Study On Activity-roasting Of Boron-rich-slag And Boron Concentrate

Boron ore is a rare chemical mineral. Boron compounds produced by using the boron ore are widely used in chemical industry, metallurgy, optical glass, national defense, atomic energy, medicine, rubber, light industry and so on. Main boron mineral resources in China are ascharite and paigeite. Ascharite which can be directly employed to produce boron compounds, has been nearly exhausted because of exploitation for many years, and can not fully meet the future needs of boron compound production. Paigeite accounts for 58 percent of the total of boron mineral resources in China. However, it is difficult to separate paigeite by conventional methods. Therefore, the expediting development and utilization of paigeite resources has a great practical significance to relieve the contradiction of boron resources in our country.In this paper, boron concentrate obtained from paigeite mineral by magnetic separation was treated by using a soda-magnetizing roasting method which calcined boron concentrate with active carbon and sodium carbonate in high temperature. Soda can react with difficult-leaching ludwigite to magnetite and soluble sodium borate and carbon can avoid magnetite being oxidized to ferric oxide in the soda-magnetizing roasting process. The magnetism of boron concentrate roasted by this method can be maintained for further magnetic separation. Boron concentrate was characterized by chemical analysis, thermal analysis and XRD. The XRD analysis shows that the major minerals of boron concentrate were biotite(K[Mg,Fe]3[Al,Fe]Si3O1o(OH,F)2,quattz (SiO2),chrysolite (Mg3[Si2O5](OH)4),magnetite (Fe3O4),fibre ascharite(Mg2(OH)[B2O4(OH)]) and ludwigite ([Mg, Fe]2Fe[BO3]O2). The effects of active carbon addition on the reactive activity and magnetism of soda-magnetizing roasting mineral were investigated, respectively. The results indicate that the suitable processing parameters are Na2CO3 addition 26.7% by weight of original mineral, calcining temperature 950℃and calcining time 2h, and the reactive activity of the calcined boron concentrate reaches 90.49% under these conditions; the content of FeO% in the calcined concentrate was increased from 0.17% to 8.40% and reactive activity was 86.8% under above conditions when adding active 4g carbon. The magnetism of calcined mineral was obviously increased and the reactive activity was slightly reduced after the addition of active carbon. Secondly, the effects of sodium activated calcination and calcified calcination on improving the reactive activity of boron-rich-slag obtained from ludwigite by pyrometallurgical process were investigated, respectively. The XRD characterization and reactivity analysis of boron-rich-slag indicated that the major mineral phases of boron-rich-slag were suanite and forsterite, and reactivity of boron-rich-slag is 50%. The influences of additive addition and roasting temperature on the reactive activity of boron-rich-slag were investigated with CaCO3 as additive. The result indicates that the reactive activity of boron-rich-slag was increased with the addition of CaCO3 increasing. The reactive activity of boron-rich-slag was increased from 50% to 86% when 18g of CaCO3 was added into 30g of boron-rich-slag and the boron-rich-slag was calcined at 950℃for 2h. In addition, when taking the calcium oxide as additive, the reactive activity of boron-rich-slag is close to 80% lower than that of CaCO3 with the same conditions. On the other hand, the reactive activity of boron-rich-slag was increased from 50% to 79.62% when 8g of Na2CO3 was added into 30g of boron-rich-slag in sodium activated calcination process and the boron-rich-slag was calcined at 950℃for 2h. The reasons for improving the reactivity of boron-rich-slag can be ascribed to the formation of crystalline Ca3(BO3)2 by the reaction of CaO obtained from CaCO3 with vitrious B2O3 and the formation of crystalline sodium borate by the reaction of Na2O formed from Na2CO3 with vitrious B2O3 in calcified calcination process.