Alum salts are commonly used as coagulants in the purification of surface water for potable supplies. The large volumes of waste alumina-rich sludge generated are a waste management problem and are currently disposed of at landfill sites.
As-received alum sludge was calcined at various temperatures and then blended variously with Portland cement, ground granulated blast-furnace slag (GGBS) and limestone. The raw and calcined alum sludge was characterized to probe its physical and chemical properties. The raw alum sludge is an amorphous aluminium hydroxide precipitate. Upon thermal treatment, the sludge undergoes an η-alumina transition and finally crystallizes to thermodynamically stable corundum at 1100oC.
The pozzolanic activity of calcined alum sludge was assessed by determining Strength Activity Indices (ASTM C618). In cement-sludge blends the reactivity increased with increasing calcination temperature, but remained poor. Ternary cement-GGBS-sludge blends showed improved performance when the sludge was calcined at 825oC, with slightly decreased performance following calcination at higher temperatures. However, addition of limestone to the blend led to further improved performance, out-performing a CEM I-GGBS-limestone reference. This is due to synergy between aluminates in the calcined sludge and limestone powder.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)