Comparison of fly ash leaching methods

Five leaching methods (serial batch leaching procedure (SBLP), synthetic groundwater leaching procedure (SGLP), mine water leaching procedure (MWLP), 3 TIER integrated framework leaching protocol (3TIER), and toxicity characteristic leaching procedure (TCLP)) were compared using two samples, a class F fly and a class C fly ash. Each method was tested in triplicate, according to the published procedure, and leachate was analyzed for 23 elements. The procedures were compared on the basis of elemental availability, defined as the cumulative elemental release per kg of sample, and the variation in extraction with increased L/S as a surrogate for long term release. Higher availability values were obtained with the SBLP and MWLP, which cover a range of pH’s and 3TIER, which uses EDTA to form soluble complexes. SGLP, a high pH procedure, and TCLP, mildly acidic, generally produced lower availability values. Cumulative elemental extraction as a function of L/S in SBLP, MWLP and 3TIER generally agreed within an order of magnitude.