No abstract

This paper addresses the ability of five low-cost reactive materials to remove Zn, Pb, and Cd from Fe-poor, circum-neutral pH metal mine water in Mid-Wales, UK. Compost, fly ash, waste shell material, iron ochre, and a mixture of blast furnace slag (BFS) and basic oxygen furnace slag (BOS) were used in a series of small-scale passive treatment cells to assess metal removal from mine drainage initially containing, on average, 23.5 mg/L Zn, 0.5 mg/L Pb, and 0.05 mg/L Cd. Trial treatment cells contained between 1.5 and 12 kg of reactive media, had a 15 min residence time, and treated a discharge of up to 1 L per minute. Fly ash from a peat-fired power station was found to be the most effective material for metal removal, with concentrations reduced to 0.02 mg/L Zn, 0.0069 mg/L Pb, and 0.0001 mg/L Cd from over 1,000 L of water (between 98.6 and 99.9% removal). The other materials initially achieved high levels of metal removal (between 75 and 99.9% Zn, Pb, and Cd removed); however, all of the materials were saturated with Zn after less than 200 L of water had been treated. Metal sorption ranged from 21.4 mg/g Zn for the peat fly ash to 0.0015 mg/g Cd for the compost and BOS/BFS slag. The results of the pilot-scale field trials can be scaled to demonstrate that a modest-sized fly ash treatment cell (2.6 ? 2.6 ? 1 m) in size would be sufficient to remove 90% of the total metal load (Pb, Zn, and Cd) from this 10 L/min mine water discharge for a 1 year period. Importantly this research demonstrates that passive treatment for metal mine drainage can comply with water quality directives but cannot be considered a ?walk-away? solution; it requires modest (potentially annual) maintenance.Peer reviewe

Many abandoned mine sites in Cornwall, UK, are characterised by elevated concentrations of arsenic which can cause contamination of surrounding soil and water resources. Often these sites have important historical and cultural value that requires access to be maintained, despite the potential toxicity of As. In west Cornwall, the potential for As contamination has been recognized within the Industrial World Heritage site focused on the Mineral Tramway and mining sites mines in the Gwennap and Camborne mining districts. The major abandoned mine sites, arsenic calciner and milling sites along a proposed tourist route in this area have been assessed for As toxicity and bioavailability taking into account the proximity of footpaths to areas of potential contamination. Arsenic concentrations up to 3.3% were found in soils along the proposed footpaths and exposed mine spoil, with 55% of all total As values above the UK criteria for contaminated industrial soil of 640 mg/kg in surface soil. Using a Physiologically Based Extraction Test (PBET), the maximum amount of As observed to be bioavailable varied from 4 mg/kg through to a maximum of 9,000 mg/kg with a positive correlation between total As concentrations and bioavailable As concentrations. Mineralogical and selective extraction evaluation identified that the PBET-released As is not so much associated with total As concentrations, but is positively correlated to As held within the weak ‘ionic-held’ As, strongly adsorbed As, As associated with amorphous iron and calcium oxide phases, and poorly crystallized As(V) salts. The data reported here have been used to develop a risk assessment of the sites and propose management strategies to mitigate these risks.

No abstract

The increase in terminal velocity of large water drops in the presence of vertical electric fields has been measured in a wind tunnel and found to be negligible (0.1 m sec−1 change per 1 kv cm−1 field increment). Preliminary work indicates decreases of similar magnitude in oblique electric fields.