Synthesis of Ca-Al layered double hydroxide from concrete sludge and evaluation of its chromate removal ability

Concrete sludge is an industrial waste slurry containing hydrated cement, aggregates and water. The main components of concrete sludge are CaO, SiO2, Al2O3 and small amounts of metal oxides such as Fe2O3 and MgO. In this study, the calcium component of concrete sludge was used as a raw material for the synthesis of Ca-Al type layered double hydroxide (LDH). The chromate removal ability of the LDH was examined using a potassium chromate solution containing 180 mg/L chromate. The LDH showed a high chromate removal ability with a concentration decrease of up to 0.4 mg/L. The chromate is removed in the form of CrO42 − by anion exchange with NO3− in the Ca-Al NO3 LDH.