M. Zaki Mubarok

Effects of Several Parameters on Nickel Extraction from Laterite Ore by Direct Bioelaching Using Aspergillus niger and Acid Rock Drainage from Coal Mine as an Organic Substrate

Aspergillus niger is a prominent fungi that has been used for bioleaching of nickel laterite ore and commercial production of citric acid. Series of shake flask bioleaching assays have been conducted to study the effects of ore type, ore particle size distribution, solid percentage, and substrate volume percentages as well as sulphur addition on the nickel extraction from Indonesian laterite ore. Acid rock drainage (ARD) from local coal mine was used as a substrate for carbon and nutrient sources of the fungus. The results show that saprolite ore exhibits a better leaching with fungal metabolic acids than limonite. The highest nickel extraction of saprolite ore was 43%, which was obtained from the shake flask bioleaching assays with ore particle size distribution of -60+80 mesh, pulp density of 2.5%, and ARD substrate volume percentage of 10%, after 24 days of incubation. For both saprolite and limonite ore samples, coarse particle size ditribution of -60+80 mesh provides a better nickel extraction than the finer ore particle size. The addition of potato dextrose agar and fresh innoculum after 16 incubation days generated a re-increase of nickel extraction, indicating the refreshment of the active fungus. Based on the results, it was found that Aspergilus niger growth can take place with an organic substrate of liquid ARD obtained from coal mining area.

Effects of Individual Use, Mixed Culture and Sulfur Addition on the Effectiveness of Nickel Laterite Ore Bioelaching with Penicillium verruculosum and Galactomyces geotrichum

The type of fungi used in fungal bioleaching influence the effectiveness of metals extraction due to the dissimilarity of each microorganism survival in environments with certain metals content. Several metals have prominent toxicities to certain type of fungi, which result in low metals extraction and leaching rate. In the present work, the influences of individual use of Penicillium verruculosum and Galactomyces geotrichum on the nickel extraction from Indonesian laterite ore are compared with the fungis mixed culture. The effect of sulfur addition in the mixed culture of Penicillium verruculosum and Galactomyces geotrichum on the sulfate ion formation was also investigated. Shake flask bioleaching assays have been performed in a medium growth of Indonesian food production waste over the course of 28 days. It was observed that mixed culture of Penicillium verruculosum and Galactomyces geotrichum has a higher effect in nickel extraction compared with the use of individual fungi for both saprolite and limonite ores. For saprolite ore, the fungi species of Galactomyces geotrichum demonstrated a greater nickel extraction than Penicillium verruculosum. In contrast, the extraction of nickel from limonite ore by Penicillium verruculosum was slightly more effective than Galactomyces geotrichum. The addition of elemental sulfur in the mixed culture was found to generate sulfate anion, having a significant increase in its concentration with time and decreasing solution pH within 28-day of incubation. The proportion of sulfur addition must be optimized in order to avoid ore surface passivation with the excess of sulfur. XRD analysis detected the presence of un-oxidized sulfur on surface of the leaching residues along with the biomass.