The effect of temperature on the desorption of gold cyanide from activated carbon

Abstract

Activated carbon is used worldwide for the extraction of gold cyanide from leached pulps. The elution of gold cyanide is usually conducted by soaking the loaded carbon in an alkaline solution of cyanide in a column, followed by a rinse with water at temperatures higher than 100° C. Because the effects of temperature, cyanide addition and ionic strength are confounded to an extent, little has been published with which to model the dynamic behaviour of this complex process. An attempt is made in this paper to isolate and quantify the effect of temperature on the desorption of gold from activated carbon. A mathematical model for the desorption process is presented in a summarized form, and is shown to predict experimental data satisfactorily. An increase in temperature results in a decrease in the adsorption and in an increase in the decomposition of cyanide. An activation energy of 87.1kJ mol −1 was determined for the decomposition of cyanide, which occurs mainly by hydrolysis at elevated temperatures. The isosteric heat of adsorption of gold cyanide decreased from 18.2 to 8.8kJmol −1 when a pre-treatment of cyanide was used prior to desorption. Therefore, the gold equilibrium becomes less sensitive to temperature after pre-treatment with cyanide. The desorption of gold cyanide seems to be more sensitive to the cation concentration at high temperatures. An increased temperature increases the maximum of the elution profile, and therefore enhances significantly the dynamics of desorption.