1. Alexis, J., 1980. Cleaning coal and refuse fines with the Humphreys spiral concentrators. Mining Engineering, Aug.: 1224
2. Anastassakis, G.N., 2004. Beneficiation of the Greek lignites. Coal Preparation, 24:19
3. Burt, R.O., 1984. Gravity concentration technology. Elsevier, Amsterdam
4. Chammas, E.P., Hondrellis, E., Iskou, H., Tamam, D., Anastassakis, G., Frangiskos, A.Z., and Frogoudakis, E., 1999. A study on the beneficiation of lignite of Servia area (Kozani, Northern Greece) by heavy media separation. Mineral Wealth J., 112: 17 (In Greek with extended English summary)
5. Chammas, E.P., Hondrellis, E., Anastassakis, G., and Frangiskos, A.Z., 2000. A study on the beneficiation of coal from Servia area (Kozani, Northern Greece) by jigging and tabling. Mineral Wealth J., 115: 17 (In Greek with extended English summary)