Extraction of Al and Na from red mud by magnesium oxide sodium carbonate sinter process

Abstract

The sintering of Bayer’s process waste residue: Red mud along with magnesium oxide and sodium carbonate is adopted for recovery of aluminum and sodium followed by leaching. This is facilitated by the high temperature reaction of magnesium oxide sodium carbonate and DSP in the red mud to produce an insoluble dimagnesium silicate, magnesium ferrite, magnesium titanate and a soluble sodium aluminate. A variation of the red mud magnesium oxide sodium carbonate sinter process using half the magnesium oxide of existing methods has been investigated. The magnesium to silicon ratio was reduced from 2 to 1 producing a sodium magnesium silicate (Na₂Mg₂SiO₄) rather than the dimagnesium silicate (Mg₂SiO₄) insoluble phase produced in the existing above sinter method. Synthetic red mud magnesium oxide sodium carbonate sinter products were investigated to understand the phases produced during sintering at varying temperatures and the chemistry of extraction. The target phases and morphological behaviors were seen in XRD and SEM and the highest extractions were produced from a sinter temperature of 900°C for 4 h. A two-stage (105°C / 60 min, 105°C / 240 min) water or caustic leaching process was found to be most effective for extraction. Sodium and aluminum extractions were 99 and 98.7% respectively. The experimental method devised was then used to treat red mud and the target phases were produced. An extraction of sodium and aluminum respectively was achieved. Silicon extractions were below 2%.

Key word: Red mud, sinter, leaching, extraction.