Fixation of treated phosphate waste and its use in concrete

Currently, in Israel, phosphate acidic wastes formed during the production of phosphoric acid (H3PO4) using hydrochloric acid (HCl) are stored in large ponds. At present, this waste is only neutralized using lime (CaO) or calcite (CaCO3). This paper investigated the potential use of Class F (<20% CaO) coal fly ash (FA) as a fixation reagent of the neutralized hazardous phosphate industry waste. Studies have shown that FA can be an efficient scrubber and fixation reagent for various kinds of acidic toxic waste. Several analytical techniques including ICP-AES, ICP-MS, SEM-EDX, and XRD, ion penetration and compression/flexure strength tests (according to ASTM C1202, IS26/4.1, and 4.2 protocols), as well as leaching experiments (EN12457-2) were used to study the fixation quality and potential utilization of the fixated product as partial substitute to sand in concrete. Scrubbing phosphate waste with the FA was found to effective in reducing the leaching rate of toxic trace elements. Moreover, the use of aggregates as a partial substitute for sand in concrete improves the mechanical and chemical properties and is environmental safe. Thus, these procedures would eliminate costly treatment and storage of these toxic wastes relatively inexpensively as well as enhance industrial concrete for civil engineering projects.