Efficient recovery of precious metals from process solutions is essential for improving process economics

Efficient recovery of precious metals from process solutions is essential for improving process economics. Traditionally, precious metals are relatively effectively recovered from waste streams via precipitation or cementation. However, these approaches have a number of drawbacks, including poor water balance, creation of environmentally unfriendly waste streams, and losses of precious metals. Ion exchange technology is an alternative for the recovery of precious metals from waste or low-grade streams. This technology allows the recovery of the precious metals to extremely low levels (micrograms per litre) with relatively high upgrade ratios from the solution onto the resin without major water balance concerns, while the impact on the environment could be minimized or avoided (Korkisch, 1988). Research was conducted on the recovery of platinum group metals and gold from different low-grade and waste streams from one of the pharmaceutical firm in South Africa by means of ion exchange. Various functionalities and matrices (granular and fibrous) of ion exchange materials were evaluated. The results from these studies indicated that in some cases ion exchange could be very effective for the recovery of precious metals, and that the PGM concentration could be reduced to < 1 mg/L. The upgrading ratios of the various PGMs onto the specific fibres were relatively high for the specific streams evaluated, which might in some cases justify incineration of the loaded material instead of stripping and recycling the adsorbent. The cost of direct incineration for one of the waste streams tested would be less than 1% of the

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value of the PGMs recovered. However, the adsorbent has to be carefully selected and the process design optimized for each specific stream.
3.1.2 Introduction Waste streams generated during the manufacture of different pharmaceutical components/drugs may contain significant amounts of platinum group metals (PGMs) and gold (Au). Currently, industries are using mainly precipitation and cementation techniques for the recovery of valuable metals from low-grade and waste streams. However, there are major drawbacks in using these technologies, including incomplete recovery of valuable metals and generation of waste streams that carry significantly more contaminants than the original waste streams. There is therefore a need to use alternative technology to precipitation/cementation, which would allow the costeffective and efficient recovery of precious metals, with low or minimal additional environmental implications. Ion exchange and/or adsorption technology can resolve difficulties associated with the recovery of precious metals from low-grade and waste streams by minimizing waste generation and improving the overall economics of the process. Smopex® and SuperLig® materials are widely known as an option for recovery of valuable metals in the precious metals industry. However, the cost of these materials (typically much greater than US$200 per kilogram) often prevents industry from considering them for waste treatment. Over the past few years extensive research has been performed on the application of conventional ion exchange (IX) materials for the recovery of PGMs and Au from various low-grade streams. A number of South African companies provided some of their low-grade streams, which are currently treated via precipitation or cementation for PGM recovery. The current paper reports on a few successful examples of the potential of ion exchange technology for the treatment of such streams. Ion exchange can be designed to result in highly efficient recovery of PGMs and Au, often without the addition of further contaminants. The test work programme for the evaluation of the various ion exchange materials for the recovery of precious metals from various streams was as follows:
? Selection of the most promising functional groups commercially available on ion exchange materials
? Evaluation of granular and fibrous ion exchangers
? Comparison of equilibria and fixed bed breakthrough profiles.

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Detailed results and information on the streams and materials that where tested are not provided in this paper due to confidentiality. Nevertheless, the major benefits of conventional ion exchange for the treatment of some low-grade/waste streams containing precious metals are highlighted.