Oxidation of arsenite by dissolved oxygen, manganese and iron oxyhydroxides in aqueous solutions

Oxidation of dissolved arsenite was studied in 0.05M and 0.7M NaCl aqueous solutions. The experimental conditions included a range of pH (3 to 9), presence and absence of ambient light, presence and absence of oxygen, and presence and absence of amorphous and crystalline Mn and Fe oxyhydroxides at (Mn - Ox and Fe-Ox) constant solid: solution ratios of 0.0002. All experiments were conducted at a temperature of 23 +/- 4°C and initial arsenite concentration of approximately 100 ppb. Arsenic speciation was determined both in the aqueous phase and in the combined solid and aqueous phases.; Aqueous arsenite oxidation by oxygen alone is slow. Light, pH, and ionic strength had no effect on the oxidation rate of arsenite by dissolved oxygen. In the presence of manganese- and iron oxyhydroxides (Mn-Ox and Fe-Ox), the oxidation of arsenite is rapid: within 15 minutes, more than 80% of the initial As(III) was oxidized to As(V) by crystalline and amorphous Fe-Ox, and by amorphous Mn-Ox. In the presence of crystalline Mn-Ox, more than 20% of the initial As(III) was oxidized within the first 5 minutes of the experiment. Dissolved oxygen was not essential for the arsenite oxidation by the metal oxides. (Abstract shortened by UMI.)...