Durability study of a solidified mercury-containing sludge

Abstract

To more efficiently dispose of hazardous wastes, the durability of a solidified mercury-containing sludge was studied. A sludge sample was obtained from a chloro-alkali plant and solidified using a commercially available sludge treatment agent (STA II). The solidified monoliths were then subjected to physical and chemical durability tests. The physical durability tests (the freezing and thawing test and the wetting and drying test) were followed by the measurements of unconfined compressive strength and mercury concentration resulting from the toxicity characteristic leaching procedure (TCLP), if possible. The multiple TCLP (MTCLP), developed by this author, was employed for the chemical durability test. It was found that the smaller the sludge-to-binder ratio (S/B) was, the better the physical and chemical properties of a solidified monolith would have. This conclusion was a result of the various durability tests, unconfined compressive strength measurements, and TCLP test. All solidified specimens were broken during the freezing and thawing test except the one with S/B = 0.5, which was found to be degraded in terms of compressive strength and leaching toxicity as well. Results of the wetting and drying test also showed that all solidified specimens were degraded as evidenced by the compressive strength and TCLP leachate concentration measurements. The multiple TCLP test was carried out to determine the long-term stability of the solidified specimens subjected to cyclic erosion and leaching by acid precipitation. The test results in this study showed that solidification with the binder STA II has reduced the cumulative amount of mercury leached from 10.57/dg to less than 0.66/dg by weight.