γ-Radiolytic desulphurisation of some high-sulphur Indian coals catalytically accelerated by MnO 2

Abstract

γ-Radiolysis of acidic aqueous coal slurries is a novel and effective method for the simultaneous oxidative desulphurisation and demineralisation of high-sulphur coals. This method is capable to selectively remove the inorganic and organic forms of sulphur simultaneously through the in situ-generated H 2O 2 and other radiolytic products. In effect, there is neither any appreciable degradation of coal matrix nor any loss in the caking property and volatile matter content of the coals after the removal of sulphur. However, significant removals of sulphur and mineral matter are effected at rather high γ-dose (175×10 4 Gy or so). Therefore, for the process to be economically viable and commercially adaptable, the applied γ-dose needs to be somehow substantially brought down, at which the same level of desulphurisation could be achieved. Catalytically, accelerating the radiolysis process is one such possibility to effect the desulphurisation step at a low γ-dose. Reported in this paper are the results of investigations on the desulphurisation and demineralisation of high-sulphur (sulphur content in the range 3–5.5%) Churphy, Chalang and Bapung coals of Meghalaya by γ-radiolytic process catalysed by MnO 2. The maximum removal of total sulphur (15.6%, 30.0% and 29.8%) at 30×10 4 Gy in the presence of MnO 2 and the simultaneous removal of mineral matter (20.0% and 18.5% from Churphy and Chalang coals at 30×10 4 Gy and 12.0% from Bapung coal at 45×10 4 Gy) are at par with removals at 175×10 4 Gy without MnO 2, which has been attributed to MnO 2 catalytically accelerating the radiolytic process via the formation of highly reactive MnO under the action of γ-rays. All the other features of non-catalysed radiolytic desulphurisation such as stabilisation of the slurry and coal not becoming radioactive during irradiation, increase in the heating value, improvement in the caking property, no appreciable degradation of coal matrix after removal of sulphur from the coals remain the same.