Flotation tests of synthetic mixtures of celestite (SrSO(4)) and calcite (CaCO(3)) minerals using sodium dodecyl sulfonate as collector were carried out using a factorial experimental design 2(3). The independent experimental variables included celestite grade in the feed (50% and 90% SrSO(4)), conditioning pH (6.5 and 9) and sodium silicate depressant concentration (10(-5) and 10(-3) M). All experiments were performed at a constant collector concentration (10(-4) M) and conditioning time of 15 min. The response variables were recovery and grade of SrSO(4) in the concentrate. The factors that had the greatest effect on the grade and recovery of celestite were the celestite grade in the feed (L) and the depressant concentration (C); also the combination of these factors significantly affected the response variables. The highest celestite yield (96% recovery, 98% grade) was obtained when a 90% of celestite grade in the feed was used. (C) 2003 Elsevier Science B.V. All rights reserved.