Page 581 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

Resin: (1) An ion-exchange resin is a special type of synthetic Vinyl group: The compound, H 2 C¼¼CH 2 , which is attached
polymer, i.e., macromolecule or poly-electrolyte, to the benzene ring in a styrene polymer and which
which is insoluble and may be visualized as an elastic provides the basis for attachment of additional
three-dimensional network to which ion-active monomers. Also, vinyl may be attached to the
groups are attached (Dow Chemical, 1964, p. 3). lower position of the benzene ring to provide cross-
(2) Ion-exchange resins are poly-electrolyte gels. linkage to other styrene polymers.
Cation-exchangers in H form and anion-exchangers Weak-acid ion-exchanger: A cation-exchange resin in
þ
in OH form may be considered as insoluble acids which incomplete ionization occurs; for example,

and bases, respectively (Helfferich, 1962, p. 81). when the functional group is carboxylate, i.e.,
Reticular: From Latin reticulum little net. (1) Resembling a –COO ;H þ does not dissociate readily from its

net in appearance or structure. (2) Resembling a net attached site, except at high pH; thus they are not
in operation or effect. (http:==unabridged.merriam- functional at low pH. A solution equivalent would be
webster.com) carbonic acid, H 2 CO 3 acid or acetic acid, HAc.
Sieman: A measure of specific electrical conductivity (same Weak-base ion-exchanger: An anion-exchange resin in
as ‘‘mhos,’’ which is the reciprocal of ‘‘ohms’’). The which incomplete ionization occurs; e.g., when the
standardized measurement involves immersing a functional group is >NH 2 ,OH does not dissociate
þ

standard cell in water and reading, at specified voltage, readily from its attached site, except at low pH; thus
the current between two platinum electrode plates, they are not functional at high pH.
each 1.0 cm 1.0 cm, separated by 1.0 cm. Often the Wet capacity: Exchange capacity per unit volume of swollen
units mS=cm are used in lieu of the SI units, S=m. The resin (Dow, 1964, p. 10).
2 6
Zeolite: (1) Crystalline aluminosilicates composed of con-
conversion is, (S=m) (m=cm 10 ) (mS 10 =S) ¼
4
4
mS 10 =cm. In other words, multiply (S=m) by 10 to nected cage-like structures which are large enough
to house a small number of guest molecules, generally
get (mS=cm). For example, EC(seawater) 5.5 S=m ¼
55,000 mS=cm. See also specific electric conductance. <20 angstroms, (see Van Tassel et al., 1994, p. 925).
Softening: Removal of hardness-causing ions; as a rule, the (2) Zeolites are the aluminosilicate members of the
predominant one is calcium with magnesium being family of microporous solids known as ‘‘molecular
the second in concentration. sieves.’’ The term molecular sieve refers to a par-
Specific electric conductance: A measure of the electrical ticular property of these materials, i.e., the ability
conductivity of water, usually given in Siemans or to selectively sort molecules based primarily on
micro-Siemans. Examples are: de-ionized water, a size exclusion process. This is due to a very
0.05 mS=cm; distilled water, 0.05 mS=cm; Lake regular pore structure of molecular dimensions. The
Tahoe, 97 mS=cm; Lake Mead, 850 mS=cm; Atlantic maximum size of the molecular or ionic species that
Ocean, 43,000 mS=cm. See also, Sieman. can enter the pores of a zeolite is controlled by
Stoichiometric: Refers most often to a chemical reaction in the dimensions of the channels. (3) The zeolite
which molecular ratios are defined in accordance taxonomy is
with a ‘‘balanced’’ equation.
silicates=tectosilicate subclass (the framework
Strong-acid ion-exchanger: A cation-exchange resin in which silicates)=zeolite group=
complete ionization occurs; for example, when the
Analcime family
functional group is sulfonate, i.e., –SO 3 ,H dissoci-

þ
Chabazite family
ates readily from its attached site. A solution equivalent
Gismondine family
would be sulfuric acid or hydrochloric acid.
Harmotome family
Strong-base ion-exchanger: An anion-exchange resin in
Heulandite family (includes Clinoptiloltie)
which complete ionization occurs; for example,
Natrolite family
when the functional group is a quaternary amine,
Stilbite family
e.g., –N –,or –N (CH 3 ) 3 ,OH dissociates readily
þ
þ

from its attached site. A solution equivalent would (http:==www.galleries.com=minerals=silicate=tectosil.
be sodium hydroxide. htm).
Styrene monomer: A vinyl group attached to a benzene ring. (4) As noted in the text, zeolite minerals occur
Polystyrene, with di-vinyl benzene cross-linking, is a (by definition) in nature and include some 54 struc-
common constituent of synthetic resins. tures, e.g., amicite, analcime, barerite, bellbergite,
Sulfonic acid functional groups: The complex –SO 3 which bikitaite, goggsite, brewsterite, chabizite, clinoptilolite,

forms a bond with the benzene ring of a polystyrene cowlesite, etc. (http:==en.wikipedia.org=wiki= zeolite).
molecule and which has an exchangeable site for a The mineral zeolites are distinct from the synthetic
cation. zeolites (see text). Some mineral structures have been
Valence: The ionic charge of an atom in the solution phase created by synthesis, however, which are given differ-
[The cation, e.g., Na , loses an electron and the ent names under the same zeolite framework type
þ
anion, e.g., Cl , gains an electron]. (illustrated in Table 16.1).