Study of mineralogy and leaching behavior of stabilized/solidified sludge using differential acid neutralization analysis Part I: Experimental study

In this work, differential acid neutralization analysis, chemical analysis of selected leachates and mineralogical study (XRD and SEM-EDS) are combined to investigate the relationship between mineralogy and leaching behavior of hydroxide sludge doped in Zn and Cr stabilized/solidified by hydraulic binders. The leaching behavior of stabilized hydroxide sludge is controlled by the dissolution of portlandite (pH similar to 12) followed by the dissolution of AFt/AFm and hydrogarnets (pH between 12 and 10) and finally the dissolution of ettringite and of the siliceous matrix of C-S-H (pH < 10). The zinc behavior is independent of the main components and is controlled by the dissolution of calcium hydroxizincate and its reprecipitation as hydroxyde or its adsorption on C-S-H. Chromium release is linked to the sulfate one due to a substitution in AFt/AFm phases. The proposed combination of tests is highly pertinent to establish the links between mineralogy and leaching behavior. Nevertheless, the hypotheses formulated are insufficient to implement a behavioral model to describe the leaching behavior. (C) 2009 Elsevier Ltd. All rights reserved.