| The use of calcium-containing industrial solid waste to solidify and stabilize heavy metals was the main method for remediation of heavy metal-contaminated sites at home and abroad.The solidifying agent was mixed into the polluted soil to stabilize the properties of the polluted soil and the soil environment.In this paper,taking Cr（VI）contaminated soil as the research object of remediation,a directional regulation method of alkali-induced slag-based cementitious material solidifying agent was established,and a new solidifying agent for Cr（VI）contaminated soil was developed.The law of toxic leaching of Cr（Ⅵ）-contaminated solidified soil,Mechanics and Water Seepage and Cr（VI）solidifying mechanism were studied by toxic leaching test,soil column test,Mechanical test,penetration test and microscopic test（XRD,SEM,XPS,FTIR）.The main conclusions were as follows:（1）A new type of solidifying agent material was proposed.The toxicity leaching test showed that the concentration of 78 mg/kg Cr（Ⅵ）contaminated soil was 10-30%,and the test leaching was lower than the threshold value of 5 mg/L.380 mg/kg Cr（Ⅵ）contaminated soil concentration with curing agent content of 30%,the leaching was lower than the threshold value of 5 mg/L;when the solidifying agent content is 20%,the leaching of ZJ2～ZJ9 samples was lower than the threshold value of 5 mg/L.1000mg/kg Cr（Ⅵ）contaminated soil concentration when the dosage of solidifying agent was 30%,the leaching was lower than the threshold value of 5 mg/L.The optimal ratio of slag/desulfurized gypsum/Na OH for each component of the solidifying agent was determined to be 41:8:1.Through the soil column model test,the Cr（VI）concentration of the exudate from the lower layer of the model was maintained at0.025～2.057 mg/L within 60 days,and the concentration of Cr（VI）in the soil column pore liquid was 9～10 cm from the bottom layer for other layers.1.03～1.56times of the concentration,and the concentration of Cr（Ⅵ）at other depths remained basically average.（2）Through a series of indoor mechanical and infiltration tests,the water seepage and mechanical laws of Cr（Ⅵ）-contaminated solidified soil were studied.The results show that the more the solidifying agent was added,the greater the strength of Cr（Ⅵ）-contaminated soil and the smaller the permeability coefficient.The unconfined compressive strength of the contaminated cured body was up to 10.22 MPa,the lowest permeability coefficient was 1.35×10-9cm/s,and the internal friction angle and cohesion are up to 66°and 334 k Pa.The Cr（VI）concentration had a certain inhibitory effect on the hydration reaction of the solidifying agent.The lower the Cr（VI）pollutant concentration,the greater the unconfined compressive strength.（3）Taking the toxic leaching concentration,unconfined compressive strength and permeability coefficient as the research objectives of the dry-wetting cycle test,after one dry-wetting cycle,the unconfined compressive strength increased to 12.59MPa at the highest,and the Cr（Ⅵ）leaching concentration also decreased.After 2～4drying and wetting cycles,the unconfined compressive strength decreased to2.99～9.94 MPa,the leaching concentration increased to 0.334～5.824 mg/L,and the permeability coefficient increased to 4.79×10-8～1.3×10-6cm/s,when the dosage of curing agent was 10%,the permeability coefficient increases by up to 3 orders of magnitude after 4 drying and wetting cycles.（4）The curing mechanism was studied by microscopic tests（XRD,FTIR,XPS and SEM）.The results showed that the solidifying agent for Cr（VI）was mainly physical encapsulation,and the minerals formed by the hydration products were mainly quartz,feldspar,and calcium hydroxide.Zeolite,limestone,and tobermorite,etc.Secondly,part of Cr（VI）is reduced to Cr（III）,which reduces the toxicity of heavy metal soil and achieves the purpose of solidifying Cr（VI）.Under the effect of drying and wetting cycles,the solidified bodies of Cr（VI）polluted soils all formed new hydration products,such as muscovite,kaolinite and alumite.The solidification mechanism of Cr（VI）is still based on reduction and encapsulation. |
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