Study On The Preparation And Property Of Magnesium Hydroxide And Magnesium Composite Flocculant

With the improvement of environmental legislation, environmental treatment agent isrequested to be greener and safer. Mg（OH）₂, as an environmentally friendly watertreatment agent, has strong buffing and absorbing abilities. Therefore, it is more and morepopular to employing Mg（OH）₂as a commonly used environmental treatment agent.Liaoning Province is famous for its rich magnesium resources, especially magnesite,processing85.0%of magnesite reserves in China and20.0%of the whole world. To obtainMg（OH）₂by hydration of MgO calcined by magnesite has become a very effective way toraise local magnesium resources utilization rate as well as magnesium chemical productadded value.In order to solve problems of high requirement of environmentally friendly Mg（OH）₂maked on particle size, specific surface area, high MgO hydration condition as well as lowhydration rate, this paper, based on previous studies, by using MgO as material andthrough single factor experiment, tries to find out best process conditions to getenvironmentally friendly Mg（OH）₂of high purity, high activity and high processingperformance. By treating Ni wastewater with Mg（OH）₂get in experiment above asadsorbent, this paper ascertains the absorbing optimum conditions and illustrates absorbingproperties with adsorption thermodynamics and kinetics. Based on primary experiment ofcomposite flocculant synthesis by using Mg（OH）₂and chitosan as materials, this paperstudies reactive black dyeing wastewater decolorization effect by composite flocculantand makes comparison between single flocculant and composite flocculant.Results in this paper show that, best hydration experiment condition is temperature：338K, time：1h, catalyst：9.0%, dispersant：5.0%（of MgO），dispersant dosing time：20min after reaction starts. On the condition mentioned above, Product D₅₀is0.62μm;hydration rate is95.1%; Specific surface is106.30m2/g. During hydration, the higher activity of magnesium oxide has, the higher for hydration rate to get. In consideration ofcatalyst choice, among all those four kinds of catalysts, salt catalysts have greater influenceon MgO hydration than alkaline catalysts. Effect comparison of four catalysts are asfollows: ammonium acetate> ammonium chloride> sodium hydroxide> carbamide.Higher catalyst dosage, shorter hydration time and lower hydration temperature can lead tosmaller Mg（OH）2particle size and larger specific surface area. A good control ofdispersant dosage and addition time can bring lower Mg（OH）2agglomeration, largerspecific surface area and smaller particle size.The best condition for Mg（OH）₂to remove Ni（Ⅱ）, which is0.50g/L Mg（OH）₂dosage,308K absorbing temperature and15min absorbing time, leads decolorization ratioup to99.9%. Ni（Ⅱ）’s s absorption by Mg（OH）2is qualified with Langmuir absorptionisotherm and Pseudo-second-order process.The main adsorption process is chemicaldasorption. Analysis of thermodynamics shows that Ni（Ⅱ）’s absorption by Mg（OH）2isspontaneous endothermic reaction.Mg（OH）2-chitosan composite flocculant is got in the experiment. Infraredspectrometry and Uv spectrometry shows that chitosan structure has changed with newfunctional group-NH₂-C（S）NH₂-added to amino group and that Mg2+has coordinationwith-COOH in chitosan and-NH₂-C（S）NH₂-separately. When the water is in alkalinecondition（pH≈12.0） and composite flocculant dosage reaches57.14ml/L, decolorizationratio for composite flocculant to treat reactive black dyeing wastewater will be as high as99.7%. Compared with pure Mg（OH）₂or chitosan, Mg（OH）₂-chitosan compositeflocculant has advantages of less dosage and high decolorization ratio: compositeflocculant dosage is only33.2%of pure chitosan and31.7%of pure Mg（OH）₂on sameconditions.