Distinguishing Adsorption and Surface Precipitation of Phosphate on Goethite (α-FeOOH)

Surface modification of goethite by phosphate for enhancement of Cu and Cd adsorption

“…And the surface charges tended to be negative at higher pH. The zeta potential for the pristine goethite was positive when the solution pH was higher than 7.9; while the IEP for the phosphate-modified goethite shifted from 7.9 to 6.3, which was consistent with the reported result [22]. The decreased IEP and the evident shift of EM indicated that phosphate ions were strongly bound to the goethite surface since outer-sphere complex (not directly adsorbed on the surface) with phosphate would not change the surface charge [23].…”

Phosphorus sorption and buffering mechanisms in suspended sediments from the Yangtze Estuary and Hangzhou Bay, China

“…When the initial phosphate concentrations are higher than 12 mg L −1 , on the other hand, the adsorption capacities increase rapidly. This suggests that precipitation reactions may occur during the adsorption process at high initial phosphate concentrations (Li and Stanforth, 2000). Phosphate exists as HPO 2− 4 during the adsorption process because the pH of this experimental system is 8.…”

Arsenate and cadmium co-adsorption and co-precipitation on goethite

“…In the case of As(V) precipitation on goethite, the goethite crystal must dissolve to contribute iron to build up surface precipitate. Goethite dissolution takes place primarily along the 0 1 0 and 0 0 1 faces (the ends and sides of the lath-shaped goethite crystals) rather than on the 1 1 0 face, the face on which As(V) adsorption occurs [38]. The poorly crystalline ferric arsenate is suggested to be the component of the surface precipitate of As(V) on ferrihydrite by XRD and Raman studies [39].…”

“…However, the broader and weaker band on goethite compared with the reference, suggests the poorly crystalline of Cd surface precipitation. Surface precipitation of anions occurs at the expense of adsorbent during experiments involving high anion concentration [38]. In the case of As(V) precipitation on goethite, the goethite crystal must dissolve to contribute iron to build up surface precipitate.…”