Effect of chemical and thermal activations on the properties of rice husk ash-based solidified wastes

Strength development, leachability and microstructure of heavy metals from the solidified waste using synthesis rice husk ash (sRHA) and lime blended at the weight ratio of 1:1 were used as binders. The heavy metal-containing sludge was used at the level of 0 wt.%, 30 wt.%, and 50 wt.% dry weight, respectively. The sample specimens with and without 1.5 wt.% of sodium silicate (SiO2/Na2O = 1.0) were cured under the ambient condition and elevated temperature curing at 50°C for 24 hr. Experimental results showed that the introduction of sodium silicate solution and elevated temperature curing to sRHA-based solidified waste containing 30 wt.% of heavy metal sludge gave one day strength of 20 kg/cm2 compared to 0.9 kg/cm2 for the control sample. XRD patterns indicated that most metal-sulfides present in the sludge were appeared in the solidified waste and SEM coupled with EDX techniques reveal these metal-sulfide particles were trapped within the lime-sRHA matrices. In addition, cumulative leaching behavior by tank test (EA NEN 7375:2004) showed that solidified waste containing up to 30 wt.% of heavy metal sludge was suitable to dispose in a secured landfill.