Effects of Various Additives on the Solidification of Oily Sludges: A Bench-Scale Study

In preparation for closure of a RCRA hazardous waste site in Northern California, the oily impounded sludges will be solidified in situ using a cementitious system in order to support the closure cover. To determine mix ratios of additives to be used to solidify the sludges in the impoundments, treatability testing was completed. The testing consisted of first mixing the sludge with additives in small batches to determine the effect of various types and combinations of additives on the unconfined compressive strength (by pocket penetrometer testing) of the solidified material. Information learned in this testing was used to determine mix ratios to be tested in larger batches to evaluates caling changes and test for unconfined compressive strength by a more reliable method. The appropriate mix ratio determined in the second set of tests will be used as a guide to solidify the impounded sludge in situ.

Data from the impoundment tested indicates the largest observed effect on the final strength of the solidified material was due to varying the amount of fly ash added. Varying the amount of cement had a lesser observed effect on the final strength of the material. The data also indicates an increase in the strength of solidified material with the addition of relatively small amounts of bentonite in addition to other additives. Further increases in the amount of bentonite did not appear to affect the final strength.