Modification And Pollution Control Performance Of Soil-Cement-Bentonite Vertical Isolation Barrier

With the development of the industrial economy,in the process of mining,dressing and smelting of metal mineral resources,a large number of industrially polluted sites are generated.It not only pollutes the ecological environment and affects the health of residents,but also seriously hinders the sustainable development of my country’s land resources.Vertical isolation barriers can effectively control the migration of pollutants.It plays an important role in the restoration of industrial polluted sites and the reuse of land.Our country’s vertical isolation technology and related research started relatively late.There are mainly the following problems:There is a lack of a simple basic material that can take into account both impermeability and strength properties;the research on the chemical compatibility of the isolation barrier and pollutants has not received enough attention;there is insufficient research on the blocking timeliness of isolation barriers in polluted environments.The paper is based on the national key research and development project（NO.2019YFC1803601）.The research methods are mainly theoretical analysis,laboratory experiments and numerical simulations.The basic ratio of soil-cement-bentonite vertical isolation barrier materials,the modification effect of silica fume and its blocking performance on pollutants were studied.The main research results are as follows:（1）Through nine groups of different soil-cement-bentonite material ratios,the fluidity and mechanical laboratory tests were carried out.The effects of cement content,bentonite content and curing time on material strength and anti-seepage performance were analyzed.The contribution of bentonite to the uniaxial compressive strength of the material is not obvious,and the effect on the permeability coefficient of the material is obvious.The permeability of the material is inversely proportional to the bentonite content.Cement has a significant effect on the uniaxial compressive strength and permeability coefficient of the material.Its content is proportional to the uniaxial compressive strength and inversely proportional to the permeability coefficient.（2）Choose from 5 silica fume replacement ratios to replace the cement in the material.The effect of silica fume content on the strength and impermeability of the material was investigated.The action mechanism of silica fume on the pores of the filling material and participating in the hydration reaction was analyzed.The improvement of material properties by silica fume is mainly concentrated in the later stage of curing.There is little change to the early strength and impermeability of the material.In the later stage,with the increase of silica fume content,various properties of the material have been significantly improved.（3）Using Zn SO₄ as the pollution source liquid,carry out the pollution liquid immersion test of the modified isolation material.The chemical compatibility of modified isolation materials under the long-term action of pollutants was explored.Within a certain range,adding silica fume can effectively improve the anti-seepage performance of the material under the action of polluted liquid.However,the excessive content of silica fume will aggravate the damage of the material and cause the surface of the sample to fall off.（4）A three-dimensional model of a mining and metallurgical pollution site was established.Through COMSOL simulation software,the migration law of pollutants in the site under the action of isolation barriers with different thicknesses and permeability characteristics is obtained.The blocking timeliness of different isolation barriers to pollutants was calculated.It is considered that the isolation barrier with a thickness of 0.5m and a permeability coefficient of 1.5×10^-8cm/s can meet the engineering requirements.