M. Dey

Iron and manganese removal in a vertical flow reactor for passive treatment of mine water.

Settling lagoons are a common feature of passive mine water treatment schemes but tend to require large surface areas, this makes them unfeasible in the numerous locations where space is limited. A novel pilot-scale vertical flow reactor has been built at the Taff Merthyr former colliery site. The vertical flow system is designed to replace conventional settling lagoons and decrease the surface-area requirements. To achieve this, the system is designed to take advantage of the surface-catalysed oxidation of Fe(II) on ochre surfaces and the (self)filtration of an ochre bed. This paper presents results from the first four months of operation and details iron and manganese removal. The system receives net-alkaline water from the abandoned colliery, the water quality is typically pH 6.9, with Fe TOT of 9 mg/l. The results show that the vertical flow reactor achieves higher iron removal rates (typically between 10 and 20 g/m 2 /d) compared to the settling lagoon (typically < 5 g/m 2 /d). The vertical flow reactor achieves these removal rates with a smaller residence time, often half that of the settling lagoon. Manganese is present in the influent in low concentrations (~0.8 mg/l). Operating data show that about 50 % of Mn can be removed in the vertical flow reactor in 24 hrs compared to just 5 % in 24 hours in the settling lagoon. Longevity of the reactor will depend on maintaining an acceptable permeability in the bed. Although the permeability fell rapidly at first, the indications are that it is stabilising near to 10 -4 m/s. Additional