Ferrite Formation using Precipitate in the Treatment of Acid Mine Drainage for Reducing its Volume

Ferrite formation in precipitates by a two-step neutralization process in which magnesium oxide (MgO) was used as the first neutralizer and sodium hydroxide (NaOH) as the second was applied to acid mine drainage (AMD) from the Horobetsu mine, an abandoned sulfur mine, in Hokkaido, Japan, to reduce the volume of precipitates to be disposed. Batch neutralization experiments with MgO and continuous flow experiments by the two-step neutralization were conducted in the laboratory and the actual AMD treatment plant. The results showed that the heavy metals in the AMD were successfully removed by the process, and that the precipitates were magnetized by the neutralization in the continuous flow experiments although there was Al and Si in the AMD that could have prevented the formation of ferrite. This indicates that ferrite can be formed from the precipitates after removing most of the soluble Al and Si by the first neutralization. The change in the chemical forms of the iron precipitates and preventing gypsum and calcite formation in the precipitates by MgO result in a volume reduction of precipitates by two thirds for this AMD when compared with conventional processes.