ALUMINIUM ETCHING WASTE SOLUTIONS IMMOBILISED IN FLY ASH GEOPOLYMERS

摘要

The aluminium anodising process is inevitably accompanied by the release of concentrated and diluted alkaline and acid waste effluents. The concentrated waste solutions contain approximately 15-45 g/l free NaOH and 60-120 g/l Al. These solutions are difficult to handle and have a large negative value. It is here proposed to use another industrial byproduct, coal fly ash, to produce a geopolymer of concrete strength. Alkali activated coal fly ash is known to result in geopolymeric bodies. The activator (NaOH, KOH or silicate solution) accounts for the major raw material cost. By using the waste sodium aluminate solutions from the etching of aluminium an ‘all-waste’ geopolymer is produced. Geopolymers were thus made from coal fly ash, blast furnace slag, the etching waste solution and some extra KOH. The weight ratio ash:slag:water:activator was kept near 30:15:10:10. The results show that compressive strengths between 40 and 60 MPa can be obtained. This is lower than what can be obtained with the same fly ash and K-silicate as activator, but is still in the range of normal concrete. The black colour of the solution did not have a marked effect on the appearance of the product. As a conclusion, it can be said that the proposed solution is a win-win-win situation. Triple win, because it solves the problem of the Al etching waste solutions, it uses a residue from coal combustion and it produces a building material with almost zero CO2 emission.