Copper removal from diluted cyanide wastewater by electrolysis

Abstract

Metal electroplating processes can use cyanide as reagent, generating large amounts of industrial wastewaters containing cyanide and heavy metals. These wastewaters are usually treated by chemical precipitation, generating toxic slugs consisting of metallic hydroxides and sulfides. This work aims at developing an electrolytic cell in order to recover the copper from diluted solutions simulating the wastewaters from the rinsing of copper electroplated disks, for coins manufactured in the Brazilian Mint, and, as a secondary target, to oxidize the free cyanide at the same time. The influence of some process variables was evaluated by thermodynamic and voltammetric studies. The solution flow rate and temperature increase favor copper deposition. It was also verified, by voltammetric and electrolytic tests, that the presence of copper oxide on the anode surface catalyses cyanide oxidation. The best results were obtained for a temperature of 50°C, a solution flow rate of 0.37 mL/s, and after a 3‐h electrolysis, when the copper and free cyanide concentrations were, respectively, 0.70 and 0.08 mg/L, for an electric current of 1.5 A, and, respectively, less than 0.50 and 0.08 mg/L, for an electric current of 2.0 A. © 2011 American Institute of Chemical Engineers Environ Prog, 32: 52–59, 2013.

Enhanced destruction of Cu(CN)32− by H2O2 under alkaline conditions in the presence of EDTA/pyrophosphate

“…In addition, H 2 O 2 deprotonated and existed as H 2 O À when the pH of solution was above 12.0 [29]. So the effect of pH on Cu(CN) 3 2À oxidation was investigated in the range of …”

“…No obvious change for the absorption peaks at the two wavelengths was observed before 30 min. It is indicated that Cu(CN) 3 2À was the dominant species in the solution before 30 min. Two new peaks at 223 nm and 234 nm were observed at 45 min instead of the absorption peaks at 238 nm, which was assigned to the absorption of Cu(CN) 2 -À [21,36].…”

“…, and Cu(CN) 2 À [3]. All forms of cyanide in wastewater must be adequately treated before being allowed to discharge due to its high toxicity.…”

“…In this experiment, we simulated the cyanides in the effluent. Both CN À and Cu(CN) 3 2À concentrations were about 1.0 mM. Cu(CN) 3 2À solution was prepared by addition of cuprous cyanide powder to sodium cyanide solutions at a CN À /Cu(I) molar ratio of 4.0:1.0 [27].…”

“…To analyze the pathway of cyanide oxidation with H 2 O 2 , intermediates of cyanide oxidation were identified in the course of Cu(CN) 3 2À oxidation. As shown in Fig.…”