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Title: Mechanisms of the removal of metals from acid and neutral mine water under varying redox systems
Author: Florence, Kay
ISNI:       0000 0004 5355 1500
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2015
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This thesis investigates the effectiveness of a passive treatment technology for Fe removal from low pH metal mine water. In addition, the use of electrocoagulation (EC) in removing Zn from circumneutral mine water and acid mine drainage AMD) was studied. Using an advanced oxidation process (AOP) followed by EC converted Fe(II) from coal mine drainage to a stable magnetic form of Fe. Research also studied the use of Cu electrodes in removing high concentrations of metals and sulphate from AMD. A 1 m³ field pilot scale vertical flow reactor (VFR) for passively treating an average flow of 0.6 L/min was deployed for 414 days. The system was gravity fed and removed an average of 65% of the Fe from pH 3 AMD. Potential removal mechanisms are a combination of bacterially mediated Fe(II) oxidation by Ferrovum myxofaciens and filtration of Fe nanoparticles. The build-up of the ochre bed did not compromise the permeability of the VFR. Mineralogical and microbiological studies combined with PHREEQC modelling show that the main mineral precipitated in the VFR is schwertmannite. Using EC, it was shown that the addition of Fe from neutral mine water by electrical dissolution of an Fe electrode resulted in Zn to be removed at a near neutral pH through a combination of co-precipitation and adsorption reactions. An inert Pt electrode rapidly removed 70 mg/L of Fe(II) from coal mine water by AOP applying 5 A during 4 min treatment. A second stage treatment adding Fe by electrical dissolution of Fe electrodes generated the required Fe(II):Fe(III) ratio and Eh-pH conditions to form magnetic Fe (magnetite). Further investigations into EC proved that the removal of sulphate and metals from AMD was highly effective when adding Cu from a copper electrode at 40 min at 5 A with aeration. Sulphate was reduced from 1324 mg/L to 112 mg/L without leaving Cu in solution. ESEM images and mineralogical studies of the precipitates showed that the mineral cuprite is formed. This has future potential implications for metal recycling/recovery from AMD.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)