Study On The Hydrothermal Hydrolysis Of Fe(Ⅲ) To Hematite In Hydrometallurgical Zinc Smelting

At present,the environmental pollution caused by a large number of scrap iron slag has been paid much attention in zinc hydrometallurgy industry.The hematite residue has potential value due to its characteristics of stable,high iron content and big-density.It is the most ideal iron slag in zinc hydrometallurgy at the present.The hematite process involves oxydrolysis of ferrous sulfate and hydrolysis of ferric sulfate,the latter is the key.In this paper,hydrothermal hydrolysis of Fe（Ⅲ）to hematite was carried out in the sulfate solution containing Fe（Ⅲ）.The main contents and results are as follows:（1）The experimental study of hydrothermal hydrolysis of Fe（Ⅲ）to hematite has been carried out in Fe₂（SO₄）₃-H₂O system.The effects of temperature,time,initial Fe（Ⅲ）concentration,agitation speed,initial acid concentration on the iron removal process were investigated,the physical and chemical properties of the iron slag were analyzed by modern analytical methods,such as laser particle size analyzer,scanning electron microscope and X ray diffractometer.The results show that increasing the temperature,prolonging the reaction time,decreasing the initial Fe（Ⅲ）and acid concentration have obvious effect on hydrothermal hydrolysis of Fe（Ⅲ）to hematite.These not only can improve the iron removal efficiency,but also can effectively inhibit the formation of metastable phase such as basic ferric sulfate and carphosiderite,and reduce the content of sulfur in the hematite residue.It is helpful to obtain high-purity hematite residue.The agitation speed has obvious effect on the morphology and particle size of hematite residue.（2）The process of hydrothermal hydrolysis of Fe（Ⅲ）to hematite was further studied in Fe₂（SO₄）₃-ZnSO₄-H₂O system.The effects of temperature,time,initial Fe（Ⅲ）concentration,zinc ion concentration,hematite seed addition on the iron removal process were investigated.The results show that the iron removal efficiency was more than 96%,and the iron content of hematite precipitate is higher than 64%,sulfur content is lower than 1.6%,and zinc content is about 0.2%under the conditions of temperature of 200℃,retention time of 4h,initial Fe（Ⅲ）concentration of 15g/L,zinc ion concentration of 80g/L,agitation speed of 400r/min,seed addition of 25g/L.（3）The metastable phase such as basic ferric sulfate and carphosiderite is easy formed in the process of hydrothermal hydrolysis of Fe（Ⅲ）to hematite.It can transform to stable phase hematite in the case of increasing the temperature and prolonging the reaction time,and the iron content of the hematite residue can be increased and the sulfur content can be reduced.（4）In the process of hydrothermal hydrolysis of Fe（Ⅲ）to hematite,the existence of zinc sulfate can reduce the activity of acid in the solution,increase the speed of hydrolysis of Fe（Ⅲ）and the efficiency of iron precipitation significantly,and can effectively expand the stable range of hematite,play a very important role in the formation of hematite,and the increase of zinc sulfate concentration will not affect the zinc content of precipitate.According to the two systems of Fe₂（SO₄）₃-H₂O and Fe₂（SO₄）₃-ZnSO₄-H₂O,the existence of zinc sulfate can improve the initial Fe（Ⅲ）upper limit concentration and shorten the reaction time of the hydrolysis of Fe（Ⅲ）to hematite.