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Session Chairman: D.J. Donaldson, Consultant, 18160 Cottonwood Road #158, Sunriver, OR 97707
LAYERED DOUBLE HYDROXIDES FOR TREATMENT OF BAYER PROCESS LAKE WATER: A.J. Perrotta, Alcoa Technical Center, Alcoa Center, PA 15069-0001, F.S. Williams, Alcoa Alumina & Chemicals, L.L.C., Point Comfort, TX 77978-0101, L. Stonehouse, Alcoa of Australia, Kwinana R & D, Western Australia
Layered double hydroxides (LDHs) or the so-called anionic clays are the analog of the extensively studied family of cationic smectite clay minerals. The successful treatment of Bayer lake waters requires the removal of anions, both inorganic and organic; thus, the utilization of these anionic clays are ideally suited for this process. Insitu crystallization of layered double hydroxides have resulted in the removal of anions from Bayer lake water at two different refineries. Data on the removal of anions and their selectivity for intercalation in the layered double hydroxide indicates that the order of removal is CO3, C2O4, SO4. The monovalent chloride ion is least preferred but also can be extracted at significant levels at the higher level of treatment. The total organic carbon (TOC) is also lowered significantly. Measurements on succinate and malonate, both diacids, show a significant reduction at the higher levels of treatment. Successful regeneration of hydrocalumite show the thermal products of mayenite and calcium oxide which can then be recrystallized in lake water with concomitant further reduction in anion content. Additional experiments using ultrasonic radiation show an enhanced carbonate removal through increased calcite formation.
TECHNICAL PECULIARITIES AND VIABILITY OF HYDROTHERMAL TREATMENT OF RED MUD: Károly Solymár, Janos Steiner, József Zõldi, ALTAK Consulting Ltd. H-1125 Budapest, Zsolna u.31-33. Hungary
The regeneration of the chemically bound caustic soda and alumina from red mud was studied in laboratory and pilot plant scale between 260 and 320°C as a function of caustic soda concentration and final A/C ratio of the liquor, lime dosage and retention time. The pilot plant tests have been carried out in a tube digester facility of 3.0 m3/h designed by HUNGALU ALUTERV-FKI Ltd. and the test work was performed in cooperation with the team from the Almásfuzitó Alumina Refinery. At 260-320°C iron-rich iron-aluminium-hydrogarnets (Ca-Al-Fe-hydrosilicates) were formed allowing 90-95% Na2O and 20-70% Al2O3 content of red mud to be recovered as a function of the final A/C ratio with a specific lime consumption of 2.5-3.0 kg CaO/kg regenerated NaOH. The tube digester was found as an adequate equipment. The viability of the process highly depends on the price ratio of the caustic soda and burnt lime. The latest development in red mud separation also increased the viability of the hydrothermal treatment of red mud.
EXPLOITING THE RHEOLOGY OF BAUXITE RESIDUE IN TAILINGS DISPOSAL STRATEGIES: N. Pashias, D.V. Boger, Advanced Mineral Products Research Center and Department of Chemical Engineering, The University of Melbourne, Parkville, Victoria 3052, Australia
This paper demonstrates how an understanding of the complex rheological properties of bauxite residue suspensions can be exploited in the implementation of a dry disposal strategy. Comparative data are presented for bauxite residue generated from three refineries in Australia and from refineries in Jamaica, Suriname, and Brazil. The necessary properties for optimum handling of the residue at high concentrations and for dry stacking and/or slope deposition are established.
3:15 pm BREAK
MOBILITY ON MUD: Danys Morin, Société d'électrolyse et de Chimie Alcan Ltée, Vaudreuil Works, Jonquiére, Québec
The Vaudreuil Alumina plants use deep thickeners to prepare their red mud for disposal in a 60 ft. high wet stack. Management of this stack requires four-seasons access to the pipework and occasional dust suppression procedures. From peak to foothills the stack can display all the phases of fluidity present in the mud. Vaudreuil has developed a family of vehicles to provide the required access from a 25 tonne amphibian to spread gypsum on the mud to control dusting, to a 1.5 tonne tractor-trailer for personnel transport. This paper describes the units in detail and explains how the characteristics of the mud can be used to give a good load-bearing capacity.
OPTIMIZATION OF GRINDING OF ALUMINAS IN THE ROTARY-VIBRATION MILL AND THEIR EFFECT ON PHYSICAL PROPERTIES OF MOULDERS: Mariusz A. Wojcik, Tomasz Gajda, University of Mining and Metallurgy, Faculty of Materials Science and Ceramics, av. Mickiewicza 30,A-3, 30-059 Cracow, Poland; Ansgar Luttermann, Fachhochschule Munster, Fachbereich Chemieingenieurwesen Stegerwaldstrasse 39,d-48565 Steinfurt, Germany
The properties of high alumina ceramics are strongly influenced by the properties of the starting raw materials such as the grain size distribution and their morphology. Due to this, the grinding operation is an important step in the process of ceramic mass production. The investigations presented show that compared to other mills, the use of a rotary vibration mill will reduce time of grinding, the energy consumption and yield finer powders. The aim of these investigations was to obtain alumina powders with d50 approximately 3 um and d90 close to 10 um. Two different starting materials were tested. The process of grinding was performed according to various parameters such as filling ratio, amount of grinding media, alumina and water, ball set and frequency. The influence of ratios between the grinding media, alumina and water are shown. The influence of ball size, time and frequencies on the kinetics of grinding are shown. Finally the effect of alumina grinding on the physical properties such as green and fired density and shrinkage are shown and discussed in this paper.
RESULTS OF TESTS OF THE FINE GRINDING OF ALUMINA IN THE ROTARY-VIBRATION MILL WITH LOW FREQUENCY OF VIBRATION: Jan Sidor, Mariusz A. Wojcik, University of Mining and Metallurgy, Faculty of Materials Science and Ceramics, av. Micklewicza 30, a-3, 30-059 Cracow, Poland
Results of the investigations of the fine grinding of alumina (below 0.5-2µm) were presented in this paper. Tests were carried out in the laboratory rotary-vibration mill with a low frequency of vibration below 16 Hz at two sets of work. In the first set, the mill chamber had both rotary and vibration movements, while in the second one, the mill chamber made only the vibration movement such as in the case of a classic vibration mill. Results show that it is possible to obtain a high purity alumina with low energy consumption in both sets.
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