Predicting HCN gas generation in the SAR

The SART (Sulphidization, Acidification, Recycling and Thickening) process is a novel industrial technology used in gold mining to recover cyanide and copper from cyanide solutions. Since the operation of this process involves hydrogen cyanide (HCN) generation, the design of the process must provide full control on gaseous HCN evolution to ensure personnel safety. Even though gas extraction and scrubber systems play a fundamental role in the control and reduction of potentially dangerous HCN levels, currently there are no formal methods to estimate the HCN generation in the SART process in order to afford a robust design for the extraction and scrubber systems. The objective of the present work is to propose a general methodology to predict the generation of HCN gas in the SART process. For this purpose, a mathematical model was developed, supported by the phenomenology of the process and considering the system's operational conditions. This model considers the chemical equilibrium of HCN in solution, the liquid–gas phase equilibrium and the mass transfer phenomena between the liquid and gas phases. The results predicted by the model have indicated very low rates of HCN gas generation (1–12 mg/m2/h), showing HCN concentrations below 4 ppm at the inlet of the scrubbing system under typical operational conditions. In addition, it was found that the agreement of HCN gas is controlled by the liquid mass transfer resistance and, due to this reason, that the correct adjustment of operational parameters of the SART process can maximize the liquid mass transfer resistance, avoiding HCN volatilization.