Gold Mining Effluent Research Articles

Electrochemical Oxidation of Ammonia-Laden Wastewater in the Mining Industry

Ammonia is a common contaminant in municipalities where human waste causes nitrification of local water bodies. In mining, ammonia contamination occurs as a byproduct of biological water treatment, from the use of ammonium nitrate fuel oil in explosives, and from the exposure of ammonia rich soils during the excavation process. In particular, gold mine effluent represents a significant source of ammonia and nitrogen-based contaminants. Current biological and abiotic treatment processes are difficult to employ at the scale required at mine sites due to the high operating costs, or are limited in effectiveness due to a lack of natural resources required to facilitate the treatment. This article evaluates the use of electrooxidation as a cost effective alternative to treating ammonia-laden wastewater in mining applications. Two mixed metal oxide electrodes are assessed in this article: IrO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>/Ti and RuO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>/Ti anodes. A Monte Carlo simulation is performed to determine a probabilistic range of capital and operating expenditure for a mining operation deploying an electrooxidation wastewater treatment system. The lowest capital cost of operating the electrochemical treatment occurs at a current density of 200 A/m<inline-formula><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula>, where the number of cells required for treatment is minimized.

Mercury removal from gold mining wastewater using palm oil fuel ash (POFA)

Mercury is a harmful element that commonly accumulates in the environment through anthropogenic activities such as gold mining. This study aimed to examine the use of palm oil fuel ash (POFA) as an agricultural waste to remove mercury in gold mining wastewater. The technology applied in this study was adsorption and precipitation. POFA was first washed until neutral then mixed with gold mining effluent with time variation of 30, 60, 90 minutes. Next, precipitate it for 30 minutes. The adsorbent dose used in this study was 250 mg with 1 litre effluent. The maximum adsorption efficiency observed in this study was 96.77%. The utilization of POFA as an adsorbent reduced mercury levels in wastewater below the allowed released mercury level to the environment (0.0025 mg Hg/L). Results indicate that reducing mercury from gold mining wastewater by utilizing POFA was simple, effective, and low-cost to be implemented.

Removal of Cyanide and Other Nitrogen-Based Compounds from Gold Mine Effluents Using Moving Bed Biofilm Reactor (MBBR)

Mining operations generate effluents containing pollutants such as ammonia, nitrite and nitrate as a result of blasting operations. Cyanide compounds such as free cyanide, cyanate and thiocyanate are also present when cyanide is used in the gold recovery process. In most cases, mine effluent stored in the ponds eventually needs to be discharged to the environment; however, the levels of contaminants often exceed the discharge limits hence cannot be discharged without treatment. Several treatment solutions exist for the removal of nitrogen compounds and cyanide. Reverse osmosis is often perceived as a good solution as it produces an effluent of high quality. However, reverse osmosis also produces a brine which is recycled to the ponds, gradually increasing the total dissolved solids (TDS) in the ponds over time. Biological treatment offers an alternative to reverse osmosis with the added benefit that nitrogen compounds are fully converted to innocuous nitrogen gas, which is released to the atmosphere, thereby offering a more sustainable treatment solution. Moving Bed Biofilm Reactors (MBBR) have been used successfully at several mines. In Quebec, a two stage MBBR was installed to remove OCN, SCN and NH4-N from the effluent prior to discharge. The MBBR plant has been in operation for 4 years; operating data will be presented to show that a fully compliant non-toxic effluent is discharged under a wide range of operating conditions. In Ghana, pilot trials were conducted at a gold mine to demonstrate complete removal of nitrogen compounds including CN, NH4-N, NO2-N and NO3-N using a four- stage MBBR system. Results from both systems are presented.

Water conservation in mining industry by integrating pressure-oriented membrane processes for nitrogen-contaminated wastewater treatment: Bench and pilot-scale studies

The water footprint of mining sectors can be drastically diminished by practicing water reuse. Membrane processes can be successfully employed to such purpose, while allowing the concentration of solutes for further recovery. Despite its potentialities, the interaction between the effluents and the membrane represent key factors that impact operation and costs, and should be better understood. To this, this study assessed ultrafiltration – reverse osmosis (UF-RO) processes to the treatment of a gold mining effluent from the blasting stage, contaminated with nitrogen compounds. Both laboratory and pilot scale tests were performed. Parameters like transmembrane pressure and water recovery fraction were evaluated in terms of operational performance and economic impact. It was possible to perform a steady-operation at a recovery fraction around 80 % for RO in pilot scale, at 6 bar. Permeate quality met the standards for industrial reuse after pH adjustment, and nitrogen and ammonia were successfully concentrated. Fouling did not affect RO performance even at higher recovery fractions. Costs associated to treatment were estimated in US$ 0.488 / m3, where 55 % of expenditure was related to wastewater disposal. The system has proven to be a feasible alternative from both technical and economic standpoint, offering the potential to save around 367,000 m3/year of fresh-water. Furthermore, RO concentrate might be used for fertigation, which can drastically reduce the volume of wastewater and related costs related to its disposure.

Forward osmosis as an opportunity for acid mining effluent reuse - An assessment of concentration polarization effects on forward osmosis performance and economic aspects

ABSTRACT Forward osmosis (FO) was investigated for treating an acid gold-mining effluent. Draw solution reconcentration by reverse osmosis (RO) was simulated and the FO-RO system economically evaluated. FO presented a rejection of 92.2% for total As and >98.5% for all other ions investigated. Concentration polarization caused a severe reduction in JFO. RO could operate as an additional barrier, with rejection >99.9%. FO-RO presented an estimated capital expenditure of 2,292,444 USD. It was found that Js was more critical in reducing permeate costs than JFO. Nevertheless, the FO-RO system could generate a high-quality effluent, indicating an opportunity to water reuse.

Potensi Penggunaan Abu Terbang Cangkang Sawit sebagai Adsorben Logam Arsen dari Air Limbah Tambang

Arsenic is a dangerous compound that accumulates in nature as a result of anthropogenic activities, one of which is gold mining. Effluent originating from the remaining mining is simply abandoned even though it contains Arsenic which is above the threshold set by the Government of the Republic of Indonesia. The purpose of this study was to analyze the ability of palm shell fly ash to remove arsenic in the residual gold mining effluent. The technology applied in this study was absorption by direct mixing followed by settling and filtering. The maximum arsenic removal efficiency achieved in this study was valued at 81.98%. The longer the contact time between the palm shell fly ash and the waste sample, the less the amount of Arsenic in the waste water will be. The results of this study indicate that the method of removing arsenic from wastewater using palm shell fly ash is very effective, easy to apply and cheap in terms of the cost required.

Technical and economic potential of high-temperature NF and DCMD for gold mining effluent reclamation

Direct contact membrane distillation (DCMD) and high-temperature nanofiltration (NF) were compared in terms of technical and economic aspects for the treatment of pressure oxidation process (POX) real effluent. Tests were carried out in bench scale and differences in fouling behavior and its impacts on NF and MD performance were evaluated. High pollutants rejection rates were observed for both systems (>92.4 %). However, DCMD had better permeate quality and lower energy requirement, which contributed significantly to its lower operational costs due to use of the effluent residual heat. CAPEX and OPEX were estimated at US$/m3 2.251 for NF and US$/m3 0.233 for DCMD. DCMD application represents a saving of US$ 45,138.3 annually supplying 250,768.3 m3 of high-quality reuse water. At the end, this research allowed for a better comprehension of these membrane technologies, preventing the production of waste and increasing efficiencies in the uses of energy, water, and resources.

Pragmatic strategy for the removal of ammonia from gold mine effluents using a combination of electro-coagulation and zeolite cation exchange processes: A staged approach

Considerable amount of water is frequently used in gold mine for dust suppression and ore processing. The generated effluent mainly contains heavy metals, suspended solid and ammonia. This paper investigates the ammonia removal from mine effluent by a natural zeolite-adsorption process. Preliminary experiments showed that the fresh zeolite has a higher ammonia removal efficiency. Based on the results of adsorption isotherm, Langmuir isotherm model was found to be well fitted with the experimental data with a maximum adsorption capacity of 8.7 mg N g−1 zeolite. As the ammonia concentration in the mine effluent was not exceeding 30 mg L−1, column adsorption capacity was around 0.85 mg g−1; however, the regeneration of zeolite by 0.6 M NaCl was ineffective after third adsorption/regeneration cycle. To overcome this challenge, electrocoagulation process was introduced as a pre-treatment step to remove suspended solids and metal cations. With current density of 1.14 mA cm−2 and 20 min of reaction time, more than 90 % of suspended solid, turbidity and total metal cations were precipitated. For an optimal scenario, the adsorption capacity of zeolite increased up to 2.3 mg.g−1. Electrocoagulation for raw effluent significantly prolongs the life span of zeolite because the adsorption of trivalent metal cations on zeolite is irreversible.

Impacts of gold mine effluent on water quality in a pristine sub-Arctic river

Impacts of mining on water quality are a great concern in the Arctic region. This study evaluated the impact of pre-treated mine effluent on river water quality. The study was conducted along the Seurujoki River in sub-Arctic Finland, which is impacted by Kittilä gold mine. The study analyzed water quality and hydrological data upstream and downstream of the mining area over an eight-year period, including a tailing dam leakage event in 2015. The analysis focused on water quality determinants such as electrical conductivity (EC), sulfate, antimony, manganese, and total nitrogen (Ntotal). Descriptive statistics on river water at four stations along the river corridor showed negative impacts of mining activities on the recipient water body. In order to find an indicator for water quality, correlation analysis between the water quality determinants was carried out. It identified EC as a good indicator for continuous water quality monitoring, especially to detect mining accidents such as partial failure of a tailings dam. The results showed increasing contaminant concentrations due to mining as more mine effluent was generated over time. A linear mixed model was developed to predict the coefficient of different elements affecting EC at river water monitoring stations impacted by mining effluents. The results provide new information on how to assess mining water impacts and plan future water quality monitoring.

Sorption-desorption profile of Au(III) onto silica modified quaternary amines (SMQA) in gold mining effluent

This work aim to study sorption-desorption of Au(III) onto silica modified quaternary amines (SMQA) in gold mining effluent. Synthesis SMQA was conducted by methylation silica modified ammine (SMA) that synthesized by sol-gel process of silica gel (SG) from rice hull ash and APTMS. Characterizations this material by FT-IR, XRD, SEM-EDS and GSA analyzer show that the material has characteristic parameter of SMQA. Sorption study of sorption Au(III) on SMQA was carried out by batch system with optimum pH 5. Sorption capacity was 74.47 mg/g (Langmuir) with 24 kJ/mole sorption energy (electrostatic interaction). Kinetics sorption studies by Lagergren, Ho, and RBS models shows that the sorption Au(III) in this research have the suitable condition with RBS models. Sorption study reveal that –N+(CH3)3 is the most responsible site for Au(III) sorption. Desorbed Au(III) in batch system using Na2S2O3, SC(NH2)2, and KSCN as desorption agent in HCl solution was there are no significant different value (Na2S2O3 = 94.2 %; SC(NH2)2 = 95.2 %; KSCN = 95.2 %). However, for safer eluent it was recommend to use Na2S2O3 or SC(NH2)2. The reusability of SMQA was four times sorption-desorption cycle before at fifth cycle desorbed Au(III) was decreased. The application of SMQA in gold mining effluent by column system (SPE) sample in Sarolangun, Jambi, Indonesia shows that recovered Au(III) was 0.000593 % in 2 g sample.

Effect of the electrocoagulation process on the toxicity of gold mine effluents: A comparative assessment of Daphnia magna and Daphnia pulex

Mine effluents must meet discharge criteria for both physicochemical parameters and toxicity. While chemical precipitation is efficient for the treatment of metallic elements in mine effluents, the removal of sulfates, as a source of salinity and potential toxicity, is limited by gypsum solubility. This study evaluated the efficiency of electrocoagulation (EC), an emerging process to treat mine water, in removing sulfates and acute toxicity in two gold mine effluents (E1 and E2), before and after treatment (Fe-electrodes, 30 min at 20 mA/cm2, and pH near neutrality). Standard toxicity tests were conducted on two daphnia species, Daphnia magna (standard test species) and Daphnia pulex (more common in cold climate). Four uncontaminated surface waters (S#1 to S#4), which originated from different watershed lithologies, were also used as dilution media with E1 to assess water quality effect on toxicity response. Statistical analyses using the Student’s t-test showed no significant difference in immobility or mortality caused by surface waters on either D. magna or D. pulex species (p > 0.05). However, higher toxicity was observed with both daphnia when reconstituted hard water was used for testing of the treated effluent E2. The present study highlights the toxicity effect added by EC despite a sulfates-related salinity decrease of >7.5%. Further research should identify and confirm the potential sources of observed toxicity.

Determination and detoxification of cyanide in gold mine tailings: A review.

Cyanide is among the most toxic chemicals widely employed in the cyanidation process to leach precious minerals, such as gold and silver, by the minerals processing companies worldwide. This present article reviews the determination and detoxification of cyanide found in gold mine tailings. Most of the cyanide remains in the solution or the slurries after the cyanidation process. The cyanide species in the gold tailings are classified as free cyanide, weak acid dissociation, and metallocyanide complexes. Several methods, such as colorimetric, titrimetric, and electrochemical, have been developed to determine cyanide concentrations in gold mine effluents. Application of physical, natural, biological, and chemical methods to detoxify cyanide to a permissible limit (50 mg L-1) can be achieved when the chemical compositions of cyanide (type of species) present in the tailings are known. The levels of cyanide concentration determine the impact it will have on the environment.

Key Microbes and Metabolic Potentials Contributing to Cyanide Biodegradation in Stirred-Tank Bioreactors Treating Gold Mining Effluent

ABSTRACT Microbial community and metabolic potential changes in a biological wastewater treatment reactor were investigated using phylogenetic and functional profile analysis from 16S rRNA-gene-based pyrosequencing. Stirred-tank bioreactors fed by cyanide-containing synthetic solutions were inoculated with a sewage sludge and the cyanide-degrading microbial consortium. A better cyanide degradation was observed in the reactors containing the phylum Proteobacteria, but lower efficiency was observed when Firmicutes and Bacteroidetes were dominant. This study shows the important role of phylum Proteobacteria for the cyanide-containing wastewater treatment in the gold processing plant and contributes the fundamentals about the microbial community exposed to the cyanide.

Comparison of Nanofiltration and Direct Contact Membrane Distillation as an alternative for gold mining effluent reclamation

Effluent reuse is becoming an environmentally-economically viable option for industries that have been struggling with environmental/legislative pressure and high costs of water supply and effluents discharge. Mining effluents are promising for reuse, but for this, (hazardous) metals and ions such as sulfate must be removed efficiently. This study aimed to compare the technical-economic performance of Nanofiltration (NF) and Direct Contact Membrane Distillation (DCMD) on gold mining effluent treatment. The results showed that both technologies are promising for mining effluent reclamation as high pollutants removal rates were observed (rejection >73% and >96% for NF and DCMD, respectively). DCMD showed lower flux than NF and was limited to operate up to permeate recovery rate (RR) of 40% due to severe fouling (CaSO4 precipitation), but produced a higher quality permeate with no reuse restriction, low energy requirement and lower associated costs due to use of the effluent residual heat. Capex and Opex (for membrane lifespan of 1–5 years) were estimated at US$ 575,490.30 and 2.00–2.10 US$/m3 for NF and US$ 305,483.85 and 0.13 to 0.27 US$/m3 for DCMD systems. The permeate reuse would reduce water consumption in 490,560 m3 year−1, which represents almost 50% of the industrial water demand.

Influence of ferric iron source on ferrate’s performance and residual contamination during the treatment of gold mine effluents

Ferrate [Fe(VI)] is increasingly used for the treatment of several contaminants in drinking water and municipal/industrial waste water. Recent findings also show that Fe(VI) is a promising alternative for the treatment of gold mine effluents contaminated by cyanides (CN−), thiocyanates (SCN−), and ammonia nitrogen (NH3-N). However, the ferric [Fe(III)] salt used in Fe(VI) synthesis could affect this alternative’s efficiency and costs, as well as residual contaminants in the treated effluent. The objective of this study was to evaluate the influence of three Fe(III) salts on the performance of Fe(VI) in the treatment of gold mine effluents and the residual contaminants produced in the process. To do so, the performance of wet Fe(VI) synthesized with ferric nitrate [Fe(NO3)3], ferric chloride (FeCl3), or ferric sulfate [Fe2(SO4)3] was evaluated for the treatment of a real gold mine effluent, with final adjustment of pH at ∼7. The results showed that for the effluents treated with Fe(VI) synthesized in the presence of Fe(NO3)3, the final NO3− concentrations were 4 times higher relative to those in the treated effluents with Fe(VI) synthesized from either FeCl3 or Fe2(SO4)3. The use of Fe2(SO4)3 in the wet Fe(VI) preparation did not entail a significant increase of the final SO42− concentrations, which were very similar to initial ones (1220 vs. 1012 mg/L). At the same time, Fe(VI) synthesized from Fe2(SO4)3 was the only one to remove the CN− and NH3-N almost totally (∼99%). Finally, the production yield of Fe(VI) with FeCl3 was lower than Fe2(SO4)3 or Fe(NO3)3 (3400 vs. 5500 and 5635 mg/L, respectively). This low yield production of Fe(VI) from FeCl3 entails more costly production costs. Thus, Fe2(SO4)3 is potentially the most appropriate Fe(III) salt source for Fe(VI) synthesis for use in the treatment of contaminated mine effluents.

Integrated UF–NF–RO route for gold mining effluent treatment: From bench-scale to pilot-scale

This study focused on the performance of an UF–NF–RO integrated system treating a gold mining effluent from the pressure-oxidation stage in order to concentrate metals, and recover acid and water. Aspects such as the most suitable cross-flow velocity, cleaning procedure, and water recovery fraction were evaluated. For cross-flow velocities, a threshold value of 1.5 × 10−2 m/s was found for NF and RO stages. Besides, the system had its best performance while operating at recovery fractions of 90%, 40–50%, and 50% for UF, NF, and RO, respectively. Concentration factors of 2.0 and 2.7 were found in metals from the NF retentate and sulfuric acid from the RO retentate respectively. For cleaning purposes, hydrochloric and oxalic acid demonstrated the best cost-benefit. A long-term operation inside the mining company was assessed and the results confirmed that NF and RO association allowed for the recovery of a purified acid stream, which may be reused in the ore processing; the production of a metal enriched stream, that can be transferred to a subsequent metal recovery stage; and the generation of high quality reuse water. The total cost of the proposed route was US$ 1.137/m3 of effluent, including UF and NF concentrate neutralisation.

Integration of two-stage nanofiltration with arsenic and calcium intermediate chemical precipitation for gold mining effluent treatment

ABSTRACTThe aim of this study was to evaluate an innovative treatment route for gold-mining effluents rich in calcium, arsenic, and sulfate. This treatment route comprised two nanofiltration (NF) stages and a two-step intermediate precipitation. Arsenic and iron coprecipitation (first step) and calcium carbonate precipitation (second step) were assessed aiming to treat the first-stage NF concentrate and increase the permeate recovery rate in a second-stage NF. The pH, the molar ratio of Fe/As (first step), and the molar ratio of CO3/Ca (second step) were optimized by using rotational central composite design. Under optimal conditions, the arsenic removal was 99.8% (at pH = 7.0 and Fe/As = 4.0), and the calcium removal was 99.5% (at pH 11.5 and CO3/Ca = 3.5). The supernatant of Ca precipitation had very basic pH and had to be acidified before the second-stage NF. The pH 8.5 proved to be the best one regarding retention efficiency and flux. The flux decay of the second-stage NF was attributed to both osmotic pressure increase and reversible fouling resistance. It was concluded that the proposed treatment system is efficient for the treatment of gold-mining wastewater, ensuring higher production of treated effluent and an easy disposable of the final concentrate.

Nanofiltration applied in gold mining effluent treatment: Evaluation of chemical cleaning and membrane stability

The objectives of this study were (1) to determine the best conditions of chemical cleaning of a nanofiltration (NF) membrane (NF90) employed in the treatment of gold mining effluent, and (2) to investigate the effects of continuous exposure to mining effluent and an acid cleaning agent on NF characteristics. NF fouling was mainly due to inorganic species, and calcium sulfate (CaSO4·0.5H2O) was identified over membrane surface. Therefore, acid solutions were the most efficient in membrane cleaning, and among them hydrochloric acid (HCl) showed the best performance. Cleaning without recirculation (soak) was not effective and thus 90-min recirculation was chosen as the best cleaning procedure. The NF membrane was exposed to the effluent and to the combined effluent and HCl solution for 285days. Modifications in hydrophobicity, effective pore radius, fouling, and surface charge were observed. The retention of magnesium sulfate and glucose by the membrane exposed to the combined effluent and cleaning solution was statistically lower, what endorses the importance of cleaning conditions optimization. No indication of degradation of the polymeric material of the membrane was observed. Thus, the results of this study are promising and demonstrate the robustness of NF technology for gold mining effluent treatment.

Integrated ultrafiltration-nanofiltration membrane processes applied to the treatment of gold mining effluent: Influence of feed pH and temperature

ABSTRACTThis study aimed to evaluate the effect of feed pH (2.2 - original effluent pH – up to 6.0) and temperature (20 up to 40°C) on the performance of integrated ultrafiltration (UF) and nanofiltration (NF) applied to gold mining effluent. pH increase led to a significant decrease in UF permeate flux. NF showed high retention efficiencies of ions when temperature was below 30°C. Retention of high-valence counter-ions to balance the charge of retained co-ions seemed to be the strongest NF mechanisms. Process performance at feed pH of 5.0 was superior in terms of fouling, retention efficiency, and investment cost.

NANOFILTRATION AND REVERSE OSMOSIS APPLIED TO GOLD MINING EFFLUENT TREATMENT AND REUSE

Abstract - Gold mining and ore processing are activities of great economic importance. However, they are related to generation of extremely polluted effluents containing high concentrations of heavy metals and low pH. This study aims to evaluate the optimal conditions for gold mining effluent treatment by crossflow membrane filtration regarding the following variables: nanofiltration (NF) and reverse osmosis (RO) membrane types, feed pH and permeate recovery rate. It was observed that retention efficiencies of NF90 were similar to those of RO membranes though permeate fluxes obtained were 7-fold higher. The optimum pH value was found to be 5.0, which resulted in higher permeate flux and lower fouling formation. At a recovery rate above 40% there was a significant decrease in permeate quality, so this was chosen as the maximum recovery rate for the proposed system. We conclude that NF is a suitable treatment for gold mining effluent at an estimated cost of US$ 0.83/m³. Keywords : Gold mining effluent treatment; Nanofiltration (NF); Reverse Osmosis (RO); Feed pH; Permeate recovery rate.