Mercury speciation and dispersion from an active gold mine at the West Wits area, South Africa.

Total mercury (HgTOT), inorganic mercury (IHg), and methylmercury (MHg) were determined in dry season waters, sediments, and tailings from an active mine which has long history of gold exploitation. Although HgTOT in waters was generally low (0.03 to 19.60 ng L(-1)), the majority of the samples had proportions of MHg of at least 90 % of HgTOT which denotes a substantial methylation potential of the mine watersheds. Mercury was relatively high in tailing materials (up to 867 µg kg(-1)) and also in the mine sediments (up to 837 µg kg(-1)) especially in samples collected near tailing storage facilities and within a receiving water dam. Sediment profiles revealed mercury enrichment and enhanced methylation rate at deeper layers. The presence of IHg and decaying plants (organic matter) in the watersheds as well as the anoxic conditions of bulk sediments are believed to be some of the key factors favoring the mercury methylation at the site.

Removal of toxic elements from aqueous solution using bentonite modified with L-histidine.

This study proposes the use of bentonite modified with L-histidine for the removal of Cu, Co, Cr, Fe, Hg, Ni, U and Zn from aqueous solutions such as those impacted by acidic drainage. The surface areas of natural bentonite and bentonite-histidine were 73.8 and 61.2 m(2) g(-1), respectively. Elemental analysis showed an increase in the amount of carbon (0.258%) and nitrogen (0.066%) for the bentonite-histidine. At a fixed solid/solution ratio, the operating variables affecting the adsorption of metal ions from aqueous solution such as pH, initial concentration, contact time and temperature were studied in batch mode. The Freundlich isotherm model yielded a better fit than the Langmuir for the adsorption of Cu, Co, Ni and Zn, implying adsorption on a heterogeneous surface. Adsorption kinetics followed a pseudo-second-order model, suggesting chemisorption as the rate-limiting step. The apparent activation energy was greater than 40 kJ mol(-1) for Cu, Zn, Ni, Co and U, which is characteristic of a chemically controlled reaction. Thermodynamic constants ΔG and ΔH showed that the adsorption of metals was endothermic and spontaneous. Adsorption of heavy metals onto bentonite-histidine was efficient at low pH values, meaning that the adsorbent could be useful for remediating acid mine water.

Simple and efficient ion imprinted polymer for recovery of uranium from environmental samples.

Ion imprinted polymer material (IIP) was prepared by forming ternary complexes of uranyl imprint ion with 1-(prop-2-en-1-yl)-4-(pyridin-2-ylmethyl)piperazine and methacrylic acid followed by thermal copolymerization with ethylene glycol dimethacrylate as the cross-linking monomer in the presence of 1,1'-azobis(cyclohexanecarbonitrile) initiator and 2-methoxy ethanol porogenic solvent. HCl solution (5 mol/L) was used to leach out the uranyl template ion from the IIP particles. Similarly, the control polymer (CP) material was also prepared exactly under the same conditions as the IIP but without the uranyl ion template. Various parameters such as solution pH, initial concentration, aqueous phase volume, sorbent dosage, contact time and leaching solution volumes were investigated. SEM, IR and BET-surface area and pore size analysis were used for the characterization of IIP and CP materials. The extraction efficiency of the IIP and CP was compared using a batch and SPE mode of extraction. The optimal pH for quantitative removal is 4.0-8.0, sorbent amount is 20 mg, contact time is 20 min and the retention capacity is 120 mg of uranyl ion per g of IIP. The IIP prepared demonstrated superior selectivity towards coexisting cations and therefore it can be used for selective removal of uranium from complex matrices.

Multi-walled carbon nanotubes as adsorbents for the removal of parts per billion levels of hexavalent chromium from aqueous solution.

The adsorption capabilities for the removal of parts per billion levels (ppb) of hexavalent chromium by three adsorbents namely activated carbon, functionalized multi-walled carbon nanotubes (MWCNTs) and unfunctionalized multi-walled carbon nanotubes were investigated as a function of contact time, initial solution pH, initial Cr(VI) concentrations and the presence of competing anions. The unfunctionalized MWCNTs showed the highest adsorption capability with up to 98% of a 100 ppb Cr(VI) solution being adsorbed. Both functionalized and non-functionalized MWCNTs showed a superior adsorption capability to that of activated carbon. The removal of Cr(VI) was higher at lower pH. Furthermore, the uptake of Cr(VI) was hindered by the presence of the competing anions, Cl(-) and SO(4)(2-). Both Langmuir and Freundlich isotherms have been used to describe the Cr(VI) adsorption process. The major mechanisms for Cr(VI) removal have been identified as an ion exchange mechanism, intraparticle diffusion and electrostatic interactions. The adsorbed Cr(VI) could also be desorbed readily from the MWCNTs surface at high pH.