Exprimental Study On Leaching Characteristics Of Alkaline-cement Solidified/stabilized Heavy Metal Zinc-contaminated Soil

The pollution and acidification of soil are more and more serious due to the rapid development of industrialization and urbanization in our country.At present,one of the most frequently-used remediation methods in the treatment of contaminated soil is the Solidification/Stabilization.Acid rain infiltration not only promotes the release of toxic heavy metals in the soil,but also dissolves the cement.Therefore,it is necessary to study and explore the influence of acid rain on the leaching characteristics of the solidified/stabilized heavy metal contaminated soil.Based on the project of National Natural Science Foundation of China?2013GJMS0495?,using cement-alkaline as compound solidifying additive,through the soil column leaching test method,the unconfined compressive strength characteristics,leaching characteristics and microstructure changes of zinc-contaminated soil with cement-alkaline solidification before and after leaching of soil column are analyzed and discussed in this paper.The main conclusions obtained are as follows:?1?The unconfined compressive strength of zinc-contaminated soil with cement-alkali waste solidification decreased with the increase of zinc ion concentration and alkali waste content before and after leaching of soil column,and increased with the increase of curing time.The unconfined compressive strength of solidified zinc-contaminated soil was reduced after leaching soil column.The unconfined compressive strength of the sample was slightly lower than that of distilled water after leaching with acid solution.It was indicated that alkali waste has a certain buffering effect on acid rain.In addition to the curing age of 0 days and the initial zinc ion concentration of 1%samples,the unconfined compressive strength of cement-alkali waste solidified zinc contaminated soil had reached 0.35MPa of the United States of contaminated soil repair strength standard before and after leaching.?2?The permeability coefficient of zinc-contaminated soil with cement-alkali waste solidification increased with the increase of zinc ion concentration and alkali waste content,and decreased with the increase of curing time.The permeability coefficient of solidified zinc contaminated soil was larger than that of distilled water after leaching with acid solution.However,the pH value of the leachate of zinc-contaminated soil with cement-alkali waste solidification decreased with the increase of zinc ion concentration,and increased with the increase of alkali waste content and curing time.So,the concentration of Ca²⁺in the leachate of zinc-contaminated soil with cement-alkali waste solidification increased with the increase of initial zinc ion concentration and alkali waste content,but decreased with the increase of curing time.The concentration of Zn²⁺in the filtrate of zinc-contaminated soil with cement-alkali waste solidification decreased with the increase of the amount of alkali waste and curing time.With the increase of leaching time,the pH value of the leachate of zinc-contaminated soil with cement-alkali waste solidification decreased.The pH value of the leachate leached by the acid solution was lower than that of the filtrate leached by the distilled water.So,The concentration of Ca²⁺in leachate of solidified zinc-contaminated soil leached by acid solution was higher than that of the filtrate leached by the distilled water.With the dissolution of Ca²⁺,the concentration of Zn²⁺increased.The Zn²⁺leaching concentrations of all the samples tested in this paper were far less thanthe provisions of China's environmental standard value of 100mg/kg.?3?Based on SEM and XRD tests of cement-alkaline solidified/stabilized zinc-contaminated soil,it is concluded that complex physical and chemical reactions Inside of the sample,resulting in a large number of C-S-H,C-A-H,scolecite and complex.?4?Through a series of macroscopic and microscopic tests,it is found that the cement-alkaline as a compound curing agent has a good curing effect on heavy metal zinc.The curing mechanism of alkaline to zinc ions and the buffering mechanism of alkaline to acid rain is mainly due to the adsorption of Zn²⁺and H⁺by anions enriched on the surface of alkaline and scolecite formed by cement-alkaline-soil.