Leaching Of Sub-Grade Copper-Zinc Ore Based On The Application Of Electrochemically Treated Waste-Dump Acid Water Chanturiya Е.L.1, Samusev А.L.2 1 Russia, Moscow, Leninskiy prospect, 6, 119991 Mining Institute of National University of Science and Technology "MISIS" E-mail:
[email protected] 2 Russia, Moscow, Krjukovsky tupik, 4, 111020 Institute of Comprehensive Exploitation of Mineral Resources, Russian Academy of Sciences E-mail:
[email protected]
Abstract Feasibility of use of electrochemically treated waste-dump acid waters for the intensification (2.8 - 6.0-fold) of leaching of sub-standard sulphidic copper-zinc ores is experimentally determined. The technology provides the usage of a product of the electrochemically treated waste-dump acid waters with high concentration of oxidants. The mechanism of the intensification of the leaching process consists in the acidification of sulphides by hypochlorite ions, MnO4 -, Fe3 + and the dissolved oxygen with formation of easily dissoluble compounds and micro defects on the surface and in the bulk of sulphidic minerals that results in the intensive infiltration of the leaching solution into its volume and the accelerated desorption of newly formed chemical products. The laboratory and full-scale tests with sub-grade copper-zinc ores proved the efficiency of application of electrochemically treated waste-dump water. Copper and zinc concentration of 1.5 - 3.0 g/dm3 in productive solutions required for the subsequent processing by cementation method were provided with 20.2% increase of copper and 14.4% increase of zinc recovery as compared with a standard flow sheet of sulphuric acid leaching. The use of electrochemically treated waste-dump acid waters for leaching of copper-zinc ores allows to receive the additional production and to improve environmental ecological conditions.
Keywords leaching, copper-zinc ore, hypochlorite, waste-dump water, electrochemical treatment 1. Introduction Long-year development of solid mineral deposit by traditional physical and engineering methods has resulted in significant depletion of ore balance-sheet reserves, deterioration of their quality, accumulation of great tonnage of mineral mining and smelting wastes as well as industrial waste water. In many cases metal concentration in industrial waste water (from mines and waste dumps, etc.) is similar to that of conventional hydro mineral feedstock, namely mineralized water and brines. At the same time, sub-grade ore dumps and industrial waste waters form a long-term source of environmental contamination (Chanturiya, V. A., 2008). Arrangement and intensification of forced leaching is one of the methods minimizing the harmful environmental effect of such sources. Presently, leaching methods are mainly used for the processing of oxidized copper-zinc ores containing 0.1 to 3% of copper and zinc. In this case, sulphuric acid solutions are
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used as a basic solvent (Chanturiya, V. A., Minenko, V.G., Koporulina, E.V., Samusev, A.L., Chanturiya E.L., 2011). However, the basis of mineral reserves and resources of the copper-zinc industry is formed by pyrite deposits with main minerals are pyrite, chalcopyrite and sphalerite. Application of sulphuric acid solutions for leaching of such mineral feedstock is not efficient, as sulphuric acid is not able to oxidize it in the absence of extra oxidizers. Such agents as Fe3+, hydrogen peroxide, sodium hypochlorite, oxygen, etc., are used as oxidizers, as their application results in sulphide sulphur oxidation to SO42- ions and conversion of non-ferrous metals into liquid phase. One of the most promising methods of liquid phase saturation with oxidizers is electrochemical technology of water conditioning, which is able to specifically regulate physical-chemical properties and gas composition of liquid media without application of any agents (Fazlullin, M.I., 2001; Tikhonov, V.I., Volkov, A.A. 2002). For the investigation of the mechanism of intensifying the process of copper-zinc ore leaching with the application of electrochemically treated waste-dump water with high concentration of oxidizers some specially designed experiments were carried out to estimate the effect on the variation of the structure and chemical composition of the mineral surface.
2. Experimental Work Sulphide minerals (pyrite, chalcopyrite, sphalerite), sub-grade Cu-Zn ores and waste dumps (Table 1), waste-dump water (Table 2), man-made model solutions formed the subject matter of the research.
Table 1 Chemical composition of copper-zinc ore from Uchalinskoe deposit Component Fe SiO2 Stotal Al2O3 CaO Zn Content, % 22.6 23.2 31.2 7.3 5.3 2.8 Table 2 Chemical composition of waste-dump water Component Fetotal Ca2+ Stotal 3 Concentration, mg/dm 66 440 1.1
Mn2+ Zn2+ 370 56
Cu 0.7
Cu2+ 56
Na+ 48
Research was performed with the use of optical and analytical electronic microscopy, sorption method of measurement of sulphide material specific surface. Research into leaching was performed with a modular test bench set (Figure 1). The test bench set is helpful for the investigation of the process of useful components leaching for a broad range of ore size on a continuous basis. Research of electrochemically treated of waste-dump water was performed with the laboratory diaphragmless cell at 250 A/m2 current density, with addition of NaCl salt.
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Figure 1 Modular test bench set for ore leaching on the continuous basis As a result of the following cell reactions: at the anode: 2Cl- - 2e → Cl2↑ at the cathode: 2Н2О +2е→ Н2 ↑+ 2ОНin the volume Cl2 + H2O → HCl + HClO → 2H+ + ClO- + Clthe concentration of available chlorine ions in waste-dump water increases to 1.5 g/dm3. 3. Results and Discussions It has been found that application of modified electrochemically treated waste-dump water results in sulphide oxidation by available chlorine ions, MnO4-, Fe3+ ions and oxygen, with the formation of readily soluble copper and zinc complexes, sulphates, hydroxides and oxides, etc. (Figure 2). It also results in the intensive defect and pore formation in near-surface layers of the mineral material. Data on the formation of pores and microcracks on the surface of copper-zinc ore are proved by the investigation of the specific surface of sulphide minerals. As a result of interaction of sulphide minerals with electrochemically treated wastedump water the specific surface of pyrite, sphalerite and chalcopyrite increased 1.4 -, 3.3- and 5.6- time accordingly, as compared with the treatment by sulphuric acid solution (Figure 3). Data on the expansion of the specific surface of sulphides are proved by optical analysis of the mineral surface. After the contact with electrochemically treated wastedump water the formation of new phases of easily soluble complexes and the element sulphur layer on the surface of sulphide minerals were found (Figures 4-5). This mechanism implies intensive oxidation of sulphide by available chlorine ions, MnO4- and Fe3+ ions and oxygen accompanied by the destruction of mineral matrix with the formation of defects and microcracks that results in the intensive penetration of
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the leaching solution into the mineral volume and accelerated desorption of newly formed chemical products.
Figure 2 Iron, copper and zinc mineral film formed on the surface of Cu-Zn ore, oxidized manganese complexes after the contact with electrochemically treated waste-dump water The effect of electrochemically treated waste-dump water characterized by high concentration of oxidizers on the rate of dissolution was studied with monomineral samples of pyrite, chalcopyrite and sphalerite. To compare the results some experiments were carried out with the application of original waste-dump water and sulphuric acid solutions. The experiments (Figure 6) showed that in case of wastedump water electrolysis product application the rate of chalcopyrite, sphalerite and pyrite dissolution is 2.8 – 7.3-time higher as compared with the application of sulphuric acid solution. Research of the effect of current density, duration of treatment and NaCl original concentration on the efficiency of hypochlorite solution production has identified the most reasonable parameters of electrochemical treatment as follows: Is=250 A/m2, t treat = 10 minutes, СNaCl = 20 g/dm3. Bench tests have proved high efficiency of the proposed conditions of waste-dump water electrochemical treatment, which intensify the process of leaching of sub-grade copper-zinc ores from Uchalinsky GOK. The desired 1.5÷3.0 g/dm3 copper and zinc concentrations for the subsequent processing of productive solutions by cementation method were provided after 100-day leaching. In this case copper and zinc recovery was 86.4% and 43.0% accordingly. At the same time, copper and zinc recovery with the application of sulphuric acid solution was of 66.2% and of 28.6% respectively. The technological scheme of leaching copper-zinc ores using electrochemical water treatment technologies and the main technological equipment are shown on the Figure 7.
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specific surface m2/g
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 1
2
3
Original Sulfuric acid Electrochemically
Figure 3 Variation of the specific surface of sulphide minerals (1 – pyrite; 2 – chalcopyrite; 3 – sphalerite) in the interaction with different solvents
Figure 5 Element sulphur layer on the
surface of chalcopyrite
surface of sphalerite
mg/g*days
Figure 4 Newly formed phases on the 16 14 12 10 8 6 4 2 0 1
2
3
waste-dump water sulphuric acid solution electrochemically treated waste-dump water
Figure 6 Monomineral samples dissolution rate (1 –Chalcopyrite, 2 – Pyrite, 3 – Sphalerite)
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Figure 7 The technological scheme of heap leaching copper-zinc ores 4. Conclusions Thus, on the basis of modern research methods findings the mechanism of intensifying the process of copper-zinc ore heap leaching is determined, which implies the formation of readily soluble copper and zinc complexes on sulphide surface and accompanied by the destruction of mineral matrix with the formation of defects and microcracks under the effect of modified chlorine ions of electrochemically treated waste-dump water. This has let the authors propose the efficient method of integrated processing of sub-grade copper-zinc ore and mineralized water, which is rather helpful for the enhancement of leaching rate, end-to-end non-ferrous metal recovery and utilization of industrial waste water that is important for the industry and facilitates the improvement of environmental situation in the region. The decision on the patent grant for invention named "The way the heap leaching of oxidized and mixed copper-zinc ore" has been obtained (authors: V.A. Chanturya, E.L. Chanturya, V.G. Minenko, A.L. Samusev, A.I. Kaplin). Order № 2010147041/03 (067 950).
5. Acknowledgments Authors express thanks to the school of thought of Academician of Russian Academy of science V. Chanturiya for the support and scientific guidance.
References Chanturiya, V. A., (2008) Innovation Processes in Technologies for the Processing of Refractory Mineral Raw Materials. ISSN 1075 – 7015 Geologiya Rudnykh Mestorozhdeniy, 50 (6) 491–501. Chanturiya, V. A., Minenko, V.G., Koporulina, E.V., Samusev, A.L., Chanturiya E.L. (2011) Grounding the efficiency of application of electrochemical technology of water treatment for the processes of ore heap leaching. “Fiziko-tekhnicheskiye problemy razrabotki poleznykh iskopaemykh. 5 115-124. Fazlullin, M.I. (2001) Heap leaching of noble metals. M.: Academy of Mining Sciences. Tikhonov, V.I., Volkov, A.A. (2002). Science 296, 2363. 6 September 21 to 24, 2014 San Luis Potosi, Mexico
