Kaolinite and Lead in Saturated Porous Media: Facilitated
and Impeded Transport
Huiming Sun
1
; Bin Gao
2
; Yuan Tian
3
; Xianqiang Yin
4
; Congrong Yu
5
; Yiquan Wang
6
; and Lena Q. Ma
7
Abstract: Laboratory experiments and mathematical modeling were used to explore the dynamics of kaolinite and Pb in water-saturated
porous media. Batch adsorption experiments were used to obtain the adsorption isotherms of Pb onto kaolinite and quartz sand. Both
kaolinite and sand adsorbed Pb from water, but the adsorption capacity of kaolinite was about 30 times higher than that of sand. Saturated
sand columns were used to examine the transport behaviors of Pb and kaolinite. The presence of kaolinite in the saturated porous media
enhanced the mobility of Pb. The presence of Pb on kaolinite and grain surfaces, however, reduced the transport of kaolinite. Additionally,
an experiment in which clean kaolinite was passed through sand contaminated with Pb indicated that mobile kaolinite could scavenge the
absorbed Pb from the sand surface to facilitate Pb transport. Simulations from the Langmuir model and an advective-dispersive transport
model matched well with the experimental data collected from the batch adsorption and column breakthrough studies.
DOI: 10.1061/ASCEEE.1943-7870.0000250
CE Database subject headings: Porous media; Mathematical models; Water treatment; Water pollution; Experimentation.
Author keywords: Colloid; Colloid-facilitated transport; Kaolinite; Pb; Porous media; Modeling.
Introduction
Ubiquitous in soil and aquatic systems, natural colloids defined
as particles with a diameter smaller than 10 m have attracted
much attention recently because of their potential environmental
and health risks. Although it is known that mobile colloids can
enhance the mobility of contaminants, there are not many experi-
mental studies focusing on colloid-facilitated contaminant trans-
port in water-saturated porous media Sen and Khilar 2006. After
entering water-saturated media, most of the chemical contami-
nants and natural colloids interact with each other and with the
surrounding media. These interactions may alter the dynamic be-
havior of colloids, contaminants, and their complexes, and in-
crease the difficulty to understand the fate and transport of
contaminants in the media.
Lead Pb is a toxic heavy metal commonly found in the en-
vironment. Recent studies suggest that natural colloids such as
clay minerals can enhance the mobility of Pb in soils under cer-
tain conditions Gao et al. 2010. However, there is limited re-
search exploring the transport behavior of Pb in porous media,
especially in regard to how colloids can alter the transport behav-
ior of Pb in water-saturated porous media. It is therefore crucial to
examine the enhanced transport of Pb in water-saturated porous
media.
This study was designed to improve the current understanding
of colloid-facilitated contaminant transport in saturated porous
media. A clay colloid kaolinite and a heavy-metal contaminant
Pb were used in laboratory experiments to examine their trans-
port and cotransport behaviors in water-saturated sand columns.
Our objectives were 1 to compare the filtration and transport of
kaolinite and Pb in water-saturated porous media; 2 to examine
the effects of Pb on the transport of kaolinite in saturated porous
media; 3 to examine the effects of kaolinite on the mobility of
Pb in saturated porous media; and 4 to test whether existing
models can be used to simulate the transport behavior of colloids
and Pb in water-saturated porous media.
Materials and Methods
Materials
Kaolinite powders EM Science, Gibbstown, N.J. were used to
make colloids according to the procedures reported by Gao et al.
2004. The mean sizes of the kaolinite colloids, as determined by
photon correlation spectroscopy, did not vary significantly during
the experiments and equaled 0.80 m. Kaolinite-Pb complex
suspension was made by mixing 50 mL of the colloidal kaolinite
suspension with 50-mL, 50-ppm Pb
2+
PbNO
3
, Fisher Scientific,
Pittsburgh. After 24-h shaking, the mixture was centrifuged to
1
Graduate Student, College of Resources and Environment, Northwest
A&F Univ.,Yangling, Shanxi 712100, China; and, Visiting Student, Dept.
of Agricultural and Biological Engineering, Univ. of Florida, Gainesville,
FL 32611.
2
Assistant Professor, Dept. of Agricultural and Biological Engineer-
ing, Univ. of Florida, Gainesville, FL 32611 corresponding author.
E-mail: bg55@ufl.edu
3
Graduate Student, Dept. of Agricultural and Biological Engineering,
Univ. of Florida, Gainesville, FL 32611.
4
Graduate Student, College of Resources and Environment, Northwest
A&F Univ.,Yangling, Shanxi 712100, China; and, Visiting Student, Dept.
of Soil and Water Science, Univ. of Florida, Gainesville, FL 32611.
5
Graduate Student, Dept. of Agricultural and Biological Engineering,
Univ. of Florida, Gainesville, FL 32611.
6
Professor, College of Resources and Environment, Northwest A&F
Univ., Yangling, Shanxi 712100, China.
7
Professor, Dept. of Soil and Water Science, Univ. of Florida, Gaines-
ville, FL 32611.
Note. This manuscript was submitted on August 30, 2009; approved
on April 2, 2010; published online on April 7, 2010. Discussion period
open until April 1, 2011; separate discussions must be submitted for
individual papers. This technical note is part of the Journal of Environ-
mental Engineering, Vol. 136, No. 11, November 1, 2010. ©ASCE,
ISSN 0733-9372/2010/11-1305–1308/$25.00.
JOURNAL OF ENVIRONMENTAL ENGINEERING © ASCE / NOVEMBER 2010 / 1305
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