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 ~ 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.