Mine waste characterization, management and remediation

Mining is a vital part of the Global economy, but the extraction of metals, metalloids, and other mineral products generates vast quantities of liquid and solid waste. Currently the volume is estimated at several thousand million tons per annum, but is increasing exponentially as demand and exploitation of lower-grade deposits increases. The high concentrations of potentially toxic elements in these wastes can pose risks to ecosystems and humans, but these risks can be mitigated by implementing appropriate management or remediation schemes. Although there are a large number of such schemes available, there is still a need to research the processes, products, and effectiveness of implementation, as well as the nature of the mine wastes themselves. This Special Issue is aimed at bringing together studies in the areas of mine waste characterization, management, and remediation, to review the current state of knowledge and to develop improvements in current schemes. Fourteen manuscripts are published for this Special Issue, and these are summarized below.[...

Enhancing As(V) adsorption and passivation using biologically formed nano-sized FeS coatings on limestone: implications for acid mine drainage treatment and neutralization

The iron-reducing bacterium Acidiphilium cryputum JF-5 and a sulfate reducing bacterium (SRB) collected and purified from the mine drainage of a copper mine in the northwest of Sichuan Province, China, were used to biologically synthesize nano-sized FeS-coated limestone to remove As(V) from solution. The adsorption efficiency of As(V) is improved from 6.64 μg/g with limestone alone to 187 μg/g with the FeS coated limestone in both batch and column experiments. The hydraulic conductivity of the columns are also improved by the presence of the nano-sized FeS coatings, but the solution neutralization performance of the limestone can be reduced by passivation by gypsum and Fe(III) precipitates. Calculations for FeS-coated limestone dissolution experiments show that the process can be described as nCa.sol=At1/2-nCa,gyp. The results suggest that FeS-coated limestone may be an effective medium for remediating As(V)-bearing solutions such as acid mine drainage in systems such as Permeable Reactive Barriers

Microbial oxidation of arsenite in a subarctic environment: diversity of arsenite oxidase genes and identification of a psychrotolerant arsenite oxidiser

Background: Arsenic is toxic to most living cells. The two soluble inorganic forms of arsenic are arsenite (+3) and arsenate (+5), with arsenite the more toxic. Prokaryotic metabolism of arsenic has been reported in both thermal and moderate environments and has been shown to be involved in the redox cycling of arsenic. No arsenic metabolism (either dissimilatory arsenate reduction or arsenite oxidation) has ever been reported in cold environments (i.e. < 10°C). Results: Our study site is located 512 kilometres south of the Arctic Circle in the Northwest Territories, Canada in an inactive gold mine which contains mine waste water in excess of 50 mM arsenic. Several thousand tonnes of arsenic trioxide dust are stored in underground chambers and microbial biofilms grow on the chamber walls below seepage points rich in arsenite-containing solutions. We compared the arsenite oxidisers in two subsamples (which differed in arsenite concentration) collected from one biofilm. 'Species' (sequence) richness did not differ between subsamples, but the relative importance of the three identifiable clades did. An arsenite-oxidising bacterium (designated GM1) was isolated, and was shown to oxidise arsenite in the early exponential growth phase and to grow at a broad range of temperatures (4-25°C). Its arsenite oxidase was constitutively expressed and functioned over a broad temperature range. Conclusions: The diversity of arsenite oxidisers does not significantly differ from two subsamples of a microbial biofilm that vary in arsenite concentrations. GM1 is the first psychrotolerant arsenite oxidiser to be isolated with the ability to grow below 10°C. This ability to grow at low temperatures could be harnessed for arsenic bioremediation in moderate to cold climates

In situ arsenic oxidation and sorption by a Fe-Mn binary oxide waste in soil

The ability of a Fe-Mn binary oxide waste to adsorb arsenic (As) in a historically contaminated soil was investigated. Initial laboratory sorption experiments indicated that arsenite [As(III)] was oxidized to arsenate [As(V)] by the Mn oxide component, with concurrent As(V) sorption to the Fe oxide. The binary oxide waste had As(III) and As(V) adsorption capacities of 70 mg g−1 and 32 mg g−1 respectively. X-ray Absorption Near-Edge Structure and Extended X-ray Absorption Fine Structure at the As K-edge confirmed that all binary oxide waste surface complexes were As(V) sorbed by mononuclear bidentate corner-sharing, with 2 Fe at ∼3.27 Ǻ. The ability of the waste to perform this coupled oxidation-sorption reaction in real soils was investigated with a 10% by weight addition of the waste to an industrially As contaminated soil. Electron probe microanalysis showed As accumulation onto the Fe oxide component of the binary oxide waste, which had no As innately. The bioaccessibility of As was also significantly reduced by 7.80% (p < 0.01) with binary oxide waste addition. The results indicate that Fe-Mn binary oxide wastes could provide a potential in situ remediation strategy for As and Pb immobilization in contaminated soils

Computer simulations of the interactions of the (012) and (001) surfaces of jarosite with Al, Cd, Cu2+ and Zn

Jarosite is an important mineral on Earth, and possibly on Mars, where it controls the mobility of iron, sulfate and potentially toxic metals. Atomistic simulations have been used to study the incorporation of Al3+, and the M2+ impurities Cd, Cu and Zn, in the (0 1 2) and (0 0 1) surfaces of jarosite. The calculations show that the incorporation of Al on an Fe site is favorable on all surfaces in which terminal Fe ions are exposed, and especially on the (0 0 1) [Fe3(OH)3]6+ surface. Incorporation of Cd, Cu or Zn on a K site balanced by a K vacancy is predicted to stabilize the surfaces, but calculated endothermic solution energies and the high degree of distortion of the surfaces following incorporation suggest that these substitutions will be limited. The calculations also suggest that incorporation of Cd, Cu and Zn on an Fe site balanced by an OH vacancy, or by coupled substitution on both K and Fe sites, is unfavorable, although this might be compensated for by growth of a new layer of jarosite or goethite, as predicted for bulk jarosite. The results of the simulations show that surface structure will exert an influence on uptake of impurities in the order Cu > Cd > Zn, with the most favorable surfaces for incorporation being (0 1 2) [KFe(OH)4]0 and (0 0 1) [Fe3(OH)3]6+

River sediment geochemistry and provenance following the Mount Polley mine tailings spill, Canada:The role of hydraulic sorting and sediment dilution processes in contaminant dispersal and remediation

The failure of the Mount Polley tailings storage facility (TSF) in August 2014 was one of the largest magnitude failures on record, and released approximately 25 Mm3 of material, including c. 7.3 Mm3 of tailings into Hazeltine Creek, part of the Quesnel River watershed. This study evaluates the impact of the spill on the geochemistry of river channel and floodplain sediments and utilizes Pb isotope ratios and a multi-variate mixing model to establish sediment provenance. In comparison to sediment quality guidelines and background concentrations, Cu and V were found to be most elevated. Copper in river channel sediments ranged from 88-800 mg kg-1, with concentrations in sand-rich and clay/silt-rich sediments being statistically significantly different. Concentrations in river channel were believed to be influenced by hydraulic sorting during the rising and falling limbs of the flood wave caused by the tailings spill. Results highlight the importance of erosive processes, instigated by the failure, in incorporating soils and sediments into the sediment load transported and deposited within Hazeltine Creek. In this instance, these processes diluted tailings with relatively clean material that reduced metal concentrations away from the TSF failure. This does however, highlight environmental risks in similar catchments downstream of TSFs that contain metal-rich sediment within river channels and floodplain that have been contaminated by historical mining

Origin and Fate of Vanadium in the Hazeltine Creek Catchment following the 2014 Mount Polley Mine Tailings Spill in British Columbia, Canada

This is the final version. Available on open access from American Chemical Society via the DOI in this recordResults are presented from the analysis of aqueous and solid-phase V speciation within samples collected from the Hazeltine Creek catchment affected by the August 2014 Mount Polley mine tailings dam failure, Canada. Electron microprobe and XANES analysis found that V is present as V3+ substituted into magnetite, and V3+ and V4+ substituted into titanite, both of which occur in the spilled Mount Polley tailings. Secondary Fe oxyhydroxides forming in inflow waters and on creek beds have V K-edge XANES spectra exhibiting E½ positions and pre-edge features consistent with the presence of V5+ species, suggesting sorption of this species on these secondary phases. PHREEQC modelling suggests that the stream waters mostly contain V5+, and the inflow and pore waters contain a mixture of V3+ and V5+. These data, and stream, inflow and pore water chemical data, suggest that dissolution of V(III)-bearing magnetite, V(III,IV)-bearing titanite, V(V)-bearing Fe(-Al-Si-Mn) oxhydroxides, V-bearing Al(OH)3 and/or -clay minerals may have occurred. In the circumneutral pH environment of Hazeltine Creek elevated V concentrations are likely naturally attenuated by formation of V(V)-bearing secondary Fe oxyhydroxide, Al(OH)3 or clay mineral colloids, suggesting that the V is not bioavailable. A conceptual model is presented describing the origin and fate of V in Hazeltine Creek that is applicable to other river systems.Natural Environment Research Council (NERC

Geochemistry of As-, F- and B-bearing waters in and around San Antonio de los Cobres, Argentina, and implications for drinking and irrigation water quality

Spring, stream and tap waters from in and around San Antonio de los Cobres, Salta, Argentina, were sampled to characterize their geochemical signatures, and to determine whether they pose a threat to human health and crops. The spring waters are typical of geothermal areas world-wide, in that they are Na-Cl waters with high concentrations of Astot, As(III), Li, B, HCO3, F and SiO2 (up to 9.49, 8.92, 13.1, 56.6, 1250, 7.30 and 57.2 mg L-1, respectively), and result from mixing of deep Na-Cl brines and meteoric HCO3-rich waters. Springs close to the town of San Antonio have higher concentrations of all elements, and are generally cooler, than springs in the Baños de Agua Caliente. Spring water chemistry is a result of mixing of deep Na-Cl brines and meteoric HCO3 waters. Stream waters are also Na-Cl type, and receive large inputs of all elements from the springs near San Antonio, but concentrations decrease downstream through the town of San Antonio due to mineral precipitation. The spring that is used as a drinking water source, and other springs in the area, have As, F and B concentrations in excess of WHO and Argentinian drinking water guidelines. Evaluation of the waters for irrigation purposes suggests that their high salinities and B concentrations may adversely affect crops. The waters may be improved for drinking and irrigation by dilution with cleaner meteoric waters, mineral precipitation or by use of commercial filters. Such recommendations could also be followed by other settlements that draw drinking and irrigation waters from geothermal sources

Defects and impurities in jarosite: A computer simulation study

Computer modelling techniques involving a rigid ion model have been used to investigate the defect structure and impurity site preferences in end-member K-jarosite. Calculated intrinsic vacancy energies show that the K2SO4 neutral cluster, with an energy per species of 1.34 eV, will be the most common defect in the pure phase. Defect reactions leading to vacancies on the Fe site have high energies, in excess of 4.0 eV per species, and are thus unlikely to occur in great numbers. However, the calculations show that divalent metal cations can be incorporated onto the Fe site via solution reactions with oxides leading to the formation of goethite. Calculated solution reactions are exothermic and thus predicted to be highly favourable. At K sites substitutions occur in the order Cd > Zn > Cu, but will be limited due to endothermic solution energies and structural considerations