Study On Mechanisms And Applications Of Water Sensitivity In Porous Media

On the basis of prior studies,this paper first researched the factors that impacted the water sensitivity of porous media,such as hydrochemistry factors (salt salinity and its rate of decrease,pH value and cationic form)and hydrodynamic force(flow rate)with the laboratory experiments that the saltwater and freshwater replacing each other in the level sand-column, secondly,the article also researched the characteristic of different clays' (kaolin,illite,smectite)water sensitivity and their contents effecting on water sensitivity,which could offer theoretical basis to build the impenetrable purdah or underground seepage wall.Finally,according to the features of particle release and migration on the process of water sensitivity,creative experiments were done to study these phenomena on removing pollutions of the heavy metals and organic pollutants.The result of salt salinity effect experiment showed that particles didn't release until the salt salinity of flow fluid decrease by some gradient to a critical value and then cause the permeability to change,that was,induce the water sensitivity happening.The critical salinity determined by this experiment was about 0.06mol/L.In the experiment of pH effects,one could discover that the quantity of released particles was the least in acidic condition(pH= 2.04)and most in alkali condition(pH=6.88)That was,the tendency of particle release in high pH value was far more than that in low pH value.The result of hydrodynamic experiment indicated that the greater the fluid flow rate, the greater the shear stress between hydrodynamic force and particles,the easer the migration of particles from porous media.The critical flow rate confirmed by this experiment was 21 ml/min.In order to study the water sensitivity of different cations,this experiment took LiCl,KCl,NH₄Cl,MgCl₂,CaCl₂ as examples to determine the critical salinity of salt solution containing following cations:Li⁺,K⁺,NH₄⁺,Mg²⁺, Ca²⁺.The results indicated that the critical salinity of LiCI,KCl,NH₄Cl were 0.05±0.005mol/L,0.05±0.005mol/L and 0.01±0.005mol/L respectively,but MgCl2 had no critical salt concentration as the quantity of particle release was too small and there was no particle release law.Not only couldn't CaCl₂ induce particle release,but it also inhibit the phenomena obviously.Clay minerals in porous media are the main substances whose contents and kinds directly influenced the degree of water sensitivity.In process of water sensitivity,the permeability of sand columns,contenting various calys,such as kaolin,illite,smectite,were all reduced as the content increased,but the decreasing rate and degree were greatly different.Among them,the permeability decreased by only one grade when the contents of kaolin increased from 1%to 7%(weight ratio).And there were not slight reduction of hydraulic conductivity when the flowing fluid was changed to fresh water in both illite-sand system and kaolin-sand system.However,the permeability of smectite-sand could be reduced sharply when the flowing fluids were changed from seawater to fresh water and the changing range was increase with the increase of smectite's contents.When the smectite's content reached 3%-4%,no water could flow through sand column.Taking Hg²⁺ion and phenol(C₆H₅OH)as examples,the effect of hydrodynamic condition and water sensitivity on particle release was researched to study the influence of water sensitivity on the migration of heavy metals underground and organic pollutant.The result indicated that the removing rate of Hg²⁺ion and phenol(C₆H₅OH)were 31.68%and 55.71%respectively when only the saltwater filters through the sand columns polluted by them and there were still stayed lots of pollutants.But in the same hydrodynamic conditions, the values were 67.55%and 43.43%after water sensitivity happened.Under the coactions of hydrodynamic function and water sensitivity,the total removing rates were 99.23%and 99.14%,that was,most of pollutants in sand columns could be removed effectively in this method.