Experimental study on solidification/stabilization of Cr(VI) contaminated soil by alkali-activated ground granulated blast furnace slag

Alkali-excited ground granulated blast furnace slag (GGBFS) can be used in solidification of contaminated soil as an alternative to cement, and is low energy consumption and low carbon emission. However, application of GGBFS in solidification/stabilization of chromium(Cr)-contaminated soil has attracted less attention and the curing effect and mechanism are still unclear. Based on the reduction capacity of GGBFS and the gelling ability after alkali excitation, solidification/stabilization of soil with Cr content of 2000 mg/kg (including 1210 mg/kg Cr(VI) ) is carried out. The results are compared with those of PC. Leaching toxicity, immobilization efficiency and unconfined compressive strength analyses are performed to study the treatment effects. The pH, reduction efficiency, chemical morphology, mineral composition and microscope images are analyzed to investigate the related mechanism. The results show that the leached Cr concentration after treated by GGBFS was significantly lower than that of PC. At a GGBFS dosage of 20% and a curing period of 28 d, the leached total Cr and Cr(VI) decrease to 2.12 and 1.09 mg/L, which meet the regulation limit for landfill disposal. The strength of GGBFS treated soil is obviously higher than that of PC. Valence states analysis shows that S2- in GGBFS can effectively reduce Cr(VI) to Cr(III) with a reduction efficiency as high as 96.0%, which avoid the inhibition of Cr(VI) to the hydration process. Additional reduction agent is not needed when treating such (Cr)-contaminated soil with GGBFS. After the GGBFS treatment, more unstable Cr is transformed to stable forms and the Cr mobility is significantly reduced. Also, more hydrated gels are generated for cementation of soil particles, resulting in better sealing effect and higher strength. This study provides a scientific basis for the stabilized/solidified of Cr(VI)-contaminated soil using GGBFS.