Research On High Value-added Resource Utilization Of Zinc In Blast Furnace Dust

In the process of iron and steel production,3%zinc-containing dust and sludge of crude steel output is generated due to flue gas dust removal and wastewater treatment,which is of great recycling value.The zinc element in blast furnace dust was enriched by pyrolytic reduction and volatilization;secondly,zinc-rich dust was leached by wet method with sulfuric acid;finally,nano-zinc oxide was prepared by direct precipitation method.The subject research provides a new idea for the efficient utilization of zinc resources in metallurgical dust and sludge.The main conclusions are as follows:（1）Taking blast furnace bag dust as the research object,the effects of Ca CO₃addition,temperature and time on zinc volatilization rate during the reduction process were studied.When adding Ca CO₃to the dust,increasing the addition amount or raising the reduction temperature,a higher zinc volatilization rate can be obtained in a shorter time.Under the same conditions,without the addition of Ca CO₃,the volatilization rate of zinc increased from 52.96%to 76.26%;with the addition of 10 wt.%Ca CO₃,the volatilization rate of zinc increased from 62.32%to 98.98%.（2）In the process of carbothermal reduction by adding Ca CO₃ to dust,CO₂,the decomposition product of Ca CO₃,promotes the gasification reaction occurs,which improves the indirect reduction,and the other decomposition product,Ca O,acts as an active site and further promotes the reaction and increases the volatilization rate of zinc.（3）Taking zinc-rich dust as the research object,the effect of leaching process parameters on zinc leaching rate was studied by single factor experiment.The optimal parameters of the leaching process are:sulfuric acid concentration of 2 mol·L^-1,temperature of 60℃,time of 90 min,liquid-solid ratio of 8:1,at this time,the zinc leaching rate is 95%.（4）Based on single factor experiment,the leaching process was optimized by orthogonal experiment method.The order of significance of factors is:sulfuric acid concentration>liquid-solid ratio>temperature>time.The optimal solution is:sulfuric acid concentration of 2.0 mol·L^-1,liquid-solid ratio of 8:1,temperature of 60°C,and time of90 min.Under these conditions,the leaching rates of zinc and iron are 95.15%and 8.47%,respectively.Kinetic studies using a condensation model show that the leaching process of zinc-rich dust is controlled by a chemical reaction with an apparent activation energy of 14.45 k J·mol^-1 and reaction order of 0.6.After purification,the zinc leaching solution contains almost no impurities and can be used to prepare nano-zinc oxide.（5）Nano-zinc oxide was prepared by neutralizing the precipitated zinc leaching solution with sodium hydroxide and sodium carbonate,and the effect of preparation process on the morphology of nano-zinc oxide was studied.The sodium hydroxide precipitation experiment showed that the molar concentration of OH^-increased from 3times to 5 times that of Zn²⁺,the phase of the precipitate changed from Zn（OH）₂ to Zn O,and the morphology changed from flake to rod;when the temperature increased from50°C to 70°C,the precipitate phase was Zn O,and the morphology changed from rod-like to a mixture of flakes and rods.The sodium carbonate precipitation experiment showed that the precipitation product was basic zinc carbonate,and linear nano-zinc oxide could be obtained by calcining at 400°C for 30 min.Using blast furnace dust as raw material,it is feasible to prepare nano-zinc oxide by high temperature reduction-acid leaching-direct precipitation process,which provides a possible idea for realizing the resource utilization of blast furnace dust.