Formation of biogenic sulphides in the water column of an acidic pit lake: biogeochemical controls and effects on trace metal dynamics

Abstract

Production of H 2 S by bacterial sulphate reduction in the water column of Cueva de la Mora pit lake (SW Spain) may favour an important selfmitigating capacity with respect to metal pollution. The interaction of bacterially produced H 2 S with dissolved metal(loid)s provokes the precipitation of various sulphides, which in turn form a 10 m-thick turbidity layer below the redoxcline. The main goal of this study was to identify the main factors driving the formation of these sulphide precipitates and their impact on the pit lake water quality. Given the severe geochemical conditions found in this lake (low pH, high metal concentrations), our findings may be relevant for a wide spectrum of environmental systems where BSR-based biotechnologies are applied. The water column has been studied by spatially resolved samplings and detailed chemical analyses, physicochemical profiling and geochemical modelling. The suspended particulate matter forming the turbidity has been chemically and mineralogically characterized. Our results suggest that the low pH (3.0-4.0) and the high metal concentrations are not inhibitory for the sulphate-reducing bacteria (SRB). The intensity of sulphide precipitation seems to be closely related with the activity of SRB, which in turn appear to depend on the availability of organic carbon produced in the photic zone. The relative location of oxygen and iron gradients and the redoxcline thickness are influencing the development of the sulphate reducing zone. The most common sulphides are CuS, As 2 S 3 and ZnS, though formation of some other minor phases (PbS, CdS, NiS) has been also detected and/or deduced by geochemical calculations. Metal sulphide precipitation has provoked a complete removal of Cu from the monimolimnion (though it is still present at concentrations of 5.5 mg/L in the mixolimnion) and a net decrease in highly toxic trace metals (Cd, Pb, U, Th) and metalloids (As, Sb).

Recent Developments for Remediating Acidic Mine Waters Using Sulfidogenic Bacteria

“…Copper sulfide, for example, is far less soluble than ferrous sulfide (respective log K sp values of −35.9 and −18.8) and therefore CuS precipitates at pH 2, whereas FeS needs much higher pH to precipitate. Diez-Ercilla et al [ 31 ] have also demonstrated that selective precipitation of metal sulfides occurs naturally in Cueva de la Mora pit lake (SW Spain) and the geochemical calculations match perfectly with the results of chemical and mineralogical composition. Ňancucheo and Johnson [ 3 ] showed that it was possible to selectively precipitate stable metal sulfides in inline reactor vessel testing two synthetic AMDs in acidic conditions (pH 2.2–4.8).…”

Metabolic adaptation of a Chlamydomonas acidophila strain isolated from acid mine drainage ponds with low eukaryotic diversity

“…The accumulated metals may then be harvested and processed to allow metal recovery (Minoda et al, 2015;Raikova et al, 2016). Alternatively, highly acid and metal tolerant microalgae such as the PM01 strain, may have an important role in sustaining SO 4 -reducing bacteria by providing organic carbon and thus increasing the efficiency of AMD remediation microbial bioreactors (Diez-Ercilla et al, 2014;Ňancucheo and Johnson, 2012;Totsche et al, 2006). For example, it was demonstrated that microalgal addition to mine tailing mesocosms containing pyrite-oxidizing bacteria caused higher production of alkalinity, higher concentrations of ferrous Fe, and increased immobilization of Cu and Zn (N ancucheo and Johnson, 2011).…”

Microbially mediated aluminosilicate formation in acidic anaerobic environments: A cell‐scale chemical perspective

“…Of particular interest is the anoxic bottom layer of these lakes, in which the absence of Fe(III) (omnipresent in oxidizing environments) allows detailed study of the geochemical behavior of other important dissolved substances such as Al or SiO 2 (aq.) (Diez‐Ercilla et al., ; Sánchez‐España et al., ). The special geochemical conditions of these anoxic environments include very high ionic strengths ( I e = 0.5–0.7), salinity close to seawater (36–37‰, mainly caused by SO 4 2− , Fe 2+ and Mg 2+ , instead of Na + and Cl − ), extreme concentrations of dissolved metals (Table S1) and carbon dioxide (up to 5 g/L; Sánchez‐España et al., ), and a pH slightly above 4.0, which is close to the typical pH for Al precipitation in these environments (Figure S1).…”

“…We focused on Herrerías‐Guadiana (GUA) and Cueva de la Mora (CM), two well‐characterized acidic pit lakes in SW Spain whose biogeochemistry and limnology have been extensively studied (Diez‐Ercilla, Sánchez‐España, Yusta, Wendt‐Potthoff, & Koschorreck, ; Falagán & Johnson, ; Falagán, Sánchez‐España, & Johnson, ; Sánchez‐España, Boehrer, & Yusta, ; Sánchez‐España, Diez, & Santofimia, ; Sánchez‐España, Yusta, & Diez, ; Sánchez‐España et al., ; Wendt‐Potthoff, Koschorreck, Diez, & Sánchez‐España, ). These artificial lakes formed after the flooding of abandoned metal mine pits of the “ Iberian Pyrite Belt ” mining district and represent unrivaled natural laboratories for the study of biogeochemical processes at extremely acidic conditions (e.g., Sánchez‐España et al., , ).…”

“…Of particular interest is the anoxic bottom layer of these lakes, in which the absence of Fe(III) (omnipresent in oxidizing environments) allows detailed study of the geochemical behavior of other important dissolved substances such as Al or SiO 2 (aq.) (Diez-Ercilla et al, 2014;Sánchez-España et al, 2016). The special geochemical conditions of these anoxic environments include very high ionic strengths…”