Engineering mechanical properties and mechanism of carbonated solidified lead-cadmium contaminated clay with steel slag curing agent

Recently, treating heavy metal-contaminated soil in a green, effective and harmless way has gradually become a research hotspot and also a difficulty. Hence, this study presents a novel environmentally friendly composite, formed by sodium hydroxide (used as an activator), desulfurized gypsum, and steel slag (S-GS). The main objective of this study is to synthetically evaluate the potential use of S-GS for solidifying Lead-Cadmium contaminated clay under the condition of carbonation curing. Moreover, the samples’ characteristics are investigated according to the tests of unconfined compressive strength (UCS), freeze–thaw cycle, Synthetic Precipitation Leaching Procedure (SPLP), and a series of microscopic tests. The results indicate that the carbonation curing can effectively improve the strength of the S-GS solidified contaminated clay, and also help to reduce the toxic leaching amount of lead and cadmium in samples, mainly due to the formation of carbonate or basic carbonate precipitation of the heavy metal in the process of carbonation, and the heavy metal is stabilized in the soil through adsorption and the packing effects of cementitious substances. Besides, within 120 days, the strength of solidified soil samples increases in the form of a power function with the increasing standing time. But compared with the uncarbonated samples, carbonation curing has an inhibiting effect on the strength growth of samples at longer ages. Additionally, carbonation curing can effectively improve the ability of the freeze–thaw cycle resistance for the S-GS solidified lead-cadmium composite contaminated clay.