Search

This work explored the potential of clinoptilolite, molybdenum sulphide (MoS2), and MoS2-clinoptilolite composite in lead (Pb) removal from aqueous medium and industrial mining wastewater. MoS2-clinoptilolite composite was successfully prepared by a hydrothermal method. The surface properties, structure, and composition of the synthesized composite and the parent compounds were analyzed by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The removal efficiency of lead from aqueous solution was studied in batch-mode experiments. The MoS2-clinoptilolite was used for the removal of Pb ions (50 mg/L) from an aqueous solution: ~100% of the Pb was removed with a MoS2-clinoptilolite dose of 0.075 g, pH 6 at 328K within 90 min. The adsorption capacities of Pb onto MoS2-clinoptilolite were found to be higher than those onto clinoptilolite. Metal ion adsorption behavior was well explained by the Freundlich model, that is, multilayer adsorption of Pb molecules occurred on the heterogeneous surface of adsorbents in case of clinoptilolite, while in the case of MoS2-clinoptilolite, the Langmuir model was suitable, that is, the adsorption occurred on a monolayer surface. The rate of Pb adsorption was explained by pseudo-second-order model suggesting that the adsorption process is presumably chemisorption. Thermodynamic parameters such as ΔH°, ΔS°, and ΔG° were calculated, which indicated that the adsorption was spontaneous and exothermic in nature. The selectivity of each adsorbent for Pb was also tested by adding the adsorbents to real gold mine water which contains competitive metal ions

In this research, insoluble nanosponge β-cyclodextrin (β-CD) polyurethane was modified with phosphorylated multiwalled carbon nanotubes (pMWCNTs) and further decorated with titanium dioxide and silver nanoparticles. This modification of β-CD polyurethane was achieved through subsequent reactions of amidation, cross polymerization, using a functional linker such as diisocyanate, and sol-gel. The new polymeric nanobiosorbent obtained was characterized by Fourier-transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM); for surface area analysis, the Brunauer-Emmett-Teller (BET) method was employed. The developed nanobiosorbent, with a high surface area (352.5 m2 g−1), favors the adsorption of trichloroethylene (TCE) and Congo red (CR) dye from wastewater samples using a batch method. The solution pH, adsorbent dosage effects, isotherm, kinetic, thermodynamic as well as regeneration and desorption studies on the adsorption mechanism were also explored. The nanobiosorbent maximum capacities of removal from the Langmuir model were respectively, 27507 mg g−1 (TCE) and 146.96 mg − (CR dye). The adsorption mechanisms of TCE and CR dye were well-established and taking place via an endothermic process

In this study, the hydrochemical characteristic changes of open-pit groundwater (OPGW) near a closed metalliferous mine proposed for drinking and irrigation usage were investigated. Water samples from an OPGW in O’Kiep were collected in April (dry season) and August (wet season), 2017. Data analysis methods, such as the coefficient of variation, correlation coefficient, piper trilinear plot analysis and sodium adsorption ratio (SAR) among others were used to assess of the seasonal variation in the OPGW quality. The hydrochemical characteristics of the OPGW were also compared with drinking water guidelines. Based on the results, it was evident that the OPGW quality varied seasonally. The most abundant cation and anions were Ca2+ and SO42−, with recorded concentrations of 631 and 6020 mg/L, (dry season); 541 and 4450 mg/L (wet season), respectively. The OPGW was relatively rich in SO42− > Cl− > Mg2+ > Ca2+ > Na+ > K+ during the dry season; however, these cations and anions were reduced during the wet season with Cl− and Na+ subsequently increasing. PHREEQC indicated that cation exchanges played a significant role in the OPGW chemistry with Sb and Ca appearing to be the minerals with the highest precipitation potential followed by Cu7S4 and Blaubleil, respectively. Covellite, CdSe2 and NiSe were likely to be in equilibrium while Ca3Sb2 will remain in a dissolution state. Furthermore, the seasonal fluctuation in the OPGW quality characteristics was attributed to the water table level fluctuations and the water quality did not satisfy the guidelines stipulated by the South African National Standard, SANS241-1 (2015) and World Health Organisation, WHO (2011). The trilinear piper plot classified the OPGW into three types: Ca2+–Mg2+–Cl−–SO42; Ca2+–Mg2+–F−; and Ca2+–Mg2+–SO42−. Overall, the SAR values were within the permissible levels for irrigation purposes; however, long-term use of the OPGW might be detrimental for plant growth

Mercury is one of the most toxic, harmful element present in water that severely affects human health. Many traditional as well as advanced technologies were developed to remove mercury from wastewater. In this study, sulfur copolymers containing micro and macro porous structure were prepared via inverse vulcanization technique and used to capture the mercury ions from wastewater. Initially, porogens with varying particle size were added to the sulfur and cross-linker mixture, later the obtained solid copolymers was treated with water to generate porous structure with different porosicity. Structure of the prepared sulfur copolymer was confirmed by FTIR, NMR spectroscopy and the surface morphology studied by SEM indicate the presence porous structure relating to the size of the porogen. Thermal properties analyzed by DSC and TGA supports the stability of the copolymer. Obtained sulfur foams were used to capture mercury ions from water and studied the adsorption behaviour using different isotherm and kinetics models. The adsorption kinetics showed a pseudo-second-order rate equation and the metal ion diffusion was found to be a combination of both intraparticle and liquid film diffusion mechanisms. The adsorption capacity improved with the increasing porosity in the sulfur foam and the adsorption isotherm suggested that the mercury ions were captured via both physical and chemical adsorption mechanism. Modification in the sulfur foam porosity can significantly influence the mercury ion adsorption capacity. The main advantage of this technique is the use of surplus sulfur and one step preparation method which can be scalable and cost effective.

Spent coffee grounds were transformed into biochar using a hydrothermal method. Some of the biochar product was pre-treated through surfactant impregnation with sodium dodecyl sulphate (SDS) to enhance its adsorption capacity. The non-treated(NT) and pre-treated(PT) biochars were characterized using FTIR spectroscopy and SEM-EDS analyses, which revealed that the products had the potential for adsorption of heavy metals from solution and confirmed the successful impregnation of biochar with SDS surfactant. The two adsorbents were then used for the removal of cadmium from solution and the adsorption behavior and capacity determined through adsorption isotherm, kinetic, and thermodynamic studies. It was found that the cadmium was adsorbed in several concentric layers on the surface of the adsorbents through a chemisorption mechanism. The PT biochar was identified as a superior adsorbent, with a capacity of qe = 10.67 mg/g compared to the NT biochar with qe = 4.82 mg/g. The adsorption of cadmium onto the PT biochar was further determined to be spontaneous and endothermic. It was therefore concluded that the PT biochar shows potential as an adsorbent and could be considered for implementation in the treatment of metal-polluted effluents

A clay-biochar composite was prepared through slow pyrolysis of a mixture of bentonite clay and sweet sorghum bagasse. The adsorption of cationic dyes, namely, toluidine blue (TB) and malachite green (MG), by the clay-biochar composite was investigated to determine the adsorption mechanism and its sorption potential. Bentonite clay, sweet sorghum biochar and the bentonite-biochar composite were characterized through X-ray fluorescence (XRF), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) analyses. For the adsorption study, the effects of exposure time, initial dye concentration and temperature were investigated. The findings clearly illustrated the complex physico-chemical properties of the clay-biochar composite encompassing distinct features of bentonite clay and biochar, therefore confirming successful preparation. The adsorption of MG was found to occur on a heterogeneous surface as predicted by the Freundlich isotherm model, while the adsorption of TB occurred mostly at a monolayer surface described by the Langmuir isotherm model. The adsorption equilibrium data was best described by the pseudo-second order kinetic model for all adsorbents. The estimated adsorption capacity of the clay-biochar composite (12.1255 mg/g for MG and 9.9356 mg/g for TB) suggests improved adsorption capacity of the biochar after incorporation of clay. The thermodynamic study revealed that the adsorption of dyes was mostly a spontaneous and exothermic process. The adsorbent investigated in this study showed good potential for the removal of cationic dyes from aqueous solution and could be considered for the remediation of water polluted by industrial effluents

Water insecurity is a growing concern globally and the role of groundwater and aquifers in buffering the effects of climate variability and change is increasingly acknowledged due to extended periods of drought in arid regions. Water security can only be fully realised with a more robust understanding of groundwater as a water resource, especially in the O'Kiep area which is in Namaqualand, South Africa. Results of analyses of groundwater samples (n = 8) indicated that pH values met acceptable standards for drinking, while the total dissolved solids (TDS) and electrical conductivity (EC) were however not within the recommended limits. The chemical composition of the groundwater indicated Eh values −34.1 to −87.2 mV, indicative of reducing geochemical conditions with the most abundant ions being Cl-, SO42-, NO3-, F-, Na+, Ca2+, Mg2+ and K+. Furthermore, some of the ions were not within the guidelines, i.e. Cl−, SO42+, Na+, Ca2+ and Mg2+, but all the potential toxic elements, namely: Al, S, As, Cd, Cr, Co, Cu, Fe, Mn, Hg, Ni, Se, V, Zn and CN, were within acceptable values for drinking groundwater as recommended by the SANS241-1 (2015) and WHO (2011). Hydrogeochemical characteristics of the water indicated that the continuous consumption of the groundwater without pretreatment might result in possible human health risk as the Groundwater Quality Index (GWQI) confirmed that the groundwater quality could be classified as being of moderate concern. Furthermore, the hydrogeochemical indices (CaCO3/Cl and Mg/Ca) and cationic exchange values indicated that the aquifer is of inland origin while the piper trilinear diagram revealed that the groundwater type in the area is categorised as sodium – potassium – chloride – sulphate- (Na–K–Cl–SO4), carbonate – chloride – sulphate- (CaCO3–Cl–SO4) and sodium – chloride (Na–Cl) type water. Additionally, the Sodium Adsorption Ratio (SAR) values up to 11.7 indicated that the groundwater is brackish and its excessive usage may have undes

This study reports on the biodegradation of free cyanide (FCN) by cyanide degrading bacteria (CDB) that were isolated from mining wastewater and thiocyanate containing wastewater. The performance of these isolates was compared to cryopreserved CDBs that were used in previous studies. The performance of the isolates to degrade FCN was studied in batch cultures. It was observed that the CDB from the thiocyanate wastewater showed higher biodegradation rates (2.114 g CN−. L−1.O.D600 nm−1.h−1) compared to the isolates from the mining wastewater. The isolates from the cryopreserved CDBs and from the mining wastewater achieved a biodegradation rate of 1.285 g CN− L−1.O.D600 nm−1.h−1 and 1.209 g CN−.L−1.O.D600 nm−1.h−1, respectively. This study demonstrated that the source of the organisms plays a significant role on FCN biodegradation

The water purification process at Eskom includes a reverse osmosis (RO) treatment plant. There are several limitations to this process depending on the water characteristics. The most common problems limiting the success of water purification include scaling, biological fouling and corrosion. This study is mainly focused on reducing scale forming agents in the RO system. Scaling is the precipitation of calcium and magnesium salts onto the equipment, primarily the RO membrane. These salts start to precipitate once the salt concentration in the water is higher than the allowable solubility constant. These salts can be removed from the water by a process called coagulation-flocculation. The success of such process is partly dependent on the type of flocculant and the dosage used. In this study the performances of one coagulant namely Rheofloc 5023 in combination with three flocculants including Rheofloc 5414, Genesys genefloc and AR floc 100 were tested at various dosages for the reduction of conductivity assimilated with ions in the RO retentate from coal power plant was investigated at 40 and 60oC. The AR floc 100 was determined to be the optimum flocculant required for the RO reject treatment. The optimum flocculant dosage resulted in 1 ppm along with a Rheofloc 5023 coagulant dosage of 0.7 ppm

For environmental and aesthetic purposes it has become essential that mine dump rocks either blend into the environment or be used in the production of other products. Lately, there has been a constant need to produce more durable road and construction material and to develop an alternative for granite countertops and flooring. For the visibility of road surface material and the aesthetic aspect of countertops, the colouring of mine dump rocks was considered. A cost effective and environmentally friendly process was suggested to colour mine dump rocks. In this study different colouring agents for three mine dumping rocks, dolomite, quartzite and dolerite, were investigated. The aim was to create lasting colours that have a high wear resistance to weather conditions. Coloured dolomite can be used as road and construction material, coloured quartzite as countertops while coloured dolerite can serve as a replacement for road surfaces

This study reports on the biodegradation of free cyanide (FCN) by cyanide degrading bacteria (CDB) that were isolated from mining wastewater and in thiocyanate containing wastewater. The performance of these isolates was compared to cryopreserved CDBs that were used in precious studies. The performance of the isolates to degrade FCN was studied in batch cultures. It was observed that the CDB from the thiocyanate wastewater showed higher biodegradation rates (2.114 g CN- .L-1.O.D600nm -1.h-1) compared to the isolates from the mining wastewater. The isolates from the cryopreserved CDBs and from the mining wastewater achieved a biodegradation rate of 1.285 g CN- .L-1.O.D600nm -1.h-1and 1.209 g CN- .L-1.O.D600nm -1.h-1 , respectively. This study demonstrated that the source of the organisms plays a significant role on FCN biodegradation

Several nanoparticles (Cu2O, SnO, ZnO) have been intensively studied and applied in wastewater treatment research, with TiO2 gaining popularity because of its stability, affordability, large band gap, recyclability and its efficiency in photocatalysis. This study reports on the influence of solubilising matrices on TiO2 nanoparticle synthesis. A Wet Chemical Method was used to synthesis TiO2 nanoparticles by solubilising TiCl4 in three types of solvents: water, toluene and methylene chloride. Physical, chemical and optical properties of the TiO2 nanoparticles obtained from these various solubilising agents were characterised by XRD, UV-Vis, FTIR and SEM. Results were compared for each solvent with TiO2 nanoparticles solubilised in water having the best properties