Environmental Chemistry of Soils

411 Pages·1994·15.51 MB·English

by  Murray B. McBride

ENVIRONMENTAL CHEMISTRY OF SOILS
ENVIRONMENTAL
CHEMJSTRY OF SOILS
Murray B. McBride
:'\l"ew York Oxford
OXFORD UNIVERSITY PRESS
1994
:.9
Oxford University Press
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Copyright © 1994 by Oxford University Press, Inc.
Published by Oxford University Press, Inc.
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All rights reserved. No part of this publication may be reproducted,
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Library of Congress Cataloging-in-Publication Data
McBride, Murray.
Environmental chemistry of soils / Murray McBride.
p. em. Includes index.
ISBN 0-19-507011-9
1. Soil chemistry. I. Title.
S592.5.M39 1994 631.4'I-dc20 93-1552
987654
Printed in the United States of America
on acid-free paper
TO JAN AND DEVIN
3.,.,d to the many generations of farmers in my family,
'"
,·.hose inherited knowledge of the soil
s not to be found in a book.
Preface
....
-\n ordinary housefly, if placed within a hollow clear glass globe having a single hole for
~n outlet, generally escapes rather promptly. But a bee, under like circumstances, seldom
:-<.Capes. This ... does not indicate superior wisdom on the part of the fly-quite the
:0ntrary. For the fly, dashing hither and thither in planless flight, chances upon the exit,
.\ hereas the bee, flying steadfastly towards the light, continues to try to force its way
:hrough what must seem to it to be queerly resistant atmosphere.
From the preface to Colloid Chemistry, Vol. III, J. Alexander, 1931
Science has numerous examples of a deficient or even incorrect theory explaining the
Jbservations at hand, only later to be found unsound. Although it has been said that
:here is nothing so practical as a good theory, faulty theories can be quite damaging
:0 the progress of science. How do we know which models or theories to accept or
reject? For nonscientists, there is an expectation that science can provide precise and
:ertain answers to problems of society and questions about the physical world. Those
·.\ho teach and do research in science know that the answers are usually far less than
:ertain. In fact, some scientists believe that certainty about any scientific theory is
:lever completely achievable. After all, a theory is only a plausible hypothesis that
~ains scientific acceptance, but further investigation may well replace it with a better
Theory.
Much of soil science is empirical rather than theoretical in practice. This fact is
3. result of the extreme complexity and heterogeneity of soils, which are impossible
to fully describe or quantify by simple chemical or physical models. It is not unusual
for working solutions to be found for soil chemical problems with little, or even fal
lacious, understanding at a fundamental level. The simplicity of the empirical
approach becomes the seed of its undoing, because the primary advantage of the
scientific method, predictive capability, is curtailed or lost. On the other hand, the
universality of chemical principles and laws (i.e., theories) permit processes to be
described in such a way that soil chemical behavior can be understood and predicted
in many situations not yet studied.
This book is an attempt to describe soil chemistry within the bounds of estab
lished chemical principles. It avoids as much as possible the more empirical descrip
tions and models, instead stressing concepts that build from our present knowledge
of inorganic, organic, and physical chemistry as well as surface science. It is hoped
that a consistent, and not too complex, conceptual framework has been constructed
that will help to explain the many seemingly disparate facts and observations that
constitute the chemical behavior of soils. The emphasis is on environmental as
opposed to agricultural topics, compared with most texts in soil chemistry, recogniz-
viii PREfACE
ing that a major challenge of the future is to protect the soil ecosystem from the
pollutants of an industrial society.
Regarding the structure of the book, the reader will find numerous sections that
are denoted with a smaller type size. These sections elaborate upon certain concepts,
but are not considered essential to a broad understanding of the topic. As this book
was written with the intention that it be used as a textbook of soil and environmental
chemistry, it is suggested that the level of the course being taught would determine
whether such sections ar&tappropriate for study. The reader will also notice that
rather few references are made to the technical literature. This again reflects the main
purpose of the book, to serve as a text rather than a scientific reference. Although
many hundreds of scientific papers were consulted in writing this book, it was
decided to reference only those from which specific information was used in the text.
Reader are encouraged to review the list of suggested additional reading, from which
a large body of important references can be obtained.
Some of the new concepts found in this book are original (if any idea can be truly
so), but most have been distilled from advanced texts and research papers, or origi
nate from interactions with peers and outstanding graduate students with whom I
have worked over the years. I will not try to acknowledge the many individuals who
had a strong influence on my thinking. However, I am particularly indebted to Dr.
Max Mortland, who instilled in me an interest in understanding clay surface pro
cesses at the molecular level.
June 1993 M. B. McB.
Ithaca, N.Y.
Contents
1. Review of Chemical Principles 3
2. Soil Solids: Composition and Structure 31
3. Ion Exchange 63
4. Chemisorption and Precipitation ofInorganic Ions 121
5. Soil Acidity 169
6. Mineral Weathering and Formation 207
7. Oxidation-Reduction Reactions 240
8. Salt-Affected and Swelling Soils 273
9. Trace and Toxic Elements in Soils 308
10. Organic Pollutants in Soils 342
Useful Constants and Unit Conversions in Chemistry 395
Index 397
/
ENVIRONMENTAL CHEMISTRY OF SOILS
.~
/
1
Review of
Chemical Principles
1.1. INTRODUCTION
This chapter reviews those chemical principles that will be particularly useful for a
fundamental understanding of soil chemistry. The reader may not wish to read this
chapter before going on to the main text dealing with soil chemistry, but may prefer
to refer back to specific sections within this chapter when unfamiliar or difficult
chemical concepts are encountered in the text.
1.2. THE NECESSARY CONCEPTS
1.2a. Gram Molecular Weight (Mole)
Most equations of theoretical chemistry are expressed in terms of the number of
atoms or molecules in a system rather than their weight. The same number of atoms,
6.023 X 1023 (Avogadro's number), is contained within one gram atomic weight of
each element. Similarly, this number of molecules is contained in 1 gram molecular
weight of each compound. Because gram atomic weight and gram molecular weight
are cumbersome terms, they are replaced by the abbreviated term mole, which stands
for the amount of an element or compound containing Avogadro's number of atoms
or molecules. For example, there are Avogadro's number of carbon atoms in 12
grams of pure carbon (graphite or diamond), and there are Avogadro's number of
water molecules in 18 grams of pure water. That is, the gram mol°ec ular weight of
H 0, determined from the atomic weights of its constituent Hand atoms, is (2 X
2
1) + (1 X 16) = 18.
In soil chemistry, mole is also used to denote Avogadro's number of fundamental
charge units on surfaces or ions, symbolized by mole( +) or mole( - ) depending on
the sign of the charge. For example, 1 mole ofCaH ions carries 2 moles( +) of charge.
1.2b. Types of Chemical Bonding /'
The important kinds of bonds formed between atoms are summarized below.
3