Sulfur Isotope Fractionation as an Indicator of Biogeochemical Processes in an AMD Passive Bioremediation System

Abstract

Sulfate, the main dissolved contaminant in acid mine drainage (AMD), is ubiquitous in watersheds affected by coal and metal mining operations worldwide. Engineered passive bioremediation systems (PBS) are low-cost technologies that remediate sulfate contamination by promoting (1) precipitation of sulfate-bearing compounds, such as schwertmannite and gypsum; and (2) microbially-mediated sulfate reduction (BSR) to sulfide with subsequent precipitation of sulfide minerals. In this study, chemical and sulfur isotopic data are used to infer multiple pathways for sulfate sequestration in the Tab-Simco PBS. By simultaneously monitoring sulfate concentrations and δ 34 S SO 4 values at four sampling points across the PBS, we (1) identified that the organic layer within the bioreactor was the primary site of BSR processes contributing to sulfate sequestration; (2) observed seasonal variations of BSR processes; (3) estimated that initially the BSR processes contributed up to 30% to sulfate sequestration in the Tab-Simco bioreactor; and (4) determined that BSR contribution to sulfate sequestration continuously declined over the PBS operational lifetime. Together, our results highlight the utility of combining geochemical and microbial fingerprinting techniques to decipher complementary processes involved in sulfur cycling in a PBS as well as the value of adding the sulfur isotope approach as an essential tool to help understand, predict, prevent and mitigate sulfate contamination in AMD-impacted systems.

Stable Isotope Imprints during Pyrite Leaching: Implications for Acid Rock Drainage Characterization

“…Pyrite leaching experiments demonstrate that the quantitative conversion of pyrite to sulfate results in only minor sulfur isotope fractionation (∆ 34 S SO4-FeS2 ) under acidic, aerobic-biotic, or abiotic conditions ranging between −1.3% and +0.4% [63,[70][71][72][73][74]. In addition, processes like precipitation and dissolution of secondary sulfate phases were demonstrated to produce negligible S isotope fractionation (e.g., ∆ 34 S schwertmannite-sulfate −0.2% -+0.3% and ∆ 34 S H-jarosite-sulfate +0.3% -+1.1% ) [75][76][77]. Although these relatively small S isotope fractionation factors allow the identification of the parent sulfides in ARD-impacted water, the seasonal precipitation and dissolution cycles of sulfate minerals might cause small variations in the isotopic composition of sulfate as well.…”

“…This would help to improve our ability to evaluate the chemical evolution of both mine waste material and the impacted water systems, potentially informing ARD control measures in a timely manner. In addition to tracking ARD generation and transportation, isotopes also can be used in evaluating the effectiveness of different remediation methods, for example, passive treatment systems [75,149].…”

Forecast of AMD Quantity by a Series Tank Model in Three Stages: Case Studies in Two Closed Japanese Mines

“…However, since our results of the statistical calculation (details are shown below) suggested that some mines have required AMD treatment for over 150 years [13,14] and other groups suggested that more than 1000 years of treatment will be necessary [15] in the current situation, more sustainable treatment to reduce both AMD generation [16,17] and treatment cost [18] is needed. To reduce the treatment cost of the addition of chemicals and of sludge generation, for example, a passive treatment that utilizes the natural environment of mines, such as topography, plants, and microorganisms, has attracted attention as a sustainable AMD treatment based on new concepts [19][20][21]. Several researchers are trying to successfully reuse this sludge as an industrial material [22,23].…”

THE ABIOTIC STRESS RESPONSE OF HYDROPONIC VETIVER GRASS (Chrysopogon zizanioides L.) TO ACID MINE DRAINAGE AND ITS POTENTIAL FOR ENVIRONMENTAL REMEDIATION

“…For field purposes, these results have shown that handheld meters for DO and conductivity could serve for on-site monitoring of plant health and metal reduction, respectively. Common trends among metals were observed; from the largescale experiment, vetiver accumulated greater Fe (17,300 µg g -1 ), Al (3405 µg g -1 ), Mn (1080 µg g -1 ), Zn (113 µg g -1 ) and Cr (62.3 µg g -1 ), with lower Ni (41.2 µg g -1 ), Cu (24.6 µg g -1 ) and Pb (5.37 µg g -1 , [3][4][5] Fe, Al, and Mn. 4 Several plants have been screened for AMD tolerance, including Typha latifolia, Scirpus validus, and many others.…”

“…Effect of Vetiver grass treatment on dissolved SO 4 2-(mean±SD, n = 3 biological replicates) of the Tab-Simco AMD across planting densities (4,3,2 and no plants) over time (0, 10, 20 and 30 days). ..................................................27…”