Field trial of an ion exchange based metal removal technology in the treatment of mine waters

A pilot scale field trial for a novel metal removal technology in the treatment of mine waters was performed using mine water from White Tip, part of the former Snailbeach lead mine in Shropshire, United Kingdom (UK). The water is circum-neutral pH and contains elevated zinc (Zn), lead (Pb) and cadmium (Cd). The novel treatment process is based on ion exchange (IE) using a bespoke mesh in a rotating disc reactor. Effects of process parameters such as regeneration of mesh, residence time (RT) and rotation speed (RS) of the discs were investigated. Treatment performance of the system was consistent for the removal of Zn and Pb whereas for Cd it was more variable. The order of removal efficiencies was Pb (75.04%) > Zn (64.18%) > Cd (22.37%). Accordingly, 4.15 kg of Zn, 5.22 g of Pb and 5.55 g Cd were removed from 131.46 m3 of mine water in 170 days. Amongst the other metals / metalloids removed by the system include iron (Fe), aluminium (Al), manganese (Mn), copper (Cu), barium (Ba), arsenic (As), nickel (Ni), boron (B), chromium (Cr) and small amounts of sodium (Na), potassium (K) and strontium (Sr). Similarly, non-metallic water quality parameters removed by the system include acidity, suspended solids (SS), alkalinity and small amounts of nitrate (NO3-N) and total anions. The system generated a small amount of ammoniacal nitrogen (NH3-N), sulfate (SO4-S) and hardness. An average rise of pH by ~0.5unit in treated water was observed. Performance of the treatment system was not significantly affected by the regeneration of the mesh and RS of the discs. The treatment process was not affected by the temperature variations in the range of 0.7°C to 20°C. Maximum removals of metals were observed when RT≥1.33 hours.