Reduction of ash and sulfur contents of low-rank Turkish semicoked lignite by high intensity dry magnetic separation

A combination of semicoking followed by a permanent roll magnetic separator (PERMROLL) has been used for the upgrading of a Turkish low-rank lignitic coal. The lignite samples were subjected to a low temperature carbonization process at 600 °C and then upgraded by the PERMROLL. Under optimum conditions, carbonization of lignite particles in -9+0.5 mm size range which contained 12.18 wt.% ash and 3.38 wt.% total sulfur produced a product containing 25.90wt.% ash and 3.19wt.% total sulfur all reported on a dry basis. Dry magnetic separation employing the PERMROLL upgraded this product to 11.20wt.% ash and 1.40wt.% total sulfur with a recovery of 31.52wt.% based on feed to the carbonization process. The mechanism of desulfurization is discussed on the basis of the presence of iron in the coal that complexes with sulfur to form a magnetic product upon semicoking and its subsequent removal by magnetic separation.