Study On Deep Extraction Of Vanadium From Calcified Acid Leaching Tailings

The acid leaching filter residue produced by the"calcification roasting-acid leach-ing"process of vanadium slag is called the vanadium extraction tailings.Only the vana-dium industry in my country produces more than 1.2 million tons of vanadium extrac-tion tailings each year,which contains 1.4%to 1.7%V₂O₅,and the vanadium content is relatively high.The storage of vanadium extraction tailings on the ground not only caused serious environmental problems but was also a waste of resources.Vanadium is mainly contained in the vanadium extraction tailings in a low-valence state,and there is the phenomenon of being wrapped and blocked,making it difficult for vanadium to be deeply leached.At present,the techniques for extracting vanadium from the tailings of vanadium extraction include:pressurized acid leaching;mechanical activa-tion-reroasting;normal pressure high concentration acid leaching;ultrasonic enhanced acid leaching.These technologies have problems such as high energy consumption and high requirements for equipment safety performance,which are difficult to promote on a large scale.Therefore,the proposal of a safe and effective enhanced vanadium extrac-tion technology has become very critical.The vanadium extraction tailings produced by the calcification roasting-acid leaching of Panzhihua Iron and Steel as raw materials is used in the thesis.Based on the hydrometallurgical field coupling strengthening technology and chemical additive strengthening technology,because of the silicate and spinel coating in the vanadium ex-traction tailings,and the blockage of calcium sulfate dihydrate,it was proposed to use electric field coupling Ca F₂ to destroy the package structure.In view of the difficulty of leaching the low valence vanadium in the vanadium extraction tailings,a method of electric field coupling H₂O₂ to oxidize vanadium was proposed.The experiments and kinetics research of regular leaching process,chemically enhanced leaching process,and electric field coupling enhanced leaching process of vanadium extraction tailings were carried out.The main conclusions and research results are as follows:(1)For the characterization and analysis of the vanadium extraction tailings,the contents of V,O,Fe,Ca,Ti,Si,Mn and other elements in the vanadium extraction tail-ings measured by XRF were 1.42%,32.26%,27.18%,8.82%,7.22%,7.10%,3.95%respectively.SEM characteristic analysis showed that the vanadium extraction tailings appeared wrapped and agglomerated,presenting three forms.One form was an irregular layered structure,and the second form was a rod-like structure wrapped by an irregular layered structure.In addition,It can be seen that there are a large number of fine parti-cles attached to the uneven layered surface.XPS analysis shows that there are V(III),V(IV),V(V)in the vanadium extraction tailings,the contents are 12.39%,65.58%,and22.02%respectively;V,O,Ca,Mn,Fe,S are concentrated on the same position on the tailings surface by the surface element distribution test.Combined with XRD analysis results,the main phases in the vanadium extraction tailings are Ca SO₄·2H₂O,Fe₉Ti O₁₅,Fe₂O₃,(Mn,Fe)(V,Cr)₂O₄,and vanadium mainly exists in the spinel structure.(2)Based on the perspective of phase destruction and low-valent vanadium oxida-tion,experiments were carried out.The improvement of the leaching efficiency in the regular leaching process is limited.When the leaching time is 80 min,the leaching temperature is 80?,the volume ratio of sulfuric acid to water is 1:4,and the leaching rate is only 40.01%.In the regular leaching process,the wrapped phase was not effec-tively destroyed,and the low-valent vanadium was not leached out by oxidation.The chemical additives H₂O₂ and Ca F₂ were used to intensify the leaching process,and it was found that Ca F₂ promoted the decomposition of the encapsulated phase,and H₂O₂promoted the oxidation of low-valent vanadium.When the leaching conditions are:leaching time of 80 min,leaching temperature of 80?,sulfuric acid to water volume ratio of 1:4,n(H₂O₂/V)of 7:1,Ca F₂ addition amount of 3 wt.%,the leaching efficiency reaches 53.68%.The(Mn,Fe)(V,Cr)₂O₄ diffraction peaks in the slag after the electric field coupling H₂O₂ and Ca F₂ enhanced leaching have disappeared,and the overall peak intensity in the leaching filter residue is weaker than that in the original slag.Under the action of an electric field,Ca SO₄·2H₂O became Ca SO₄·0.67H₂O with a lower water content.When the leaching time is 60 min;the leaching temperature is 80?;the vol-ume ratio of sulfuric acid to water is 1:4;and n(H₂O₂/V)is 7:1;the additional amount of Ca F₂ is 3 wt.%and the current density is 1000 A/m²,the leaching efficiency is increased to 71.22%,and the residual vanadium content is 0.41%.(3)After the electric field was introduced,on the one hand,it is coupled with Ca F₂to effectively destroy the wrapped phase,releasing more vanadium-containing phases to react with the leaching agent.On the other hand,the oxidizing groups(O₂,·OH)gener-ated by the electric field anode combine with H₂O₂ to oxidize the low-valent vanadium,thereby increasing the leaching rate of vanadium and reducing the residual vanadium content.The particle size test and scanning electron microscope observation of the filter residues in different leaching processes showed that the particle size of the filter resi-dues obtained by the electric field coupling enhanced leaching was smaller than the fil-ter residues obtained by chemical strengthening and regular leaching,and the weight ratio was larger than the surface,and the surface of the slag particles was cleaner.(4)Based on the principle of kinetic analysis,the kinetic characteristics of regular leaching,chemically enhanced leaching,and electric field coupling enhanced leaching system were studied.The results show that the speed control steps in the three leaching systems are solid film diffusion,and the reaction model is a shrinking core model.The kinetic equation of the regular leaching system can be expressed as:1+2(1-x)-3(1-x)^2/3=D·exp(-32.98/RT),and the apparent activation energy is 32.98 k J/mol;the kinetic equa-tion of the chemically enhanced leaching system can be expressed as:1+2(1-x)-3(1-x)^2/3=D·exp(-29.27/RT),and the apparent activation energy is 29.27 k J/mol.Under the electric field coupling enhanced leaching system,the kinetic equation is:1+2(1-x)-3(1-x)^2/3=D·exp(-25.36/RT),and the apparent activation energy is 25.36k J/mol.