Journal of Environmental Management 155 (2015) 58e66
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Removing heavy metals from wastewaters with use of shales accompanying the coal beds ska*, Ewa Siedlecka Beata Jabłon Cze˛ stochowa University of Technology, Institute of Environmental Engineering, 60a Brzeznicka St., 42-200 Cze˛ stochowa, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 June 2014 Received in revised form 7 February 2015 Accepted 12 February 2015 Available online
A possibility of using clay waste rocks (shales) from coal mines in the removal of heavy metals from industrial wastewaters is considered in this paper. Raw and calcined (600 C) shales accompanying the coal beds in two Polish coal mines were examined with respect to their adsorptive capabilities for Pb, Ni and Cu ions. The mineralogical composition of the shales was determined and the TG/DTG analysis was carried out. The granulometric compositions of raw and calcined shales were compared. Tests of adsorption for various Pb(II), Ni(II) and Cu(II) concentrations were conducted and the pH before and after adsorption was analyzed. The results indicate that the shales from both coal mines differ in adsorptive capabilities for particular metal ions. The calcination improved the adsorptive capabilities for lead, but worsened them for nickel. The examined shales have good adsorptive capabilities, and could be used as inexpensive adsorbents of heavy metal ions, especially in the regions where resources of shale are easy accessible in the form of spoil tips. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Adsorption Heavy metals Shales Industrial wastewaters
1. Introduction Intensive development of civilization contributed to polluting the natural environment with heavy metals, which contaminated soils, water, plants and animals. Regardless of chemical forms of occurrence, heavy metals increasingly contaminate the natural ska and Deska, 2012). environment (Ociepa et al., 2013; Tkaczyn Among many known sources of heavy metals polluting the environment, the raw or insufficiently treated industrial and municipal wastewaters are especially troublesome. Many workshops and small industrial or manufacturing plants which use chemical and electrochemical processing of metals do not have their own wastewater treatment plants and the wastewater is piped directly into the municipal sewerage. For example, copper, lead and nickel are introduced into the environment as a result of non-ferrous metals mining and processing, in plating plants and tanneries as well as during manufacturing alloys, pigments, paints, batteries, accumulators, cables, electrodes, etc. (Bartkiewicz, 2002; Janecka et al., 2009). The quality of underground waters is also threatened by waters infiltrating from ponds in which some dangerous
* Corresponding author. ska),
[email protected]. E-mail addresses:
[email protected] (B. Jabłon czest.pl (E. Siedlecka). http://dx.doi.org/10.1016/j.jenvman.2015.02.015 0301-4797/© 2015 Elsevier Ltd. All rights reserved.
wastes were deposited, e.g. post-flotation wastes from mechanical enrichment of Zn, Pb and Cu ores (Kupich and Girczys, 2008). Law restrictions regarding water pollution alongside an increase of requirements concerning high quality water compel to create more efficient and ecologically safe methods of wastewater treatment. Industrial plants are often obliged for pre-treatment of wastewater if contamination exceeds the permissible standards specified in the law and the contract with the sewerage owner (Franus, 2010). The most prevalent methods of heavy metal removal from wastewater are conventional precipitation methods, the cost of which is currently lower comparing to other methods, e.g. ion-exchange on ionites. However, one disadvantage of the conventional precipitation methods is generation of large amounts of slime and sludge, which are troublesome to control (Ulmanu et al., 2003). The solution could be to introduce membrane methods, biochemical or physical and chemical methods, e.g. based on adsorption processes, or the use of these methods in conjunction with the conventional ones (Nawrocki and Biłozor, 2000). The efficiency of the methods is diverse, and the conditions of their implementation often require preserving strict technological regimes. Highly efficient methods of metal removal from wastewaters are usually connected with an expansion of a technological system, and consequently, with growth of costs. Therefore, new technological solutions using inexpensive non-conventional materials in the wastewater treatment are still desirable (Petrus et al., 2001).
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Among efficient synthetic sorbents used in wastewater treatment, special attention is paid to active carbons and ion-exchange resins (Bansal and Goyal, 2005). However, their disadvantage is the high production cost. Potential sources of cheap sorbents can be some natural and biogenic minerals available in large amounts as well as some wastes generated during extraction and processing of some minerals. Such natural sorbents of mineral origin are carboniferous shales accompanying the coal beds in the form of intergrowths in many coal basins all over the world. In Poland, they occur in the Upper Silesian Coal Basin and the Lublin Coal Basin (Jelínek et al., 2011). From a mining point of view, shale is a useless waste accompanying the coal extraction. It is obtained during mining works connected with preparations of the coal bed for extraction as well as at the stage of coal enrichment in the processing plants. So far, the carboniferous shales accompanying the coal beds are often used in civil engineering and technical works as an aggregate, as well as for land reclamation and levelling the lands deteriorated by mining activity (Kozioł and Kawalec, 2008; _ n ska, 1997). Skarzy This paper presents the results of preliminary research focused on the usefulness of carboniferous waste rocks (shales) to obtain very cheap adsorbents. Since calcination leads to significant changes in the skeletal structure of the material and can enlarge the specific surface area, we tested both the raw and calcined shales. The shales were examined with respect to their adsorptive capabilities for Pb, Ni and Cu ions. The mineralogical composition of the shales was determined and the TG/DTG analysis was carried out. Granulometric compositions of the raw and calcined shales were compared. Adsorption examinations for various Pb(II), Ni(II) and Cu(II) concentrations were undertaken and the pH analysis before and after adsorption was carried out. 2. Methodology The tested shales come from roofs, floors and intergrowths of j coal presently exploited coal beds in the Ziemowit and the Poko j, respectively). mines (hereinafter referred to as Ziemowit and Poko The material was taken from the coal recovery system of the coal dressing plants. Ziemowit exploits the coal beds in the southeastern region of the Upper Silesian Coal Basin deposited in the sediments of Łaziska layers, which form one of the lithostratigraphic links of the Cracow sandstone series. The Łaziska layers are built from sequences of various sediments, mostly sand and clay. In such a sandy-coal sequence, thin layers of claystone or mudstone j exploits coal in often enclose the roofs and floors of coal beds. Poko the layers of the Upper Carboniferous, in which two characteristic formations can be distinguished: paralic e enclosing the lower layers in the profile, and limnic e lying over those forms (Dembowski, 1972). The research of adsorption of heavy metals from water solutions on clay minerals was carried out in static conditions (McGroddy and Farrington, 1995). The shale was milled down to grain size below 200 mm and brought to an air-dry state by desiccation. In the next step, the granulometric composition was ascertained using an LAU-10 analyzer (laser analyzer of granulometric composition, manufactured in the Institute of Mineral Building Materials in Poland). The mineralogical composition was determined using Xray diffractometry on a Philips XRD X’PERT PRO PW3710 device using CoKa radiation (the qualitative phase analysis was based on ASTM and ICDD PDF 4 þ databases, the quantitative analysis used the Rietveld method). The thermal analysis was performed on a SETARAM LABSYS TG-DTA/DSC derivatograph. The experiments were carried out on synthetic solutions, which were made based on analytically pure compounds of copper, nickel and lead containing ions of one of these metals whose initial
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concentration was comparable to their concentration in industrial wastewaters. The research of heavy metals adsorption from aqueous solutions was done on suspensions of clay minerals at a concentration of 2%. The suspensions were supplemented with aqueous solutions of heavy metals of initial concentrations of 5, 25, 50, 250, 500, 1000, 2500 and 5000 mg/dm3. A rotational vibrator shook the prepared samples for a period of two hours at a temperature of 20 C before they were placed in a dark room and left for 22 h. As a next step, the solution was decanted and the sediment was removed by a centrifugal clarifier (MWP-2) at 2500 rpm. The concentration of heavy metals ions in the eluates was determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, Thermo Elemental IRIS Intrepid II XSP DUO). In addition, the pH of both the initial and equilibrium solutions after adsorption was measured with an ELMETRON CPC-401 pH meter. Adsorptive capabilities of an adsorbent can often be improved by thermal processing. To investigate this possibility in the case of the tested shales, the research on static adsorption was also carried out after calcining the shale in a muffle furnace by oxidation at a temperature of 600 C. The value of the temperature was chosen according to suggestions given by Klimczyk (2009) and Kiedik et al. (1976). The powdered material was inserted into cold muffle and then it was calcined at a temperature of 600 C for two hours. The time of thermal processing was counted from the moment of reaching the desired temperature. As a next step, the furnace was turned off and the calcined material was left inside the furnace until cooling down. The adsorption on thermally processed materials was carried out in the same way as in the case of raw shale. The mass of adsorbed metal per unit of sediment mass, q, was calculated as follows:
q¼
Ci Ce V m
mg ; g
(1)
where: Ci, Ce e initial and equilibrium concentrations of metals (mg/dm3), V e solution volume (dm3), m e mass of used sediments (g). Three measurement series were conducted for each sample type and the mean values were used in further calculations. 3. Results and discussion 3.1. Mineralogical composition Shale in its natural state typically has a grey tint, exhibits apparent fissility and is laminated with organic matter (carbon). The mineralogical composition of the shales from Ziemowit and j is presented in Table 1. It is similar in both coal mines, and Poko only differs in the share of particular constituents. The XRD patterns of the tested rocks revealed the following constituents: a) illite e its share in Ziemowit (38.1%) is about twice as high as j (18.5%), in Poko
Table 1 Percentage mineralogical composition on average of the investigated shales. Mineral
Chemical formula
Quartz Kaolinite Illite
SiO2 Al4[Si4O10](OH)8 (K,H3O)1,6(Al2,88Fe0,64Mg0,5) (Si6,9Al1,1O20) (OH)4 (Mg5Al)[AlSi3O10](OH)8 aFe2O3 e
Chlorite Hematite Organic matter
Coal mine Ziemowit
j Poko
21.1 14.2 38.1
31.3 23.4 18.5
18.3 0.2 8.1
10.5 0.6 15.7
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b) quartz (very fine-grained) e it dominates in the samples j (31.3%), and is the second biggest constituent in from Poko the samples from Ziemowit (21.1%), c) kaolinite (moderately arranged), d) chlorite (slightly ferruginous clinochlore), e) traces of hematite (below 1%). A strongly dispersed amorphous carbonaceous substance gives the examined sediments a grey tint. Exemplary XRD patterns of the tested shales are shown in Figs. 1 and 2. In compliance with the Polish standard, the ash content from which the loss of ignition can be evaluated is determined at a temperature of 815 C. The determined ash contents (incombus j are tible constituents) in the tested shales from Ziemowit and Poko equal to 91.9% and 84.3% respectively. It follows that the material j has more combustible constituents (mass decrement from Poko during calcination in this case equals 15.7%). A two-hour calcination at 600 C causes carbonization of the organic matter and changes the appearance of the shale. The samples which were processed thermally exhibited a lighter and more reddish shade than the raw samples. The reddish tint, which is characteristic for thermally processed sediments, originates from finely dispersed hematite. It was observed that some part of carboniferous substance occurring inside the shale grains remained unprocessed. On the average, the carbon content in the modified samples equalled 0.64% for Zie j. The XRD patterns of the calcined shales mowit and 0.3% for Poko indicate a decrease in kaolinite content and the presence of a product of its transformation, probably pyrophyllite. The reflection lines of illite and quartz remain unchanged.
j. Fig. 2. XRD pattern of the shale from Poko
3.2. TG and DTG analysis Heating the samples of shales in air at a rate of 10 C/min up to a temperature of 1000 C causes the transformations depicted as TG and DTG curves, presented in Figs. 3 and 4. The TG and DTG curves of the tested shales show two mass decrements. The first noticeable mass decrement, which occurs in the temperature range 50e200 C, is mainly connected with removing the hygroscopic and interlayer water. The dehydration in shales from Ziemowit leads to a mass decrement and is registered on the DTG curve with maxima at 51 and 115 C. However, the decrement does not exceed 2% of the initial sample mass. It is even smaller for the samples from j (about 1%). Poko In the temperature range 250e400 C, the mass decrement is small e it is probably related to the removal of water being the part of hydrated ferrites and aluminium oxides. A large mass decrement
Fig. 3. TG/DTG curves of the shale from Ziemowit.
j. Fig. 4. TG/DTG curves of the shale from Poko
occurs above 300 C, especially in the range of temperature 400e650 C, with exhibited endothermic effect visible on the DTG curve. It is related with exuding the chemically combined water from clay minerals. Individual clay minerals have their characteristic temperatures at which the highest dehydration of the chemically combined water occurs (in particular heating conditions). The temperatures are approximately 560e580 C for the group of kaolinite, 535e570 C for illite and 685 C for montmorillonite (Stoch, 1974). The maxima of mass decrement and the endothermic maxima in the examined Fig. 1. XRD pattern of the shale from Ziemowit.
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rocks are shifted towards lower temperatures as the kaolinite dehydroxylation decreases (Fig. 3 and 4). Therefore, the shift of the endothermic maximum down to a temperature of ca. 480 C, which is visible on the DTG curves, confirms over 10% content of the mineral in the tested samples (see Table 1). This effect does not apply to quartz, whose peak temperature is constant and equals 575 C. However, the endothermic reaction of polymorphic transformation of quartz does not result in mass change. The mass decrement of clayey fraction, visible on the TG and DTG curves above 700 C, suggests the presence of accessorial chlorites. The range of combustion temperature of organic substance is extremely varied. It usually begins between 200 and 250 C and ends between 400 and 700 C. For the examined samples, the combustion of organic substance occurs between 200 and 700 C, which is registered in the DTG curve as a large valley (Fig. 3 and 4). The exact evaluation of the substance content is problematical, because thermal effects of combustion of organic substance that is present in the examined rocks often interact with the effects of dehydroxylation of clay minerals (mainly kaolinite). The total mass decrement accompanying the two reactions equals about 17% for j. the samples from Ziemowit and 20% for the samples from Poko Thermogravimetric analysis of shale samples from the two coal mines shows that their mineralogical composition is similar. Differences only occur in the percentage of the mineral constituents, the degree of hydration, and the structural stability manifesting in shifts of peaks in the derivatographic curves.
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j. Fig. 6. Granulometric composition of raw and calcined shale from Poko
Table 2 j. Granulometric composition in shales from Ziemowit and Poko Grain size, mm
Share, % j Poko
Ziemowit
1e10 11e60 61e100 101e200 Total
Raw
Calcined
Raw
Calcined
62 31 6 1 100
46 33 12 9 100
78 20 2 0 100
45 36 12 7 100
3.3. Granulometric composition The granulometric analysis of raw and calcined shales shows three dominating grain classes: 0e10 mm, 11e60 mm and 61e100 mm (Fig. 5 and 6). Their percentage share is presented in Table 2. The class of the finest grains (1e10 mm) is the dominant fraction in the examined shale samples. Its percentage equals 62% j, respectively. and 78% for the raw shale from Ziemowit and Poko j has about 16% more of the finest grains The raw shale from Poko than its counterpart from Ziemowit, which contains larger amount of bigger grains. Calcination of shales decreases the share of the finest grains. In addition, relatively big grains (101e200 mm) appear indicating that grains have been glued into clusters. 3.4. Adsorption analysis 3.4.1. Adsorption isotherms Based on the experiments, the amounts of adsorbed metals were found and the adsorption isotherms q ¼ f(Ce) for Pb, Ni and Cu on the raw and calcined shales were determined. The Freundlich,
Langmuir and Elovich adsorption isotherms, most commonly used in quantitative description of adsorption, were used. They establish a relation between the mass of adsorbate per unit mass of the adsorbent, also called the adsorption capacity (q, mg/g), and the adsorbate concentration in the fluid in equilibrium (Ce, mg/dm3). The Freundlich adsorption isotherm is a purely empirical formula, and has the following form:
q ¼ KF Cen ðmg=gÞ;
where KF and n are empirical constants depending on the adsorbent and adsorbate at a fixed temperature (Nawrocki and Biłozor, 2000). Coefficient KF is a measure of adsorption capacity: the greater the surface accessible for adsorbate particles the greater the value of KF. Parameter n, where 0 < n < 1, expresses the intensity of adsorption. The curves corresponding to small values of n grow abruptly for small concentrations and slowly for greater ones, indicating roughly equal adsorption over the whole range of tested concentrations. In contrast, the curves for n close to 1 resemble straight lines and correspond to adsorption almost proportional to the concentration. The Langmuir adsorption isotherm has the following form:
q¼Q
Fig. 5. Granulometric composition of raw and calcined shale from Ziemowit.
(2)
KL Ce ðmg=gÞ; 1 þ KL Ce
(3)
where KL and Q are constants for each pair of adsorbate and adsorbent at a given temperature. Coefficient Q (mg/g) is the monolayer adsorption capacity, towards which q tends asymptotically for large Ce. Constant KL (dm3/mg), referred to as the Langmuir adsorption constant, reveals the strength of adsorbateeadsorbent interaction. Larger values of KL result in curves abruptly growing for small concentrations and almost constant at a level of Q for others. Hence, the greater the value of KL the lower the concentration at which the saturation of the adsorbent
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occurs. When compared with the Freundlich equation, both Q and KF are scaling factors reflecting the adsorption capacity, and both KL and n determine the shape of the isotherm. However, the Freundlich isotherm returns unlimited values of q for large Ce, whereas the Langmuir isotherm is more realistic and gives q limited by Q. The Elovich isotherm has the following form:
q q ; ¼ KE Ce exp qm qm
(4)
where qm and KE are empirical constants depending on the adsorbate and adsorbent. Constant qm (mg/g) is called the Elovich maximum adsorption capacity, and KE (dm3/mg) is the Elovich equilibrium constant. Eq. (4) indicates that the amount of adsorbed substance in equilibrium increases with the adsorbate concentration, but the proportionality coefficient decreases exponentially with increasing q. Coefficients KF, n, Q, KL, KE and qm are usually determined from linearized forms of the isotherm equations. By taking logarithm of both sides of the Freundlich equation one obtains
log q ¼ n log Ce þ log KF ;
(5)
where logq is expressed as linear function of logCe with coefficients logKF and n. The Langmuir equation can be linearized in several ways, but usually the best results are obtained using the following form:
Ce 1 1 ¼ Ce þ ; Q QKL q
(6)
where Ce/q is a linear function of Ce with coefficients 1/Q and 1/QKL. The linear form of the Elovich isotherm is as follows:
ln
q q ¼ lnðqm KE Þ : Ce qm
(7)
The linearized forms allow us to use the linear regression method. The values of KF, n, Q, KL, KE and qm determined from the experimental data and Eqs. (5)e(7) using the least squares method are shown in Tables SI1e3 (on-line supplementary information). The coefficients of determination for the linearized Freundlich, Langmuir and Elovich adsorption isotherms fall into the range 0.757e0.991, 0.288e0.994 and 0.287e0.881, respectively. Apart from the Langmuir and Elovich isotherms for Ni, the adsorption isotherms fit the experimental data quite well. The Freundlich isotherm for Ni provides a better data fit, but the results for Pb and Cu are ambiguous, because the differences in coefficients of determination for both isotherm types are small. The Elovich isotherm usually has the smallest coefficient of determination, and values of q exceed significantly the value of qm, which indicates that the adsorption does not obey the Elovich isotherm. However, it should be noted that the values of the best linear fit parameters usually do not minimize the sum of squares of residuals for the original Eqs. (2)e(4). An improvement can be made by using a nonlinear regression, which significantly lowers the sum of squares of residuals for individual curves when compared to the linear regression (see the rightmost parts of Tables SI1e3), and thus, gives a better curve fitting. All three adsorption isotherms show similar values of the coefficient of determination. This indicates that the adsorption on the shales has a mixed nature and is non-uniform and nonspecific, which probably originates from nonhomogeneity of the material. Adsorption sites can differ considerably in energy, depending on whether they are located on an edge or in a defect position. The experimental data and the Freundlich isotherms from nonlinear regression for Pb, Ni and Cu adsorption
j are on the raw and the calcined shale from Ziemowit and Poko depicted in Figs. 7, 9 and 11. 3.4.2. Lead The adsorption isotherms of Pb(II) on raw material show that shale from Ziemowit has slightly better adsorptive capabilities. However, the differences between the isotherms on shales from both coal mines are not significant, e.g. the adsorbed amount of Pb(II) at the highest initial concentration equalled 29 mg/g for the j. Lead shows a relatively shale from Ziemowit and 28 mg/g for Poko strong affinity for the structure of clay minerals due to its ion radius, which is similar to the ion radius of potassium (133 pm for Pb(II), 138 pm for K). Taking into account zinc, copper and lead, it is the latter which mainly diffuses into the structure of clay minerals. The better adsorptive capability for lead on raw shale from Ziemowit arguably results from the domination of illite in its mineralogical composition (see Table 1), in which exchange of potassium and lead ions is the most intensive (Choma-Moryl and Rinke, 2005). In addition, the shale from Ziemowit contains more chlorites, on which the amount of adsorbed Pb is about twice the amount of adsorbed Zn, Cd and Cu (Kyzioł 1995). The calcined shale is a better adsorbent for lead when compared to the raw one (Fig. 7). At the highest initial concentration, the j amount of lead adsorbed on the shale from Ziemowit and Poko equalled 30.5 mg/g and 33 mg/g, respectively. Hence, out of the tested samples the best adsorbent of Pb ions is thermally modified j. In this case, calcining at a temperature of 600 C shale from Poko improved the adsorptive and partially catalytic capabilities of the carboniferous barren rocks. It caused the removal of chemically combined water from the clayey substance and a loss in carbonaceous substance (Figs. 3 and 4). The thermal activation probably made the surface active sites accessible for lead ions, as well as led to changes in the crystalline structure of the shales from both mines (Heller-Kallai, 2006). The adsorption capacities with respect to Pb(II) for the tested samples of raw and thermally modified shales reached up to 29 and 33 mg/g, respectively. In comparison to other natural adsorbents, the examined rocks have similar or better adsorptive capabilities. For example, the highest adsorptive capacity for kaolinite ranges from 9.4 mg/g (TBA-kaolinite) to 12.1 mg/g (acid activated kaolinite), and for montmorillonite from 22.2 mg/g (TBA-montmorillonite) to 34 mg/g (acid activated montmorillonite) (Bhattacharyya and Sen Gupta, 2008; Sen Gupta and Bhattacharyya, 2005; Bhattacharyya and Sen Gupta, 2006). The adsorption percentage of Pb(II) was about 98% for low initial concentrations, and lowered with the increase of initial concentration, falling to about 15e30% for higher concentrations (Fig. 8). For initial concentrations in the range 250e1000 mg/dm3, the adsorbed amount of lead ions on the thermally modified samples of shale from both mines was about 20e35% larger than in the raw samples.
j. Fig. 7. Adsorption isotherms of Pb(II) on shales from Ziemowit and Poko
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j. Fig. 8. Adsorption percentage of Pb(II) on shales from Ziemowit and Poko
j. Fig. 9. Adsorption isotherms of Ni(II) on shales from Ziemowit and Poko
j. Fig. 10. Adsorption percentage of Ni(II) on shales from Ziemowit and Poko
j. Fig. 11. Adsorption isotherms of Cu(II) on shales from Ziemowit and Poko
3.4.3. Nickel j was the best adsorbent of nickel e the The raw shale from Poko highest adsorption capacity was equal to 24.5 mg/g (Fig. 9). The raw j shale from Ziemowit and the thermally modified shale from Poko have lower adsorptive capabilities. At an initial concentration of
63
5000 mg/dm3, they adsorbed 17.5 and 15 mg/g of Ni ions, respectively. The weakest adsorbent of nickel was the calcined shale from Ziemowit e it only adsorbed 11 mg/g of Ni for the highest initial concentration. The values of adsorption capacity are lower than for active carbons ACF-307 and ACF-310, for which the highest adsorptive capacity fell into the range 19.5e25 mg/g (Goyal et al., 2001). The values are similar to those obtained for kaolinite, montmorillonite and their acid activated forms, for which the Langmuir monolayer capacity is in the range 7.1e21.3 mg/g (Bhattacharyya and Sen Gupta, 2008). The results shown in Fig. 9 prove that calcination of shales significantly reduces their capabilities of combining Ni ions. The calcination of shale removed almost all interpacket water and OH groups on the surface of aluminosilicate. This resulted in lowering the number of negatively charged active sites on the adsorbate surface. Similar results on Ni(II) adsorption have been obtained for bentonite calcined at a temperature of 750 C for a period of 6 h łkowska et al., 2006). A decrease in Ni(II) adsorption due to (Zio desorption of acid groups has also been observed in the case of active carbons calcined at a temperature of 650 C, although these carbons maintain a large part of surface non-acidic groups (Bansal and Goyal, 2005). The adsorption percentage of Ni ions depends on their initial concentration. In general, it lowers with increasing initial concentration of Ni in the tested materials (Fig. 10). It is worth noting that the thermally modified shale from Ziemowit exhibits very weak adsorptive capabilities for nickel. Its adsorption percentage for low initial concentrations is about 40e60% less than for the other materials. For an initial concentration of 5000 mg/dm3, the Ni adsorption percentage ranged from 4% for the raw shale from Ziemowit up to about 10% for the other samples. For initial concentrations from the range 5e50 mg/dm3, the Ni adsorption percentage was in the range from 98 down to 70% for the raw shale j. and from 93 down to 40% for the modified shale from Poko 3.4.4. Copper The changes in Cu(II) concentration due to static adsorption are depicted in Fig. 11. For the highest initial concentration (5000 mg/ dm3), the adsorbed amount of Cu(II) was equal to 21.5 mg/g and j and Ziemowit, respectively. 10.5 mg/g for the raw shales from Poko In the case of calcined shales it was 17.5 and 15.5 mg/g, respectively. j and the Thus, the best Cu adsorbent is the natural shale from Poko worst is the raw shale taken from Ziemowit. The examined shales have Cu(II) adsorptive capabilities similar to or better than other natural adsorbents. For example, the adsorption capacity of kaolinite, montmorillonite and their acid-activated forms in the equilibrium solution at pH < 6 equals 9.2, 31.8, 10.1, 32.3 mg/g, respectively (Bhattacharyya and Sen Gupta, 2011). The adsorption percentage for Cu versus the initial concentration of Cu(II) is depicted in Fig. 12. In the case of the raw shale from j (the best adsorbent out of the tested samples), it fell from Poko 100% for an initial concentration of 5 mg/dm3 down to 46% for 250 mg/dm3. For an initial concentration of 5000 mg/dm3, it equalled 8.6% for the raw shale and about 7% for the calcined one. 3.4.5. Adsorption summary The amount of metals adsorbed by the examined samples of shales satisfies approximately relation Pb(II) > Cu(II) > Ni(II). The adsorption isotherms for Cu(II) and Ni(II) (Fig. 9 and 11) indicate that the adsorption capacity does not exceed 5 mg/g if the metal concentration is lower than approximately 100 mg/dm3. Above a concentration of 250 mg/dm3, the adsorption intensity rises slightly for Cu(II) and Ni(II) and considerably for Pb(II) (Fig. 7). The results on adsorption of Cu(II) and Pb(II) stay in agreement with those obtained for clay minerals extracted from tertiary sand
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j. Fig. 12. Adsorption percentage of Cu(II) on shales from Ziemowit and Poko
sediments (Franus et al., 2005). From the obtained results it can be stated that the examined shales adsorb metals in relatively large j adsorbs Ni(II) and Cu(II) better amounts. The raw shale from Poko than its counterpart from Ziemowit. Better adsorptive capabilities j originate from its granulometric and of the shale from Poko mineralogical composition. As shown in Table 2, the shale contains mostly the finest fraction ( Cu(II) > Ni(II). 2. Among the tested samples, the best adsorbent for nickel and j, and for lead e the shale copper was the raw shale from Poko calcined at 600 C. 3. Calcination at 600 C significantly improved the adsorptive capabilities only for lead. In the case of nickel, it worsened them. As for copper, it decreased the adsorptive capability in the shale j, whereas increased it in the shale from Ziemowit. from Poko 4. The adsorption percentage is high for low concentrations of adsorbed ions of Pb(II), Ni(II) and Cu(II), and lowers with increasing concentration. 5. The tested shales, both raw and calcined, differ in adsorptive capabilities. The differences originate from heterogeneity of material surface. 6. The examined shales could be used in removal of heavy metals from industrial wastewaters. It is especially reasonable in the regions where resources of shales are easily accessible in the form of spoil tips and the cost of their use would be much lower in comparison to other adsorbents, e.g. active carbons. Acknowledgements This work was financially supported by the Institute of
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Environmental Engineering of the Czestochowa University of Technology under BS/PB-401-304/11. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2015.02.015. References Adebowale, K.O., Unuabonah, I.E., Olu-Owolabi, B.I., 2008. Kinetic and thermodynamic aspects of the adsorption of Pb(II) and Cd(II) ions on tri-polyphosphatemodified kaolinite clay. Chem. Eng. J. 136, 99e107. Bansal, R.Ch, Goyal, M., 2005. Activated Carbon Adsorption. Taylor & Francis Group, LLC. w Przemysłowych. Wyd. Naukowe PWN, Bartkiewicz, B., 2002. Oczyszczanie Sciek o Warszawa. (Treatment of Industrial Wastewaters, in Polish). Bhattacharyya, K.G., Sen Gupta, S., 2006. Pb(II) uptake by kaolinite and montmorillonite in aqueous medium: influence of acid activation of the clays. Colloids Surf. A Physicochem. Eng. Asp. 277, 191e200. Bhattacharyya, K.G., Sen Gupta, S., 2008. 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