TY - JOUR
T1 - Natural Red Earth as a low cost material for arsenic removal
T2 - Kinetics and the effect of competing ions
AU - Rajapaksha, Anushka Upamali
AU - Vithanage, Meththika
AU - Jayarathna, Lakmal
AU - Kumara, Chanaka Kapila
PY - 2011/4
Y1 - 2011/4
N2 - This study investigates the effect of reaction time and competing ions on As retention on Natural Red Earth (NRE). The initial As [As(III) or As(V)] concentrations were varied between ∼10-5 and ∼10-4 M for competitive adsorption studies while samples were spiked with ∼2.67μM As for kinetic studies. Batch experiments were performed for solutions with different concentrations of PO43-, NO3- and SO42- (5.26×10-5, 8.06×10-4, and 2.60×10-3M, respectively) as competing ions for the two systems. One system had controlled conditions (pH 5.5, 0.01M NaNO3) while the second is uncontrolled (no pH control and no NaNO3). Kinetic data were best described by a pseudo-second order model demonstrating strong interaction between As species and >FeOH and AlOH sites on the NRE surface. The equilibrium solid phase concentrations for As(III) and As(V) were observed as ∼20 and ∼12.5μg/g, respectively. The time taken to equilibrium was the same (90min) for both As species. Competitive adsorption isotherm experiments showed a greater effect of PO43- on the reduction of adsorption of both As species than with SO42- and NO3-. Arsenic(III) agreed with the Langmuir equation signifying monolayer formation while As(V) adsorption was in accord with a Fruendlich isotherm indicating multilayer adsorption. FTIR spectra indicated an inner sphere bonding of arsenate and Fe-O sites with PO43- while an outer-sphere weak complexation was observed with NO3-. The substrate appears to show a potential for a similar rate of adsorption under both controlled and uncontrolled conditions indicating its possible use in domestic water filters to remove As from water.
AB - This study investigates the effect of reaction time and competing ions on As retention on Natural Red Earth (NRE). The initial As [As(III) or As(V)] concentrations were varied between ∼10-5 and ∼10-4 M for competitive adsorption studies while samples were spiked with ∼2.67μM As for kinetic studies. Batch experiments were performed for solutions with different concentrations of PO43-, NO3- and SO42- (5.26×10-5, 8.06×10-4, and 2.60×10-3M, respectively) as competing ions for the two systems. One system had controlled conditions (pH 5.5, 0.01M NaNO3) while the second is uncontrolled (no pH control and no NaNO3). Kinetic data were best described by a pseudo-second order model demonstrating strong interaction between As species and >FeOH and AlOH sites on the NRE surface. The equilibrium solid phase concentrations for As(III) and As(V) were observed as ∼20 and ∼12.5μg/g, respectively. The time taken to equilibrium was the same (90min) for both As species. Competitive adsorption isotherm experiments showed a greater effect of PO43- on the reduction of adsorption of both As species than with SO42- and NO3-. Arsenic(III) agreed with the Langmuir equation signifying monolayer formation while As(V) adsorption was in accord with a Fruendlich isotherm indicating multilayer adsorption. FTIR spectra indicated an inner sphere bonding of arsenate and Fe-O sites with PO43- while an outer-sphere weak complexation was observed with NO3-. The substrate appears to show a potential for a similar rate of adsorption under both controlled and uncontrolled conditions indicating its possible use in domestic water filters to remove As from water.
UR - http://www.scopus.com/inward/record.url?scp=79952623972&partnerID=8YFLogxK
U2 - 10.1016/j.apgeochem.2011.01.021
DO - 10.1016/j.apgeochem.2011.01.021
M3 - Article
AN - SCOPUS:79952623972
SN - 0883-2927
VL - 26
SP - 648
EP - 654
JO - Applied Geochemistry
JF - Applied Geochemistry
IS - 4
ER -