# Modelling Leaching Using C-S-H Solid Solutions
## 2 Materials and Methods  
[PERSON] et al. [18] reported that there are over 45 published C-S-H gel solubility models with Ca/Si ratios (mol/mol) of greater than 0.8. These, however, do not include those C-S-H solid solutions developed for the emdata18 [15] database, namely, tobormorite-jennite, CSH3T, and CSHQ. These C-S-H solid solutions were employed here to predict the expected changes in pH, Ca, and Si against changing Ca/Si ratios using the PHREEQC geochemical code. The measured data from 777 C-S-H gel equilibrated solutions for pH, Ca (mmol/L), and Si (mmol/L), taken from [PERSON] et al. [18], are shown in Figure 1. Using the selection criteria used by [PERSON] et al. [18], namely, a curing temperature range of 17-30 \({}^{\circ}\)C and a curing time of \(\geq\)1 week, the final Ca/Si ratio of the C-S-H was measured, calculated, or calculable, the liquid phase was fully characterised, and the data were real. \begin{table}
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**Author** & **Summary of Contributions** \\ \hline [PERSON] et al. [30] & A leaching model was developed using PHREEQC to simulate the leaching of Pb, Cd, As, and Cr from cementitious wastes in the presence of simple and complex leachates. The model provided good agreement with the measured data and demonstrated its appropriateness for longer-term predictions. \\ \hline [PERSON] et al. [31] & Here, leaching was modelled by controlling the dissolution of the alkalis (K\({}_{2}\)O and Na\({}_{2}\)O), portlandite, C-S-H, and ettringtite. The C-S-H was modelled using a non-ideal solid-solution aqueous solution (SSAS) between it (CaH\({}_{2}\)SiO\({}_{4}\)) and portlandite. \\ \hline [PERSON] [32] & In this work, PHREEQC was employed to account for the leachate as a complex reactive/transport system. The focus of the study was the dynamic leaching of monolithic porous materials, with the leachate acting as a complex reactor where chemical and inter-phase mass transfer and convection processes take place. The model was validated using analytical solutions of the system from equations with good comparisons. \\ \hline [PERSON] et al. [33] & The researchers used PHREEQC to model the leaching of Ca, Mg, Al, and Pb from carbonated and uncarbonated cement–waste samples. The predicted and measured experimental results gave good comparisons. \\ \hline [PERSON] et al. [34] & This work focused on the reactivity of coal fly ash in aqueous solutions, developed a PHREEQC model to determine the quantities of different solid phases comprising the coal fly ash. The numerical predictions, again, gave good comparisons with the experimental data and confirmed the feasibility of the approach. \\ \hline [PERSON] et al. [35] & The antimonate (Sb(OH)\({}_{6}\)\({}^{-}\)) leaching in hydrated cement pastes was modelled using adsorption isotherms with cement minerals. PHREEQC was used to model the pH and carbonation-dependent leaching of matrix elements (i.e., Ca, Al, Si, Fe, S, and C) using total elemental concentrations and the carbonate concentration. \\ \hline [PERSON] et al. [36] & The leaching potential of pervious concrete and its capacity for immobilizing common urban run-offs, including Cu, Pb, and Zn, were investigated. PHREEQC equilibrium modelling showed that mixing interstitial alkaline matrix waters with capillary pore water could re-produce the observed water chemistry. \\ \hline [PERSON] et al. [37] & This work presented a long-term study of fly ash-blended concrete in a low- and intermediate-level radioactive waste (LII\(W\)) repository. The modelling was undertaken using PHREEQC thermodynamic equilibrium calculations combined with the CEMDATA18 database. \\ \hline [PERSON] et al. [38] & Simulations of the leaching of selected metals under plaster and mortar over a 18-month period in accordance with the Construction Products Regulation (CPR) [39] were produced. The PHREEQC-Matlab coupled model used the Lawrence Livermore National Laboratory (LLNL) thermodynamic database to reproduce the experimental results with a high degree of accuracy. \\ \hline \end{tabular}
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