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Intl' Conf. on Chemical, Integrated Waste Management & Environmental Engineering (ICCIWEE'2014) April 15-16, 2014 Johannesburg

Acid Mine Drainage Treatment Using Constructed

Tumelo Seadira, Jeffrey Baloyi, Mpfunzeni Raphulu, Richard Moutloali, and Aoyi Ochieng

 while copper and cadmium are present in smaller amounts; Abstract—The present study was conducted to investigate the however, metal concentrations in AMD are variable and removal of present in using highly dependent on the mineral composition of the ore being . Acid mine drainage samples were collected mined [2]. Frequently, the most important sites for the from Mpumalanga (South Africa) and they were characterized for generation of AMD are the discharge from open pits, heavy metals and sulphate concentrations (with pH ranging between 2.6 and 2.7). Three constructed (all packed similarly) were expulsion from underground shafts, as well as ore built and employed to treat acid mine drainage samples with different stockpiles [3]. Thus, the water that spews from these mines is metal concentrations. The structural properties of the packing essentially a toxic end-product of underground mining materials were characterized using Energy-dispersive X-Ray activities. Moreover, because the formation of AMD is Spectroscopy (EDX) and Brunauer–Emmett–Teller (BET) for affected by mineralogy as well as other variables, the chemical compositions and surface area, respectively. The effect of formation of AMD will differ from one area to another, which pH on constructed wetlands packing materials adsorption efficiencies was studied. The effect of hydraulic retention time (HRT) on the renders the predictive capacity with regard to its formation - as efficiency of the constructed wetland was also studied. Samples were well as occurrence - both costly but also of ambiguous taken at the inlet and outlet of the constructed wetlands for metal reliability [4]. The extreme pH and high ionic content are concentration analysis using Atomic Absorption Spectrophotometer responsible for highly toxic , and its handling (AAS). At the end of the experiment, metal concentrations in requires expensive storage, remediation and disposal sediment were also analyzed using AAS and X-Ray Fluorescence techniques. (XRF). At the end of the experiment percentage removals were: Fe (86.54 - 90.4%), Cr (56.2 - 64.5%), Mg (56.2 - 67.88%), Ca (77.1 - AMD can be neutralized using chemicals like lime, 100%) and 100% for Be, Zn, Co, Ni, and Mn removal was achieved. carbonate, hydrated lime, caustic soda, soda ash and this The removal of sulphate (30%) was also achieved. Therefore, results results in the production of voluminous (solids in this show that constructed wetlands have potential for treating acid mine sludge comprise 5%) and this sludge disposal represents a drainage arising from tailing dumps. further environmental problem and additional cost [5]. Thus, high cost of conventional clean up technologies has caused Keywords— constructed wetland, acid mine drainage, hydraulic economic pressure and has motivated engineers to search for retention time creative, cost-effective and environmentally sound ways to treat AMD. In the past decades, therefore, research efforts I. INTRODUCTION have been directed towards wetlands as an alternative low cost CID mine drainage (AMD) is drainage water means of removing heavy metals from AMD besides Acharacterized by high metal ion concentrations and low domestic, commercial and industrial waste water [6]. Both pH. It is produced when sulphide minerals, present in mine natural and artificially constructed wetlands can be efficient , are oxidized as they are exposed to water and treatment technologies with minimum inputs, low investment atmospheric [1]. The oxidation of sulphide costs, low operating costs and no external energy input [7]. releases dissolved ferrous iron and acidity into the water, Constructed wetlands are engineered systems that have been which in turn releases other metal ions. Metals, such as iron, designed to employ natural processes including , manganese, and zinc are usually present in high amounts, , and microbial activity to treat contaminated water. Constructed wetlands possess the merits of low-cost and low- Tumelo Seadira is with the Center of Renewable Energy and Water , Vaal maintenance, and are capable of removing various University of Technology and Advanced Material Division, Mintek, RSA, including heavy metals, nutrients, organic matters, and micro- (phone: +2711 709 4182; fax: +2711 793 2413; e-mail: [email protected]). pollutants [8]. In addition, constructed wetlands have been Jeffrey Baloyi is with the Centre of Renewable Energy and Water, Vaal recently used for treating various wastewater types including University of Technology and Advanced Material Division, Mintek, RSA, (e- point source domestic , acid mine drainage, agricultural mail: [email protected]). Aoyi Ochieng is with the Centre for Renewable Energy and Water, Vaal wastewater, landfill , and non-point source storm University of Technology, RSA, (e-mail: [email protected]). water runoff [9]. Constructed wetlands consist of properly Mpfunzeni Raphulu is with Advanced Material Division, Mintek, RSA, (e- designed basins that contain water, a substrate, and, most mail: [email protected]). Richard Moutloali is with Advanced Material Division, Mintek, RSA, (e- commonly, vascular plants (Emergent macrophytes such as mail: [email protected]). planting cattail and plating ). These components can be

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Intl' Conf. on Chemical, Integrated Waste Management & Environmental Engineering (ICCIWEE'2014) April 15-16, 2014 Johannesburg manipulated in constructing a wetland. Other important TABLE II BET SURFACE AREA OF CW PACKING MATERIAL components of wetlands, such as the communities of microbes 2 and aquatic invertebrates, develop naturally. Surface area (m /g) Average pore width (nm) Clinoptilolite 36.7 7.3 Four mechanisms affect metal removal in wetlands [10]: (1) Coarse 351 48 adsorption to fine textured sediments and organic matter [11], (2) precipitation as insoluble salts (mainly sulphides and C. Characterization of constructed wetlands packing oxyhydroxides), (3) absorption and induced changes in material biogeochemical cycles by plants and , and (4) The EDX analysis for the constructed wetland packing deposition of due to low flow rates. All these material was done using FEI NOVA NANOSEM 200. processes lead to the accumulation of metals in the substrate Micromeritics ASAP 2020 Surface Area and Porosity of wetlands. The efficiency of systems depends strongly on (i) Analyzer was also used to obtain the BET surface areas of the inlet metal concentrations and (ii) hydraulic loading [12]. constructed wetland packing material. Many contradictory results have been reported regarding D. Experimental procedure wetland plants and their role in the overall remediation process Three un-vegetated constructed wetlands were packed with of metals in wetlands. In many studies, plant metal uptake has 30 mm of sand in the first compartment, 30 mm of natural been demonstrated to play a minor role in the overall zeolite in the second compartment, and 30 mm of in the remediation of metals [12]-[14], whereas other studies have third compartment. The influent was pumped into the wetlands found the opposite [15]-[16]. Moreover, macrophytes are using a peristaltic pump through a PVC tube with aligned considered to be only temporary metal storage sites for the holes to produce a laminar flow, and hydraulic retention time duration of the growing season, which could imply negative (HRT) was carefully determined. effects on water quality during plant senescence [17]. In E. Water sampling and analysis contrast, some species are displaying higher metal concentrations in dead tissue [18], which can be as a result of The wastewater samples (250 ml) were collected at the inlet minor leakage of accumulated metals during plant and outlet of each CW for a month. Atomic absorption decomposition and because dry weight in dead plant tissue is spectrometer and ion chromatograph were used to determine less than in living tissue due to the lack of organic matter. total concentrations of heavy metals and sulphate in wastewater. Knowledge of the metal concentrations in plant and shoots is important, since it has been demonstrated that high F. Substrate sampling and analysis shoot concentrations can harm grazing animals [19]. The main Samples (100 g each) were taken at the inlet and the outlet at objective of this study was to treat AMD and assess the the end of the experiment for analysis. The substrates samples feasibility of using un-vegetated constructed wetland. were dried in an oven until constant weights were reached and ground using mortar and pestle. Subsequently, they were II. MATERIALS AND METHODS sieved through a 53 μm sieve and then wet digested in HNO3 for 24 hours to obtain the total fraction. Atomic absorption A. Wetland Design spectrophotometer was used to analyze the metal Three pilot- scale unvegetated wetland units made of acrylic concentrations in sediments. plates with dimensions of 100 cm x 35 cm x 35 cm was constructed. An impermeable film was placed at the bottom G. Data analysis and sides of the basins. Each CW was divided into two The percentage removal (Ro) of metals from water passing compartments. Three CW were layered with sand in the first through the wetlands was calculated as: compartment and clinoptilolite in the second compartment as a main adsorbent. The wetlands were constructed at Mintek. Ro = [Me]in – [Me]out × 100 (1) B. Materials [Me]in The AMD samples were collected in August 2013 at where [Me]in refers to the metal concentration in water Mpumalanga, South Africa. The surface water sample was flowing into the wetlands and [Me]out refers to the metal taken from an open pit in the mining area at different depth concentration in water flowing out of the wetlands. levels. Three 100L polypropylene drums were used to store the samples (collected from three locations), which is in III. RESULTS AND DISCUSSION accordance to commonly accepted sampling procedures [20]. A. Constructed wetland packing material characterization of the sample was carried out in the laboratory using Morphological observation of clinoptilolite and silica were a portable vacuum filter and a 0.45 µm Millipore filter. A 250 performed using a scanning electron microscopy (SEM). The ml of the sample was taken for characterization of toxic heavy metals and sulphates, and the rest of the sample was stored in analysis showed the surface of the adsorbents was rough and the cool place. porous, and the structure was compact and presented clearly alveolate holes. Fig. 1 shows the SEM analysis of

clinoptilolite, and silica respectively.

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Intl' Conf. on Chemical, Integrated Waste Management & Environmental Engineering (ICCIWEE'2014) April 15-16, 2014 Johannesburg

(a) (b) became weak and the adsorption efficiency also increased. The above fact related to the effect of pH on adsorption is also supported by several studies [22]-[23]. 2- Adsorption of SO4 ions was also investigated at the end of the experimental runs. The maximum SO42- adsorption at pH of 3 was 56.7%, and 50% for clinoptilolite, and silica respectively. At the pH of 5 the maximum SO42- adsorption was 50%, and 41.7% for clinoptilolite, and silica respectively. These findings implied that the pH adjustments slightly

Fig.1 SEM Images of (a) Clinoptilolite, (b) Silica increased the adsorption efficiencies of both clinoptilolite and silica, therefore for the rest of the study, pH adjustments were The energy-dispersive x-ray spectroscopy (EDX) analysis not considered. Again, since constructed wetlands operates at was performed for clinoptilolite and silica respectively. A long hydraulic retention times (1-7 days), it is believed that the chemical analysis of the adsorbents is presented in Table I. remaining Fe(II) concentration would be removed by other This study showed that the natural zeolite contained a processes such as precipitation/co-precipitation, and complement of exchangeable sodium, potassium, and calcium sedimentation that take place in constructed wetlands. which can be replaced with heavy metals. The adsorption capabilities of zeolite result from a net negative charge on the structure of fine-grain silicate minerals. This negative charge is neutralized by the adsorption of positively charged species, giving clinoptilolite the ability to attract and hold cations such as heavy metals. The large surface area of clinoptilolite also contributes to the high adsorption capacity [21]. Silica chemical analysis showed it contains no exchangeable ions (such as sodium, potassium, calcium) for cation exchange process to take place. Therefore the large surface area of silica is what contributes to high adsorption capacity. Table II shows the BET surface area and distribution of pore width of the constructed wetland packing materials. Fig. Fig. 2(a) Adsorption of Fe(II) by clinoptilolite, and silica as a B. Effect of pH on adsorption efficiency of the CW packing function of pH: contact time 3 h, pH 3, 60°C, C0 62 mg/l material Preliminary batch studies were done in order to investigate the effect of pH on the adsorption efficiencies of the constructed wetland packing material. Fig. 2 shows the effect of pH on the adsorption of Fe(II) by clinoptilolite, and silica. The pH ranged was from 3 to 5, and each experiment was run for three hours. The maximum Fe(II) adsorption at pH of 3 was 70.4%, and 71.7% for clinoptilolite, and silica respectively. At the pH of 5, the maximum Fe(II) adsorption efficiency was 86.47%, 74.2% for clinoptilolite, and silica respectively. The effect of pH can be explained considering the surface charge on the adsorbent material. When pH was Fig. 2(b) Adsorption of Fe(II) by clinoptilolite, and silica as a low, hydrogen ion with high concentration was predominant in function of pH: contact time 3 h, pH 5, 60°C, C0 62 mg/l. adsorption onto the adsorbent. The adsorbent surface was positively charged, which prevented Fe(II) adsorption. When C. Acid Mine Drainage Characterization According to analysis conducted in this study, samples of TABLE I CHEMICAL COMPOSITIONS OF CW PACKING MATERIALS groundwater in the mining area typically show high Element Clinoptilolite(wt.%) Silica sand(wt.%) concentration of sulphates, low pH and elevated metal Oxygen 47.83 54.51 concentrations (Table III), confirming previously reported 7.23 0.72 results [24]-[26]. Acid mine drainage samples were Silicon 38.77 44.77 Potassium 1.65 - characterized for toxic heavy metals and sulphates. High Iron 0.91 - sulphate and iron content are a result of pyrite oxidation Calcium 1.56 - during the formation of AMD. The pH ranged from 2.55 - 2.7. Sodium 1.66 - Magnesium 0.39 - Other metals such as Al, Ca, Mg, and Si were present in the mine drainage in large quantities, while Li, Be, Zn, Co and Mn pH was elevated, the positive charge on the material surface were present in low quantities. No traces of Cr, V, Pb, Cu, Cd,

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Intl' Conf. on Chemical, Integrated Waste Management & Environmental Engineering (ICCIWEE'2014) April 15-16, 2014 Johannesburg

Sn, and Ag were detected during characterization. Therefore, TABLE III all the water samples were spiked with varying concentrations ACID MINE DRAINAGE CHARACTERIZATION of Cr(VI) in order to simulate Cr(VI)-laden-acid-mine- Douglas North Middelburg Steam drainage. Discharge Coke and Coal T&DB Decant (DND) (SSC) (TDB) D. Heavy metals removal in constructed wetlands pH 2.7 2.65 2.55

SO4(mg/l) 2690 3595 6055 All three constructed wetlands were fed with acid mine Fe (mg/l) 280.815 148.483 20.776 drainage wastewater sampled at different points. The first Al (mg/l) 246 143.333 9.95 constructed wetland was fed with the sample taken at Douglas Ca (mg/l) 80.188 389.986 450.245 Li (mg/l) 0.413 4.157 3.99 North Discharge (DND); the second wetland was fed with the Be (mg/l) 0.063 0.082 0.05 Middelburg Steam Coke and Coal (SCC); and the third Mg (mg/l) 46 216 211 wetland with the sample from T&DB Decant (TDB). Si (mg/l) 80.182 38.711 50.482 Zn (mg/l) 5.7 8.6 1.55 Instantaneous samples of influent and effluent wastewater Cu (mg/l) <0.05 <0.05 <0.05 were Pb (mg/l) <0.05 <0.05 <0.05 taken manually for heavy metal and sulphates determination V(mg/l) <0.05 <0.05 <0.05 during treatment. The effect of hydraulic retention time on the Co (mg/l) 1.729 2.727 0.559 efficient removal of heavy metals and sulphates was investigated. Though the redox potential was not monitored in Ni (mg/l) 2.6 3.187 0.867 this study, this parameter might be useful to explain the metal Mn (mg/l) 6.095 35.852 11.771 behaviour in the wetland sediment. Nevertheless, the pH and Cd (mg/l) <0.05 <0.05 <0.05 oxidizing conditions favoured partitioning of soluble metals to Sn (mg/l) <0.05 <0.05 <0.05 the solid phase, by precipitation and sorption to solids matter Ti (mg/l) <0.05 <0.05 <0.05 [27]. The removal of heavy metals and sulphates for three Cr (mg/l) +200 +600 +1000 pilot-scale wetland systems are shown in Fig.3. Ag (mg/l) <0.05 <0.05 <0.05 The effect of hydraulic retention time (HRT) was *+, concentration was below detection, therefore spiked into the wastewater. investigated between 3 – 5 days. Metal concentrations were significantly lower in the outlet than in the inlet. After three wetlands was 30%. days, the highest metal average metal retention was attained by Fe (68.86%), Ca (69.35%), Cr (63%), Al (47.97%), Mg (33.5%), Si (26.42%) and 100% removal was achieved for Be, Zn, Co, Ni, and Mn. After five days, the highest metal average metal retention was attained by Fe (100%), Ca (79.69%), Cr (68%), Al (22.15%), Mg (51.1%), Si (36.39%) and 100% removal was achieved for Be, Zn, Co, Ni, and Mn. The sulphates removal after three days was 34.9%, and after five days it 21.9%. Therefore, hydraulic retention time of 5 days was chosen as the best operating parameter for all three constructed wetlands. During the experiment, removal efficiencies of heavy metals and sulphates fluctuated. The concentration of some heavy metals in the outlet of the wetlands decreased, while for some, the concentration of the heavy metals increased. At the end of the experiment (20 days), the highest metal average metal retention was attained by Fe (90.39%), Cr (64.5%), Mg (67.88%); 100% removal was achieved for Ca, Be, Zn, Co, Ni, and Mn; however, Al and Si concentration increased by 17.9% Fig.3 Heavy metals and sulphate removal during treatment AMD and 2.7% respectively in the first constructed wetland. For the treatment with constructed wetlands: (a) DND; (b) SSC; (c) TDB second constructed wetland, the highest metal average metal retention was attained by Fe (86.45%), Cr (56.17%), Mg As mentioned earlier, the efficient reduction of the metals and sulphate contents are due to adsorption, precipitation/co- (67.1%); 100% removal was achieved for Ca, Be, Zn, Co, Ni, and Mn; however, Al and Si concentration increased by precipitation, and sedimentation. The adsorption capacity by 17.48% and 2.7% respectively. For the third constructed cation exchange or non-specific adsorption depends upon the wetland, the highest metal average metal retention was physico-chemical environment of the medium, the properties attained by Fe (83.62%), Cr (56.4%), Mg (64.23%); 100% of the metals concerned and the concentration and properties of other metals and soluble ligands present [6]. More than removal was achieved for Ca, Be, Zn, Co, Ni, and Mn; however, Al and Si concentration increased by 14.6% and 50% of the heavy metals can be easily adsorbed onto 2.7% respectively. The sulphates reduction in all constructed particulate matter in the wetland and thus be removed from the

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Intl' Conf. on Chemical, Integrated Waste Management & Environmental Engineering (ICCIWEE'2014) April 15-16, 2014 Johannesburg water component by sedimentation [28]. Brix [29] reported depends on the decomposition procedure, and that certain that factors that affect antimony adsorption include iron metals are better recovered by one method compared to the concentration [as Fe(III)], pH and contact time. other. They further proposed that factors that affect the Iron, aluminium and manganese can form insoluble extraction efficiency are losses due to volatilisation depending compounds through hydrolysis and/or oxidation that occur in on the drastic conditions of the decomposition procedure, the wetlands. Thus leads to formation of variety of oxides, nature of the organic material to be decomposed, the metal oxyhydroxides and hydroxides [30]. Iron removal depends on that is subsequently to be determined, and optimal digestion pH, oxidation–reduction potential and the presence of various time in acids. These factors could be the possible reason why anions [31]. Trivalent iron, Fe3+ may be removed simply by some of the metals were below detection limit. Therefore, raising pH to 3.5 with sufficient retention period. Stark et al., XRF was employed to analyze the concentrations of the rest of [32] reported Fe removal to be nearly 100% after 8 years of the metals that were below detection when using AAS. Metal operation at SIMCO wetlands. Divalent iron, Fe2+ is highly concentrations were significantly higher in the wetlands outlet soluble in water that has low dissolved oxygen up to pH 8. than in the intlet, except for Ni, Be, and Li that were below 3+ Thus first the Fe2+ needs to be oxidized to Fe at pH less than detection in all samples (Table IV). 4 or 5 when bacteria also plays a role of catalyst so as to TABLE IV oxidize ferrous to ferric iron [33]. METALS CONCENTRATION IN SEDIMENTS Douglas North Middelburg Aluminum can precipitate as aluminum hydroxides around Discharge Steam Coke and T&DB pH close to 5 [34]. Manganese removal is the most difficult to (DND) Coal (SSC) Decant be achieved because its oxidation takes place at a pH close to Inlet Outlet Inlet Outlet Inlet Outlet 8 [35]. Bacteria play an important role in the oxidation of Mn since they accelerate the oxidation of Mn2+ to Mn4+. pH 2.7 2.85 2.65 2.8 2.55 2.85 Precipitation and co-precipitation in the removal of heavy S (mg/l) 2237 7328 2210 1010 5080 1040 metals is an important adsorptive mechanism in wetland Fe (mg/l) 2440 7776 2082 1080 5793 9888 sediments. The formation of insoluble heavy metal Al (mg/l) 15 591 14 571 16 561 precipitates is one of the many factors limiting the bioavailability of heavy metals to many aquatic ecosystems. Ca (mg/l) 288 7512 124 7887 1874 7272 Co-precipitation is also an adsorptive phenomenon in wetland Mn (mg/l) 103 149 128 182 210 183 sediments. Heavy metals co-precipitates with secondary Cr (mg/l) 256 172 378 490 185 562 minerals in wetlands. Metals such as copper, nickel, zinc, and Si (mg/l) 4090 3100 3750 3580 4660 3640 manganese are co-precipitated in Fe oxides and cobalt, iron, nickel and zinc are co-precipitated in manganese oxides Mg (mg/l) 5 53 <5 49 <5 41 [34],[36]. Zn (mg/l) <5 59 <5 66 <5 60 Chromium is present as Cr(VI), which is relatively mobile Co (mg/l) <5 1.9 <5 2.6 <5 2.3 and after release into the pore, it migrates downward into the Ni (mg/l) <5 <5 <5 <5 <5 <5 reducing zone and precipitates as Cr(OH)2 [37]. The hydrolysed form of Cr(VI) is readily absorbed by hydrous Fe Li (mg/l) <5 <5 <5 <5 <5 <5 and Mn oxides [38]. Be (mg/l) <5 <5 <5 <5 <5 <5 Swedlund and Webster (2001) found that at pH 4 and 2- below, nearly 40% of SO4 present is adsorbed onto the Fe oxyhydroxides and oxy-hydroxysulphates. These finding are The concentration of sulphur in all samples indicated that it relatively similar to the ones found in this study. Although the moves from bottom sediment layers to the sediment-water ability of clinoptilolite based constructed wetland has interface [41]. This also suggests that there is enrichment of demonstrated the ability to reduce sulphate concentration, sulphur below the suboxic/anoxic interface, indicating that literature relating to sulphate reduction could not be found. sufficient oxidants must be present to generate sulphides; Further work is required to determine the mechanism of namely metal oxides, which interact with sulphur species to sulphate reduction, be it chemical, biochemical, physical or a form sulphides [42]. The significant relationship of sulphur combination thereof. with trace metals shows that these trace metals are precipitated as metal sulphides and are also responsible for the fixation of E. Metal concentrations in sediments trace metals in core sediments [43]. The metal concentrations in sediments were obtained by concentrated HNO3 extraction at the end of the experiment. IV. CONCLUSION However, it seems that the acid extraction was achieved for In this study, significant metal reduction has been Fe, Si, Ca, and Mg since the rest of the metals concentrations demonstrated in three pilot-scale constructed wetlands. It was were below detection when analysed using AAS. Oduoza and found that the hydraulic retention time (HRT) of 5 days lead to Miaphen [40] assessed the suitability of various methods in the maximum removal of the metals. Therefore constructed the extraction of trace metals and pollutants in aquatic wetland treatment process has a potential to remove heavy sediments. They reported that the extraction efficiency metals from acid mine drainage. Again, it is feasible to treat

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Intl' Conf. on Chemical, Integrated Waste Management & Environmental Engineering (ICCIWEE'2014) April 15-16, 2014 Johannesburg acid mine drainage with constructed wetland since the packing [18] Fritioff Å. & Greger M., 2007. Fate of cadmium in Elodea canadensis. materials are not costly and also because there is a vast land in Chemosphere 67: 365-375aquatic plant Potamogeton natans. Chemosphere 63: 220-227. Africa not being utilized or which is neither suitable for [19] Stoltz E. & Greger M., 2002 Accumulation properties of As, Cd, Cu, Pb human settlement nor agricultural purposes. Although this and Zn by four wetland plant species growing on submersed mine paper involves the study of mechanism of heavy metal tailings. Exp. Environ. Bot. 47: 271-280. [20] Hermond, H.F., Fechner-Levy, E.J., 2000. Chemical Fate and Transport removal in wetlands it is still part of a long-term investigation in the Environment. Academic Press, San Diego, USA. into the practical application of the technique. Further studies, [21] Cadena, F., Rizvi, R., and Peters, R.W., 1990, Feasibility studies for the with special emphasis on heavy metal removal and sulphate removal of heavy metals from solution using tailored bentonite, in Hazardous and Industrial Wastes, Proceedings of the Twenty-Second mechanisms in wetlands, is still required. Mid-Atlantic Industrial Waste Conference, Drexel University. 77–94. [22] Akil, A., Mouflih, M., Sebtim S., 2004, Removal of heavy metal ions ACKNOWLEGMENTS from water by using calcined as a new adsorbent. J. Hazard. Mater, (112) 183 -190. This work was carried out in and financially supported by [23] Munther, I.K., 2004, Zinc and cadmium adsorption on low-grade Mintek. Tumelo Seadira and Jeffrey Baloyi are M. Tech phosphate, Sep. and Puri. Tech. 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