Stabilization of Red Mud Using Ground Granulated Blast Furnace Slag by Geopolymerization Technique

Abstract

Red mud is an alkaline by-product which is generated during the processing of bauxite. Generally red mud is considered as a waste material which is disposed into large lagoons. Red mud contains large amount of Fe2O3, Al2O3 and small amounts of CaO, SiO2 and some valuable metals such as titanium however it devoid of reactive alumino-silicates. As red mud is highly alkaline, it is possible to stabilize red mud by adding industrial waste materials rich in alumino-silicates by geopolymerization. The main principle involved in geopolymerization is the chemical reaction between alumino-silicate materials with highly alkaline solution to form amorphous to semi crystalline inorganic polymers. In the present research work an attempt has been made to stabilize red mud using ground granulated blast furnace slag. The amount of slag is varied as 0%, 10%, 20%, 40%, 60% and 80% by weight of the red mud-slag mixture. For each combination of red mud-slag the Atterberg’s limits, pH value, differential free swell value, compaction characteristics corresponding to light compaction and heavy compaction energies and unconfined compressive strength (UCS) are determined. Further additional doses of sodium hydroxide (NaOH) as an alkali activator varying as 2%, 4%, 8%, 12% of dry mass of the above red mud-slag mixes were given to accelerate the geopolymerization process. The UCS values of specimens were determined after curing periods of 0, 3, 15, 30 and 60 days. It is observed that mere addition of slag to red mud, without any alkali activator, improves the unconfined compressive strength substantially. An addition 4% NaOH with 40% slag gave a compressive strength of 14 MPa after a curing period of 60days. Hence it can be concluded that red mud can be stabilized effectively by the addition of little amount of alkali and ground granulated blast furnace slag.