Kinetic investigation of Hg (II) photoreduction using TiO2-immobilized on calcium alginate beads: Effect of ferric ion and organic compound

To overcome the separation problems of powder TiO2, the TiO2 was immobilized on calcium alginate beads (Alg/TiO2). These synthesized beads were applied to reduce toxic Hg(II) to Hg(0) in aqueous solution under ultraviolet irradiation. In the system without Alg/TiO2 or UV light, no Hg(II) reduction was observed. The
reduction of Hg(II) was approximately 9.9 and 78% when the system was exposed to ultraviolet irradiation with blank beads and Alg/TiO2, respectively. Photoreduction of Hg(II) increased with increasing pH, initial Hg(II) concentration, catalyst dosage. Addition of Fe(III) ions and citric acid improved the photoreduction of Hg(II). The kinetic analysis of the photoreduction showed that the removal of Hg(II) best fitted with the pseudo first-order kinetic. The optimal conditions for Hg(II) photoreduction were found to be: pH 8, 2 g/L of the photocatalyst and 100 mg/L of initial Hg(II) concentration. Moreover, Alg/TiO2 can achieve 75% photoreduction activity up to the third cycles. The results show that Alg/TiO2 are promising materials to effectively treat wastewater containing Hg(II).