Use of Aluminium powder coating effluent for the geopolymerisation of coal fly ash, ferrochrome slag and gold mine tailings: A comparison and Life Cycle Inventory

Aluminium powder coating effluent with potassium hydroxide (KOH) were used in the geopolymerisation of coal fly ash (CFA), ferrochrome slag (FeCr) and gold mine tailings (GMT). In order to come up with a green synthesis route, curing was done at ambient conditions for 56 days. The synthesised geopolymers for CFA, FeCr and GMT were identified as CFA-GP, FeCr-GP and GMT-GP respectively. FeCr-GP, CFA-GP and GMT-GP had an unconfined compressive strength (UCS) of 25.5 MPa, 8.1 MPa and 6.1MPa after 28 days of curing using 6 M KOH. CFS-GP and FeCr-GP were effective in the stabilisation of heavy metals as the leachability of heavy metals was below allowable limits whilst GMT-GP was not effective. This was due to the presence of calcium silicate hydrate and calcium aluminate silicate hydrate in CFA-GP and FeCr-GP. These geopolymerisation products were absent in the microstructure of GMT-GP. The long-term use of CFA-GP and FeCr-GP did not pose any significant heavy metal pollution capability as the static leaching results were below the building material protocols whilst the use GMT-GP presented a significant environmental pollution threat. The use of FeCr-GP produced 270 kg CO2 per tonne of geopolymer resulting in a 19.4% reduction in carbon emissions as compared to the use of cement brick. Furthermore, more FeCr-GP had a 24 h water absorption rate of less than 9%. The geopolymerisation of CFA-GP and FeCr- GP with APCE can therefore be a method to reduce the pollution potential of these materials.