The Preparation Of High Quality Synthetic Rutile By Yunnan Ilmenite

In recent years, the chloride process is the development tendency of the worldwide titanium pigment industry. Although the chloride method is very popular in our country, there are still a lot of problems, especially in the manufacture of high quality raw materials. The problem of raw materials has been the biggest impediment of our titanium industry. The only way to rid our dependence on imported ores is finding a suitable way to manufacture high quality synthetic rutile by the local ores. In the production of synthetic rutile, the method of hydrochloric acid leaching was widely used by many factories, as its high leaching rate of impurities and hydrochloric acid have the use of recycled.In this study, large amounts of theoretical analysis and experimental researches were investigated about Yunnan ilmenite. In this study, the leaching behavior of oxidized ilmenite, reduced ilmenite and untreated ilmenite were investigated. The untreated Yunnan ilmenite was shown to be less reactive for leaching with hydrochloric acid, and has a high fine rates(about 30~40%). Both the reduced ilmenite and oxidized ilmenite were shown to be more reactive for leaching, but the reduced ilmenite has a high fine rates(about 30~40%). However, the oxidized ilmenite had a low fine rate(about 5%).When utilize the process of hydrochloric acid atmospheric pressure leaching, we did a series of experiments. Studies have shown that it needs a high acid concentration and ratio of liquid to solid, and the TiO2 content in leaching product can not higher then 91%. Pressure leaching can lower the acid concentration and reduce the leaching time. The investigation shown that only use 20% hydrochloric concentration the leaching product can get a good quality(TiO2 92%) when adapting one step pressure leaching process. But it needs a large ration of liquid to solid. What’s more, the condition of high acid concentration(about 12~13%) and low iron concentration(44g/L) of the mother liquid has the largest effect on the recovery of the hydrochloric acid. When utilizing a two step pressure leaching process which the first stage leaching using the mother liquid of the second stage leaching and the second stage leaching using the fresh acid(20% hydrochloric acid). Both stages utilized liquid to solid ratio of 5:1, leaching temperature of 140℃, leaching pressure of 0.175 MPa and leaching time 4h. Utilizing two step pressure leaching has a significant influence to acquire the high quality synthetic rutile, low down the liquid to solid ratio and improve the quality of the mother liquid(7% acid concentration and 75g/L iron concentration).In order to find out the reaction mechanism and control step of the hydrochloric acid leaching of Yunnan ilmenite, we conducted a series of experiments. The mechanism of leaching indicated that, the diffusion in residual layer was the rate–determining step for the dissolution of iron both in un-treated and oxidized ilmenite. The apparent activation energy for leaching of un-treated and oxidized ilmenite was estimated to be 62.45 and 55.21 kJ/mol, respectively. The apparent activation energy for pressure leaching oxidized ilmenite was estimated to be 24.64 kJ/mol.A mechanism of the formation of fine materials was proposed through analyzing the behavior of dissolution and hydrolyzation of titanium. The only way to minimize the fine materials is increasing the proportion of heterogeneous nucleation once the way of leaching was determined. The key is to make sure the ore resist smashing, and low down the proportion of hydrolyzing on the crushed ores. The untreated ilmenite need a long time to hydrolyze, this makes the surface of the ore easy to be broken. As the large amount of needle crystals and cracks on the surface of the reduced ilmenite make the ore easy to be crashed. What’s more, the surface of the hydrolyzation products was covered by little needle crystals. The external hematite of oxidized ilmenite was dissolved in the solution in the initial stage of leaching, the rutile crystal can be exposed and acted as a crystal core of the dissolved titanium dioxide. After that, the dissolved titanium will hydrolyze on the crystal core. When a dense product layer was formed, the hydrolyzation will mainly occur on the internal surface of the product layer. Simultaneously, the dissolved titanium in the solution hydrolyze on the outside surface of the product layer. This makes the leaching products of the oxidized ilmenite have a low rate of fine materials.