually recovered via the froths, whereas the gangues (hydrophilic minerals) remain in the pulp as tails. Conversely, the gangues can be separated into the float fraction during reverse flotation (Wills and Finch, 2015). Typically, monazite is associated with gangue minerals such as ilmenite, rutile, quartz, and zircon, with differing minerals association and liberation characteristics, hence requires ore-specific flotation regimes to achieve appreciable separation. Flotation of monazite from oxides and silicate gangue minerals has been investigated by numerous researchers (Abaka-Wood et al., 2016; Abeidu, 1972; Cheng et al., 1993; Cuthbertson, 1952; Ren et al., 1997). Though the flotation process of monazite could be different from that of other REE minerals such as bastnasite and xenotime, fatty acids (sodium oleate, oleic acid, linoleic acid, etc) and hydroxamates are typical collectors used in REE minerals beneficiation because of the similarity in REE on the cationic sites of the REE minerals’ surfaces (Cheng et al., 1993; Jordens et al., 2013; Ren et al., 1997; Xia et al., 2014). Starch, sodium silicate, sodium sulphide, tartaric, and citric acids have been identified as depressants used during the flotation of REE minerals (Abeidu, 1972; Bulatovic, 2007; Fuerstenau, 2013; Houot et al., 1991; Jordens et al., 2013; Pol’kin et al., 1967; Xia et al., 2015). Fatty acids have been used as collectors for REE mineral flotation due to their availability, but have been shown to be unselective, requiring significant amount of depressants to achieve substantial selective separation. Fatty acids have been shown to adsorb onto monazite at pH ranges where zeta potential is negative, hence the mechanism of adsorption is regarded as chemisorption (Cheng et al., 1993; Fuerstenau, 2013; Jordens et al., 2013). Furthermore, the choice of depressants used in REE minerals flotation is dependent on the gangue minerals present in the ore. Iron oxides can be recovered by direct flotation using anionic collectors or inverse flotation of siliceous gangue using both anionic and cationic collectors (Arantes and Lima, 2013; Araujo et al., 2004). Fatty acids are known to adsorb on the surface of hematite by means of chemical bonding which has been established by researchers (Abaka-Wood et al., 2017b; Filippov et al., 2014; Han et al., 1973; Joseph-Soly et al., 2015; Quast, 2000; Quast, 2006; Quast, 2015; Shibata and Fuerstenau, 2003). Silicate minerals, typically quartz have been reported to float poorly in the presence of anionic collectors, and will require surface activation by cationic impurities, at differing pulp pH to achieve flotation (AbakaWood et al., 2017a; Fuerstenau and Somasundaran, 2003). However, when they tend to be co-recovered along with valuable minerals, they could be depressed using both starch and sodium silicate (Abaka-Wood et al., 2017a; Chelgani et al., 2015; Satur et al., 2016). A review of the literature and previous model minerals studies (Abaka-Wood et al., 2017a; Abaka-Wood et al., 2017b) suggest that both monazite and hematite can be floated using fatty acids, hence the need for depressants that will selectively hinder the recovery of hematite. Starch has been used as a universal depressant for iron oxides. The depression action of starch basically involves the coating of low energy hydrophobic surface with hydrophilic film in order to prevent air bubble attachment. Depression of hematite and other iron oxides

1.1. Study objective A critical review of the literature has indicated a lack of knowledge and data on the recovery of monazite from hematite and quartz in a unit ore system, using sodium oleate flotation. In a previous single minerals flotation investigation (Abaka-Wood et al., 2017b), it was identified that sodium oleate is capable of producing a comparatively selective monazite recovery from hematite and quartz, although the similarity in monazite–oleate and hematite–oleate adsorption warrants the use of depressants. This hypothesis gave the motivation for this study and has stimulated the focal research question: “Can the rare earth oxides (REO) in monazite be selectively floated from hematite and quartz mixtures using sodium oleate as a collector in the absence and presence of conventional depressants?” If this is possible then key opportunities will be identified in the quest to develop a cost-effective method for recovering and upgrading REE minerals from typical low grade tailings. The economic and processing benefits will be significant as hydroxamic acid and sodium dodecyl sulphate have been reported to be comparatively unselective and very expensive (Abaka-Wood et al, 2017b, Espiritu and Waters, 2018). Furthermore, the information obtained from this study will inform researchers and stakeholders in addressing the scientific and technological challenges of developing processing methods to concentrate and extract REE from typical low grade tailings. In the present investigation, the selective flotation of REO (in monazite) from low grade hematite–quartz mixture was carried out using sodium oleate as a collector in the presence of sodium silicate and starch as depressants. The differences in the physicochemical properties of monazite, hematite, and quartz in mixed minerals system, were exploited with the target of producing rich monazite (REO) concentrate. Specifically, the flotation recovery and upgrade of REO from a model mixture as a function of sodium oleate dosage and depressants dosage were studied. Prior to these, the flotation kinetics of monazite, hematite, and quartz as a function of pulp pH and sodium oleate dosage were determined to set the basis for subsequent separation tests. A detailed literature review was conducted on flotation kinetics modelling (Amelunxen et al, 2014; Amelunxen et al, 2018; Bulatovic, 2007), but the classical model methodology was used in this research to provide a common basis for comparism with previous work (Abaka-Wood et al 2017a). However alternative kinetic modelling methodologies will be considered in future works. 2. Experimental 2.1. Materials A mixture of minerals to mimic the major mineralogical composition of typical South Australian complex, low grade REE-bearing tailings was studied for flotation separation. The feed used in this investigation comprised of three model minerals: monazite (RZ Mines Pty Limited, Australia), hematite (Australia Bulk Minerals, Australia) and quartz (Aldrich, Australia). Samples were pulverised and screened to obtain 80% < 75 µm and analysed for their chemical and mineralogical compositions. The chemical composition of the model minerals which were obtained via Inductively coupled plasma mass spectrometry (ICPMS) measurements to aid in subsequent mineral phase identification is shown in Table 1. Quantitative X-ray diffraction (QXRD) was carried out on each sample to determine their respective bulk mineralogical 2

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the surface of minerals.

Table 1 Chemical analysis data of minerals obtained via ICP-MS analysis. Element

Hematite

Monazite

Quartz

Fe (%) Si (%) Al (%) La (ppm) Ce (ppm) Nd (ppm)

67.90 0.60 0.64 – – –

0.34 1.48 – 96,600 196,000 89,400

0.23 45.30 0.40 – – –

(1) The mixed minerals flotation tests involved the recovery of REO in the absence and presence of depressants, at the optimum pulp pH (9) condition selected from the single minerals microflotation tests. The flowsheet presented in Fig. 1b was used. The influence of increasing sodium oleate dosage (500–3000 g/t) and depressants dosage (500–4000 g/t) on REO recovery and upgrade were ascertained. (2) The synergetic impact of the depressants [sodium silicate (SS) and starch (ST)] on the selective recovery of REO, using a multistage flotation test was also studied. Fig. 2 shows the flotation flowsheet used for this test, consisting one roughing stage followed by scavenging of the rougher tails. The roughing test was carried out over 5 min, where concentrates were collected at 0.5, 1, 3, and 5 min cumulatively. The resulting tails were then reconditioned with the appropriate dosages of collector and depressants, and then floated over 5 min, with the same concentrate-recovery pattern as in the roughing stage. The concentrates and tails obtained were analysed for their chemical composition.

Table 2 Identified crystalline phases in mineral samples via QXRD analysis. Mineral Sample

Identified phase

Chemical formula

Content (%)

Monazite

Cerium phosphate Neodymium Phosphate Lanthanum Phosphate

Ce2(PO4)3 Nd2(PO4)3 La2(PO4)3

45 35 20

Hematite

Hematite Goethite

Fe2O3 FeO(OH)

95 5

Quartz

Quartz

SiO2

100

To ensure good reproducibility of the results, each separation test was replicated at least three times and the arithmetic means of the data and their pure errors determined and reported at 95% confidence interval.

composition and the results are presented in Table 2. Acidified starch (Grain Processing Corporation, U.S.A) and sodium silicate (Coogee Chemicals, Australia) were used as depressants, whilst sodium oleate (Sun Ace, Australia) was used as a collector. Dilute solutions of hydrochloric acid and sodium hydroxide (Aldrich, Australia) were used as pH modifiers. A 0.8 wt% of monazite (by mass) was mixed in 1:1 hematite–quartz ratio to form the feed used in the mixed minerals separation tests. The head grade analysis of the mixture obtained via ICP-MS is presented in Table 3.

2.2.1. Flotation kinetics expressions The variation in the recovery of mineral particles over time is characterised as the flotation kinetics of the mineral and can be calculated from the expression (Muganda et al., 2011; Owusu et al., 2014);

R (t ) = Rmax (1 − e−kt )

where R(t) and Rmax are the recovery at time, t and maximum recovery, respectively, and k is the distributed rate constant. The distributed rate constant is defined as the rate constant of the single floatable mineral species. A modified flotation rate constant called the undistributed rate constant (k*) which considers both maximum recovery and distributed rate constant was calculated using the expression (Chipfunhu et al., 2012; Owusu et al., 2014; Sripriya et al., 2003);

2.2. Flotation procedures A 250 mL microflotation cell (Instytut Metali Niezelaznych, Gliwice, Poland) was used in the flotation of single minerals to ascertain the flotation kinetics of the minerals. In the flotation of the single minerals, 10 g dried feed sample was pulped in 250 mL of distilled water. The agitation and airflow rates were set at 720 rpm and 1.5 L/min, respectively during the conditioning and flotation processes. Single minerals microflotation tests were carried out at five different pulp pH (3–11) and three sodium oleate dosages (500–3000 g/t) with a total flotation time of 10 min. Fig. 1a illustrates the flowsheet of the microflotation tests carried out. For mixed minerals separation, the following two forms of tests were carried out using 1.2 L Denver flotation cell on 25 wt% pulp feed. The impeller speed (800 rpm) and air flow rate (3.5 dm3/min) were maintained constant during conditioning and flotation in all tests. The pulp was mixed for 5 min and the pH was adjusted using dilute HCl or NaOH solution and allowed to stabilise at pH 9. The reagents (sodium oleate and depressants) were added to the pulp in succession and conditioned for 5 min each to ensure enough contact of reagents onto

k∗ =

Content (%)

Ce2O3 (%) La2O3 (%) Nd2O3 (%)

0.44 0.21 0.18

Total REO (Ce + La + Nd)2O3 Fe (%) Si (%)

0.83 32.7 23.7

kRmax 100

(2)

Selectivity index which shows whether the selective recovery/separation of the valuable mineral(s) from the gangue mineral(s) remains unchanged at varying flotation conditions was calculated based on the undistributed rate constant and is expressed as;

SI (A/ B ) =

k ∗ of mineral A k ∗ of mineral B

(3)

where SI(A/B) is the selectivity index of mineral A over B. 2.2.2. Results presentation For the mixed minerals flotation tests, REO grade, as presented is the sum of Ce2O3, La2O3, and Nd2O3 grades, as these were the major oxides in the monazite sample. The recovery of Ce2O3, La2O3, and Nd2O3 were identical at 95% confidence level in all the flotation tests, hence the average of the recoveries of Ce2O3, La2O3, and Nd2O3 has been reported as REO recovery (for each test conducted). Enrichment ratio, which is the ratio of the grade of an element or mineral in a flotation concentrate to that in the feed, a key indicator for measuring the performance of a flotation system, was used and is expressed as;

Table 3 Head (feed) grade of mixed minerals feed used in this investigation obtained by ICP-MS analysis. Chemical species

(1)

Enrichment or upgrade ratio (E ) =

c f

(4)

where c is the grade of the valuable element/oxide/mineral in the 3

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Fig. 1. Flotation flowsheet used in (a) single and (b) mixed minerals flotation tests.

Fig. 2. Flowsheet configuration of the multistage flotation test conducted on the low grade feed mixture at pH 9.

concentrate and f is the corresponding feed grade.

3. Results and discussions 3.1. Flotation kinetics of monazite, hematite, and quartz 3.1.1. Effect of pulp pH on flotation kinetics The influence of variation in pulp pH from 3 to 11 (at an increasing interval of 2) on flotation kinetics of monazite, hematite, and quartz was investigated. Figs. 3 and 4 show the results obtained for monazite and hematite, respectively, whilst varying the pulp pH from 3 to 11 at 1000 g/t sodium oleate dosage. The results showed that, the flotation recovery of both monazite and hematite is pulp pH-dependent. However, the recovery of monazite is generally higher compared to hematite, at all the pulp pH tested, except at pH 3, where the recovery of hematite was higher. The values of flotation rate constants obtained using Eqs. (1) and (2) are shown in Table 4. The results show that an increase in pH from 3–9, resulted in an increase in monazite flotation recovery from 17 to 74% and a corresponding increase in flotation rate from 0.32–1.80 min−1. Similarly, the flotation recovery of hematite increased from 28–53% for

Fig. 3. Flotation recovery of monazite as a function of flotation time for five pulp pH at 1000 g/t sodium oleate dosage.

4

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Fig. 4. Flotation recovery of hematite as a function of flotation time for five pulp pH at 1000 g/t sodium oleate dosage.

Fig. 6. Flotation recovery of monazite as a function of flotation time for three sodium oleate dosages of 500–3000 g/t at pulp pH 9.

Table 4 Flotation kinetics data of monazite and hematite at pulp pH 3–11 using 1000 g/ t sodium oleate. pH

3 5 7 9 11

k* (min−1)

3.1.2. Effect of sodium oleate dosage on flotation kinetics To investigate the influence of sodium oleate dosage on the selectivity of monazite separation from hematite and quartz, a series of tests was conducted by increasing sodium oleate dosage from 500–3000 g/t. It was observed that the increase in sodium oleate dosage could not float quartz. The effect of sodium oleate dosage on the recovery of monazite and hematite at pulp pH 9 are shown in Figs. 6 and 7, respectively. The results show that the increase in sodium oleate dosage has a significant impact on the recovery of both monazite and hematite. Table 5 is a summary of the flotation rate constants (k*) and maximum recoveries (Rmax) of monazite and hematite at increasing sodium oleate dosage. An increase in sodium oleate dosage from 500–3000 g/t resulted in an increase in monazite recovery from 44–96% and an increase in flotation rate constant from 0.88–2.24 min−1. Similarly, an increase in hematite recovery from 33–80% and a corresponding increase in the rate from 0.26 –1.87 min−1 was observed when sodium oleate was increased from 500–3000 g/t. From Fig. 7, hematite recovery appears to increase after 10 min when 500 g/t sodium oleate was tested. This suggests a longer duration is required to attain maximum hematite recovery at 500 g/t sodium oleate. From Fig. 8, the selectivity of monazite over hematite is shown to deteriorate as sodium oleate dosage was increased. This is reasonable as the flotation rate and recovery of both monazite and hematite were enhanced as sodium oleate dosage was increased.

Rmax (min−1)

Monazite

Hematite

Monazite

Hematite

0.32 0.63 0.61 1.80 0.56

0.59 0.57 0.49 0.78 0.44

17 51 49 74 27

28 35 31 53 20

an increase in rate from 0.59–0.78 min−1 when pulp pH was increased from 3–9. Quartz flotation was not achieved at all the pulp pH investigated, which is consistent with the literature that quartz requires the use of activators to aid in flotation recovery in the presence of sodium oleate (Fuerstenau and Somasundaran, 2003). The selectivity of monazite over hematite as a function of pulp pH is shown in Fig. 5. Generally, the selectivity of monazite increased as the pulp pH increased and peaked at pH 9, and thereafter decreased at pH 11. Pulp pH 9 was thus selected as suitable for monazite recovery in subsequent tests.

Fig. 5. Selectivity index of monazite over hematite as a function of pulp pH at 1000 g/t sodium oleate. Dashed horizontal lines represent point where equal fractions of monazite and hematite report into flotation concentrate (SI = 1.0).

Fig. 7. Flotation recovery of hematite as a function of flotation time for three sodium oleate dosages of 500–3000 g/t at pulp pH 9. 5

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increase in REO recovery from 68–98%, with a decrease in concentrate grade from 1.49–1.31%. For the same increase in sodium oleate dosage, hematite (Fe2O3) recovery increased from 66–77%, whilst quartz (SiO2) recovery also increased from 24–37%. The increased recovery of the gangue minerals (Fig. 9a) explains the decrease in REO concentrate grades (Fig. 9b) obtained. Although SiO2 flotation could not be achieved during the single minerals’ flotation tests, the recovery of SiO2 into the concentrates during the mixed minerals flotation tests could be attributed to SiO2 surface activation by cations such as Fe3+ (dominant) and REE+. Fuerstenau and Somasundaran (2003) indicated that SiO2 requires surface activation by cations, typically but not limited Fe3+, Ca2+, and Al3+ to stimulate flotation in the presence of oleate collectors. Furthermore, fine SiO2 particles in the feed (80 < 75 µm) could also be recovered via entrainment as shown in a previous work by Wang et al. (2016). However, SiO2 recovery remained low (< 40%). This may be attributed to the fact that maximum SiO2 recovery is attained at pH < 5, in the presence of Fe3+ cations (Fuerstenau and Somasundaran, 2003). From the results obtained, it is obvious that the use of sodium oleate to achieve high REO recovery from mixed minerals is possible but requires the use of depressants to enhance selectivity.

Table 5 Flotation kinetics data of monazite and hematite at differing sodium oleate dosages (500–3000 g/t) at pH 9. Sodium oleate dosage (g/t)

500 1000 3000

k* (min−1)

Rmax (min−1)

Monazite

Hematite

Monazite

Hematite

0.88 1.80 2.24

0.26 0.78 1.87

44 74 96

33 53 80

3.2.2. Effect of sodium silicate on REO recovery and upgrade Sodium silicate has been widely used for suppressing iron oxides and silicates during flotation (Satur et al, 2016). The adsorption of hydrolysis products of sodium silicate onto Fe2O3 and SiO2 surfaces decreases their floatability (Bulatovic, 2007; Satur et al., 2016). Based on the previous separation tests, 3000 g/t sodium oleate was selected as the required dosage for maximum REO recovery. Three different sodium silicate dosages (500, 1000, and 4000 g/t) were tested in the presence of 3000 g/t sodium oleate at pH 9. Fig. 10 provides the recovery of REO, Fe2O3, and SiO2 from the low grade hematite–quartz feed mixture in the absence and presence of sodium silicate. The results in Fig. 10 show that sodium silicate could effectively promote the selective recovery of REO from the feed, but the performance deteriorated when significantly high dosage (4000 g/t) is used. Effective separation of REO from the mixture was achieved with 500–1000 g/t sodium silicate, although some fraction of REO was lost to the tails. For example, at 500 g/t sodium silicate dosage, 87% REO was recovered along with 54% Fe2O3 and 25% SiO2, which indicates that 11% of the recoverable REO (at 3000 g/t sodium oleate with no depressants) was lost to the tails. A further increase in sodium silicate dosage to 1000 g/t resulted in a decrease in Fe2O3 and SiO2 recoveries to 24% and 15%, respectively, whereas REO recovery decreased to

Fig. 8. Selectivity index of monazite over hematite as a function of sodium oleate dosage at pH 9. Dashed horizontal lines represent point where equal fractions of monazite and hematite report into flotation concentrate (SI = 1.0).

3.2. Mixed minerals flotation 3.2.1. Flotation recovery of REO in the absence of depressants Prior to investigating the selective flotation of REO from the low grade hematite–quartz mixture, a series of tests was conducted at pulp pH 9, where sodium oleate dosage was increased from 500–3000 g/t to ascertain the required dosage to attain maximum REO recovery in the absence of depressants. Results obtained are shown in Fig. 9. The increase in sodium oleate dosage enhanced REO recovery (Fig. 9a), with a corresponding decrease in concentrate grade (Fig. 9b). For instance, an increase in sodium oleate dosage from 500–3000 g/t saw a significant

Fig. 9. (a) Flotation recovery of REO, Fe2O3, and SiO2 and (b) REO grade in flotation concentrates from mixed minerals as a function of sodium oleate dosage at pH 9. Dashed continuous line indicates REO head grade in the feed mixture. 6

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Fig. 10. Influence of sodium silicate dosage (0–4000 g/t) on (a) flotation recovery of REO, Fe2O3, and SiO2 and (b) REO grade in flotation concentrates in the presence of 3000 g/t sodium oleate at pH 9. Dashed horizontal line represents feed grade.

6.25% (E = 7.53). Overall, 89% Fe2O3 and 90% SiO2 were rejected via the rougher–scavenger flotation test. The results suggest that the synergetic action of the depressants and scavenging of the rougher concentrate enhanced the selectivity of REO.

84%. The depression action of sodium silicate was unselective at 4000 g/t sodium silicate, where REO recovery decreased sharply to 20%, with Fe2O3 (10%) and SiO2 (10%) recoveries remaining lower. Specifically, sodium silicate was more effective in inhibiting Fe2O3 recovery than that of SiO2. The results agree with that reported by Qi et al. (1992), where sodium silicate was found to be efficient depressant towards Fe2O3 at pH 7–11 during the flotation of phosphate minerals (e.g. apatite and monazite). The significant decrease in Fe2O3 and SiO2 recoveries resulted in comparatively higher REO concentrate grades as shown in Fig. 10b. Although the REO concentrate grades were high, a sharp decrease was observed as sodium silicate dosage was increased to 4000 g/t. This can be attributed to the unselective REO loss to the flotation tails.

4. Discussion Typically, pulp pH plays a significant role in the flotation of minerals. In this work, monazite flotation using sodium oleate increased with increasing pulp pH, where maximum recovery was achieved at pulp pH 9. This could be as a result of the chemical interaction between monazite and sodium oleate at pH > the isoelectric point (IEP) of monazite (6.5) as shown in a previous study (Abaka-Wood et al., 2017b). In the previous study, sodium oleate was identified to chemisorb onto monazite surface above neutral pH, whereas the interaction at acidic pulp condition was predicted to be mainly by physisorption (Abaka-Wood et al., 2017b). Chemisorption of sodium oleate is dictated by mainly strong covalent bonding, whereas physisorption occurs via electrostatic and hydrogen bonding, which may be weaker, consequently impacting on the flotation performance (Fuerstenau and Somasundaran, 2003). The experimental results presented in this study show that flotation of monazite is pH-dependent, which is consistent with those reported by Dixit and Biswas (1969), Espiritu and Waters (2018), and Pavez et al. (1996). The decrease in flotation recovery above pH 9, is consistent with the concentration of REE(OH)2+ ions formed when the monazite is solubilised (Cheng et al, 1993). Cheng et al. (1993) measured the adhesive strength of monazite surface with respect to sodium oleate as a function of pH, where the concentration of REE hydroxyl species decreased above pH 9. The results have also shown that pulp pH also affects hematite flotation with sodium oleate, which is consistent with results reported in the literature by Joseph-Soly et al. (2015). Similar to monazite, at pulp pH conditions above the IEP, the dominant mechanism of oleate adsorption, particularly in the neutral to alkaline pH region is described as chemisorption, forming ferric oleate species (Abaka-Wood et al., 2017b; Han et al., 1973; Joseph-Soly et al., 2015). From the results, hematite recovery reaches a maximum at pH 9. This corroborates with that reported by Han et al (1973) where significant adsorption of oleate species onto hematite occurred at pH greater than 8. However, the comparatively lower flotation recovery at pH < 9 may be attributed to unstable ferric oleate species formed (particularly at low Eh conditions) which agrees with results presented by Joseph-Soly et al. (2015). The

3.2.3. Effect of starch on REO recovery and upgrade In order to have a common base for comparing the efficiency of the two depressants, three different starch dosages (500, 1000, and 4000 g/ t) were also tested in the presence of 3000 g/t sodium oleate at pH 9. The results obtained for increasing starch dosage from 0–4000 g/t in the presence of 3000 g/t sodium oleate have been shown in Fig. 11. The selectivity of REO was enhanced with the increase in starch dosage, although a general decrease in flotation recovery was observed. For example, an increase in starch dosage from 500–1000 g/t resulted in a decrease in REO recovery from 89 to 65% with a corresponding increase in grade from 2.32–5.56%, whilst Fe2O3 and SiO2 recoveries decreased from 50–11% and 21–7%, respectively. In terms of REO grade, the best result was attained when 4000 g/t starch was used, where a grade of 8.18% at 9% recovery was obtained. The results suggest that, indeed REO can also be selectively separated from Fe2O3 and SiO2 using starch as a depressant. However, the efficiency of the process is dependent on the starch dosage. With significant amount of REO lost to the tails at 4000 g/t of each depressant dosage, 1000 g/t of either depressant was considered optimum in the presence of 3000 g/t sodium oleate for recovering and upgrading REO from the feed mixture. 3.3. Flotation response in the presence of sodium silicate and starch mixture A detailed metallurgical balance of the test conducted using the flowsheet in Fig. 2 (described in Section 2.2) is presented in Table 6 and Fig. 12. From the metallurgical balance data, 61% of the REO content in the feed was recovered into the final flotation concentrate at a grade of 7

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Fig. 11. Influence of starch dosage (0–4000 g/t) on (a) flotation recovery of REO, Fe2O3, and SiO2; and (b) REO grade in flotation concentrates in the presence of 3000 g/t sodium oleate at pH 9. Dashed horizontal line represents feed grade.

concentrate grades when sodium silicate was used. This agrees with that presented by Chelgani et al. (2015), that although sodium silicate is an effective depressant, it slightly decreases monazite floatability. However, the comparatively higher REO recoveries in the presence of sodium silicate could be associated with the ability of sodium silicate to activate monazite surface (Beloglazov and Osolodkov, 1936; Chelgani et al., 2015; Sørensen and Lundgaard, 1966). In terms of REO upgrade, starch is clearly superior with enrichment ratios ranging 2.81–9.86, compared with 2.10–4.98 when sodium silicate was used. In a similar study by Abaka-Wood et al. (2017a), the use of sodium silicate in the presence of oleic acid produced better REO recovery and upgrade compared to starch. The differences in the outcomes suggest that indeed the oleate form/type affects the performance of a flotation system where sodium silicate and starch are used. Future work to unravel the detailed interactions between differing oleate forms and REE minerals (typically monazite) is recommended, as there is a paucity of knowledge and data in the literature. A similar work has been undertaken by Quast (2006) where different forms of fatty acids were tested during hematite flotation. From Fig. 14a and b, comparatively higher proportions of the gangue minerals were removed from the concentrates when starch was used. This suggests that starch is more effective in decreasing Fe2O3 and SiO2 recoveries than sodium silicate. A similar result was reported by Shi et al. (2014) for calcite depression with sodium silicate and starch during sodium oleate flotation, where starch showed superior depressing ability in the absence of lattice ions. Starch has also been

Eh values measured in the present work ranged between 120 and 180 mV which is agrees with low Eh measured by Joseph-Soly et al. (2015). On the other hand, the sharp decrease in hematite floatability with the increase in pH from 9 to 11, could be associated with the competition for adsorption site on hematite surface between oleate and hydroxyl ions, and the likelihood of oleate ions forming solution micelles instead of ferric oleate (Joseph-Soly et al., 2015). Overall, monazite and hematite have similar interaction with sodium oleate, which impacts negatively on flotation selectivity. This challenge is exacerbated in ores, where quartz and hematite form the bulk of the gangue constituents. Ferric ions from hematite are likely to cause quartz surface activation to promote quartz recovery during sodium oleate flotation. From previous studies, sodium silicate and starch have been identified as key depressants of hematite and quartz. It is not the purpose of this paper to review the depressant mechanisms of sodium silicate and starch as they have been well documented in the literature (Araujo et al., 2004; Bai et al., 2019; Bulatovic, 2007; Filippov et al., 2013; Hanna and Somasundaran, 1976; Laskowski et al., 2007; Moreira et al., 2017; Qi et al., 1992; Satur et al., 2016; Somasundaran and Wang, 2006; Turrer and Peres, 2010; Yang et al., 2017). Fig. 13 compares the flotation recovery and upgrade of REO from low grade model mixtures when sodium silicate and starch were used, respectively. The depressants performance in terms of REO recovery and upgrade is dependent on the depressant type and dosage used. Flotation achieved significantly higher REO recoveries with lower

Table 6 Metallurgical balance of the flotation test conducted using flowsheet presented in Fig. 2. Product

Feed Rougher conc. (RC) Rougher tails. (RT) Scavenger conc. (SC) Scavenger/Final tails Composite conc. (RC + SC)

Mass recovery (%)

100 2 98 9 89 11

REO

Fe2O3

SiO2

Grade (%)

Recovery (%)

Fe grade (%)

Recovery (%)

Si grade (%)

Recovery (%)

0.83 11.31 0.60 2.23 0.45 6.25

100 27 73 34 39 61

32.70 28.80 32.78 32.30 32.83 31.73

100 2 98 9 89 11

23.70 13.40 23.91 23.80 23.92 22.66

100 1 99 9 90 10

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Fig. 12. Metallurgical balance of REO distribution in the rougher–scavenger flotation flowsheet (in Fig. 2).

Fig. 13. Comparison of (a) REO recovery and (b) REO enrichment ratio in flotation concentrates obtained from low grade hematite–quartz mixtures.

demonstrated to flocculate iron oxides, which reduces the amount of iron oxides recovered by entrainment (Liu et al., 2006). Furthermore, some laboratory scale direct flotation of iron ores using fatty acids, have shown that sodium silicate has limited efficency in depressing silicate minerals (Araujo et al., 2004; Casquet, 1995.; Luz, 1996; Vieira, 1995). The multistage (rougher–scavenger) flotation test also showed promising results, with significant REO upgrade, although recovery was lower compared with those obtained during the single stage flotation tests which can be attributed to the synergistic impact of combining sodium silicate and starch. Fig. 15 compares the results of REO recovery and grade during the rougher stages when the depressants were used individually to when they were mixed in the presence of 3000 g/t sodium oleate. This approach highlights the significance of synergism of the depressants in the recovery and upgrade of REO. Synergism of the depressants can be considered to improve flotation selectivity of REO by, (i) enhancing the depressing ability and selectivity of sodium silicate and starch, (ii) enhancing the selectivity of sodium oleate for REO, and (iii) reducing the sensitivity of sodium oleate in the flotation of both Fe2O3 and SiO2.

5. Conclusions This work investigated the flotation kinetics of monazite in comparison with hematite and quartz using sodium oleate as a collector. The influence of pulp pH and sodium oleate dosage, respectively on the flotation kinetics of monazite, hematite, and quartz was tested in a microflotation study. Maximum flotation recovery of both monazite and hematite occurred at alkaline pH (9) condition. The selectivity of monazite over hematite was enhanced at pH 9 and shown to deteriorate with increased sodium oleate dosage. The flotation conditions investigated were unfavourable for quartz recovery. The flotation kinetics data indicated depressants are required to achieve selective flotation recovery of monazite from hematite–quartz mixtures using sodium oleate. The challenge of monazite flotation selectivity from hematite–quartz mixtures was aggravated by quartz surface activation by soluble cations from hematite and monazite resulting in the entrained recovery of quartz. In order to depress hematite and quartz, sodium silicate and starch were tested. Both depressants produced desirable results, but 9

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Fig. 14. Comparison of (a) Fe2O3 removed and (b) SiO2 removed from flotation concentrates obtained from low grade hematite–quartz mixture. The percentage of gangues removed was calculated as a fraction of the those recovered when the test was conducted using 3000 g/t sodium oleate in the absence of depressants.

Fig. 15. Comparison of REO (a) recovery and (b) grade in rougher flotation concentrates obtained from low grade hematite–quartz mixture.

However, a rougher–scavenger flotation test conducted with mixed sodium silicate–starch produced a final concentrate recovering 61% REO at a grade 6.25% (E = 7.53) at Fe2O3 and SiO2 contamination levels of 11% and 10%, respectively. The results suggest that REO can be separated selectively from hematite–quartz rich ores by means of flotation using sodium oleate with sodium silicate and starch as depressants. The research outcome is crucial in deciding on the flotation conditions (sodium oleate dosage, depressant type and dosage, and pulp pH) for recovering and upgrading valuable REE minerals from iron oxide–silicate rich tailings/ores. Unlike model minerals, real ores are complex and have liberation challenges which can affect the overall flotation separation output.

starch was superior in terms of decreasing the recoveries of both hematite and quartz, thus producing higher REO upgrade. Starch produced a higher grade of REO due to the adsorption of thick, hydrated film onto hematite and silicon sites of quartz; and subsequent flocculation of hematite versus the formation of insoluble silicates when sodium silicate reacts with metallic ions (in hematite and quartz) which is comparatively less effective. However, these mechanisms need to be investigated further. The separation of REO from low grade hematite–quartz mixture (assaying 0.83% REO) in the absence of depressants was unselective, where 3000 g/t sodium oleate recovered 98% REO (E = 1.58) along with 77% Fe2O3 and 37% SiO2. The use of depressants in the presence of 3000 g/t sodium oleate produced the following rougher flotation concentrates:

Acknowledgement

• 1000 g/t sodium silicate: 84% REO assaying a grade of 4.13% (E = 4.98), 23% Fe O , and 15% SiO . • 1000 g/t starch: 65% REO assaying a grade of 5.56% (E = 6.70), 11% Fe O , and 7% SiO . • 1000 g/t sodium silicate + 1000 g/t starch: 27% REO assaying 2

2

3

3

This work was supported by the Australian Government Research Training Program Scholarship and Future Industries Institute of the University of South Australia, Adelaide.

2

2

References

11.31% (E = 13.63), 2% Fe2O3, and 1% SiO2.

Abaka-Wood, G.B., Addai-Mensah, J., Skinner, W., 2016. Froth flotation of Monazite from Mixed Minerals. In: Chemeca (Ed.), Chemeca Conference 2016. Engineers Australia,

10

Minerals Engineering 141 (2019) 105847

G.B. Abaka-Wood, et al.

depressants for iron ore flotation. Miner. Eng. 49, 1–6. Laskowski, J., Liu, Q., O'Connor, C.T., 2007. Current understanding of the mechanism of polysaccharide adsorption at the mineral/aqueous solution interface. Int. J. Miner. Process. 84 (1–4), 59–68. Liu, Q., Wannas, D., Peng, Y., 2006. Exploiting the dual functions of polymer depressants in fine particle flotation. Int. J. Miner. Process. 80 (2–4), 244–254. Luz, J.A.M., 1996. Anionic flotation of itabirite tailings: study on alternative reagents and polyphasic process modelling, CPGEM-UFMG, pp. 253. Montes-Sotomayor, S., Houot, R., Kongolo, M., 1998. Flotation of silicated gangue iron ores: mechanism and effect of starch. Miner. Eng. 11 (1), 71–76. Moreira, G.F., Peçanha, E.R., Monte, M.B., Leal Filho, L.S., Stavale, F.J.M.E., 2017. XPS study on the mechanism of starch-hematite surface chemical complexation. 110, 96–103. Muganda, S., Zanin, M., Grano, S.R., 2011. Influence of particle size and contact angle on the flotation of chalcopyrite in a laboratory batch flotation cell. Int. J. Miner. Process. 98 (3–4), 150–162. Owusu, C., e Abreu, S.B., Skinner, W., Addai-Mensah, J., Zanin, M., 2014. The influence of pyrite content on the flotation of chalcopyrite/pyrite mixtures. Miner. Eng. 55, 87–95. Pavez, O., Brandao, P., Peres, A., 1996. Adsorption of oleate and octyl-hydroxamate on to rare-earths minerals. Miner. Eng. 9 (3), 357–366. Pavlovic, S., Brandao, P.R.G., 2003. Adsorption of starch, amylose, amylopectin and glucose monomer and their effect on the flotation of hematite and quartz. Miner. Eng. 16 (11), 1117–1122. Peres, A., Correa, M., 1996. Depression of iron oxides with corn starches. Miner. Eng. 9 (12), 1227–1234. Pol’kin, S.I., Ilie, P., Solnyshkin, V.I., Zakharov, A.E., 1967. Selective Desorption of Sodium Oleate from Pyrochlore, Zircon and Monazite by Sodium Sulfide. In: Plaksin, I.N. (Ed.), Flotation Properties of Rare Metal Minerals. Primary Sources, New York, USA, pp. 46–56. Qi, G.W., Parentich, A., Little, L., Warren, L., 1992. Selective flotation of apatite from iron oxides. Int. J. Miner. Process. 34 (1–2), 83–102. Quast, K., 2000. A review of hematite flotation using 12-carbon chain collectors. Miner. Eng. 13 (13), 1361–1376. Quast, K., 2006. Flotation of hematite using C6–C18 saturated fatty acids. Miner. Eng. 19 (6), 582–597. Quast, K., 2015. Use of conditioning time to investigate the mechanisms of interactions of selected fatty acids on hematite Part II laboratory investigations. Miner. Eng. Ren, J., Lu, S., Song, S., Niu, J., 1997. A new collector for rare earth mineral flotation. Miner. Eng. 10 (12), 1395–1404. Satur, J.V., et al., 2016. Flotation of rare earth minerals from silicate–hematite ore using tall oil fatty acid collector. Miner. Eng. 89, 52–62. Shi, Q., Feng, Q., Zhang, G., Deng, H.J.M.E., 2014. A novel method to improve depressants actions on calcite flotation. 55, 186–189. Shibata, J., Fuerstenau, D., 2003. Flocculation and flotation characteristics of fine hematite with sodium oleate. Int. J. Miner. Process. 72 (1), 25–32. Somasundaran, P., Wang, D., 2006. Solution Chemistry: Minerals and Reagents. Elsevier. Sørensen, E., Lundgaard, T., 1966. Selective Flotation of Steenstrupine and Monazite from Kvanefjeld lujavrite. Danish Atomic Energy Commission, Roskilde, Denmark. Sripriya, R., Rao, P., Choudhury, B.R., 2003. Optimisation of operating variables of fine coal flotation using a combination of modified flotation parameters and statistical techniques. Int. J. Miner. Process. 68 (1), 109–127. Turrer, H.D.G., Peres, A., 2010. Investigation on alternative depressants for iron ore flotation. Miner. Eng. 23 (11–13), 1066–1069. Vieira, A.M., 1995. Study on the technical feasibility of concentrating a mine waste containing iron. M.Sc. Thesis, CPGEM-UFMG, pp. 145. Wang, L., Peng, Y., Runge, K., 2016. Entrainment in froth flotation: the degree of entrainment and its contributing factors. Powder Technol. 288, 202–211. Wills, B.A., Finch, J., 2015. Wills' Mineral Processing Technology: An Introduction to the Practical Aspects of Ore Treatment and Mineral Recovery. Butterworth-Heinemann. Xia, L., Hart, B., Chelgani, S., Douglas, K., 2014. Hydroxamate Collectors for Rare Earth Minerals Flotation, Conference of Metallurgists 2014. Canadian Institute of Mining, Metallurgy and Petroleum, Vancouver, Canada, pp. 9. Xia, L., Hart, B., Douglas, K., 2015. The role of citric acid in the flotation separation of rare earth from the silicates. Miner. Eng. 74, 123–129. Yang, S., Li, C., Wang, L.J.P.T., 2017. Dissolution of starch and its role in the flotation separation of quartz from hematite. 320, 346–357.

Adelaide, Australia, pp. 605–612. Abaka-Wood, G.B., Addai-Mensah, J., Skinner, W., 2017a. Selective flotation of rare earth oxides from hematite and quartz mixtures using oleic acid as a collector. Int. J. Miner. Process. 169, 60–69. Abaka-Wood, G.B., Addai-Mensah, J., Skinner, W., 2017b. A study of flotation characteristics of monazite, hematite, and quartz using anionic collectors. Int. J. Miner. Process. 158, 55–62. Abeidu, A.M., 1972. The separation of monazite from zircon by flotation. J. Less Common Metals 29 (2), 113–119. Amelunxen, P., Sandoval, G., Barriga, D., Amelunxen, R., 2014. The implications of the froth recovery at the laboratory scale. Miner. Eng. 66, 54–61. Amelunxen, P., LaDouceur, R., Amelunxen, R., Young, C., 2018. A phenomenological model of entrainment and froth recovery for interpreting laboratory flotation kinetics tests. Miner. Eng. 125, 60–65. Arantes, R., Lima, R.M.F., 2013. Influence of sodium silicate modulus on iron ore flotation with sodium oleate. Int. J. Miner. Process. 125, 157–160. Araujo, A., Viana, P., Peres, A., 2004. Reagents in iron ores flotation. Miner. Eng. 18 (2), 219–224. Bai, S., Ding, Z., Fu, X., Li, C., Lv, C., Wen, S., 2019. Investigations on soluble starch as the depressant of hematite during flotation separation of apatite. Physicochem. Probl. Miner. Process. 55 (1), 38–48. Beloglazov, K.F., Osolodkov, G.A., 1936. Effect of the alkalinity of the pulps on flotation of apatite. Rep Leningr Min Inst 1, 26–30. Bulatovic, S.M., 2007. Handbook of Flotation Reagents: Chemistry, Theory and Practice: Volume 1: Flotation of Sulfide Ores. Elsevier. Casquet, R.Q., 1995. Mineralogical and Technological Characterisation of the Itabirite Iron Ore from the Alegria South Mine. Ouro Preto-MG, CPGEM-UFMG, pp. 240. Chelgani, S.C., Rudolph, M., Leistner, T., Gutzmer, J., Peuker, U.A., 2015. A review of rare earth minerals flotation: monazite and xenotime. Int. J. Min. Sci. Technol. 25 (6), 877–883. Cheng, T.-W., Holtham, P., Tran, T., 1993. Froth flotation of monazite and xenotime. Miner. Eng. 6 (4), 341–351. Chipfunhu, D., Zanin, M., Grano, S., 2012. Flotation behaviour of fine particles with respect to contact angle. Chem. Eng. Res. Des. 90 (1), 26–32. Cuthbertson, R.E., 1952. Froth flotation of monazite from heavy gravity minerals. Google Patents. Dixit, S., Biswas, A., 1969. pH-Dependence of the flotation and adsorption properties of some beach sand minerals. Trans. Soc. Min. Eng. AIME 244 (2), 173–178. Ehrig, K., McPhie, J., Kamenetsky, V., 2012. Geology and mineralogical zonation of the Olympic Dam Iron Oxide Cu-U-Au-Ag deposit. Society of Economic Geologists, Inc., South Australia, pp. 31. Espiritu, E., Waters, K., 2018. Flotation studies of monazite and dolomite. Miner. Eng. 116, 101–106. Filippov, L., Severov, V., Filippova, I., 2014. An overview of the beneficiation of iron ores via reverse cationic flotation. Int. J. Miner. Process. 127, 62–69. Filippov, L.O., Severov, V.V., Filippova, I.V., 2013. Mechanism of starch adsorption on Fe–Mg–Al-bearing amphiboles. Int. J. Miner. Process. 123, 120–128. Fuerstenau, D., 2013. Design and development of novel flotation reagents for the beneficiation of Mountain Pass rare-earth ore. Miner. Metall. Process. J. 30 (1), 1–9. Fuerstenau, M.C., Somasundaran, P., 2003. Flotation. In: Fuerstenau, M.C., Han, K.N. (Eds.), Principles of Mineral Processing. SME, New York, pp. 245–300. Geoscience-Australia, 2012. Australia’s Identified Mineral Resources 2011. Geoscience Australia, Canberra. Geoscience-Australia, 2014. Australia’s Identified Mineral Resources 2013. Geoscience Australia, Canberra. Han, K., Healy, T., Fuerstenau, D., 1973. The mechanism of adsorption of fatty acids and other surfactants at the oxide—water interface. J. Colloid Interface Sci. 44 (3), 407–414. Hanna, H.S., Somasundaran, P., 1976. FIotation of salt- type minerals. In: Fuerstenau, M.C. (Ed.), Flotaton, A.M. Gaudin Memorial Volume. AIME, New York, pp. 197–272. Houot, R., Cuif, J.-P., Mottot, Y., Samama, J.-C., 1991. Recovery of rare earth minerals, with emphasis on flotation process. Mater. Sci. Forum Trans. Tech. Publ. 301–324. Jordens, A., Cheng, Y.P., Waters, K.E., 2013. A review of the beneficiation of rare earth element bearing minerals. Miner. Eng. 41, 97–114. Joseph-Soly, S., Quast, K., Connor, J.N., 2015. Effects of Eh and pH on the oleate flotation of iron oxides. Miner. Eng. 83, 97–104. Kar, B., Sahoo, H., Rath, S.S., Das, B., 2013. Investigations on different starches as

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