Hybrid zero-valent iron process for removing heavy metals and nitrate from flue-gas-desulfurization wastewater

摘要

In this paper, we present and discuss the results from the first field demonstration of the hybrid zero-valent iron (hZVI) technology for removing selenium (Se), mercury (Hg), and nitrate from the flue-gas-desulfurization (FGD) wastewater of a coal-fired power plant. By hybridizing zero-valent iron with magnetite and Fe(II) species, the hZVI technology creates a self-sustaining highly-reactive mixture that can achieve rapid reduction, transformation, immobilization and mineralization of various heavy metals, oxyanions and other impurities from aqueous streams in a near-neutral pH environment. The hZVI technology was demonstrated in a 5-week continuous-flow field test conducted on a 30-1 fluidized bed system at a power plant. The prototype consistently reduced Hg from ca. 50 to <0.005 μg/L and Se (mostly as selenate) from ca. 3000 to <7 μg/L. Nitrate was reduced from ca. 25 to <0.2 mg/L. In addition, arsenic, cadmium, chromium, nickel, lead, zinc, and vanadium were all reduced to near- or sub-ppb levels. The TCLP test on the spent solids found that the leachate contained <0.1 mg/L Se, <0.2 μg/L Hg and <0.1 μg/L As, all below their respective regulatory limits for non-hazardous waste designation. With limited chemical consumption and solid waste production, the hZVI technology has a competitive process economics in comparison with other advanced metal treatment solutions. The hZVI technology can be a cost-effective solution to many current and emerging problems in water/wastewater treatment and help industries comply with the increasingly stringent environmental regulations.