TY - JOUR

T1 - Far from equilibrium basaltic glass alteration

T2 - The influence of Fe redox state and thermal history on element mobilization

AU - Stranghoener, Marius

AU - Dultz, Stefan

AU - Behrens, Harald

AU - Schippers, Axel

N1 - Funding Information: The project was funded by the German Science Foundation (DFG), priority program ICDP, grant BE 1720/39-1 . Funding Information: The project was funded by the German Science Foundation (DFG), priority program ICDP, grant BE 1720/39-1. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

PY - 2020/3/15

Y1 - 2020/3/15

N2 - Elemental release from basaltic glasses at far from equilibrium conditions was investigated as a function of the Fe redox state (Fe(II)/Fetot = 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 °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.

AB - Elemental release from basaltic glasses at far from equilibrium conditions was investigated as a function of the Fe redox state (Fe(II)/Fetot = 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 °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.

KW - Alteration

KW - Basaltic glass

KW - Element mobilization

KW - Fe redox state

KW - Thermal history

UR - http://www.scopus.com/inward/record.url?scp=85078679852&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2020.01.005

DO - 10.1016/j.gca.2020.01.005

M3 - Article

AN - SCOPUS:85078679852

VL - 273

SP - 85

EP - 98

JO - Geochimica et cosmochimica acta

JF - Geochimica et cosmochimica acta

SN - 0016-7037

ER -