Heavy-metal removal using liquid membrane

Experiments have been conducted to obtain the optimum conditions of hydrogen ion concentration of feed and strip phases and concentration of the carrier ALAMINE 336, in the extraction of Cr(VI) and Hg(II) using two different types of liquid membranes-bulk liquid membrane and emulsion liquid membrane. Experiments have also been carried out to find the effect of metal loading and the effect of extraction time on metal flux.

Influence of pH on the retention of heavy metal ions by fly ash

Clay liners have been widely used to contain toxic and hazardous wastes. Clays adsorb the contaminant cations due to their exchange capacity. To improve the performance of the clay liner, fly ash, a waste material arising out of combustion of coal has been studied as a pre-filter material. The results indicate that fly ash has the potential to retain heavy metal ions. This study concerns the retention of zinc by fly ash. The influence of pH on retention as well as leaching characteristics are examined. The results obtained from the retention experiments by permeameter method indicate that fly ash retains the zinc ions through precipitation in the pores as well as onto the surface when the ambient pH value is more than 6.9, and only through adsorption when the pH value is less than 6.9. It has been observed that fly ash did not release the retained zinc ions when the pH value is between 3.5 and 10.0. Hence, the retention of zinc ions by fly ash is likely to be permanent since the pH of most of the landfill leachates are between 3.7 to 8.8.

Biosorption of heavy metal ions from aqueous and cyanide solutions using fungal biomass

A waste fungal biomass containing killed cells of Aspergillus niger was efficiently used in the removal of toxic metal ions such as nickel, calcium, iron and chromium from aqueous solutions. The role of different parameters such as initial metal ion concentration, solution pH and biomass concentration on biosorption capacity was established. The maximum metal uptake was found to be dependent on solution pH and increased with biomass loading upto 10g/L. The adsorption densities for various metal ions could be arranged as Ca>Cr (III)>Ni>Fe>Cr (VI). The effect of the presence of various metal ions in binary, ternary and quaternary combinations on biosorption was also assessed. Ni uptake was significantly affected, while that of Cr (VI) the least, in the presence of other metal ions. Uptake of base metals from an industrial cyanide effluent was studied using different species of fungi such as Aspergillus niger, Aspergillus terreus and Penicillium funiculosum and yeast such as Saccharomyces cerevisiae which were isolated from a gold mine. Traces of gold present in the cyanide effluent could be efficiently recovered. Among the four base metal contaminants present in the cyanide effluent, zinc was found to be most efficiently biosorbed, followed by iron, copper and lead. The role of both living and dead biomass on biosorption was distinguished and probable mechanisms illustrated.

Identification of source of heavy metal contamination in a site - a case study

Accidental spills and improper disposal of industrial effluent/sludge containing heavy metals onto the open land or into subsurface result in soil and water contamination. Detailed investigations are carried out to identify the source of contamination of heavy metals in an industrial suburb near Bangalore in India. Detailed investigation of ground water and subsurface soil analysis for various heavy metals has been carried out. Ground water samples were collected in the entire area through the cluster of borewells. Subsurface soil samples were collected from near borewells which were found to contain heavy metals. Water samples and soils samples (after acid digestion) were analysed as per APHO-standard method of analysis. While the results of Zn, Ni and Cd showed that they are within allowable limits in the soil, the ground water and soils in the site have concentration of Cr+6 far exceeding the allowable limits (up to 832 mg/kg). Considering the topography of the area, ground water movement and results of chromium concentration in the borewells and subsurface it was possible to identify the origin, zone of contamination and the migration path of Cr+6. The results indicated that the predominant mechanism of migration of Cr+6 is by diffusion.

Heavy metal pollution in sediments at shipbreaking area of Bangladesh

The research was carried out to assess the trace metal concentration in sediments of ship breaking area in Bangladesh. The study areas were separated into Ship breaking Zone and Reference Site for comparative analysis. Metals like Iron ( Fe) was found at 11932 to 41361.71µg.g-1 in the affected site and 3393.37 µg.g-1 in the control site. Manganese (Mn) varied from 2.32 to 8.25 µg.g-1 in the affected site where as it was recorded as 1.8 µg.g-1 in the control area. Chromium(Cr), Nickel (Ni), Zinc(Zn) and Lead (Pb) were also varied from 22.89 to 86.72 µg.g-1; 23.12 to 48.6;83.78 to 142.85 and 36.78 to 147.83 µg.g-1 respectively in the affected site whereas these were recorded as 19; 3.98; 22.22 and 8.82 µg.g-1 in the control site. Copper (Cu); Cadmium (Cd) and Mercury (Hg) concentration were varied from 21.05 to 39.85; 0.57 to 0.94 and 0.05 to 0.11 µg.g-1 in the affected site and 33.0; 0.115 and 0.01 µg.g-1 in the control site. It may conclude that heavy metal pollution in sediments at ship breaking area of Bangladesh is at alarming stage.