Study On The Iron Removal Behavior And Thermodynamic Analysis Of Hematite In High Potassium Sodium Solutio

Iron is one of the main impurity elements in raw materials cont aining zinc.No matter what kind of raw material was used to extract zinc,the separation of iron is an inevitable process.Among the currently available iron removal processes,iron precipitation as hematite from hydrometallurgical process solutions is un doubtedly the most potential technology for iron removal without waste residue.The neutralized raffinate of acid leaching solution of secondary zinc oxide powder has the characteristics of high concentration of K⁺and Na⁺.How to control the formation and transformation of jarosite in the process of iron removal,so that the iron in the solution was finally precipitated in the form of hematite is a difficult problem for the iron removal by the hematite process in the solution with high concentration K⁺and Na⁺.It is also an urgent problem to be solved in the production of the current combination of pyro-hydrometallurgical processes of secondary zinc resources.Thermodynamics and quantum chemistry were used to analyze the phase transformation law of jarosite,and the behavior of potassium and sodium in the process of iron removal by hematite process under various control conditions was systematically studied.It provides theoretical basis and data support for obtaining the optimal process conditions for iron removal from the solution with high concentration K⁺and Na⁺.The thermodynamic equilibrium of sulfate between solid and liquid phase is the bottleneck of high-efficiency iron removal technology by hematite process.However,it is difficult to measure the solubility of the closed system in high temperature.The solubility of sulfate system was studied by thermodynamic model,providing an alternative method for obtaining the solubility phase diagram of the sulfate at high temperature.The specific research work s and results were summarized as follows:（1）In the actual solution system,the effects of temperature,agitation speed,and seed addition on the iron removal effect of hematite process in the solution with high concentration K⁺and Na⁺were studied.The iron removal residue and solution after iron removal was characterized by modern analysis and testing methods such as multi-element composition,chemical phase,XRD and SEM-EDS.The optimized technical conditions were as follows:reaction temperature 185°C,reaction time 3 h,oxygen partial pressure 0.4 MPa,seed addition 15 g/L,and stirring speed 500 rpm.Under these conditions,high-quality iron residues can be obtained.The iron content of residue is 59%,sulfur content is 3.22%,potassium content is 1.31%,sodium content is 0.17%,zinc content is 0.94%,and the iron con centration of solution after iron removal is less than 4.1 g/L,reaching the current technological standard of hematite process for iron removal.（2）The molecular dynamics calculation results show that Na-jarosite is more difficult to form and easier to decompose than K-jarosite,which is consistent with the calculation results of thermodynamics.The first part to decompose in the jarosite unit cell is the O-H bond.The study on the oxidation reaction kinetics of ferrous iron showed that with the increase of stirring speed,the oxidation rate of ferrous i ron accelerated,resulting in an increase of the concentration of ferric ions in the solution,which was conducive to the formation of jarosite.The stirring speed determines the phase composition of the iron removal residue,which is the key point to real ize the iron removal by hematite process in the solution with high concentration K⁺and Na⁺.（3）In the simulated solution,it is found that when potassium ion exist ed alone in the solution is greater than 1 g/L,there is large amounts of jarosite in iron removal residue,resulting in the reduction of residue grade.It can not be utilized as resource.As the introduction of sodium ions,the sulfate ions were introduced into the solution,leading to a reduction of the solubility of ferro us sulfate and incomplete oxidation of ferrous ions.If the ratio of sodium ion to potassium ion concentration is greater than1:1,with the increase of sodium ion concentration,the cell of sodium ion in the solution are increasing.The collision frequency of the cell between[Fe₃（SO₄）₂（OH）₆]^-and Na⁺is increasing,increasing the probability of the formation of Na-jarosite in the solution.The Na-jarosite formation in the reaction process was enhanced and it is rapidly transformed into hematite.On the contrary,K-jarosite was preferentially generated during the reaction process and was not easily converted into hematite.This results in the decrease of iron content and the increase of potassium and sulfur content in the residue.When the ratio of sodium ion to potassium ion concentration increases to 4:1 or above,the iron content of residue is>55%,sulfur content is<4%,and total iron concentration after iron removal is<1.7 g/L.Hematite residue and iron removal solution in accordance with the technical standards of hematite process.The concentration of fluorine ion and chloride ion in the solution before iron removal has a great influence on the concentration of total iron and ferrous iron in the solution after iron removal,which may be ca used by the negative salt effect.（4）The solubility calculation model of Pitzer equation was established because the experimental measurement of solubility of the closed system at high temperature is difficult.16 types of systems contaning 20 groups of the solubility data of ternary system were verified and calculated.It involves the solubility calculation of the ternary system containing Zn²⁺,Mg²⁺,Mn²⁺,and Cu²⁺.The calculated results are in good agreement with the experimental values.It is also shows that Pitzer equation can be used to calculate the solubility of hematite process solution system.Aiming at the problem that Pitzer equation is highly empirical and needs 3-4 parameters with unclear physical meaning to describe a single electro lyte system,the two parameter s e MIVM model was introduced.The results show that the accuracy of e MIVM calculation results can not be compared with Pitzer equation due to the error accumulation.Therefore,Pitzer equation was used to calculate the solubility of the sulfate system.（5）There are few the experimental data of sulfate solubility at high temperature.However,the ternary ion interaction parameters of Pitzer equation must be fitted by a certain amount of experimental data.Aiming at the contradiction between the two parties,a new method was proposed,which only uses the solubility data at the eutectic point to fit this parameter.This reduces the experimental data required for fitting.The solubility phase diagrams of the binary Fe SO₄-H₂O system,Zn SO₄-H₂O system,K₂SO₄-H₂O system,and Na₂SO₄-H₂O system at high temperature were calculated by the Pitzer equation and the empirical relationship between the dissolution equilibriu m constant and the temperature.The relationship between the parameters and the temperature is given,and the calculated results are in good agreement with the experimental values,providing essential parameters for the thermodynamic calculation of the multicomponent system in the later stage.Through the calculation of the solubility of the key ternary system,it was proved that the fitting method of the ternary parameter is an effective calculation way,provid ing an excellent calculation mode for the solubility calculation of the multi-component system at high temperature.