室温条件下青海湖水中镁离子浓度对沉淀碳酸钙同质多像类型的调控  

The effect of magnesium concentration on polymorphs of calcium carbonate from Qinghai Lake water at room temperature

作　　者：杨康 李红[1] 雷云[1] 牛元哲 冯诗海 YANG Kang;LI Hong;LEI Yun;NIU Yuan-zhe;FENG Shi-hai(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China)

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,陕西西安710069

出　　处：《岩石矿物学杂志》2021年第3期571-580,共10页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金项目(41272115,41572086)。

摘　　要：青海湖是我国唯一报道过的现代湖底沉积物中白云石、方解石和文石等多种碳酸盐矿物共存的高原内陆咸水湖泊。以青海湖水和除菌青海湖水作为载体,以CaCl_(2)和MgCl_(2)·6 H_(2)O作为反应原料,在实验室常温条件下采取控制变量法制备出不同浓度Mg^(2+)参与下的钙质沉淀物,探讨Mg^(2+)浓度对沉淀物类型的影响。仅添加CaCl_(2)时,青海湖水中的沉淀物主要是石膏(CaSO_(4)·2 H_(2)O)和球霰石(CaCO_(3));在添加CaCl_(2)的同时添加MgCl_(2)·6 H_(2)O,沉淀物的石膏消失,完全转变成碳酸盐矿物,包括方解石和球霰石;当湖水中Mg^(2+)浓度为0.62 mol/L时,球霰石消失,沉淀物变为方解石和文石;随着Mg^(2+)浓度继续升高,文石含量稳步增加,方解石含量则逐渐减少,当Mg^(2+)浓度达到1.22 mol/L或更高时,方解石全部消失,沉淀物仅剩文石。实验结果表明,青海湖水中较高浓度的SO_(4)2-对碳酸钙晶体生长有抑制作用,而额外加入的Mg^(2+)可以解除SO42-的抑制作用,使得Ca^(2+)与HCO_(3)-和CO_(3)2-结合形成碳酸钙。此外,碳酸钙的同质多像类型也明显受到Mg^(2+)浓度的控制,随着湖水中Mg^(2+)浓度增加,方解石、球霰石不再稳定,而文石逐渐占主导地位,当Mg/Ca值达到6.1时,反应产物中仅有文石稳定存在。The Qinghai Lake is the only modern inland saltwater lake in China where dolomite,calcite and aragonite are reported to coexist in lake bottom sediments.To discuss the influence of magnesium on the polymorphs of calcium carbonate,the authors chose Qinghai Lake water and sterilized Qinghai Lake water as the reaction solution and CaCl_(2)and MgCl2·6 H2O as the reactants,and precipitated calcium sulfate and calcium carbonate by the method of variable-controlling with different concentrations of Mg^(2+)at laboratory room temperature.When only CaCl_(2)was added into Qinghai Lake water,gypsum(CaSO_(4)·2 H_(2)O)and vaterite(CaCO_(3))were precipitated.However,when CaCl_(2)and MgCl_(2)·6 H_(2)O were added together into the lake water,gypsum disappeared,and the synthetic products changed to calcium carbonate,including calcite and vaterite.When Mg^(2+)concentration in lake water water increased to 0.62 mol/L,vaterite disappeared,and the products were composed of calcite and aragonite.With the increasing of Mg^(2+)concentration,the content of aragonite rose steadily,while content of calcite decreased gradually.When Mg^(2+)concentration rose to 1.22 mol/L or higher,calcite disappeared completely,only aragonite was precipitated from the solution.These results indicate that the SO42-in lake water inhibited the formation of CaCO_(3)under the condition of no or very low concentration of Mg^(2+).However,when extra Mg^(2+)added into the lake water,they could release the inhibition of SO_(4)2-,and then Ca2+were free to combine with HCO_(3)-and CO_(3)2-to form calcium carbonate.In addition,the polymorphs of synthetic calcium carbonate was obviously controlled by Mg^(2+)concentration.With the increase of Mg^(2+)concentration in the lake water,calcite and vaterite were no longer stable,while aragonite was gradually dominant.When Mg/Ca reached 6.1,only aragonite was stable in the reaction product.

关 键 词：青海湖 石膏 碳酸钙 镁离子 文石 

分 类 号：P578.6[天文地球—矿物学]