Polluted river sediments from the North region of France: Treatment with Novosol® process and valorization in clay bricks

Construction and Building

MATERIALS

Construction and Building Materials 22 (2008) 755–762

www.elsevier.com/locate/conbuildmat

Polluted river sediments from the North region of France: Treatment with NovosolÒ process and valorization in clay bricks Zoubeir Lafhaj

a,*

, Mazen Samara a, Franck Agostini a, Linda Boucard a, Fre´de´ric Skoczylas a, Guy Depelsenaire b

a b

Ecole Centrale de Lille, Laboratoire de Me´canique de Lille, CNRS UMR 8107, Cite´ Scientifique, Villeneuve d’Ascq, 59651 Ce´de`x, France HSE – Health, Safety, Environment, Direction Centrale Recherche et Technologie, Solvay, Rue de Ransbeek 310, B-1120 Bruxelles, Belgium Received 29 December 2005; received in revised form 12 December 2006; accepted 29 January 2007 Available online 26 March 2007

Abstract The paper presents results of studies on the valorisation of polluted river sediments from the North region of France. The first objective of this study is to validate the treatment of polluted sediments with the NovosolÒ process. This process is based on the stabilization of heavy metals in the solid matrix by phosphatation and the destruction of organic matter by calcination. The results of environmental tests carried out on treated sediments showed that polluted sediments became inert. In addition, the physical characterisations of treated sediments classify them as sandy silt. Thus treated sediments were used as a brick making raw material. The second objective of the study is to determine the optimal mix-design. Four mix-designs were studied with treated sediment ratio varying from 0% to 45%. Physical, mechanical and chemical properties of these bricks were evaluated. The results obtained indicated that sediment proportion is an important parameter in determining the brick quality. Increasing the sediment content resulted in a decrease of brick compressive strength (though it is still higher than that of standard brick) and a decrease of its resistance to freezing and thawing. Leaching tests, performed according to different standards on substituted brick samples, showed that the quantities of heavy metals leached from crushed bricks were within the regulatory limits. The 35% ratio of substitution appeared to be the most effective considering physical, mechanical and chemical aspects. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: River sediments; Heavy metals; Phosphatation; Calcination; Clay bricks

1. Introduction Channels and ports must be dredged regularly to maintain normal maritime and river activities, thus a great number of industries congest the channels by tipping sediments out [1]. Over the next 15 years, a volume of three million m3 of polluted river sediments is to be dredged in the North of France. These sediments contain both organic and inorganic contaminants, which can end up in drains, rivers, and coastal waters, thus contaminating water resources and polluting the environment. The pollution of these sediments is linked to the industrial history of the region, *

Corresponding author. Tel.: +33 3 20 33 53 65; fax: +33 3 20 33 53 52. E-mail address: [email protected] (Z. Lafhaj).

0950-0618/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2007.01.023

where certain activities, like iron and steel industries, metallurgy of nonferrous ores and energy sectors, remain polluting. Since international and European laws have become more stringent, sediments have to be treated as waste material. Sea deposit will no longer be licensed as this causes serious damage to marine fauna and flora. Therefore, their management has become an environmental and economical concern for a large number of countries [2]. The dredging operation and the effect of dredged material disposal in open water have been largely investigated [3,4]. Storage in confined disposal facilities requires large spaces and long term monitoring. However, land filling is less accepted by the public opinion. Treatment processes permit a reduction in toxicity and volume of dredged material, but in comparison with open-water and upland dis-

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posal, the treatment cost is not yet competitive enough [5]. This underlines the necessity to find ecological valorisation paths for the processed sediments to make these alternatives economically competitive. Thus, researchers have started to study alternative ways to incorporate large amounts of processed sediments into different aspects of construction and building materials, where raw sediments have to be treated before being valorised. In recent decades, several types of waste materials have been assessed as raw materials for brick making, for example lightly contaminated harbour sediments [6–8], reservoir sediments mixed with fly ash [9], dried sludge collected from industrial wastewater treatment [10–12], incinerated sewage sludge ash [13–15], fly ash [16], granite sawing waste materials [17], water treatment residuals with excavation waste soil [18] and steel dust [19]. Considering their perpetual availability, particle sizing and their chemical composition, sediments are regarded as a suitable raw material for brick production. Clay bricks generally consist of natural clay and sand. This material can tolerate the presence of different types of waste materials even in considerable percentages. The present work aims at studying the feasibility of incorporating treated river-sediments, with different percentages, into the production of fired clay bricks. The influence of sediment proportion was therefore examined. We start with a description of the NovosolÒ process used for the treatment of polluted sediment. The next section deals with the characterisation of raw and treated sediments. Finally, experimental results and the incorporation of treated sediment in clay bricks are established. 2. The NovosolÒ process In this study polluted sediments were stabilised using the NovosolÒ process (Fig. 1) which consists of two major phases: phosphatation and calcination. This process was developed and patented by the Solvay Company [20]. During the phosphatation phase, raw sediments are mixed with phosphoric acid H3PO4 (2–3.5%) in a tubular reactor. The addition of phosphoric acid allows, in the presence of calcite, the formation of calcium phosphates minerals.

Raw Sediments (50 % H2O)

These minerals are known for their low solubility and their ability to fix heavy metals [21]. Numerous studies have assessed the efficiency of these compounds for heavy metal remediation of contaminated soils [22,23], fly ashes and municipal solid wastes [24–28]. The calcination phase consists of calcining the phosphated sediments at P650 °C in a rotary kiln, in order to break down the organic matter (polycyclic aromatic hydrocarbons, dioxins and pesticides). It increases the product toughness, reduces the volumes of processed materials after treatment and allows a better stabilization of metal phosphates. The treatment of one ton of raw sediments with a water content of 50% costs 75€. Gaseous emissions resulting from the treatment process (essentially H2S and CO2 and traces of heavy metals) are chemically treated using activated charcoal and sodium bicarbonate (NeutrecÒ double-filtration dry sodium bicarbonate process patented by Solvay for flue gas cleaning and recycling of residues [29]). Two types of solid waste are generated by this treatment: industrial waste incinerator (IWI) fly ash (20 kg per ton of sediment) and residual sodium chemicals (RSC: 7–13 kg per ton of sediment). The chemical composition of IWI is very complex (based on heavy metal oxides). This residue is chemically stabilised to be incorporated in road-building materials. The RSC are chemically treated and filtered where a raw brine and filtration cake are obtained. The brine is purified and injected into sodium carbonate production. 3. Characterization of raw and treated river sediments 3.1. Raw sediment The sediments used come from the Nord-Pas-de-Calais region (France). Two types of sediments were analyzed. The first one (Araw) was dredged in the channels of Lille, and the second one (Braw) was taken from the river La Marque in the North of France. Table 1 gives the concentrations of heavy metals in these two types of raw river sediments, where five metal species of daily concern were selected (cadmium, chromium, copper, lead and zinc). French levels of reference, given by the Official Journal [30], are also reported in this table. Below level N1, the potential impact is regarded, in principle, as neutral or neg-

Phase1: Phosphatation Fixing of heavy metals into stable crystal phases Ca10(PO4)6(OH)2 → Ca10-

Phase2: Calcination Oven (> 650˚C) Drying beds

Thermal treatment

YMeY(PO4)6(OH)2

Phosphoric acid H3PO4 (2-3.5%)

Gas treatment (Active charcoal)

Storage of treated sediments

Valorization

Fig. 1. Schematic representation of the NovosolÒ process.

Z. Lafhaj et al. / Construction and Building Materials 22 (2008) 755–762 Table 1 Total concentrations of heavy metals in two types of raw river sediments in mg/kg on dry material Element

Cadmium (Cd)

Chromium (Cr)

Copper (Cu)

Lead (Pb)

Zinc (Zn)

Araw Braw Level N1 Level N2

10.4 27.4 1.2

516 940 90

190 425 45

318 922 100

2020 3966 276

2.4

180

90

200

552

ligible. Between levels N1 and N2, further investigations may prove necessary depending on the project considered and on the extent to which action level N1 is exceeded. Beyond N2 level, additional investigation is generally necessary since significant indices suggest a potentially harmful impact of the operations [31]. From Table 1 we can observe that raw sediments exhibit high concentrations of heavy metals and the values of type B are higher than those of type A. This scatter is due to different industrial activities in the areas where these sediments have been dredged. We also note that the values for both types largely exceed level N2. As an example, the concentration of Zn increases from 2020 to 3966 (mg/ kg). Both values largely exceed N2 level which is equal to 552 (mg/kg). Finally, results presented in Table 1 emphasis that polluted raw sediments have to be treated before being valorized. On the other hand these sediments contain 15.6% (on dry basis) of organic matter [32]; thus, to avoid the uneven surface texture of bricks, they need to be calcined before being introduced into brick production. 3.2. Application of the NovosolÒ process to raw river sediments The NovosolÒ process was applied to raw sediments. Table 2 shows the average results of a leaching test carried out on both raw and treated sediments in accordance with the French standard [33]. The limits, given by the Commission of European communities and described in the Official Journal of the European Community [34], are reported in this table. From Table 2, it can be observed that the quantities of heavy metals leached from treated sediments are smaller than those of raw ones, and these values are largely within the regulated limits, thus treated sediments are considered as inert waste.

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As an example, the concentration of Zn drops from 1.21 mg/kg in polluted sediments to 0.30 mg/kg in treated ones. As the limit value for waste acceptance as inert material is equal to 4, we can conclude that for Zn, the material can be considered as inert. 3.3. Physical and chemical characterisation of treated sediments The processed material is a new material and its characteristics have to be established. The treated sediment can be described as an odourless, fine grained powder of low apparent density (0.93 g cm 3) and a particle density of 2.85 g cm 3 (comparable to that of clay 2.6–2.7 g cm 3). The individual granules making up the bulk material are generally angular to round in shape and composed mainly of agglomerates of fine particles, which gives them a high specific surface area and the ability to absorb a lot of water. The porosity of these sediments was measured and it was found to be very high (48–55%). Mineralogical and chemical analyses considered most pertinent to the future use in commercial brick making were undertaken on the treated sediments. The diffractograms show that these sediments are composed mainly of quartz (SiO2). It also reveals a marked presence of hematite (Fe2O3), calcite (CaCO3) and some feldspar traces [anorthite: (Ca,Na)(Si,Al)4O8]. The chemical composition of the treated sediments is given in Table 3 [42]. The presence of hematite gives an encouraging support for the beneficial use of these sediments in brick making, as iron is recognised to posses good fluxing properties [13,14]. A granular characterisation of treated sediments was carried out. The results are given in Table 4.

Table 3 Chemical composition of treated sediments (%) SiO2

Al2O3

Fe2O3

MgO

CaO

Na2O

K2O

P2O5

SO3

LOI

54.33

8.22

14.27

1.72

10.89

0.68

1.49

3.49

0.8

3.68

Table 4 Granular distribution of treated sediments Granular distribution

Sand fraction

Silt fraction

Clay fraction

Treated sediments (%)

20.61

74.43

4.96

Table 2 Concentrations of main heavy metals in the leachates of raw and treated sediments according to French standards in mg/kg on dry material Element

Raw sediment

Treated sediment

Limit values for waste acceptable as inert L/ S = 10 (l/kg)

Limit values for waste acceptable as nonhazardous L/S = 10 (l/kg)

Cd Cu Zn Ni Pb

<0.03 5.97 1.21 4.63 <0.2

<0.03 0.87 0.301 0.08 <0.2

0.04 2 4 0.4 0.5

1 50 50 10 10

Z. Lafhaj et al. / Construction and Building Materials 22 (2008) 755–762

In particle sizing, the treated sediments are seen to be mainly composed of silt to fine sand particles, thus the grain size distribution classifies them as sandy silt. The liquid limit (the water content at which a soil changes from a plastic state into a liquid state) was determined using the Atterberg’s test [35]. A value of 50.21% was found. The plastic limit (the water content at which a soil changes from a solid into a plastic state) could not be determined using this test because of the non plastic behaviour of this material, thus a methylene blue adsorption test was conducted using the French normalization standard [36]. This test gives a semiquantitative evaluation of clay activity in these sediments. A value of (0.075) was obtained, which explains the non plastic behaviour of this material.

80

70

Temperature / deg

758

60

50

40

30 0

4. Valorisation of treated river sediments in clay brick

500

1000

1500

2000

2500

3000

3500

4000

56

64

Time / minutes

4.1. Materials and methods

Fig. 2. Drying program of bricks.

Table 5 Mix-designs prepared for the production of clay bricks (wt% on dry material) Mix-design

Sand (%)

Treated sediments (%)

Clay (%)

F0% F25% F35% F45%

20 20 20 20

0 25 35 45

80 55 45 35

1000

800

Temperature / deg

The valorisation study involved the incorporation of various proportions of treated sediments into the production of clay bricks. In order to obtain various samples containing different percentages of treated sediments, brick specimens were prepared with different treated sediment/ clay ratios. Clay and sand were obtained from a local brick factory. The mix-design currently used at this factory is composed of the following raw material components (on a dry weight basis): 42% of clay, 30% of sand and 28% of silt. Clay was ground before being added with sand to the mix-designs. Four separate mix-designs were fabricated. Their compositions (dry weight basis) are shown in Table 5 together with their respective identification codes. The quantity of sand was fixed at 20% for all mix-designs, while sediment addition varied from 0% to 45%.These mixdesigns were first dry-blended in a Z-blade mixer, and then a sufficient amount of water was added to bring them to an appropriate level of plasticity. After tempering, the four plastic bodies were formed into test specimens using a laboratory extruder. A vacuum machine was used to expel the air from the mixture to avoid cracking during firing. Atterberg’s test was conducted to establish the plastic nature of mix-designs. Brick specimens were dried off in a tunnel dryer under a temperature varying from 34 to 80 °C following the drying schedule demonstrated in Fig. 2.

600

400

200

0 0

8

16

24

32

40

48

Time/ h Fig. 3. Heating program of bricks.

Brick specimens are then fired in the tunnel kiln of the local brick factory at 1010 °C according to the firing procedure described in Fig. 3, where the temperature was raised at a heating rate of 0.5 °C per minute up to 573 °C (quartz point), then up to 930 °C at a rate of 0.8 °C per minute, and later up to the peak temperature at a rate of 0.3 °C per minute. The processed material is a new material which needs to be defined and characterised. The produced bricks underwent a series of tests according to French standards including compressive strength, freeze and thaw resistance, water absorption, efflorescence and heavy metal leaching to determine the properties of this new material.

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4.2.1. Atterberg’s test The results of the Atterberg’s test carried out on all mixdesigns are given in Table 6. These results indicate that the plasticity index (PI) is inversely proportional to the amount of added sediments, thus the addition of treated sediments lowers the plastic properties of the mixture and decreases its bonding ability. The values of the plasticity index (PI) classify all mixdesigns as low-plastic mixtures. 4.2.2. Water absorption Water absorption is a key factor affecting the durability of a material and its resistance to natural environment. High water absorption may facilitate the ingress of aggressive species in the material and accelerate its deterioration. Low water infiltration into the brick indicates a good durability of the brick and resistance to the natural surroundings. A water absorption test was done using the procedure as described in the French standard [37]. Table 7 presents the results of the water absorption test for all mix-designs. We can observe that all mix-designs are within the regulatory limit and the water absorption of the bricks increases with increased sediment addition. The addition of treated sediments decreases the bond ability of the mixture and increases the internal pore size of the brick. As a result the quantity of absorbed water increases. On the other hand the presence of calcite (CaCO3) influences the porosity evolution during firing. At temperatures around 800 °C, calcite is transformed into microporous calcium oxide (CaO). This transformation is accompanied by an increase in porosity [38]. In presence of water vapour, the lime is converted into portlandite (Ca(OH)2). This process generates crystallization pressure in the pores originally occupied by CaO, resulting in cracks development producing further increase in porosity which is directly related to the water absorption [39].

are cylinders of 37 mm diameter and 72 mm height. They were cored from larger cylinders and then rectified to make the sample faces smooth and parallel. The compressive strength of the cylindrical specimens was measured using a 30 kN Instron mechanical press. The results obtained are shown in Fig. 4. The presented result is an average of measurements performed on three samples taken from the same core. It can be noticed that the strength is affected by the amount of sediment incorporated into the brick. The increase of sediment proportion results in a decrease of the mechanical strength. This result is in accordance with the water absorption results, where it has been stated that the addition of treated sediments results in an increase in the internal pore size. Thus the brick becomes more porous, which results in a decrease in mechanical strength. As an example of the results obtained, we present in Fig. 5 the compressive strength at failure for F35% in MPa. Roughly, the stress–strain curve can be divided into two characteristic parts. The first part represents the closing of cracks, where an increase of strain is observed without a significant increase in stress. The second represents the linear ascending branch, observed until the specimen 50

Mechanical strength / MPa

4.2. Results and discussion

Liquid limit (%)

Plastic limit (%)

Plasticity index

F0% F25% F35% F45%

39.2 37.8 36.1 34.25

20.8 20.75 23.7 23.7

18.4 17.05 12.4 10.55

42.23

40 31.20

35 30

25.58

25 20 15 10 5 0

25

35

45

Sediment addition / % Fig. 4. Effect of sediment proportion on the compressive strength. 35

30

25

Stress / MPa

Mix-design

43.70

45

0

4.2.3. Compressive strength Resistance to compression is a key parameter in determining the ability of a material to be used in construction; it is considered as a good indicator of quality. The samples Table 6 Effect of sediment proportion on the plastic nature of the mixture

759

20

15

10

5

Table 7 Water absorption coefficient of brick samples (%)

0 0

F0%

F25%

F35%

F45%

Regulatory limits

5.3

6.34

8.06

10.39

40

0.002

0.004

0.006

0.008

Strain Fig. 5. Stress–strain diagram (F35%).

0.01

760

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failed. In this example the failure was noted at approximately 33 MPa. It should be noted that the compressive strength of all sediment amended brick samples is still comparable to that of standard bricks (18–20 MPa). 4.2.4. Freezing and thawing resistance Freezing and thawing durability of brick has been studied by several researchers in many cold climates, and it may be defined as the product’s ability to withstand freezing and thawing conditions. Researchers have suggested that pore size and pore size distribution in a clay brick directly influence its durability [40]. As saturated bricks freeze, various pressures can develop within the void system. These pressures are further magnified by the freezing of additional water that enters the porous body during warming periods. Continuous cycles of freezing and thawing can eventually lead to significant expansion and deterioration in the form of cracking, spalling, or surface scaling. Five specimens of each mixture were selected. They were firstly oven-dried at 105 °C, cooled in a drying room at 25 °C and weighted. After drying, they were pre-soaked in water at 15 °C for 48 h in steel containers in such a way as to allow the bottom of the samples the same exposure conditions as other surfaces. Test specimens were then subjected to 25 cycles of freezing and thawing. The freezing portion of the cycle consisted in placing test specimens on a steel platform at 17.8 °C for 4 h. Thawing was accomplished by immersing test specimens in water at 12 °C for 15 h. After the completion of 25 cycles, test specimens were placed in open air for 24 h, and then oven-dried at 105 °C, so that the specimen’s weight loss could be determined. The results are shown in Table 8. From Table 8 we can note that there is no evident relation linking the percentage of treated sediment to the perTable 8 Weight loss in brick specimens after 25 cycles of freezing and thawing Mix-design

F0%

F25%

F35%

F45%

Average weight loss (%)

0.14

0.17

0.36

0.19

Table 9 Results of the efflorescence test F0% F25% F35% F45%

Not Not Not Not

effloresced effloresced effloresced effloresced

centage of, weight loss. We can observe that the weight losses for all substitution ratios are less than 1% (the limit given by the French standard [37]). In addition, neither cracking, nor breakage occurred on all the specimens tested. Thus we can conclude that all specimens have successfully passed the test of qualification of bricks. 4.2.5. Efflorescence Specimens of the four mix-designs (F0%, F25%, F35% and F45%) were prepared. Each sample was placed vertically in a perfectly clean individual watertight shallow pan according to its greater dimension. Samples were partially immersed in distilled water to a depth of approximately 25 mm. Each container was covered with a plastic sheet with an opening through which the specimen passed to keep a constant level of water in the pan. Samples were set for 4 days at room temperature, and then they were oven-dried at 60 °C for 24 h. After drying, samples were carefully examined and no efflorescence was observed for all tested specimens. Table 9 elucidates the results obtained for all the samples tested. Barium carbonate (BaCO3) was added to each mixdesign (7 g/kg) to prevent any tendency for efflorescence owing to the presence of soluble salts, thus turning them into insoluble compounds and preventing their migration to the surface of the brick during drying. 4.2.6. Heavy metal leaching 4.2.6.1. French Standard [33]. Table 10 shows the average values of leaching test undertaken on three different samples of each mix-design in accordance with the French standard, where brick samples were crushed and sieved (<4 mm) and then leached with distilled water. Results showed that the concentrations of the selected metal species (Cd, Cu, Ni, Pb and Zn), for all mix-designs, are below the regulatory limits. The quantities of metals leached out of the fired bodies are less than those of treated sediments, thus metals were either being immobilised within the glassy melt phase or converted to low solubility metal oxides during the firing process. For Zn, values of 0.055, 0.06, 0.225 and 0.04 mg/kg were obtained for F0%, F25%, F35% and F45%, respectively. Nevertheless, these values are less than the regulated limit (4 mg/kg). 4.2.6.2. TCLP-USEPA 1986. The TCLP test [41] is considered as a practical test which is more representative of low pH conditions, like a material subjected to acid rain. Table

Table 10 Results of the leaching test undertaken on brick specimens in accordance with the French standard in mg/kg on dry material Element

F0%

F25%

F35%

F45%

Limit values for waste acceptable as inert L/ S = 10 (l/kg)

Limit values for waste acceptable as nonhazardous L/ S = 10 (l/kg)

Cd Cu Zn Ni Pb

<0.02 <0.03 0.055 <0.07 <0.20

0.02 0.05 0.06 0.03 <0.25

<0.03 1.73 0.225 0.093 <0.2

0.02 0.08 0.04 0.05 <0.25

0.04 2 4 0.4 0.5

1 50 50 10 10

Z. Lafhaj et al. / Construction and Building Materials 22 (2008) 755–762 Table 11 Concentrations of heavy metals in the leachates of brick specimens leached with acetic acid in mg/kg on dry material Element

F0%

F25%

F35%

F45%

Regulated TCLP limit

Cd Cu Zn Ni Pb

<0.02 0.1 1.63 0.33 <0.2

0.08 0.52 3.06 0.34 <0.5

0.1 0.76 3.28 0.56 <0.5

0.16 1.2 4.92 0.92 <0.5

1.00 15 25.00 – 5.00

11 shows the results of the TCLP test undertaken on different samples of F0%, F25%, F35% and F45%. As shown in Table 11, the metal concentrations for all mix-designs are higher than those obtained by the French procedure, but they are still far below the regulated TCLP limits. We can also observe, as for the French standard test, that the quantities of metal leached out of the fired bodies are less than those of treated sediments, confirming that the firing process led to better stabilisation of heavy metals. For Zn, values of 1.63, 3.06, 3.28 and 4.92 mg/ kg were obtained for F0%, F25%, F35% and F45%, respectively. These values are largely within the TCLP limit (25). The results in Tables 10 and 11 indicate that sediment amended brick specimens can be considered as non hazardous materials. 5. Conclusion This study has demonstrated the feasibility of using polluted river sediments, after treatment, as a partial sand and clay substitute in brick manufacture. The studied sediments came from the North of France. These sediments exhibit high concentration of heavy metals and organics. They were treated using the NovosolÒ process which consists of two separate phases: phosphatation and calcination. The results showed that the treatment procedure led to the stabilisation of most heavy metals in the solid matrix by forming insoluble metal phosphates. Treated sediments have been constructively and successfully incorporated into bricks with different proportions ranging from 25% to 45% (dry basis). The sediment proportion in the mixture has had an important impact on the quality of the brick. The increase in sediment proportion resulted in a decrease in compressive strength, but it is still comparable to that of standard brick (18–20 MPa). The substituted bricks have successfully passed the different tests required by French standards in order to assess the suitability of a brick to be used in construction, for example: freezing/thawing tests and water absorption tests were detailed in this study. Considering physical, mechanical and chemical results, the 35% ratio of substitution of treated sediments in bricks seems to be the most effective one. Acknowledgements This study was funded in part by Solvay, Voies Navigables de France and Briquetteries du Nord companies.

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