Critical evaluation of treatment strategies involving adsorption and chelation for wastewater containing copper, zinc and cyanide

Industrial wastewater containing heavy metals and cyanide requires treatment for removal of both metals and cyanide before disposal. Conventional methods for treatment of such wastewater involve alkaline-chlorination for cyanide destruction, followed by pH adjustment for metal precipitation, and subsequent removal of precipitate by solid-liquid separation processes. However, excessive sludge production, slow metal precipitation kinetics, and inefficient metal removal due to poor settling and aggregation of metal precipitates, are major drawbacks of the above process. This has rekindled interest in alternative metal removal strategies involving metal adsorption and metal chelation. The objective of the study described in this paper is to critically evaluate treatment strategies involving some indigenous adsorbents and a low-cost chelating agent for treatment of a simulated wastewater containing copper and zinc, complexed with cyanide. Treatment strategies involving three adsorbents, sulfonated coal, biosorbent G. lucidum, and iron oxide coated sand (IOCS), and a chelating agent, insoluble agro-based starch xanthate (IAX), were tested. The evaluation procedure involved comparison of the performance of these treatment strategies with that of conventional treatment. Results indicate that treatment using the chelating agent IAX has the greatest potential as an alternative to the conventional treatment technique. The three adsorbents tested, although reported to be very effective in removing copper and zinc from pure systems, exhibit diminished metal removal capacity in the presence of cyanide, and hence are unsuitable. (C) 2002 Elsevier Science Ltd. All rights reserved.