Distinct mechanisms of stibnite (SbS) oxidative dissolution mediated by acid-generating and alkali-generating microorganisms within a wide pH range.

Indigenous microorganisms in antimony mining areas facilitate stibnite dissolution over a wide pH range, yet their mechanisms remain poorly studied. Herein, the acid-generating Bosea sp. AS-1 and the alkali-generating Pseudomonas sp. PS-3 were selected to interact with stibnite (SbS) under initial acidic (pH value = 5) and alkaline (pH value = 8) conditions, respectively. Results indicated that AS-1 and PS-3 promoted stibnite dissolution compared to the sterile control irrespective of initial pH conditions, but through distinct mechanisms. AS-1 oxidized sulfide to sulfate by regulating the expression of SoxB and SoxC genes, thereby driving the stibnite dissolution and oxidation. Up to 18.63 mg/L total antimony (Sb(tot)) was released and the dissolved Sb(III) was completely oxidized to Sb(V). Moreover, AS-1 prevented the passivation layer formation by inhibiting sulfur oxidation intermediates accumulation. Conversely, PS-3 could not oxidize sulfur, but produced more extracellular polymeric substances which bound microorganisms closely to stibnite. The stibnite dissolution was facilitated through pH elevation from 5.0 to above 9.0 mediated by PS-3, releasing up to 35.56 mg/L Sb(tot). However, the accumulated sulfur oxidation intermediates facilitated the passivation layer formation, inhibiting further dissolution of stibnite. Additionally, less than 44 % of the soluble Sb(III) was oxidized to Sb(V). These results contribute to understanding the microbial-mediated transformation, mobilization and oxidation of antimony.