Leachability of trace metal elements from fly ash concrete: Results from column-leaching and batch-leaching tests

This paper deals with the effect of leaching conditions on the leachability of trace metal elements from concrete incorporating two fly ashes. The dat a from the column-leaching rests to simulate wetting and drying and batch-l eaching tests using buffered acetic acid and synthetic acid rain as leachan ts, are discussed The United States Environmental Protection Agency (EPA) R egulatory Method 1311-Toxicity Characteristic Leaching Procedure (TCLP) was used as a reference. The results indicated that, regardless of the type of the fly ash used, the percentage of fly ash, and,the water-cementitious ratio (w/cm) of the conc rete, none of the trace metals analyzed (As, Cd, Cr, Cu, Pb, Se, and Zn) in the leachates from the fly ash concrete samples exceeded the regulated con centration la els specified in the TCLP leaching test. The concretes incorp orating the fly ashes are, therefore, considered stable. In the batch- and column-leaching tests, the leached trace metal levels from the fly ash conc retes were also well below the regulatory levels for the leachate quality c riteria. The fly ash content and w/cm did not appear to have significant effect on t he leachability of the trace metal elements when using column-leaching test s and the 24-week batch-leaching test. The observed concentrations of metal s leached using synthetic-acid rain were less than that observed for the bu ffered acetic acid. This is consistent with the pH dependence of the leacha bility of the metals. For Se, all measured values of the leachates from the four different types of tests were at or below the detection limit. Cadmium, Q Ni, Pb, and Fe in the leachates from the fly ash concretes were also measured at or near det ection limits or at levels below or similar to those of the control portlan d cement concrete. Arsenic, and to a lesser extent Cu and Zn, Ir ere the on ly metals that showed any significant leaching trends in the tests. Arsenic showed a correlation ber-rr een the metal content in fly ash and the conce ntrations of the metals leached from the fly ash concrete. Similar correlat ions for Zn and Cu were not observed.