Anion leaching from refinery oily sludge and ash from incineration of oily sludge stabilized/solidified with cement. Part I. Experimental results

This paper presents the leaching behavior of anions (SO₄ ^2- and CrO₄^2-) from refinery oily sludge and ash produced by incineration of oily sludge, stabilized/solidified (s/s) with two types of cement, I42.5 and II42.5. Anion leaching was examined using a 5-step sequential toxicity characteristic leaching procedure (TCLP) test. A single TCLP extraction resulted in limited sulfate release (<50 mg/L) for s/s ash and significant sulfate release (<850 mg/L) for s/s oily sludge. Chromate release was <1 mg/L for s/s ash and nondetectable for s/s oily sludge. The sequential TCLP tests resulted in increased leaching for both sulfate and chromate. In general, the increase of liquid-to-solid ratio (TCLP leachant-to-waste ratio) resulted in increased leaching of sulfate from solidified samples compared to untreated oily sludge, ash and cement. In contrast, chromate leaching decreased by s/s process. A qualitatively similar leaching behavior for SO₄^2-, even for radically different wastes such as oily sludge and ash, solidified with two different types of cement was observed.