The effect of anionic dispersants on grindability of different rank coals G. Atesok * , M. Ozer, F. Boylu, H. DV ncer Istanbul Technical University, Mining Faculty, Mining Engineering Department, Mineral Processing Division, 34469, Maslak, Istanbul Received 5 October 2004; received in revised form 1 May 2005; accepted 9 May 2005 Available online 8 August 2005 Abstract The effect of PSS (Sodium Polystyrene Sulphonate) and NSF (Naphthalene Sulphonate Formaldehyde Condensate) chemicals used to control the pulp rheology on the grindability of coals was studied. Zonguldak region bituminous coal and Istanbul region brown coal samples that high and low rank were used. Wet grinding tests with two coal samples were performed with or without PSS and NSF under constant grinding conditions: solid ratios ranged from 50% to 60% with 0–60 min grinding periods. In the present study, grinding conditions of coal with high pulp solid ratio were improved through the lowering of the viscosity of the coal by using the dispersing agents, PSS and NSF, during the grinding stage and evaluation were made by using the befficiency factorQ . It is possible to increase the amount of finely ground bituminous coal from Zonguldak by 20% and 16%, if optimum concentrations of PSS (0.3%) and NSF (0.7%) are used, respectively. Whereas, the increase in the case of finely ground lignite from Istanbul was 32% and 20%, respectively. D 2005 Published by Elsevier B.V. Keywords: grinding; dispersant; viscosity; energy; coal 1. Introduction Crushing and grinding are size reduction process in minerals processing circuits. Comminution processes consume approximately 50% of energy used in mineral processing (Austin et al., 1984). Energy con- sumption is about 5–20 kW h/ton of ore in fine grinding, however, this figure increases 20–100 kWh/ton of ore in ultra fine grinding. Therefore, it presents utmost importance to design size reduction especially grinding circuits (Austin et al., 1984). Pulp rheology plays a significant role in wet fine grinding processes and it affects the efficiency of grinding. Pulps show differences as pulp rheology depending on the different solids ratios (Ryncarz and Laskowski, 1977). Pulp viscosity, is especially, an important parameter in grinding. A number of investigators have studied the effect of pulp rheology in ball mill grinding for many years. Those investiga- tions especially focused on the grinding of ceramic 0301-7516/$ - see front matter D 2005 Published by Elsevier B.V. doi:10.1016/j.minpro.2005.06.004 * Corresponding author. Tel.: +90 0212 285 61 78; fax: +90 0212 285 61 28. E-mail address: atesok@itu.edu.tr (G. Atesok). Int. J. Miner. Process. 77 (2005) 199– 207 www.elsevier.com/locate/ijminpro