Preliminary Study Of Preparation Of Magnesium Hydroxide Through Lime Method With Megnesium-containing Wastes

In this dissertation, the preparation process of magnesium hydroxide by utilizing magnesium sulfate wastewater generated from the nickel production of laterite were investigated. Based on the previous work of method of lime milk, firstly the preparation process of high-purity magnesium hydroxide was obtained, secondly the influence of lime quality on the product purity was studied through the experiment of different quality lime, finally the process conditions of improving velocity of slurry filtration was explored by crystal kinds and flocculate kinds.For the preparation process of high-purity magnesium hydroxide, aiming at the problem of high calcium content in the product, based on the previous work of method of lime milk, set the product purity as assessment indicators, firstly the accuracy and feasibility of product analysis methods were determined by the recovery experiments, and then the changement of the product purity was studied by the adjustment of the process conditions for the experiment of improved process. As a result, the recoveries of magnesium hydroxide and calcium oxide were from95%to105%; the products with the content of magnesium hydroxide reaching98.95%and the calcium oxide content about0.05%were prepared by the adjustment of the process conditions. It indicated that the products with the content of calcium oxide below0.1%could be prepared by the improved process.For the experiments of studying the lime quality on the product purity, set the product purity as assessment indicators, firstly the calcium oxide, calcium hydroxide and calcium carbonate content in different lime were measured,and then experiment with different lime. Results showed that four kinds of lime quality(the mass fraction of calcium oxide and calcium carbonate in the lime) from high to low in turn were as follows:changzhou kefa lime, shanghai fengxian lime, industrial lime, tangshan lime, and the product purity produced by these lime reduced successively:the content of magnesium hydroxide reduced from98.95%to96.23%, the content of calcium oxide increased from0.05%to0.56%. It indicated that the influence of different lime quality on the product purity was big, and the quality of lime higher, the purity of product higher.For the experiment of aming at improving the velocity of slurry filtration, set the velocity of slurry filtration as assessment indicators, meanwhile record the product purity. Firstly the influence of seed amount, crystal grain size, aging time and aging temperature on the velocity of slurry filtration were studied by the crystal kinds for the experiment of improved process; meanwhile the influence of different molecular weight and different addition of PAM were studied by the flocculate kinds for the experiment of improved process. As a result, the velocity of slurry filtration of450mL slurry by buchner funnel9cm in diameter through the suction filter cases could be reduced from90min to43min, and the influence on the product purity was little; the velocity of slurry filtration could be reduced from90min to12min with1%[η]=13.18dL/g PAM, but the product purity was lowest:the content of magnesium hydroxide was97.05%, the content of calcium oxide was2.50%. It indicated that reducing the velocity of slurry filtration was feasible by crystal kinds and flocculate kinds, contrast the product purity produced by the two methods, crystal kinds was a better method in the experiments.The study of magnesium hydroxide preparation process could be important and useful in the further research of the preparation and industrial application of high-purity magnesium hydroxide by exploiting magnesium rescources.