An attempt has been made in this paper to investigate effect of collector type, particle size distribution, collector dosage, air flow rate, pulp density and wash water rate parameters on modified flotation parameters on sphalerite flotation in a flotation column. In the experimental studies, the fractional recoveries after 0.5, 1, 2, 3, 5, 10 and 20min of flotation time were fitted to first-order kinetic model R=R-infinity[1 - exp(-kt)], where R is recovery at t time, R-infinity is ultimate recovery and k is the first-order rate constant was used to draw the time-recovery curves. Two parameters, the ultimate recovery (R.) and first-order rate constant (k), were then obtained from the model to fit an experimental time-recovery curve. A modified flotation rate constant (K-m) defined as product of R-infinity and k, i.e., K-m = R(infinity)k, and selectivity index (SI) defined as the ratio of the modified rate constant of mineral I to the modified rate constant of mineral II (SI = K. of mineral I/K-m of mineral II), which could be collectively called "modified flotation parameters", were calculated for each test and it was used to measure of flotation separation selectivity of sphalerite over pyrite. Timed batch tests on ground ore using a pilot flotation column and subsequent recovery and grade of experimental data and modified flotation parameters indicated that the optimum parameters are as follows: Dithiophospates collector type, finer particle size distribution (d(80) = 0. 125 mm), low collector dosage (500 g/t), low air flow rate (1.30 cm/s), high pulp density (20% solids) and high wash water rate (0.5 L/min). (c) 2006 Elsevier B.V. All rights reserved.