Mechanism for the Bio-Oxidation and Decomposition of Pentlandite: Implication for Nickel Bioleaching at Elevated pH

Green extraction of nickel and valuable metals from pyrrhotite samples with different crystallographic structures through acidophilic bioleaching

Nowadays, due to the strategic status of nickel in the global market, utilizing its disregarded resources like low-grade nickel containing pyrrhotite is of significant importance. A comprehensive set of experiments and analyses were performed to determine the bioleaching capability and mechanism for nickel extraction from hexagonal and monoclinic pyrrhotite. Over 95% Ni extraction was achieved from the hexagonal pyrrhotite sample. Ni extraction from the monoclinic sample reached its maximum value of 67% and 90% at 3% pulp density, with mixed mesophilic and moderately thermophilic cultures, respectively. Characterization analyses indicated that jarosite and elemental sulfur formation in mixed mesophilic bioleaching reduced the samples' bio-oxidation rate and metal dissolution. The kinetics study revealed that the controlling step in thermophilic bioleaching is the chemical reaction; however, the mixed control model was best fitted on mesophilic data. Electrochemistry studies confirmed bioleaching results and indicated that monoclinic pyrrhotite's oxidation rate under the operating conditions is faster than hexagonal pyrrhotite, and the temperature positively correlates with the oxidation rate. Toxicity assessment analysis showed that the final residues of both bioleached samples could be considered environmentally safe.

Influence of organic acids on pentlandite bioleaching by Acidithiobacillus ferrooxidans LR

Bioleaching is a bio-hydrometallurgical process of solubilizing metals from low-grade sulfide ores by microbial action employing chemolithoautotrophic microorganisms capable of promoting redox reactions. Organic acids have been applied in bioleaching once can act in two different ways; providing hydrogen ions for mineral acidolysis and complexing metals due to their chelating capacity. This study investigates the synergy of different organic acids (acetic, ascorbic, citric, lactic, and oxalic) and Acidithiobacillus ferrooxidans LR pentlandite bioleaching. The addition of oxalic acid had a positive effect on the Ni extraction during pentlandite biological-chemical leaching after 15 days, and the yields observed were 45.6% (26.5 mg Ni/g ore). The yields for Co extraction were meager, and Co extraction values were found to only 2.8% (1.6 mg Co/g ore) in the presence of citric acid. A design of experiments with mixtures was used to evaluate the interaction of organic acids in bioleaching. According to simplex-centroid experiments, only citric acid presented a statistically significant effect and has contributed in a synergistic form in pentlandite biological-chemical leaching in the presence of A. ferrooxidans. This study provides a new synergistic bioleaching system to improve Ni and Co extraction from sulfide ores.

Editorial on Special Issue “Surface Chemistry in Mineral Processing and Extractive Metallurgy”

“Mineral Processing” and “Extractive Metallurgy” are the key operations for the entire mining, metallurgy, and chemical industries [...]