# Solubility, speciation and thermodynamics of Fe in reducing aqueous KCl solutions

## TL;DR

This study examines how iron dissolves and behaves in potassium chloride solutions under reducing conditions, providing new data for environmental and nuclear waste applications.

## Contribution

New experimental data and thermodynamic models for Fe solubility in KCl solutions under reducing conditions are presented.

## Key findings

- Solubility of Fe(OH)2 and Fe2(OH)3Cl was measured across pH and ionic strength ranges.
- Thermodynamic and SIT activity models were developed for the Fe2+–K+–H+–Cl−–OH−–H2O system.
- Results improve predictions of iron behavior in nuclear waste and geochemical contexts.

## Abstract

The solubility of two well-characterized Fe(ii) solid phases (i.e., Fe(OH)2(cr) and Fe2(OH)3Cl(cr)) were investigated in batch undersaturation solubility experiments conducted over a wide range of pHm (7.5 ≤ pHm ≤ 10.5) and ionic strength (0.01 M ≤ I ≤ 4.0 M KCl). Solid phase characterization was carried out using XRD including Rietveld analysis, providing key insights into their phase composition and crystallite size. Chemical, thermodynamic and SIT activity models were derived for the system Fe2+–K+–H+–Cl−–OH−–H2O(l) on the basis of the comprehensive experimental dataset. Solubility constants determined in this work and contribute to improving the description of Fe chemistry under very reducing conditions, and can be implemented in thermodynamic databases and geochemical calculations of relevance, e.g. in the context of nuclear waste disposal.

Iron corrosion phases influence chemical conditions in several anthropogenic applications. New experimental data and thermodynamic models derived in this work allow accurate predictions of Fe behavior under relevant environmental conditions.