| Cement-based S/S of sludge confronted the problems of consuming the large amount of cement and high pH leaching from solidified sludge. This research utilized calcium-bentonite as additive to assist cement-based S/S of sludge. Unconfined compressive strength (UCS) test and leach test were conducted to assess its effect by measuring UCS of the solidified sludge, leaching ratio of heavy metal, COD and pH of leachate from the solidified sludge. The results show that compressive strength of the solidified sludge increases remarkably after adding calcium-bentonite, and when half of cement content of 0.4 (to sludge by weight)is replaced by bentonite, strength of the solidified sludge increases nearly 6 times. Furthermore, volume of the solidified sludge after adding bentonite changes small. With calcium-bentonite adding, leaching Zn, Pb and pH from the solidified sludge appears in a declining trend, zinc and lead leaching ratios decrease from 6.9% to 0.25%, 9.6% to 5% respectively and pH decreases from 12.3 to 12.1. Copper would be leached out as organics dissolve at high pH or natural drying conditions, which increases leaching ratio of copper from sludge. However, bentonite can reduce these bad influences and improve stability of copper stable in the solidified sludge. |
