Page 564 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Ion-Exchange 519

The nomenclature used by Dow Chemical (1964, p. 4) is: 16.1.4.4.11 Density: Bulk and Particle
The relation between the dry bulk density and the dry particle
density is
Type DVD % Mesh Size Ionic Form
r ¼ (1 P)r (16:2)
Dowex 50 X8 20–50 Na b s
in which
r b is the bulk density of ion-exchanger in packed-bed (kg
The type is Dowex 50t which has 8% DVD cross-linking 3
dry resin=m bulk volume of resin in packed-bed)
(meaning 8 molecules of DVD combine with 92 molecules of
P is the porosity of packed-bed (volume of voids=volume
styrene to form the resin material) and mesh size 20–50
of packed-bed)
(meaning most of the resin passes mesh 20 and is retained
r s is the density of dry solid ion-exchanger (kg dry
by mesh 50). The ion-active group is sulfonic acid, i.e., 3
resin=m solid resin)
–SO 3 , which is strongly acidic. The ionic form of the par-

ticular resin in the example is Na , meaning the strongly
þ
16.1.4.4.12 Swelling
acidic –SO 3 , groups are combined with Na þ counterions.

A resin swells as it takes up moisture. The degree of swelling
The Na ions are the exchangeable ions.
þ
depends upon the particular resin and the degree of cross-
An example of a strong-base anion-exchanger is Dowex
linkage, i.e., percent DVD. As an example, Dowex 50 H þ
Marathon A, Type I, styrene-DVB gel, quaternary amine, resin has a ratio of swollen bead diameter=dry bead diameter
with total exchange capacity 1.3 eq=L (28.4 kg=ft 3 as
2.0 at 2% DVD to 1.4 at 10% DVD.
CaCO 3 ); water content is 50%–60%, UC ¼ 1.1, mean particle
size ¼ 575 50 mm, total swelling (Cl ! OH ) ¼ 20%, par- 16.1.4.5 Aluminas

3
ticle density ¼ 1.08, shipping weight ¼ 670 g=L (42 lb=ft );
The removal of fluoride ion is also associated with alumina,
pressure drop is 0.5 bar=m bed depth at HLR ¼ 36 m=h which is selective for other ions, e.g., metals, sulfates, nitrates.
2
(14.8 gpm=ft ), T ¼ 258C (from http:==www.dow.com=
The fluoride-removal cycle involves (Fleming, 1986, p. 162):
liquidseps=pc= jump=dowex= dm_a.htm).
(1) filtration with influent adjustment of pH to pH 5.5; (2)
backwash with treated water; (3) regeneration with 1% NaOH;
16.1.4.4.8 Mesh Sizes (4) rinse with treated water; (5) neutralization with 0.5% H 2 SO 4 .
Size equivalents of the U.S. Standard mesh sizes are (Dow Commercial names for aluminas include: Alcoa W-100
Chemical, 1964, p. 15): with selectivity for certain cations, and exchange capacity of
0.75 meq=g; Alcoa F-1 (replaced by Alocoa DD-1), used for the
removal of arsenic (trivalent and pentavalent). Alcoa F-1 has
Mesh Range Screen Analysis Particle Diameter (mm) been used for removals of orthophosphates, e.g., H 2 PO 4 ,

2
3
16–20 Wet 1.168–0.84 HPO 4 ,PO 4 ; pyrophosphates, e.g., P 2 O 7 ;tripolypho-
4
3
20–50 Wet 0.84–0.297 sphate, e.g., P 3 O 10 ; and hexametaphosphate, e.g., (PO 3 ) 6 .
3
50–100 Dry 0.297–0.149 As to physical characteristics, the aluminas resist oxida-
100–200 Dry 0.149–0.074 tion, do not swell, and have high crushing strength, abrasion
200–400 Dry 0.074–0.038 resistance, and low chemical solubility. Other characteristics,
from a product data sheet, gave: Al 2 O 3 ¼ 92.2%; moisture ¼
3
3
5% maximum; bulk density 674.31 kg=m (42 lb=ft ); surface
2
As seen, the larger sizes are sieved wet, while the smaller area ¼ 290 m =g (Whittaker, Clark, Daniels, South Plainfield,
sizes are sieved dry. NJ, Activated Alumina #4204, CAS#1344-28-1). Alcoat F-1
activated alumina was reported as being available in several
16.1.4.4.9 Moisture mesh sizes, e.g., 1=4 8, 8 14, 14 28, 28 48, 48 100,
100, 325, and was packed as sling bags, paper bags, and
The fraction moisture, fM, is defined, fM ¼ [r(moist)
r(dry)]=r(dry); from this the relation between moist density, drums (Alcoa, 1989).
r M , and dry density, r D , is, r M ¼ r D (1 þ fM).
16.1.4.5.1 Activated Alumina
16.1.4.4.10 Density: Moist and Dry Particle Activated alumina is formed by dehydrating amorphous alu-
3
The density of resins are 800–848 g=L (50–53 lb=ft )as minum hydroxide, i.e., Al(OH) 3 . It is a mixture of amorphous
and crystalline aluminum oxide of approximate composition,
shipped, with moisture content reported as 45% in the Na þ
Al 2 O 3 . The adsorption process involves surface complexation
form and 53% in the H þ form (ranges for Dowex 50 and
and exchange of hydroxide ions for the contaminants. The
Amberlite IR-120). For reference, a laboratory determination
selectivity sequence is
(Abdelrasool, 1992) of seven samples of Dow AGW50-X8
cation-exchange resin, H þ form for of moist density (as
2
OH > H 2 AsO 4 > F > SO 4 > HCO 3 > Cl
packed) and dry density after oven drying were r(moist)
> NO 3 (Chwirka et al:, 2000):

0.82 (g=mL) and r(dry) 0.52 (g=mL), with fM 0.58.