Remediation of metal-contaminated wastewaters using novel treatment system configurations that harness the sorption capacity of hydrous ferric oxide (HFO)
Discharges from abandoned base metal mines are by far the single biggest source of toxic metals (e.g. Zn and Cd) to the aquatic environment of England and Wales (Mayes et al., 2013). Because mining is a globally important source of aquatic pollution and due to the pervasive nature of this pollution, low cost, low carbon solutions are sought to alleviate the problem (‘passive’ treatment). ‘Compost bioreactors’ are one passive option, and such a treatment system has been operating, largely effectively, at the abandoned Force Crag mine site in the Lake District National Park, since 2014.
The Force Crag system has worked to good effect, and similar successes have been recorded elsewhere in the world, but there are some important constraints to the use of compost wetlands: (1) their absolute size, which is often substantial, (2) the potential for such systems to release nuisance odours (hydrogen sulphide), (3) maintenance of long-term permeability of organic substrates for such systems, (4) the large volume of metal-containing compost that will be generated and will require disposal, and (5) the temperature-dependence of the biological treatment processes, which can result in substantial reductions in metal removal during colder periods.
It may be possible to overcome the limitations of current passive treatment technologies reliant on biological processes by utilising iron-containing wastes and products (and potentially other materials), to rapidly adsorb divalent metals in novel treatment systems. The high sorption capacity of hydrous ferric oxide (HFO) has long been known (Dzombak and Morel, 1990). But that knowledge has yet to be translated into engineering applications in the form of treatment systems that are demonstrably reliable at larger scales. In addition, there is a ready source of HFO generated as waste from coal mine water treatment, which is currently disposed of, at high cost, to landfill (4500 tonnes / annum of iron-rich sludge are generated (Jarvis and Moorhouse, 2019)). This project will therefore investigate novel engineering configurations for treatment systems that harness the high sorption capacity of HFO as a treatment media.
The UK Coal Authority currently operates some 75 full-scale treatment systems for abandoned coal mine water treatment, all of which generate HFO that has the potential for reuse. However, the geochemistry of these solid phases varies between locations, depending on the mine water chemistry and the exact treatment process used. A first step in the research will therefore be to conduct analysis of these solids, coupled with sorption tests, to understand what specific characteristics of any particular HFO make it a more or less effective sorbent.
Building on preliminary work undertaken by a former Master of Engineering student (Moore, 2019), the research will then explore the influences of different physical and chemical factors on the effectiveness of HFO as a sorbent media e.g. initial contaminant concentration, pH, hydraulic residence time, HFO grain size.
The final phase of the research will focus on the engineering design of possible configurations of treatment units that could effectively harness the sorptive capacity of HFO (of a physical and chemical form determined in the earlier parts of the research). This may involve re-purposing of existing treatment technologies, or design of entirely new configurations. Either way, bench-scale proof-of-principle experiments will be undertaken as a forerunner to pilot-scale system design, installation and monitoring.
The student will be based in the School of Engineering at Newcastle University, with visits to Durham for specific analytical work, as and when required, and potentially also to Exeter. Initially the project will involve field work to collect and analyse HFO samples. The project will then involve periods of lab work, with subsequent detailed analysis work undertaken at Newcastle and Durham Universities. Once designed and built, in the final phase of the work the research will involve regular trips to a field site (location to be confirmed) to undertake monitoring of a pilot-scale HFO treatment unit.
Field and lab techniques will include water quality measurements, ICP-OES and ICP-MS analysis for metals concentrations, sequential extraction procedures to investigate mobility of adsorbed metals and potential for metal recovery, XRD and SEM analyses of solids, and MÃ¶ssbauer spectroscopy to determine and monitor solid iron phase composition and transformation during initial phases of research.
Detailed literature review work; training in field and laboratory techniques.
Commencement of laboratory based work, focusing initially on lab-based investigations, with design of pilot-scale unit towards the end of Year 2; possible conference attendance / presentation towards end of year.
Installation and monitoring of pilot-scale HFO treatment unit; specialist training in statistical analysis and other training as required; attendance at international conference. Commence thesis write up.
Thesis write up and preparation of journal article(s) as appropriate.
In addition to the IAPETUS doctoral training process, the student will receive training in all aspects of field and laboratory techniques by the very experienced technical staff at Newcastle University, with equivalent training at Durham for specific techniques. The student will therefore gain key skills in both routine and advanced sampling and analysis techniques for inorganic constituents of water and solids. The student will be actively encouraged to attend relevant taught MSc modules on the wide range of programmes delivered both within the School of Engineering and elsewhere, thus widening their knowledge base. Courses in relevant data analysis techniques will be followed by the student (e.g. statistical analysis), and the supervisory team will lead on guiding the student on how to go about preparation of international peer-reviewed journal papers and delivery of conference presentations; key skills for a successful researcher.
References & further reading
Mayes, WM, Potter, HAB, Jarvis, AP (2013) Riverine flux of metals from historically mine orefields of England and Wales. Water Air & Soil Pollution, 224:1425.
Dzombak, DA & Morel, FMM (1990) Surface Complexation Modeling: Hydrous Ferric Oxide. John Wiley & Sons, New York.
Jarvis, AP & Moorhouse, A (2019) Passive treatment of metal-polluted drainage: Approaches, challenges, and possible future developments. In Proceedings of the WISSYM 4th International Mining Symposium, Chemnitz, Germany, 9 – 11 Oct. 2019.
Moore, JAC (2019) Effective engineering configurations for water treatment systems that utilise hydrous ferric oxide (HFO). Unpublished MEng thesis, Newcastle University, UK.
Dr Adam Jarvis, Newcastle University
T: 0191 208 4871