An electrochemical sequential injection method to investigate the adsorption of selenite on Fe(III) polyhydroxy cations intercalated vermiculite.

A sequential injection - square wave anodic stripping voltammetry (SI-SWASV) method for determination of Se(IV) at a gold working electrode was developed to investigate the adsorption of Se(IV) onto vermiculite intercalated with Fe(III) polyhydroxy cations. The limits of detection and quantification were 0.060 and 0.20 μmol L, respectively (4.7 and 15.7 μg L). The linearity was up to 1.0 μmol L, and the sampling throughput was 18 analyses h. The proposed approach is a low-cost alternative to more expensive spectrometric methods. Adsorption onto vermiculite intercalated with Fe(III) polyhydroxy cations removed 93% of Se(IV) from a 1.0 μmol L solution (250 mL) after 5 min of contact time with 625 mg of adsorbent. Adsorption isotherms (25.0 ± 0.5 °C) were fitted by the Freundlich equation resulting in 1/n = 0.51 ± 0.03 and K = (1.584 ± 0.002) × 10 μmol g L (r = 0.995). Fitting by the Langmuir equation resulted in an adsorption constant of 0.026 ± 0.008 L g and adsorption capacity of 47 ± 5 μmol g (3.7 ± 0.4 mg g) (r = 0.97). This capacity was higher than that found for several other iron oxides, but lower than that obtained for oxide/hydroxide-based Fe(III) nanoparticles.