Adsorption of arsenic in the surface sediment of the Daliao River Estuary in China

The objectives of this study were to investigate the fraction and sorption of As in the surface sediments of the Daliao River Estuary (DRE). Results indicated that the total As (TAs) content in the sediments ranged from 9.03 to 14.38 mg kg ^-1 and averaged 11.96 mg kg ^-1. The As in the residual fraction and amorphous Fe (Al) oxyhydroxides bound fraction had TAs contents of 30.5 and 30.1%, respectively. The maximum As adsorption capacities (Qmax) and As-binding energy constant (K,J for Langmuir isotherm equations were in the range of 115.94-488.02 mg kg ^-1 and 0.109-0.581 L mg ^-1, respectively. Native adsorption arsenic (NAAs) and the zero equilibrium arsenic concentration (EAsC ₀) ranged from 0.21 to 4.09 mg kg ^-1 and 0.002 to 0.045 mg L ^-1, respectively. Compared EAsC ₀ with actual As concentration in overlying water, the sediments showed a trend of releasing As. The molar ratio of As/Fe in the sediments of DRE showed sorption capacity of the sediments to As was undersaturated. 55.6-65.3%, 14.937.8%, 0.5-1.6%, and 1.6-23.5% of the total amounts of As sorbed was transferred to the specifically sorbed fraction, amorphous Fe (Al) oxyhydroxides bound fraction, crystalline Fe (Al) oxyhydroxides bound fraction, and residual fraction, respectively; showing Fe oxides is a major sorbent of As in the sediments.