Preparation Of Magnesium Hydroxide Based On Salt Lake Brine And Its Adsorption To Methyl Orange And Cr(Ⅵ)

During the development of salt lake resources,the by-product magnesium chloride was discharged in large quantities,and the accumulation of many years resulted in the imbalance of the composition of the salt lake,resulting in"magnesium damage".The preparation of magnesium hydroxide from brine is an effective way to consume bischite.By changing the physical and chemical properties of magnesium hydroxide surface,its application performance can be affected.Based on this,this paper is based on the material preparation and adsorption performance exploration,and by changing the reaction conditions and modification conditions,the crystal growth law of magnesium hydroxide（MH）prepared by reverse precipitation is studied.The interface interaction between chitosan quaternary ammonium salt and magnesium hydroxide at（001）and（101）planes was calculated by DFT.The prepared magnesium hydroxide is applied to the removal of methyl orange and Cr（VI）in water,which solves the problem of environmental waste water to a certain extent and realizes the environmental protection concept of"treating waste with waste".The conclusions of this paper are as follows:（1）The effect of reaction conditions on the growth of magnesium hydroxide crystals was elucidated.The results of XRD analysis,particle size distribution and chloride content show that:With the increase of Mg²⁺ion concentration and reaction temperature,it is favorable for the growth of magnesium hydroxide（001）crystal plane.The increase of Mg²⁺ion concentration and the prolongation of aging time increase the chloride content of magnesium hydroxide.The particle size of magnesium hydroxide is greatly affected by reaction conditions,crystal plane growth and polarity.Hexagonal flaky magnesium hydroxide with（001）crystal face size of 131～194?,particle size D50of 1.64～9.32μm,and chloride content<0.1%can be prepared by reverse precipitation from salt lake brine-ammonia.The maximum adsorption capacity of the conditioned magnesium hydroxide for methyl orange was 150.49 mg/g.（2）The law of the modification conditions on the crystal growth of magnesium hydroxide was revealed.The crystal face of magnesium hydroxide（101）modified by cationic chitosan quaternary ammonium salt（HACC）is relatively thin;Nonionic polyethylene glycol 6000（PEG6000）was modified to obtain hexagonal flaky magnesium hydroxide with good crystallinity,and its（001） planes were superimposed and grown.Anionic sodium linoleate(C₁₈H₃₁Na O₂)was modified to obtain petal-shaped magnesium hydroxide,which showed lipophilicity.The maximum adsorption capacity of the prepared magnesium hydroxide on methyl orange was MH-（HACC）:220.10 mg/g>MH-（PEG6000）:168.18 mg/g>blank group:150.49 mg/g>MH-(C₁₈H₃₁Na O₂):129.66 mg/g.The adsorption was in accordance with the pseudo-first-order kinetics and Langmuir adsorption isotherm model.（3）The interfacial interaction between chitosan quaternary ammonium salt and magnesium hydroxide（001）and（101）planes was explored.DFT calculation results show that the adsorption energy of chitosan quaternary ammonium salt on the（101）surface is lower（Eads/（101）=-2.35e V,Eads/（001）=-2.06e V）,combined with the shortest bond length,bond angle and The charge density map,the analysis suggests that the interaction between magnesium hydroxide and the terminal hydroxyl groups of chitosan is hydrogen bonding in nature.The HACC/Mg（OH）₂ composite has a significant effect on the removal of medium and low concentrations of Cr（VI）.It reaches the adsorption equilibrium at 200 min,and the maximum adsorption capacity is 34.8 mg/g.Order kinetics and Langmuir adsorption isotherm model.It can be seen that by adjusting the reaction conditions and modification conditions,the crystal growth of functionalized magnesium hydroxide prepared by reverse precipitation of salt lake brine-ammonia water can be regulated,and the problem of environmental wastewater can be solved to a certain extent.