Enhanced arsenic sorption by hydrated iron (III) oxide-coated materials--mechanism and performances.

Mechanism and performances of arsenic(III) [As(III)] and arsenic(V) [As(V)] sorption onto hydrated iron(III) oxide (HFO)-coated materials were investigated at neutral pH where arsenic occurs in both molecular and ionic forms. Arsenic sorption by HFO-coated materials was proven to be a multistage process consisting of both macropore and intraparticle diffusion. Higher mass-transfer velocities were obtained for As(III), which is attributed to the beneficial features of HFO. Equilibrium studies revealed the spontaneous and favorable nature of the arsenic sorption process. The maximum sorption capacity and the Gibbs free energy values indicated that HFO-coated materials exhibit more affinity towards As(III). The Langmuir and Freundlich isotherm models revealed both the chemical and physical nature of the sorption process, while the Dubinin-Radushkevich model indicated that physical sorption is a more dominant process with HFO-coated materials.

Determination of inorganic arsenic species in natural waters--benefits of separation and preconcentration on ion exchange and hybrid resins.

A simple method for the separation and determination of inorganic arsenic (iAs) species in natural and drinking water was developed. Procedures for sample preparation, separation of As(III) and As(V) species and preconcentration of the total iAs on fixed bed columns were defined. Two resins, a strong base anion exchange (SBAE) resin and a hybrid (HY) resin were utilized. The inductively-coupled plasma-mass spectrometry method was applied as the analytical method for the determination of the arsenic concentration in water. The governing factors for the ion exchange/sorption of arsenic on resins in a batch and a fixed bed flow system were analyzed and compared. Acidity of the water, which plays an important role in the control of the ionic or molecular forms of arsenic species, was beneficial for the separation; by adjusting the pH values to less than 8.00, the SBAE resin separated As(V) from As(III) in water by retaining As(V) and allowing As(III) to pass through. The sorption activity of the hydrated iron oxide particles integrated into the HY resin was beneficial for bonding of all iAs species over a wide range of pH values from 5.00 to 11.00. The resin capacities were calculated according to the breakthrough points in a fixed bed flow system. At pH 7.50, the SBAE resin bound more than 370 microg g(-1) of As(V) while the HY resin bound more than 4150 microg g(-1) of As(III) and more than 3500 microg g(-1) of As(V). The high capacities and selectivity of the resins were considered as advantageous for the development and application of two procedures, one for the separation and determination of As(III) (with SBAE) and the other for the preconcentration and determination of the total arsenic (with HY resin). Methods were established through basic analytical procedures (with external standards, certified reference materials and the standard addition method) and by the parallel analysis of some samples using the atomic absorption spectrometry-hydride generation technique. The analytical properties of both procedures were similar: the limit of detection was 0.24 microg L(-1), the limit of quantification was 0.80 microg L(-1) and the relative standard deviations for samples with a content of arsenic from 10.00 to 300.0 microg L(-1) ranged from 1.1 to 5.8%. The interference effects of anions commonly found in water and some organic species which can be present in water were found to be negligible. Verification with certified reference materials proved that the experimental concentrations found for model solutions and real samples were in agreement with the certified values.