Study On Particle Release In Porous Media

Basing on the investigations of the natural geography,geology and hydrogeology conditions downstream the Dagu River,combining with the collecting,processing, chemical composition and physical properties analyzing of the samples(sand sample, water sample and clay mineral),the particle release in porous media are studied by laboratory batch and column experiments in this paper.The impacting factors on the particle release in porous media is analysed according to colloid and surface chemistry theories,such as critical fluid velocity,critical salt concentration,critical ratio of salinity decrease,critical ionic strength and pH value etc.are analyzed deeply. Particle release experiments show that:â‘ The fluid shear stress can lead to the particle releasing phenomenon when the fluid velocity of seawater,50%seawater add 50% freshwater and freshwater is over 90m/d,58 m/d and 55m/d respectively,but the released quantity is limited;â‘¡For the NaCl solution,its critical salt concentration which can cause particle release is 0.06±0.005mol/L.Critical salt concentration is the characteristic of univalent cation and the values are different due to various cations. The critical salt concentrations of Li⁺,K⁺,NH⁴⁺ are 0.05±0.005mol/L,0.05±0.005 mol/L and 0.01±0.005mol/L respectively,but Mg²⁺ and Ca²⁺ don't have critical salt concentration;â‘¢Under neutral condition,the critical ratio of salinity decrease of NaC1 solution is 0.012 mol/L.Only when the concentration difference between displacing solution and displaced one higher than this value can cause particle releasing;â‘£Ca²⁺ has a strong restraining effect on particle release process,for mixed solution of NaCl and CaCl₂,the critical ionic strengths which lead to particle release decline to 0.02mol/L and 0.007mol/L when Ca²⁺ molar percentages are 5%and 10% respectively,which is far below than the critical concentration of NaCI solution;⑤Tests also indicate that the pH has significant impact on particle release.The release time and particle quantity is far less at acidic condition than alkaline one.There are second time particle release phenomenons when using distilled water displace the sand column which was released at acidic condition,and the released quantities are more than that at first time.There are not second time particle release at alkaline and neutral condition.