Influence of microbial activity on the physical properties and strength of ilmenite and magnetite ores

Abstract

The influence of microorganisms on the physical properties and strength of ilmenite and magnetite ores was determined in culture studies and laboratory tests of rock parameters such as absorption, porosity, elastic wave velocity, and uniaxial compressive strength. Initial pH condition was determined in the culture experiments, and then abiotic and biotic oxidation tests were performed to determine variations in pH, physical properties, and the strengths of the two ferruginous ore rocks. For ilmenite and magnetite ores, average initial values were, respectively, 0.185% and 0.496% for porosity, 0.046% and 0.123% for absorption, 1919 m/s and 1467 m/s for elastic wave velocity, and 432 MPa and 168 MPa for uniaxial compressive strength. The pH of ilmenite ore at the end of the abiotic and biotic oxidation tests was in the range of 3.82–4.26 and 2.20–2.57, respectively, while that of magnetite ore was 4.02–5.16 and 1.50–1.90, respectively. In magnetite ore, the changes in porosity and absorption due to the biotic oxidation test were larger than those observed in the abiotic oxidation test, while the variations in ilmenite ore due to both tests (abiotic and biotic oxidation) were small. The differences in porosity and absorption between the abiotic and biotic oxidation tests were larger in magnetite ore than in ilmenite ore, while the elastic wave velocity was smaller in magnetite ore than in ilmenite ore. In addition, the variations in uniaxial compressive strength due to the abiotic oxidation test were not significantly different than initial values in both ilmenite and magnetite ores, while variations caused by the biotic oxidation test were relatively large in both ferruginous ore rocks. Our results suggest that variations in the physical properties and strength of ilmenite and magnetite ores are largely dependent on microbial activity.