Removal Of Impurities From Brine Of Jilantai Salt Lake And Preparation Process Of Ultrafine Magnesium Hydroxide Powder As A Byproduct

Taking the comprehensive utilization of brine from Jilantai Salt Lake as the background, a process was experimentally studied on removing impurities from brine of Jilantai Salt Lake and preparing ultrafine magnesium hydroxide powder as a byproduct in order to provide qualified brine for 30000 tons/year of soda unit, and to increase the utilizable benefit of the brine. The first part in the present work is to explore the process for removing impuritiesfrom Jilantai Salt Lake. On the basis of production cost and benefit for removal of impurities, different methods of removal of impurities were compared, including lime-soda, sodium hydroxide-soda, ammonia-soda method, and lime-soda method was taken as the method of removing impurities method. Effects of system temperature, precipitation time, agitation speed and concentrations of lime slurry on the removal magnesium from brine were examined and suitable range of every techniques condition were obtained by means of single-factor test. The results show that the appropriate conditions for the removal of impurities are as follows: reactant time, 25 min; molar ratio of magnesium ions to lime slurry ,1:1.1; concentration of lime slurry ,2～3mol·L^-1; reactant temperature, 60℃; agitation speed ,60～70 rpm; the quantity of magnesium hydroxide seed added, 350g·m^-3 brine; quantity of PAM 120g·m^-3 brine, respectively. The content of impurities in the purified brine meets the requirement for producing soda. Sedimentation result of magnesium hydroxide is improved when process conditions above mentioned were adopted.In the second part, the exploration was made on the process of preparing ultrafine magnesium hydroxide with precipitate as raw material, in which precipitate was obtained by disposal of impurities from brine. Firstly, the acidification and purification conditions of the precipitate were determined. The acidification conditions are as follows: reaction temperature, 20℃～25℃; reaction time ,40 min; and pH of the hydrochloric acid leaching solution , 7.0～7.5. The purification conditions are in the following: reaction temperature ,20℃～25℃; reaction time,30 min; molar ratio of calcium ions to magnesium sulfate ,1:1.1; the quantity of ethanol , 5ml.The results indicate that the removal yield of calcium ions using hydrochloric acid leaching liquor was 95.26%. The preparation of ultrafine magnesium hydroxide powders was conducted by chemical precipitation method with hydrochloric acid leaching solution purified and ammonia as raw materials, and suitable amount of PEG2000 as dispersant. Influence of system temperature, precipitation time, agitation speed and concentration of ammonia on the mean particle size of magnesium hydroxide particles were studied The samples obtained from the proper conditions were characterized by X-ray diffraction(XRD) , transmission electron microscopy (TEM), infrared absorption spectrometry (IR) and the particle size distribution analyzer. The results show that the mean particle size of magnesium hydroxide is 89.5nm, with flake shape, fine dispersion, hexagonal crystalloid configuration The sample specifications coincide with the standard stipulated in HG/T3607-2000.