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Removal of Toxic Heavy Metal Ions from Aqueous Solutions using Substrate Materials made from Low-Grade Natural Minerals

This work has been carried out in collaboration with Central Metallurgical Research and Development Institute, Cairo, Egypt under CSIR-ASRT, Egypt Scientific Collaborative Programme. The objective of the project was to explore the possibilities of using low-grade minerals for the removal of different toxic ions such as chromium, cadmium, arsenic etc. from the effluents of a zinc plant. Under the project low grade natural minerals namely low grade rock phosphate and pyrophyllite were studied as substrate materials for the removal of heavy metals ions namely lead, zinc and copper from synthetic solutions as well as from the real industrial effluents obtained from Hindustan Zinc Ltd. The substrate materials were evaluated in the form of powder as well as balls in two different compositions prepared from the substrate materials for carrying out effluent treatment studies in packed columns. The studies were carried out to optimize the required weight of the balls of the substrate materials and number of treatment cycles using a single charge for a fixed volume of the effluent for bring down its heavy metal ion concentration in the permissible limit. The results show that it is possible to bring down the concentration of heavy metal ions (such as lead) in the permissible limits (0.05 mg/l) from the initial level of 3.4 mg/l for 20 litres of the effluent by using 1.2 kg of the substrate material balls in 10 cycles.

 Development of Glazing Material Drum Filter Cake

The secondary zinc industry mainly utilizes zinc ash as raw material for producing zinc. After roasting, the raw material is leached out with sulphuric acid followed by treatment with activated MnO2 . The solution is taken for polishing followed by electrolysis while the pH of the residue slurry is adjusted and the solids are filtered using a drum filter. The solid residue, known as drum filter cake (DFC), contains silica, alumina, lead and zinc compounds. The presence of lead makes DFC hazardous. A grant-in-aid project from the Ministry of Environment and Forests (MOEF) was undertaken to utilize the DFC for making value added products. On consideration of intrinsic contents, frit compositions have been developed wherein the toxic species are complexed in a glass with toxicity level within permissible limits.

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