Statistical modelling of sulphuric acid leaching of TiO2, Fe2O3 and Al2O3 from red mud

Sulphuric acid leaching of Ti, At and Fe (which make up the 'Red mud' waste from Etibank Seydisehir Aluminium Plants, Turkey), has been studied using statistically designed experiments. The effects of five factors, namely: temperature, leaching time, acid normality, solid-to-liquid ratio, stirring rate on leaching yield of TiO2, Al2O3 and Fe2O3, have been investigated. Experiments have been planned by factorial design and orthogonal central composite design methods. The following models have been obtained by means of variance analysis at 92.5% confidence level. Y-TiO2 = 64.1087 - 5.2264 X-1 + 22.6566 X-2 - 1.3085 X-3 - 9.2821 X-4 + 1.4675 X-5 -7.0354 X-1(2) - 5.8515 X-2(2) + 1.2055 X-4(2) + 8.9975 X1X2 - 2.6113 X1X4 - 1.7837 X1X5 + 1.5350 X2X3 + 1.9550 X2X5 + 2.9287 X3X4 - 1.3838 X3X5 Y-Fe2O3 = 13.2686 + 8.9664 X-1 + 16.7172 X-2 - 10.2664 X-4 + 3.2134 X-5 + 6.9270 X-2(2) + 4.2107 X-4(2) + 9.9694 X1X2 - 4.7119 X1X4 - 7.6144 X2X4 + 2.5906 X2X5 - 5.5756 X3X5 Y-Al2O3 = 68.2351 + 8.4249 X-1 + 2.1984 X-2 + 1.9705 X-3 + 4.0853 X-5 + 3.9794 X-1(2) + 4.2312 X1X2 - 2.7225 X1X4 + 3.1000 X2X3 + 2.5750 X2X5 where X-1 is temperature, X-2 is acid concentration, X-3 is stirring speed, X-4 is solid-to-liquid ratio, and X-5 is reaction time.