New Technology Study On The Production Of Magnesium Hydroxide

Magnesite as a natural Magnesium carbonate,is a main source of magnesium,can also be used for the production of various of magnesia products.These products are widely used in metallurgy,chemicals,building materials and other industries.Although our country is rich in magnesite reserves,the resource of high grade magnesite is more and more absent.Low grade magnesium contains Ca,Si,Al,Fe impurities.Contaminated environment and huge waste of resources are caused by lots of magnesite.Therefore,the comprehensive utilization of low-grade magnesite resources is imminent.Magnesium hydroxide is an important inorganic chemical product and intermediates,with a flame retardant,smoke suppression,filled with safe,low price.It can be widely used in environmental protection,medicine,electronics,chemicals,metallurgy and other fields for the promotion of the national economy development of great significance.This paper presents a new process routed with low-grade magnesite as raw material of magnesium hydroxide,and to explore the feasibility and process conditions for the preparing magnesium hydroxide.It was of great significance to achieve low-grade magnesite resource comprehensive utilization.Firstly,the technics condition of the light burning powder obtained by calcining magnesite was discussed through lots of the experiments.The optimum experimental condition were obtained:the calcining temperature 750?,the calcining time 2 h.The light burning powder had the highest activity.Secondly,the controlling process of magnesium sulfate leaching light-burned powder was studied.The effect of the leaching rate under the reacting temperature,the reacting time,the stirring intensity,steamed ammonia environment and different magnesium ion concentrations were investigated by designed experiments in this paper.The results showed that the controlling steps of ammonium sulfate leaching process were ammonia desorption,strengthening of the process to increase the rate of ammonia desorption.And the magnesium ion concentration had an effect on the equilibrium conversion rate.The higher the initial magnesium ion concentration was,the lower the rate of light burning powder was.And the optimum experimental condition were obtained:under normal pressure,the concentration of ammonium sulfate was 0.06 mol/L,the ratio of ammonium sulfate to light calcined power at 1.2:1,the reacting temperature 90?,the reacting time was 2h,the stirring intensity of 400 r·min^-1,the light calcined powder granularity 96?m.The extracted rate of Mg reached to 95%under these conditions.The result of X-ray diffraction indicates that the sample was magnesium sulfate.Finally,calcium hydroxide as precipitant and calcium chloride as intermediate was introduced to solve the separation problem of calcium sulfate precipitation and magnesium hydroxide precipitation.The effects of the concentration of magnesium chloride,the reacting time,the reacting temperature,the stirring intensity,the aging time on the yield of magnesium hydroxide were studied through experiments.The optimum experimental condition were obtained:the ratio of calcium chloride to calcium hydroxide at 1:0.95,the concentration of calcium hydroxide was 1.79 mol/L,the concentration of calcium chloride was 0.1 mol/L,the reacting time was 30 min,the reacting temperature 90?,the stirring intensity 50 r·min^-1,the aging time 1 h.The content of magnesium hydroxide is more than 97%.The shape of particles is flaky and the thickness is about 100 nm.