Evaluation of Leaching Tests for Cement Based Immobilization of Hazardous Compounds

A range or arsenic containing compounds, including arsenic trioxide, pentoxide and a lead arsenate insecticide have been stabilized using formulations of cement alone, cement + lime and cement + ferrous sulfate and subsequently exposed to a range of leaching regimes in order to compare their effectiveness for metal stabilization. Leaching tests used were two regulatory tests, the Toxicity Characteristic Leaching Procedure (TCLP) and the Australian Bottle Leaching Procedure (ABLP), as well as column leaching. Arsenic leachate concentrations from cement-stabilized lead arsenate insecticide were similar when subjected to either the TCLP or ABLP using the same leachant. Lead, known to be immobilized by means different to that of arsenic, yielded varying leachate concentrations when using either of the regulatory tests, even though the leachant was of the same type. The leaching of calcium influences the filtered arsenic leachate, whereas the leaching of lead is greatly affected by leachate pH. As expected, both regulatory tests generally proved to be very severe in terms of the masses of the hazardous constituents leached when compared to conceptually more realistic column leaching scenarios. Sodium arsenate-containing formulations behaved anomalously, with column leaching tests resulting in larger arsenic masses being leached than the regulatory tests. Sodium arsenate, known to inhibit cementation reactions, serves as a reminder of the perils that can be faced when generalizing the results obtained from leaching tests.