Gold Mine Tailings Research Articles

Measurements of radon exhalation from a South African gold mine tailings using sealed tube method

To date, approximately 6000 tons of uranium has been disposed of onto tailings dams per year by gold mining activities in South Africa. These uranium bearing tailings dumps contain significant amounts of radium and are therefore possible sources of substantial amounts of radon gas. Due to the large sizes of these dams, measurements of the radon exhalation for the whole dam using established and conventional methods become time consuming and labour intensive. In this study, radon exhalation rates from a gold mine tailings dam around mining area of Odendalsrus were measured using passive “sealed tube” method and CR-39 gas etched track monitors known as Radon Gas Monitors (RGMs). Twenty samples were collected at the depths ranging from 90 cm to 1 m from the tailings for exhalation rate measurements. Radon exhalation rates from these samples were found to vary from 0.0410 ± 0.0042 Bq/m2 · s to 0.440 ± 0.045 Bq/m2 · s with a mean value of 0.102 ± 0.021 Bq/m2 · s and a standard deviation of 0.087 Bq/m2 · s. The results of these measurements show very high radon exhalation rate and radium content from one particular sample which requires further investigations.

Novel Materials for Myco-Decontamination of Cyanide-Containing Wastewaters through Microbial Biotechnology

This study examined the effectiveness of decontamination of industrial cyanide-containing water using mycelium-based lignocellulosic materials. These results suggest that fungi biomass and plant substrates can be used successfully in the treatment of wastewater contaminated by cyanide. Fungi were isolated from old wood samples taken from a tailing dam with high cyanide content (more than 20 years in semi-submerged condition). All isolated fungi belonged to the genus Fusarium. Fusarium oxysporum Schltdl. is most effective for biodegradation of cyanide-containing wastewaters (even at low temperatures). The most optimal lignocellulosic composition for production of mycelium-based biomaterial for biodegradation of cyanide wastewater consists of a uniform ratio of Siberian pine sawdust and wheat straw. The high efficiency of mycelium-based materials has been experimentally proven in vitro at 15-25 ° C. New fungal biomaterials are provide decrease in the concentration of cyanide ions to 79% (P <0.001). Large-scale cultivation of fungi biomass was carried out by the periodic liquid-phase cultivation. The submerged biomass from bioreactor was used as an inoculum for the production of mycelium-based materials for bioremediation of cyanide wastewater in situ (gold mine tailing).

Pollution Assessment of Potentially Toxic Elements (PTEs) in Soils around the Yanzhuang Gold Mine Tailings Pond, Pinggu County, Beijing, China.

The accumulation of tailings from gold mining and smelting may result in PTE pollution. We investigated PTE contamination from a large amalgamated gold mine tailings pond in Pinggu County, Beijing. In November 2017, 30 soil samples were collected around the tailings pond. The concentrations and pollution degree of PTEs in the samples and the sources of Sb, As, Cd, Cu, Pb, Zn and Hg were analyzed. The average concentration of these elements in soil samples near the tailings pond (16.24, 28.29, 0.99, 171.04, 263.25, 99.73, 0.72 mg/kg, respectively) were higher than their corresponding standard values and background values of the study area. The geoaccumulation index showed that the pollution degree of As, Pb and Hg was moderate, while Sb and Cu present non-pollution to moderate pollution. The average EF values of the elements were Sb (38.31), As (4.23), Cd (0.71), Cu (3.68), Pb (21.24), Zn (0.82) and Hg (5.29), respectively. The environmental risk assessment developed throughout the PERI method indicated that Sb, As, Hg and Pb were the main pollutants in the study area. The three quantitative risk indicators (RI, Igeo and EF) were positively correlated, and all of them indicated that PTEs had significant pollution to the local area. Thus, Sb, As, Pb, Cu, and Hg pollution should be highly concerning. Multivariate statistical analysis shows that the pollution of PTEs was mainly caused by the accumulation of tailings ponds after gold mining and smelting. The research result is of great significance for the prevention and control of soil pollution of PTEs near the tailings pond.

Valorisation of mine waste - Part I: Characteristics of, and sampling methodology for, consolidated mineralised tailings by using Witwatersrand gold mines (South Africa) as an example

The quest for steady primary supplies of critical raw materials (CRMs) creates significant waste, which is inevitably generated at each phase of mining and mineral processing. Waste from extraction, separation and refinement of non-renewable natural resources is accumulated globally and creates not only environmental hazards but also economic possibilities. Mine waste management is an expensive and prolonged task but unavoidable. Mine tailings, especially historical ones, can contain economically feasible resources, and given the right condition, such tailings could be reutilised through a waste valorisation concept. A prominent example are the Witwatersrand gold mine tailings in South Africa, which have been reused in small-scale projects. Tailing reutilisation is only possible if a sound classification, sampling and resource modelling framework is established to thoroughly and accurately profile the economic, environmental, health and geometallurgical aspects. Our study on valorisation of mine waste is presented in two parts: Here, in Part I, we focus on the essential components of a mine waste valorisation framework that includes the characterization and development of a systematic sampling framework for consolidated mineralised tailings. The development of a mine waste valorisation framework will hopefully enable worldwide reduction and reutilisation of mine waste.

Phytoextraction potential of halophyte plants under industrial multi-metal contaminated sites

The present research evaluated the phytoremediation potential of three selected plant species Tamarix. spp, Haloxylon. spp and Malcolmia Africana to remediate gold mine tailings in the center of Iran. To improve the ecological capability of the tailing dam and contaminated soil, two treatments of contaminated (tailing dam) and control (surrounding area of the gold mine) were chosen. The associated tailing and plants' shoot and root samples were collected and analyzed for total metal concentrations of Cobalt, Chromium, Strontium, Thorium, Titanium and Uranium. Translocation Factor (TF), BioAccumulation Coefficient (BAC) and Bioconcentration Factor (BCF) were estimated to assess the plant species potential for phytoremediation. Results indicated that Tamarix. spp showed the best growth on contaminated site (by height of 44.05 cm and weight of 105.3 mg) as compared to Haloxylon. spp and Malcolmia Africana. Metal accumulation rate was observed to be maximized in all three species; by 28.37%, 35.5% and 12.96% of Sr and 20.28%, 9.85% and 31.7% of Ti for Tamarix. Spp, Haloxylon. Spp and Malcolmia Africana, respectively. The study showed that Malcolmia Africana is the best accumulator of Strontium with TF, BAC and BCF of higher than one for both control and contaminated treatments. Also Tamarix. spp can translocate large amounts of Strontium, Thorium, Titanium and Uranium from roots to shoots as well as Strontium and Titanium for Haloxylon. spp.

Screening the phytoextractability of trace metals by Aloe cryptopoda Baker and Aloe vera (L.) Burm.f. cultivated on mine tailings

Considering the impact that mining has on the environment, especially by metal-contaminated tailings, and the legal South African requirements for post mine rehabilitation, the study aimed to investigate whether plant species of the Aloe genus could act as phytoextractors of heavy metals. By means of controlled experiments, plant biomass and trace metal contents of leaves of Aloe cryptopoda and A. vera grown in gold and platinum mine tailings were evaluated to assess their performance in heavy metal polluted soil and their potential as phytoextractors. A. vera had the higher productivity levels in general, although both species showed decreased biomass production in the contaminated soil over time. A. cryptopoda had the higher trace metal concentrations, similar to those of phytoremediators recommended in other studies and can, therefore, be used as a viable phytoextractor of especially chromium and copper.

Synthesis and characterization of coal fly ash and palm oil fuel ash modified artisanal and small-scale gold mine (ASGM) tailings based geopolymer using sugar mill lime sludge as Ca-based activator

The continuous accumulation of artisanal and small-scale gold mining (ASGM) tailings in the Philippines without adequate storage and disposal facility could lead to human health and environmental disasters in the long run. In this study, ASGM tailings was simultaneously stabilized and repurposed as construction material via geopolymerization using coal fly ash, palm oil fuel ash and a powder-based alkali activator. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) identified iron sulfides in the tailings containing arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn), which could be released via weathering. The average unconfined compressive strengths (UCS) of tailings-based geopolymers at 14 days curing were 7.58 MPa and 7.7 MPa with fly ash and palm oil fuel ash, respectively. The tailings-based geopolymers with palm oil fuel ash had higher UCS most likely due to CASH reaction product formation that improved strength formation. The toxicity characteristic leaching procedure (TCLP) results showed very low leachabilities of As, Pb and Fe in the geopolymer materials suggesting ASGM tailings was effectively encapsulated within the geopolymer matrix. Overall, the geopolymerization of ASGM tailings is a viable and promising solution to simultaneously stabilize mining and industrial wastes and repurpose them into construction materials.

Changes in physicochemical properties on a chronosequence of gold mine tailings

Understanding the trajectory of changes in substrate physicochemical properties is critical for revegetation of mine tailings. The study tracked changes of selected physicochemical properties as proxies of pedogenesis over time and across different topographic positions on a chronosequence of six abandoned gold tailings (10, 17, 35, 82, 92 and 110 years) compared to soils from reference areas. The hypotheses were: (1) plant macronutrients: total and mineral nitrogen (N), plant available phosphorus (P), potassium (K), organic carbon (OC) and fine particle content significantly increase with substrate age and approach that of natural reference soils, (2) substrate pH, electrical conductivity (EC) and bulk density decrease with tailings age, (3) topography (relief) and depth had significant effect on the tailings properties. Substrate samples were collected from four depths (0–5 cm; 5–15 cm, 100 cm and 300 cm) on the tops, upper and lower slope positions of the tailings dumps and two reference sites 200 m and 2 km away. Total N and available P significantly increased with dump age matching reference conditions in the top 5 cm on the oldest (110 years) dump. Organic carbon(OC) and pH initially significantly declined between the disposal time (0 years) and 10 years but fluctuated thereafter. Bulk density significantly decreased with tailings age. Texture and EC did not significantly vary with dump age. Slope position (relief) had significant effect (p < 0.05) on total N, available P, and EC. Available P and EC increased from the dump top to the base while total N fluctuated. Total N significantly decreased with depth and was highest in the 0–5 cm layer. The interactive effect of dump age and slope position was significant for EC only. A PCA based on all measured parameters showed higher similarity of the older dumps (82–110-years) to the two reference sites. Overall, the results suggest that more than 110 years are required for macronutrients on gold mine tailings to match reference conditions while the other parameters require shorter periods and fluctuate above and below reference conditions. Nevertheless, changes in tailings properties appeared to be correlated to dynamics in vegetation and biological crusts that were observed to increase in cover with substrate age.

Preparation of eco-friendly one-part geopolymers from gold mine tailings by alkaline hydrothermal activation

Environmental and economic issues caused by several tailings storages have attracted worldwide attention; therefore, these urgently need to be solved cost-effectively. In this study, gold mine tailings rich in Si and Al oxides were activated by an alkaline hydrothermal method for use as precursors to produce a one-part geopolymer. The results indicated that the crystalline mineral phases in tailings were partially or completely decomposed by alkaline hydrothermal activation. However, this decomposition depended heavily on the alkali content, temperature, and time. The decomposed tailings were converted to the amorphous sodium aluminosilicate reactant, thereby making tailings a reactive starting material. Subsequently, the one-part geopolymer was prepared from the activated tailings and slag by just adding water without adding any extra alkaline activator. By adding 60 wt% of slag, the one-part geopolymer with an optimum compressive strength value of 33.5 MPa at 28 days was obtained. This was much higher than that of the control sample containing raw tailings without any pretreatment. The high strength could have been because of the amorphous sodium aluminosilicate formed in the activated tailings that could dissolve in water to create alkaline conditions, which could effectively activate the pozzolanic activity of the slag. The main geopolymerization product was the glassy calcium-sodium aluminosilicate hydrate (C(N)-A-S-H) gel, which acted as a binder to closely connect the residual solid particles and form a hardened geopolymer material.

A comparison between ferrochrome slag and gold mine tailings based geopolymers as adsorbents for heavy metals in aqueous solutions: Analyzing reusability and sustainability

Ferrodirome slag (FeCr-GP) and gold mine tailings (GMT-GP) based geopolymers were synthesized and used as adsorbents of heavy metals in aqueous solutions. Batchwise adsorption experiments were used to determine the effect of solid loading (S/L), temperature and time on the adsorption of Cu, Ni and Mn. X-ray diffraction studies showed that GMT-GP was amorphous with calcium aluminium silicate hydrate as the geopolymerization product leading to an increased surface area while GMT-GP had a significant reduction in the intensity of crystalline peaks as compared to the precursor. FeCr-GP could adsorb above 99% of the metal ions (Cu2+, Ni2+ and Mn2+) in solution with an initial metal concentration of 400 ppm at 298, while GMT-GP could only adsorb at least 98% of the metal with an initial metal concentration of 200 ppm. The adsorption was accompanied by a pH rise from 2.3 to 4.5 and 4.8 for GMT-GP and FeCr-GP, respectively. The maximum adsorption capacity of FeCr-GP was double that of GMT-GP. FeCr-GP could be desorbed using HCl and reverse osmosis water and could be used for a further three cycles without significant loss in adsorbing ability, while desorption of GMT-GP resulted a reduction in adsorption capability.

Heavy Metals Tolerance Potential of Fungi Species Isolated from Gold Mine Tailings in Ghana

Introduction: Heavy metal contamination has necessitated a less expensive and non-destructive clean-up technique such as mycoremediation. This study aimed to isolate, identify, and evaluate the tolerance of fungi species in different concentrations of heavy metals for their potential use in bioremediation. Materials and Methods: Fungi were isolated by serial dilution and spread plate techniques from gold tailings and their tolerance to different concentrations of As, Cd, Cr, Cu, Pb, Zn (as potential bioremediation candidates) was evaluated. Fungal radial growths were recorded daily over a 14 days’ incubation period to establish their tolerance levels using the Tolerance Index. Results: Five isolated fungi species belonged to the genera Aspergillus, Trichophyton, Rhizopus, Trametes, and Trichoderma. Except for Trichophyton rubrum, the other fungi species were tolerant to all Cr concentrations (0 – 100ppm), but no significant difference was observed in mycelia growth compared to their controls. With high tolerance index ranging from 0.91 to 1.02, Trichoderma viride and Rhizopus oryzae were tolerant to all Cu concentrations (0 – 125ppm). High tolerance was exhibited by Trametes versicolor to Cd at 25 and 50 ppm, and by Rhizopus oryzae at 25 ppm, but no significant difference was found in mycelia growth. Rhizopus oryzae tolerated all As and Pb concentrations with high tolerance index ranging from 0.81 to 1.00. It also tolerated Zn at 200-600ppm concentration with a tolerance index from 0.80 to 0.91. Conclusion: The selective nature of these fungi species for specific heavy metal tolerance indicates their potential for selective use as effective bioremediative clean up agent of heavy metals contaminated sites.

Impacts on aquatic biota from salinization and metalloid contamination by gold mine tailings in sub-Arctic lakes.

Precious metal mining activities have left complex environmental legacies in lakes around the world, including some sites in climatically sensitive regions of the Canadian sub-Arctic. Here, we examined the long-term impacts of past regional gold mining activities on sub-Arctic lakes near Con Mine (Yellowknife, Northwest Territories) based on sediment core analysis (paleolimnology). In addition to receiving metal(loid)s from roaster stack emissions, the study lakes were also influenced by salt-rich mine drainage from Con Mine tailings. Water samples from these lakes had some of the highest concentrations for salinity-related variables (e.g. Ca2+, Cl-, Na+) and metal(loid)s (e.g. As, Cu, Ni, Sb) in the Yellowknife area. Furthermore, the presence of halophilic diatom (Bacillariophyceae) taxa (Achnanthes thermalis and Navicula incertata) in the recent sediments of Keg and Peg lakes suggest that the extreme saline conditions are strongly influencing the present biota, more than 10 years after the cessation of gold mining activities at Con Mine. The sedimentary metal(loid) profiles (e.g. As, Cu, Ni) of Kam Lake tracked the influence of regional gold mining activities, particularly those at Con Mine, while the algal assemblages recorded the biological responses to salinization and metal(loid) pollution (e.g. marked decreases in diatom species richness, Hill's N2 diversity, and chrysophyte cyst:diatom valve ratio). At Kam Lake, the algal assemblage changes in the post-mining era were indicative of climate-mediated changes to lake thermal properties (e.g. rise in planktonic diatoms), nutrient enrichment related to urbanization (e.g. increase in eutrophic Stephanodisucs taxa), and/or a combination of both stressors. The lack of biological recovery (i.e. return to pre-mining assemblages) is consistent with investigations of mine-impacted lakes in temperate regions where elevated contaminant levels and emerging stressors (e.g. climate warming, land-use changes) are influencing lake recovery.

Potential low-cost carbon-based adsorbent from gold mine tailings for anionic dye removal.

In this study, a mesoporous carbon (CMK-3) was successfully synthesized using mesoporous silica (SBA-15) prepared from gold mine tailings (sample CGMT) for removal of anionic dye from aqueous solution. For comparison, CMK-3 was prepared by the same method from pure silica (sample CT), and the other CMK-3 sample was prepared by a one-pot route mixing with Pluronic P123 (sample CP). The effect of the carbonization time on the synthesis of all CMK-3 samples was investigated, and the samples were characterized by X-ray diffraction and N2 adsorption-desorption. The sample with the highest surface area was chosen as an adsorbent, for each CMK-3 obtained from different methods. Batch adsorption experiments were studied to determine the influence of pH, contact time, and initial dye concentration. The adsorption kinetics obeyed the pseudo-second-order model. All carbon-based adsorbents were observed to be quite effective for the removal of dye with adsorption percentage in the order of CP > CT > CGMT. The maximum adsorption capacities were 188.99 and 204.57 mg·g-1 for CT and CGMT, respectively. The comparative results of all carbon-based adsorbents show that CGMT can be applied as a low-cost alternative to CT for dye removal.

Galvanic effect of pyrite on arsenic release from arsenopyrite dissolution in oxygen-depleted and oxygen-saturated circumneutral solutions

Arsenopyrite (FeAsS), the most common arsenic-bearing mineral, is usually found associated with pyrite (FeS2) in gold mining tailings. This work examined the galvanic effect of FeS2 on As release from FeAsS oxidation in circumneutral media under oxygen-depleted and oxygen-saturated conditions. The oxidation experiments were conducted with a flow-through reactor in the absence of FeS2 particles and in the presence of different contents of this sulfide. The results indicated that the permanent, physical contact between FeAsS and FeS2 particles causes an increase in the accumulated As release, mainly under O2-saturated conditions. At 30% wt. FeS2, the increases relatively to FeS2-free conditions were 82% and 117% in O2-depleted and O2-saturated solutions, respectively. At steady-state, the As release rates increased from (4.9 ± 0.5)× 10−4 µmol m−2 s−1 (0% wt. FeS2) to (1.1–1.9)× 10−3 µmol m−2 s−1 (5–30% wt. FeS2) under O2-saturated conditions. Analysis of FeAsS samples after oxidation revealed oxidized particles partially or entirely covered by precipitates with different sizes, shapes and compositions (e.g., As−S−bearing ferrihydrite, elemental sulfur, and As−O phases). A fine (3–4 nm thick) amorphous layer of S−As−bearing ferric oxy-hydroxide was also identified on oxidized FeAsS, with Fe(III) and As(III) species.

Distribution of Heavy Metals Fractionation in Gold Mine Tailing Amended with Non-Coated and Iron-Coated Rice Husk Ash

ABSTRACT The determination of heavy metals fractionation in the environment is necessary to predict their mobility and bioavailability. This study was carried out to evaluate the effects of rice husk ash (RHA) and iron-coated rice husk ash (Fe-RHA) on As, Cd, Cr, Cu, Mn, Pb and Zn fractionation in gold mine tailings. The tailings were amended with either 0%, 5%, 10%, and 20% (w/w) of RHA or Fe-RHA and the samples were incubated at 60% of field capacity for 80 days. The amount of metals in different fractions at different intervals was determined using a sequential extraction procedure. The results showed that the addition of RHA increased the pH of tailings. The highest pH (9.09) was recorded in samples treated with 20% RHA. However, the addition of Fe-RHA reduced the pH values at all rates and incubation period, compared to the control. The lowest pH (7.17) was recorded in samples treated with 20% Fe-RHA. Both RHA and Fe-RHA increased the easily exchangeable As in the tailings from17.564% to 25.820% at samples treated with 20% RHA and 21.070% at Fe-RHA samples but decreased the carbonate-bound and organic fractions. However, the opposite results were observed for Cd (60.940% to 43.250%), Cr (2.214% to 1.560%), Cu (3.106% to 1.312%), Mn (62.149% to 43.740%), and Zn (9.853% to 1.325%) when tailings amended with 20% RHA. The results suggest that the addition of RHA or Fe-RHA can reduce the availability of cationic heavy metals in the tailings but will increase the availability of anionic metalloids such as As.

The CO2 adsorption performance of aminosilane-modified mesoporous silicas

Aminosilane-modified MCM-41 and SBA-15 mesoporous silicas were synthesized using sodium silicate extracted from gold mine tailings slurry in this study. Pure silica source was used in the synthesis of mesoporous silica in order to compare differences in textural properties and amine loading with differences in CO2 adsorption performance. CO2 adsorption analysis of the synthesized samples was carried out at 25, 75 and 100 °C. The results showed that the aminosilane-modified MCM-41 from slurry and aminosilane-modified SBA-15 from pure silica have the highest adsorption capacities of 1.55 and 1.37 mmol g−1, respectively. As a result, it was found that the CO2 adsorption capacities of the aminosilane-modified samples were increased by increasing the amine contents and the specific surface area. From three kinetic models (pseudo-first-order, pseudo-second-order model and Avrami’s equation), Avrami model well represented the adsorption kinetic data for all adsorbents and revealed that multiple reaction pathway occurred in the CO2 adsorption. In addition, aminosilane-modified samples presented good regenerability after four adsorption–desorption cycles.

Alkaline Activation of Basic Oxygen Furnace Slag Modified Gold Mine Tailings for Building Material

The mining industry generates large quantities of waste as tailings. The tailings have an adverse environmental impact. This study explored the utilization and stabilization of Barberton gold mine tailings (GMTs) and basic oxygen furnace slag (BOFS) to synthesize geopolymers for other applications. The geochemical, chemical, and geotechnical properties of GMT, BOFS, GMT geopolymer, and GMT: BOFS geopolymer were also studied. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) were used as alkaline activators. The highest unconfined compressive strength (UCS) recorded for GMT geopolymers cured for 5 days at the elevated temperature of 90°C was 4.31 MPa and 6.59 MPa for NaOH and KOH, respectively. GMT: BOFS geopolymer attained the UCS of 20.0 MPa and 25.7 MPa, with NaOH and KOH, respectively, at the same curing conditions. Characterization of the binders showed that BOFS was a good source of calcium, which had a positive effect on the geopolymer gels by balancing the ionic charges. The developed GMT: BOFS geopolymers satisfied the minimum requirements for nonfacing building masonry as stipulated by the ASTM C34‐17a, ASTM C129‐14c 0076a, and the SANS 227: 2007 for burnt clay masonry units and can be used as a mine backfill paste and for lightweight civil applications. The geopolymers passed the toxicity characteristic leaching procedure (TCLP), and the results yielded low heavy metals concentration, indicating that the geopolymers will not leach to the environment.

Biostabilization of Gold Mine Tailings for Mitigating Fugitive Dust Emission Using Cyanobacteria

Biostabilization of Gold Mine Tailings for Mitigating Fugitive Dust Emission Using Cyanobacteria

Mineralogical and Geochemical Characterization of Gold Mining Tailings and Their Potential to Generate Acid Mine Drainage (Minas Gerais, Brazil)

For more than 30 years, sulfide gold ores were treated in metallurgic plants located in Nova Lima, Minas Gerais, Brazil, and accumulated in the Cocoruto tailings dam. Both flotation and leaching tailings from a deactivated circuit, as well as roasted and leaching tailings from an ongoing plant, were studied for their acid mine drainage potential and elements’ mobility. Detailed characterization of both tailings types indicates the presence of fine-grain size material hosting substantial amounts of sulfides that exhibit distinct geochemical and mineralogical characteristics. The samples from the ongoing plant show high grades of Fe in the form of oxides, cyanide, and sulfates. Differently, samples from the old circuit shave higher average concentrations of Al (0.88%), Ca (2.4%), Mg (0.96%), and Mn (0.17%), present as silicates and carbonates. These samples also show relics of preserved sulfides, such as pyrite and pyrrhotite. Concentrations of Zn, Cu, Au, and As are higher in the tailings of the ongoing circuit, while Cr and Hg stand out in the tailings of the deactivated circuit. Although the obtained results show that the sulfide wastes do not tend to generate acid mine drainage, leaching tests indicate the possibility of mobilization of toxic elements, namely As and Mn in the old circuit, and Sb, As, Fe, Ni, and Se in the tailings of the plant that still works. This work highlights the need for proper management and control of tailing dams even in alkaline drainage environments such as the one of the Cocoruto dam. Furthermore, strong knowledge of the tailings’ dynamics in terms of geochemistry and mineralogy would be pivotal to support long-term decisions on wastes management and disposal.

The effect of heavy metals on thiocyanate biodegradation by an autotrophic microbial consortium enriched from mine tailings

Bioremediation systems represent an environmentally sustainable approach to degrading industrially generated thiocyanate (SCN−), with low energy demand and operational costs and high efficiency and substrate specificity. However, heavy metals present in mine tailings effluent may hamper process efficiency by poisoning thiocyanate-degrading microbial consortia. Here, we experimentally tested the tolerance of an autotrophic SCN−-degrading bacterial consortium enriched from gold mine tailings for Zn, Cu, Ni, Cr, and As. All of the selected metals inhibited SCN− biodegradation to different extents, depending on concentration. At pH of 7.8 and 30 °C, complete inhibition of SCN− biodegradation by Zn, Cu, Ni, and Cr occurred at 20, 5, 10, and 6 mg L−1, respectively. Lower concentrations of these metals decreased the rate of SCN− biodegradation, with relatively long lag times. Interestingly, the microbial consortium tolerated As even at 500 mg L−1, although both the rate and extent of SCN− biodegradation were affected. Potentially, the observed As tolerance could be explained by the origin of our microbial consortium in tailings derived from As-enriched gold ore (arsenopyrite). This study highlights the importance of considering metal co-contamination in bioreactor design and operation for SCN− bioremediation at mine sites.Key points• Both the efficiency and rate of SCN−biodegradation were inhibited by heavy metals, to different degrees depending on type and concentration of metal.• The autotrophic microbial consortium was capable of tolerating high concentrations of As, potential having adapted to higher As levels derived from the tailings source.