Around 60 Mt of coal fly ash is produced annually within the EU by coal combustion. This fly ash is utilised for about 50% in the cement and concrete industry and in civil construction works. Both applications are of low or even negative economic value. The other 50% of fly ash produced is simply dumped, a practice which is becoming more and more expensive. Actually, this does not comply with the present ideas on sustainable -economically driven management of raw materials and environment. Coal fly ash consists for more than 99% of useful components of which about 70-80% are glassy aluminium/silicon components. The potentially environment threatening heavy metals are present only in trace amounts, mainly on the shell of the particles. Looking at the proportion of the useful components and threatening ones, one should realize that there is a need to separate the useful components from the potentially threatening ones. However, the major elements, silicon and aluminium, are built in the glass phase of the fly ash. A problem is that the glass phase is surrounded by the mullite fraction, which is very difficult to distract. Another problem is that a part of the aluminium can be present in coordination states >4, which is unfavorable for the glass destruction. Thus it is important to find a method for the liberation of those components from the glass structure. In the SILEX project it will be endeavoured to increase the recovery of silicon to an industrial interesting amount (circa 80% of the silicon present in fly ash), e.g. by means of alkaline treatment, high L/S ratio's, microwave assistance and sonochemistry.
If the results of the project are positive: - the reuse of fly ashes could be increased - the economically interesting minerals could be produced - new sources of benefits to the producers of fly ashes would be generated - the minerals could be used on the market for environmental technoloBE97-4061
Funding SchemeCSC - Cost-sharing contracts
2628 CJ Delft