Photoinduced reduction of high concentration Hg(II) to Hg2Cl2 from acid wastewater with the presence of fulvic acid under anaerobic conditions.

In order to recover mercury from high concentration Hg(II) acid wastewater, UV irradiation was used to reduce Hg(II) to Hg2Cl2 with the presence of fulvic acid and chloride ion. When simulated wastewater with Hg(II) concentration of 1000 mg L-1 was treated, > 90% of Hg(II) removal efficiency was achieved under the condition of extra Cl- dosage of 5 g L-1, FA dosage of 2 g L-1, pH of 3.0 and 120 min of UV irradiation. Kinetics study showed that the photoreduction process could be well described by pseudo-first order kinetic mode, and the Hg(II) reduction rate was tested to be 0.0422 min-1. Characterization results indicated that FA-Hg(II) complexes were firstly formed and then broken down into smaller molecules after the UV treatment, in which process highly reductive species (i.e. COO, COOH) were produced. These reductive species mediated the reduction of Hg(II). With the presence of Cl-, Hg2Cl2 was practically the only detected Hg-based product in the photoreduction process. This technique was also employed to treat CODCr analysis wastewater (initial Hg(II) concentration > 1000 mg L-1). With 90 min of reaction, most of the Hg(II) was removed from the system leaving less than 30% that could be further treated by chemical participation or adsorption method.