Organic Acid Biogeneration by <i>Aspergillus niger </i> and its Utilization for Indirect Bioleaching of Nickel Laterite Ore

Abstract

This paper discusses the results of indirect bioleaching test works of nickel laterite ore by the assistance of Aspergillus niger. Series of metabolic acid biogeneration shake-flask experiments were performed to investigate the effects of substrate type, nitrogen and phosphate dosages, the presence of magnesium and manganese salts, as well as aeration of the culture media on the effectiveness of the metabolic acid biogeneration. The investigation results showed that after 16 days of incubation, the solution pH of 1.44 was obtained from the acid biogeneration using cassava starch as carbon source in the presence of 0.1% (w/w) KH2PO4, 1% (w/w) (NH4)2SO4 and 0.25 g/L of MgSO4 under aerated condition. Leaching experiments of limonite and saprolite ore samples were carried out by using the generated metabolic acids at various ore particle size distributions, solid to liquid ratio and temperature. The highest nickel extraction percentage of 88.9% was obtained from the leaching of saprolite ore at 95°C, stirring speed of 400 rpm, particle size distribution of-80+100 mesh, solid to liquid ratio of 4.65 g/mL after 240 minutes, while that of 84.9% was obtained from the leaching of limonite ore at 95°C, stirring speed of 400 rpm, particle size distribution of-80 +100 mesh and solid-liquid ratio of 5.2 g/ml after 1440 minutes. The leaching of saprolite ore by using the biogenerated acids was selective to magnesium, with co-extracted Mg of only 1.5% after 24h of the agitation leaching test.