Reclamation of abandoned coal mine wastes using lime cake by-products in Korea.

Abstract:

In Korea, there are hundreds of abandoned and closed coal mines in the steep mountain valleys due to economic downturns in the mining industry. Enormous amounts of coal waste from these mines were dumped on the slopes, which cause sediment and acid mine drainage to be discharged directly into streams.

A limestone slurry by-product (lime cake), which is produced during the manufacture of soda ash, was investigated for its potential use in reclaiming the coal waste. The lime cake is fine grained, has low hydraulic conductivities (10 -8 to 10 - 9 cm sec -1 ), high pH, high electrical conductivity due to the presence of CaO, MgO, and CaCl 2 as major components, and trace amounts of heavy metals.A field experiment was conducted ; each plot was 20 x 5 m in size on a 56% slope. Treatments included a control (waste only), lime (CaCO 3), and lime cake. The lime requirement (LR) of the coal waste to pH 7.0 was determined, and treatments consisted of adding 100%, 50%, and 25% of the LR.

The lime cake and lime were applied in either a layer between the coal waste and topsoil or mixed into the topsoil and coal waste. Each plot was hydroseeded with grasses, and planted with trees. In each plot, soils, surface runoff, and subsurface water were collected and analyzed, and plant cover was measured.The lime cake treatments increased the pH of the coal waste from 3.5 to 6, and neutralized the pH of the runoff and leachate of the coal waste from 4.3 to 6.7. Moreover, the surface cover of seeded species was significantly increased; sufficient acidity in the coal waste was neutralized in the 25% LR plots to allow seed germination.