Oxidation of cyanide in effluents by Caro’s Acid

Caro’s Acid (peroxymonosulphuric acid: H₂SO₅) is a powerful liquid oxidant made from hydrogen peroxide that has been adopted for the detoxification of effluents containing cyanides in gold extraction plants in recent years.The present work reports the findings of a study on the kinetics of aqueous cyanide oxidation with Caro’s Acid. Experiments were conducted in batch mode using synthetic solutions of free cyanide. The experimental methodology employed involved a sequence of two 2³ factorial designs using three factors: initial [CN⁻]: 100–400 mg/L; H₂SO₅:CN⁻ molar ratio: 1–1.5–3–4.5; pH: 9–11; each one conducted at one level of Caro’s Acid strength which is obtained with the H₂SO₄:H₂O₂ molar ratio used in Caro’s Acid preparation of 3:1 and 1:1. The objective was the evaluation of the effect of those factors on the reaction kinetics at room temperature. Statistical analysis showed that the three investigated variables were found to be significant, with the variables which affected the most being the initial [CN⁻] and the H₂SO₅:CN⁻ molar ratio. The highest reaction rates were obtained for the following conditions: H₂SO₅:CN⁻ molar ratio = 4.5:1; pH = 9; and Caro’s Acid strength produced from the mixture of 3 mol of H₂SO₄ with 1 mol of H₂O₂. These conditions led to a reduction of [CN⁻] from an initial value of 400 mg/L to [CN⁻] = 1.0 mg/L after 10 min of batch reaction time at room temperature. An empirical kinetic model incorporating the weight of the contributions and the interrelation of the relevant process variables has been derived as: −d[CN⁻]/dt = k [CN⁻]^1.8 [H₂SO₅]^1.1 [H⁺]^0.06, with k = 3.8 (±2.7) × 10⁻⁶ L/mg min, at 25 °C.     

Biological treatment of cyanide by natural isolated bacteria (Pseudomonas sp.)

Biological treatment is a proven process for the treatment of mining effluents such as tailings, wastewaters, acidic mine drainage etc. Several bacterial species (Pseudomonas sp.) can effectively degrade cyanide into less toxic products. During metabolism, they use cyanide as a nitrogen and carbon source converting it to ammonia and carbonate, if appropriate conditions are maintained. In this study, nine strains of Pseudomonas sp. were isolated and identified from a copper mine. Two (CM5 and CMN2) of the nine bacteria strains were used in a cyanide solution. Some important parameters in the biological treatment process were tested and controlled: pH, cell population and CN⁻ concentration. Tests were conducted to determine the effect of the type of bacterial strains on the treatment of cyanide. Laboratory results indicated that biological treatment with Pseudomonas sp. might be competitive with other chemical treatment processes. This paper presents the results of an investigation of a biological treatment system for cyanide degradation in a laboratory batch process.     

Degradation of thiocyanate in aqueous solution by persulfate activated ferric ion

Thiocyanate formation from cyanidation of gold bearing ores is becoming a more common problem during gold processing. In this work, the application of an advanced oxidation process based on the use of persulfate (S₂O₈²⁻) as an environmentally friendly oxidant in the presence of ferric ion for destruction of a persistent and non-volatile inorganic contaminant, such as thiocyanate, in aqueous solutions is reported for the first time. The influence of various reaction parameters like ferric ion and persulfate dosage, initial thiocyanate concentration and the influence of radical scavenger are examined. An accelerated reaction using S₂O₈²⁻ to destroy thiocyanate can be achieved via chemical activation with Fe³⁺ to generate highly reactive sulfate anion-radicals (SO₄⁻). The results showed that degradation efficiency was negligible when persulfate was used alone, ferric ions significantly improved the degradation efficiency of thiocyanate at ambient temperature. Under the optimum molar ratios ([S₂O₈²⁻]:[SCN⁻] = 5:1 and [S₂O₈²⁻]:[Fe³⁺] = 1:0.2), 99% of thiocyanate present in aqueous solution at the initial concentration range of 1.72–17.2 mM was degraded within 60 min of reaction time. To evaluate the contribution of reactive free radicals generated through Fe(III)-mediated activation of persulfate to thiocyanate degradation, quenching experiments using methanol as the radical quenching agent were carried out. The obvious decrease in thiocyanate oxidation efficiency in the presence of methanol confirmed that the radical-based pathway was the dominant mechanism in Fe³⁺/S₂O₈²⁻ system. The degradation of thiocyanate was accompanied by the formation of cyanide as the main final product of the reaction. Thus the catalytic oxidation of thiocyanate makes it possible to return NaCN into the production process for leaching of precious metals. The work presents an efficient and environmentally acceptable wastewater treatment process applicable in mining facilities utilizing cyanidation of sulfide ores and/or concentrates.     

An amperometric method for measuring cyanide in CIP/CIL circuits

A silver rotating disc electrode has been used to measure the ionic cyanide (CN⁻_(aq)) concentration in gold leaching circuits amperometrically. When the electrode is held at 0.1 V vs SHE the current flow is proportional to the cyanide concentration. In laboratory solutions the correlation coefficient ranged from 0.9999 at 30 °C to 0.9995 at 50 °C. The method is free from interference from the anions expected at gold plants, except sulphide, which, if present, can be removed by precipitation with lead(II).Cyanide bound up in stable metal complexes decreases the available CN⁻, and is not measured by the method. Other than by complexation, the metals ions studied did not interfere with the method. CN⁻_(aq) converted to HCN_(aq) at low pHs is also not measured except on addition of a pH buffer. The results are consistent with those from a silver nitrate titration, that also does not measure HCN_(aq) or strongly complexed cyanide.Laboratory and field trials have shown that the method will work in leaching slurries without filtration, but regular electrode cleaning is required to ensure accurate results.     

Evaluation of the ASTERTM process in the presence of suspended solids

The ability to recycle and reuse process water is a major contributing factor toward increased sustainability in the mining industry. However, the presence of toxic compounds has prevented this in most bioleaching operations. The ASTER^TM process has been used for the bioremediation of cyanide (CN) and thiocyanate (SCN⁻) containing effluents at demonstration and commercial scale, increasing the potential for recycling of the treated effluent. The process relies on a complex consortium of microorganisms and laboratory tests have shown that the biomass retention, in suspended flocs or attached biofilm, significantly improved SCN⁻ degradation rates. The current research evaluated the process performance in the presence of suspended solids (up to 5.5% m/v) ahead of implementation at a site where complete tailings removal is not possible. Experiments were performed in four 1 l CSTRs (with three primary reactors in parallel at an 8 h residence time, feeding one secondary reactor at a 2.7 h residence time). Stable operation at the design specifications (5.5% solids, 100 mg/l SCN⁻ feed, effluent SCN⁻ <1 mg/l) was achieved within 50 days, including a period of adaptation. The pH had the most significant effect on performance, with significant inhibition below pH 6. The presence of gypsum and anhydrite phases in the fresh tailings was most likely responsible for the observed decrease in pH. A maximum SCN⁻ degradation rate of >57 mg/l/h was achieved, despite no obvious floc formation. Microbial ecology studies (16S rRNA clone library) revealed reduced diversity relative to reactors operated without suspended solids.     

Decolorizing dye wastewater from the agate industry with Fenton oxidation process

The aim of this work was to investigate the efficiency of Fenton’s reaction in the treatment of the effluents generated by the agate industry. Experiments with different dosages of Fenton’s reagents (H₂O₂ and FeSO₄) were carried out and the treated wastewater quality was analysed in terms of colour, turbidity, suspended solids, COD, surface tension, and sludge generation. Results showed that 2 mL L⁻¹ of H₂O₂ (32–36.5%) and 0.16 g L⁻¹ of FeSO₄ dosages are enough to completely decolourise the effluent, remove suspended solids, reduce the organic content and increase the surface tension. Optimised Fenton’s conditions were used to investigate by GC–MS the organic products remaining in the degradation process. The analysis of the mass spectrum of the compounds present in the wastewater after degradation by the Fenton’s process showed the presence of xylene, linear and branched hydrocarbons, phenolic compounds, and nitrogenated phenol as residual compounds. Thus Fenton’s reaction may be used as a potential chemical oxidant for the treatment of dye organic effluents.     

Phytoextraction of gold and copper from mine tailings with Helianthus annuus L. and Kalanchoe serrata L.

To examine the feasibility of gold phytoextraction, and the corresponding uptake of copper that is induced at the same time, field and laboratory scale experiments were carried out using mine tailings from the Magistral mine in Sinaloa State, Mexico. The locally available plant species Helianthus annuus L. (sunflower) and Kalanchoe serrata L. (magic tower) were used in this work, in combination with the chemical amendments: sodium cyanide (NaCN), ammonium thiocyanate (NH₄SCN), ammonium thiosulphate (NH₄)₂S₂O₃, and thiourea [SC (NH₂)₂] to promote gold uptake. The results show that for K. serrata, average copper concentrations were increased to above 4 mg/kg and gold concentrations to above 9 mg/kg in the dry matter of aerial tissues. For H. annuus average copper concentrations were increased to 118 mg/kg in roots, 141 mg/kg in stem and, 119 mg/kg in leaves while average gold concentrations were increased to 15 mg/kg in leaves, 16 mg/kg in roots and, 21 mg/kg in plant stems. Poor health of plants after treatment with chemicals to induce gold uptake could be a function of toxic concentrations of other trace elements such as copper in the plants. Our results confirm that phytoextraction technology can be used to recover precious metals from mine tailings, and that at the current market price for gold, this recovery may be economic. However, our results also highlight the differential response of plant species to copper and gold in the ground, and the importance of choosing the correct chemical to induce metal uptake.     

Effect of thiocyanate on BIOX® organisms: Inhibition and adaptation

Stringent environmental legislation and the desire to become zero discharge have motivated mining operations to treat and recycle process water. Cyanidation tailings effluent contains elevated concentrations of cyanide and thiocyanate (SCN⁻), precluding recycling to the BIOX® process without prior treatment to reduce SCN⁻ to below 1 mg/l. The current study investigated the effect of SCN⁻ on individual microbial species. Iron oxidation by Leptospirillum ferriphilum was not affected by SCN⁻ concentrations below 0.5 mg/l, with concentration dependent inhibition observed between 0.75 and 1.25 mg/l and complete inhibition of iron oxidation above 1.25 mg/l. Sulphur oxidation by Acidithiobacillus caldus showed a similar trend, with limited inhibition below 1.25 mg/l and almost complete inhibition above 1.25 mg/l. Repeated sub-culturing at low concentrations induced adaptation, with adapted cultures currently growing at SCN⁻ concentrations of 7 mg/l. The phenomenon of inhibition at low concentration, with subsequent adaptation was repeated in stirred tank reactors, leaching a pyrite/arsenopyrite concentrate.     

The influence of pH value and adding pulverized fuel ash on the SBR treatment system

According to a great deal of experimental findings and theoretical analysis, when the COD of inlet is 1 000∼1 200 mg/L, NH₃-N is 200∼250 mg/L, the periodic time of operation is 24 h, the aeration time is 16 h and the sludge density is 5 000∼7 000 mg/L, COD of outlet is 150∼200 mg/L, NH₃-N is less than 25 mg/L, the volume load of COD and NH₃-N remove 0.50 and 0.12 kg/(m³·d) respectively. Meanwhile, studied the influence of various crafts parameter change on the treating effect and absorbing the yielding water of the SBR reactor with pulverized coal ash for improving the removing effect of COD and chromaticity further.     

Selective elution of the gold cyanide complex from anion exchange resin using mixed solvents

This study is concerned with the use of mixed solvents for the elution of the cyanide complexes of copper and gold from Purolite A500, a strong-base anion exchange resin. The mixed solvents investigated include acetone + water, dimethylsulfoxide + water and N-methyl-2-pyrrolidone + water. Three types of counterions are employed in each of the mixed solvents: CN⁻, Cl⁻ and OH⁻. The effects of counterion concentration and mixed solvent composition on the elution of the complexes are examined. High recoveries of the gold cyanide complex are achieved in the mixed solvents at relatively low counterion concentrations. In contrast, the recoveries of the copper cyanide complexes are 1–3 orders of magnitude lower for the given initial loading of the metals on the resin. The selectivity of the elution process for gold is discussed in terms of the degree of solvation of the various anions in the mixed solvents. The results of this study point to the possibility of using mixed solvents to develop an elution process that is selective for gold over multivalent cyanide complexes.     

The application of wood ash as a reagent in acid mine drainage treatment

The paper deals with a possible utilisation of wood ash as a reagent in treating acid mine drainage (AMD) from opencast mining of brown coal. Wood ash samples were obtained having combusted deciduous and coniferous tree wood in a household furnace. The dominant mineral phases in wood ash are calcite, quartz, lime and periclase. The used AMD is characteristic of high contents of sulphates, iron, manganese, heavy metals and low pH. The AMD treatment process included dosing of wood ash to adjust pH values about 8.3 (a dose of 0.5 g l⁻¹) or calcium hydroxide (a dose of 0.2 g l⁻¹) for comparison. The reaction time was 20 min. Dosing of wood ash in AMD resulted in an increase of pH in solution from 3.5 to 8.3, which caused the removal of metal ions mainly by precipitation, co-precipitation and adsorption. Comparing the application of Ca(OH)₂ in AMD treatment, at an almost identical pH value the concentrations fell in both cases for Fe, Mn, As, Co, Cu, Ni, Zn, Mg, Al and Mo. Applying wood ash the drop was even more distinct in Mn, Zn and Mg. The results of sedimentation tests in an Imhoff cone confirm that the settling capacities of sludge using wood ash are significantly better than when using calcium hydroxide in acid mine drainage treatment.     

Review of rate constants for thiosulphate leaching of gold from ores,concentrates and flat surfaces: Effect of host minerals and pH

A review of literature data for different types of sulphide concentrates and gold ores has been carried out to examine the impact of host minerals and pH upon gold leaching. Analysis of initial rate data over the first 30–60 min of gold leaching from sulphide concentrates or silicate ores over a range of ammonia, thiosulphate, and copper(II) concentrations, pH (9–10.5) and temperatures up to 70 °C shows the applicability of a shrinking sphere kinetic model with an apparent rate constant of the order k_ss = 10⁻⁶–10⁻³ s⁻¹. The dependence of apparent rate constant on pH and initial concentrations of copper(II) and thiosulphate is used to determine a rate constant k_Au(ρr)⁻¹ of the order 1.0 × 10⁻⁴–7.4 × 10⁻⁴ s⁻¹ for the leaching of gold over the temperature range 25–50 °C (ρ = molar density of gold, r = particle radius). These values are in reasonable agreement with rate constants based on electrochemical and chemical dissolution of flat gold surfaces: k_Au = 1.7 × 10⁻⁴–4.2 × 10⁻⁴ mol m⁻² s⁻¹ over the temperature range 25–30 °C. The discrepancies reflect differences in surface roughness, particle size and the effect of host minerals.     

Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach

The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca²⁺. This resulted in increased removal of sulphate as CaSO₄·2H₂O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO₄·2H₂O. The results of this study would have implications on the design of treatment methods relevant for different mine waters.     

The Effects of Sulfate on the Physical and Chemical Properties of Actively Treated Acid Mine Drainage Floc

It is important to consider floc properties when designing acid mine drainage treatment (AMD) systems. Relatively few studies have evaluated the effects of neutralizing base, neutralization pH, and sulfate in solution on floc properties in active treatment systems. We used NaOH and NH₄OH as neutralizing bases, 0:1, 2.5:1, and 5:1 SO₄:Fe molar ratios, and neutralization pH of 7, 8, and 9 in laboratory studies. Neutralizing cation, sulfate content, and neutralization pH had significant effects on floc mass and volume, but SO₄:Fe ratio was the most important parameter. Settled floc volumes were slightly larger in the sodium system. Floc mass and volume both decreased with increasing pH. Floc generated in the presence of sulfate required significantly more time to reach a total suspended solids discharge limit of 70 mg L⁻¹, had slower initial settling rates, and smaller settled volumes than floc generated without sulfate. The systems we studied were less complicated than actual AMD, but understanding the effects of sulfate, neutralizing cation, and neutralization pH on floc properties may help to design more efficient treatment systems. Choosing the appropriate treatment chemical and designing adquate pond sizes will ultimately increase treatment efficiency and improve stream water quality.     

Quality Assessment of Mine Water in the Raniganj Coalfield Area,India

In a qualitative assessment of mine water from the Raniganj coalfield, 77 mine water samples were analyzed to assess water quality and suitability for domestic, industrial, and irrigation uses. The pH of the mine water ranged from 6.5 to 8.8. Total dissolved solids (TDS) ranged from 171 to 1,626 mg L⁻¹; spatial differences between the TDS values reflect variations in lithology, activities, and prevailing hydrological regime. The anion chemistry was dominated by HCO₃ ⁻ and SO₄ ²⁻. On average, Cl⁻ contributes 10 and 19% of the total anionic balance, respectively, in the Barakar and Raniganj Formation mine water. F⁻ and NO₃ ⁻ contribute <2% to the total anions. The cation chemistry is dominated by Mg²⁺ and Ca²⁺ in the mine water of the Barakar Formation and Na⁺ in the Raniganj Formation mines. Much of the mine water, especially of the Barakar Formation area, has high TDS, total hardness, and SO₄ concentrations. Concentrations of some trace metals (i.e. Fe, Cr, Ni) were found to be above the levels recommended for drinking water. However, the mine water can be used for irrigation, except at some sites, especially in the Raniganj Formation area, where high salinity, sodium adsorption ratio, %Na, residual sodium carbonate, and excess Mg restrict its suitability for agricultural uses.     

Simultaneous oxidation and immobilization of arsenite from refinery waste water by thermoacidophilic iron-oxidizing archaeon,Acidianus brierleyi

The use of a thermophilic acidophilic iron-oxidizing archaeon, Acidianus brierleyi, was investigated for oxidation and immobilization of As(III) from acidic refinery waste water. Some As(III) oxidation was measured in all Ac. brierleyi cultures independently of the presence or concentration of Fe(II) in bulk solution; the exception was at initial Fe(II) concentration ([Fe(II)]_ini) of 1000 mg l⁻¹ where As(III) oxidation became markedly facilitated and consequently approximately 70% of As was immobilized as amorphous ferric arsenate. Providing 1000 mg l⁻¹ Fe(III) instead of Fe(II) did not show the same effect, implying the importance of Fe(III) be microbially-produced and complexed in the archaeal EPS (extracellular polymeric substances) region for effective As(III) oxidation. The reaction towards secondary mineral formation shifted from ferric arsenate to jarosite at [Fe(II)]_ini of >1000 mg l⁻¹. Furthermore addition of jarosite seed crystals retarded the As(III) oxidation rate at [Fe(II)]_ini of 1000 mg l⁻¹. The observations indicate that by setting the appropriate bulk Fe(II)/As(III) ratio in Ac. brierleyi culture to achieve a certain concentration of Fe(III) within the EPS region, but at the same time to avoid jarosite formation, it is possible to maximize the As(III) oxidation rate and thus As immobilization efficiency. This study describes for the first time microbially-mediated simultaneous oxidation and immobilization of As(III) as ferric arsenate, using a thermoacidophilic iron-oxidizing archaeon, Ac. brierleyi.     

Influence on shallow ground water by nitrogen in polluted river

The main purpose of the research is to discuss the influence on ground water by NH₄-N in polluted river and river bed. In the lab-scale experiment three kinds of natural sand were chosen as infiltration medium, and polluted rivers were simulated by domestic sewage, after 10-month sand column test it was found that NH₄-N came to adsorption saturation on the 17th day in coarse sand and on the 130∼140th day in medium sand, then had a higher effluent concentration because of desorption. It is concluded that NH₄-N easily moved to ground water. When the concentration of NH₄-N in Liangshui River were 46.86, 26.95 mg/L, that in groundwater are less than 1.10 mg/L. It is found that Liangshui River have a little influence on groundwater because of bottom mud, thickness and character of the infiltration medium under the river bed and seepage quantity of river water. Clean water leaching test states that after the silt is cleared away and clean water is poured, NH₄-N in the penetration media under the polluted river is obviously carried into ground water, and ground water is polluted secondly. Supported by the National Natural Science Foundation of China(40772165)     

The Combined Impact of Mine Drainage in the Ankobra River Basin,SW Ghana

This study assessed the combined effects of seven large-scale gold mines, one manganese mine, and scattered artisanal gold mining sites on the quality of water in the Ankobra Basin in a geologically complex terrain. Water samples from streams, boreholes, hand dug wells, and mine spoil were analysed. Scatter plots of trends among measured parameters were used to assess drainage quality and differential impacts. Drainage quality exhibits wide seasonal and spatial variations; the geology strongly influences the water chemistry. Areas with low pH (<5.5), and high sulphate ions and trace ions are suggestive of acid mine drainage while sites with high pH (>7.5), HCO₃ ⁻, subdued SO₄ ²⁻, and high trace ions are suggestive of sites where acid neutralization is effective. High metal sources are largely confined to mining operations in the Birimian formation with ores containing more than 2% sulphides. However, restricted high metal regimes are observed in drainage in the Tarkwaian formation associated with scatted sulphide-bearing dolerite dykes in the operational areas of the Tarkwa and Damang mines. Earlier studies disputed sulphides in the Tarkwaian formation until recently, when acid-generating dykes were discovered in operating pits. The most degraded waters emanate from the Prestea and Iduapriem mines, and to a lesser extent, the Nsuta mine sites, all mining Birimian rocks. The Tarkwa mine showed minimal metal loading. Zn, Cu, Ni, As, SO₄, pH, and specific conductance are essential and adequate parameters in determining if acid drainage is taking place at these sites, and are recommended for routine mine environmental monitoring.     

Microbially Mediated Thallium Immobilization in Bench Scale Systems

Results from bench-scale tests for thallium remediation in mining-impacted water are presented and removal mechanisms are discussed. The source water consisted of surface runoff mixed with groundwater from an inactive gold mine in central Montana. Bench scale columns were operated under continuous flow for 225 days to test for microbially-mediated thallium immobilization. Various compositions of straw and steer manure in a gravel matrix provided a source of organic nutrients and sulfate-reducing bacteria sufficient to initiate and maintain microbial sulfate reduction up to 270 mmol/m³d. Hydraulic residence times of 2.7 days produced an aqueous thallium effluent concentration below the analytical detection limit of 2.5 μg/L at 20°C in all the tested columns. These effluent levels were achieved for influent dissolved thallium concentrations varying from 450 to 790 μg/L. An increase in pH between influent (pH 6.9) and effluents (pH 7.5) was observed. Hydraulic conductivity remained relatively constant during the course of the experiments and varied for the different test columns between 0.2 and 10 cm/s. The highest k-values were observed in the horizontal flow column. In addition to the column tests, sterile serum-vial experiments were performed to confirm that thallium sulfide (Tl₂S) formation and precipitation was the most likely mechanism for thallium removal. Data from the bench-scale experiments were utilized for the design of an on-site pilot-scale passive treatment system.     

Extraction of hydrogen cyanide from waste solutions of cyaniding circuit for sulfide flotation concentrates

The process for extraction of hydrogen cyanide to decontaminate solutions produced at cyaniding of sulfide flotation concentrates is developed. The centrifugal-bubbling apparatus is employed as a reactor. The regularities of HCN formation in an acid medium are established in investigation into kinetics of SCN⁻ thiocyanate oxidation by hydrogen peroxide H₂O₂ in presence of Fe²⁺, Fe³⁺ and pH ≤ 3.5. In the process proposed the evolved HCN is adsorbed by NaOH solution and returned to the circuit of leaching of gold and silver as NaCN, and the waste cyaniding solution is discharged into a waste dump, where it is mixed with industrial water to be utilized to transport flotation tailings. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 98–105, January–February, 2009.