Use of marble cutting sludges for remediating soils and sediments contaminated by heavy metals

Authors

  • Carmen Pérez-Sirvent,

    Corresponding author
    1. Department of Agricultural Chemistry, Geology and Pedology, Faculty of Chemistry, University of Murcia, Murcia E-30100, Spain
    • Department of Agricultural Chemistry, Geology and Pedology, Faculty of Chemistry, University of Murcia, Murcia E-30100, Spain
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  • María Luz García-Lorenzo,

    1. Department of Agricultural Chemistry, Geology and Pedology, Faculty of Chemistry, University of Murcia, Murcia E-30100, Spain
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  • María José Martínez-Sánchez,

    1. Department of Agricultural Chemistry, Geology and Pedology, Faculty of Chemistry, University of Murcia, Murcia E-30100, Spain
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  • José Molina-Ruiz,

    1. Department of Geography, Faculty of Geography, University of Murcia, Murcia E-30100, Spain
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  • Jorge Marimon,

    1. Department of Agricultural Chemistry, Geology and Pedology, Faculty of Chemistry, University of Murcia, Murcia E-30100, Spain
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  • María Cortes Navarro

    1. Department of Agricultural Chemistry, Geology and Pedology, Faculty of Chemistry, University of Murcia, Murcia E-30100, Spain
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Abstract

The addition of marble-cutting sludge to soils and sediments was assessed as a possible way of remediating heavy metal contamination. Two sediments from a site affected by historic mining activities and two sediment samples obtained from a highly industrialized area were used for the study. The samples were mixed with marble-cutting sludge providing four stabilized samples from which forty leachates were studied. The results suggest that the addition of this sludge, consisting mainly of carbonates, to heavy metal polluted sediments, decreases available metal forms. The leached solutions showed a nontoxic effect when they were submitted to the Microtox® bioassay. The carbonate content plays a role in the chemical stabilization of metals and in lowering the toxicity of these types of samples. © 2010 American Institute of Chemical Engineers Environ Prog, 2010.

INTRODUCTION

Human activities have introduced numerous potential hazardous trace elements in the environment. Although heavy metals are released in varying quantities into the soil from parent materials, increasing environmental contamination has been caused by human activities, such as mining, smelting, fossil fuel combustion, fertilizers industry, and waste disposal [1]. Contamination of heavy metals in the soil is a major concern because of their toxicity and threat to human life and environment. These heavy metals may adversely affect soil ecology, agricultural production, or product quality and water quality [2].

Several remediation techniques have been developed to mitigate heavy metal contamination of soils. The ex situ extractive technologies are rarely adopted because of high risks and costs related to the use of hazardous extractants and the consequent need of treating secondary effluents [3].

A number of alternative options have therefore been investigated which are regarded as less intrusive and more cost-effective. One technology that has received a considerable amount of attention is in situ immobilization of heavy metals. In situ chemical immobilization is a remediation technique that decreases the concentration of dissolved contaminants by sorption or precipitation [4]. Chemical immobilization by means of soil amendments has been recently investigated as a valuable alternative technique for a wide range of contaminated sites. A number of natural or synthetic materials, such as carbonates, phosphate rocks [5], cement [6], zeolites [7, 8], municipal biosolids [9], and red mud [10, 11] have been recently tested in order to evaluate their ability to immobilize toxic trace metals. These amendments can lead to the immobilization of metals in a variety of ways.

A high amount of sludge waste (5 MT/yr in Murcia Region) is produced from the natural-stone cutting industry. Disposal of this waste is difficult due to the high amounts produced and the unfavorable physicochemical characteristics of this material. The sludges investigated in this study were originated from the marble-cutting industry in the Region of Murcia. These sludges have a clayey-silt or finer particle size, an high calcium carbonate content in excess of 95% and a high salt content, mainly sodium chloride (which is used in the marble cutting process). These characteristics make their use for industrial purposes or as agricultural amendment, inadvisable.

The present study assesses the use of the waste sludge remaining after the cutting of marble as stabilisers of heavy metals in sediments polluted by different activities, including mining and industrial activities.

The application of this approach to sediments contaminated with heavy metals by different activities was carried out in order to determine if this technology could be considered a viable solution for the remediation of heavy metal contaminated sites. Their use would decrease the risks associated with the presence of heavy metals in soils due to the in situ stabilization and immobilization effects of calcium carbonate, and reuse of the wastes present an alternative to the current disposal practice of sending the waste to landfill. The effect of using this approach on organisms has been assessed by the inexpensive, rapid and simple Microtox® method [12].

This technology was previously applied in wastes from metal mining activities [13]. In this study is expected to generalize the application of this technology to wastes from other activities, particularly pyrite ashes from fertilizers industry.

MATERIALS AND METHODS

Sampling Sites

Areas affected by mining and chemical industrial activities were selected to determine if a marble-cutting sludge could be applied to heavy metal contaminated sites to reduce the mobility and toxicity of Cd, Pb, and Zn.

Two sediment samples were collected in Portman Bay (P1, P2), near to the mining district of La Unión (Murcia, SE Spain). Another two sediment samples were collected in Escombreras Valley (E1, E2) (Murcia, SE Spain).

Portman bay was mined from the time of the Roman Empire to 1991 when the activity ceased. Since 1957, the wastes from the metal mining operations were discharged directly to the sea in the inner part of Portman Bay, and later, they were also discharged to sea at a greater distance from the shore. From Lavadero Roberto (one of the biggest flotation plants in the world, which treated about 1000 tonnes/day), wastes were discharged by pipe directly into the western part of the bay, from where currents washed them toward the shore. During its working life, Lavadero Roberto discharged 57 million tonnes of steriles, made up of ore materials (sulphides as galena, pyrite, and sphalerite), phyllosilicates, such as chlorite and muscovite, siderite, iron oxides, and alteration products such as jarosite or alunite. In addition, chemical residues from reagents (xanthates, cyanures) used in ore floatation, were also discharged with the mining wastes [14].

Samples E1 and E2 were collected in the vicinity of a sulphuric acid plant. Pyrite ashes are obtained as a result of the sulphuric acid production process during the roasting of pyrite ores. These wastes, which are generally landfilled or dumped into the sea, could cause serious land and environmental pollution problems due to the release of acids and toxic substances. Pyrite ashes are accepted as a hazardous waste because it contains considerable amounts of heavy metals [15].

Marble industry in Murcia Region is mainly located in the northwest. However, there are some exploitation located close to the study area. Then, marble-cutting sludges for this study were collected from a marble exploitation located in the Campo de Cartagena from a dewatering pond next to the samples location.

Material Collection and Characterization

Sediment samples from the surface (0–25 cm) were collected. Five subplots for soil sampling were selected at the centre and on the diagonal lines of a square grid (10 × 10 m). Samples were collected with a shovel in each subplot, then mixed and homogenized and a subsample (about 2 kg) was taken. After that, sediment samples were mixed with marble-cutting sludges in a 1:1 proportion to produce four stabilized sediment samples (MC-P1, MC-P2, MC-E1, and MC-E2), being homogeneously mixed before the mixture was introduced in the columns.

The sediment samples (P1, P2, E1, E2) and marble-cutting sludges (MC) were air dried and sieved to <2 mm before general analytical determinations and for the stabilization/immobilization assay.

The pH and electrical conductivity (EC) were determined in a 1:5 (w/v) suspension of soil in ultrapure water (MilliQ). The concentration of Cd, Pb, and Zn in the sediment samples and marble-cutting sludges was determined by a microwave digestion method according to the standard digestion method [16].

The Zn content in the digest was determined by flame atomic absorption spectrometry (FAAS) using a Perkin-Elmer 1100B Atomic Absorption Spectrophotometer. The concentrations of Cd and Pb were determined by electrothermal atomization atomic absorption spectrometry (ETAAS) using an Unicam 929 AASpectrometer. Detection limits for target metals were 0.02 mg L−1 for Zn, 0.0002 mg L−1 for Cd, and 0.001 mg L−1 for Pb.

A semiquantitative estimation of the mineralogical composition of the samples was made by X ray diffraction (XRD) analysis using Cu-Kα radiation with a PW3040 Philips Diffractometer. X-powder software was used to analyze the x-ray diffraction patterns obtained by the crystalline powder method [17]. The powder diffraction file (PDF2) database was used for peak identification, taking into account that the determination of minerals from soils by XRD analysis is not accurate below a limit of 5% of the total weight in a sample (depending on the crystallinity of individual minerals).

The reliability of the results was verified by analyzing standard reference materials (SRM 2709 San Joaquin Soil and SRM 2711 Montana Soil).

The results showed RSD values close to 5% and agreed with the certified values. All reagents were of analytical grade or Suprapur quality. Stock solutions were Merck Certificate AA standard and high quality water (MilliQ), was used in all the experiments. Plastic and glassware were cleaned by soaking in a 14% (v/v) HNO3 acid solution for 24 h and then rinsing with ultrapure water. Spikes, duplicates and reagent blanks were also used as a part of our quality assurance/quality control.

Column Leaching Experiment

A column experiment was used to simulate heavy metal migration in columns filled with either pure sediments or a mixture of sediment and marble-cutting sludges. A 150 g sample of either sediment (P1, P2, E1, and E2) or mixtures of sediment and marble-cutting sludge (MC-P1, MC-P2, MC-E1, and MC-E2) were placed in 40 cm × 5 cm PVC columns.

Chemical immobilization treatments were evaluated using solute transport experiments with repacked soil columns similar to methods described by Selim and Amacher (1996) [18]. The material was kept at the bottom of the column, through which the leach solution percolated. Teflon filters were placed between the soil matrix and end caps on each end of the column to prevent loss of fines from the soil column. Soils were saturated with deionized water and the resulting leachate was collected and analyzed for heavy metal concentration and pH values after 48 h. Column effluent was passed through Teflon tubing and an in-line 0.45 mm filter before collection into glass test tubes.

Ecotoxicity Test

The potential risk of polluted sediments to biota and the stabilisation effect was studied by applying the Vibrio fischeri bioluminiscence test [19] to aqueous solutions. Microtox® bioassay is based on the inhibition of the bioluminescence marine bacteria V. fischeri, a bacterium used extensively in the assessment in ecotoxicology.

In this test, the bioluminiscence emitted by the bacteria is reduced in the presence of polluting agents and this reduction is directly related to the relative toxicity of the sample. The toxicity is expressed as the agent concentration which produces a 50% reduction of the initial luminescence (EC50) after 15 min of contact time [20]. Bioluminescent responses were measured using a Microtox Model 500 analyser. A basic test was conducted with the reference standard for each fresh vial of bacteria used to ensure the validity of the test method [21].

The Microtox® bioassay was applied to the 40 leachates, 20 from leaching assays of non-stabilized samples and 20 leachates from stabilized sediments.

Statistical Analysis of the Data

The MINITAB software v.15 was used for a multivariate analysis, including correlation matrixes, principal components and factor analysis. Pearson's product moment correlation coefficients were used to produce a correlation matrix and then identify possible relationship between trace element content and soil properties.

Factorial analysis permits a statistical approximation for analyzing interrelations between a large number of variables. Factorial analysis was carried out by the principal components extraction method and varimax normalized rotation of the factors. Varimax rotation ensures that each variable is maximally correlated with only one principal component while having a near-zero association with the other components [22].

RESULTS AND DISCUSSION

General Characteristics of the Samples and Sludges

The chemical characteristics of the sediments and cutting-marble sludges are given in Table 1. Sediments were acidic, ranging from 2.3 to 6.1 and with a mean pH value of 4. Electrical conductivity ranged from 2.6 to 6.4 dS m−1. The marble cutting sludges had a basic pH and low electrical conductivity.

Table 1. General characteristics of sediments and marble cutting sludges.
 pHEC (dS m−1)Pb (mg kg−1)Zn (mg kg−1)Cd (mg kg−1)
P14.15.54200590035
P23.42.975006400.4
E16.12.6127036639583
E22.36.45998497936
Marble cutting sludges9.50.5160.5

Pb content ranged from 4200 mg kg−1 in P1 to 12703 mg kg in E1. Zn concentration ranged from 640 mg kg−1 to 66395 mg kg−1 and Cd concentration ranged from 0,4 mg kg−1 in P1 and 83 mg kg−1 in E1. Maximum values for Pb, Cd, and Zn were found in E1.

Table 2. Mineralogical composition of samples and marble cutting sludges (%).
%P1P2E1E2Marble cutting sludges
Phylosilicates2 2  
Clinochlore3    
Quartz1812431
Jarosite1578 11 
Siderite1721   
Pyrite25  26 
Magnetite19    
Hematite  2850 
Greigite  1  
Gypsum  1510 
Akaganeite  30  
Calcite    38
Dolomite    60
Feldspars    1

X-ray diffraction results suggested that sediments with mining origin show different degree of supergene alteration (Table 2). Jarosites are often precipitated during the oxidation of sulphide-bearing rocks by meteoric solutions. Then, higher jarosite percentage in P2 showed that this sediment is more altered than P1. E1 comes from an area with industrial activity and its mineralogical composition is similar to those from mining areas, affected by supergene alteration (pyrite and jarosite) while E2 is very mixed with pyrite ash wastes. X-ray results of the marble cutting sludges showed that are mainly constituted by calcite and dolomite.

Leachates

Tables 3 and 4 show the general characteristics of the leachates from Portman Bay and Escombreras sediments. Leachates of nonstabilized samples had acidic pH values (mean values of 3.5, 2.6, 2.3, and 6.3, respectively). The electrical conductivity (dS m−1) was high in the first leachate of all the samples, but gradually fell as a result of the washing effect. As regards the metals, the Pb concentration of the nonstabilized leachates was not very high because it was retained in the solid phases (anglesite and jarosite phases), while the higher Zn values were due to its greater solubility and mobility (hexahydrite). The soluble Cd concentrations showed a similar trend to the Pb.

Table 3. General characteristics of leachates of Portman samples (MC:marble cutting).
LeachatespHEC (dS/m)Eh (mV)Pb (mg/L)Zn (mg/L)Cd (mg/L)EC50 (%)
1P13.28.55110.51460.60.64
1MC-P17.63.7104<dL<dL<dL28.3
2P13.43.55100.2980.41.01
2 MC-P17.80.9100<dL<dL<dLNontoxic
3P13.93.64920.07600.43.56
3 MC-P18.10.6123<dL<dL<dLNontoxic
4P13.62.64840.06380.34.14
4 MC-P17.90.6123<dL<dL<dLNontoxic
5P13.62.24820.06300.34.69
5 MC-P17.90.8145<dL<dL<dLNontoxic
6P13.62.04610.06230.24.41
6 MC-P18.00.6152<dL<dL<dLNontoxic
7P13.71.43670.04180.27.62
7 MC-P18.00.6151<dL<dL<dLNontoxic
8P13.81.43690.04160.29.15
8 MC-P18.10.6153<dL<dL<dLNontoxic
9P13.91.43750.03150.18.36
9 MC-P18.60.5152<dL<dL<dLNontoxic
10P13.71.13660.02120.0811.38
10 MC-P18.20.6150<dL<dL<dLNontoxic
1P22.215.46000.071530.20.28
1 MC-P28.51.8136<dL<dL<dLNontoxic
2P22.95.95830.031170.10.48
2 MC-P28.70.6161<dL<dL<dLNontoxic
3P23.11.35840.0250.10.66
3 MC-P28.60.5175<dL<dL<dLNontoxic
4P23.00.6581<dL2<dL1.75
4 MC-P28.70.4190<dL<dL<dLNontoxic
5P23.11.0580<dL0.8<dL2.48
5 MC-P28.50.4186<dL<dL<dLNontoxic
6P22.90.8578<dL0.7<dL2.9
6 MC-P28.50.3195<dL< dL<dLNontoxic
7P22.80.9575<dL0.7<dL4.68
7 MC-P28.50.3201<dL<dL<dLNontoxic
8P23.01.2600<dL0.6<dL4.78
8 MC-P28.50.3189<dL<dL<dLNontoxic
9P23.11.0590<dL0.5<dL6.53
9 MC-P28.50.3190<dL<dL<dLNontoxic
10P23.00.7582<dL0.4<dL6.65
10 MC-P28.50.2192<dL<dL<dLNontoxic
Table 4. General characteristics of leachates of Escombreras samples (MC:marble cutting).
LeachatespHEC (dS/m)Eh (mV)Pb (mg/L)Zn (mg/L)Cd (mg/L)EC50 (%)
1E15.84.23210.62380.82.37
1 MC-E17.51.92350.020.03<dLNontoxic
2E15.92.93320.51840.44.57
2 MC-E17.83.12060.020.06<dLNontoxic
3E16.12.63330.41330.34.97
3 MC-E17.92.62320.0060.1<dLNontoxic
4E16.22.43330.04920.26.95
4 MC-E18.12.2194<dL0.2<dLNontoxic
5E16.82.03190.03690.29.32
5 MC-E17.82.1205<dL0.3<dLNontoxic
6E17.01.93100.02580.110.22
6 MC-E17.92.0210<dL0.3<dLNontoxic
7E16.81.92810.02410.112.11
7 MC-E18.02.0194<dL0.3<dLNontoxic
8E16.81.92870.02360.0913.71
8 MC-E18.02.0212<dL0.3<dLNo toxic
9E16.91.92970.01330.0818.16
9 MC-E18.11.9215<dL0.2<dLNontoxic
10E16.71.93090.01310.0718.91
10 MC-E18.21.9194<dL0.2<dLNontoxic
1E22.112.24950.936105.72.44
1 MC-E27.92.3149<dL0.2<dLNontoxic
2E22.37.45060.48151.22.45
2 MC-E28.02.1150<dL0.1<dLNontoxic
3E22.53.65140.2680.12.68
3 MC-E27.82.2143<dL<dL<dLNontoxic
4E22.33.8538<dL700.19.81
4 MC-E27.82.2146<dL<dL<dLNontoxic
5E22.43.6595<dL310.113.26
5 MC-E27.92.1157<dL<dL<dLNontoxic
6E22.44.0626<dL430.119.27
6 MC-E28.02.2161<dL<dL<dLNontoxic
7E22.24.6613<dL640.128.91
7 MC-E27.90.6168<dL<dL<dLNontoxic
8E22.45.9611<dL970.336.03
8 MC-E28.00.7173<dL<dL<dLNontoxic
9E22.55.1636<dL640.2Nontoxic
9 MC-E28.01.1169<dL<dL<dLNontoxic
10E22.44.5628<dL440.1Nontoxic
10 MC-E28.20.6167<dL<dL<dLNontoxic

The results of the Microtox® bioassay showed that all leachates, except 9E1 and 10E1, were sensitive to the test. Highest toxicity was found in the first and second lixiviate of each sample. The EC50 values obtained could be explained both by the presence of soluble heavy metals and by their acidity.

After mixing the samples with the marble-cutting sludges, the pH of all the leachates rose substantially, reaching values of 7.5–8.5 (Tables 3 and 4). The electrical conductivity values were lower than those observed in the original leachates. The concentration of the trace element studied was below than their detection limits in almost all the leachates. When the Microtox® bioassay was carried out in these leachates, the test was only positive in 1MC-P1 leachate, but with an EC50 value considerably higher than that obtained with the leachate of the nonstabilized sample. These results suggest that the stabilization/immobilization technique applied to the different samples is effective because the EC50 values were greatly increased.

Statistical Results

Matrix Correlations

Portman Bay Samples.

The Pearson correlation matrix (Table 5) demonstrated that the pH was positively correlated with the EC50, meaning that high pH values correspond to high EC50 values. In addition, negative correlations are established between EC50 and Zn and Cd concentration. The capacity of the sludge to modify the pH leads to the adsorption and precipitation of the metals present in solution as carbonates, minimising their mobility and decreasing toxicity.

Table 5. Pearson correlation matrix on Portman samples (*P value < 0.05).
 pHECPbZnCd
EC−0.445*    
Pb−0.1410.371   
Zn−0.2750.901*0.609*  
Cd0.0240.2940.889*0.530* 
EC500.944*−0.503*−0.349−0.610*−0.486*

On the other hand, EC50 was negatively correlated with electrical conductivity, that is, toxicity decreases when increases salt content since Vibrio fischeri is typical of marine environments and tolerant to high salt content.

Escombreras Samples.

The Pearson correlation matrix (Table 6) showed that the pH was negatively correlated with the electrical conductivity. However, pH was positively correlated with EC50. Low pH values increases mobility of metals and bacteria mortality.

Table 6. Pearson correlation matrix on Escombreras samples (*P value < 0.05).
 pHECPbZnCd
EC−0.750*    
Pb−0.360*0.686   
Zn−0.373*0.818*0.766*  
Cd−0.392*0.828*0.804*0.996* 
EC500.585−0.415*0.522*0.514*0.450*

Moreover, Zn, Pb, and Cd content were positively correlated with EC50, because high heavy metal concentrations decreases EC50, meaning that toxicity rises.

Principal Components Analysis (PCA)

A multivariable dynamic system generally has more variables than distinct modes of behavior. Hence, the behavior of some of the variables is similar and may be correlated. Principal component analysis (PCA) finds the underlying modes of behavior by means of a singular value decomposition of the data matrix. The PCA results suggest that first and second components showed eigenvalues greater than 1 and the final factor solution represent 84% of the variance in the data, satisfying premises to choose them as representative of the data.

PCA permits us to determine the number of factors to choose for the Factor Analysis. Table 7 shows the results of Factor Analysis with two components and Varimax rotation for the leachate samples. F1 contains electrical conductivity and Pb, Zn, and Cd concentration, suggesting that target metals showed similar behavior. F2 includes pH and EC50. PCA results for lixiviates suggested that first and second lixiviate of nonstabilized samples showed low EC50 and pH values and variable heavy metal content.

Table 7. Principal component factor analysis of the correlation matrix rotated factor loadings and communalities, varimax rotation.
 F1F2
  1. The data in bold corresponds to the maximum values.

pH−0.171−0.958
EC0.6240.475
Pb0.8570.190
Zn0.9570.068
Cd0.9660.115
EC50−0.195−0.844

Leachates of stabilized samples form a compact group which corresponds to high pH values, high EC50 values and low heavy metal content. On the other hand, lixiviates of nonstabilized samples are in he first and second quadrants, characterized by variable heavy metal concentration, acidic pH, and high toxicity (Figure 1).

Figure 1.

PCA Score plot of selected variables.

CONCLUSIONS

The toxicity results obtained for the leachates gives an estimation of the ability of marble cutting residues to immobilize heavy metals and hence reduce the toxicity of sediments. The addition of these wastes reduces significantly the toxicological effect of the leachate to the tested organism. In addition, the use of marble cutting residues for the remediation of soils polluted by heavy metals constitutes an excellent option, since they could be applied in sediments affected by mining activities and also in industrial sediments polluted by heavy metals. Calcium carbonate-rich wastes treatment is able to produce more stable heavy metal compounds and, hence, reduce the risk to the ecosystem biota, as it was confirmed by bioassay results.

The Microtox method is suitable for a fast toxicity evaluation of leachates generated in different phases of the sediments polluted by heavy metals. This method does not discriminate the cause of the toxicological problem, such as high concentration of heavy metals, acidity, high salt content, etc. For this reason, other methods have to be applied for the contamination diagnosis.

Acknowledgements

The authors are grateful to the Spanish MICINN (Project CTM 2008/04567) for financial support.

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