Research On The Technological Condition In Slurry Electrolysis Of Higy-silver Galena Concentrate

This paper studies the technological conditions in Slurry Electrolysis of the high-silver galena concentrate, preliminarily explores the leaching mechanism of galena in Slurry Electrolysis, and estimates the feasibility for Slurry Electrolysis process to replace lead pyrometallurgy. The main research contents and their conclusions are as follows:The effects of cathodic current density, initial Pb concentration in slurry and the electrolysis temperature on the lead leaching rate and the cathodic current efficiency of the galena Slurry Electrolysis in silicofluoric acid system were studied. It was concluded that because higher electrolysis temperature is not available, the leaching rate of galena is very low and silicofluoric acid system is not suitable for galena Slurry Electrolysis.Using acidic chloride solution as the medium is the mainstream in Slurry Electrolysis. In such system, through investigating its cell voltage, lead leaching rate, cathodic current efficiency and studying the behavior regularity of lead and silver, meanwhile, considering practical operation, the suitable condition in the Slurry Electrolysis of high-silver galena was determined as: yO(Cr)230g/L, p (Fe)-rl5g/L, liquid-solid ratio 15 M, pHl.O, electrolysis temperature 70"C, cathodic current density 150A/m , electrolysis time 1 Oh, and changing diaphragm every 3 hours. Under such condition, the main technical and economic results of galena Slurry Electrolysis are as follows:Leaching rate of lead/% >98Lead content of leaching residue /% 1.31Purity degree of cathodic lead powder /% 91.82Leaching rate of silver /% 80.15Cathodic current efficiency /% 70.12An experimental process jwas given, which is quite complex compared to traditional pyrometallurgy process.Preliminary probe into the leaching mechanism of galena in Slurry Electrolysis shows that in acidic NaCl solution, PbS is oxidized by Fe(III) accompanied by its chemical dissolution. According to S. H. Kim's conclusion.let A= , where aH, is the activity degree of tT in solution, Z aFe(Ill) isthe total activity degree of Fe(III) in solution. If A value is less than 4, PbS being oxidized by Fe(III) is the predominant way of leaching. If A value is more than 4, then the chemical dissolution of PbS prevails. Under our experimental conditions, A is far less than 4, so PbS being oxidized by Fe(III) is the main leaching way, which has been verified though the SEM analysis of the leaching residue.It is not feasible to replace lead pyrometallurgy with Slurry Electrolysis process. The main reasons lie in: Fine and close lead product can be got in cathode in silicofluoric acid system, but restricted by silicofluoric acid's decomposition in higher temperature, the leaching rate of galena is very low. On the other hand, because the solubility of Pb is very limited in chloride system, only lead powder can be got in cathode, which is very active and quickly oxidized into PbO. No matter how to deal with the PbO powder, the cost is greatly increased. What is more, after Slurry Electrolysis, Ag is quite meanly distributed among cathodic lead powder, leaching residue and leaching liquor, which makes the extraction of Ag complicated and increases the cost also. As a result, high additional value of high-silver galena makes no sense and the advantage for Slum' Electrolysis to process raw material with high additional value is lost. Lead belongs to low-priced metals with abundant reserves. As for its cost, Slurry Electrolysis cannot compete with the low-cost pyrometallurgy process centered by self-heating smelting.