Effect of steel slag on foam drying and carbonation properties of dredged slurry–dried soil mixtures

A continuous treatment process using steel slag powder including foam drying and carbonation processes (termed the SSFD-C method) is a novel technology previously developed in our laboratory. It has achieved the first application of steel slag carbonation technology to recycle dredged slurry with high moisture content. The SSFD-C method presents a promising avenue for achieving large-scale reuse of dredged materials in a cost-effective and environmentally sustainable manner. This study provides a comprehensive mechanistic analysis of the SSFD-C method, with a particular focus on the impact of steel slag on the foam drying and carbonation performance of both dredged slurry and dried soil (DS). In particular, the mixed soil (MS), mixed directly of steel slag and dredged soil, was prepared as a reference group to better understand the effect of the drying process on the carbonation properties of DS. The results showed that in the drying process, the foam drying efficiency of the slurry exhibited a nonlinear relationship with steel slag content, such that the efficiency first increased and then decreased as the steel slag content increased. The effect of steel slag content on the foam drying efficiency of slurries is the outcome of multi-factor coupling. Moreover, the moisture content, the density, and the appearance of the foamed slurry after drying are not reliable indicators for optimizing the foam drying efficiency of slurries by the steel slag admixture. In the carbonation stabilization/solidification (S/S) process of the DS, it was found that the carbonation strength of DS increased with the increasing steel slag content involved in the drying process, but was inferior to that of MS with each corresponding steel slag content. Based on the pH test and composition analysis of DS compared with MS, it was found that the deterioration of carbonation performance of DS is related to a lower pH value induced by the consumption of Ca(OH)2 (CH) during the drying process. The recovery of carbonation strength of DS after lime hydrate (LH) excitation increased with the higher steel slag composition in DS. The carbonation activity of DS did not disappear after the drying process but recovered to a certain extent after alkali excitation. This study provides a theoretical foundation and practical guidance for the effective application of the SSFD-C method in the dredged slurry with high moisture content.