Demineralization Study of Low Grade Indian Coal by Aqueous Caustic Leaching
Low grade coal is the cheapest fossil fuel and widely distributed among all over the world. The use of low grade coal producing high ash that leading to environmental pollution due to generation of large amount of solids and gaseous pollutants. Physical beneficiation techniques method may not adequate remove the mineral matter from the coal, so to develop more efficient technologies for production of clean coal. An attempt has been made in the present work tries to upgrade the high ash (over 50 %) Indian coal from MCL (Mahanadi Coal Limited) Odisha, by using alkaline (NaOH) leaching. To study the effect of leaching parameters (time, temperature and concentration) and the particle size for that, the leaching experiments were conducted in a stainless steel batch reactor of 2.5 l capacity with controlled heating facility. Initially, the coal sample with mesh size (−16+100 mesh) was leached with 50–150 g/L NaOH solution at 100 °C for one hour. The maximum percent demineralization was 28 % obtained which at concentration of 100 g/L leaching and further, it decreases at higher concentration of alkali solution due to formation of insoluble sodium complex (sodium-aluminosilicate) which restrict demineralization. The variation of mineral composition in the coal due to the leaching effect of before and after treatment was done by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. The calorific or heating value of coal also improved by the leaching effect due to the removal non-carbonaceous mineral matter.