Kinetic Study for the Extraction of Gold and Silver from an Ore Comparing Lixiviants Sodium Cyanide and DEZO using Moderate Pressures

Abstract

In recent decades cyanide is the most widely used for the extraction of gold and silver, for being economical and efficient, however, other alternatives have been considered because of its toxicity to the environment, for this reason in this work we study a new leaching agent that seeks to be a viable alternative to cyanide, which is commercially called DEZO and is considered ecological due to the low quantity of the main complexing agent which is cyanate, and other components such as sodium oxide, nitrogen, ammonium, calcium, iron, which is used for gold and silver extractions. For the development of the study a gold and silver ore provided by the mining company "Las Chispas", located in Arizpe, Sonora, Mexico, was used. The ore contains 15.50 g/T of Au and 1550 g/T of Ag. Leaching was carried out at moderate pressures using sodium cyanide and DEZO as lixiviants for Au and Ag extraction. XRD and SEM–EDS analyses confirm the presence of quartz, fluorite and argentite species. Pressure leaching was performed using NaCN, with conditions of T = 70 °C and P = 0.62 MPa, NaCN [300 mg/L], -270 mesh, 20% solids, time 1 h and 600 rpm, obtaining 98.3% extraction of Au and only 8.8% of Ag. Next, pressure leaching was performed using the DEZO eco-friendly lixiviant, with conditions of T = 70 °C and P = 0.62 MPa, NaCNO [300 mg/L], -270 mesh, 20% solids, time 1 h and 600 rpm, obtaining 93.9% Au extraction and only 7.7% Ag. Subsequently, the adjustment of the shrinking core model was performed by varying the temperature in the pressure leaching, the activation energy (Ea) using both leaching reagents (NaCN and DEZO) was less than 20 kJ/mol, which defines that the gold and silver leaching are controlled by diffusion through the product layer.