Experimental Study On Permeability Of Polymer-modified Bentonite

Municipal solid waste continues to increase in modern society.At present,sanitary landfill is still the main disposal method of waste at home and abroad.The core problem of landfill disposal is whether the anti-seepage cushion can safely block the landfill leachate and avoid polluting the surrounding water sources.C urrently,Geosynthetic clay liner（GC L）is widely used in the anti-seepage layer of landfills,and the sodium bentonite（Na-B）,which is the main component of GC L,will cause changes in internal structure and increase in hydraulic conductivity when it is subjected to strong erosive leachate,causing hidden safety hazards in la ndfills.Polymer-modified bentonite（PMB）can effectively improve the chemical compatibility of Na-B in contact with erosive leachate and improve the anti-seepage performance.However,the existing research on the permeability of Na-B and PMB is still not comprehensive and in-depth,in particular,the influence of the permeability on the polymer parameters,the types and concentration of erosive leachate needs further study.In view of the above problems,the paper took Na-B and PMB as the research objects,based o n laboratory tests,studied the permeabili-ty of Na-B and PMB in different types and concentrations of solution,proposed the index of reflecting bentonite hydraulic conductivity rapidly,and the corresponding microscopic mechanism was studied.The main research contents and achievements are following:（1）The permeability of Na-B and PMB in different types and concentrations of erosion fluids was studied systematically.For Na-Bs and PMBs with different polymer contents,the permeability tests were carried out based on the flexible wall permeameter,and the osmotic solution was Na C l solution,KC l solution,Ca C l₂ solution,Mg C l₂ solution,Na₂SO₄ solution with different concentrations and simulated landfill leachate;the test results show that the hydraulic conductivity of Na-B and PMB increases with the increase of the concentration of these osmotic solutions,but there is a saturated solution concentration,when the concentration of the solution is higher than the saturated concentration,the hydraulic conductivity of Na-B and PMB will not increase with the increase of the concentration of the osmotic solution;the order of the erosivity of ions in the osmotic solution is Ca²⁺>Mg²⁺>K⁺>Na⁺>Cl^->SO₄^2-;the hydraulic conductivity of PMB is lower than Na-B as a whole;and the optimum content of polymer in PMB is 5%.（2）Based on the comparative tests,the index that can reflect the permeability of bentonite rapidly was proposed.For Na-Bs and PMBs,the free swell tests and the liquid limit tests were carried out.The test results show that in Na Cl solution,KC l solution,Ca Cl₂ solution and Mg C l₂ solution,when the soil sample is Na-B,the free swell index and the liquid limit can be used as the index to reflect the permeability rapidly,when the soil sample is PMB,the liquid limit is more suitable than the free swell index to reflect the permeability rapidly;in different anions solution,the liquid limit is more suitable than the free swell index to reflect the permeability rapidly;in the solution of mixed various cations,the liquid limit is more suitable than the free swell index to reflect the permeability rapidly.（3）The microcosmic mechanism of Na-B and PMB hydraulic conductivity evolution was carried out.The Stud ies show that the cation valence and cation concentration of the osmotic solution affect the hydraulic conductivity of bentonite by inhibiting the osmotic swelling of the bentonite,while the principle of polymer reducing the hydraulic conductivity of bentonite is that polymer blocks the flow path between particles by forming a three-dimensional network hydrogel,making the permeation channels more narrow and tortuous,thereby reducing the hydraulic conductivity.