Among other methods that have been suggested to reduce impurities include, the contacting of streams of ore slurries simultaneously with oxidising and reducing agents to dissolve the aluminium content (Choi et al. 1982), the use of fluorosilicic acid (Harel & Shapira, 2006 and Russ & Smith, 1985), and the application of pH control after digestion with various acids or acid mixtures to selectively precipitate iron and aluminium trihydrate in separate steps (Barnett and Mezner, 2002). However, most of these methods have not yet been utilized industrially, presumably due to engineering difficulties or high cost.