Electrolyte effects on surface chemistry of basaltic glass in the initial stages of dissolution
Electrolyte effects on surface chemistry of basaltic glass in the initial stages of dissolution
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溶解初期电解质对玄武岩玻璃表面化学的影响
DOI：
10.1016/j.chemgeo.2016.01.027
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发表时间：
2016
期刊：
影响因子：
3.9
通讯作者：
Deubener
中科院分区：
文献类型：
--
作者：
Behrens;Helsch;Deubener
为了理解溶液组成对玄武岩玻璃溶解速率的影响，表面化学的详细知识是很重要的。在这里的zeta电位（Zeta电位）作为一个特征参数的表面电荷的大小在固-液界面被用来确定在玄武玻璃溶解的初始阶段的表面化学的离子效应。在一个系统的方法粉末合成玄武玻璃分散在溶液中的不同阳离子（Na+、K+、Mg 2+、Ca 2+、Ba 2+、Zn 2+和Al 3+的NO3−盐）和阴离子（F−、Cl−、I−、NO3−、SO 42 −、C2 O 42 −、HPO 42 −的Na+盐），浓度分别为0.1、0.5、1.0、2.5和5.0 mmol/L。在理想的环中性pH值下，在长达12，000 h的时间序列中追踪了离子对玻璃表面的亲和力，其特征在于吸附等温线。通过使用二次中性质谱法（SNMS）的深度剖析，确定了改变层的形成的玻璃化学组成的变化。玻璃的溶解通过4000 h后释放的Si的量来量化。在前3 h反应时间内去离子水中的Si的显著减少归因于碱金属和碱土金属阳离子从玻璃表面的解吸以及带负电荷的Sisingle键O −位点的形成。与去离子H2O中的实验相比，添加阴离子导致更强的负初始pH值，表明表面位点上有显著的阴离子吸附，对于F−、C2 O 42 −和HPO 42 −最明显。在添加二价阳离子时，初始的pH值增加，表明带负电荷的表面位点的中和。随着时间的推移，从负到正的pH值得到了显着的转变，最显着的Ca 2+和Zn 2+。三价Al ~（3+）的加入直接导致了正电子发射，表明在玻璃表面上有很强的吸附。随着实验的进行，λ的符号再次反转为负值。电荷反转的原因还不完全清楚，可能与阳离子吸附超过负表面电荷和玻璃表面的铁氧化物浓度有关。经过~ 2000 h反应时间后，将大多数电解质添加物的pH值调整为略负的pH值，直到实验结束，表明达到了表面位点组成的最终状态。溶液中一价Na+和K+的存在抑制了玻璃中Si的释放，而二价阳离子则加速了Si的释放。似乎去质子化的三键Sisingle键O −位点被一价阳离子中和-它们的优先结合也通过化学分析表明-有利于聚合，导致Si释放较慢。Al ~（3+）的加入可能形成了三重键，抑制了Si的释放。F-、C2 O 42-和HPO 42-的存在明显增强了玻璃的溶解，很可能是通过增加网络形成阳离子的配位，从而削弱了键。在玄武玻璃表面上观察到的正电荷的产生是显著的，并且可以在自然系统中提高玄武玻璃表面对来自孔溶液、阴离子、溶解的有机物质以及细菌细胞壁的带负电荷的化合物的吸附能力。
For an understanding of the effect of solution composition on the dissolution rate of basaltic glass detailed knowledge of surface chemistry is important. Here the zeta potential (ζ) as a characteristic parameter of the magnitude of surface charge at the solid–liquid interface was used to determine ionic effects on surface chemistry in initial stages of basaltic glass dissolution. In a systematic approach powdered synthetic basaltic glass was dispersed in solutions of different cations (NO3−salts of Na+, K+, Mg2 +, Ca2 +, Ba2 +, Zn2 +, and Al3 +) and anions (Na+salts of F−, Cl−, I−, NO3−, SO42 −, C2O42 −, HPO42 −), each in concentrations of 0.1, 0.5, 1.0, 2.5, and 5.0 mmol/L. ζ was traced in time sequences up to 12,000 h at ideally circumneutral pH. Ion affinities to glass surfaces were characterized by sorption isotherms. A change of glass chemical composition by the formation of altered layers was determined by depth profiling using secondary neutral mass spectrometry (SNMS). The dissolution of the glass was quantified by the amount of Si released after 4000 h.A marked decrease of ζ in deionized water within the first 3 h reaction time is assigned to the desorption of alkali and alkaline earth metal cations from the glass surface and formation of negatively charged Sisingle bondO−sites. The addition of anions resulted in stronger negative initial ζ values in comparison with the experiment in deionized H2O indicating marked anion adsorption on surface sites, most obvious for F−, C2O42 −and HPO42 −. The initial ζ was increased upon the addition of divalent cations indicating neutralization of negatively charged surface sites. Over time a striking shift from negative to positive ζ was obtained, most markedly for Ca2 +and Zn2 +. The addition of trivalent Al3 +resulted directly in positive ζ indicating a strong adsorption on glass surfaces. With the progress of the experiment the sign of ζ reversed to negative values again. The reason for charge reversal is not fully understood and might be related with cation adsorption exceeding the negative surface charge and a concentration of Fe oxides at the glass surface. After an ~ 2000 h reaction time ζ adjusted for most electrolyte additions to slightly negative ζ until the end of the experiment, indicating that a final state in the composition of surface sites was reached. The presence of monovalent Na+and K+in solution suppressed Si release from the glass, whereas it is accelerated by bivalent cations. It appears that the neutralization of deprotonated triple bondSisingle bondO−sites by monovalent cations – their preferential binding is also indicated by chemical analysis – favors polymerization resulting in slower Si release. Upon the addition of Al3 +it is likely that triple bondSisingle bondOsingle bondAlsingle bondOsingle bondSitriple bond bonds are formed, which can suppress Si release. The presence of F−, C2O42 −, and HPO42 −clearly enhances glass dissolution, most probably by increasing the coordination of network forming cations, hereby weakening bonds. The observed generation of positive ζ on basaltic glass surfaces is remarkable, and can improve in natural systems the adsorption capability of the basaltic glass surface for negatively charged compounds from pore solution, anions, dissolved organic matter and also bacterial cell walls.
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