| The present separation processes of gold and antimony from gold-antimony alloys require high content of precious metals in gold-antimony alloys. Furthermore, there are some disadvantages in the processes, such as high cost, high energy consumption, and low direct recovery of valuable metals. The process for the electrorefining of lead most often described in the literature and applied industrially is the Betts’ process. It also has some problems such as environmental pollution and harmful to human health. Aimed at solving the problems mentioned above, a kind of new alkaline electrolysis process containing xylitol was proposed in this thesis. To our knowledge, the electro-system is a new one and there have no report on electo-separation of gold-antimony alloys and electrorefining of lead with this system.There are four parts included in this thesis.The first part of the thesis is the study on the dissolving ability of Sb2O3 and PbO in alkaline solutions containing polyhydric organic compounds (glycerol, xylitol and tartaric acid). In this part, experimentals based on orthogonal array table (L9) and single factor were utilized to determine the optimum dissolution conditions. The influences of concentrations of polyhydric organic compounds and sodium hydroxide on the dissolved amount were studied in detail. The reaction mechanism was also discussed. The dissolving performance of some other metal oxides, such as CuO, NiO, Bi2O3, etc., in alkaline solutions containing polyhydric organic compounds was studied as well. The experimental results show that the Sb2O3 and PbO could be dissolved easily in alkaline solutions containing polyhydric organic compounds. The concentrations of polyhydric organic compounds and sodium hydroxide have significant effects upon the dissolved amount, while the dissolution temperature and time have few effects. The resultant may be metal alkoxides. In this part, the electrolyte used in the electrolytic experiments was prepared.The second part of this thesis is the study on the electrochemical stability of xylitol in alkaline solutions and the electrode reaction mechanism of Sb/Pb in this electrolyte, with the electrochemical measurement technologies, such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), etc.. The purpose of this part is to provide better understanding of the underlying electrode reaction mechanisms and some other information for the application of the alkaline electrolyte in the hydrometallurgy of gold-antimony alloys and lead. The experimental results of CV tests show that the chemical stability of xylitol is high and there is no redox in the potential ranges where the Sb and Pb have redox. So the electrolyte could be used in the electro-separation of gold-antimony alloys and electrorefining of lead. Apparent activation energy, apparent transfer coefficient, exchange current density, and the reaction order were obtained by LSV technique. According to experimental results of the CV test under different scan rates, the electrode reaction of Sb and Pb is deduced to be so highly irreversible. The electrodeposition mechanisms of Sb and Pb in the alkaline solutions containing xylitol were explored and the theoretical kinetics equations of electrode reaction velocity were derived. The values of the kinetics parameters calculated from the theoretical equations are agreed with the experimental ones which indicate the hypothesized mechanisms are correct. The analysis of CA, using theoretical model, shows that the Sb electrodeposition and Pb electrodeposition both adjust to a three-dimensional growth under progressive nucleation limited by diffusion. The potential have significant effect on growth rate crystal and saturated number density of nucleation active site. The diffusion coefficient and the saturated number density of nucleation active site were evaluated by analyzing the potentiostatic transients.The third part of the thesis is the process study of electro-separation of gold-antimony in alkaline solutions containing xylitol. Single factor experiments were carried out to investigate the influences of the experimental parameters, such as the electrolyte composition, current density, temperature, etc., on the current efficiency and energy consumption. The optimal experimental parameters are as follows: stainless steel is choosed for the cathode material, temperature is 50℃, NaOH concentration is 2.00-2.50 mol·L-1, xylitol concentration is 0.79-1.00 mol·L-1,Sb concentration is 0.45-0.50 mol·L-1,electrode distance is 4 cm, current density is 100 A·m-2. Based on the laboratory-scale experimental results, the pilot test was carried out. The pilot test results show that with the new electrolyte system, gold and silver are accumulated in the anode slime and the precious metals and Sb are separated from each other effectively. The purity of the cathode Sb is 96.96%. The content of gold and silver in cathode Sb are 0.67 g·t-1 and 0.66 g·t-1, respectively. The current efficiency and energy consumption are 97.28% and 514.01 kW-h·r-1Sb, respectively.The fourth part of the thesis is the process study of electrorefining of lead in alkaline solutions containing xylitol. Single factor experiments were carried out to investigate the influences of the experimental parameters, such as the electrolyte composition, current density, temperature, etc., on the current efficiency and energy consumption. The optimal experimental parameters are as follows:temperature is 40-50℃, NaOH concentration is 2.00-2.50 mol·L-1, xylitol concentration is 0.79 mol·L-1, Sb concentration is 0.39-0.48 mol·L-1, electrode distance is 4 cm, current density is 120-160 A-m-2, gelatin and potassium sodium tartrate are used as compound additive. The optimal experimental results show that the valuable elements, such as Sb, Bi, and Ag are accumulated in the anode slime. Most of arsenic is enriched into the anode slime, either. The low content of impurities leads to high purity of cathode lead which meets the requirement of GB469-831. The current efficiency and energy consumption are 98.75% and 109.87 kW-h-t-1Pb, respectively.In this new electro-separation process, gold-antimony alloy with relatively low gold content is used as anode instead of alloy with higher gold content. So the oxidation-cupellation process and fluosilicic acid electrolysis in the traditional process, which is high energy consumption, low recovery, and harmful to human health, could be replaced by this new process. The recovery of valuable element, such as Au, Sb, Pb, Cu, etc., will be improved and the mineral resources are made full use of with the new process. In this thesis, the new electrolysis process is also suggested to apply in the lead elecrorefing for its high current efficiency, low energy consumption and environmental friendly. This provides an alternative way for lead refining which differs from Betts’ process. |
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