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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.

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The behavior of platinum group metals (PGMs) during their recovery with smelting of spent automotive ceramic catalysts powder in the presence of metallic copper at elevated temperatures is studied in this paper. Two different metal recovery mechanisms proved to be active in this process: 1) Wetting of micro-dispersed particulates of PGMs in the slag by molten copper, formation of copper droplets with attracted microparticles of PGMs and settling of the molten droplets of Cu-PGMs alloy through the slag at the bottom of the crucible ("wetting"); 2) Settling of solid PGMs microparticles through the molten slag and formation of a solid solution with the molten copper at the bottom of the crucible ("settling"). The PGMs are divided in two separate groups. Platinum has under the same experimental conditions substantially higher recovery in comparison with the palladium and rhodium that behave as a group having almost identical recoveries. The heavier Pt is recovered primarily in big extent (almost 88%) through the "settling" mechanism while Pd and Rh are recovered following a more balanced mixture of both mechanisms with the "settling" one to be again more important (66% for Pd and 57% for Rh). Slag viscosity is the most important physical property and the design of an appropriate slag system is the most important issue in developing an efficient process for the recovery of PGMs.

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