Mine Process Water Research Articles

Removal of arsenic from alkaline process waters of gold cyanidation by use of Fe3O4@SiO2@TiO2 nanosorbents

In this paper, the use of titania functionalised magnetic nanosorbents for rapid removal of arsenic from the alkaline process waters of gold cyanide leaching systems is considered. The Fe3O4@SiO2@TiO2 nanosorbent synthesised via a two-stage hydrolytic process was characterised by scanning electron microscopy - energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), use of a superconducting quantum interference device (SQUID) and Brunauer-Emmett-Teller (BET) specific area methods. Batch adsorption tests showed that both As(III) and As(V) could be adsorbed onto the surface of nanosorbent in around 4h, with the maximum adsorption capacity of 31.4mg/g and 10.2mg/g for As(III) and As(V), respectively, at pH 9. As demonstrated in competitive adsorption tests, the Fe3O4@SiO2@TiO2 nanosorbent performed well in simulated solutions of gold mining process waters with high ionic strengths and complex matrices, presenting a 21.3mg/g integrated adsorption capacity for As(III) and As(V). The loss in capacity of the Fe3O4@SiO2@TiO2 nanosorbent after four consecutive adsorption-regeneration cycles was less than 40%. On the whole, the good arsenic adsorption capacity, easy preparation and magnetic separability coupled with reusability make it a potentially attractive material for the removal of arsenic from gold cyanidation process waters.

Initial environmental impacts of the Obed Mountain coal mine process water spill into the Athabasca River (Alberta, Canada)

On October 31, 2013, a catastrophic release of approximately 670,000m3 of coal process water occurred as the result of the failure of the wall of a post-processing settling pond at the Obed Mountain Mine near Hinton, Alberta. A highly turbid plume entered the Athabasca River approximately 20km from the mine, markedly altering the chemical composition of the Athabasca River as it flowed downstream. The released plume traveled approximately 1100km downstream to the Peace-Athabasca Delta in approximately four weeks, and was tracked both visually and using real-time measures of river water turbidity within the Athabasca River. The plume initially contained high concentrations of nutrients (nitrogen and phosphorus), metals, and polycyclic aromatic hydrocarbons (PAHs); some Canadian Council of Ministers of the Environmental (CCME) Guidelines were exceeded in the initial days after the spill. Subsequent characterization of the source material revealed elevated concentrations of both metals (arsenic, lead, mercury, selenium, and zinc) and PAHs (acenaphthene, fluorene, naphthalene, phenanthrene, and pyrene). While toxicity testing using the released material indicated a relatively low or short-lived acute risk to the aquatic environment, some of the water quality and sediment quality variables are known carcinogens and have the potential to exert negative long-term impacts.

The use of poly(vinylidenefluoride-co-hexafluoropropylene) for the preparation of polymer inclusion membranes. Application to the extraction of thiocyanate

Abstract The successful use of the solvent evaporation casting technique for the preparation of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) based polymer inclusion membranes (PIMs) is described for the first time. PIMs consisting of 70 wt% PVDF-HFP as the base polymer and 30 wt% Aliquat 336 as the carrier were prepared by the solvent evaporation casting and phase inversion techniques from solutions of the membrane components in tetrahydrofuran (THF) and N,N-dimethylformamide. These PIMs were compared in terms of their ability to extract the thiocyanate anion as a model target chemical species whose removal from gold mining process and tailings waters is of considerable technological and environmental interest. Best results were achieved with the PIMs produced by solvent evaporation from THF solutions. These membranes were translucent, flexible and homogeneous. Scanning electron microscopy images did not reveal the presence of a pore structure. The 30 wt% Aliquat 336 PVDF-HFP-based PIMs also exhibited significantly higher extraction and back-extraction rates for SCN− and long-term stability compared to PVC-based PIMs containing the same Aliquat 336 concentration. The results obtained in this study indicate that the use of PVDF-HFP as the base polymer in PIMs, prepared by conventional solvent evaporation casting, improves their performance in comparison to PIMs with traditionally used polymers such as poly(vinyl chloride) (PVC) and cellulose triacetate (CTA).

Use of Electrocoagulation with Aluminum Electrodes to Reduce Hardness in Tunisian Phosphate Mining Process Water

This study evaluated electrocoagulation using Al electrodes for removal of non-carbonate hardness in phosphate mining process water. Examination of process parameters identified optimal conditions for hardness removal at pH 7, a NaCl concentration of 4 g/L, a current density of 22.2 mA/cm2, an inter-electrode distance of 2 cm, a stirring speed of 450 revolutions per minute, and a treatment time of 30 min. Production of primary coagulant during electrolysis improved removal of both calcite and magnesium hydroxide. The optimized hardness removal was highly efficient, with an overall removal rate of 83.8 % at 30 min of retention time.

Advanced material and approach for metal ions removal from aqueous solutions.

A Novel approach to remove metals from aqueous solutions has been developed. The method is based on a resin free, solid, non-toxic, microcrystalline bisphosphonate material, which has very low solubility in water (59 mg/l to ion free Milli-Q water and 13 mg/l to 3.5% NaCl solution). The material has been produced almost quantitatively on a 1 kg scale (it has been prepared also on a pilot scale, ca. 7 kg) and tested successfully for its ability to collect metal cations from different sources, such as ground water and mining process waters. Not only was this material highly efficient at collecting several metal ions out of solution it also proved to be regenerable and reusable over a number of adsorption/desorption, which is crucial for environmental friendliness. This material has several advantages compared to the currently used approaches, such as no need for any precipitation step.

Electricity generation from tetrathionate in microbial fuel cells by acidophiles

Inorganic sulfur compounds, such as tetrathionate, are often present in mining process and waste waters. The biodegradation of tetrathionate was studied under acidic conditions in aerobic batch cultivations and in anaerobic anodes of two-chamber flow-through microbial fuel cells (MFCs). All four cultures originating from biohydrometallurgical process waters from multimetal ore heap bioleaching oxidized tetrathionate aerobically at pH below 3 with sulfate as the main soluble metabolite. In addition, all cultures generated electricity from tetrathionate in MFCs at pH below 2.5 with ferric iron as the terminal cathodic electron acceptor. The maximum current and power densities during MFC operation and in the performance analysis were 79.6mAm−2 and 13.9mWm−2 and 433mAm−2 and 17.6mWm−2, respectively. However, the low coulombic efficiency (below 5%) indicates that most of the electrons were directed to other processes, such as aerobic oxidation of tetrathionate and unmeasured intermediates. The microbial community analysis revealed that the dominant species both in the anolyte and on the anode electrode surface of the MFCs were Acidithiobacillus spp. and Ferroplasma spp. This study provides a proof of concept that tetrathionate serves as electron donor for biological electricity production in the pH range of 1.2–2.5.

Industrial products and wastes as adsorbents for sulphate and chloride removal from synthetic alkaline solution and mine process water

Abstract Two limestones and two solid wastes were tested as adsorbents for chloride and sulphate ion removal from synthetic and real alkaline process mining water. The composition and surface structure of the adsorbents were analysed by ED-XRF, XRD, SEM and MIR spectroscopy and the nitrogen adsorption method. The optimal adsorption time and amount of adsorbent were determined by batch analysis with an anion concentration of 20 mg/L. In synthetic solution adsorbents removed 99% of SO42− and 96% of Cl− and in real process water the removal rate was 85% and 74% for SO42− and Cl−, respectively. It was found that equilibrium could successfully be fitted to the Langmuir, Toth and BiLangmuir adsorption isotherms.

Reduction and Complexation of Copper in a Novel Bioreduction System Developed to Recover Base Metals from Mine Process Waters

An integrated bio-processing scheme was devised and tested in the laboratory for recovering copper, or other base metals, from pregnant leach solutions (PLS) using a two-step process involving both iron-reduction, and sulfate-reduction for H2S generation and sulfide precipitation, as a potential alternative to conventional SX-EW. Reduction of ferric iron in the PLS was achieved using iron-reducingAcidithiobacillusspp. andSulfobacillus thermosulfidooxidansin column reactors containing elemental sulfur as electron donor. Analysis of the column reactor effluents showed not only that most of the ferric iron was reduced to ferrous, but also that all of the copper (II) had been reduced to copper (I), i.e. cuprous copper. This copper (I) appeared to be complexed as it was not oxidized when exposed to ferric iron nor precipitated as a copper-sulfide when exposed to either sodium sulfide or H2S. The data suggested that copper (II) was reduced and the resulting copper (I) complexed, with both reactions probably mediated by sulfur oxy-anions produced indirectly by the bacteria, in the anoxic sulfur column bioreactors. It was also noted that copper (I) produced chemically by reduction of copper (II) by hydroxylamine was more toxic to axenic cultures ofAcidithiobacillusspp. andSb. thermosulfidooxidansthan was the copper (I) in the column effluent liquors.

Investigation of hydrogeochemical processes in groundwater resources located in the vicinity of a mine process water dam

The study aims to identify and describe the dominant hydrogeochemical processes and their contribution to the overall groundwater quality of an aquifer situated in the vicinity of a mine process water dam. The study site is located in a typical Karoo Basin of Southern Africa. Groundwater samples were collected from a network of boreholes designed to monitor the migration of contamination from the mine process water dam during a five year period from November 2007 to November 2011. The study utilises the expanded Durov diagram, bivariate plots and correlation coefficients statistics to analyse groundwater chemistry data. Based on analyses of the groundwater chemistry the study area was divided into two hydrogeochemical zones; the fresh background and contaminated groundwater. Fresh water in the background aquifer is characterised by a Na+–HCO3- hydrochemical groundwater type. Groundwater in the contaminated zone comprises of Mg2+–Cl− and Na+–Cl−, two main hydrochemical water types. High levels of EC and TDS that ranges from 63.10 to 1870mS/m and 690–11443mg/l respectively were measured in the contaminated groundwater indicating that the aquifer has been affected by saline water from the dam. Major ions of Mg2+, SO42- and Ca2+ measured in the contaminated portion of the aquifer are positively correlated to the conservative Cl− indicating that these ions were derived from the same saline source (dam). The study identified albite dissolution as the main hydrogeochemical process responsible for the evolution of fresh groundwater chemistry in the background aquifer. The aquifer on the down gradient of the process water dam is contaminated by saline water that evolved from the dam. There is evidence to show that the mine process water dam poses a serious threat of contaminating the groundwater with salts. A recommendation was therefore made to the responsible authorities to consider decommissioning of the facility given that the mine operations ceased some years back.

New microbiological strategies that enable the selective recovery and recycling of metals from acid mine drainage and mine process waters

AbstractApproaches currently used for remediating acid mine drainage (chiefly active chemical treatment and passive bioremediation systems) have a number of major detractions, including their failure to recover potentially valuable metals from these waters. Bioremediation strategies that utilize reactor-housed microorganisms can circumvent this problem, but have tended not to be widely used due to their relatively high costs. We have devised innovative approaches for remediating mine waters that use acidophilic bacteria to remove metals either as oxidized or reduced phases, using modular bioreactors that are designed to operate at minimal cost and to generate products that have commercial value. A composite system is described that combines microbial oxidation of ferrous iron with abiotic precipitation of ferric iron as schwertmannite, a mineral that has commercial value as an absorbent of arsenate and other environmental pollutants, and as a pigment. Sulfidogenic bioreactors maintained at acidic pH values are used to selectively precipitate metal sulfides, such as CuS. Tests with synthetic mine drainage containing mixtures of soluble metals confirmed that these systems can generate relatively pure mineral deposits from complex acid waters. The units are designed to be configured differently, according to the nature of the mine water requiring treatment.

Highly treated mine waters may require major ion addition before environmental release

Mining operations often use passive and/or active water treatments to improve water quality prior to environmental release. Key considerations in choosing a treatment process include the extent to which the water quality is actually improved, and the potential residual environmental risks of the release of such water. However, there are few published studies concerning the environmental impacts of treated waste waters. This study used toxicity identification evaluation (TIE) methods to quantify and identify the “toxic” constituents of a highly-treated water (distillate) produced by brine concentration of a mining process water. Exposure of five freshwater species (Chlorella sp., Lemna aequinoctialis, Hydra viridissima, Moinodaphnia macleayi and Mogurnda mogurnda) to a concentration range of the distillate (0, 25, 50 and 100%) found that it was toxic to H. viridissima (50–100% effect when exposed to 100% distillate). TIE tests demonstrated that the effect wasn't due to residual ammonia (~1mgL−1N) or trace organics, and unlikely to be due to manganese (Mn; 130–230μgL−1). Conversely, addition of 0.2 and 0.5mgL−1 calcium improved the growth rate of H. viridissima by 61 and 66%, respectively, while addition of calcium, sodium and potassium (0.5, 1.0 and 0.4mgL−1, respectively) to levels comparable to that in the local aquatic environment resulted in 100% recovery. Further assessment on the likelihood of residual metal toxicity indicated that Mn concentrations in the distillate were at levels that could inhibit the growth of H. viridissima. Ultimately, the results demonstrated that ion deficiency should be considered as a potential stressor in risk/impact assessments of the discharge of treated wastewaters, and these may need to be supplemented with the deficient ions to reduce environmental impacts. The findings have highlighted the need for water managers to consider the possibility of unintended environmental risks from the discharge of highly-treated wastewaters.

Treatment of wet peat mining process water with acrotelm peat

Mechanical dewatering of wet mined peat produced peat mining process water (PMPW) with low pH (5.49) and high total suspended solids (TSS 432 mg L−1), Al (1.39 mg L−1), Fe (4.36 mg L−1), Hg (37.1 ng L−1), MeHg (0.485 ng L−1), Zn (55 μg L−1), total nitrogen (TN 7.92 mg L−1), total phosphorus (TP 303 μg L−1) and true colour (532 TCU). High removal efficiencies were calculated for acrotelm peat filters (mesocosms) used to treat PMPW (TSS 45–83%; particulate organic carbon (POC) 47–89%; metals 53–100%; TN 85%; TP 81%), though final mesocosm leachate concentrations did not all achieve Canadian Water Quality Guidelines. In one study, mesocosm leachate had higher colour and dissolved organic carbon (DOC) concentrations than PMPW. Our mesocosm studies suggest an initial reduction in PMPW solids be considered by industry before peatlands are used as treatment systems.

Low temperature removal of inorganic sulfur compounds from mining process waters

Process water and effluents from mining operations treating sulfide rich ores often contain considerable concentrations of metastable inorganic sulfur compounds such as thiosulfate and tetrathionate. These species may cause environmental problems if released to downstream recipients due to oxidation to sulfuric acid catalyzed by acidophilic microorganisms. Molecular phylogenic analysis of the tailings pond and recipient streams identified psychrotolerant and mesophilic inorganic sulfur compound oxidizing microorganisms. This suggested year round thiosalt oxidation occurs. Mining process waters may also contain inhibiting substances such as thiocyanate from cyanidation plants. However, toxicity experiments suggested their expected concentrations would not inhibit thiosalt oxidation by Acidithiobacillus ferrivorans SS3. A mixed culture from a permanently cold (4-6 °C) low pH environment was tested for thiosalt removal in a reactor design including a biogenerator and a main reactor containing a biofilm carrier. The biogenerator and main reactors were successively reduced in temperature to 5-6 °C when 43.8% of the chemical oxidation demand was removed. However, it was found that the oxidation of thiosulfate was not fully completed to sulfate since low residual concentrations of tetrathionate and trithionate were found in the discharge. This study has demonstrated the potential of using biotechnological solutions to remove inorganic sulfur compounds at 6°C and thus, reduce the impact of mining on the environment.

Isotopic disequilibrium during uptake of atmospheric CO2 into mine process waters: implications for CO2 sequestration.

Dypingite, a hydrated Mg-carbonate mineral, was precipitated from high-pH, high salinity solutions to investigate controls on carbon fixation and to identify the isotopic characteristics of mineral sequestration in mine tailings. δ(13)C values of dissolved inorganic carbon content and synthetic dypingite are significantly more negative than those predicted for equilibrium exchange of CO(2) gas between the atmosphere and solution. The measured δ(13)C of aqueous carbonate species is consistent with a kinetic fractionation that results from a slow diffusion of atmospheric CO(2) into solution. During dypingite precipitation, dissolved inorganic carbon concentrations decrease and δ(13)C values become more negative, indicating that the rate of CO(2) uptake into solution was outpaced by the rate of carbon fixation within the precipitate. This implies that CO(2) gas uptake is rate-limiting to CO(2) fixation. δ(13)C of carbonate mineral precipitates in mine tailings and of DIC in mine process waters display similar (13)C-depletions that are inconsistent with equilibrium fractionation. Thus, the rate of carbon fixation in mine tailings may also be limited by supply of CO(2). Carbon sequestration could be accelerated by increasing the partial pressure of CO(2) in tailings ponds or by using chemicals that enhance the uptake of gaseous CO(2) into aqueous solution.

Hydrotalcite Formation for Contaminant Removal from Ranger Mine Process Water

Process water from the Ranger Uranium Mine requires treatment to meet stringent environmental water quality criteria. The acidic water contains substantial SO4, metals, and U. One novel treatment method under consideration is the use of Na-aluminate to both neutralise the process water and precipitate hydrotalcites. Hydrotalcites are a class of Mg–Al layered double hydroxide minerals with a typical endmember chemical composition: Mg6Al2(A)(OH)16·n(H2O), where A = CO3 2−, SO4 2−, etc. Many acidic wastewaters contain Mg and/or Al in sufficient abundance for hydrotalcite formation upon addition of alkali to achieve solution pH > 5, and Mg and/or Al to attain a Mg:Al ratio of 2 to 3:1. The utility of hydrotalcites lies in their ability to incorporate a range of cationic (Cu2+, UO2 2+), metalloid (AsO4 3−), and (oxy)anionic contaminants (CrO4 2−). The broad spectrum removal of contaminants, including U, also indicates that hydrotalcites and their derivatives could potentially be used as a containment material in nuclear waste repositories. In this study, Ranger process water derived from extraction of U from chloritic schist was treated with Na-aluminate sourced from Bayer process liquor, in combination with NaOH or Ca(OH)2. Hydrotalcites formed as the primary mineral during process water neutralisation with the ability to simultaneously remove a suite of contaminants from solution.

Sulfate Reduction at pH 5 in a High-Rate Membrane Bioreactor: Reactor Performance and Microbial Community Analyses

High rate sulfate reduction under acidic conditions opens possibilities for new process flow sheets that allow the selective recovery of metals from mining and metallurgical waste and process water. However, knowledge about high-rate sulfate reduction under acidic conditions is limited. This paper investigates sulfate reduction in a membrane bioreactor at a controlled pH of 5. Sulfate and formate were dosed using a pH-auxostat system while formate was converted into hydrogen, which was used for sulfate reduction. Sulfide was removed from the gas phase to prevent sulfide inhibition. This study shows a high-rate sulfate-reducing bioreactor system for the first time at pH 5, with a volumetric activity of 188mmol SO(4)(2-)/I/d and a specific activity of 81mmol SO(4)(2-) volatile suspended. The microbial community at the end of the reactor run consisted of a diverse mixed population including sulfate-reducing bacteria.

Biodegradation of cyanide containing effluents by Scenedesmus obliquus

Biological degradation of cyanide has been shown a viable and robust process for degrading cyanide in mining process wastewaters. Several algal cultures can effectively degrade cyanide as carbon and/or nitrogen source for their growth. In this study, cyanide effluent degradation by Scenedesmus obliquus was examined. Gold mill effluents containing WAD cyanide concentration of 77.9 mg/L was fed to batch unit to examine the ability of S. obliquus for degrading cyanide. Cyanide was reduced down to 6 mg/L in 77 h. Microbial growth and metal uptake of Zn, Fe and Cu was examined during cyanide degradation. The cells well adapted to high pH and the effluent contained cyanide and the metals. It is important that Zn level reduced down 50%, of the starting concentration. pH was kept at 10.3 to prevent loss of cyanide as HCN, due its volatile nature. The bio treatment process was considered to be successful in degrading cyanide in the mine process water.

Sulfate Reduction under Acidic Conditions in High Rate Bioreactor Systems for Treatment of Mining and Metallurgical Waste and Process Water

Sulfate Reduction under Acidic Conditions in High Rate Bioreactor Systems for Treatment of Mining and Metallurgical Waste and Process Water

Optimum deposition for sub-aerial tailings disposal: model applications

Large volumes of the tailings produced as a result of mineral and energy production are disposed of on the Earth's surface. A major concern of mining operations is how to minimize the environmental impact and reduce the storage volume of tailings. In addition, pressure to optimally use scarce water resources, especially in arid regions, is critical. Maximum recycle and reuse of mine process waters is thus an important consideration. The sub-aerial deposition technique is a promising approach for dealing with these problems. Although it has existed for decades, its use still involves many technical challenges. Among these, an important concern is the selection of the optimum depositional parameters to achieve the desired results. A rational method for evaluating the optimum depositional design parameters for sub-aerial tailings disposal is proposed. The optimum deposition design method using the DOSTAR model is presented along with field performances at two operating mines. The comparisons between the predicted results and field observations demonstrate excellent agreement.

English

There are many mature Cu heap leach facilities in the western United States that will face closure in the next decade. However, there is little published information on the response of groundwater systems to the cessation of leaching. Copper dump leaching was conducted on the Bingham Canyon Eastside waste rock dumps between 1963 and 2000. Leach water discharging from the toe of the waste rock dumps had a typical pH of 2.9 and a total dissolved solids concentration of about 90,000 mg/L. During active leaching this water was recirculated, but now it is neutralized as it enters the mine's tailings and process water circuit. With the end of leach water application, average annual flows discharging from the toe of the dumps have declined rapidly from 1500 L/s in 1998 to approximately 45 L/s in 2004. Average acidity in water discharging from the toe of the dumps declined by almost thirty percent between 2000 and 2005, and since 2003, most solute concentrations have declined by about ten percent. The only exception is Cu concentration which has increased by a factor of four since 2000. Water quality in the underlying saturated bedrock has also begun to improve. Since 2000, sulfate concentrations have declined by a third, alkalinity has increased, and Cu and Zn concentrations have declined by up to ninety percent in water from tunnels that receive at least a portion of their inflows from beneath the waste rock footprint. Water quality in bedrock and alluvium down gradient of the dump toe began to improve after the leach water collection system was upgraded between 1994 and 1996. Arithmetic mean sulfate concentrations in down gradient alluvial monitoring wells declined from a high of 6000 mg/L in 1994 to less than 1000 mg/L in early 2004. These data illustrate how the groundwater system responds to the termination of waste rock and heap leach operations and may provide a useful analogue for the closure of other Cu heap leach operations.