ABSTRACT:

The effective management of acid sulfate or pyritic soils is a major issue for many coastal regions in Australia. Drainage and subsequent aeration of potential acid sulfate soils often leads to pyrite oxidation and the acidification of the soil and groundwater. A numerical model has been developed to calculate the rate and magnitude of pyrite oxidation in acid sulfate soils, and the distribution of oxidation products such as H+, SO4 2- and Fe3+ within the soil profile. The pyrite oxidation model includes vertical diffusion of oxygen from the atmosphere through soil macropores, lateral diffusion of dissolved oxygen from the macropores into the soil matrix, and the consumption of dissolved oxygen in the acid sulfate soil layers by pyrite oxidation. The acidity generated by various drain management strategies is demonstrated.

INTRODUCTION

The amount of acidic pyrite oxidation products generated at a site, or the effectiveness of potential acid sulfate soil management techniques that rely on better management of the groundwater table, can be assessed by using simulation models that consider the groundwater hydrology at a site and its relationship to oxidation of pyrite. Considerable effort has been placed into the development of analytical and numerical solutions for modeling the oxidation of pyrite or other similar sulfidic minerals (eg. Wunderly et al., 1996). Development of these models has been mainly focused on better understanding of the generation of acidic leachate from waste rock dumps and tailings lagoons associated with discard from sulfidic mineral mining activities, and as such, are only partly applicable to the study of sulfidic soils. Only one pyrite oxidation model has been designed specifically for the simulation of acid generation and transport in sulfidic soils (Bronswijk et al., 1993). However, this model only simulates oxygen transport and pyrite oxidation in one dimension.

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