Determination of free cyanide in mineral leachates

Abstract

Cyanide leaching is a common process by which metals, e.g., silver and gold, can be extracted from ores and related materials. This paper describes an automatic flow injection system for the determination of free cyanide in samples from leaching processes.

The sample is injected into a carrier stream, which is merged with a flowing reagent stream. The reagent stream contains sodium hydroxide together with a trace of cyanide and these optimise the solution composition for detection by a cyanide ion-selective electrode. A working range of 10–1 000 p.p.m. is covered with a sample rate of 120 h^–1. Sample recoveries compared excellently with a titrimetric procedure and a short-term repeatability study on a sample gave a mean value of 306.5 ± 7.4 p.p.m. at the 95% confidence level. The method selectivity, with particular reference to metal-cyanide complexes, is also discussed. The technique is applicable to process control as well as process development.