Mineral Processing EFFECT OF LEAD NITRATE ON CYANIDATION OF ANTIMONIAL REFRACTORY GOLD AND SILVER ORES MSc.Oktay CELEP Assoc. Prof. Dr. brahim ALP Assoc. Prof. Dr. Hacı DEVEC Department of Mining Engineering, Karadeniz Technical University, Turkey ABSTRACT This paper deals with the effect of the addition of lead nitrate and ultra-fine grinding on the cyanidation of an antimonial refractory gold and silver ore. The results indicated that the recovery of gold was enhanced by 10%, but, silver extraction did not improve with adding lead nitrate or increasing its concentration. Fine grinding (e.g. down to-5μm) did not produce the desired effect on the extraction of Au and Ag. Keywords: gold; silver; refractory ores; antimony minerals; lead nitrate; cyanidation INTRODUCTION The refractoriness of gold ores is linked with their inherent mineralogical features [1, 2] Low gold or silver recoveries in cyanidation are sometimes caused by the sulphide minerals in ores [3]. Lead nitrate is often added to alleviate the negative effect of sulphides present, enhance gold recovery and lower cyanide consumption, although it could be also detrimental to the process at excessively high levels [4]. It was suggested [5] that in a cyanide solution, lead reacts with gold to form AuPb 2 , AuPb 3 and metallic lead and accelerates the gold dissolution [6]. However, it is claimed that, if formed, lead hydroxide film decreases gold extraction rate. The Akoluk ore (Ordu / Turkey) having a complex mineralogical composition is an antimonial sulphide ore. The ore consists of predominantly quartz, illite/kaolinite group clay (52.2% SiO 2 ) and barite (17.1% Ba), and to a less extent, sulphide minerals such as pyrite, sphalerite, zinkenite and stibnite. Pyrite, andorite and zinkenite are the main gold and silver-bearing components in the ore. Gold particles containing silver also occur as associated with framboidal pyrite and as inclusions within Sb-S and (-Pb) minerals. Celep et al., [7] suggested that the refractoriness was induced by the dissemination and encapsulation of the very fine gold and silver particles largely within the carbonates, oxides and sulphides and, to a small extent, within silicates present in the ore matrix. Earlier studies on the ore showed that the extraction of gold and silver was severely limited (50% Au and 19 Ag) [8]. Antimony minerals do not form stable complexes with cyanide and consequently the presence of cyanide in solution does not appreciably affect the stability of the metal species formed. Under the conditions applied for gold leaching, antimony sulphide minerals decompose to Sb 2 O 2 - and Sb 2 O 3 - (stibnite and stibnate). Dissolution of these minerals has a detrimental effect on gold and silver extraction. This effect is thought to 639 B21