Adsorption of Arsenite and Fluoride on Untreated and Treated Bamboo Dust - Management of Natural Resources in a Changing Environment - page 163

Determination of Anion Exchange Capacity
Theanionexchangecapacity(AEC)wasdeterminedconductometrically.0.2gof
the adsorbent in 20 mL conductivity water was titrated against standardAgNO 3
solution.ThetitrationwasrepeatedforstandardNaClwiththesameAgNO 3 solu-
tion and the equivalence point in each case was obtained. From the difference in
volumes of AgNO 3 solutions required, AEC was calculated using the formula,
AEC= NV / W where N is the normality of AgNO 3 solution and V is its volume
required by W g of the adsorbent.
Adsorption Experiments
The adsorption experiments were carried out by batch adsorption process, in which
50 mL of aqueous adsorbate solution was mixed with 1 g of the adsorbent in an
Erlenmeyer flask (polypropylene Erlenmeyer flasks were used for F − adsorption).
Themixturewasagitatedinathermostaticwaterbathshaker(NavyugIndiaQ5247)
for a pre-determined time interval and the mixture was centrifuged. Unadsorbed
As(III) in the supernatant was determined using atomic absorption spectrometer
(VarianSpectrAA220usinghydridegenerator,wavelength192.5nm,lampcurrent
5mA,slitwidth0.5nm,workingrange0-100 ʼg/mL).Unadsorbedluoridewas
estimatedusingSPDNSreagentspectrophotometrically(ShimadzuUV1800).
When the effect of pH was studied, the pH of the adsorbate solution was adjusted
by adding aqueous solution of 0.01 N NaOH or 0.01 N HNO 3 in drops. The condi-
tions for different sets of experiments are given in Table 1 .
Results and Discussion
Effects of pH
The pH of the aqueous solution is a significant controlling factor in adsorption
mechanism. The experiments were conducted by varying pH of the solution from
6.0 to 8.5 and taking 1.5 mg/L luoride and 100 ʼg/L arsenite solutions at room
temperaturefor4hand5hrespectively.Theamountadsorbedperunitmassofthe
adsorbents ( q e ) increased up to pH = 7 in both the cases (Fig. 1 ), but the increase was
not as sharp for arsenite as it was for fluoride.
Inbasicmedium,adsorptiondecreased.AspHincreasedtoward7.0,theanions
had to compete with increasing number of hydroxyl ions in the solution resulting in
less adsorption. Similar results were obtained by using pumice (Malakootian et al.
2011 ).As pH increased toward 7.0, the anionic species, H 2 AsO 3 − , increased and
thusmoreAs(III)uptakewasexpectedduetospeciicbinding.Relativeadsorption
inhibition was observed at basic pH range and could be attributed to the accumulation