Research On Stability Of Soda Residue Solidified/Stabilized Heavy Mental Contaminated Soils Under Wetting-Drying Cycles

Stabilization/solidification technology is widely recognized for remediation of heavy metal contaminated soils around the world because of its effectiveness and economy.While in complex natural environment,the strength and chemical stability of solidified/stabilized contaminated soils under wetting and drying cycles may be affected.Therefore,studying of the strength,leaching and microstructure characteristics of solidified/stabilized contaminated soils have a great benefits on understanding the remediation mechanism and predicting the long-term stability of the solidified soil.Based on the project supported by National Natural Science Foundation（No.41172273）and（No.41372281）,strength tests,leaching tests and microstructure tests are performed to study the long-term stability of solidified/stabilized chromium and zinc contaminated soils with cement and soda residue under cyclic wetting and drying.The main findings obtained from the tests are shown as follows:（1）Through the study of the strength stability of solidified contaminated soils under wetting and drying cycles,we learn that with increase of the wetting and drying cycle,rate of the cumulative mass loss of solidified/stabilized chromium contaminated soils gradually increases;Which to zinc contaminated soils,increases slower,and the loss of overall quality of zinc contaminated soils is greater than the chrome;UCS of stabilized soils first increases which is minor and then decreases with the increase of wetting and drying cycle;UCS strength of solidified/stabilized chromium contaminated soils is bigger than zinc contaminated soils;Compared with the zinc contaminated soils,the chromium contaminated soils can be better stabilized;UCS strength of soil with 30%curing agent is better than which with 20%.（2）Through the study of the chemical stability of solidified contaminated soils under wetting and drying cycles,we learn that the pH and Ca²⁺ of soak liquid of two solidified contaminated soils decreases with the increase of wetting and drying cycle;To the leaching amount of Ca²⁺,solidified chromium contaminated soils is bigger than zinc contaminated soils,soil with 20% curing agent is smaller than 30%.TCLP and semi-dynamic leaching experiments are operated to study and compare the leaching characteristics of solidified heavy metal contaminated soils.It was found that,in the TCLP test,pH of leaching solution of specimens with different curing agent contents decreased with the increase of wetting and drying cycle;The concentration of Cr3+ and Zn2+in leaching solution decreased first and then increased with the increase of wettingand drying cycle,and the leaching amount of Cr3+ is bigger than Zn2+.In the semi-dynamic leaching experiment,pH of leaching solution fluctuation in a small scope;the total leaching amount of ions increased with the time of immersion,and increased with the increase of wetting and drying cycle.Ion diffusion coefficient of solidified soil decreased first then increased with the increase of wetting and drying cycle.（3）SEM and XRD are used to study the variation of the microstructure characteristics of solidified soil AFter wetting and drying cycle.The influence of wetting and drying cycle,the type of heavy metal ions and solidified agent type on microstructure characteristics are obtained.This will help us to better explain the remediation mechanisms of solidified soil by combining with the Macroscopic mechanical properties.