Mg(BO_(2))_(2)在MgSO_(4)和MgCl_(2)-MgSO_(4)水溶液中分解的相平衡与物种化学平衡  

Phase Equilibria and Species Chemical Equilibrium of Mg(BO_(2))_(2)Decomposed in MgSO_(4)and MgCl_(2)-MgSO_(4)Aqueous Solutions

作　　者：魏凤单 周桓 郝晴 赵鋆 阎波[2] WEI Feng-dan;ZHOU Huan;HAO Qing;ZHAO Yun;YAN Bo(College of Chemical Engineering and Materials Science,Tianjin,300457,China;College of Marine and Materials Environmental Science,Tianjin,300457,China)

机构地区：[1]天津科技大学化工与材料学院,天津300457 [2]天津科技大学海洋与材料学院,天津300457

出　　处：《盐湖研究》2022年第4期1-14,共14页Journal of Salt Lake Research

基　　金：国家自然科学基金(批准号:U1707602,U1407204)。

摘　　要：硫酸镁亚型盐湖老卤是MgCl_(2)、MgSO_(4)的饱和溶液体系,富集了Mg、B、Li等元素。本文针对含硼水盐体系热力学难以表达的问题,开展了硼在水盐体系存在形态及其平衡关系的研究。利用易于水解的Mg(BO_(2))_(2)作为硼源,借助拉曼光谱和X射线衍射(XRD)为检测手段,定量研究Mg(BO_(2))_(2)在MgSO_(4)-H_(2)O、MgSO_(4)-MgCl_(2)-H_(2)O体系中水解硼物种转化规律。结果表明:(1)Mg(BO_(2))_(2)在MgSO_(4)溶液中的水解固相为MgB_(2O)(OH)_(6)、MgB_(4)O_(7)·9H_(2)O和Mg(OH)_(2);在MgSO_(4)-MgCl_(2)-H_(2)O溶液中水解固相为Mg 2B 6 O 11·15H_(2)O、MgB_(4)O_(7)·9H_(2)O、Mg_(2)Cl(OH)_(3)·4H_(2)O。(2)Mg(BO_(2))_(2)在MgSO_(4)溶液中水解,液相硼物种主要有B_(3)O_(3)(OH)_(4)^(-)、B_(3)O_(3)(OH)_(5)^(2-)、B(OH)_(4)^(-)、B_(4)O_(5)(OH)_(4)^(2-)、H_(3)BO_(3),其分布受MgSO_(4)浓度影响很大,MgSO_(4)浓度从0增加至饱和,B_(3)O_(3)(OH)_(4)^(-)始终占总硼量的50.07%以上,B_(3)O_(3)(OH)_(5)^(2-)占液相总硼从4.77%上升至37.16%为第2化学物种。(3)在MgSO_(4)-MgCl_(2)-H_(2)O溶液中,硼物种的主要形态有B_(3)O_(3)(OH)-4、B_(3)O_(3)(OH)52-、B(OH)-4,其分布随[Cl 22-]/([Cl 22-]+[SO_(4)2-])变化很大,在MgCl_(2)和MgSO_(4)的共饱溶液中,分别占液相总硼量的58.91%,14.62%和12.81%。(4)液相硼物种之间平衡关系的活度商ln Q,不仅与溶液pH、水活度有关,还与MgSO_(4)、MgCl_(2)摩尔浓度呈二元线性关系,这样就可将硼在H_(3)BO_(3)-NaOH体系物种分布关系的ln Q扩展到(MgSO_(4),MgCl_(2),MgSO_(4)-MgCl_(2))水溶液的多元体系。由此获得硼物种的量化关系,可为推算硼在水盐体系的物种分布,进而计算含硼电解质溶液热力学性质提供依据。Bittern of magnesium sulfate subtype salt lake is saturated with MgCl_(2) and MgSO_(4),which enriches elements of Mg,B and Li.Expressing the thermodynamics of water salt system containing boron is difficult,the existing species and chemical equilibrium of boron in water salt system were studied.In this paper,the decomposition and species equilibrium behaviors of Mg(BO_(2))_(2) in MgSO_(4) and MgSO_(4)-MgCl_(2) aqueous solution were quantitatively studied by means of Raman spectroscopy and X-ray diffraction(XRD).The results are as follows.(1)The solid phases of Mg(BO_(2))_(2) decomposed in MgSO_(4) solution are MgB_(2)O(OH)_(6),MgB_(4)O_(7)·9H_(2)O and Mg(OH)2.And the decomposed solid species in MgSO_(4)-MgCl_(2) aqueous solution are Mg_(2)B_(6)O_(11)·15H_(2)O,MgB_(4)O_(7)·9H_(2)O,Mg_(2)Cl(OH)_(3)·4H_(2)O.(2) Liquid species of Mg(BO_(2))_(2)decomposed in MgSO4 aqueous solution were determined to be B_(3)O_(3)(OH)_(4)^(-),B_(3)O_(3)(OH)_(5)^(2-),B(OH)_(4)^(-),B_(4)O_(5)(OH)_(4)^(2-) and H 3 BO 3.And with the MgSO_(4)concentration from 0 to saturation,B_(3)O_(3)(OH)_(4)^(-) accounts for more than 50.07%of the total boron quantity,and B_(3)O_(3)(OH)_(5)^)2-_increases from 4.77%to 37.16%;(3)In MgSO_(4)-MgCl_(2) aqueous solution,B_(3)O_(3)(OH)_(4)^(-),B_(3)O_(3)(OH)_(5)^(2-) and B(OH)_(4)^(-) are the main species,when MgCl_(2) and MgSO_(4) are co-saturation solution,respectively accounting for 58.91%,14.62%and 12.81%.(4)The activity quotient ln Q between boron species is mainly related to pH of liquid,also limited to water activity,meanwhile,it takes the linear relationship with molar concentrations of MgSO_(4) and MgCl_(2).So,ln Q in H_(3)BO_(3)-NaOH system can be extended to the multicomponent system of(MgSO_(4),MgCl_(2)and MgSO_(4)-MgCl_(2)) aqueous solution.Therefore,the quantitative relationship of boron species can be obtained,which can provide a basis for calculating the species distribution of boron in salt water system and the thermodynamic properties of boron containing electrolyte solution.

关 键 词：Mg(BO_(2))_(2) MgSO_(4)体系 拉曼光谱 化学平衡 溶液结构 

分 类 号：O645.16[理学—物理化学]