Effect of temperature on column bioleaching of a refractory gold ore

Low-grade, finely disseminated refractory sulfide gold ores associated with high arsenic are ubiquitous resources all over the world. Since heap bio-oxidation is an economic and promising biotechnology to recover gold, low grade, high organic carbon and arsenic bearing gold ores from Zhesang Mines in China were chosen for this purpose to study the key factors that would affect biooxidation. Pyrite and arsenopyrite (particle size 0.002-0.22 mm) were the main minerals from Mineral Liberation Analysis (MLA). Column biooxidation and cyanidation of mineral size < 10 mm were evaluated for its potential for gold extraction. Results showed that temperature was the main factor influencing sulfide oxidation. 58-67 % of sulfide was oxidized at 35-45 degrees C after > 240 days of biooxidation with mixed mesophiles, while higher sulfide-S dissolution (77%) was obtained at 60 degrees C. Sulfide-S fraction distribution revealed higher mineral decomposition, finer fractions and eventually higher sulfide oxidation at 60 degrees C. Jarosite and scorodite were found from the residues at 60 degrees C by SEM and EDX, which implies higher temperature accelerated arsenic precipitation. No elemental sulfur was detected during the biooxidation at 35-60 degrees C. After bio-oxidation, column cyanidation was successfully demonstrated recovery of gold from the residues, with gold extraction rate reaching 66%.