Precious Metal Extraction from Liquid Photographic Wastes

Abstract

Waste generating from photographic industry contains metals, which basically need to recover due to either economic reasons or to treat and remove the toxic metals before it can discharge into environment. Extraction of precious metals such as silver from this waste is very attractive. However, selection of the right technique is crucial in order to obtain relatively pure products. Solvent extraction may offer some advantages over other techniques. In solvent extraction process, selection of the right extractant, which offers high selectivity and capacity is important especially when involves extraction of metal from mixed diluted metals solution like photographic wastes. Therefore, different types of extractants were examined in this study in term of their capability and selectivity in extracting metals from photographic waste. It was found that the Cyanex 302, dithizone and tetramethylthiuram disulfide are most promising extractants amongst others in extracting silver. It was found that also more than 90% of silver was extracted using only 0.05M extractant. This result shows that extractants containing sulfur donor atoms have high selectivity towards silver compared to other metals. Stripping of extracted metals from organic-loaded metals solution using various stripping agents such as nitric, hydrochloric and sulphuric acids shows that nitric acid gives a good capability to strip silver from metal loaded tetramethylthiuram disulfide and Cyanex 302. Metal loaded dithizone could not be stripped using these acids. Further study shows that the extent of extraction process depends on, not only on extractant concentration but also on the initial pH of the liquid photographic waste.