Effect of Composite Stabilizer on the Stability of Heavy Metal Containing Sludge
The occurrence of heavy metals is an important factor restricting the utilization of sludge resources.The three stabilizers,calcium carbonate(CaCO3),hydroxyapatite(HAP),and sepiolite were selected and added to the tested sludge.The addition ratios were 2%,5% and 10% of the dry sludge weight.After 21 days,the leaching toxicity and heavy metal morphology were researched via the quartering method.The results indicate that the three stabilizers have weaker stabilizing effects on Cd.In addition,the total amount of HAP is inverse-ly proportional to the stability effect of As.Therefore,after compounding the three stabilizers in proportion,the effects of each group′s ratio on stabilization of heavy metals in sludge was explored using the same method.The results indicated that the best result achieved when the mass ratio of HAP to sepiolite to CaCO3 was 1∶1∶1.At this ratio,the stabilization rate of Cd in the sludge reached over 80%,and the leaching stabilization effi-ciencies of As,Cr,Pb and Cu were close to 100% .Only the stabilization efficiency of Zn and Ni showed no significant change compared to a single stabilizer.The stable states of Cd,Cr,Pb and Cu showed no signifi-cant change or even decrease compared to the previous single stabilizer.But the composite stabilizer can in-crease the proportion of residual states,the morphology of As,Zn and Ni did not show significant changes.The synergistic effect between composite stabilizers promotes the transformation of Cd,Cr,Pb and Cu forms to more stable states.
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