Toward Sustainable Solution for Biooxidation of Waste and Refractory Materials Using Neutrophilic and Alkaliphilic Microorganisms—A Review

Abstract

The significant increase in economic concern and environmental restrictions has resulted in increasing interest in biotechnological solutions. The application of acidophilic, sulfur-oxidizing microorganisms in biomining and in the treatment of waste matrices has been extensively explored. However, to surmount the current challenges encountered by the industrial use of acidophiles, there is an opportunity for neutrophilic and alkaliphilic microorganisms to be comprehensively considered for the biooxidation of refractory sulfide materials. This review, for the first time, provides a detailed study of neutrophiles and alkaliphiles that have potential for oxidizing sulfur-containing wastes and sulfide refractory ores to recover entrapped metals especially gold in a sustainable manner. The study illustrates the applicability of neutrophilic and alkaliphilic microorganisms to provide better and sustainable alternatives for the recovery of metals from wastes from various sources as well as refractory materials. The microorganisms summarized in this review have been successfully used in oxidizing different sulfide sources by achieving high oxidizing efficiencies (>80%) in numerous technologies. The fundamentals of biooxidation along with possible mechanisms involved in the biooxidation have been discussed in detail.

A developing novel alternative bio-oxidation approach to treat low-grade refractory sulfide ores at circumneutral pH

“…The more significant growth using 10 g/L sodium thiosulfate could be attributed to its metabolic characteristic since T. thioparus is an obligately chemolithotrophic bacteria that obtains its energy mainly from the oxidation of reduced sulfur compounds such as thiosulfate presented in the culture medium (Kelly et al, 2015). Reduced sulfur species are used as electron donors and oxygen is utilized as an electron acceptor to generate an electron flow in the cell membranes required to satisfy the bacterial metabolism through phosphorylation reactions (Kelly et al, 2015;Lee et al, 2021). Therefore, an increase in the concentration of sodium thiosulfate in the range 2-10 g/L seems to have helped to enhance the metabolism of T. thioparus, which resulted in an augment in OD 600 > 0.6 with a bacterial density of 1.2 × 10 6 cells/mL.…”

“…In standard bio-oxidation plants, pH control accounts for ca. 30% of the total operational cost comprising sulfuric acid, lime, and limestone (Aswegen et al, 2007;Lee et al, 2021). Prior to cyanide leaching at alkaline pH, neutralizing reagents, e.g., slaked lime and limestone, are applied to generate effluents with near-neutral pH and avoid acid mine drainage (AMD) (Darvanjooghi et al, 2022).…”

“…Prior to cyanide leaching at alkaline pH, neutralizing reagents, e.g., slaked lime and limestone, are applied to generate effluents with near-neutral pH and avoid acid mine drainage (AMD) (Darvanjooghi et al, 2022). Moreover, highly acid pH operations could have more risk of leaving residual acid in cyanide leaching, which could lead to cyanide release as HCN (Lee et al, 2021). Hence, conducting an oxidative pretreatment out of the extreme acidic pH range would prevent the generation of undesirable waste streams and diminish the concentration of reagents required in the neutralization stage, bringing potential economic and environmental advantages.…”

“…A bio-oxidation pretreatment performed out of the extreme acidic pH zone must contemplate neutrophilic sulfur-oxidizing bacteria instead of acidophilic microorganisms. Neutrophilic bacteria include microorganisms that can thrive at pH > 4 but have a more favorable growth at a circumneutral pH between pH 6.0 and 8.0 (Kelly et al, 2015;Lee et al, 2021). Most neutrophiles are commonly found in soils, wastewater, and marine freshwater and have an important role in the natural sulfur cycle on earth (McNeice et al, 2022).…”

“…Most of the strains investigated includes but are not limited to Citrobacter, Halothiobacillus, Nocardioides, Parapedobacter, Rhodobacter, Rhodopseudomonas, Starkeya, Thiobacillus, Thermithiobacillus, and Thiomonas. Recent research has emphasized the efficacy of neutrophilic microorganisms in oxidizing reduced sulfur species, especially in gaseous waste streams such as hydrogen sulfide (H 2 S) which is preferentially oxidized to sulfate in batch experiments (Lee et al, 2021). The effectiveness of the desulfurization of H 2 S with neutrophilic bacteria has led to its industrial implementation in H 2 S odor control in industrial waste encompassing BIOREM technologies Inc. and ALKEN ENZ-ODOR R 8 Alken-Murray Corporation (Alken-Murray, 2006;Biorem Technology Inc, 2015).…”