Performance of lime-BHA solidified plating sludge in the presence of Na2SiO3 and Na2CO3

This research investigated the performance of lime-BHA (black rice husk ash) solidified plating sludge with 2 wt% NaO from Na2SiO3 and Na2CO3 at the level of 0, 30 and 50 wt%. The sludge was evaluated for strength development, leachability, solution chemistry and microstructure. The lime-BHA solidified plating sludge with Na2SiO3 and Na2CO3 had higher early strength when compared to the control. The addition of Na2SiO3 and Na2CO3 increased the OH− concentration and decreased the Ca2+ and heavy metal ions in solution after the first minute. The XRD patterns showed that the addition of Na2SiO3 resulted in the formation of calcium silicate hydrates, while the addition of Na2CO3 resulted in CaCO3. The heavy metals from the plating sludge, especially Zn, were immobilized in calcium zincate and calcium zinc silicate forms for the lime-BHA with and without Na2SiO3 solidified wastes, while samples with Na2CO3 contained Zn that was fixed in the form of CaZnCO3. The cumulative leaching of Fe, Cr and Zn from the lime-BHA solidified plating sludge decreased significantly when activators were added, especially Na2CO3.