胶体颗粒对不同粒径饱和多孔介质渗透性的影响

探讨胶体颗粒在多孔介质中迁移所发生的物理、化学及生物作用过程,在许多学科中具有重要的科学意义。采用室内石英砂柱实验,开展了定水头条件下不同浓度和粒径的胶体颗粒在饱和多孔介质中的运移行为研究。共使用了3种胶体粒径、3种浓度的胶体溶液和3种粒径范围的石英砂。实验表明:多孔介质的相对渗透系数K/K0(K为各时刻计算所得的渗透系数,K0为初始渗透系数)减小程度与颗粒浓度成正比;胶体颗粒越大,越易在表层沉积,而小颗粒易向下部迁移,但总体来看粒径效应没有浓度效应明显;当胶体颗粒在不同粒径的饱和多孔介质中迁移时,粒径大的多孔介质各段K/K0均有明显降低,而粒径小的只在表层变化明显。不同条件下总体相对渗透系数与时间之间呈二次方相关关系,但当多孔介质粒径较小时,相关性不显著。介质渗流流速及砂柱不同位置胶体颗粒浓度变化与介质渗透性变化相对应。用扫描电镜(Scanning Electron Microscope,SEM)进行定性表征,进一步说明胶体颗粒会堵塞多孔介质孔隙影响其渗透性。实验中发现当输入浓度C0小于0.5 g·L–1且dp/Dp>0.018(dp为胶体颗粒粒径,Dp为石英砂算数平均粒径)时,会出现多孔介质局部K/K0增大的现象。

Effect of Colloidal Particle on Permeability of Saturated Porous Media Different in Particle Size

【Objective】It is of great scientific significance to study physical,chemical and biological processes of the migration of colloidal particles in saturated porous media.Therefore,it is essential to determine factors affecting the migration and deposition of colloidal particles in saturated porous media.【Method】An in-lab quartz sand column experiment was conducted to study migration behavior of colloidal particles in the sand column.The colloidal particles,were poured into saturated porous media with water solution of a set water head.The experiment was designed to have three levels of particle size of the colloidal particles,three levels of concentration of the colloidal solution and three levels of particle size of the quartz sand in the column.【Result】Results show that K/K0 of the media was reduced to an extent that was positively related to concentration and particle size of the colloidal particles in columns treated with colloidal particles the same in particle size.The smaller the size of the colloidal particles with the same concentration,the larger the K/K0 of the overall column and the AB segment(surface layer)at the end of the experiment,and the smaller the K/K0 of the lower EG segment(bottom layer),indicating that large particles were more likely to deposit in the surface layer,while small particles were to move to the bottom.As a whole,the particle size effect was not as noticeable as the effect of change in particle concentration.When the colloidal particles migrated through the porous media different in particle size,K/K0 of each segment of the porous media large in particle size was significantly lower,while it was only low in the surface layer of the column of sands small in particle size.Regression analysis of temporal variation of the overall relative permeability coefficient with other factors shows a quadratic relationship between the two with R2 being greater than 0.92 except in a few cases,which indicates good correlations.However,the correlation was not significant when the porous media were small in particle size.Analysis of velocity variation indicates that the higher the colloidal particles in concentration and particle size and the porous medium in particle size,the faster the decline of flow rate.Comparison between columns treated with colloidal particles different in concentration and in different particle,separately shows that large particles concentrated mostly in the upper part of the sand column,while small particles did in the lower part,which corresponded to the change of the medium in permeability.Qualitative characterization of the columns with a scanning electron microscope displays significant deposition of colloidal particles on the surface of the porous media after the experiment,which further demonstrates that colloidal particles could clog pores of the porous media,thus affecting their permeability.Secondly,the deposition of colloidal particles in the porous media increased K/K0 under certain conditions,which was related to concentration C0 of the input and diameter ratio dp/Dp(dp stands for colloidal particle size,and Dp for arithmetic average particle size of the quartz sand)of the particles.Phenomena of rising local permeability coefficient would appear when dp/Dp was higher than 0.018 and C0 was lower than 0.5 g·L–1.【Conclusion】Generally speaking,the colloidal particles migrating in porous media may clog the pores of the media physically,and hence reduce their permeability.Particle size and concentration of the colloidal particles tested and particle size of the porous media are main factors affecting migration and deposition of the colloidal particles in saturated porous media.