{"title":"Size fractionation of montmorillonite colloids through saturated porous media and their heterogeneous contribution to the transport of Pb2+","authors":"Lulu Lu , Xiaochen Peng , Zhiwei Chen , Kunyu Wen , Usman Farooq , Taotao Lu , Zhichong Qi , Weifeng Chen","doi":"10.1016/j.clay.2025.107808","DOIUrl":null,"url":null,"abstract":"<div><div>The size fractionation of colloids is an important process while they migrate through porous media. To date, the information about the contribution of the size fractionation of clay colloids on heavy metal mobility during their co-transport process is limited. Herein, taking montmorillonite as a typical clay mineral, the size fractionation characteristics (> 2.0 μm, 1.2–2.0 μm, 0.45–1.2 μm, 0.1–0.45 μm, and < 0.1 μm) of colloidal montmorillonite particles after passing through saturated sand and their different contribution to Pb<sup>2+</sup> transport were investigated. The results indicated that the extent of Pb<sup>2+</sup>-mobilizing ability of colloids at pH 7.0 was higher than that at pH 5.0, ascribed to more Pb<sup>2+</sup> adsorbed to the colloids and greater mobility of colloids at higher pH values. Generally, the contribution of colloid size fractions on Pb<sup>2+</sup> mobility followed the order of (> 2.0 μm) > (< 0.1 μm) > 0.45–1.2 μm > 0.1–0.45 μm ≈ 1.2–2.0 μm, which depended on the colloid size distribution in the effluents (i.e., the larger proportion of fractions exhibited greater contribution to the enhancement of Pb<sup>2+</sup> mobility in this work). However, the relative contaminant-mobilizing abilities of different colloid size fractions (obtained by normalizing the fraction-facilitated Pb<sup>2+</sup> breakthrough with the respective fraction breakthrough) increased with the decrease in colloid size, which stemmed from the relatively higher mobility and greater metal-binding capacities of smaller size fractions. Additionally, the differences in the relative contaminant-mobilizing abilities of different fractions decreased with decreasing sand grain sizes (20–40 mesh (0.425–0.85 mm), 40–60 mesh (0.25–0.425 mm), and 60–80 mesh (0.178–0.25 mm)), which was related to the different mobility of the colloid size fractions. In summary, these findings indicate that size fractionation of natural colloids plays a critical role in heavy metal mobility and retention in groundwater systems.</div></div>","PeriodicalId":245,"journal":{"name":"Applied Clay Science","volume":"271 ","pages":"Article 107808"},"PeriodicalIF":5.3000,"publicationDate":"2025-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Applied Clay Science","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0169131725001139","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
The size fractionation of colloids is an important process while they migrate through porous media. To date, the information about the contribution of the size fractionation of clay colloids on heavy metal mobility during their co-transport process is limited. Herein, taking montmorillonite as a typical clay mineral, the size fractionation characteristics (> 2.0 μm, 1.2–2.0 μm, 0.45–1.2 μm, 0.1–0.45 μm, and < 0.1 μm) of colloidal montmorillonite particles after passing through saturated sand and their different contribution to Pb2+ transport were investigated. The results indicated that the extent of Pb2+-mobilizing ability of colloids at pH 7.0 was higher than that at pH 5.0, ascribed to more Pb2+ adsorbed to the colloids and greater mobility of colloids at higher pH values. Generally, the contribution of colloid size fractions on Pb2+ mobility followed the order of (> 2.0 μm) > (< 0.1 μm) > 0.45–1.2 μm > 0.1–0.45 μm ≈ 1.2–2.0 μm, which depended on the colloid size distribution in the effluents (i.e., the larger proportion of fractions exhibited greater contribution to the enhancement of Pb2+ mobility in this work). However, the relative contaminant-mobilizing abilities of different colloid size fractions (obtained by normalizing the fraction-facilitated Pb2+ breakthrough with the respective fraction breakthrough) increased with the decrease in colloid size, which stemmed from the relatively higher mobility and greater metal-binding capacities of smaller size fractions. Additionally, the differences in the relative contaminant-mobilizing abilities of different fractions decreased with decreasing sand grain sizes (20–40 mesh (0.425–0.85 mm), 40–60 mesh (0.25–0.425 mm), and 60–80 mesh (0.178–0.25 mm)), which was related to the different mobility of the colloid size fractions. In summary, these findings indicate that size fractionation of natural colloids plays a critical role in heavy metal mobility and retention in groundwater systems.
期刊介绍:
Applied Clay Science aims to be an international journal attracting high quality scientific papers on clays and clay minerals, including research papers, reviews, and technical notes. The journal covers typical subjects of Fundamental and Applied Clay Science such as:
• Synthesis and purification
• Structural, crystallographic and mineralogical properties of clays and clay minerals
• Thermal properties of clays and clay minerals
• Physico-chemical properties including i) surface and interface properties; ii) thermodynamic properties; iii) mechanical properties
• Interaction with water, with polar and apolar molecules
• Colloidal properties and rheology
• Adsorption, Intercalation, Ionic exchange
• Genesis and deposits of clay minerals
• Geology and geochemistry of clays
• Modification of clays and clay minerals properties by thermal and physical treatments
• Modification by chemical treatments with organic and inorganic molecules(organoclays, pillared clays)
• Modification by biological microorganisms. etc...