Irkutsk National Research Technical University, Irkutsk, Russia:

A. P. Mironov, Associate Professor at the Department of Mathematics, Institute of High Technologies
V. V. Elshin, Head of the Process Automation Department, Institute of High Technologies
А. Е. Ovsyukov, Senior Lecturer at the Process Automation Department, Institute of High Technologies, e-mail: a-ovsyukov@rambler.ru

At present, high-temperature desorption of gold from activated carbon with alkali solutions constitutes one of the basic processes in gold recovery through sorption. This paper considers the process of batchwise high-temperature desorption of gold from activated carbon with the aim of confirming the operating conditions (temperature, NaOH concentration, specific load) on the basis of a process model. The process model was developed earlier, and it accounts for the fact that this process involves multiple stages, and namely, formation of an intermediate compound of the type [AuCNOH]^– during the intermediate process stage and decomposition of the dicyanoaurate (I) anion [Au(CN)₂]^– to the forms that are not recoverable during desorption. Results of the experimental study and initial modelling were taken as the basis for selecting the initial range of operating conditions. The following ranges were used for modelling: 100–200 ^oC for temperature; 4–60 h^–1 for specific load; 0.2, 0.6, 1 % for NaOH concentration. The results of the modelling provided values of the effective mass transfer coefficient and Biot criterion for a variety of temperatures depending on the specific load. The authors also describe a response surface indicating how, with the NaOH concentration being constant, the process temperature and the specific load influence the recovery of gold and the formation of metal gold, which is not recoverable during desorption. Kinetic curves are presented that show how the gold recovery changes and what compounds gold forms in the carbon under various operating conditions. The authors confirmed that the following operating conditions: temperature — 175 ^oC, specific load — 12 h^–1, NaOH concentration — 0.2%, — are optimal for the process. They also show when the process can be most efficient with the simultaneously rising elution temperature and specific load. Rising alkali concentration and temperature and low specific load make the process shift toward the formation of metal gold, which is not recoverable during desorption.

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