| Lead-zinc tailings contain a variety of toxic and harmful heavy metals.The lead-zinc tailings treated harmlessly and targeted extensive utilization is carried out according to the comprehensive nature of the treated tailings,thereby realizing the coordination of mining resource utilization and the development of ecological environmental protection is of great significance.In this study,two kinds of lead-zinc tailings samples were taken as research objects.First,supercritical CO2 extraction technology was used to extract the heavy metals Pb,Zn,Cu,Cr,Ni,etc.in the lead-zinc tailings and studied their extraction effects.For the evaluation index,the influence of factors such as the amount of complexing agent on the extraction rate of each heavy metal during the supercritical CO2 extraction process was investigated,and the optimal extraction process of heavy metal ions and the influencing factors were obtained through orthogonal experiments.The effects of this process on the properties of tailings samples were analyzed based on the leaching toxicity analysis,XRD patterns,and SEM results of lead and zinc tailings before and after the supercritical carbon dioxide extraction reaction.Furthermore,the supercritical extraction process was simulated by a shrinking kernel model through model selection,model assumption,and model fitting.Finally,the treated lead-zinc tailings were used as adsorbents to treat Cr6+ in simulated wastewater,and the adsorption performance of the lead-zinc tailings was discussed using the adsorption rate and the amount of adsorption as evaluation indicators.The effects of tailing amount,adsorption time,and initial adsorption concentration were investigated through single-factor experiments.The optimal process conditions for Cr6+ adsorption in simulated wastewater by lead-zinc tailings were obtained through orthogonal experiments.The process was fitted by the kinetic model and adsorption isotherm model,and the regeneration adsorption capacity of lead-zinc tailings was observed.The main concern of this study is the use of tailings resource and the removal of heavy metal ions.At the same time,it can provide the theoretical support for application of industrial through supercritical extraction process simulation.The results indicated that:(1)the supercritical carbon dioxide extraction technology has a better extraction rate for heavy metals in mixed systems in tailings,and explained that the treatment effect of Pb is the best.The Pb extraction rates in both tailings can reach 67.76%and 72.69%,the effect of different factors on the extraction rate of Pb is extraction pressure>extraction temperature>extraction time.The supercritical carbon dioxide extraction process has little effect on the micromorphology and mineral composition of tailings,but the leaching toxicity of tailings samples after supercritical carbon dioxide extraction reduced significantly.(2)Shrinking nucleus model can better simulate the process of supercritical CO2 extraction of heavy metals in mixed systems.The results indicated that the time and pressure factors were responsible to increase the extraction rate of Pb.The effect of pressure on the extraction rate is more significant.At the same time,the[1-(1-x)]1/3=kt model has a high correlation coefficient for the fitting of this process,and the process of supercritical CO2 treatment of heavy metals in lead-zinc tailings is the interface chemical reactions are reactions that control steps.According to the model fitting,extraction kinetic equations of two different tailings were obtained,and the activation energies of the respective reactions were 14.6 kJ/mol and 13.2 kJ/mol,respectively.(3)The use of lead-zinc tailings as an adsorbent has good adsorption performance for Cr6+ in simulated wastewater.At low concentrations,the adsorption efficiency can reach 99.19%.When the tailing amount was 8 g and the initial concentration was 50 mg/L,after 24 hours of adsorption,the lead-zinc tailing adsorption capacity was 163.72 mg/g.The results of the adsorption mechanism indicated that the pseudo-second-order kinetics can better fit the adsorption of Cr6+ in simulated wastewater by lead-zinc tailings,and the adsorption process is mainly controlled by chemical adsorption.At the same time,the Langmuir isotherm adsorption model indicates that the process is monolayer adsorption.Through adsorption regeneration experiments,the adsorption amounts of lead-zinc tailings after three elutions were 90.91%,84.21%,and 78.28%of the original adsorption amounts,respectively,indicating that the lead-zinc tailings have good adsorption ability and regeneration performance. |
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