REDUCTIVE-OXIDATIVE PRETREATMENT OF A STIBNITE FLOTATION CONCENTRATE - THERMODYNAMIC AND KINETIC CONSIDERATIONS

The thermodynamics and kinetics of reductively decomposing stibnite (S b2S3), a refractory sulphide, using an acidified solution of chromium( II) ions in a chloride medium (for Au recovery) have been considered. Results show that well over 80% reduction of stibnite to antimony (Sb) and hydrogen sulphide (H2S) is achieved, the extent of reduction bein g pH and reductant concentration dependent. The contrasting temperatur e sensitivity above and below 90 degrees C (363K) suggests that two ra te controlling modes are operative: diffusion in the range 60-90 degre es C(333-363K) and chemical reaction above 90 degrees C. Although up t o 80% reduction of the sulphide host mineral (Sb2S3) occurred, very li ttle gold (<16%) was liberated. A sequential reductive-oxidative pretr eatment of the stibnite ore achieved 90% gold liberation. This strongl y suggests that in the stibnitic ores, the sulphide species are not wh olly responsible for the reported refractoriness. Gold may be in submi croscopic form as finely disseminated fine particles or in solid solut ion as aurostibnite (Au3S) which requires further oxidative treatment after the sulphide decomposition. (C) 1998 Published by Elsevier Scien ce Ltd. All rights reserved.