A simulation model for the leaching of borate in soils and pulverised fuel ash

Abstract

AbstractA layer model for predicting the leaching of unadsorbed anions from unstructured soils has been extended to enable forecasts of the effects of rainfall on the redistribution and losses of weakly adsorbed ions, such as borate, to be made. The model is based on easily measured parameters including field capacity and the initial water and borate contents of each of the soil layers and calculates the redistribution of borate from the excess rainfall over evaporation. The partitioning of borate between the adsorbed and solution phases during leaching is calculated using a modified Langmuir isotherm equation. An advantage of the model is that it requires no specially fitted parameters which must be derived from separate leaching experiments. The model was tested against the results of published experiments on the leaching of borate from soil columns. Agreement with the experimental data was good and only marginally inferior to the agreement obtained using a more sophisticated model which required more detailed input information. The model was also used to forecast the amount of rainfall needed to reduce the concentration of borate in a sample of pulverised fuel ash (PFA) to a non‐toxic level. The results were consistent with the limited experimental data available. There was also reasonable agreement between the predictions of the model and the results of an experiment in which borate was leached from columns of PFA using a limited range of irrigation treatments.