Testing Iron Removal in a Trifurcated Pilot Plant for Passive Treatment of Circum-neutral Ferruginous Mine Water

摘要

A trifurcated pilot plant was implemented at an abandoned mine site for passive treatment of circum-neutral, ferruginous seepage water. Purpose of the composite system was to investigate the suitability of serially connected settling ponds, wetlands and sediment filters for passive iron removal in accordance with the strict compliance limit of 1 mg/L. After demonstrating reproducibility at equal flow rates in the three identical lines, hydraulic variation was used to develop comparison data for sizing of a full scale passive system. The multi-stage setup proved successful, reducing relatively low iron concentrations of app. 10 mg/L in the influent to compliance level in the effluent. System monitoring provided evidence that physico-chemical removal of suspended ferric hydroxides is a critical step in natural iron removal and may even become the rate-determining step for thoroughly oxygenated, circum-neutral mine waters. Area-adjusted removal rates were relatively low because of low hydraulic loading. Dependence of both treatment efficiency and area-adjusted removal on hydraulic loading was demonstrated during the variation period, showing direct and inverse relationships at graded flow rates, respectively. Ultimately, a more extensive and higher resolution database is necessary for pilot plant upscaling to full scale.