【作者】 刘辉；

【导师】 罗仙平；

【作者基本信息】 江西理工大学 ， 环境科学， 2022， 硕士

【摘要】 在盐湖资源开发过程中,副产氯化镁被大量排放,多年的积累造成盐湖的成份失衡,形成“镁害”。通过卤水制备氢氧化镁是消纳水氯镁石的有效途径。而且改变氢氧化镁表面物理化学性质,能够影响其应用性能。基于此,本论文立足于材料制备和吸附性能探究,通过改变反应条件和改性条件,研究反向沉淀法制备氢氧化镁（MH）的结晶生长规律;并通过DFT计算,分析壳聚糖季铵盐与氢氧化镁在（001）和（101）面的界面相互作用。制备的氢氧化镁应用于水体中甲基橙和Cr（VI）的去除,在一定程度上解决环境废水的问题,实现“以废治废”的环保理念。本论文得到的结论如下:（1）阐明了反应条件对氢氧化镁结晶生长的规律的影响。XRD分析、粒径分布、氯根含量等结果表明:Mg²⁺浓度和反应温度的提高,有利于氢氧化镁（001）晶面的生长。Mg²⁺浓度的增大、陈化时间的延长使得氢氧化镁的氯根含量增大。氢氧化镁的粒径受反应条件及晶面生长、极性影响较大。通过盐湖卤水-氨法反向沉淀能够制备得到（001）晶面尺寸在131～194?、粒径D50在1.64～9.32μm,氯根含量<0.1%的六方片状氢氧化镁,优化条件的氢氧化镁对甲基橙的最大吸附容量为150.49 mg/g。（2）揭示了改性条件对氢氧化镁结晶生长的规律。阳离子型壳聚糖季铵盐（HACC）改性的氢氧化镁（101）晶面相对变薄;非离子型聚乙二醇6000（PEG6000）改性得到结晶度好的六方片状氢氧化镁,其（001）面发生叠加生长。阴离子型亚油酸钠(C₁₈H₃₁Na O₂)改性得到花瓣状的氢氧化镁,显亲油性。制备的氢氧化镁对甲基橙的最大吸附量依次为MH-（HACC）:220.10 mg/g>MH-（PEG6000）:168.18 mg/g>空白组:150.49 mg/g>MH-(C₁₈H₃₁Na O₂):129.66 mg/g。吸附符合准一级动力学和Langmuir吸附等温模型。（3）探究了壳聚糖季铵盐与氢氧化镁（001）和（101）面的界面相互作用。DFT计算结果表明壳聚糖季铵盐在（101）面的吸附能更低（Eads/（101）=-2.35e V、Eads/（001）=-2.06e V）,结合最短键长、键角和电荷密度图,分析认为氢氧化镁和壳聚糖末端羟基之间的相互作用在本质上是氢键。HACC/Mg（OH）₂复合材料对中低浓度Cr（VI）去除效果显著,其在200 min达到吸附平衡,最大吸附容量为34.8 mg/g,其吸附速率优于空白组,吸附符合准一级动力学和Langmuir吸附等温模型。可见,通过对反应条件和改性条件的调控,能够对盐湖卤水-氨水反向沉淀制备功能化氢氧化镁的结晶生长进行调控,并在一定程度上解决环境废水的问题。更多还原

【Abstract】 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.更多还原