Gold recovery from copper-gold tailings by ammoniacal thiosulphate leaching

Abstract

Ammoniacal thiosulphate leaching is a safer method to apply for gold leaching because it does not involve the use of cyanide. It has been found to be a better method than other leaching methods. It is non-toxic and environment-friendly for gold extraction. In this study, the method was developed especially for gold leaching from copper-gold tailings samples. Various factors such as copper(II) sulphate concentration, ammonium thiosulphate concentration, pH, solid-liquid ratio, temperature and rotation speed were studied to determine optimum conditions for leaching. It was found that the most suitable condition were 0.07 M copper(II) sulphate, 0.5 M ammonium thiosulphate, pH = 10, solid-liquid ratio = 1:10, room temperature (30 ºC), rotation speed = 400 rpm and 5 h leaching time. Flame atomic absorption spectrometry was used to analyse the concentration of gold after the leaching process was performed. The performance of ammoniacal thiosulphate leaching method was evaluated by standard material No. ST 279. It was found that the precision of ammoniacal thiosulphate leaching method considered from relative standard deviation value was 2.28%. The accuracy which was considered from the recovery value was 97.63%. The detection limit of gold by flame atomic absorption spectrometry was 0.006 mg/l. The ammoniacal thiosulphate leaching method with optimum condition was applied for gold extraction from copper-gold tailings from northeastern part of Thailand. The results indicated that gold concentration from the ammoniacal thiosulphate leaching method was in the range of 65.52-89.50 g/t. Recovery by the ammoniacal thiosulphate leaching method was greater than 90% as was confirmed by the fire assay standard method.