Novel carbonation solidification process for recovery of Zn-contaminated slurry: Strength and leachability aspects

In this study, a continuous process of foam drying pre-treatment with steel slag powder and carbonation so-lidification (SSFD-C) was used to recycle zinc-(Zn-) contaminated slurry, which achieved the first imple-mentation of accelerated carbonation technology in contaminated slurry recovery. Unlike conventional carbonation solidification methods, the steel slag component of the slurry also underwent a drying process as part of the SSFD-C process. During the drying process, the mechanism whereby the contaminating Zn ions interacted with steel slag, and the effects of these interactions on the carbonation efficiency and mechanical properties of the carbonated soil (CS) were investigated by testing CO2 uptake and unconfined compressive strength (UCS). In addition, the stabilizing effects of the drying and carbonation processes on Zn contamination were evaluated by establishing pH values and Zn leaching concentrations of the dried soil (DS) and CS under water/acid leaching. This study makes several important contributions to the existing literature on Zn contamination and its effect on the UCS of CS. We found that Zn contamination negatively impacted the UCS of CS by impairing its carbonation efficiency. Additionally, it was found that both drying and carbonation processes can efficiently reduce acid-leached Zn concentration by 45-85% compared to untreated contaminated samples. It was established that Zn contamination is stabilized as Zn(OH)2 in DS and CS specimens through an X-ray diffractometry and derivative thermogravimetric analysis. Furthermore, our study highlights the benefit of carbonation in stabilizing Zn leaching, as it lowers the pH value of water-leached samples.