Page 557 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

512 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

the first column is removed for recharge; the second column is came into being and included, –P –, and >S –. As a note
þ
þ
place at the beginning; a third standby column that has been anion-exchangers did not exist prior to the development of
recharged is placed in the second position. synthetic resins (foregoing from Helfferich, 1962, p. 47).
16.1.2.1.3 Cross-Linked Polystyrene Resins
16.1.2 HISTORY
The ‘‘Adams and Holmes’’ patents were purchased by IG-
The field of ion-exchange has its origins in science in the Farbenindustrie A.G., where the development and production
modern sense of conducting systematic inquiry to discover of ion-exchanger resins have continued since 1936. In 1945,
knowledge. Practice is built on this knowledge (Rohm and G. F. d’Alelio, in the United States, patented his synthesis
Haas, 1989). process of incorporating sulfonic acid groups into cross-
linked polystyrene resins. This development formed the
16.1.2.1 Science basis for the modern industry in ion-exchange resins. The
The ion-exchange principle was discovered byH.S. Thompson, polystyrene anion-exchange resins were developed in 1949.
an English agricultural chemist, who in 1848 noted that in Further development was directed toward synthesizing resins
treating a soil with ammonium sulfate or ammonium carbonate, with specific ion-exchange properties. Presently, a wide var-
most of the ammonium was absorbed and Ca 2þ (then identified iety of such resins are commercially available. Kunin (1983)
as ‘‘lime’’ since the ion theory had yet to be developed) was viewed the development of anion-exchange resins as the final
released (Kunin, 1958). Thompson reported this finding to breakthrough that paved the way for the widespread develop-
J. Thomas Way, who followed up, during the period 1850– ment of the ion-exchange technology.
1854, with asystematic study.Way found that: (1) the exchange
of calcium and ammoniums ions noted by Thompson was 16.1.2.1.4 Maturing of Ion-Exchange Technology
verified; (2) the exchange of ions in soils involved equivalent Liberti and Helfferich (1983, p. v) and Millar (1983a, p. 2)
quantities; (3) certain ions were exchanged more readily than viewed the 1950s as the ‘‘Golden Age’’ in the development of
others; (4) the extent of exchange increased with concentration, synthetic resins for ion-exchange. During this period, the
reaching a leveling-off value; (5) aluminum silicates present in technology of ion-exchange was developed and the founda-
soils were responsible for the exchange; (6) exchange materials tions were laid for modern theory. By 1982, they viewed ion-
could be synthesized from soluble silicates and alum; and (7) exchange as a ‘‘mature’’ technology. As an index of activity,
exchange of ions differed from physical adsorption. These worldwide ion-exchange production in thousands of cubic
principles remain inviolate. It is not clear how all of this was meters was: 1967: 60; 1970: 70; 1974: 138; 1977: 125; and
explainedwithout the ionictheory of solutions, i.e., as proposed in 1981: 140 (Millar, 1983a, p. 4). Of the amount sold in
3
by Arrhenius, van’t Hoff, and Ostwald in the 1880s (Servos, 1981, >120,000 m resin was polystyrene strong-acid or
1990, pp. 35–45). strong-base gel resins in bead form.

16.1.2.1.1 Zeolites
16.1.3 APPLICATIONS
In 1858, Eichhorn established the principle of reversibility of
the ion-exchange reaction. He showed also that natural zeolites Ion-exchange has been applied for softening in water treat-
acted as ion-exchangers, which comprised hydrated double ment, ammonia removal in wastewater treatment, demineral-
silicates (Behrman, 1925, Applebaum, 1925). According to ization for various industrial purposes, and specific ion
Behrman (1925) this early work laid the theoretical foundation removal in hazardous wastes.
for ion-exchange practice, which was not to commence until the
early part of the twentieth century with the work of German 16.1.3.1 Municipal Use
chemist, Robert Gans. Gans developed aluminum silicates as Softening of water is the removal of ‘‘hardness’’ ions (that
‘‘synthetic zeolites,’’ which had a higher exchange capacity than consume soap), which are mostly Ca 2þ and Mg 2þ (see Chap-
the natural ones, and established their utility in treating sugar ter 21). Water-softening practice began in 1905 with the first
solutions to replace K ion with Ca 2þ ion to increase the yield of municipal softening plant which used precipitation. In 1906,
þ
crystallizable sugar, and for softening waters (Kunin, 1958). Professor Robert Gans, Director of Chemistry of the German
Geological Survey, obtained a patent for softening water by
16.1.2.1.2 Resins ‘‘base-exchange’’ (AWWA, 1951). The first applications were
In 1935, two British scientists, B.A. Adams and B.L. Holmes for hotels, apartments, laundries, and boiler feed water
found that synthetic resins had ion-exchange properties. They (Applebaum, 1925). The Permutit Co., which was related to
made the first ion-exchange resins and learned how to add the well-known German company, I.G. Farber, had the
different ionic groups (Dorfner, 1972). They showed that stable patents of Gans and had forged ahead in developing the ion-
high-capacity cation-exchange resins could be prepared by add- exchange technology for water treatment.
ing sulfonic acid groups, and that anion-exchange resins could In 1920, the discovery of the New Jersey greensands
be prepared by adding polyamine groups. Later, strong-base (glauconite) made ion-exchange economically feasible for
quartenary amines were developed, i.e., –N –, –N (CH 3 ) 3 , municipal water softening (AWWA, 1951). The greensands,
þ
þ
etc. Still later, i.e., before 1962, other strong base groups (which are not zeolites) had a higher rate of exchange than the