Abstract

ASCUNA R., Víctor B. et al. Treatment of cyanide solutions and precipitation of cyanicide metals by reaction with hydrogen peroxide and caustic soda, the perso method; obtaining economically useful sludge. Rev. Bol. Quim [online]. 2018, vol.35, n.5, pp.155-161. ISSN 0250-5460.

Abstract Combination of hydrogen peroxide and caustic soda in solution, denominated by the authors "Perso method", results in the formation of a strong oxidant, which is effective in the detoxification of total cyanide and precipitation of complex metals that are found in solutions. The present work shows the technical feasibility of reusing water from the gold tailings instead of fresh water (as in agriculture or in the mining process) avoiding the saturation of cyanicide metais in the operation circuit. After a chemical treatment at an optimum pH, follows the obtaining of a solution with a lesser amount of cyanicide metals, impacting favorably in the production of better quality doré bars. The hexagonal experimental design was applied which involves a series of tests of different molar ratios of hydrogen peroxide and caustic soda, time (min) vs concentration of total cyanide, and concentration of copper and silver. The process was fast and efficient. With an initial concentration of 200 mg/l of free cyanide, 2.2 mg/L of silver, 200 mg/1 of copper and a molar ratio of (H₂O₂ NaOH)/(CN^-) = 8, it was possible to achieve a final concentration of 1.5 ppm of cyanide, 1 ppm Ag, 5 ppm Cu. In contrast, a molar ratio of (H₂O₂ NaOH)/(CN^-) = 12, afforded a final concentration of 0.8 ppm of cyanide, 0.8 ppm Ag and 2 ppm Cu, in the same time of reaction (45 min). The precipitate of metals such as silver and copper characterized as economically usable sludge, has an economic interest in the market.

Keywords : Total cyanide; Free cyanide; Cyanide oxidation.

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