Lysimeter study of water and salt dynamics in a saline metallurgical waste

In Germany, mounds of solid wastes (mainly rock salt, NaCl) from potash mining produce large amounts of briny runoff which are frequently conveyed into surface waters. This study was conducted to evaluate a saline, fine-grained aluminum recycling by-product as soil substitute in a surface barrier over potash mining waste mounds. Four free-drainage lysimeters were monitored for three years under field conditions. Two lysimeters were filled with a by-product from aluminum recycling, and the other two with a mixture of this by-product and a coal combustion waste. Precipitation, evaporation, discharge, as well as pressure head in three depths were measured continuously. Electrical conductivity in the discharge and in suction cup solutions from four depths was used to monitor desalinization. It was found that mean annual discharge from the pure metallurgical waste and from the mixture was 39% and 24% of rainfall. Materials were sufficiently leached to support growth of ryegrass (Lolium perenne, L.) after 444 (pure metallurgical waste) and 281 mm (mix) of seepage, or 28 months of lysimeter operation. We conclude that the mix seems the better material for an engineered mine-waste surface barrier.