In this study, a three-level Box-Behnken factorial design combined with Response Surface Methodology (RSM) for modeling of process parameters of spiral concentrator for the separation of ultrafine chromite has been developed. The three significant operational parameters of spiral concentrator, such as feed rate (m(3)/h), feed pulp density (% solids by wt.), splitter position (radial distance from the central axis in cm) were considered for the investigation. The obtained results were evaluated with the Box-Behnken factorial design, RSM and also Quadratic Programming (QP). Second-order response functions were produced for Cr2O3 in terms of grade (%) and recovery (%) of the concentrate fraction. Taking advantage of the QP, it was observed that maximum grade of 51.05% Cr2O3 achieved at the feed rate of 1.2 m(3)/h, feed pulp density of 14.81% solids by wt, and splitter position of 12 cm. Similarly, maximum Cr2O3 recovery of 46.73% can be achieved at the same feed rate, feed pulp density of 10% solids by wt. and 16 cm of splitter position. Predicted values of responses obtained using model equations were in good agreement with the experimental values. The influence of the process variables of the spiral concentrator on grade and recovery of concentrate fraction was presented and discussed. (C) 2012 Elsevier B.V. All rights reserved.