Desilication of fly ash and development of lightweight construction blocks from alkaline activated desilicated fly ash

Massive reserves of power plant fly ash dumps in South Africa have necessitated the development of different processes for effective remediation to achieve zero waste generation by secondary processes. Silica was leached from fly ash (FA) at the optimum conditions of a leaching time of 6 h, 3 M KOH, 500 rpm agitation speed, 25 liquid to solid ratio and a leaching temperature of 100°C. A lightweight construction block (LWCB) was developed from desilicated fly ash (DFA) and KOH. It was found that the optimum synthesis conditions were 10 M KOH, +0.075-0.300 mm DFA and a curing temperature of 40°C for 12 h, 80°C for 12 h and 100°C for 24 h. The development of strength was through the formation of Kalsilite. The LWCB met the minimum requirements for ASTM C34-13, C129-14a and South African standard (SANS227: 2007).