Shahrood University of Technology Journal of Mining and Environment 2251-8592 Articles in Press 2026 07 04 Eco friendly bio depression of pyrite using halophilic Bacillus mojavensis during chalcopyrite flotation in seawater 3837 10.22044/jme.2026.17655.3510 EN Sasan Mirshekari Department of Mining Engineering, Amirkabir University of Technology (Tehran Polytechnic), Iran Mehdi Iranajad Department of Mining Engineering, Amirkabir University of Technology (Tehran Polytechnic), Iran Hossein Kamran Haghighi Department of Mining Engineering, Amirkabir University of Technology (Tehran Polytechnic), Iran Journal Article 2026 04 29 In recent years, the use of microorganisms in the flotation of sulfide minerals has gained significant attention, particularly in processes requiring reduced chemical consumption and the utilization of saline water. The targeted application of microorganisms can improve flotation process conditions. Halophilic bacteria, as salt tolerant species, can be beneficial in selectively depressing pyrite during flotation. This study aimed to investigate the effect of the halophilic bacterium Bacillus mojavensis on enhancing the separation of chalcopyrite from pyrite in froth flotation using seawater. Experiments were conducted at five pH levels, and changes in recovery, flotation kinetics, and contact angle were evaluated. The results showed that the presence of the bacterium improved process selectivity and enhanced chalcopyrite flotation behavior at pH values between 6 and 10, while bacterial performance decreased at pH 4 and pH 12. The maximum recovery improvement was observed at pH 8, where chalcopyrite recovery increased from 55.11% to 62.04%, and the kinetic constant K was higher than that of the bacteria free sample. Contact angle measurements indicated that the bacterium significantly reduced pyrite hydrophobicity (from 73.73° to 46.7°) without causing noticeable changes in chalcopyrite (~75.8°); this behavior was attributed to the selective adsorption of EPS and bacterial cells on the pyrite surface, leading to its surface deactivation. The findings suggest that Bacillus mojavensis, due to its salt tolerance and stability in neutral to alkaline pH ranges, is a suitable candidate for use in seawater-based flotation circuits and low chemical consumption processes involving pH regulators.