Development of Chemical Reduction and Air Stripping Processes to Remove Mercury from Wastewater

Abstract

20This study evaluates the removal of mercury from wastewater using chemical reduction and air stripping 21 using a full-scale treatment system at the Savannah River Site. The existing water treatment system 22 utilizes air stripping as the unit operation to remove organic compounds from groundwater that also 23 contains mercury (C ~ 250 ng/L). The baseline air stripping process was ineffective in removing 24 mercury and the water exceeded a proposed limit of 51 ng/L. To test an enhancement to the existing 25 treatment modality a continuous dose of reducing agent was injected for 6-hours at the inlet of the air 26stripper. This action resulted in the chemical reduction of mercury to Hg(0), a species that is removable 27 with the existing unit operation. During the injection period a 94% decrease in concentration was 28 observed and the effluent satisfied proposed limits. The process was optimized over a 2-day period by 29 sequentially evaluating dose rates ranging from 0.64X to 297X stoichiometry. A minimum dose of 16X 30 stoichiometry was necessary to initiate the reduction reaction that facilitated the mercury removal.

Pilot‐Scale Removal of Total and Hexavalent Chromium From Groundwater Using Stannous Chloride

“…Ideal reduction of Cr(VI) to Cr(III) by Sn(II) was assumed to follow the chemical equation shown in Figure . Accordingly, the stoichiometric MDR would be 1.5, and although other Cr(III) and Sn(IV) hydrolysis products likely form, the primary products (and potential precipitates) were assumed to be Cr(OH) 3 (s) and SnO 2 (s) (Kaprara et al , Haynes et al , Pinakidou et al , Mathews et al , Jackson et al , Brandhuber et al ). Thermodynamic modeling software also supported SnO 2 (s) as the most favorable solid to form.…”

“…Stannous chloride is not currently listed as a drinking water treatment chemical by NSF International (NSF/ANSI ) (although it is listed as such by UL []), as its uses are primarily associated with food preservation, dye manufacturing, metallization, plating, tanning, and pharmaceutical industries (USNLM ). Other than the work by Lai and McNeill () and Brandhuber et al (), which were part of the same study, SnCl 2 for water treatment has been limited to its use as (1) a precursor for novel Cr(VI) reductants/adsorbents (Kaprara et al , Pinakidou et al ), (2) a reductant for the treatment of dissolved mercury (Mathews et al , Jackson et al ), and (3) a corrosion inhibitor in distribution systems (Hozalski et al , ). Compared with Fe(II) RCF, which forms Fe(OH) 3 (s) and other hydrolysis products (e.g., Fe(OH) 2+ ), oxidation of Sn(II) to Sn(IV) has been shown to form relatively insoluble stannic oxide or cassiterite (SnO 2 (s)) as opposed to other Sn(IV) hydrolysis products (e.g., Sn(OH) 3 + ) that would be relevant to coagulation (Kaprara et al , Haynes et al , Mathews et al , Jackson et al , Brandhuber et al ).…”

Western Sector In-Situ Chemical Oxidation Project: Initial Results Following Injection Activities (U)

“…This mobilization will impact the operation of subsurface corrective action programs as effluents will have to consider regulatory aspects associated with environmental release of mercury. The presence and release of mercury from DNAPL has impacted the groundwater pump and treat system such that technologies have been developed to address the removal of ionic mercury (Hg +2 ) using chemical reduction and air stripping (Jackson et al 2013) The current paradigm for the presence of mercury is that as DNAPL is removed through chemical oxidation of organic compounds (TCE and PCE) in the aqueous phase, dissolution rates of these compounds from the non-aqueous phase will increase, reducing the mass (volume) of DNAPL present in the subsurface. As DNAPL mass is removed through dissolution, elemental mercury will become oxidized and form highly soluble mercury chloride complexes in the aqueous phase.…”

The effects of a stannous chloride-based water treatment system in a mercury contaminated stream

“…A stannous chloride-based Hg treatment system was installed in 2007 at an air stripper tower (which was originally designed to treat groundwater for organic contaminants) located at the Outfall Tributary ( Fig. 1) (Jackson et al, 2013).…”