I. Giannopoulou

UTILIZATION OF ALUMINA RED MUD FOR SYNTHESIS OF INORGANIC POLYMERIC MATERIALS

Red mud is a residue coming from the metallurgical treatment of bauxite with the Bayer process. Million of tons of red mud are produced annually worldwide and disposed of on land, degrading vast areas. Therefore, red mud utilization is a first-priority issue for any alumina plant. In the present work, the potential use of red mud for synthesis of inorganic polymeric materials through geopolymerization process was studied. The main focus was the production of inorganic polymeric materials that could be used in the construction sector as artificial structural elements such as massive bricks. The geopolymerization process involves a chemical reaction between red mud and alkali metal silicate solution under highly alkaline conditions. The product of this reaction is an amorphous to semi-crystalline polymeric structure, which binds the individual particles of red mud transforming the initial granular material to a compact and strong one. The effect of main synthesis parameters—like solid-to-liquid ratio, caustic soda as well as soluble silica concentrations, and metakaolin addition—on the properties of red mud-based inorganic polymeric materials was investigated. The results showed that the produced materials have high compressive strength, very low water absorption, satisfactory apparent density, and excellent fire resistance. Therefore, this work proved that the red mud-based inorganic polymeric materials have promising properties and have the potential to be used as artificial structural elements in the construction sector.

Use of Ionic Liquids as Innovative Solvents in Primary Aluminum Production

Today, the primary aluminum production is based on two processes: (a) the Bayer process and (b) the Hall–Heroult process. Both processes deal with several economic and environmental drawbacks. The production of aluminum is an energy intensive process, consuming 53–61 GJ/t of aluminum, while huge amount of red mud and gaseous emissions are inevitably produced through the whole process. The utilization of a new family of solvents called ionic liquids (ILs) in the primary aluminum production is the subject of this paper, which examines the possibility of dissolving metallurgical alumina, hydrated alumina, and bauxites in 1-ethyl-3-methyl-imidazolium hydrogen sulfate ([Emim]HSO4). The results show that hydrated alumina can be dissolved relatively easily at 210°C, forming a melt that contains 9% w/w of dissolved alumina, which is higher than the alumina content in Hall–Heroult melts. Bauxites can also be directly dissolved in this IL with iron presenting higher dissolution than aluminum, while silicon dissolution is negligible.

ELECTRODEPOSITION OF RARE EARTH METALS IN IONIC LIQUIDS

In this paper the available literature on the application of ionic liquids in rare earth metals electrodeposition, is briefly discussed and the main electrochemical properties of ionic liquids, in relation with such applications, are presented. In addition, the results of a preliminary investigation for the suitability of pyrrolidinium‐based ionic liquids on the electrodeposition of lanthanum are presented.

VALORIZATION OF ALUMINA RED MUD FOR PRODUCTION OF GEOPOLYMERIC BRICKS AND TILES

The production of red mud in almost 1 to 1 mass ratio in relation to metallurgical alumina renders its valorization a first-priority issue for any alumina plant. The huge amount of red mud produced annually all over the world renders necessary the development of several valorization alternatives so that each alumina plant to have the ability to choose among them the ones that are more proper taking into account geographical and economic parameters. The use of red mud as a filler in production of geopolymeric massive bricks and tiles seems to be a technically feasible valorization alternative. The red mud/metakaolin and the red mud/slag geopolymeric systems proved to be effective and the materials produced have promising mechanical, satisfactory physical and excellent thermophysical properties.