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Section 8. Chemistry
Section 8. Chemistry
Grigorenko Dmutro Oleksandrovich, National Technical University of Ukraine "Kiev Polytechnic Institute”, Chemical Technology Faculty, student Byk Mykhaylo Volodumurovich, National Technical University of Ukraine "Kiev Polytechnic Institute", Chemical Technology Faculty, Associative Professor E-mail: bmv2000@ukr.net
Investigation of copper cementation process by iron from used electrolytes and ore leaching solutions
Abstract: Copper cementation is widely used for waste water purification and metal extraction. The process of copper cementation from acid copper sulphate solution was studied by gravimetric and electrochemical methods. It was sown that initial stages of copper deposition on mild steel surface has exponential dependence from time. On the base of obtained results the new equipment for continuous copper cementation process proposed.
Keywords: copper cementation, sulphate solution, continuous process, kinetics of initial deposition.
Large tonnages of dilute copper-bearing solutions (0.5 to 3.0 g/l Cu), produced principally from the in situ, dump, and percolation leaching oflowgrade ores and mine wastes and from electrorefining operations, have become the potential source of copper in many parts of the world. Such solutions are too dilute in copper for direct electrowinning, gaseous reduction, or chemical precipitation. Cementation, which involves the precipitation of an electropositive metal from a solution by an electronegative one, is one of the most ancient, yet economical and efficient, hydrometallurgical processes for the recovery ofdissolved metal values from such dilute solutions, as well as for the purification of leach liquors [1; 2]. This process is extensively applied to the removal of copper from zinc sulphate leach liquors, of copper from nickel sulphate leach liquors; and to the recovery of copper from dilute runof-mine solutions, spent electrolyte, and leach liquors arising from low-grade copper ores [3; 4].
Cementation is described as the electrochemical precipitation of a metal by another more electropositive metal. This process has been used for centuries in hydrometallurgy for the purification of leaching solutions, and also for recovering toxic and precious metals from industrial waste streams [5].
Experimental: Most of the solutions used in this work were synthetic but at the end of the study, a real
sulphuric leaching solution was used. All the solutions were prepared with demineralised water and using analytical grade reagents added as sulphates. Electrochemical experiments were conducted in three-electrode cell. Reference electrode was Ag/AgCl/Cl-. All potential on plots were calculated vs. standard hydrogen electrode. The 1; 0.1 and 0.01 М CuSO4 and H2SO4 solutions were used as electrolyte, platinum as counter electrode, working electrodes — mild steel (99.98 % Fe) and copper (99.99 %) were used. At the laboratory equipment test rich copper ore leached by sulphuric acid solution was used as test solution for cooper cementation process.
Results and discussions: The weight measurements were conducted on modified laboratory scales with accuracy of 0.0005 g. Investigated samples from mild steel were hanged on weights arm and immersed into solution contains copper sulphate and sulfuric acid. At copper cementation process copper deposited on steel surface and iron dissolve and diffuse to the bulk of aqueous phase. The overall reaction expressed by
Cu 2+ + Fe 0 = Fe 2+ + Cu 0. (1)
The result of such exchange reaction was weight increasing on 63.546 - 55.845 = 7.701 g. on every mole of deposited copper ions.
The weights changes were calculated into current values according to Faradays law and plot vs. time on Fig. 1.
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Investigation of copper cementation process by iron from used electrolytes and ore leaching solutions
Fig. 1. Kinetic of copper cementation determined by weight method:
1) 1 M CuSO4 + 1 M H2SO4; 2) 0.1 M CuSO4+0.1 M H2SO4; 3) 0.01 M CuSO4+0.01 M H2SO4
It is obvious that in case of 0.1 M CuSO4+0.1 M H2SO4 solution we reach maximum velocity of cementation process and it increases with time. Formed copper film was not uniform and still has no limitation on copper ion transport to bare ferrous surface. In concentrated solution 1 M CuSO4 + 1 M H2SO4 the non porous film formed and cementation process occurred onto formed
film that results in gradually decreases in reaction velocity. In the case of the most diluted solution 0.01 M CuSO4+0.01 M H2SO4 the reaction velocity also decreases due to low copper concentration.
The electrochemical measurements were conducted on steel and copper electrodes. Results for steel electrodes presented on Fig. 2.
Fig. 2. Electrochemical measurements on steel electrode: 1) 1 M CuSO4 + 1 M H2SO4; 2) 0.1 M CuSO4+0.1 M H2SO4; 3) 0.01 M CuSO4+0.01 M H2SO4.
As one can see steel potential shifts to more negative values at copper and sulfuric acid concentrations decreasing.
Dissolution currents and velocity of hydrogen evolution also decreased with concentrations. In the most diluted solution the steel potential is near corrosion
potential of steel in acid solution. At increasing of copper and acid concentration the potential ofworking electrode shifts to more positive values.
Electrochemical measurements on copper electrode were conducted to exclude cementation process and investigate copper reduction and dissolution Fig. 3.
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Section 8. Chemistry
Fig. 3. Electrochemical measurements on copper electrode:
1) 1 M CuSO. + 1 M H2SO4; 2) 0.1 M CuSO. + 0.1 M H2SO4; 3) 0.01 M CuSO. + 0.01 M H2SO4
The copper potential also shifts to more negative values at copper and sulfuric acid concentrations decreasing. The limiting current of copper reduction decreases with copper concentration decreasing. This process has diffusion limitation, so log of limiting current proportional to magnitude of copper ions concentration. From 1 to 0.1 M decreasing of copper concentration the log of copper dissolution current decreases on one magnitude. But from 0.1 to 0.01 M concentration decreasing the log of dissolution current does not decreased so much. This
phenomenon can be explained by low concentration (0.01 M) of sulphate anions. These anions are necessary to combine formed copper ions into copper sulphate to maintain solution electroneurality.
On the basis of obtained weight and electrochemical the best conditions for copper cementation reaction on mild steel were chosen (mixture of 0.1 M copper and sulphuric acid).
For continues process ofcopper cementation reaction the new laboratory equipment proposed (Fig. 4) [6].
Fig. 4. Laboratory equipment scheme for copper cementation process
Proposed equipment contains drum (1) immersed into container (3) with electrolyte (diluted electrolyte for printed circuit board or copper ore leaching solution). On outer drum surface was coated by magnetic film (1). Thin steel foil stripes hold by magnetic forces on drum surface. When steel stripes completely dissolve they added from special batcher (6). At steel contact with solution in container and sprinkled solution from nozzles (5) the cementation process occurred. Copper powder fall off onto container (3) bottom, where by pump (4) feed up separator (8). Clear solution retuned onto nozzles and separated copper powder filtered
and dried. The drum (1) rotates by electric engine (7) for uniform washing of surface by working solution. Used solution pumped off to ferrous sulphate crystallization.
On such equipment we investigate copper cementation process on artificial solution and diluted solutions for print circuit board and leaching solution of copper ore. The final copper concentration reach 0.5-0.3 g/l.
Conclusions: Process of copper cementation process on mild steel stripes was investigated. It was noted that the best copper and sulfuric acid concentration for cementation process are 0.1 M. The new equipment for continuous process of copper cementation proposed.
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Electrochemical synthesis and sensor properties of polyaniline (PANI) films of different oxidative state
References:
1. Agrawal R. D., Kapoor M. L. Theoretical considerations of the cementation of copper with iron.//Journal of the South African institute of mining and metallurgy. - 1982. - № 4. - P. 106-111.
2. Бабенко С. А., Пинигин С. А., Тасоев Р. И. Исследование процесса цементации меди железными стружка-ми.//Известия Томского политехнического института им. С. И. Кирова. - 1976. - Т. 75. - С. 92-95.
3. Stankovic V., Serbula S. and Janceva B. Cementation of copper onto brass particles in a packed bed.//Journal of Mining and Metallurgy. - 2004. - Vol. 40 B (1). - P. 21-39.
4. Panao Ana S. I. , Jorge M. R. de Carvalho, Maria J. N. Correia Copper Removal from Sulphuric Leaching Solutions by Cementation.//Centre of Chemical Processes, Technical University of Lisbon, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal.
5. Nazim Muhammad M. S. Reduction of copper sulphate with elemental iron for preparation of copper nanoparticles. -The Petroleum Institute of United Arab Emirates. - 2011. - 137 p.
6. Заявка U 2015 02808 (3120) Украша МПК (2015.01) С25 С 5/00 Апарат для безперервного вилучення мщ i3 розчишв шляхом цементацп. [Текст] / Лшючева О. В., Григоренко Д. О., Бик М. В., Донченко М. I. (Украша) № U 2015 02808 (3120); заявл. 27.03.15.
Zhuk Vitalii Petrovich, National Technical University of Ukraine ".Kiev Polytechnic Institute", Chemical Technology Faculty, student Byk Mykhaylo Volodumurovich, Chemical Technology Faculty, Associative Professor E-mail: bmv2000@ukr.net Motronyk Tetiana Ivanivna, Chemical Technology Faculty, Associative Professor
Electrochemical synthesis and sensor properties of polyaniline (PANI) films of different oxidative state
Abstract: Thin polyaniline (PANI) films are known as good optical gas sensors. To improve these properties we have developed new robust transparent PANI films obtained at different electrochemical condition. We demonstrate that PANI films have an increased surface area; give strong, fast and reversible optical sensor responses to ammonia. In case of ammonia-air gas mixtures we demonstrate that the PANI films give linear optical responses to ammonia gas in concentration ranges of 10-114 ppm.
Keywords: polyaniline (PANI), electrochemical oxidation, ammonia sensor, oxidation state.
oxide (chinoide, imine) fragment (В) [1-4].
In the most common case PANI can exist in all intermediate states from completely reduce form to oxide [1-4]. Ratio for abovementioned amine and imine’s fragments in PANI can be change by chemical or electrochemical oxidation/reduction [5].
Modern interest for PANI arises after discovering its semi-conductive properties. The fist works of such direction was [6-8].
It is well known that a polyaniline term describes a class of compounds that has formula:
Thus chemical structure of PANI contains repeating chains as:
reduced (benzoid, amine) fragment (А);
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