Removal of As(V) from aqueous solutions by iron coated rice husk
A
lignocellulosic material extracted from rice husk (Oryza sativa),
Vietnam, was modified as a new adsorbent
for the removal of As(V) ions from aqueous solution. Iron was coated
onto this adsorbent by hydrolization of
ferric nitrate while adding an alkaline solution drop wise into the
batch type reactor. The adsorption of As(V)
ions from aqueous solution on coated rice husk was then studied at
varying pH, As(V) concentrations, contact
times, ionic strength, and adsorbent amounts. The minimum contact time
to reach equilibrium is about 6 h.
The adsorption of As(V) anions on the coated rice husk was found to be
highly pH dependent due to Coulomb
interactions between As(V) species in solution and positively charged
surface groups RH-FeOOH, as well as
formation of chelate complexes with naturally occurring carboxyl and
carbonyl functional groups in the ma-trix. As(V) adsorption on
Fe(III)-coated rice husk (RH-FeOOH) from aqueous solution was studied in
the pH
range 2–10. The main effects of pH on adsorption are estimated by
considering both the behavior of As(V)
ions (hydrolysis and hydroxide precipitation) and the effect of pH on
coordination. A strong effect of pH
was demonstrated at pH 4.0 with a maximum percentage for removal of
As(V) ions 94%. Although both
Langmuir and Freundlich isotherms have been used to characterize the
adsorption of As(V), the Langmuir
modelfitted the equilibrium data better than Freundlich model and
confirmed the surface homogeneity of
adsorbent. The maximum adsorption capacity is determined as 2.5 mg/g of
adsorbent at pH 4.0 for the
Fe(III)-coated rice husk. It is concluded that initial As(V)
concentration has an effect on the removal efficiency
of RH-FeOOH. Higher adsorption of As(V) was observed at lower initial
concentrations. RH-FeOOH as a low
cost material is effective for the removal of As(V) ions and may become a
valuable adsorbent to improve
the ground water quality in Vietnam.
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