Spinel's Active Carbon Composites for Cyanide Ion Oxidation Catalysis in the Mining Industry

摘要

Cyanide salts have been employed for precious metals recovery, despite their toxicity. Various methods have been used for cyanide ion transformation into non-toxic substances like cyanate. For that reason, Co-Fe and Cu-Fe spinels-active carbon composites have been synthesized as efficient materials for wastewater treatment in the mining industry using the impregnation method. For spinels-active carbon composites preparation, active carbon microporous with 1000 m2/g was employed. Co-Fe spinel's-active carbon composites were prepared by mixing a 0.3 M solution of cobalt nitrate hexahydrated with a solution of iron nitrate nonahydrated 0.3 M in a molar ratio Fe/Co = 2 in the presence of active carbon. In the case of Cu-Fe spinels-active carbon composites, a 0.3 M solution of copper nitrate trihydrated with iron nitrate nonahydrated in a molar ratio of Fe/Cu = 2 were mixed with the same active carbon described above. In both cases, the mixtures were agitated for 2 hours and spinels precipitation was accomplished through pH regulation at a value of 12 with a 0.3 M solution of NaOH. The synthetized composites were calcined at 750 °C for 4 hours and treated with a 2 % v/v sulfuric acid solution in order to leach copper and cobalt oxides present on carbons surface. The obtained samples were characterized by X-ray diffraction (DRX), atomic absorption spectrophotometry and scanning electronic microscopy (SEM-EDS) analysis. In order to assess catalytic behavior of both composites, oxidation tests were performed. In all essays an air flow of 180 NL/h was introduced in a 500 mL reactor which contained a synthetic sodium cyanide solution of 500 mg/L with a pH of 10.5. Both spinel-active carbon composites showed 80 % of cyanide ion oxidation in 4 hours with minimal copper and cobalt dissolution. Both composites probed to be promising heterogeneous catalysts for cyanide oxidation in wastewater treatment.