The necessity of arsenic (As) removal from metallurgical wastewaters is increasing. Despite its wide recognition as a natural oxidant, the utility of Mn oxide for scorodite production is mostly unknown. In acidic solutions containing both As(III) and Fe2+, simultaneous oxidation of the two progressed by MnO2 and the resultant As(V) and Fe3+ triggered the formation of crystalline scorodite (FeAsO4·2H2O). At 0.5% or 0.25% MnO2, 98% or 91% As was immobilized by day 8. The resultant scorodite was sufficiently stable according to the TCLP test, compared to the regulatory level in US and Chile (5 mg/L): 0.11 « 0.01 mg/L at 0.5% MnO2, 0.78 « 0.05 mg/L at 0.25% MnO2. For the oxidation of As(III) and Fe2+, 54% (at 0.5% MnO2) or 14% (at 0.25% MnO2) of initially added MnO2 remained undissolved and the rest dissolved in the post As(III) treatment solution. For the Mn recycling purpose, the combination of Mn2+-oxidizing bacteria and biogenic birnessite (as homogeneous seed crystal) was used to recover up to 99% of dissolved Mn2+ as biogenic birnessite ((Na, Ca)0.5(MnIV, MnIII)2O4·1.5H2O), which can be utilized for the oxidation treatment of more dilute As(III) solutions at neutral pH. Although further optimization is necessary, the overall finding in this study indicated that Mn oxide could be utilized as a recyclable oxidant source for different As(III) treatment systems.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering