Section Six
NEW WASTE PROCESSES
59    USE OF TAILORED ZEOLITES FOR REMOVAL OF
BENZENE AND TOLUENE FROM WATER
Fang Gao, Environmental Engineer
JOAB Inc.,
Las Cruces, New Mexico 88004
Fernando Cadena, Associate Professor
Department of Civil Engineering
New Mexico State University
Las Cruces, New Mexico 88003
Robert W. Peters, Environmental Systems Engineer
Energy Systems Division
Argonne National Laboratory
Argonne, Illinois 60439
INTRODUCTION
Cases of groundwater contamination by leaking underground storage tanks (USTs) have been
increasing throughout the United States since early 1970s.1,2,3 The most common cases are the
contamination caused by leaking gasoline USTs. It is estimated that in the United States the total
number of leaking gasoline USTs could be about 100,000 at the present time, and this figure may
increase to about 350,000 by 1995.4 Groundwater contamination by benzene, toluene and xylenes
(BTXs) is coincident with the leaking USTs since gasoline contains approximately 3% benzene, 9 to
11% toluene, or 10 to 12% xylenes as antiknock additives.
BTXs are toxic to humans. These chemicals are leukemogenic, mutagenic, teratogenic, and carcinogenic.5,6,7,8,9 This problem is compounded by potential exposure to the groundwater contaminated by
BTXs. A large portion of the U.S. population (about 50%) uses groundwater as a source of drinking
water. About 75% of the U.S. cities obtain all of part of their water supplies from groundwater.10 In
the southwest, such as New Mexico, more than 95% of the local population is dependent upon
groundwater."
Several investigators are working on the removal of BTXs from the contaminated water through
adsorption using tailored clays as adsorbents.12,13,14'15,16 Tetramethylammonium (TMA + ) is used in
their studies to tailor the clay content of the natural soils, and to improve the adsorption capacity of
the soils toward BTXs. Their results from batch isotherm studies have shown significant improvement, especially in the studies of benzene adsorption.
Under aqueous condition, the sodium ions (Na + ) sitting between the clay platelets become
hydrated, causing interplatelet expansion.15 During the tailoring process, the tetrahedral TMA* ions
enter the clay's interlamellar space and replace the sodium ions. The replacement of the hydrated
sodium ions results in some shrinkage of the interlamellar space. However, such shrinkage is limited
due to the strong holding of the rigid tetrahedrons of TMA+ ions. The interlamellar space between
the platelets and between the TMA* tetrahedrons remains stable and ample enough for benzene
molecules to enter and become adsorbed.
Previous studies on TMA+ tailored clays and clay-containing soils have shown significant improvement of BTX adsorption over their natural state.15,16,17 For example, a batch adsorption isotherm test
for benzene versus LA soil (a natural soil with 36% clay content obtained from the Los Angeles area)
shows that the linear adsorption coefficient (K) of the TMA * tailored LA soil is about 40 times
greater than that of the natural (non-tailored) LA soil.17
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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