DEVELOPMENT OF AN ACID RESISTANT TREATMENT GROUT UTILISING MODIFIED BAUXITE REFINERY RESIDUES

Alumina production by the Bayer Process creates large volumes of caustic refinery residues (red mud) and currently there is a need to find sustainable uses for refinery residues. The Basecon^TM neutralisation process results in soluble alkalinity being converted into solid alkaline hydroxide, carbonate and hydroxy-carbonate minerals. The resulting neutralised red mud (Bauxsol^TM) has a high acid neutralisation capacity, as well as a high metal binding capacity. Contrary to this ARD waters are acidic, metal-rich water that are typically treated by addition of lime. However, this is a short-term solution, which does not treat the source of the problem, the excavated and exposed sulphidic rock. Consequently, a novel approach is to incorporate Bauxsol^TM into an otherwise acid susceptible ordinary Portland cement (OPC) grout and to inject this into the broken rock and bind it back as a coherent mass. By sealing a waste rock dump by means of injecting a grout with an acid-neutralising and metal-binding capacity, ARD production is treated at source by preventing, or severely reducing the rate of production.

This paper details preliminary work in the development of Bauxsol^TM-based treatment grouts for such an application. Presented are the results for the fluidity, based on a factorial analysis design, that has allowed the determination of 9 mixes that are potentially suitable for injection into waste rock material. These 9 mixes are then exposed to high concentration sulphate solutions to determine the sulphate expansion characteristics.