A rheological study of the bioleaching process of an iron ore for the elimination of gangue minerals

Abstract Bioleaching was used to dissolve zinc, phosphorus, potassium and calcium oxide found in iron concentrates using acidophilic microorganisms to enhance the iron yield. Rheological properties of the mineral pulps revealed a maximum in the zero shear-rate viscosity (0.068 Pa s) during day 5 of the process. The mineral concentrate contained hematite (Fe2O3) and magnetite (Fe3O4). Dissolution kinetics were followed in a continuous stirring tank reactor (CSTR) and pulp rheological properties were measured. Various analytical techniques were employed to evaluate the initial and final compositions of the mineral iron concentrates, such as scanning electron microscopy (SEM) and X-ray diffraction using the powder method (XRD). Data obtained from SAOS (small amplitude oscillatory shear) and simple shear were modeled using the multimodal Maxwell model and a kinetic rheological model (BMP), respectively. Up to 72% P, 91% CaO, 74% K and 53% Zn were dissolved in 5 days, where a maximum in both rheological analysis (continuous and oscillatory flow) was observed. This maximum coincided with the end of the microbial growth phase, demonstrating that the microbial growth kinetics influenced the rheological property, which can be modeled using a kinetic-like constitutive equation. The linear viscoelastic response of the pulp is consistent with the appearance of a weak gel at long times (low frequency) with relaxation exponent of n = 0.91 and gel strength of S = 0.0151 Pa sn. A generalized Maxwellian behavior with three relaxation times was observed at high frequency, associated with biofilm–particle interactions. Further investigations may consider other rheological analysis such as LAOS or stress relaxation.