Water Purification by Ion Exchange

196 Pages·1995·5.5 MB·English

by  T. V. Arden D.Sc.

WATER PURIFICATION BY ION EXCHANGE
Fronlispiece. Polystyrene sulphonic acid calion exchange bead (Magnijicalion 10 x, reduced
5/9ths on reproduction)
WATER PURIFICATION
BY ION EXCHANGE
T. V. ARDEN, D.Se., Ph.D., F.R.I.C., C.Eng.,
M.I.M.M., P.A.I.W.E.
Chcmical Director, The Permutit Company Ltd.
NEW YORK
PLENUM PRESS
LONDON
BUTTERWORTHS
Published in the U.S.A. by
PLENUM PRESS
a division of
PLENUM PUBLISHING CORPORATION
227 West 17th Street, New York, N.Y. 10011
First published by
Butterworth and Co. (Publishers) Ltd.
ISBN 978-1-4684-9038-1 ISBN 978-1-4684-9036-7 (eBook)
DOT 10.1007/978-1-4684-9036-7
©
Butterworth and Co. (Publishers) Ltd.
1968
Softcover reprint of the hardcover 1s t edition 1968
Suggested U.D.C. No. 541.183.12:628.16
Suggested additional No. 661.183.12
Libra~y qfCongress Catalogue Card Number 68-54310
CONTENTS
PREFACE VII
1. INDUSTRIAL W ATERS
Hard Water . Soft Water . Units . Typical Waters and Their
Uses' Laundering, Wool Scouring, Bottle Washing, etc .. Chemi
cal Pracessing, Metal finishing, etc .. Boiler Feed Water.
2. THE ION EXCHANGE PROCESS 13
Intraduction . The Development of Ion Exchange Resins.
3. EQlJILIBRIA AND KINETICS, AS APPLIED TO
WATER TREATMENT 26
General Cation Exchange' Hydragen Ion Exchange, Sulphonic
Resin· Hydrogen Ion Exchange, Carboxylic Resins . General
Anion Exchange' Hydroxide Ion Exchange, Strang Base Resins
. Acid Absorption, \Veak Base Resins . Kinetics.
4. UNIT WATER TREATMENT PROCESSES 49
Water Softening by Sodium Exchange· Alkalinity Removal with
Carboxylic Resins . Sulphonic Resins . Hydrogen Ion Exchange
. Acid Absorption by Weak Base Resins . Acid Absorption by
Strang Base Resins . Mixed Beds
5. COMBINATION PROCESSES 80
1. Weak Acid Cation. Sodium Exchange Cation. Degas
(WAC-Na-DG)
2. Strong Acid Cation. Weak Base Anion. Degas (SAC-WBA-DG)
3. Strong Acid Cation. Degas. Strong Base Anion (SAC-DG-SBA)
4. Strong Acid Cation. Weak Base Anion. Degas. Mixed Bed
(SAC-WBA-DG-MB)
5. Strang Acid Cation. Degas. Strang Base Anion Mixed Bed
(SAC-DG-SBA-MB)
6. Weak Acid Cation. Degas. Mixed Bed (WAC-DG-MB)
7. Weak Acid Cation. Strang Acid Cation. Degas. Anion. Mixed
Bed (WAC-SAC-Degas-(WBA)-MB)
(SBA2)
(SBAI)
8. Strang Acid Cation. Weak Base Anion. Mixed bed. Mixed Bed
(SAC-WBA-MB-MB)
9. Strong Acid Cation. Degas. Weak Base Anion. Strang Base
Anion (SAC-DG-WBA-SBA)
v
CONTENTS
6. ORGANIC POISONING OF ANION EXCHANGE
RES INS 90
The Problem' Organic Matter in Water . Poisoning of Resins
. Cleaning Poisoned Resins . The Effect of Resin Structure . Non
poisoning Resins . The Protection of Mixed Beds . Prevention of
Poisoning, Summary
7. EQUIPMENT AND SPECIAL PROCESSES 113
Standard Resin Columns . Counterftow Units . Continuous Ion
Exchange . Advantages of Continuous Ion Exchange . Special
Problems of Continuous Ion Exchange . Types of Continuous
Plant . Condensate Polishing for High Pressure Boilers . Brackish
Water Desalination by Ion Exchange· Electrodialysis
8. INDUSTRIAL APPLICATIONS 150
The Treatment of Water-Soluble Organic Compounds . Recovery
of Water and By-products from Industrial Wastes . Chromium
Plating, Recovery of Water . Anodizing, Recovery of Water and
Chromic Acid· Gold Plating, Recovery of Gold· Photographic
Solutions, Recovery of Silver . Reactivition of Metal Finishing
Solutions . Recovery of Metals by Complex Anion Formation .
Elution Chromatography . Ion Exchange as a Manufacturing
Process . Liquid Liquid Ion Exchange
INDEX 181
VI
PREFACE
This book is an attempt to fill a gap in the existing literature on
ion exchange. The many excellent works already available are of
three main types, general introductions to the subject, specialist
discussions of analytical and laboratory techniques, and advanced
theoretical treatises. In practice, in spite of the vast number of
processes which have been developed for la bora tory use, 99 per
cent of all ion exchange resins produced in the world are used in
water treatment, or closely allied applications. This book is intended
as a general survey of the principles governing the practical uses of
ion exchange resins, for the benefit of students encountering the
subject for the first time, and for the chemists and engineers in
many branches of industry whose work brings them into contact
with water treatment, but who do not have the time to study more
advanced volumes of basic theory. The background presented has
been simplified to the maximum extent found possible without
falsification, and an attempt has been made to relate each aspect
of theory to its practical consequences in full scale water treatment.
Mathematical methods have been avoided and pictorial or graphical
presentation methods used wherever possible. As the book is
concerned with general principles, rather than details of any
particular research work, references to original papers and patents
have been omitted except in the cases of special processes, which
have a single clearly defined origin. The bibliography, included at
the end, consists of books and review papers covering the various
sections of this book, and giving the detailed original references
which may be useful at a later stage of study.
The practice, adopted in several earlier works, of including
tables of equivalent resins produced by different manufacturers,
has not been followed. The total number of resins now available
is so large that a comprehensive table would be a massive item.
Moreover, as knowledge in the field has increased in recent years,
differences between individual resins previously classified as
equivalent to each other have become increasingly important.
Whenever a type of resin is described, a few examples are given
of individual resins commonly used in Great Britain, but the lists
are not intended to be comprehensive. Moreover, even in these
cases, it must be emphasized that the classification is purely the
result of my own studies of the res ins concerned. The manufacturers
VlJ
PREFACE
of ion exchange resins rarely publish their exact structures, or
manufacturing methods, and the attribution of structures to named
resins should be considered, not as statements of fact, but as per
sonal deductions from the analysis and general properties of the
materials mentioned.
The tables and graphs of operating results are quoted, with
thanks, from the records of The Permutit Company Limited. They
apply in principle to all other resins in the same general categories,
but should not be taken to apply quantitatively to any one. Readers
requiring the detailed operating characteristics of individual ion
exchange resins can obtain the figures from the information sheets
issued by all the major manufacturers; and it is hoped that a
knowledge of the general principles set out here will facilitate
understanding and comparison of the manufacturers' literature.
Certain conventions of the water treatment industry have been
followed. The hydrogen ion is written as H+, hydration being
ignored. The terms 'silica', or 'SiOz' are used, in the absence of
any more accurate general words, to refer to the various silicon
containing anions present in water. The word 'absorb' and its
derivatives are given their most generally understood meaning,
that of uptake by permeation. No particular thermodynamic
mechanism is implied.
Grateful thanks are due to Dr. T. R. E. Kressman, Mr. J. Pilot
and Mr. B. A. Sard, whose comments on the original typescript
induced a proper sense of humility, and helped to eliminate the
more glaring errors.
V11l
CHAPTER 1
INDUSTRIAL WATERS
The water used by industry for boiler feed or process purposes may
be taken from public supplies, or abstracted directly from wells,
lakes or rivers. In Great Britain, town mains water will have been
treated to render it largely clear and colourless, free from odour,
and bacteriologically sterile. I t is thus directly suitable for many
industrial purposes such as cooling, and in cases where ion exchange
treatment is used, town mains water can normally be fed directly
into the columns. Many large industrial users abstract water from
natural sources for their own use. Where these are deep wells, the
water is normally clear, colourless, and directly treatable by ion
exchange; but in cases where water is taken directly from rivers or
lakes, clarification by the classical methods of coagulation and
filtration is normally necessary. These techniques are fully described
elsewhere, and for the purposes of this book, the starting point of all
industrial ion exchange processes is a supply of clear water, free
from suspended and colloidal matter.
HARD WATER
The range of minerals contained in most natural waters is quite
limited. The cations present are normally calcium, magnesium
and sodium, while the anions are mainly chloride, sulphate and
bicarbonate, with lower concentrations of nitrate, phosphate and
silica. There are also traces of organic matter. For the majority
of natural waters, analysis of the ions mentioned above will give
the total dissolved so lids in the water. Waters occurring in regions
of unusual rock formation may differ considerably from this pattern,
but the principles which are to be discussed apply equally to waters
of unusual composition.
I t is customary to refer to waters as 'hard' or 'soft'. The former
are waters containing appreciable concentrations (over 50 p. p.m.)
of calcium and magnesium, which in Great Britain have normally
been derived from the leaching of limestone or dolomitic rocks,
by water containing free carbon dioxide. Significant concentrations
of bicarbonate are therefore also present. Calcium may be derived
INDUSTRIAL WATERS
from other types of rock, for example gypsum, CaS04.2H20, in
which case the principle ions present will be calcium and sulphate.
1t is a common convention in the water treatment industry to
refer to ions in solution in terms of certain hypothetical combina
tions. Thus calcium, magnesium and bicarbonate ions, when present
together in solution, are grouped under the term 'temporary
hardness', because on heating, all are substantially removed by
precipitation of the corresponding insoluble carbonates, with loss
of carbon dioxide into the atmosphere. Calcium and magnesium
co-existing with sulphate or chloride are known as 'permanent
hardness', since the solutions are stable to heat at normal pressure.
These imaginary combinations have no real significance, but the
two terms are convenient forms of abbreviation, and will be used in
this book in places where they cannot give rise to misunderstanding.
SOFT WATER
While the meaning of hardness is gene rally understood, the term
'soft water' is often subject to confusion. Soft waters are those which
contain less than about 20 p.p.m. Ca2+ and Mg2+, and in many
areas of Great Britain, such as the hilly regions of Wales and
Scotland, these soft waters have very low total dissolved solids:
indeed, the total of all ions may be below 50 p.p.m. As a result, it
is not uncommon to find among non-technical water users in
industry, a belief that all soft waters, including those artificially
softened, have a low mineral content. The misconception that ion
exchange softening gives results equivalent to those of distillation
is still not unknown; and it is a fairly common experience for a water
treatment contractor to be asked to supply a softener, when abrief
study of the proposed use of the water shows that complete de
mineralizing, that is, removal of aH dissolved salts, is required.
A water may, therefore, be soft, while still containing consider
able concentrations of dissolved salts. WeH waters in low-lying
areas near to the sea are often of this type, owing to ingress of sea
water through porous rock. Waters containing a preponderance
of sodium bicarbonate are also not uncommon in some countries.
EquaHy, a water containing low total solids consisting largely of
calcium salts, which is soft by ordinary standards, will be hard from
the point of view of ion exchange reactions, since the cation resin
on exhaustion will be almost fuHy loaded with calcium. For the
purpose of this book, the concept of hardness will be separated from
that of total mineral content. The terms 'hard' and 'soft' will be
used to indicate the presence or absence of calcium and magnesium
2