Alumina and Bauxite: Novel Processes and Bauxite Residue
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Anne Duncan, Hatch
Tuesday 8:30 AM
March 16, 2021
Room: RM 29
Location: TMS2021 Virtual
8:30 AM Invited
Revisiting Alternative Smelter Grade Alumina Production Processes: Andrey Panov1; Alexander Senyuta1; Andrey Smirnov1; 1RUSAL Engineering and Technological Center
In recent decades there is an increasing interest for alternative processes for smelter grade alumina production driven by intentions of producers to save on transportation costs of bauxite and alumina, to reduce the CO2 footprint and to solve the issue of alkaline bauxite residue generated currently by the Bayer process. Besides, new technologies can use high-silica feedstock located close to aluminum smelters, like kaolin clays or fly ash. The presentation shows the benefits and prospects of implementation of the new technologies in the world, and status of the development. One of such examples is UC RUSAL’s development of the alumochloride technology to produce smelter grade alumina from local kaolin feedstock. The technology and the quality of SGA were tested and approved at the mini-plant scale, and a pilot unit has already been designed. The main benefits comprise low operational costs and flexibility in selecting the raw material as it enables the use of virtually inexhaustible sources of aluminum bearing raw material, i.e. aluminum silicate ores, and thus allows reducing the transport and logistics costs. There are also other methods to produce alumina including the Pedersen process, which is currently being revisited under the Ensureal project funded under the EU Horizon 2020 program.
9:05 AM
Silicon Rich Iron Alloy from Bauxite Residue: Halvor Dalaker1; Casper van der Eijk1; 1Sintef
While the 20-50% of iron oxide contained in bauxite residue (BR) can be recovered as pig iron, this is not economically viable due to the low market price of pig iron. Silicon rich iron alloys have higher value than pig iron, and BR contains from 5-15% silicon oxide. To increase the value of the produced metal, it is attempted to maximise the silicon content of iron alloys produced from BR. This option has been explored with experiments and thermodynamic models (FactSage) focusing on BR from one legacy site and 3 alumina refineries, obtaining a maximum of 17 wt% Si in experimentally produced alloys. The paper discusses the thermodynamics around the results, looking at the influence of slag viscosity.
9:25 AM
Bauxite Residue Neutralization Potential Using Biogenic Sulfuric and Citric Acids: Patricia Silva1; Roseanne Holanda1; Andre Carmo1; Fernando Gomes1; Raphael Costa2; Caio Melo2; Adriano Lucheta1; Marcelo Montini2; 1SENAI Innovation Institute for Mineral Technologies; 2Norsk Hydro Brasil
Attenuation of high alkalinity and sodicity in bauxite residue (BR) is a fundamental requirement for its use in alternative large-scale applications, such as agriculture and building materials. The high chemical neutralization cost is one of the main limitations for broad BR use. This study applied a biotechnological approach to ameliorate BR characteristics by using ex-situ biogenic sulfuric (H2SO4) and citric (C6H8O7) acids produced by Acidithiobacillus thiooxidans and Aspergillus niger, respectively, in comparison with their analytical ACS grade equivalents. Batch tests containing BR (20% w / v) mixed with acidic solutions were conducted followed by solid (XRD, XRF, SEM) and liquid (pH, EC, ICP-OES) phases evaluation. Results showed that the biogenic H2SO4 was more effective for the BR partial pH neutralization (final pH ~8) and sodicity decreasing (35% reduction) when compared with biogenic C6H8O7 and H2SO4 ACS grade, indicating the potential of this biotechnological route for the BR amelioration prior use.
9:45 AM
Gravity Methods Applied to Bauxite Residue for Mineral Pre-concentration: Paula Araújo1; Patricia Silva1; Andre Carmo1; Marcus Vinícius Gonçalves2; Raphael Costa3; Caio Melo3; Adriano Lucheta1; Marcelo Montini3; 1SENAI Innovation Institute for Mineral Technologies; 2SENAI Innvation Institute for Mineral Processing; 3Norsk Hydro Brasil
Bauxite residue (BR) has being extensively investigated as a secondary source of raw materials such as iron, titanium, and rare earth elements (REE). However, the enrichment and recovery of particular elements are not a straightforward process, especially when it is present in the fine particle’s fractions (<100 μm). BR fines usually contains Fe, Si, Ti, Al, Ca, Na, Zr, V, among other elements, locked up into complex mineral phases. Hydrometallurgical and pyrometallurgical routes used for BR beneficiation have high recovery but prohibitive costs. On the other hand, gravity concentration methods are one of the oldest and economical ore processing operations, but its efficiency is not clear when tailings are handled. This work made an exploratory investigation considering three gravity devices - shaking table, spiral and centrifugal concentrators handling RB fines. The goal was to evaluate gravimetric methods as a pre-concentration step to improve BR interesting elements grade prior extraction process.