Cradle to cradle solution to problematic waste materials from mine and coal power station: Acid mine drainage, coal fly ash and carbon dioxide

Abstract

During mining, minerals such as FeS2 are exposed to O2, H2O, and microorganisms resulting in the oxidation and generation of acidic water. The acidic water causes chemical weathering of the adjacent rocks and leaching of potentially toxic metals and the resultant water is often termed acid mine drainage (AMD). Coal power stations produce an alkaline aluminosilicate waste material called fly ash (CFA). Modern waste resource management emphasises finding useful applications of waste generated from processes to achieve a green economy. CFA was, with additional lime and Al(OH)3 used to treat AMD at a 80L pilot scale. Most of the physical and chemical parameters of the treated water were within South African target water quality range (TWQR) for irrigation. Carbonation of the water after treatment with CFA, lime and Al(OH)3 produced water that was within the TWQR for irrigation with respect to all parameters and resulted in the sequestration of 15–123L of CO2 per 80 L of AMD treated at standard ambient temperature and pressure. CO2 reacted with Ca ions in the water and solid residues to form CaCO3. Carbonation improves the ease of disposal of CFA, the AMD quality as well as reducing the amount of CO2 emissions by coal power plants through mineral carbonation. The solid residues from the overall process are suitable for the back filling of mine voids thereby preventing AMD generation by excluding air and water. This is an innovative cradle to cradle solution for the disposal of waste materials from coal mines and power stations.