真空碳热还原锂辉石矿提取Li同时回收Si和Al的探究

Vacuum Carbothermal Reduction of Spodumene Ore to Extract Li and Simultaneous Recovery of Si and Al

针对目前锂辉石矿提锂工艺资源利用率低、对环境污染大等问题,探究一种全新的处理锂辉石矿的方法:从锂辉石矿中提取Li的同时对其中占主要成分的Si和Al进行回收。通过理论计算和实验探究表明,直接碳热还原锂辉石提取Li同时制备Al-Si合金的工艺很难实现,矿石中的SiO_(2)被还原SiC和SiO气体,无法得到单质Si,而Li Al Si_(2)O_(6)由于自身非常稳定,在实验温度范围内不会发生反应。加入Fe2O_(3)碳热还原锂辉石矿提取Li同时制备Si-Fe合金回收Al_(2)O_(3)的理论和实验探究表明,Fe2O_(3)可以有效促进锂辉石中SiO_(2)和Li Al Si_(2)O_(6)碳热还原反应的发生。还原过程中Li被还原为Li蒸气在冷凝系统中得到收集,同时在还原剩余物中可以得到Si-Fe合金和Al_(2)O_(3)。因此,本文提出添加Fe2O_(3)真空碳热还原锂辉石矿提取Li同时制备Si-Fe合金回收Al_(2)O_(3)的工艺,整个还原过程中,Li的还原率为92.69%,冷凝物中的Li2O含量为36.21%,同时在还原剩余中可以将矿石中的Al和Si以Al_(2)O_(3)和Si-Fe合金的形式有效分离。与现有的锂辉石矿提锂技术相比,本方法具有工艺流程简单,几乎不产生废水、废渣,对环境友好、资源利用率高等优点。

In recent years,lithium consumption has increased significantly owing to its extensive use in portable electronic devices,power devices such as electric vehicles,and grid energy storage.Spodumene ore is the most widely used raw material in lithium extrac⁃tion technology from ores.The existing processes for extracting Li from spodumene ore are all based on the principle of high-tempera⁃ture roasting to excite the minerals chemically.The processed spodumene ore is subsequently acid or alkali leached to extract Li from the spodumene crystal lattice.Using sulfuric acid for the above process is currently the most tested approach for extracting Li from spodumene ore.However,the existing lithium extraction technology from spodumene ore involves the conversion of the main compo⁃nents(16%~25%Al_(2)O_(3) and 50%~75%SiO_(2))in the spodumene ore while producing an acid/alkaline Al-Si-based hazardous waste.This represents a significant waste of resources,because residues from the spodumene process are difficult to handle and can cause high pollution to the environment.To address these issues regarding lithium extraction from spodumene ore,this study investigated a novel method to process spodumene ore that comprises the extraction of Li from spodumene ore and the recovery of major Si-and Al-containing compounds.Specifically:direct vacuum carbothermal reduction of spodumene ore to extract Li while preparing Al-Si alloy and vacuum carbothermal reduction of spodumene ore by adding Fe2O_(3) to extract Li,preparation of Si-Fe alloy,recovery of Al_(2)O_(3).This was based on theoretical calculations and experimental methods.First,equilibrium compositions for the carbothermal reduction reac⁃tions of Al and Si oxides reported in previous studies based on the Outotec HSC Chemistry Software HSC6.0 were used to perform ther⁃modynamic simulations on both reduction processes.Second,experimental procedures considering those theoretical calculations were carried out for the two processes.Carbothermic reduction experiments were conducted at different reduction temperatures,and the re⁃duction products were characterized using X-ray diffraction(XRD),scanning electron microscopy-energy dispersive X-ray spectrosco⁃py(SEM-EDS),and inductively coupled plasma-optical emission spectroscopy(ICP).The theoretical calculations for the direct car⁃bothermal reduction of spodumene ore to extract Li,while the preparation of Al-Si alloy,demonstrated that SiO_(2) mainly generated SiC during the reduction process,and large amounts of SiO gas were gradually generated with increasing temperature.Therefore,it was dif⁃ficult to obtain Si via the vacuum carbothermal reduction of SiO_(2).During the process,LiAlSi_(2)O_(6) reacted at approximately 1300 K,produc⁃ing Li gas and Si that eventually formed SiC and SiO gas.Al was separated from LiAlSi_(2)O_(6) as Al_(2)O_(3),which was then reduced by C to produce intermediate products such as Al4CO4 and Al_(2)CO that were eventually volatilized in the form of Al_(2)O gas.Through the simula⁃tion analysis of the vacuum carbothermic reduction process of LiAlSi_(2)O_(6) and SiO_(2),it was observed that most of Al and Si volatilized as Al_(2)O(g)and SiO(g)with increasing temperature,and Al-Si alloys were difficult to obtain.The experimental data indicated that SiO_(2) in the ore reduced to SiC and SiO gas during the process,which was consistent with theoretical calculations.However,LiAlSi_(2)O_(6) could not be reduced,and the theoretical calculations differed.This could be explained because LiAlSi_(2)O_(6) was a very stable compound that was frequently used to prepare refractory materials.The carbothermal reduction of LiAlSi_(2)O_(6) could be achieved as the temperature in⁃creased according to the thermodynamic analysis.However,the reaction might be limited by its kinetics.Therefore,direct vacuum car⁃bothermal reduction of spodumene ore to extract Li was not feasible.The theoretical calculation of extracting Li from spodumene ore by adding Fe2O_(3) vacuum carbothermal reduction to prepare Si-Fe alloy while recovering Al_(2)O_(3),it was observed that the volatilization of Si during the reduction process was effectively suppressed by adding Fe2O_(3),and the reduced Si and Fe formed Si-Fe alloy.First,LiAl⁃Si_(2)O_(6) decomposed to produce LiAlSiO4 and SiO_(2).Next,LiAlSiO4 and SiO_(2) reduced with Fe at higher temperatures to obtain a Si-Fe al⁃loy,Al_(2)O_(3) and Li(g).From the reported simulations,it could be derived that the extraction of Li by adding Fe2O_(3) through the carboth⁃ermal reduction of spodumene ore in vacuum could be feasible,comprising the preparation of Si-Fe alloy and the recovery of Al_(2)O_(3).Ac⁃cording to experimental data,spodumene ore completely reacted at 1648 K,mainly producing Si-Fe alloy and Al_(2)O_(3) phase but no Li-containing phase in the process residues.The experimental data was consistent with the calculations based on thermodynamic simula⁃tions.During the entire reduction process,the reduction rate of Li was 92.69%,and Li2O content in the condensate was 36.21%.In sum⁃mary,this study proposed a comprehensive and efficient process for the vacuum carbothermal reduction of spodumene to extract Li,in⁃cluding the addition of Fe2O_(3).It comprised the preparation of Si-Fe alloy and Al_(2)O_(3) recovery.Compared with the currently used spodu⁃mene-based lithium extraction technology,the novel reduction process barely produced wastewater or waste residues,which demon⁃strated that it could be environmentally friendly.In addition,Si-Fe alloy and Al_(2)O_(3) slag that had added value were obtained through the proposed process for the extraction of Li,which led to an efficient utilization of the elemental composition in the spodumene ore.