THE RELEASE OF MG AND FE DUE TO WEATHERING OF CHLORITE UNDER SIMULATED POST-FIRE CONDITIONS

Chlorite [(Mg, Fe ²⁺)₅Al(Si₃0₁₀)(OH)₈] is a common mineral in soils that are often exposed to wild or prescribed fire. Previous studies have shown that these fires can alter chlorite by chemical weathering as a result of ash input. This is evidenced by a change in concentration and/or the atomic placement of Mg and Fe. In order to understand the direct relationship of ash to chlorite weathering, an experiment was carried out which simulated post-fire conditions. Chlorite was weathered in solutions of rainwater filtered through soil, ash, and soil + ash over periods of one, two, three, and six months. The solutions were analyzed for concentrations of Mg and Fe released during the weathering process by Atomic Absorption Spectrophotometry. Results show that Mg concentrations for Rain and Rain + Soil solutions were near exact in concentration and increased with time. Mg concentrations in solutions of Rain + Ash and Rain + Soil + Ash showed a slight decrease approaching three months, then slightly increasing at six months. These concentrations were less than those without the ash treatment. This indicates Mg is released when conditions are acidic. The basic cations released from the ash appear to have neutralized the acidity of the rainwater, thereby slowing the weathering. Fe concentrations of solutions of Rain, Rain + Soil, and Rain + Ash were similar. Fe increased from one to two months and then decreased after three months. Fe concentrations for Rain + Soil + Ash were notably greater than all other treatments. Fe declined from one to two months, then sharply increased at three months, followed by a sharp decrease at 6 months. It appears there is a secondary reaction between the soil and the ash causing a greater release of Fe. These results will be compared to Fe and Mg released directly from the ash and soil as well as to the bulk chemistry of the chlorite before and after treatment.