Sodium Cyanide Generation by Coal Gasification

Abstract

The aim of this study was to evaluate the technological feasibility of producing sodium cyanide through coal gasification. Specifically, it examined the effects of key process parameters—temperature, experiment duration, and coal type—on the concentration of sodium cyanide in the resulting solutions, and aimed to identify the optimal operating conditions. Experiments were conducted using a laboratory-scale setup consisting of a tubular cylindrical furnace with a corundum tube as the working compartment. Lignite and charcoal, pre-crushed to increase their specific surface area, were used as feedstocks.

Sodium cyanide was produced by sorbing gaseous hydrogen cyanide (a component of the syngas) into a sodium carbonate solution. An NaOH solution (pH = 10), maintained in an ice bath, was used in the absorber system to stabilize the cyanide. The concentration of sodium cyanide in the final solution was determined using a titrimetric method. The thermodynamic modeling was performed using the HSC Chemistry 5.1 software package. When charcoal was gasified at temperatures between 600 °C and 800 °C, sodium cyanide concentrations in the range of 0.03–0.08 wt.% were obtained. However, increasing the temperature from 600 °C to 900 °C resulted in a fourfold decrease in sodium cyanide concentration under otherwise constant conditions. A regression equation was derived to express the dependence of sodium cyanide concentration on gasification temperature and reaction duration.

The findings demonstrate that sodium cyanide generation via coal gasification under laboratory conditions can yield solution concentrations comparable to those employed in gold cyanidation at industrial gold recovery plants. Establishing on-site sodium cyanide generation at gold processing facilities could significantly reduce production costs by eliminating the need for purchasing, transporting, and storing commercial cyanide reagents.