Characterization of interaction of biosurfactant-producing bacteria with pyrite minerals as an alternative to depressant reagents in the bioflotation process of copper sulfide minerals that are more environmentally friendly

Abstract

Several studies have been conducted on the benefits of bacteria to replace chemical reagents in the bioflotation process of copper sulfide minerals. Most of the processing of copper sulfide minerals is carried out by flotation by adding reagents. Flotation is one of the mineral processing processes to separate valuable minerals and their impurities by utilizing different mineral surface properties. In copper sulfide minerals there is a high sulfur content of pyrite impurities (FeS2) which must be separated or depressed (become more hydrophilic) to be separated with valuable minerals, while valuable minerals will remain hydrophobic (water-repellent). However, not all bacteria can survive at high sulfur concentrations. In this research, the interaction of biosurfactant-producing bacteria that can survive in environments with high sulfur content (Citrobacter sp. strain SKC-4) with pyrite minerals was characterized. The bacteria-pyrite interaction was observed by analyzing the elemental composition of mineral surface and the morphological changes of the sample with SEM-EDS (scanning electron microscope - energy dispersive spectroscopy). SEM observation showed the interaction of bacteria with pyrite minerals where the bacteria were able to stick and make mineral particles into complex aggregates. Moreover, the EDS results revealed that the presence of bacteria resulted in the change in the elemental composition of the pyrite mineral, which was dominated by iron (Fe), sulfur (S) and a small amount of carbon (C) which was the main element for microbial activity. Sampling for functional group testing (FT-IR Spectroscopy) was carried out on days 0,7,14, and 30 when bacteria interacted with minerals, showing a peak of C=O carbonyl bonds and carboxylic acid formation on the 7th day. The contact angle value of the pyrite decreased after 7 days of interaction with the bacteria, thus resulting in more hydrophilic pyrite minerals. From the results of the interaction characterization, the bacterium Citrobacter sp. strain SKC-4 has the potential as an alternative to a depressant reagent for a more environmentally friendly copper sulfide mineral bioflotation process.