Abstract
The Bayer process utilises high concentrations of caustic and elevated temperature to liberate alumina from bauxite, for the production of aluminium and other chemicals. Within Australia, this process results in 40 million tonnes of mineral residues (Red mud) each year. Over the same period, the energy production sector will produce 14 million tonnes of coal combustion products (Fly ash). Both industrial residues require impoundment storage, yet combining some of these components can produce geopolymers, an alternative to cement. Geopolymers derived from Bayer liquor and fly ash have been made successfully with a compressive strength in excess of 40 MPa after oven curing. However, any product from these industries would require large volume applications with robust operational conditions to maximise utilisation. To facilitate potential unconfined large-scale production, Bayer derived fly ash geopolymers have been optimised to achieve ambient curing. Fly ash from two different power stations have been successfully trialled showing the versatility of the Bayer liquor-ash combination for making geopolymers.
Highlights
Aluminosilicate inorganic polymers or geopolymers are amorphous materials that have the potential to be an alternative for Ordinary Portland Cement (OPC) binders
For a geopolymer concrete binding agent to be suitable for the replacement of Ordinary
For a geopolymer concrete binding agent to be suitable for the replacement of Ordinary Portland
Summary
Aluminosilicate inorganic polymers or geopolymers are amorphous materials that have the potential to be an alternative for Ordinary Portland Cement (OPC) binders. Typical preparation of a geopolymer binder requires a highly concentrated caustic silicate solution to be added to a source of soluble silica and alumina (usually fly ash, metakaolin or ground granulated blast furnace slag) [27]. This procedure commonly targets a reactive Si/Al ratio of around two. Further development has shown that geopolymers can be made from silica rich, class F fly ash and alumina and caustic rich spent Bayer liquors (A “Bayer liquor” is a process solution derived from the hydrometallurgical thermal caustic extraction of alumina from bauxite ore) [10] This achieves industrial synergies removing impurity laden liquor from Bayer process streams while providing an inexpensive source of caustic for the production of geopolymer concrete [33,34,35]. The present work has targeted compressive strength above 20 MPa, as this is typically specified for applications such as pathways, driveways and building footings (AS3727, 1993) [38]
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