Processing Of Sulfide Ores Research Articles

Construction of lignosulphonate-containing polymersomes and prospects for their use for elemental sulfur encapsulation

The renewable nature and natural origin of sulfite lignin (lignosulfonate) allow considering it as a potential raw material for the synthesis of valuable environmentally friendly polymer nanomaterials. To create them, a deep understanding of the relationship between the structure of the lignosulfonate macromolecule and the nature of intramolecular and intermolecular interactions is necessary, which would make it possible to control self-assembly processes and obtain nanostructures of specified sizes and morphology. The work discusses the structure formation processes occurring in the lignosulfonate – water – acetone system during the spontaneous formation of polymer nanostructures and submicrostructures. The electrostatic effects of sulfo groups and counterions under conditions of changing the medium polarity and their contribution to self-associations of lignosulfonates have been established. A state diagram was plotted for the ternary lignosulfonate – water – acetone system under conditions of induced phase separation at T = 298 K and under atmospheric pressure. The size and ζ-potential of these nanostructures and submicrostructures of lignosulfonates were estimated depending on the composition of the medium of their formation. The morphology of the resulting nanostructures and submicrostructures of lignosulfonates has been established. The vesicular nature of the aggregates (polymersomes) was confirmed, their shape being close to ideal spheroids with one hole, ranging in size from 40 to 500 nm. A multi-stage mechanism for the formation of lignosulfonate nanoassociates and submicroassociates is proposed. The encapsulating ability of our polymersomes with respect to elemental sulfur from the instant of its inception until the loss of aggregative and sedimentation stability was assessed. Lignosulfonate polymersomes can be recommended as additives to prevent the occluding effect of sulfur melts during hydrometallurgical processing of sulfide ores.

Hygienic study and forecast of atmospheric air pollution with sulfur compounds in the areas of sulfide-containing tailings

This article is devoted to the topical problem of the release into the atmosphere of mixtures of sulfur compounds from decommissioned facilities for the disposal of waste from the processing of sulfide ores of non-ferrous and noble metals. The purpose of the research was a hygienic study and forecast of atmospheric air pollution by volatile sulfur compounds emitted by decommissioned waste disposal facilities for processing sulfide ores of non-ferrous and precious metals, for information support of the system of medical and preventive technologies in mining regions. The objects of the study were two decommissioned tailing dumps of enterprises for the processing of gold ores. The assessment of the actual pollution of the surface layer of the atmosphere with dimethyl sulfide, dimethyl sulfoxide, carbon disulfide, sulfur dioxide and hydrogen sulfide was carried out according to under-flare observations. Non-linear models given by second and third order polynomials were used to predict pollution levels. A theoretical analysis of the in ‑ formation presented in the scientific literature on the interaction of structural elements of natural and technical systems that make up the mechanism of atmospheric pollution at the post-operational stage of mining technogenesis has been carried out. Based on a systematic analysis of under-flare observations conducted in the areas of location of two tailings of gold ore production, lists of priority sulfur compounds to be controlled, distinctive features of zonal atmospheric pollution for different forms of terrain adjacent to the sources were identified, non-linear models of the distribution of concentrations of priority pollutants in the surface were constructed. layer of the atmosphere, allowing a probabilistic quantitative assessment of pollution halos and inhalation risks to public health. The scientific information obtained as a result of a comprehensive study is intended for information support of the system of medical and preventive technologies in mining regions.

Modeling the impact of sulfide ore processing waste disposal facilities on the environment and human health

After the completion of the exploitation of ore deposits, atmospheric migration of sulfur compounds remains an urgent ecological and hygienic problem. The aim of the study was to obtain scientifically sound ideas about the danger of waste from the extraction and processing of sulfide ores of non-ferrous and precious metals accumulated in mining regions for the environment and public health based on the methodology of integrated modeling. The emission of sulfur compounds was studied on a full-scale model of the Ursky dump of barite–pyrite bulk (Ursk settlement, Kemerovo Region), the nature of their combined action was studied in a model experiment on Wistar rats. According to the simulation results, the main components of harmful emissions from the Ursky dump include dimethyl sulfide, dimethyl sulfoxide and sulfur dioxide, the concentrations of which in the air exceeded the normative ones by 129–170, 119–127 and 1,7 times. When exposing experimental animals with a two-component mixture of dimethyl sulfide and dimethyl sulfoxide, a partial summation of the neuro- and hepatotoxic effects of the components was noted, while a three-component mixture of dimethyl sulfide, dimethyl sulfoxide and sulfur dioxide potentiated the irritating effect. The dependences of the qualitative and quantitative characteristics of the biological effects of the isolated mixtures on the sum of the concentrations of their components and time are investigated. The proven algorithm for modeling the effects of the impact of a sulfide-containing dump on the environment and public health makes it possible to expand the possibilities of environmental expertise of environmental protection measures and assessment of risks to public health in mining regions.

Glutathione Synthetase Overexpression in Acidithiobacillus ferrooxidans Improves Halotolerance of Iron Oxidation.

Acidithiobacillus ferrooxidans is a well-studied iron- and sulfur-oxidizing acidophilic chemolithoautotroph that is exploited for its ability to participate in the bioleaching of metal sulfides. Here, we overexpressed the endogenous glutamate-cysteine ligase and glutathione synthetase genes in separate strains and found that glutathione synthetase overexpression increased intracellular glutathione levels. We explored the impact of pH on the halotolerance of iron oxidation in wild-type and engineered cultures. The increase in glutathione allowed the modified cells to grow under salt concentrations and pH conditions that are fully inhibitory to wild-type cells. Furthermore, we found that improved iron oxidation ability in the presence of chloride also resulted in higher levels of intracellular reactive oxygen species (ROS) in the strain. These results indicate that glutathione overexpression can be used to increase halotolerance in A. ferrooxidans and would likely be a useful strategy on other acidophilic bacteria. IMPORTANCE The use of acidophilic bacteria in the hydrometallurgical processing of sulfide ores can enable many benefits, including the potential reduction of environmental impacts. The cells involved in bioleaching tend to have limited halotolerance, and increased halotolerance could enable several benefits, including a reduction in the need for the use of freshwater resources. We show that the genetic modification of A. ferrooxidans for the overproduction of glutathione is a promising strategy to enable cells to resist the oxidative stress that can occur during growth in the presence of salt.

Polyurethane foam as biomass support for removal of thiosalts from flotation process water

Water recycling is a common practice in sulphide ore processing plants by flotation. Inherent thiosalts accumulation in process water often causes efficiency drop and environmental issues for wastewater discharging. Passive and active depuration methods have been applied for thiosalts removal and bio-oxidation in packed bed bioreactors can be considered the most promising option.In this work, polyurethane foam is for first time used as biomass support material in continuous bio-oxidation of thiosalts. Two columns, 15 and 197 cm in height and 8.4 cm in diameter, packed with 1 cm in edge length cubic particles were trialled. A new and fast start-up procedure was performed allowing to effectively operate them in less than seven days. Complete removal of thiosalts in real liquors were achieved with bio-oxidation rates close to 0.45 kg/hm3 and residence time lower than 7 h. Stability, robustness and versatility showed by the bioreactors allows to affirm that polyurethane foam is a suitable material as biomass support in continuous packed bed bioreactors for thiosalts bio-oxidation.

Release of particles and metals into seawater following sediment resuspension of a coastal mine tailings disposal off Portmán Bay, Southern Spain.

Portmán Bay in Southern Spain is one of the most extreme cases in Europe of anthropogenic impact on the marine ecosystem by the disposal of mine tailings resulting from the processing of sulphide ores. First, the composition and extent of the surficial deposit were investigated from geochemical and metal analysis on high spatial density of sediment samples. Then, a disturbance experiment was conducted in the coastal area off Portmán Bay in order to investigate the potential impact of mining activities on marine ecosystems. Two research vessels were used for that experiment, one performing as a trawler resuspending bottom sediments while the other monitor the behaviour of turbid plumes thus generated and the evolution of their characteristics through time by using a range of acoustic and optical tools together with water and bottom sediment sampling for biogeochemical and metal analyses. The surficial part of the submarine extension of the mine tailings deposit is highly concentrated in As, Cd, Pb, Fe and Zn with peak concentrations adjacent to the present coastline, from where they decrease seawards before reaching average values for the Mediterranean Sea around 50-m water depth. The artificially triggered resuspension of the surface layer of the deposit led to the formation of resuspension plume about 100 m in width and up to 6 m in height. Resuspended plume was composed of fine particles which rapidly aggregated into flocs of 100 μm. While the biggest particles settled rapidly, the finest fraction remained in suspension during at least 3 h. Resuspended sediment and metal concentrations in particles remained at relatively high levels throughout the experiments following triggering. Fe, Pb, and As concentrations in resuspended particles showed a continuous increase while trawling before decreasing in parallel with the settling down of the resuspended sediments. Those metals have higher affinity with fine particles than with coarse ones, so that while the coarsest fraction from sediment plumes settled first, the finest fraction remained in suspension thus increasing the metals/sediments concentration ratio. On the other hand, Cd and Zn concentrations in suspended particles did not change significantly over time, which is thought to be caused by the fast dissolution of such metals in seawater. Beyond waste dumping itself, the observed increase in some metals in marine particulate material could have a significant impact on the adjacent coastal ecosystems due to their toxicity above certain thresholds. The consequences of the resuspension experiment here presented can be extrapolated to the impact of seafloor mining activities leading to the resuspension of metal-rich particle plumes into the water column. The experimental set-up presented here may be further explored for investigating metal behaviour during seafloor mining activities.

Active destruction of pyrite passivation by ozone oxidation of a biotic leaching system

Although pyrite bio-dissolution plays an important role in the processing of sulfide ores, the formation of passivation film inhibited the further dissolution of sulfide ores. In order to enhance the dissolution of sulfide ores, a novel method for destroying the passivation film using ozone was proposed and verified. The generated passivation film inhibiting pyrite dissolution in the presence of Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans was studied. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results indicate that a passivation film mainly consisting of jarosite and polysulfide (Snn−/S0) might be formed during biotic stage, which can be eliminated with the introduction of ozone (2 g/min) in 30 min. Electrochemical results show that ozone significantly increased the electrochemical reactivity of passivated pyrite, further proving that ozone enhanced the dissolution of passivated pyrite through destroying the passivation layer. Hence, a bi-stage method for dissolution of sulfide ores can be proposed.

The Solution Interaction of Tetrathionate Ions and Sodium Isobutyl Xanthate and Its Effect on the Flotation of Galena and Chalcopyrite

Tetrathionates have been found in significantly high concentrations in recycled process waters from massive sulphide ore processing plants. These polythionates react with xanthate added to flotation pulps thus reducing xanthate dosages in solution potentially affecting flotation performance. The current study focused on the effect of the tetrathionate-xanthate reaction on sulphide mineral recoveries. Ore dissolution studies confirmed the generation of tetrathionates by copper-lead-zinc ores. In 20 min, the tetrathionates consumed more than half of the xanthate in solution at pH 7. Rest potential measurements and Fourier transform infrared spectroscopy (FTIR) showed that the degree of collector-mineral interactions of xanthate and both galena and chalcopyrite was greatly reduced in the presence of a 2000 mg/L tetrathionate solution. Microflotation tests showed that chalcopyrite recovery was less sensitive to tetrathionates as indicated by small changes in mineral recoveries. Galena was sensitive to the action of tetrathionates on the mineral surface as the galena recovery significantly declined when floated with xanthate as a collector in both a 500 mg/L tetrathionate solution and a 2000 mg/L tetrathionate solution. These fundamental results lay a sound base on which more discussion into the significance and the effect of tetrathionates on flotation performance of sulphide ores can be developed.

Investigating the Electrochemical Interaction of a Thiol Collector with Chalcopyrite and Galena in the Presence of a Mixed Microbial Community

High microbial cell counts have been recorded in sewage waters employed as process water in mineral beneficiation plants across the world. The presence of these microbes can negatively impact flotation performance through mineral passivation, although some microbes improve flotation performance as investigated in various bio-flotation studies. The current study aims to understand the electrochemical behaviour of minerals in the presence of a sodium ethyl xanthate (SEX) collector and microbes originating from a sulphide ore processing plant in South Africa. The electrochemical response was correlated to observe flotation performance. Mixed potential measurements were conducted in parallel to microflotation tests, to assess the hydrophilicity or hydrophobicity induced on sulphide minerals adapted to microbe-laden synthetic plant water. Sulphide minerals’ mixed potentials and interactions of SEX with sulphide minerals were dramatically reduced in the presence of the mixed microbial community (MMC). The observations were correlated with poor flotation efficacy noted in microflotation tests. These fundamental results shed light on how the adsorption of thiol collectors on sulphide minerals is adversely affected by microbes, prompting a discussion on flotation process monitoring when mineral beneficiation is conducted using microbe-laden water.

Impact of historical sulfide mine tailings discharge on meiofaunal assemblages (Portmán Bay, Mediterranean Sea)

Portmán Bay is one of the most contaminated and chronically impacted coastal marine areas of the world. Here, from the 1957 to 1990, about 60 million tons of mine tailings from the processing of sulfide ores were dumped directly at the shoreline. The resulting deposit provides a unique opportunity to assess the impact of mine tailings on coastal marine ecosystems after ca 30 years since the discharge has ceased. We investigated meiofaunal abundance, biomass and biodiversity along a gradient of metal concentration that overlaps with a bathymetric gradient from 30 to 60 m depth. Despite the localized presence of extremely high concentration of metals, the bay was not a biological desert, but, nevertheless, was characterized by evident signs of impact on benthic diversity. Meiofaunal variables increased significantly with decreasing metal contamination, eventually reaching values comparable to other uncontaminated coastal sediments. Our results show that mine tailings influenced the spatial distribution of meiofaunal taxa and nematode species composition. In particular, we report here that the bay was characterized by the dominance of nematode opportunistic species tolerant to high metal concentration. The effects of mine tailing discharge on meiofaunal biodiversity and composition were still evident ca 30 years after the end of the mining activities. Overall, this study provides new insights on the potential impact of mine tailings disposal and metal contamination in coastal sediments, and, can also contribute to predict the potential long-term consequences of ever-expanding deep-sea mining industry on benthic environments.

Mitigation negative effects of thiosulfate on flotation performance of a Cu-Pb-Zn sulfide ore

Thiosulfate ions are formed during processing of sulfide ores. They have a detrimental effect on flotation resulting in recovery and selectivity problems. In this work, removal/management of thiosulfate ions during flotation of a Cu-Pb-Zn sulfide ore was investigated and discussed in detail. Batch scale flotation tests were performed by using synthetic water samples of different chemical composition. Evaluation of froth stability, metal recovery and selectivity showed that presence of thiosulfate ions resulted in depression of the sulfide minerals. Oxidation of thiosulfate by hydrogen peroxide (H2O2) was applied to remove/minimize the adverse effects on flotation. H2O2 was added to process water and concentration of thiosulfate ion was decreased down to acceptable levels for flotation. H2O2 oxidized majority of thiosulfate ions to sulfate form. Increase in sulfate ion concentration influenced froth stability, but not the flotation performance which was restored after water treatment.

Novel reagents for iron and sulphur control in medium temperature leaching of sulphide concentrates

ABSTRACTHydrometallurgical leaching of sulphide concentrates of copper and nickel at medium temperature (150°C) produces residues that contain sulphur and iron-bearing minerals and phases. During leaching, and depending on various process parameters, iron may be precipitated as hematite, goethite, jarosite or other oxyhydroxides, which may be more or less crystalline. Hematite is the favoured iron precipitate, because it is the most environmentally stable and does not ad/absorb as much copper, nickel or other solution constituents during precipitation. However, the low solubility of iron during the medium temperature processing of sulphide ores can favour the formation of poorly crystalline, nano-scale iron oxide/oxyhydroxide phases. In some cases, these phases have been positively identified as the metastable ferrihydrite, which transforms into iron oxides such as goethite, hematite and magnetite over time. A better understanding of what may help drive this transformation during leaching would ultimately result in lower valuable metal losses and more stable leach residues. Higher acid concentrations result in increased copper extractions and favour the formation of hematite during concentrate leaching, rather than other metastable phases. Furthermore, commercially available water displacement formula ‘WD40®’ and other novel reagent(s) affect Fe precipitation and sulphur chemistry, leading to very different process outcomes such as improved extractions and larger, more easily separated, sulphur particles.

Reprocessing and environmental desulphurization of sulphide mining waste from sphalerite flotation: case of Chaabet El Hamra mine, Algeria

PurposeTailings generated by sulphide ore processing at Chaabet El Hamra mine contain a variety of sulphide minerals such as pyrite, marcasite, sphalerite, galena and chalcopyrite with carbonated and siliceous gangue. It is well known that the presence of pyrite can cause environmental threats, in particular the acid mine drainage risk (AMD), if there is not enough neutralizing potential. Waste chemical analyses show that the content of total sulphur (S) is more than 9 per cent, which could be possible to separate the pyrite from other heavy minerals based on interfacial property of these minerals, because the pyrite contain the sulphur-rich fraction.Design/methodology/approachIn this study, the possibility of waste reprocessing using froth flotation of sulphuric bulk and depression-heavy minerals. It is environmental desulphurization that removes much of the high S fraction.FindingsThe results obtained in terms of S recovery and residual S content are interesting after merely 12 min of flotation by addition of potassium amyl xanthate collector (140 g/t), pine oil frother (10 g/t) and activation with copper sulphate (CuSO4+; 60 g/t) and at optimum pH of 5.Originality/valueIt can be shown from waste treatment by flotation of pyrite depression sphalerite collects significant desulphurization in sulphur content is 19 per cent against 8 per cent in the initial release.

Amorphous iron phases in medium temperature leach residues and associated metal loss

Leach residues, produced during pilot and demonstration scale medium temperature (150°C) hydrometallurgical processing of sulfide ores contain amorphous/poorly crystalline and metastable nano-scale iron oxides/oxyhydroxide phases. These phases control the properties of the residue and contain a relatively high loading of the valuable (Cu, Ni) metals. Residue samples from CESL and Vale pilot and demonstration plant medium temperature processes were characterized using different techniques. Poor agreement between total iron analysis by inductively coupled plasma mass spectroscopy (ICP-MS) and quantitative X-ray powder diffraction QXRPD indicated the presence of amorphous/poorly crystalline iron oxide phases. QXRPD coupled with sequential extraction was used for quantification of the amorphous iron phases. Amorphous iron oxides/oxyhydroxides were found to be a major source of copper and nickel losses to the residue. The distribution of copper and nickel into the amorphous and crystalline iron oxide phases was determined by a two-stage sequential extraction process. Association of copper and nickel to the amorphous phases was found to be approximately 2–4 times higher than with the crystalline iron oxide phases.

Greening Chilean copper mining operations through industrial ecology strategies

Sawdust was used as cheap sorbent for the remediation of a diesel and oil fuel-contaminated mining soil whereas biosolids were evaluated as collectors and frothers in froth flotation of copper sulphide ores. The use of these waste materials in copper sulphide ore mining and mineral processing may have a positive impact on the cleaner production of copper from its natural raw sources and may decrease the deleterious effect that mining operations have on the environment. Mixtures of oil fuel contaminated mining soil and sawdust were treated in an aerobic reactor at 50.0% humidity for several days. A significant decrease (over 60.0%) of Volatile Organic Compounds (VOCs) content in these mixtures was obtained after one-month of treatment. Rougher flotation of copper sulphide ores using biosolids e from wastewater treatment plants e and humic acids e a component of biosolids e as collector and frother yielded a copper sulphide concentrate with a copper grade and copper recovery of 0.8% and 26.0%, and 3.5% and 29.7%, respectively. Biosolids and humic acids have shown to be potential candidates to partially substitute traditional organic chemicals used in industrial flotation of copper sulphide ores. This possibility opens up an alternative for greening copper sulphide ore flotation by using more environmentfriendly flotation reagents. Based on these results, a conceptual model based on industrial ecology and cleaner production principles is proposed for greening the overall copper sulphide ore processing.

Garden soil and house dust as exposure media for lead uptake in the mining village of Stratoni, Greece

The relationships between two exposure media, garden soil and house dust, were studied for Pb uptake in Stratoni village in northern Greece, an industrial area of mining and processing of sulphide ore. Lead data for the two media were assessed in terms of total and bioaccessible content, measurement and geochemical variability, and mineralogical composition. It was found that total Pb was enriched in house dust samples by a factor of 2 on average. Total Pb concentration in soil samples had a maximum of 2,040 mg/kg and reached a maximum of 7,000 mg/kg in house dust samples. The estimated variability due to measurement uncertainty was dominated by the sampling process, and the proportion of sampling variance was greater for soil samples, indicating a higher degree of Pb heterogeneity in soil on the given spatial scale of sampling strata. Although the same general spatial trend was observed for both sampling media with decreasing Pb concentration by increasing distance from the ore-processing plant, Pb in dust samples displayed the highest concentrations within a 300-600-m zone from the ore-processing facility. The significant differences which were observed in Pb speciation between the studied media were explained by differences in mineralogical composition of outdoor soil and indoor dust. Lead-enriched Fe and Mn oxides predominated in soil samples while fine galena grains (<10-20 μm diameter) were the major Pb-bearing phase in dust samples. The integrated exposure uptake biokinetic model was used to predict the risk of elevated blood lead levels in children of Stratoni. Model prediction indicated an average probability of 61 % for blood-Pb to exceed 10 μg/dl. The results underline the importance of house dust in risk assessment and highlight the effect of outdoor and indoor conditions on the fate of Pb in the particular environment of Stratoni.

The main groups of microorganisms involved in the biohydrometallurgical process

Recovery of valuable components from minerals by microorganisms and their metabolic products is recognized biotechnology reception processing of sulphide ores. To date, this technology is cost-effective and environmentally friendly. The article describes the main groups of bacteria involved in the process biohydrometallurgical extraction of metals from natural sulfide ores, and recent data on the mechanism of bacterial and chemical oxidation. The main phenotypic and genotypic properties of acidophilic chemolithotrophic bacteria involved in biohydrometallurgical processes - mesophilic and moderately thermophilic chemolithotrophic members of the genera Acidithiobacillus, Leptospirillum, Sulfobacillus. Promising uses of bacterial leaching and the possible importance of this method for obtaining metals from non-traditional minerals indicated.

Exergy accounting applied to metallurgical systems: The case of nickel processing

Exergy accounting of energy and material flows for the two main routes of nickel production (from laterites and sulphides ores) is performed so as to identify the main losses which take place in the overall chain. Accordingly, the chemical exergy of the different raw materials and utilities involved in the production of nickel is calculated. The results show that nickel processing has higher efficiencies when it is produced from sulphides than from laterites. Sulphide ore processing has efficiencies fluctuating from 0.67 to 0.79, depending on the specific technologies utilised. The higher efficiencies are reached when leaching technologies are used and on the contrary if nickel is produced from laterites, the efficiencies achieved are lower on average (0.38) due to the cost-intensive processing. The strengths and weakness of the methodology applied are discussed and compared with the exergoecology approach. If the analysis is carried out with the exergoecology methodology, the cost effectiveness of sulphides against laterites is not so evident.

Recycle of Wastewater from Lead-Zinc Sulfide Ore Flo-tation Process by Ozone/BAC Technology

Lead-zinc sulphide ore contains lead sulphide (galena), and zinc sulphide (sphalerite). In the first flotation stage, galena is rendered hydrophobic with an organic collector such as xanthate, while sphalerite is kept from floating by depressants, and in the second flotation stage, activator was used to activated zinc flotation. Since the organic regent used are different in the two flotation stage, wastewater from the second zinc flotation stage can’t be directly recycled to the first lead flotation stage. Wastewater from flotation process for concentrating lead-zinc sulphide ore often containing organic compounds such as diethyldithiocarbamate(DDTC), xanthate, terpenic oil(2# oil) and thionocarbamate esters (Z-200), are environmentally hazardous. Their removal from contaminated water and the reuse of the water is one of the main challenges facing lead-zinc sulphide ore processing plants. In this study, synthetic wastewater containing DDTC, xanthate, 2# oil and Z-200 at concentrations ranging from 21 to 42 mg/L was fed into an Ozone/Biological activated carbon (BAC) reactor. Analyses of the effluent indicated a chemical oxygen demand (COD) removal over 86.21% and Total organic carbon (TOC) removal over 90.00% were achieved under Hydraulic retention time (HRT) of 4h and O3 feeding concentration of 33.3mg/L. The effluent was further recycled to the lab scale lead concentrating process and no significant difference was found in compare with fresh water. Furthermore, lead-zinc sulphide mineral concentrating process was carried out at lab scale. The produced wastewater was treated by Ozone/BAC reactor at O3 feeding concentration of 16.7mg/L and HRT of 4h. The effluent analysis showed that TOC removal was 74.58%. This effluent was recycled to the lab scale lead-zinc sulphide mineral concentrating process and the recovery of lead was not affected. The results showed that by using Ozone/BAC technology, the lead-zinc sulphide mineral processing wastewater could be recycled.

Sodium sulfite: A promising reagent in the electrochemical oxidation of metallic silver

Among the complexing agents suitable for the electrochemical silver recovery, a promising one is sodium sulfite forming silver complexes with high stability constants: according to our data, log β1 ~ 5.3, log β2 ~ 8.2. This reagent is accessible and cheap, but nevertheless it almost never has been used for these purposes. We studied the stability of the sodium sulfite solutions in air and showed a possibility of using them for a long period. Using the methods of potentiodynamic polarization and potentiostatic electrolysis, we have studied characteristics of the process of metallic silver oxidation in the sulfite media. The anodic polarization process of the silver dissolution is shown to occur with 100% yield with respect to the consumed current. Simultaneously, on the cathode deposited up to 90% of dissolved silver. An urgent problem of chemical technology is the extraction of noble metals, particularly silver, from the electronic and jewelry scrap and similar sources. The traditional methods of the silver extraction (1-3) are based on its dissolution in the presence of oxidants in acid solution (perchloric acid, sulfuric acid, nitric acid) or complexing agents (cyanide, thiocyanate, thiourea). From these solutions, silver is isolated as insoluble salts or is reduced to metal. The main disadvantages of these techniques are the high consumption of reagents and non-selectivity of dissolution: besides silver copper, iron, and other components of the raw material are dissolved. Significantly less expensive are the methods that use electrolytic anodic oxidation of silver in specially selected electrolytes (4). Processing a material containing large amount of basic metals (copper, iron, nickel, etc.) should be performed under conditions providing selective transfer of silver in the solution. For this purpose are used the electrolytes containing thiourea (5), thiocyanate (6, 7), amino acids (8), etc. Silver can be deposited and isolated on the cell cathode. Note that the earlier proposed thiourea me- dium (2) still is widely used in the gold and silver hydrometallurgy. The study of the process of elec- trolytic oxidation and reduction of silver has been carried out in (9-11). A promising complexing agent in the processes of electrochemical oxidation of silver is sodium sulfite, the side product in processing of sulfide ores used in the manufacture of chemicals. The stability of the