| Titanium resource reserves are rich in Panxi area of China, and the proved titanium resource reserves are up to 870 million tons, belonging to rock-type ilmenite ore resources. The obtained ilmenite concentrate by beneficiation is with compact structure and high content of Ca, Mg and other impurities. To use the titanium resources in Panxi area of China on a large scale and effectively, many works for the production of Ti-rich material using Panxi ilmenite concentrate have been carried out. The high efficient and large-scale electric furnace smelting method has been chosen as main technical way and put into industrial production. However, the obtained titanium slag by electric furnace smelting from Panxi ilmenite with high content of Mg and Ca contained low TiO2 grade and high Mg and Ca content, which can not be used directly for production of titanium white by chlorination process and sponge titanium. Therefore, developing new technologies to get rid of impurities in the titanium slag is of great significance for the large-scale and efficient utilization of Panxi titanium resources.In this work, the titanium slag with high content of Mg and Ca from Pangang Company was taken as raw material, and the characteristics of titanium slag, impurities removal behavior in acid leaching process, the fundamental of activation roasting-acid leaching was systematically investigated. Based on the investigations, a new technology of producing high-quality synthetic rutile from titanium slag with high Ca and Mg content has been developed. The obtained conclusions were as follows.(1) In the titanium slag, TiO2 content was 72.24%, main impurities were Fe, Mg, Ca, Si and Al, especially, CaO+MgO content was up to 9.57%. The main mineral phases were anosovite solid solution and silicate minerals with mosaic structure, and the contents were 87.6%and 8.2%, respectively. Mg, Fe, Al impurities occurred mainly in anosovite solid solution, and Si, Ca occurred mainly in the silicate minerals.(2) The study of impurities dissolution behavior in the pressure acid leaching of titanium slag showed that pressure acid leaching could not remove impurities effectively, TiO2 grade of titanium slag only increased to about 75%. In the acid leaching process, adding NH4HF2 could strengthen dissolution of silicate minerals, however, the leaching effect of Mg, Fe, Al and other impurities dissolving in the anosovite solid solution was poor, and TiO2 grade of titanium slag was only about 80%. The poor dissolution effect of Mg, Fe, Al and other impurities dissolving in the anosovite solid solution was the main reason removing impurities and upgrading TiO2 significantly in the acid leaching.(3) The sodium salt-added roasting-acid leaching results showed that, Na2CO3 and titanium slag were mixed as mass ratio of 3:7, and roasted at 900℃for 2h, and the roasted product was leached by two periods sulphuric acid, and the leached residue was calcined, a synthetic rutile with 92.23% TiO2 grade and about 92% recovery and 0.78% CaO+MgO content was obtained.(4) The mechanical activation-sodium salt-added roasting-acid leaching showed that, after the titanium slag and Na2CO3 mixture being mechanically activated, under the same conditions as dealing with non-mechanically activated titanium slag, a synthetic rutile with 94.61% TiO2 grade and 0.68% CaO+MgO content was obtained.(5)The mechanism of sodium salt-added roasting-acid leaching showed that, the titanium slag adding Na2CO3 was roasted, sodium titanate, sodium ferrite, and the Na-Fe-Ti-O and Na-Mg-Ti-O system solid solution were produced. The impurities of sodium titanate, sodium ferrite and non-stoichiometric Na-Mg-Ti-O system solid solution substances had a good acid-solubility. During the leaching process, Na-Fe-Ti-O system solid solution was stable and the impurities were partially dissolved, and the titanium of the above compounds transformed rutile and anatase TiO2, which removed the impurities effectively and upgraded TiO2 of synthetic rutile significantly.(6) The mechanism of mechanical activation strengthening the impurities removal effect of sodium salt-added roasting-acid leaching was that mechanical activation improved the titanium slag and Na2CO3 kinetic conditions, and increased the mineral lattice defects, increased the cell volume, improved mineral lattice energy and reaction activity, which can strengthen the chemical reaction between Na2CO3 and titanium slag and promote the transformation of the anovosite into sodium titanate, sodium ferrite, Na-Fe-Ti-O and Na-Mg-Ti-O system solid solution and increase the impurities dissolution effect.(7) The activation roasting-acid leaching results of the Ti-rich material obtained by reduction-rust method showed that, under the same conditions as dealing with titanium slag, a synthetic rutile with 95%TiO2 grade and 0.69% CaO+MgO content.In this paper, based on the theories of the solid state reaction and mechanical activation, a new technology of producing high-quality synthetic rutile from titanium slag with high Ca and Mg content has been put forward its mechanism was systematically studied, and forming the fundamental of removing impurities from titanium slag with high Ca and Mg content by activation roasting-acid leaching technology. The new technology was used to deal with the Ti-rich material obtained by reduction-rust method, and good result was achieved. It is shown that the new technology has a good adaptability, and is suitable for titanium resources of high calcium and magnesium content. The study has opened up new way for large-scale and efficient use of titanium resources in Panxi area of China.
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