Physical and Chemical Characteristics of Material Containing Non-Ferrous Metals and Inorganic Aqueous Solutions
Abstract
Kinetic studies were conducted on the process of the dissolution of non-ferrous metals with the use of sulfurcontaining material as a source of leaching agent - sodium thiosulfate. It is shown that with increasing concentrations of sodium hydroxide in solution in the range of 0.1 - 1.0 M, copper recovery is increased from 21.5 to 46.2 %.
As the temperature increases from 25 to 45 ℃, copper dissolution rate in the initial moment of the time increases, then over time this figure gradually decreases with decreasing the copper content in the initial product. The value of the reaction order is 0.39. The calculated value of the activation energy in the process of leaching copper is 12.01 kJ / mol, which suggests that the analyzed process is proceeds in the diffusion mode.
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Introduction
Based on the analysis of scientific literature, it has been shown that electrochemical dissolution of sulfur-containing minerals, usually and mainly performed in acidic electrolytes, because formed low-soluble compounds, in the first instance iron, are freely soluble in acids. However, the process of leaching of sulfur-containing minerals is also possible in alkaline electrolytes (leaching of refractory ores by cyanide method). There is lack of data on the theoretical foundations of electrochemical leaching processes in alkalinecondition. Especially, there is not enough data on technological application of combined electrochemical reactions converting metals to alkaline solutions. Therefore, studying of electrochemical processes involving various minerals containing sulfide as a source for the extraction of gold and other metals to alkaline solutions is relevant, since the use of toxic solvents in industrial scale is undesirable.
It has been shown that leaching (for example, Cu) accelerates with increasing current density and temperature. A special place in the studies of electrochemical processes is taken by the reactions which transfer metals to solutions having different chemical compositions, and use the electric current - electrochemical leaching. In general, these studies relate to the consideration of the chemical processes that take place under the influence of an electric current of different parameters and different hardware design. For example, alternating current is widely used in dissolution processes[1] and in the processes of metal deposition by electrochemical methods[2, 3]. It can be said that today the possibility of the effective application of an electric current of various parameters as a kind of "chemical agent" has been experimentally demonstrated. It also helps to shift the chemical equilibrium to the desired direction. It is noted that the application of alternating electrical current provides: transmission of energy to impurity atom, facilitates its transportation, increases the rate of diffusion in the crystal, provides a recrystallization of the agent, changes the valence of the impurity atoms; creates a magnetic moment, leading to changes in chemical bonding in solid materials [4] .
Conclusion
The influence of various physical and chemical factors on the dissolution of non-ferrous metals in the process of cathodic polarization in the presence of sulphur-graphite electrode (SGE) was studied. It is shown that non-ferrous metals proceed into solution during cathodic polarization SGE. It is found that with increasing solvent concentration and temperature, the degree of extraction of metals also increases. This is due to the formation of S2O3 2- complexes with non-ferrous metals.
During the dissolution process, oxidation and sulphidation of the copper and formation of complex zinc sulfates take place, which prevent further dissolution of metals. Electrolyte concentration and temperature contribute to the increase in the solubility of metals.
Kinetic studies were conducted on the dissolution process of non-ferrous metals with the use of sulfur-containing material as a source of leaching agent - sodium thiosulfate. It is shown that with the increasing concentrations of sodium hydroxide in the solution at the range of 0.1 - 1.0 M, copper recovery increased from 21.5 to 46.2%.
As the temperature increases from 25 to 45 ℃ copper dissolution rate in the initial moment of time increases, then over time this figure gradually decreases with decreasing the copper content in the initial product. The value of the order of the reaction is 0.39. The calculated value of the activation energy in the process of leaching copper is 12.01 kJ/mol, which suggests that the process is analyzed in the diffusion mode.
Thus, it is shown that according to conducted research on leaching, dissolution of ferrous metals depends primarily on the nature of the initial content of raw material, metal structure, and products of the leaching process and the nature of the solvent.