Far from equilibrium basaltic glass alteration: The influence of Fe redox state and thermal history on element mobilization

Elemental release from basaltic glasses at far from equilibrium conditions was investigated as a function of the Fe redox state (Fe(II)/Fe-tot = 0.35 and 0.80) and thermal history (quenched annealed). A flow-through column setup was used to ensure disequilibrium of basaltic glass and solution during the entire runtime. Percolation experiments were performed at 25 degrees C for up to 500 h with intermediate sample collection. Two different pH values were adjusted, and the effect of organic matter was tested by adding oxalic acid. Element concentrations in the percolate were measured by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES).After an initial high release of elements from fresh glass surface, steady state was achieved after 240-430 h for Si at pH 5-7 and after 170-240 h for Al at pH 2. At near neutral conditions (pH 5-7) mobilization of Si is relatively high, while Fe and possibly Al are retained in precipitates. Under more acidic conditions (pH 2), the Si concentration of the solutions was very low compared to the other main constituents of the glass. Large amounts of Si-rich residues are formed after glass dissolution at pH 2. On the other hand, Fe (and Mn) is very mobile under acidic conditions, favored by complex formation with oxalic acid and chlorine. In the initial phase of the pH 2 experiments, the element release from reduced glasses is higher than from oxidized glasses. However, this trend is reversed when approaching steady state. Higher dissolution rates for oxidized glasses are predicted due to the progressive replacement of strong Si-O-Si with weaker Fe(III)-O-Si. At pH 5-7 the concentrations of elements in the percolate are too low to establish a systematic difference between oxidized and reduced glasses. Looking at the total amount of mobilized elements, the thermal history of the glasses has no significant effect in the case of oxalate-free solutions, but a noticeable increase of element release in the case of rapidly quenched glasses was observed when using 1 mM oxalic acid solution. The strong effect of oxalate on dissolution of quenched glasses is probably related to the more open glass network structure in quenched glasses. (C) 2020 Elsevier Ltd. All rights reserved.

在远离平衡的条件下，研究了玄武岩玻璃中元素的释放随铁氧化还原状态（Fe(II)/Fe - 总 = 0.35和0.80）以及热历史（淬火、退火）的变化。采用流通柱装置以确保在整个运行过程中玄武岩玻璃和溶液处于非平衡状态。在25℃下进行渗滤实验，时间长达500小时，并进行中间取样。调节了两种不同的pH值，并通过添加草酸测试了有机物的影响。采用电感耦合等离子体发射光谱法（ICP - OES）测量渗滤液中的元素浓度。在新鲜玻璃表面最初大量释放元素之后，在pH 5 - 7时硅在240 - 430小时后达到稳态，在pH 2时铝在170 - 240小时后达到稳态。在近中性条件（pH 5 - 7）下，硅的迁移率相对较高，而铁以及可能的铝则保留在沉淀物中。在更酸性的条件（pH 2）下，与玻璃的其他主要成分相比，溶液中的硅浓度非常低。在pH 2时玻璃溶解后会形成大量富硅残留物。另一方面，在酸性条件下，铁（和锰）的迁移性很强，这得益于与草酸和氯形成络合物。在pH 2实验的初始阶段，还原态玻璃的元素释放量高于氧化态玻璃。然而，当接近稳态时，这种趋势会逆转。由于强的Si - O - Si逐渐被较弱的Fe(III) - O - Si取代，预计氧化态玻璃的溶解速率更高。在pH 5 - 7时，渗滤液中的元素浓度过低，无法确定氧化态和还原态玻璃之间的系统性差异。从迁移元素的总量来看，在无草酸盐溶液的情况下，玻璃的热历史没有显著影响，但当使用1 mM草酸溶液时，观察到快速淬火玻璃的元素释放量显著增加。草酸盐对淬火玻璃溶解的强烈影响可能与淬火玻璃中更开放的玻璃网络结构有关。（C）2020爱思唯尔有限公司。保留所有权利。