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Evolution of the chemistry of Fe bearing waters during CO2 degassing

Applied Geochemistry

By:
, ,
DOI: 10.1016/j.apgeochem.2012.07.017

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Abstract

The rates of Fe(II) oxidation and precipitation from groundwater are highly pH dependent. Elevated levels of dissolved CO2 can depress pH and cause difficulty in removing dissolved Fe and associated metals during treatment of ferruginous water. This paper demonstrates interdependent changes in pH, dissolved inorganic C species, and Fe(II) oxidation rates that occur as a result of the removal (degassing) of CO2 during aeration of waters discharged from abandoned coal mines. The results of field monitoring of aeration cascades at a treatment facility as well as batchwise aeration experiments conducted using net alkaline and net acidic waters in the UK are combined with geochemical modelling to demonstrate the spatial and temporal evolution of the discharge water chemistry. The aeration cascades removed approximately 67% of the dissolved CO2 initially present but varying the design did not affect the concentration of Fe(II) leaving the treatment ponds. Continued removal of the residual CO2 by mechanical aeration increased pH by as much as 2 units and resulted in large increases in the rates of Fe(II) oxidation and precipitation. Effective exsolution of CO2 led to a reduction in the required lime dose for removal of remaining Fe(II), a very important factor with regard to increasing the sustainability of treatment practices. An important ancillary finding for passive treatment is that varying the design of the cascades had little impact on the rate of CO2 removal at the flow rates measured.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Evolution of the chemistry of Fe bearing waters during CO2 degassing
Series title:
Applied Geochemistry
DOI:
10.1016/j.apgeochem.2012.07.017
Volume
27
Issue:
12
Year Published:
2012
Language:
English
Publisher:
Elsevier
Contributing office(s):
Pennsylvania Water Science Center
Description:
13 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Applied Geochemistry
First page:
2335
Last page:
2347