Chapter 2

REVIEW OF RELATED LITERATURE

In 2004, three student-researchers namely H.A. Abrogueňa, M. S. Melancolico, and S. M.

Salimbagon studied the feasibility of using coconut husk fiber (CHF) as ion exchange

medium for industrial water softening. In their study, they have found out that “CHF

proved to be a potential alternative for the expensive synthetic resins”. (Abrogueňa, et al,

2004) The study focused on the fiber lengths and fiber drying times and their effect on the

efficiency of the CHF cation exchange system. Their findings show that CHF efficiency

increases as drying times lengthened and the fibers of length 3 mm achieved highest

efficiencies at any drying time compared to other fiber lengths. Founded on these findings,

the study “CHF in Cation Exchange for Water Softening: Process and Equipment Design”

came in as a result.

The previous study of Abrogueňa, Melancolico and Salimbagon based its theory from a

research study done by Maini and Santos (1992) and from an investigatory project by

Banuag, et al (1994). Accordingly, “ the cation-exchange characteristics of CHF is

basically due to its cellulosic composition wherein the fibrillar nature of cellulosic fibers

can promote high liquid retention and trapping of fine particles particularly near the

contacting surface.” (Maini & Santos, 1992)

Another study that showed the potentials of CHF as a good adsorbent is the one done by A.

U. Baes, S. J. P. Umali and R. L. Mercado entitled “Ion Exchange and Adsorption of Some

Heavy Metals in a Modified Coconut Coir Cation Exchanger”. According to this study

conducted by Baes et al, “the study’s experiments were carried out through potentiometric

titrations to determine the relative ability of sodium and different heavy metal cations in

replacing protons from ionogenic sites of the exchanger, which adsorbed the cations during

titration. As indicated in their results, the relative preferences for the cations follow the

sequence: Na << Ca (II) < Mn (II) < Ni (II) < Cu (II) < Pb (II)”.

While there is not much data on the cation-exchange capacity of CHF, there have been

many studies done and books written about natural and especially synthetic ion exchange

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resins. I used many of the same principles and theories that have been used in the design of

the CHF ion exchange unit.

First of these is the ion exchange equilibria, in which “the design of the ion

exchange units is based.” (Smith, 2005) The equilibrium expression for the generalized

equation:

nR-A+ + Bn+ ↔ Rn -Bn+ + nA+

From this equilibrium relation, characteristic properties of an ion exchanger can be

explored since ion exchange behavior depends very largely on the nature of the ionizable

groups. Information on the types of group present in an ion-exchange resin can be obtained

by titrating the ion-exchanger with standard acid or alkali. As the reaction is not always

rapid, the best method is to shake the sample of the resin with different amounts of acid or

alkali and, when equilibrium is attained, measure the pH of the solution and the uptake of

acid or alkali by the resin. Determinations of the titration curves of ion-exchange resins of

known structure have shown that the characteristic behavior of the ionizable groups in

simple compounds is reproduced very closely in the resin.

The experiment “Properties of an Ion Exchange Resin” by Harris (1998) made use of this

equilibrium principle in exploring the properties of a cation exchange resin, which is an

organic polymer containing many sulfonic acid groups (- SO3H). “When a cation, such as

Cu2+, flows into the resin, the cation is tightly bound by sulfonate groups, and one H+ is

released for each positive charge bound to the resin by large excess of H+ or by any excess

of any other cation for which the resin has some affinity.” (Harris, 1998)

First, known quantities of NaCl, Fe (NO3)3, and NaOH have been passed through the resin

in the H+ form. The H+ released by each cation has been measured by titration with NaOH.

Second, a sample of impure vanadyl sulfate (VOSO4.2H2O) was analyzed. A solution was

prepared from known mass reagent. “The VO2+ content can be assayed

spectrophometrically, and total cation (VO2+ and H+) content can be assayed by ion

exchange. Together, these measurements enable us to establish the quantities of VOSO4,

H2SO4, and H20 in the sample.” (Harris, 1998) And through these, the experiment has

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determined the number of ionizable groups in the cation-exchanger that in turn determined

the total exchange capacity of the resin.

Also important in this study is the principle of adsorption. In adsorption “one or more

component of a gas or liquid stream are adsorbed on the surface of the solid adsorbent to

accomplish separation.” (McCabe, et al, 2006) The principle is further understood by the

construction of an adsorption isotherm, which is “the equilibrium relationship between the

concentration in the fluid phase and the concentration in the adsorbent particles at a given

temperature.” (McCabe, et al, 2006)

The study of Brown et. al. (2001) entitled “Wastewater Treatment Using Low-Cost

Adsorbents and Waste Materials” made use of this principle. The study “has focused on

the ability of low-cost adsorbents, as compared to the more traditional adsorbents, to

remove from a high-volume waste stream, low concentrations of pollutants.” (Brown, et.

al., 2001) The low-cost adsorbents investigated in the research include peanut hulls, kudzu,

peat moss, municipal leaf compost, a shredded kenaf agrofiber, and a cotton textile waste.

Because some of these materials are more or less of the same characteristics as the coconut

husk fiber, the researcher adopted some of the study’s tests and experiments. Also, the

“pollutant removal efficiencies and capacities of these materials were compared with the

removal efficiencies and abilities of the more traditional adsorbents: activated carbon,

zeolite, bonechar, and a cation-exchange resin, as well as with the traditional wastewater

filter medium, sand.” (Brown et. al., 2001)