Estimating the longevity of limestone drains in treating acid mine drainage containing high concentrations of iron

摘要: Abstract Limestone drains are often implemented in the treatment of acid mine drainage (AMD), but when AMD contains high levels dissolved Fe their lifetime is dependent on rate precipitation hydroxide limestone surface. This study used a small-scale laboratory experiment to define longevity drain by determining thickness coating encapsulating particles system lost its maximum neutralising potential. Synthetic (100 mg/L Fe, pH 4–4.8) was pumped through column containing for 1110 h, effluent had dropped from 6.45–4.9. The decline neutralisation during due formation coatings grains. These composed lepidocrocite/goethite three distinct layers: an initial thick porous orange layer, overlain dense dark brown crust, succeeded layer loosely-bound, globules. After 744 h, marked increase occurred, and regarded as having effectively failed. At this time crust encapsulated grains, forming diffusion barrier that slowed down dissolution. Between substrate 60 μm wide void, so agitation sample would readily remove In experimental system, sufficient precipitate cause defined by: t ( years ) = surface area m 2 × 4.4 fraction retained [ + ] mg / L flowrate h . need be replaced or mechanically agitated coating, allow continue functioning at Application formula field situation shows even influent concentrations moderately high, will function well one several years. Thus, passive systems can concentration considerably greater than 1 mg/L, currently recommended limit, particularly given precipitates armouring grains may loosely bound relatively easily dislodged. Therefore, more widely applicable presently realised.