Search Results (4)

Mafic mine tailings are highly resistant to bioleaching due to their silicate-rich composition, low sulfide content, and strong buffering capacity. This study aimed to assess the potential use of heterotrophic bioleaching to promote the release of metals from mafic tailings by evaluating the organic acid production and leaching capabilities of indigenous bacterial isolates and a known lactic acid producer, Lactiplantibacillus plantarum ATCC 8014. Indigenous acid-producing heterotrophic bacteria were isolated from a vanadium-titanium-bearing magnetite tailings in Québec, Canada, and screened for organic acid production in various culture media. The most active bacteria were L. plantarum and two isolates identified by their 16S rRNA gene as Enterococcus (CBGM-1C) and Acetobacter (BL-F) sp. They produced significant quantities of lactic acids, followed by acetic, citric, and gluconic acids during glucose metabolism, through fermentative or oxidative pathways. A two-step bioleaching process was implemented, consisting of an initial organic acid production phase followed by tailings leaching at 5% pulp density over 10 days at 30 °C. Metal solubilization and mineralogical analyses demonstrated strain-dependent and metal-specific mobilization, with zinc being the only element efficiently leached (up to ~74% recovery by L. plantarum). XRD analyses confirmed partial dissolution and reduced crystallinity of key silicate phases without secondary mineral formation. These findings indicate that heterotrophic leaching can selectively mobilize more labile metals such as Zn from alkaline, silicate-rich tailings, although its overall efficiency for refractory elements remains limited under the tested conditions. Full article

Weather-enhanced sulphide oxidation accelerates CO₂ release into the atmosphere. However, over extended geological timescales, ultramafic and mafic magmatic minerals may transition from being sources of CO₂ emissions to reservoirs for carbon sequestration. Ultramafic and mafic mine tailings present a unique opportunity to monitor carbon balance processes, as mine waste undergoes instantaneous and rapid chemical weathering, which shortens the duration between CO₂ release and absorption. In this study, we analysed 30 vanadium-titanium magnetite mine tailings ponds with varying closure times in the Panxi region of China, where ~60 years of mineral excavation and dressing have produced significant outcrops of mega-mine waste. Our analysis of anions, cations, saturation simulations, and ⁸⁷Sr/⁸⁶Sr; δ¹³C and δ³⁴S isotopic fingerprints from mine tailings filtrates reveals that the dissolution load of mine tailings may depend significantly on early-stage sulphide oxidation. Despite the abundance of ultramafic and mafic minerals in tailings, dolomite dominates chemical weathering, accounting for ~79.2% of the cationic load. Additionally, due to sulphuric-carbonate weathering, the filtrates undergo deacidification along with sulphide depletion. The data in this study suggest that pristine V-Ti-Fe tailings ponds undergo CO₂ emissions in the first two years but subsequently begin to absorb atmospheric CO₂ along with the filtrates. Our results provide valuable insights into monitoring weathering transitions and carbon balance in ultramafic and mafic rocks. Full article

Mine tailings that were produced during the exploitation of the Ulveryggen siliciclastic sediment-hosted Cu deposit in northern Norway were disposed into the inner part of Repparfjorden from 1972 to 1978/1979. This study focuses on the mineralogy and geochemistry of the submarine mine tailings and underlying natural marine sediments from the inner part of Repparfjorden, as well as on the primary Ulveryggen ore. The ore mineralization from the neighboring Nussir carbonate sediment-hosted Cu deposit was studied too, due to the forthcoming mining of both deposits. Bornite and chalcopyrite are the major Cu-sulfides, and are characterized by low concentrations of potentially toxic elements including Cd, Hg, and As. The tailing material occupies the uppermost 9 cm of Repparfjorden sediments. It is characterized by predomination of a silty component with elevated Cu (up to 747.7 ppm), Ni (up to 87 ppm), and Cr (up to 417 ppm) concentrations. The high Cu concentration is related to the deposition of mine tailings. In contrast, Ni and Cr concentrations are close to those in naturally occurring stream sediments from the feeding river, Repparfjordelva, reflecting the compatibility of these elements with hosting mafic volcanics, which are widely spread in the Repparfjord Tectonic Window. Copper in the uppermost part of the sediments is bound to the acid-soluble fraction while Ni and Cr are bound to the residual fraction. Artificial placement of large masses of fine-grained material, i.e., smothering, resulted in a diminished biological activity and/or physical distortion of mostly benthic fauna, which was reflected in total organic carbon (TOC) values as low as 0.15% in the uppermost strata. Sulfide minerals are found both in natural marine sediments and in the mine tailings. They are generally well-preserved with an exception for chalcopyrite from the uppermost part of the submarine tailing, which shows signs of incipient weathering. Thermodynamic modeling confirmed that redox potential and pH are important factors in the weathering of sulfides. Available ligands contribute to the Cu speciation. In near-neutral to slightly alkaline conditions a presence of carbonates can lead to the mobilization of Cu in form of CuCO₃ complexes. Full article

Ultramafic and mafic mine tailings are a valuable feedstock for carbon mineralization that should be used to offset carbon emissions generated by the mining industry. Although passive carbonation is occurring at the abandoned Clinton Creek asbestos mine, and the active Diavik diamond and Mount Keith nickel mines, there remains untapped potential for sequestering CO₂ within these mine wastes. There is the potential to accelerate carbonation to create economically viable, large-scale CO₂ fixation technologies that can operate at near-surface temperature and atmospheric pressure. We review several relevant acceleration strategies including: bioleaching of magnesium silicates; increasing the supply of CO₂ via heterotrophic oxidation of waste organics; and biologically induced carbonate precipitation, as well as enhancing passive carbonation through tailings management practices and use of CO₂ point sources. Scenarios for pilot scale projects are proposed with the aim of moving towards carbon-neutral mines. A financial incentive is necessary to encourage the development of these strategies. We recommend the use of a dynamic real options pricing approach, instead of traditional discounted cash-flow approaches, because it reflects the inherent value in managerial flexibility to adapt and capitalize on favorable future opportunities in the highly volatile carbon market. Full article