08 05 2018 Bauxite Residue Valorisation and Best

08. 05. 2018, Bauxite Residue Valorisation and Best Practices COMBINING PYROMETALLURGICAL CONDITIONING AND DRY ACID DIGESTION OF RED MUD FOR SELECTIVE Sc EXTRACTION AND Ti. O 2 ENRICHMENT IN MINERAL PHASE Gözde Alkan Bengi Yagmurlu, Yiqian Ma, Buhle Xakalashe, Srecko Stopic, Carsten Dittrich, Bernd Friedrich

Red mud as Sc an Ti source § § § High demand due to various application areas of Ti and Sc; the utilization of red mud as a secondary resource for those metals is promising Keep the Ti. O 2 undissolved in order to increase the value of the final mineral product aiming to be used in the construction applications Selectively leach Sc (wt. %) Fe 2 O 3 Bauxite residue 43. 5 Al 2 O 3 Ca. O Si. O 2 Ti. O 2 24 10. 2 5. 5 5. 6 Sc (mg/kg) 130 § Higher amounts of Fe also dissolve together with the desired elements during acidic leaching conditions ; decreased selectivity ; difficulties during the recovery step Sc by precipitation from the pregnant leaching solution (PLS) § EAF treatment; decrease Fe content may be promising Inherent from EAF process; enriched slags in terms of Si

Silica Gelation Problem § Acidic conditions (p. H < 7), soluble silica is found as silicic acid, Si(OH)4, § These monomers are connected to each other through Si-O-Si branches and form a polysilicic acid which would afterwards form colloids. § When these colloids are connected to each other with entrapped liquid inside, gelation takes place deteriorates sample handling and solid liquid separation

Dry Digestion: Theory [Voßenkaul, 2017] minimize water; increase ionic strength ; high energy level “Dry digestion” of ore concentrates to get filterable silica aggregates

Experimental Procedure Red mud Smelting in EAF Batch mass, 1. 5 kg red mud Lignite Coke (reductant), 0. 1 x red mud Lime (flux), 0. 2 x red mud (Basic slag) Silica (flux), 0. 2 x red mud (Acidic slag) 1 hour Basic slag Acidic slag Red mud wt. % Bauxite residue Basic Slag Acidic Slag Fe 2 O 3 Al 2 O 3 Ca. O Si. O 2 Ti. O 2 Sc (mg/kg) 43. 5 24 10. 2 5. 5 5. 6 130 1. 8 38. 3 43. 2 7. 6 170 1. 4 36. 8 15. 3 38 7. 3 170

Experimental Procedure: Dry Digestion Red mud/ Slags 98 wt. % concentrated H 2 SO 4 Mixing and reaction Treated concentrate Water Leaching Mixed slurry Ti-oxide enriched residue Vacuum Filtration Sc enriched solution

Dry Digestion: Red mud § All acid amounts in the case of dry digestion ended up very poor in Ti leaching; Implies a leach residue relatively enriched in terms of Ti. O 2 § The highest 20 m. L and lowest 5 m. L acid utilization affected all elements adversely, implying an optimum acid concentration § Sc leaching was improved to 50 % by dry digestion. § Dry digestion with all amounts of acid suppressed gelation

Dry Digestion : Basic Slag § § 94 % Sc leaching efficiency was achieved by direct leaching of that slag. Within a few hours; all PLS is gelated; necessitates utilization of dry digestion Introducing concentrated sulfuric acid decreased the Si dissolution up to almost 0 %. W. r. t. direct leaching, Sc leaching efficiency decreases with dry digestion. However, a reasonable amount was still achieved (>70 %) § Increased Sc in PLS and Ti in residue when compared with red mud

Investigation of Basic Slag perovksite Ca Al Ox

Dry Digestion Residue of Basic Slag 20 m. L acid Quartz Gypsum Sudden reaction of Ca with sulfate and quarz precipitation forms a boundary layer perovksite Ca Al Ox

Dry Digestion: Acidic Slag § Direct leaching resulted in rapid gelation, which is problematic for the handling of leachate and analyses § Introducing the dry digestion method at all acid concentrations inhibited Si dissolution rates and therefore the gelation § Very promising Sc leaching efficiencies around 70 %. § Removal of Fe may end up in the formation of free Sc surfaces and hence increase leaching rates importantly with respect to red mud § All dry digestion conditions ended in very low Ti extraction, lower than 10%.

Investigation of acidic slag Increased ionic strengths; precipitation of Si. O 2 ; acid cannot reach to Ti efficiently; the lowest dissolution. High Si Ca. Al. Si-ox Ti-ox

Effect on dry digestion on gelation tendencies Redmud Redmud Acidic Slag Acidic Slag Basic Slag Treatment Direct Leaching Dry Digestion (5 m. L) Dry Digestion (10 m. L) Dry Digestion (15 m. L) Dry Digestion (20 m. L) Direct Leaching Dry Digestion (5 m. L) Dry Digestion (10 m. L Dry Digestion (15 m. L Dry Digestion (20 m. L) Direct Leaching Dry Digestion (5 m. L) Dry Digestion (15 m. L Dry Digestion (20 m. L) Gelation behavior 2 -3 days No gelation Rapid gelation No gelation 2 -3 hours No gelation Dry digestion is proved to be efficient against gelation problem

Conslucion § Introducing the dry digestion method at all acid concentrations inhibited Si dissolution rates and therefore the gelation § Acidic slag and 15 m. L acid usage was the optimal condition for high Sc (70%) extraction and enriched mineral residue in terms of Ti-oxides § Removal of Fe may end up in the formation of free Sc surfaces and hence increase leaching rates importantly with respect to red mud Ø Various temperature and times will be applied to explain kinetics Ø Reaction mechanism will be investigated

08. 05. 2018, Bauxite Residue Valorisation and Best Practices Thank you for your attention!