Recovery of Al and Na Values from Red Mud by BaO‐Na₂CO₃ Sinter Process

Abstract

The red mud BaO-Na2CO3sinter process can be used in combination with the Bayer process to recover sodium and aluminium from the red mud waste and direct it back to the process stream. This is facilitated by the high temperature reaction of BaO-Na2CO3and De-silication product (Sodalite) (DSP) in the red mud to produce an insoluble di-barium silicate, barium titanate, barium ferrite and a soluble sodium aluminate. A variation of the red mud BaO-Na2CO3sintering process using half the barium oxide of existing methods has been investigated. The barium to silicon ratio was reduced from 2 to 1 producing a sodium barium silicate (Na2BaSiO4) rather than the di-barium silicate (Ba2SiO4) insoluble phase produced in the existing BaO-Na2CO3sinter method. Synthetic BaO-Na2CO3sinter products were investigated to understand the phases produced during sintering at varying temperatures and the chemistry of extraction. The target phases and morphological behaviors of sinter products were seen in XRD and SEM and the highest extractions were produced from a sinter temperature of 1000 °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 aluminium extractions were 99% and 99.5% respectively. The experimental method devised was then used to treat red mud and the target phases were produced. An extraction of sodium and aluminium of 94% and 87% respectively was achieved. Silicon extractions were below 2%. Production benefits include sodium hydroxide savings, liquor burning, increased aluminium extraction and reduced cost of waste handling.

Towards zero-waste valorisation of rare-earth-containing industrial process residues: a critical review

“…The "MgO-Na 2 CO 3 sinter process" involves adding MgO to bauxite residue and sintering at 900-1100 °C (Meher et al, 2011a). A variant of this method is the "BaO-Na 2 CO 3 sinter process", which also achieves high alumina recovery as dissolved sodium aluminates and low silicon dissolution (Meher et al, 2011b). An alternative to the sintering process is the Orbite process which uses high temperature HCl leaching to dissolve aluminium and iron as chlorides (Boudreault et al, 2013b).…”

Red Mud as a Secondary Resource of Low-Grade Iron: A Global Perspective

“…Zhang et al [83,84] were able to recover alumina by forming andradite-grossular hydrogarnet in a hydrothermal process. The pyrometallurgical recovery involves sintering with soda (25-70 wt.%) and lime (10-50 wt.%) in the temperature range 1000-1050 • C to form water-soluble sodium aluminate, followed by leaching in water/NaOH (1.5-2 M) achieving up to 76-90% aluminum extraction [85,86]. However, some of these processing methods could be quite expensive, time consuming and produce secondary waste products as well.…”

Sintering Optimisation and Recovery of Aluminum and Sodium from Greek Bauxite Residue

“…Fe 2 O 3 + 3C → 2Fe + 3CO (5) The addition of lime, and subsequently exploration of other metal oxides into the sintering process through Meher and coworkers' efforts [31,32,39,40], focuses on capturing the free silica during sintering (Reaction (4)). Adding metallurgical coke into the system, such as Reaction (5), can encourage the recovery of iron downstream by pre-reducing hematite and other iron species.…”

“…XRD mineral identifications in Figure 19 indicates that batiferrite (Ba(Fe10Ti2)O19), ankangite (BaTi8O16) and trasicite (Ba9Fe2Ti2Si12O3(OH)) were the favorable phases that were formed experimentally, indicating that experimentally barium prefers to react with Unlike calcium-added sinter system, where the addition of excess causes potential unwanted formation of grossular-type products that inhibit aluminum recovery, barium preferentially reacts with calcium during the sintering, leaving aluminum component to bind with sodium instead. Meher et al reduced the amount of barium-to-silica mol ratio requirements to 1, and encouraging the formation of sodium barium silicate to allow for sodium and aluminum extraction (99% recovery) with decreased BaO reagent usage [39].…”