Study On Synthesis Of Brucite-based Magnesium Aluminum Hydrotalcite Study On Synthesis Of Brucite-based Magnesium Aluminum Hydrotalcite

The proven reserves of brucite minerals in China exceed 25 million tons,with high mineral grades which led to paying little attention to high-silicon brucite in the parst.Recently,high-silicon brucite minerals have aroused more attention due to a sharp reduction of brucite minerals with high grades.At present,the research on the silicon removal of high-silicon brucite mainly focuses on the flotation method,but the recovery rate of brucite is lower,and the mineral processing standards need to be further improved.To our knowledge,the chemical treatment of serpentine in high-silicon brucite for removing silicon was not reported.On the other hand,hydrotalcite-based heat stabilizers have attracted more and more attention due to the advantages of high efficiency,non-toxicity and pollution-free.However,it still faces some technical questions,such as serious particle agglomeration,non-single crystal phase,and relatively high production cost.In this paper,a sodium-calcining process was used to treat serpentine in high silicon brucite,by changing the process conditions to achieve the purpose of removing silicon;with the water-washing treated product obtained by sodium-calcining brucite as the magnesium source,hydrotalcite was synthesized by coprecipitation hydrothermal method,in order to reduce the production cost of hydrotalcite and increase the economic value of brucite.In this paper,the sodium-calcining process was used to remove silicon from the high-silicon brucite,with NaOH used as a chemical additive.The effects of NaOH content,calcining temperature,calcining time on Si content of water-washing treated products obtained by calcining brucite were investigated,respectively.The products were characterized by means of X-ray diffraction（XRD）,Fourier transform infrared spectroscopy,X-ray fluorescence spectroscopy and silicate analyzer.The results indicate that the optimal processing parameters are 3 times theoretical amount of NaOH,calcining temperature of 650℃and calcining time of3h.And the optimal precipitant for water immersion residue is CO₂.Under these conditions,Na⁺replaces the Mg²⁺of serpentine in brucite,step by step,producing soluble salt-Na₄SiO₄.The soluble salt finally can be removed by water washing.The Si content in water-washing treated products obtained by calcining brucite reaches 1.89%and the extraction ratio of Si reaches 90.1%.On the basis of the above study,hydrotalcite was synthesized by a coprecipitation hydrothermal method,with the water-washing treated products obtained by calcining brucite as the magnesium source,aluminum sulfate as the aluminum source,sodium carbonate as the carbon source,and sodium hydroxide as pH regulator.The effects of magnesium source treated with different calcination conditions,hydrothermal temperature,hydrothermal time,pH value of solution,and molar ratio of Mg/Al and Mg/CO₃^2-on the synthesis of Mg-Al hydrotalcite were systematically studied,by the means of scanning election microscopy（SEM）,X-ray diffraction（XRD）,to explore the suitable raw materials and suitable process conditions.The suitable magnesium source was synthesized under calcining conditions of twice theoretical amount of NaOH,calcining temperature of 650℃and calcining time of 3h.The optimum synthesis conditions of Mg-Al hydrotalcite were pH 9.3,the hydrothermal temperature of180℃,the molar ratio Mg/Al of 2,and the molar ratio Mg/CO₃^2-of 4.Regular hexagonal sheet crystals of Mg-Al hydrotalcite were obtained under these conditions.