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

Abstract

Sulphuric acid leaching of Ti, Al and Fe (which make up the 'Red mud' waste from Etibank Seydişehir 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 TiO<inf>2</inf>, Al<inf>2</inf>O<inf>3</inf> and Fe<inf>2</inf>O<inf>3</inf>, 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<inf>TiO2</inf> = 64.1087 - 5.2264 X<inf>1</inf> + 22.6566 X<inf>2</inf> - 1.3085 X<inf>3</inf> - 9.2821 X<inf>4</inf> + 1.4675 X<inf>5</inf> - 7.0354 X<inf>1</inf>2 - 5.8515 X<inf>2</inf>2 + 1.2055 X<inf>4</inf>2 + 8.9975 X<inf>1</inf> X<inf>2</inf> - 2.6113 X<inf>1</inf> X<inf>4</inf> - 1.7837 X<inf>1</inf> X<inf>5</inf> + 1.5350 X<inf>2</inf> X<inf>3</inf> + 1.9550 X<inf>2</inf> X<inf>5</inf> + 2.9287 X<inf>3</inf> X<inf>4</inf> - 1.3838 X<inf>3</inf> X<inf>5</inf> • Y<inf>Fe2O3</inf> = 13.2686 + 8.9664 X<inf>1</inf> + 16.7172 X<inf>2</inf> - 10.2664 X<inf>4</inf> + 3.2134 X<inf>5</inf> + 6.9270 X<inf>2</inf>2 + 4.2107 X<inf>4</inf>2 + 9.9694 X<inf>1</inf> X<inf>2</inf> - 4.7119 X<inf>1</inf> X<inf>4</inf> - 7.6144 X<inf>2</inf> X<inf>4</inf> + 2.5906 X<inf>2</inf> X<inf>5</inf> - 5.5756 X<inf>3</inf> X<inf>5</inf> • Y<inf>Al2O3</inf> = 68.2351 + 8.4249 X<inf>1</inf> + 2.1984 X<inf>2</inf> + 1.9705 X<inf>3</inf> + 4.0853 X<inf>5</inf> + 3.9794 X<inf>1</inf>2 + 4.2312 X<inf>1</inf> X<inf>2</inf> - 2.7225 X<inf>1</inf> X<inf>4</inf> + 3.1000 X<inf>2</inf> X<inf>3</inf> + 2.5750 X<inf>2</inf> X<inf>5</inf> where X<inf>1</inf> is temperature, X<inf>2</inf> is acid concentration, X<inf>3</inf> is stirring speed, X<inf>4</inf> is solid-to-liquid ratio, and X<inf>5</inf> is reaction time. © Institution of Chemical Engineers. © 2018 Elsevier B.V., All rights reserved.