Predicting laterite redox potential with iron activity and electron transfer term

Predicting the redox behavior of organic contaminants and heavy metals in soils is challenging because there are few soil redox potential ( E h ) models. In particular, current aqueous and suspension models usually show a significant deviation for complex laterites with few Fe(II). Here, we measured the E h of simulated laterites over a range of soil conditions (2450 tests). The impacts of soil pH, organic carbon , and Fe speciation on the Fe activity were quantified as Fe activity coefficients , respectively, using a two-step Universal Global Optimization method. Integrating these Fe activity coefficients and electron transfer terms into the formula significantly improved the correlation of measured and modeled E h values ( R 2  = 0.92), and the estimated E h values closely matched the relevant measured E h values (accuracy R 2  = 0.93). The developed model was further verified with natural laterites, presenting a linear fit and accuracy R 2 of 0.89 and 0.86, respectively. These findings provide compelling evidence that integrating Fe activity into the Nernst formula could accurately calculate the E h if the Fe(III)/Fe(II) couple does not work. The developed model could help to predict the soil E h toward controllable and selective oxidation-reduction of contaminants for soil remediation .