Study On The Preparation Of High-quality Magnesium And Calcium Products From Dolomite

The chemical formula of dolomite is Ca Mg（CO₃）₂,which is rich in resources and is an important raw material for the preparation of calcium and magnesium products.The main application fields of dolomite include building materials,chemistry,agriculture,environmental protection,etc.However,the utilization of dolomite is still low at this stage.In order to improve the utilization value of dolomite resources,dolomite needs to be deeply processed to produce high-end magnesium-calcium materials,such as calcium carbonate whiskers and hexagonal type magnesium hydroxide.In this paper,dolomite powder is used as raw material,firstly,dolomite powder is calcined to lightly burned dolomite lime,then ammonium salt is used as leaching agent to extract calcium and magnesium elements in dolomite,then ammonia gas is used as magnesium ion precipitant,and carbon dioxide is used as calcium ion precipitant.The hexagonal flake-type magnesium hydroxide and aragonite-type calcium carbonate whiskers were prepared by the process of calcination-ammonia-distilling-magnesium-precipitation-calcium-precipitation,and the magnesium hydroxide and aragonite-type calcium carbonate were characterized.For the calcination process,the effects of calcination temperature,heating rate,and calcination time on the weight loss rate of dolomite were investigated;in the ammonia distillation process,the effects of reaction conditions such as reaction temperature,stirring rate,and reaction time on the leaching rate of Ca²⁺and Mg²⁺were investigated.In the process of magnesium precipitation and calcium precipitation,the influence of reaction conditions such as reaction temperature,ventilation rate,and the ratio of the amount of each metal ion to precipitant substance on magnesium hydroxide and calcium carbonate products was investigated,and calcium carbonate was also discussed.The control mechanism of whisker growth process and reaction conditions on the content of each crystal form in calcium carbonate products.In the ammonia distillation process,the optimal reaction conditions were the reaction temperature of 100°C,the reaction time of 180 min,the molar ratio of calcium and magnesium to ammonium salt of 1:2.15,and the stirring rate of 400 r/min.At this time,the leaching rate of Ca²⁺was 90.2%,and the leaching rate of Mg²⁺was 81.3%.In the magnesium precipitation process,the optimal conditions were the reaction temperature of 55°C,the ammonia flow rate of 3.5 L/min,and the ammonia-magnesium molar ratio of 5:1.At this time,the conversion rate of Mg²⁺reaches 95.3%,and the surface morphology of the prepared Mg（OH）₂product is regular and thin hexagonal flakes,I001/I101=1.97,and D50 is 1.7μm.In the calcium precipitation process,the optimal conditions were the reaction temperature of 80°C,the carbon flow rate of 100 ml/min,the molar ratio of Ca²⁺to CO₂of 1:2.1,the concentration of Ca²⁺of 0.4 mol/L,and the aging time of 30 min.The surface morphology of Ca CO₃whiskers prepared by the optimal calcium precipitation experimental conditions is regular,the aspect ratio is 18-22,the whisker content is 99.5%,and the whiteness is 98.9.Using the theory of critical nucleation energy,the phenomenon that the content of aragonite crystals can be changed by adjusting the reaction temperature and the carbon-passing rate was explained,and the growth process of aragonite-type calcium carbonate whiskers was analyzed.Increasing the reaction temperature and the carbon-passing rate can reduce the critical nucleation energy,which in turn increases the crystal content of agaric in the system.At the same time,the theoretical model of anion coordination polyhedron growth element is used to explain the conditions such as Ca²⁺concentration.Too much or too low Ca²⁺concentration will affect the size and degree of polymerization of anion coordination polyhedra,which is not conducive to the formation of aragonite whiskers.