ELECTROCHEMICAL PROCESSING OF MINERALS, METALS AND MATERIALS

Authors: Przemyslaw Los, Michal Gieron, Slawomir Ruta, Przemyslaw ZaprzalskiNanometallurgy S.A., PolandIn our previous studies we have shown that potentiostatic (and potentiostatic pulse) electrolysis could be applied to obtain copper powders and nanopowders of high purity from copper industrial electrolytes. On the basis of the results a new, patent pending technologies of electrorefining and electrowining have been developed. In this paper for the first time the pilot scale test results of the technology will be presented. The properties of the cathodes obtained using a new process as well as some of its important parameters will be discussed.The new method can be implemented in the existing copper refineries without essential changes in the tank houses apart from the power supplies (rectifiers) which should fulfill certain specific requirements. There are many advantages of our process in comparison to the existing galvanostatic electrorefining and electrowining namely much higher cathode current densities can be used to obtain commercially pure (grade A) copper deposit with very high current efficiencies which can eventually contribute to factory foot print reduction and/or production scale-up. Other positive aspects of our technology result from the fact that stainless steel cathodes can be used, cathodic copper is received in broad spectrum of copper content in electrolyte from 50g/liter to 1mg/liter with the commercial purity of >99,9%, there is no co-deposition of Arsenic, there is no evolution of AsH3 gas.New layouts of electrorefining and electrowining plants will be discussed.

Broadly speaking, a liquid crystal display (LCD) contains several electro-conductive electrodes, which are sandwiched between two glass planes. These electrodes are made mainly of indium tin oxide (ITO), which is is a mixture of indium(III) oxide (In2O3) and tin(IV) oxide (SnO2).Considering that indium(III) oxide has a higher (s.p.) sublimation point (s.p. Of In2O3: 2273K) than indium(III) chloride (s.p. Of InCl3: 573K), the authors are putting forward a chloride-induced vaporization process in order to recover In, which is one of the most valuable component of the obsolete LCDs. The aim was not only to increase the recovery but also reduce the energy consumption of the process. The process includes a HCl treatment process for altering the structure of the indium(III) compound into a chloride-induced indium compound, in order to facilitate the vaporization of indium at a relatively low temperature. The chloride-induced indium compound is then vaporized. Finally, the vaporized indium compound is condensed as on a cooled surface of the apparatus and then recovered. The experimental results indicated that, by using this process, 84.3 % of indium can be recovered from LCDs of the discarded cellular phones. In addition, some thermodynamic calculations were also carried out in order to better understand the mechanism for chloride-induced vaporization of indium.

Corrosion inhibition property of N-(phenylcarbamothioyl)benzamide (PCB) on mild steel in 1.0 M HCl solution has been investigated using chemical (weight loss method) and electrochemical techniques (potentiodynamic polarization and AC impedance spectroscopy). The inhibition efficiencies obtained from all the methods are in good agreement. The thiourea derivative is found to inhibit both anodic and cathodic corrosion as evaluated by electrochemical studies. The inhibitor is adsorbed on the mild steel surface according to Langmuir adsorption isotherm. The adsorption mechanism of inhibition was supported by spectroscopic (UV-visible, FT-IR, XPS), and surface analysis (SEM-EDS) and adsorption isotherms. The thermodynamic parameter values of free energy of adsorption (∆Gads) reveals that inhibitor was adsorbed on the mild steel surface via both physisorption and chemisorption mechanism.

Anticorrosion property of N-(phenylcarbamothioyl)benzamide (PCB) on mild steel surface in 1.0 M HCl solution has been investigated using chemical (weight loss method) and electrochemical techniques (potentiodynamic polarization and AC impedance spectroscopy). The effectiveness of the inhibitor from all the methods are in good agreement. The thiourea derivative is found to inhibit both anodic and cathodic corrosion as evaluated by electrochemical studies. The inhibitor is adsorbed on the mild steel surface according to Langmuir adsorption isotherm. The adsorption mechanism of inhibition was supported by spectroscopic (UV-visible, FT-IR), and surface analysis (SEM-EDS) and adsorption isotherms. The thermodynamic parameter values of free energy of adsorption (∆Gads) reveals that inhibitor was adsorbed on the mild steel surface via both physisorption and chemisorption mechanism. The layer formation on mild steel surface was confirmed by XPS analysis.

A study on the evaluation of the effectiveness of atrazine degradation by in situ electrochemically generated ozone was conducted. Continuous atrazine degradation tests were conducted in a horizontally mounted column packed with washed sand. The purpose of these tests was to determine whether the in situ electrochemical production of the oxidants •OH/O3 is effective at reducing the atrazine concentration in the transported flux across the bed. The porous bed parameters (porosity and dispersivity) and the mean residence time of a KCl tracer in the column were determined. Atrazine degradation runs to evaluate the degradation efficacy as a function of the applied current were conducted. Fractional oxidations of atrazine of 75% and 80% were accomplished in a column containing a porous media for 0.4 A and 0.6 A respectively. The work demonstrates the potential applicability of the continuous system for in situ atrazine degradation in underground waters, and provides a basis for the future development of this technology.

Copper is a metal almost always present in gold mining effluents, since many gold ores are associated to pyrite, arsenopyrite and copper sulfides, such as chalcopyrite, chalcocite, bornite, enargite, covellite, besides native and copper oxides/carbonates. As these minerals are, in some extent, soluble in cyanide solutions, they consume dissolved oxygen and cyanide, competing with gold and silver leaching and slowing down precious metals dissolution rate. Furthermore, copper-cyanide complexes interfere with subsequent recovery processes and increase the bullion contamination. In this paper, the recovery of copper from gold mining waste streams with a lab-scale flow-by electrolytic cell was investigated. Stacks of stainless steel and titanium meshes were tested as cathodes and a ruthenium oxide layered titanium grid was used as anode. Tests with both synthetic solution and a real gold mining effluent have shown that under favorable conditions, more than 99% of the copper and all the residual gold and silver can be removed from solution in less than one hour. A preliminary analysis indicated that power consumption can be paid by the metallic copper recovered.

The cathode copper spiral elongation (SEM) is one of the parameters of the quality of copper grade A. The direct control of SEM value on the process of electrolysis is not possible due to the absence of the information about the dependence of the precipitated copper SEM on the electrolysis parameters (current density, electrolyte composition, temperature, its circulation rate, etc.). Thus, it is advisable to use the information on admixtures content in cathode copper for preliminary assessment of SEM value being in correspondence with LME requirements. For this purpose it is necessary to reveal the correlation between SEM value and the content of some admixture in copper or of their groups. In case positive relation is revealed the control can be carried out by the copper chemical composition.The task was solved with the use of Principal Components Analysis (PCA) in order to process the information on the chemical composition of the cathode copper from world-known producers of two classes. The first class – 25 copper refining operations producing copper certified by LME as grade A copper that is with assured SEM value being more than 400 mm. The second class consisted of 12 operations that had no copper brand of such quality. As soon as by its chemical composition the cathode copper of all producers corresponded to grade A, the brand absence was taken as the evidence of copper quality unconformity by SEM value.In the result there was revealed the correlation between SEM value and the content of nickel, sulphur, selenium and tellurium in copper. The correlation between SEM value and such electrolysis parameters as current density, circulation rate and electrolyte temperature is absent.The correlation between SEM value and admixtures content was verified by direct experiments, where there was used copper with variable content of the abovementioned admixtures.