M. Gattrell

The electrochemical oxidation of alkaline copper cyanide solutions

Abstract A systematic investigation of the electrochemical oxidation of copper cyanide was carried out. At low pH, cyanide destruction is believed to be catalyzed by the heterogeneous reaction involving adsorbed [Cu(CN)3]2− and possibly [Cu(CN)4]3−. At high pH, rapid oxidation of cyanide was observed around 0.75 V versus Hg/HgO with the formation of a black copper oxide film. This enhanced electrocatalytic activity is believed to be related to the formation of an active copper(III) species. The transition point between low and high pH as a function of cyanide and copper concentrations is discussed. Bulk electrolysis of a copper cyanide solution at 0.90 V oxidized most of the cyanide to cyanate. Prolonged electrolysis further oxidized the cyanate to nitrate. The copper oxide film is found to be catalytic, capable of electro-oxidizing hydroxide to oxygen and cyanate to nitrate.

Cyanide ion-selective electrode measurements in the presence of copper

The response of a cyanide ion-selective electrode (ISE) in the presence of copper has been investigated. The interferences of metal ions, like copper, on the response of the cyanide ISE prevents its use for routine direct analysis of metal cyanide containing waste water. In this work an improved understanding of the chemistry at the electrode, and the effects of different cyanide and copper concentrations and matrix pH values on the electrode response, has been developed. Based on this insight, a semi-empirical approach is described to allow calibration of the ISE enabling the estimation of total cyanide. While not as robust as, for example, total cyanide distillation, it provides an inexpensive, rapid and convenient approach for more frequent and widespread screening of industrial waste waters.

An electrochemical approach to total organic carbon control in printed circuit board copper sulfate plating baths Part I: Anode performances

An electrochemical approach to decreasing high levels of total organic carbon (TOC) in printed circuit board (PCB) copper sulfate plating baths has been investigated. The organic contaminants build-up over the course of pattern plating of PCBs, and at high concentrations they interfere with the quality of the plated copper. The electrochemical approach involves destroying the organic contaminants using electrochemical oxidation. Various anode materials (glassy carbon, lead, lead dioxide, platinum, iridium dioxide and doped tin dioxide) were screened for this application. Some corrosion data is presented for these anodes and their performance for TOC removal at various current densities has been roughly quantified using an apparent first order rate constant. The three best performing anode materials gave increasing oxidation rates going from platinum to doped tin dioxide to lead dioxide, unfortunately anode stability decreased in the same order.

An electrochemical approach to total organic carbon control in printed circuit board copper sulfate plating baths Part II: Overall system

An electrochemical system for oxidative removal of high levels of total organic carbon (TOC) in printed circuit board (PCB) copper sulfate plating baths has been developed. These organic contaminants build-up over the course of pattern plating of PCBs, and at high concentrations they interfere with the quality of the plated copper. The chemistry of the electrochemical oxidation of the plating bath contaminants was qualitatively followed using high performance liquid chromatography (HPLC) and chemical oxygen demand (COD) measurements. A complete treatment system is described and rough calculations are given showing, for a given set of conditions, how the proper choice of electrode material and current density can minimize the system cost.