Mobility of elements released from coal during CO2 sequestration

A key greenhouse emission reduction strategy is to sequestrate CO2 in the subsurface by injecting it into coal seams. We investigated the injection of CO2 into coal seams using static batch experiments conducted under similar temperature and pressure conditions to that of the formation from which the coal samples were originally obtained, in an effort to understand the mobilisation of elements released from the coal. Anthracite and high volatile bituminous coal samples (4-8 mm in size) were exposed to a solution of supercritical CO2 (ScCO2) and water at a temperature of approximately 40 degrees C and a pressure of 9.8 MPa. The results obtained indicate that elements show different mobilities after exposure to the ScCO2-H2O solution. Their mobilities are mainly influenced by the occurrence of the elements in the coal minerals. It was found that the mobilisation of elements associated with carbonate minerals was greater than that of elements associated with sulphide and sulphate minerals; which was in turn greater than that of elements associated with silicate minerals. The results also show that close attention should be paid to the potential environmental hazards that might arise if the elements are released into groundwater systems during the CO2 sequestration process.