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Israeli¯y ash is highly basic when exposed to water, due to the very low sulfur content allowed in coal imports because of the strict environmental regulations (with respect to SO x emissions). Thus, the¯y ash is a potential chemical neutralization/®xation agent for acidic wastes. In this study, coal¯y ash has been examined as a neutralization/®xation agent for acidic sludge produced from the regeneration of used engine oils. The initial results show that the¯y ash can be used as a very ef®cient neutralization/®xation agent of the sludge. Furthermore the trace elements and the organic components are ef®ciently ®xed within the¯y ash particles. The product can serve as a good aggregate in concrete production. The neutralization and ®xation processes are discussed in detail.

An extremely acidic, heavy metal-rich sludge (pH = À1.2) was scrubbed with a Class-F fly ash in order to simultaneously neutralize the acidity and stabilize the heavy metals contained in both wastes. This paper outlines the leaching behavior of the aggregate material generated by scrubbing. For proper fly ash/sludge ratios, the fly ash acted as an outstanding neutralizer for the acidic waste. Leaching of heavy metals from the aggregate samples was below the environmental limits within a pH range between 3 and 9. Subsequent washing of the leached aggregate with acidic CALWET solutions did not result in an additional release of heavy metals. It is proposed that coordinative bonding of the metal cations onto neutral surface sites and electrostatic adsorption led to stabilization of the heavy metals within the aggregate structure below hydrolysis pHs.

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