Acid Rock Drainage or Not—Oxidative vs. Reductive Biofilms—A Microbial Question

Abstract

Measures to counteract Acid Rock Drainage (ARD) generation need to start at the mineral surface, inhibiting mineral-oxidizing, acidophilic microbes. Laboratory and long-term field tests with pyrite-containing mining wastes-where carbonaceous phosphate mining waste (CPMW) was added-resulted in low acidity and near neutral drainage. The effect was reproducible and confirmed by several independent research groups. The improved drainage was shown to involve an organic coating, likely a biofilm. The biofilm formation was confirmed when CPMW was added to lignite coal waste with an initial pH of 1. Forty-five days after the addition, the coal waste was dominated by heterotrophic microorganisms in biofilms. Reviewing the scientific literature provides ample support that CPMW has physical and chemical characteristics which can induce a strong inhibitory effect on sulphide oxidation by triggering the formation of an organic coating, a biofilm, over the mineral surface. CPMW characteristics provide the cornerstone of a new technology which might lead to reduction of sulphide oxidation in mine wastes. A hypothesis for testing this technology is presented. The use of such a technology could result in an economical and sustainable approach to mine waste and water management.

Molecular regulation of conditioning film formation and quorum quenching in sulfate reducing bacteria

“…Degradation of environmental pollutants, organic matter, and maintenance of different organic cycles (e.g., C and N) require cumulative effort from microbes, including SRB exhibiting various metabolic activities. Bacterial conditioning film has been found ubiquitously even in extreme natural environments such as acid mine drainage ( Kalin et al, 2018 ), ice lakes in Antarctica ( Smith et al, 2016 ), and thermal springs ( Bhagwat et al, 2021 ) due to their metabolic plasticity. Proteobacteria, Bacteroidetes, and Cyanobacteria dominate biofilm forming bacteria in the aquatic ecosystem.…”

Acid and Metalliferous Drainage–A Global Environmental Issue

“…Among various at-sources approaches, mineral surface passivation is an appealing and viable approach for control of acid generation and has received increasing attention over the last two decades. Four main types of surface passivation layers developed to date are organics (abiotic) [25][26][27], phosphates [28,29], silicates [30][31][32] and biofilms [33,34]. Although the use of organics and phosphates can reduce pyrite oxidation, their application in the field in still challenging due to the high concentra rations of chemicals and harsh conditions needed to form organic coatings and possible secondary pollution from organic and eutrophication of freshwater environments by phosphates.…”

Characterization of Mine Waste and Acid Mine Drainage Prediction by Simple Testing Methods in Terms of the Effects of Sulfate-Sulfur and Carbonate Minerals

“…A cover system is an example of an isolation method, i.e., the use of an impermeable sheet to create a water shield with cement [8,9]. In this system, mining waste rocks, classified as non-source rocks for AMD, are commonly used as cover materials due to their low cost and easy use at mine sites compared to the abovementioned materials [10][11][12]. A cover layer comprising non-source rocks inhibits the supply of oxygen to sulfide minerals throughout the waste dump [13].…”