Extraction Of Zinc And Lead From Low Grade Zinc Oxide Ore

Zinc is one of the base metals in industry and the third most common nonferrous metal in the world,after aluminum and copper.Because of a good corrosion resistance and alloy performance,zinc is widely used in modern industry.With the increasing amount of zinc and lead in China,zinc sulfide ore,the main source of zinc metal production,is nearly exhausted.For sustainable development,the development and utilization of zinc oxide ore source are necessary.The low grade zinc oxide resources are abundance in southwestern China,which are difficult to extract and recycle valuable metals with traditional smelting process.So a new treatment process according to the characteristics of china resources has typical value on practical significance and application.In this paper,a novel method was proposed for comprehensive extracting zinc and lead element from low grade zinc oxide ore using sulfuric acid roasting and calcium chloride complex leaching.Theoretical and technical studies were carried out systematically.Zinc sulfate solution for electrolytic zinc and basic lead chloride precursor were prepared and the products of removing impurity could be a raw material for iron making.The main contents and conclusions of this paper are as follows:1.Based on the results of thermodynamic calculation,the feasibility of extracting zinc from low grade zinc oxide ore by H2SO4 roasting method is determined.2.The technology process for extracting zinc from low grade zinc oxide ore by H2SO4 roasting method is studied.This technology mainly includes two parts:roasting process and water-leaching process.At the stage of zinc extraction,according to mineral analysis by XRD and SEM,the phase transitions were determined before and after roasting and water-leaching.The effects of reaction temperature,reaction time and molar ratio of acid to ore on extraction rate of Zn,Fe,A1 were investigated.Optimum reaction conditions are obtained through orthogonal experiments.Results show that the extraction rates of Zn,Fe and A1 were 99.02%,23.78%and 77.68%,respectively,when the ores were roasted for 120 min at 673.5 K and molar ratio of acid to ore of 1.6:1.The elements of Si,Ca and Pb are accumulated in the residue.The influences of digestion temperature,time,liquid-to-solid ratio(L/S)and stirring speed on zinc extraction rate were investigated in water-leaching process.The optimal condition is temperature 363 K,L/S 5,stiring speed 300 r-min-1 and holding time 70 min.3.The technology process for removing iron and aluminum from zinc sulfate obtained by is studied.The effects of H2O2 addition,pH value,and temperature on deironing rate are investigated.The optimal conditions for this process are 3%H2O2(mass fraction)addition 4 mL,pH value 5,temperature 363 K.Under these conditions,iron and aluminum concentrations in the solution are less than 0.01 g·L-1,both of the removal rates can reach to 99%.4.Based on the results of thermodynamic calculation,the feasibility of extracting lead from zinc leach residue by acidic calcium chloride aqueous solution is determined.5.The leaching experiment of lead from zinc leach residue in acidic calcium chloride aqueous solution is studied.Six main process conditions,the solution pH,stirring rate,concentration of CaCl2 aqueous solution,L/S,leaching temperature,and leaching time,were investigated.Optimum reaction conditions are obtained through orthogonal experiments,the optimum reaction conditions were determined to be a solution pH of 1,a stirring rate of 500 r·min-1,a CaCl2 aqueous solution concentration of 400 g·L-1,a L/S of 7:1,a leaching temperature of 353 K,and a leaching time of 45 min.The leaching rate of lead under these conditions reached 93.79%,with an iron dissolution rate of 19.28%.6.The conversion reaction process of leaching lead from zinc leach residue in acidic calcium chloride aqueous solution is studied.The whole process follows the shrinking unreacted core model,and the internal diffusion of product layer is the rate-controlling step.The activation energy is calculated to be 30.76 kJ·mol-1.The apparent reaction order is 1.524.The equations of the process can be expressed as:1-(1-?)2/3-2a/3=206.23·exp(-30760/RT)·t.7.In acidic chloride complex system,adjusting the solution pH value was adopted to separate lead and iron in solution.The effects of pH value,temperature H2O2 addition and reaction time on removing iron rate are investigated.Based on orthogonal experiments,optimum reaction conditions is as follows:pH value 3;reaction temperature 323 K;H2O2 addition 1.0 mL;reaction time 15 min.The conversion rate of iron is 99.98%,loss rate of lead is 3.84%.The separation of iron and lead is identified effectively.Fe2O3 as the afterproduct is obtained by high-temperature calcination of iron precipitation.8.The acidic chloride complex solution after purification is raw material.Ca(OH)2 is the reagent for adjusting the solution pH value.The effects of pH value,reaction temperature and time on Pb precipitating are investigated.Through orthogonal experiment design,the optimal condition is as follows:pH value 7.5,reaction temperature 323 K and reaction time 7.5 min.Under these optimal conditions,the extraction rate of Pb is up to 99%.The precursor PbOHCl is obtained.