title: Observed Dependence of Colloid Detachment on the Concentration of Initially Attached Colloids and Collector Surface Heterogeneity in Porous Media.
abstract: Sand column experiments were conducted to examine the effects of the concentration of attached colloids (CAC) on their subsequent detachment upon decreasing solution ionic strength (IS). Different pore volumes of latex microparticle suspensions were injected into the columns to allow different amounts of colloids to attach at ISs of 0.001, 0.01, and 0.2 M. Then, deionized water was introduced to release the attached colloids. Results show that the fraction of attachments that were reversible to reduction of IS (FRA) increased with increasing CAC at a given IS if the sand was extensively treated using acids to reduce surface charge heterogeneity. This indicates that colloids were preferentially immobilized in sites favoring irreversible attachment and then gradually occupied reversible sites. In contrast, the FRA decreased with increasing CAC at 0.001 M in sand without the acid treatment, illustrating the opposite attachment sequence. Scanning electron microscope examinations reveal that the concave regions favored irreversible colloid attachment. Reversible attachment is likely due to immobilization on flat surfaces with charge heterogeneities, retention in stagnation point regions via secondary minimum association, ripening in the acid-treated sand, and capture of colloids by protruding asperities with charge heterogeneity in the untreated sand. At ISs of 0.01 and 0.2 M, the FRA was essentially independent of CAC in the untreated sand because the colloids were randomly attached on the sand surfaces over time.
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University , Beijing 100193, China.
authors.forename: Tiantian
authors.initials: T
authors.lastname: Li
authors.affiliation: Department of Plant and Soil Sciences, University of Delaware , Newark, Delaware 19716, United States.
authors.forename: Yan
authors.initials: Y
authors.lastname: Jin
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University , Beijing 100193, China.
authors.forename: Yuanfang
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University , Beijing 100193, China.
authors.forename: Baoguo
authors.initials: B
authors.lastname: Li
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University , Beijing 100193, China.
authors.forename: Chongyang
authors.identifier: 0000-0002-2517-3472
authors.initials: C
authors.lastname: Shen
mesh_terms: D003102:Colloids; D009994:Osmolar Concentration; D016062:Porosity; D012822:Silicon Dioxide; D012996:Solutions
chemical_list: D003102:Colloids; D012996:Solutions; D012822:Silicon Dioxide