Study On The Stabilization/Solidification Technology And Mechanism Of The Heavy Mental Contaminated Soils Treated With Soda Residue

With the rapid development of urban industrialization in China,heavy metal pollution has becoming one of the most serious environmental problems.Based on the previous studies,the stabilization/solidification?S/S?has been considered as one of the most effective methods to restore the contaminated soils.Therefore,exploring the new and cost-effective binders and revealing the immobilization mechanism are becoming the key issues,which will improve the development of the remediation technology and make it better to solve the practical engineering problems.Based on the projects supported by the National Natural Science Foundation of China?No.41172273 and No.41372281?,the paper investigated the unconfined compressive strength?UCS?and leaching properties of the heavy metal contaminated soils stabilized with cement and soda residues.And the immobilized mechanism was revealed depended on the electrical resistivity test,scan electronic microscopy?SEM?and X-ray diffraction?XRD?.The main obtained conclusions are presented as follows:?1?Based on the UCS results,increasing curing time resulted in the growth of strength and increasing the heavy metal concentration reduced the strength.Even at a high level of heavy metal concentration,the obtained strength still satisfied the remediation standard of America.Compared with Zn-contaminated soils,the stabilized Cr-contaminated soils exhibited a higher strength.?2?The leaching test results showed that the leached heavy metal ions concentration decreased with curing time increased and increased with heavy metal concentration increased.With a lower heavy metal concentration,both leached Zn²⁺ and Cr³⁺ concentrations were lower than the limited leachability.Whereas,in a high concentration condition,the leached Zn²⁺ can not meet the acceptance level.?3?Considering the results of UCS and leaching test,cement blended with soda residues stabilized Cr-contaminated soils appeared a better solidified effectiveness than that of Zn-contaminated soils.Because the presence of Zn²⁺ impeded the hydration reaction obviously,while Cr³⁺ can be immobilized in the complex compound and filled in the soil pores.?4?For the Cr-contaminated soils with a lower concentration?Cr0.1 and Cr0.5?,the optimum binder proportion was 20% with a mass ratio of 2:8?cement : soda residue?.For the Zn-contaminated soils with a lower concentration?Zn0.1 and Zn0.5?,the optimum binder proportion was 30% with a mass ratio of 5:5.For the Cr1.0 and Zn1.0 samples,the optimum binder proportion was 30% with a mass ratio of 3:7.?5?With the increase of curing time,the average electrical resistivity of stabilized soil increased.Increasing the soda residue content could increase the strength blended with a certain cement content.The average electrical resistivity of stabilized zinc contaminated soil decreased with Zn²⁺ concentration increased.The electrical resistivity exhibited a positive correlation to the UCS and a negative correlation to the leached heavy metal ions concentration.?6?Based on the results of SEM,the hydrated products such as CSH,CAH and Aft can be easily observed in the samples with curing time increased.The presence of Zn²⁺ impeded the hydrated reactions,and the hydrates were hardly found in the soils except for the plated-like Ca?OH?₂.The XRD results indicated that increasing curing time increased the quantity of produced hydrates,and the increased heavy metal content decreased it.