| With the depletion of zinc resources,it is more and more important to recycle the secondary zinc resources.Zinc dust contains a certain amount of Fe,Zn,Pb,Cu and other metal elements,how to reasonably and effectively extract Zn and Pb and other valuable metals for recycling is a very important topic.In this paper,a new selective zinc leaching process with alkaline aminoacetic acid system(Gly--H2O)was proposed,taking the zinc dust as the research object.The study and analysis of dissolution thermodynamics of ZnO-Gly--H2O system are taken as theoretical guidance.The selective leaching of zinc dust from steel mill with high zinc ferrite content was strengthened by pressure with the aid of glycolic acid ion(Gly-).Finally,better separation results of ferric acid were obtained.The main contents and conclusions of this paper are as follows:(1)The dissolution thermodynamics of ZnO-Gly--H2O system was studied at 298K.After calculation by relevant thermodynamic software,the equilibrium curves of total zinc concentration([Zn2+]T),free zinc concentration([Zn2+])and free ligand concentration([Gly-])with total zinc concentration([Gly-]T)in the range of 0?3 mol/L and p H value in the range of 6?12 were plotted.The results show that[Zn2+]T increases linearly with the increase of the[Gly-]T when p H value is constant.On the other hand,when the ligand concentration is constant,when the p H is in the range of 6 to 8,with the increase of p H value,acid leaching is weakened,the total zinc concentration in the system decreases,and the effect of Gly-plus proton is weakened.The leaching process is transformed from acid leaching to coordination leaching,and the coordination effect of Gly-and Zn2+begins to be prominent.The zinc species changed from the primary coordination ion Zn(Gly)+to the secondary coordination ion Zn(Gly)2,and the free zinc concentration in the system decreased sharply.When the p H is in the range of 8 to 10,the interaction between Gly-and Zn2+is stable,and the change of[Zn2+]T tends to be gentle.In the early stage,the secondary coordination ion Zn(Gly)2 becomes the most zinc bearing species,and in the later stage,the secondary ligand Zn(Gly)2 changes into the tertiary ligand Zn(Gly)3-,and the transformation effect becomes more obvious.When the p H is in the range of 10 to 12,the system is in an alkaline environment,and the distribution of zinc species and ligand species in the system is in the form of Zn(Gly)3-and Gly-.The precipitation of Zn2+by OH-was dominant and easy to form precipitates.A large number of free Gly-is released,[Gly-]is increasing,and[Zn2+]Tand[Zn2+]are at a very low level.(2)The process conditions of selective leaching of zinc dust with alkaline Gly--H2O system were studied.The experimental results show that the system could dissolve zinc oxide(ZnO)and zinc sulfate(Zn SO4)completely,and could also dissolve and separate part of zinc ferrite(ZnFe2O4).After the leaching of pure chemical ZnFe2O4,it was found that the Gly-system could indeed leached ZnFe2O4,but the leaching rate was not high.It may be that the iron oxide inclusion layer is easily formed during the leaching process of ZnFe2O4,which hinders the further leaching of ZnFe2O4.In the leaching experiment of chemical pure ZnFe2O4,it was found that the leaching rate of Zn did not increase significantly at the later stage of the experiment,and iron oxide coating was formed during the leaching process of ZnFe2O4,which hindered the continued dissolution and separation of ZnFe2O4.The optimal process conditions were determined by single factor experiment in the later stage:reaction time of 4h,liquid-solid ratio of 25:1,ligand[Gly-]T=3 mol·L-1,reaction temperature of 130?,p H value of 8,stirring speed of r=600 r/min,reaction pressure of 2.5 MPa.The leaching ratio of Zn was 93.70%,the leaching ratio of Fe was 8.62%.The contents of Ca,Mg,Mn and Cu in the leached solution were 11.60 mg·L-1,12.98 mg·L-1,4.64 mg·L-1 and 3.13mg·L-1,respectively.The ligand Gly-has a weak coordination ability with impurity elements Fe,Ca and Mg,and has a good selectivity.(3)The reproducibility of the experiment and the stability of the leaching ratio of Zn and Fe and the concentration of impurity elements were verified by the comprehensive experimental results.The XRD analysis of the raw dust and the leaching residue and the XPS analysis of the iron element in the leaching residue showed that ZnO and Zn SO4 phases were completely dissolved after leaching,and ZnFe2O4 was dissolved and separated after being converted into Fe2O3 in the form of leaching residue sample. |
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