| With the depletion of ores and rapid rising of the metal price, the processing of low grade, difficult processing ore becomes an important strategic aspect of the nonferrous metal industry. Theoretical and technical studies on the extraction of the valuable metals from low grade zinc ores in details were carried out with the modern testing technology and some meaningful conclusions were obtained.A new process of "low temperature roasting-water leaching, leaching solution returned to purifying process in zinc smelting system after removal of iron, chloride leaching of silver and lead from slags after water-leaching" was proposed. The thermodynamics was studied which was mainly related to the possibility of reactions about franklinite, zinc oxide, zinc silicate and sulfuric acid. This will provide the theoretical basis for the research on the processing of low grade zinc oxide ore by roasting-water leaching. At the stage of zinc extraction, according to mineral analysis by XRD,EDS and SEM, the phasa transitions were determined before and after roasting and water-leaching; the effects of various parameters, such as roasting temperature, roasting time, the amount of sulfuric acid, leaching time, leaching temperature, and liquid/solid ratio on zinc leaching rate were studied. Systematic studies indicate that high zinc leaching rate can be achieved under the following conditions:sulfuric acid addition,70%weight of zinc oxide ore; duration,2h; temperature,250℃at roasting stage; and room temperature, liquid/solid ratio4, and duration time0.5h at leaching.In this work, the dissolving characteristic and the condition converting to another phase of each phase in the systerm were studied; the equilibrium concentrations of various ions were determined based on simultaneous balance principle and charge muutrality in Ag2SO4-PbSO4-HCl-NaCl-H2O system. These provide theoretical basis for chloride leaching of silver and lead simultaneously.The dissolution kinetics of silver and lead by chloride simultaneously from residues after zinc extraction have been investigated.The dissolution kinetics followed a shrinking core model, with inter-diffusion through gangue layer as the rate determining step. This finding is in accordance with the apparent activation energy (Ea) of26.8kJ/mol (Ag) and26.5kJ/mol (Pb), and a linear relationshipbetween the rate constant and the reciprocal of squared particle size. The order of reaction with respect to sodium chloride concentration, temperature andparticle size were also achieved. The rate of reaction based on diffusion-controlled processcan be expressed by semi-empirical equations.The process of treating the residue after zinc extraction by chloride leaching was developed. The effects of experimental conditions, such as reaction temperature, sodium chloride concentration, liquid-solid ratio, acidity as well as reaction duration, were investigated. The results show that the additive does not affect leaching rate of lead while it can increase leaching rate of silver significantly. The leaching rate of silver and lead were augmented with increasing the concentration of sodium chloride and liquid-solid ratio; the amount of hydrochloric acid has little influence on the lead extraction, but has more effect on that of the silver. The optimum process conditions are obtained, which are leaching temperature90℃, sodium chloride concentration390g/l, additive amount15ml/10g residue, liquid-solid ratio7:1, acidity3ml/10g residue, time3h. Under these conditions leaching rates of lead and silver can reach about95%and90%.
|
PDF Full Text Request