Leaching tests on solidified products

This work shows the experimental results obtained by a series of extended-time leaching tests carried out on stabilized/solidified (S/S) products. The materials subjected to the leaching tests were obtained by mixing different amounts of Portland cement (C) with fly ash (FA) coming from a Hospital Solid Waste (HSW) incineration plant. Ideally, as far as contaminant release from the waste is concerned, a leaching test must be able to determine the following characteristics: 1) the compounds that can be released from the waste; 2) the maximum concentration of these compounds in the leachate; 3) the quantities released per unit mass of waste; 4) the release rate of these compounds; 5) the effects of a co-disposal of the waste. The aspect regarding concentration is relevant because the toxic effects of a number of elements, like most chemical reactions, depend on concentration. As far as the amount of release is concerned, the necessity to evaluate the maximum amount of hazardous compounds leachable from a waste under different environmental conditions is evident; moreover, it would be important to determine the possibility of accumulation of toxic compounds due to biological and chemical reactions. Furthermore, the trend of release is related to eventual physical and chemical changes occurring in the waste because of contaminant leaching from the waste matrix. The procedures applied in carrying out the extended-time leaching tests on S/S products made with HSW fly ash and Portland cement were a modified version of the IRSA - CNR acetic acid leaching test (Italian law standard leaching test) and a modified version of the proposed standard European leaching test (option C). The tests were carried out over a thirty-day period by renewing the leaching solution every 24 hours. The comparison between the extended-time and the standardized tests allowed the leaching rate for different contaminants and the leaching - controlling process to be determined.