Study On High Value-added And Green Utilization Of Zinc Oxide Ore

Zinc is an important base metal. The main source of zinc metal production is zinc sulfide ore. Currently, with the gradual depletion of zinc sulfide ore and rapid rising demand of zinc metals, research focus has been transferred to zinc oxide ore. In this paper, a novel method was proposed for extracting valuable metals from zinc oxide ore. Theoretical and technical studies were carried out with the modern technology and some meaningful conclusions were obtained. 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 zinc oxide ore by (NH4)2SO4roasting method is determined.2. The technology process for extracting zinc from zinc oxide ore by (NH4)2SO4roasting 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.1) The effects of roasting temperature, the mole ratio of (NH4)2SO4to zinc in ore and roasting time on zinc extraction rate are investigated in (NH4)2SO4roasting process. The optimal condition is as follows:roasting temperature698K,n[(NH4)2SO4]/n(Zn)=1.4and roasting time90min. The zinc extraction rate is up to93%under these conditions. Since zinc was successfully extracted out of the ore, the elements of silicon, iron, lead, strontium were enriched in the zinc extracted residual compared with the original chemical composition.2) The influences of digestion temperature, time, liquid-to-solid ratio and stirring speed on zinc extraction rate were investigated in water-leaching process. The optimal condition is temperature363K, liquid-to-solid ratio4, stiring speed350r-min-1and holding time60min. The zinc extraction rate is93%under these conditions.3. The kinetics of (NH4)2SO4roasting process is studied. This process follows the shrinking unreacted core model, and the surface chemical reaction is the rate-controlling step. The activation energy is calculated to be45.57kJ·mol-1, and the kinetic equation is expressed 1-(1-α)1/3=30.85×exp(-45570/RT)t4. The digestion kinetics of sintered clinker to extract zinc from zinc oxide ore with (NH4)2SO4roasting process is studied. The digestion process is divided into two stages:0-5min for the first stag;5-30min for the second stage. The digestion rate of zinc in the first stag is faster than that in the second stage. The rate-controlling steps of the two stages are both the outer diffusion of no product layer. The activation energies of the first and second stages are calculated to be4.150kJ·mol-1and3.553kJ·mol-1, respectively, and the kinetic equations are expressed as:The first stage:1-(1-α)2/3=0.3291×exp(-4150/RT)tThe second stage:1-(1-α)2/3=0.0478x exp (-3553/RT)t5. The effects of H2O2addition, pH value, and temperature on deironing rate are investigated. The optimal conditions for this process are3%H2O2(mass fraction) addition2mL, pH value4-4.5, temperature353K. Under these conditions, the ρFe<0.005g·L-1is in the solution.6. Ultrafine ZnO powder was synthesized by precipitation method, using zinc sulfate solution and aqueous ammonium carbonate as raw material and precipitant, respectively. The ZnO powder was hexagon wurtzite structure and spherical figure with high purity and regular crystal form.7. The decomposition kinetics of basic zinc carbonate in nitrogen atmosphere was investigated in dependence on TG-DTA analysis under different heating rates. The non-isothermal kinetic parameters were acquired by means of Doyle-Ozawa and Kissinger method respectively, and the thermal decomposition mechanism of basic zinc carbonate was also analyzed with the Satava-Sestak method. The results showed that the reaction obeyed random nucleation and subsequent growth mechanism, and the kinetic equation can be drawn as: da/dt=Ae-E/(RT)f(a)=2Ae-E/(RT)(1-a)[-ln(1-a)]1/28. The effects of the concentration of NH4HCO3, the material ratio, the reaction temperature and time on Pb and Sr extraction rate are investigated. The optimal condition is as follows:reaction temperature338K, the concentration of NH4HCO31.5mol·L-1, n(NH4HCO3)/n(Pb)=3, n(NH4HCO3)/n(Sr)=3and time210min. Under these optimal conditions, the extraction rate of Pb and Sr are up to85%and87%, respectively. 9. The conversion reaction kinetics of NH4HCO3is studied. The effects of stirring speed, material ratio and reaction temperature on Pb and Sr extraction rate are investigated. The whole process follows the shrinking unreacted core model, and the outer diffusion of no product layer is the rate-controlling step. The activation energies are calculated to be13.85kJ·mol-1and12.67kJ·mol-1, respectively. The kinetic equations of the process can be expressed as:The conversion reaction of Pb:1-(1-α)2/3-2α/3=0.2027×exp(-13850/RT)tThe conversion reaction of Sr:1-(1-α)2/3-2α/3=0.1281x exp (-12670/RT)t...