| Lithium recovery from brine has become the main trend in the international lithium industry development, so it attracts more attention for researchers to develop the advanced extraction lithium materials and the novel separation technologies for lithium recovery from brine or seawater. The chemical reaction method to remove magnesium for lithium recovery from South American brine, is not suitable for brines with high Mg/Li ratio in western China. As known, the selective adsorption technology is the best solution to recover lithium from high Mg/Li ratio brines, and the key issue is to find a low cost magnesium removal method before going on lithium recovery from brine with high Mg/Li ratio. In this paper, the MgCl2 and C4H8O2 reactive crystallization method is developed to remove Mg2+ for the decrease of the high Mg/Li ratio in brine. Magnesium will be selectively crystallized out with dioxane from brine as MgCl2·6H2O·C4H8O2 couple compound to lower the Mg/Li ratio. The MgCl2·6H2O·C4H8O2 solid can decompose easily into MgCl2·6H2O and dioxane by heating, and dioxane is recycled and reused. The proposed process is dioxane waste-free, no lithium loss in brine, low energy consumption and environmentally friendly, being a more prospect pre-treatment process to remove magnesium from brine for effective lithium recovery. The main research contents and important conclusions are summarized as follows.First, the ternary phase diagrams of MgCl2-H2O-C4H8O2 system at different temperatures (5℃,15℃,25℃,35℃ å'Œ 45℃) are studied by the isothermal method. The phase diagram study mainly focuses on region â…¡ (solid-liquid equilibria), region â…¢ (solid-liquid-liquid equilibria) and region â…£ (liquid-liquid equilibria), and the dioxane magnesium chloride reactive crystallization occurs in region â…¡. In this region, at the same MgCl2-H2O-C4H8O2 content, as the decrease of temperature, the increase of MgCl2 yield. (NIBS)/Redlich-Kister equation and Jouyban-Acree equation are used to predict the solubilities with an acceptable accuracy. X-ray single crystal diffraction and X- ray powder diffraction experiments are used to confirm the structure of MgCl2·6H2O·C4H8O2 crystal. Furthermore, Origin and Matlab softwares are used to visualize the MgCl2-H2O-C4H8O2 ternary phase diagram. The 3D ternary colormap surface and ternary contour drawing are achieved using the modules embedded in Origin software, which can achieve the visualization of digital phase diagram. From Matlab program, the triangular coordinates, annotation, grid lines, component name, can be presented. By Origin and Matlab, the solubilities with temperature change are fitted and obtained.Second, the metastable zone width of MgCl2-H2O-C4H8O2 in region â…¡ is studied using IR probe in RS-10 reaction station and ultrasound velocity probe, respectively. Based on the ultrasound velocity probe experimental results, a reliable metastable zone width information can be obtained. Regression equation is obtained from the metastable zone width data, and the supersolubility of a certain solution at a certain temperature can be calculated. The crystal morphology of MgCl2·6H2O·C4H8O2 is monoclinic, and the crystal growth rate is measured by microscopic analysis. The crystal growth kinetics suitable for ternary systems are defined and calculated. For the MgCl2-H2O-C4H8O2 ternary system, H2O and C4H8O2 act as solvent as well as reactant, both of them need to maintain a relatively high concentration in order to have a relatively fast crystal growth.Third, the non-isothermal decomposition of MgCl2·6H2O·C4H8O2 crystal is studied by TG-MS. It is found that the decomposition process in the temperature range from 25℃ to 250℃ can be divided into four stages. Doyle method, Coats-Redfern method and Malek method are used to investigate the non-isothermal decomposition mechanisms of the four stages. The isothermal decomposition of MgCl2·6H2O·C4H8O2 at the temperature between 60 ℃ and 140℃ is studied using air blast drying oven, and the optimal decomposition temperature is determined. Furthermore, fixed bed experiments under N2 flow at 100℃ and 120℃ are curried out for MgCL2·6H8O2 thermal decomposition, which will provide the theoretical basis for industrialization. |
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