Effect of sodium carbonate on alkaline self-leaching of gold from flotation gold ore

Abstract

Oxygen pressure alkaline self-leaching of gold is an environmentally friendly and smokeless leaching process. But the insoluble iron oxide generated will precipitate on the surface of parent minerals, thus reducing the oxidation reaction and gold leaching efficiency. Simultaneously, due to the different pH requirements of pyrite oxidation and gold leaching, the pH must be strictly controlled to achieve the maximum efficiency. In this work, dissolution effect and buffering effect of sodium carbonate in the gold self-leaching process were carried out. As the addition of sodium carbonate, soluble iron-carbonate complexes would be formed to remove passivation layer and expose fresh surface of pyrite, resulting in improvement pyrite oxidation rate. Meanwhile, the buffering capacity of sodium carbonate can avoid the thiosulfate decomposition and improve the concentration of thiosulfate. The maximum gold extraction efficiency of gold-bearing flotation concentrate could achieve 91.56% under the following condition: a concentration of sodium hydroxide, sodium carbonate and sodium carboxymethyl cellulose at 0.6 M, 0.3 M and 100 mg/dm3, respectively; stirring speed at 800 rpm; temperature at 308.15 K; oxygen pressure at 0.5 Mpa; leaching time of 18 h and a liquid-solid ratio of 5:1.