Bauxite (red mud) treatment

What

Red mud or bauxite is an aluminium-oxide. Applying red mud to soils is beneficial because bauxite is phosphorus-sorbing, meaning it takes up phosphorus, decreasing leaching of the contaminant into waterways. It is especially effective for soils with a low anion storage capacity (also known as phosphate retention).

The variation in anion storage capacity (also known as phosphate retention) between soil types is related to the amounts of specific iron and aluminium compounds and the type of clay minerals in the soils. This is determined by the type of rock or parent material that the soil has developed from. For example, soils developed from volcanic ash tend to have high anion storage capacity while soils developed from greywacke alluvium tend to have low anion storage capacity. Natural peat and sands also have a low anion storage capacity.

Why

Red mud can be applied directly to soils to increase the anion storage capacity of the soil and decrease phosphorus leaching. Red mud can also be used as a substitute for lime on paddocks as it is alkaline.

However, there are some limitations to using bauxite in soils including that there are few suppliers in New Zealand and if the red mud is used on paddocks for liming effect (increasing soil pH) animals need to avoid the treated area because ingestion may impair rumen function.

References