Padilla-Rodríguez, Abigail

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    Synthesis and characterization of chitosan bead/flakes for the removal of arsenic and vanadium oxyanions from aqueous solutions
    (2014) Padilla-Rodríguez, Abigail; Román, Félix R.; College of Arts and Sciencies - Sciences; Rivera, Nilka M.; Valentín, Ricky; Meléndez, Enrique; Perales-Pérez, Oscar; Department of Chemistry; Velázquez, Carlos
    Arsenic and vanadium oxyanions are contaminants that are toxic to humans, the environment and other living organisms from natural and anthropogenic sources. The Environmental Protection Agency (EPA) regulated a maximum arsenic level in drinking water of 0.010 mg/L, and vanadium is registered as a contaminant candidate list (CCL). Both contaminants have been removed using diverse techniques such as ion exchange, filtration, precipitation, electrochemicals and others. However, these techniques are expensive and their optimum conditions are not efficient for the removal of these oxyanions. Based on this, adsorption is considered as a removal technique for these contaminants at trace levels from aqueous solutions. The adsorbent used in our studies was chitosan, which is a natural, non-toxic, inexpensive, and effective material. This study uses diverse beads/flakes consisting of chitosan for the removal of V(III), V(IV), V(V), As(III) and As(V) oxyanions from aqueous solutions at trace levels. PCF removed a 99-100% for vanadium oxyanions, and 97% for As(V) oxyanion during the first two hours of contact when using 5 g/L of the adsorbent and an initial contaminant concentration of 0.500 mg/L at pH 6.0. On the other hand, Fe(III)-CB removed a 95 and 99% of As(III) and As(V) oxyanions respectively under the same conditions. These oxyanions were removed efficiently in presence of co-existing anions, such as chloride, carbonate, sulfate and phosphate. The adsorption of vanadium and arsenic species were fitted by Freundlich and Langmuir models, with Langmuir isotherm as the best fit. The maximum adsorption capacity (Q⁰) of the PCF were 12.22, 6.50, 2.58 and 5.43 mg/g for V(III), V(IV), V(V) and As(V), respectively. The protonation of the amine group in chitosan is responsible for the adsorption due to the occurring electrostatic attraction between the negative charge of the oxyanion and the positive charge of the adsorbent. The Q⁰ Langmuir parameters using Fe(III)-CB as adsorbent for As(III) and As(V) were 1.48 and 2.72 mg/g. The As(V) oxyanion adsorption is due to the formation of an inner and outer-sphere complex via ligand exchange and electrostatic attraction. On the other hand, As(III) oxyanion adsorption is due to the formation of an inner-sphere complex via ligand exchange. However, the adsorption of both arsenic species is principally for the immobilization of the ferric hydroxide onto the chitosan beads surface. Our results confirmed that PCF and Fe(III)-CB are simple, non-toxic, efficient, environmentally-friendly, reusable and cost effective adsorbents for vanadium and arsenic oxyanion removal at trace levels from aqueous solutions.