Rates and mechanisms of Fe(II) oxidation in a passive vertical flow reactor for the treatment of ferruginous mine water

This thesis presents the methodology and results of research undertaken into the rates and mechanisms of iron oxidation both in field and laboratory environments. The field based aspects of the research entailed the collection and analysis of hydrological, hydrogeochemical, and mineralogical data from two parallel treatment systems. Both systems were treating identical ferruginous, circum-neutral, coal-mine drainage, from the Taff Merthyr site, South Wales. During this study a novel pilot scale passive Vertical Flow Reactor (VFR) was trialled against a conventional settlement lagoon and the performance of both systems was compared. The second research aspect focuses on the determination of heterogeneous Fe(II) oxidation rates under laboratory conditions. Experiments were carried out under varying pH, and catalytic surface concentration and type. An analytical method was developed which allowed for the determination of both dissolved and sorbed Fe(II). The results of the field study have shown that the VFR system is capable of removing Fe at a rate greatly in excess of a conventional settlement lagoon. This therefore drastically reduces the treatment area required. In addition, due to the heterogeneous method by which the VFR operates (passing mine- water down through a bed of ochre solid), highly efficient manganese removal was also achieved. The laboratory study has shown that significant catalysis of Fe(II) oxidation can be achieved under mildly acidic pH conditions making Fe(II) oxidation (and therefore passive mine-water treatment) feasible under these conditions. Evidence is also presented for the adsorption of non-oxidisable Fe(II) onto Fe(III) (hydroxy)oxides under mildly-acidic pH conditions. A comparison was then made between field and laboratory results and a conceptual model was produced to describe the observed adsorption and oxidation characteristics