Fly ash is one of the waste products generated by coal-fired power stations. Similar to red mud, fly ash contains a high concentration of alumina (up to 35%), as well as other valuable materials. According to the International Energy Agency (IEA) Clean Coal Centre, there are 7,000 coal-fired power units worldwide, spread over 2,300 sites, of which about 620 are located in China. It is estimated that 40-50% of coal combustion by-products are re-used, primarily in low-value applications, with the remainder being sent to stockpiles. Fly ash contains alumina, silica, iron, rare metals and other valuable elements, but no viable remediation technology has previously existed.
Orbite estimates that between 495 million and 650 million tonnes of fly ash are produced annually, a figure that could increase by 50% by 2030 according to the World Coal Association.