Research On Preparation And Property Of Nanometer Magnesium Hydroxide

As one of the common nanometer materials，nanometer magnesium hydroxideis increasingly popular in flame-retardant, desulphurization, water treatment andother aspects. However, when compared with developed countries, there is still acertain gap in the quality of nanometer magnesium hydroxide. High qualitynanometer magnesium hydroxide was prepared by double dripping-reverseprecipitation method and characterized. The thermal decomposition mechanism,thermal decomposition properties and the adsorption of Cr on magnesium hydroxidewere studied. The conclusions are as follows:1) Nanometer magnesium hydroxide is prepared by double dripping-reverseprecipitation method with magnesium chloride and ammonia as raw materials. Theoptimum conditions are as follows: the reaction temperature60℃, the reaction time75min, the aging temperature20℃, the aging time3h, the molar ratio of magnesiumto ammonium1.7, the initial concentration of Mg2+1.7mol/L, the dropping time ofMgCl2is15min, the crystal type regulator is PG-006,the mass of the crystal typeregulator is0.8%to the corresponding Mg(OH)2, the dripping time of crystal typeregulator is5min, the speed of stirring is1500r/min.There has been rarely reported about the combination of double drippingmethod and reverse precipitation method for preparing nanometer magnesiumhydroxide. It is indicated that it can develop their respective advantages by thecombination of the double dripping method and reverse precipitation method toprepare nanometer magnesium hydroxide which has small and uniform size andgood dispersion.2) The results indicate that the average particle size of the product is60nm anduniform; it has hexagonal crystal system, high purity and good thermal stability. Itoccurred adsorption bonding on the surface of Mg(OH)2, which provides foundationfor the mechanism of crystal type regulator.3) The thermal decomposition properties of nanometer magnesium hydroxide are studied. It`s found that it is more suitable to use Kissinger and Starink method fordynamic analyses of nanometer magnesium hydroxide. The apparent activationenergy of thermal decomposition is132.59kJ/mol,133.02kJ/mol of the two methods.Research on the properties of the thermal decomposition of magnesium hydroxidecan promote the understanding of the change of physical and chemical nature in theprocess, which provides reference in the application of fire retardant.4) The thermal decomposition mechanism of nanometer magnesium hydroxideis studied by Coast-Redfer method and Achar method. The results show that it isconsistent with Mample one-way rule, random nucleation and subsequent growth,n=1mechanism: f(α)=1-α; G(α)=-ln(1-α). The thermal decomposition kineticsequation is established, which provides a theoretical guidance for the decompositionmechanism of magnesium hydroxide, and a theoretical basis for the thermaldecomposition behavior.5) The investigation of the combining FeSO4with nanometer magnesiumhydroxide to treat wastewater needs to go further. Firstly, convert hexavalentchromium to trivalent chromium by FeSO4, and then the trivalent chromium isadsorbed on nanometer magnesium hydroxide. It is indicated that the optimumadsorption conditions are as follows: the concentration of Mg(OH)2was500mg/L,the adsorption temperature25℃, the oscillating time20min, the pH is5. In suchconditions, Mg(OH)2has high adsorption ability, the maximum adsorption capacityis157.52mg/g It`s found that the adsorption process accords with Langmuiradsorption model, and it is monolayer adsorption and spontaneous; Lagergren twokinetic equation can characterize the kinetics of the adsorption process moreaccurately. After the first adsorption, nanometer magnesium hydroxide is renewableand it still has high adsorption ability in the secondary adsorption. The processworks well, having less solid waste, and is easy to implement and at a low cost.Therefore, there is a greater market competitiveness, which provides reference fornanometer magnesium hydroxide in wastewater treatment.