Electrochemical treatment of copper cyanide wastewaters using stainless steel electrodes

Abstract

A study was carried out to define the best conditions for the simultaneous electroxidation of cyanides and recovery of copper as a metallic deposition on the cathode from weak concentration rinse wastewaters, using plate stainless steel electrodes. A direct electroxidation process and an indirect electroxidation in a chloriderich medium were tested at pH from 10 to 13. The results show that the process of the direct electroxidation is feasible and economically convenient if conducted at pH 13. It was possible to reduce copper concentration from 470 mg−1 by 79% in 1.5 h, at an energy consumption of 17 kWh kg−1 and to recover 335.3 mg of Cu as pure metal, electrodeposited on the cathode. The CuO film formed simultaneously on the anode had catalytic properties for CN− electroidation. The efficiency of the destruction of cyanides was in the same order of magnitude, with kinetics being of first order with respect to cyanide concentration (first order reaction rate k = 0.007 min−1).

The electrochemical oxidation of alkaline copper cyanide solutions

“…In a separate experiment, the black film was scraped off and analyzed by XPS. The result matched CuO as reported in the XPS handbook and is consistent with the literature [8,15]. Though it should be mentioned that in recent work by Casella and Gatta [24], they were able to quickly transfer the film into an XPS and detected Cu(OH) 2 as well as CuO at the film surface.…”

“…In other papers, where a high copper and hydroxide concentrations were studied, a black deposit, identified as copper oxide (CuO), was formed at the anode [8,9,15] (with some copper hydroxide also associated with the film) [24]. This deposit was found to act as a heterogeneous catalyst for cyanide oxidation [8] and the oxidation of a range of organic compounds [24].I t was hypothesized [8,14] that a surface copper(III) intermediate was involved.…”

Electrochemical studies of gold ore processing wastewater containing cyanide, copper, and sulfur compounds

“…Electrochemical methods for treating copper cyanide solutions have been investigated by numerous researchers [9][10][11][12][13][14][15][16][17][18][19][20]. In electrochemical methods, while cyanide is oxidized to cyanate at the anode, copper is recovered at the cathode avoiding copper precipitation.…”

“…At higher overpotentials with sufficient hydroxide [20], an autocatalytic reaction that results in the formation of a black deposit, identified as copper(II) oxide (CuO), occurs at the anode [9,12,18] (with some copper hydroxide also associated with the film) [24]. This deposit acts as a heterogeneous catalyst for the oxidation of cyanide [9] and for a range of organic compounds [24].…”

Characterization of the catalytic films formed on stainless steel anodes employed for the electrochemical treatment of cuprocyanide wastewaters

“…The elevated cost of these materials has imposed a new trend in the investigation directed to testing alternate materials for electrodes fabrication. In this respect, interesting results have been obtained at our laboratories in lab-scale batch electrochemical reactors equipped with stainless steel electrodes [20][21][22][23] under controlled operation conditions which allow for the deposition on the anode of films which exhibit electrocatalytic properties. In this way, comparison of the efficiency of a reactor equipped with either a Ti/Pt or a plated stainless steel anode operating at an alkaline pH of 13 [19], proved the performance of the former to be only slightly better than the performance with the modified SS anode.…”