Recent trends in the treatment of cyanide-containing effluents: Comparison of different approaches

The cyanide-containing effluents originate from, e.g., mining, coking, electroplating and chemical syntheses. The form and concentration of cyanide, and the effluent matrix depend on the effluent source. Electroplating effluents contain extreme amounts of free cyanide (fCN), e.g., >50 g/L, along with metal cyanide complexes. “Raw coking effluents”, i.e. coke oven effluents after tar and ammonia separation, contain up to over 100 mg total cyanide (TCN)/L, a significant part of which is fCN. They are also contaminated with phenols, other organic compounds, and inorganic salts. They are generated in extreme quantities such as 120–150 m3/h in a plant with annual coke production of 4.2 Mt. Adequate remediation of these effluents is a challenging task, and requires specific methods for each effluent. Conventional physicochemical, chemical, and biological solutions are usually far from optimal in terms of effectiveness, environmental impact or cost. This has led to intensive research in the field of elimination of cyanide from wastewaters. This work will provide a review of recent advances in this research area. In contrast to most previous reviews, this work offers a general overview of innovative methods of different types (oxidation, flocculation, adsorption, electro(dia)lysis, photocatalysis, bioassimilation, biocatalysis). The processes are characterized in terms of their suitability for different effluents, as well as their efficiency, scalability, and cost, where data are available. The study attempts to highlight the most promising solutions. These are likely to include principally the combinations of different (physico)chemical and biological approaches able to eliminate various forms of cyanide along with other contaminants.