Conference Agenda

In the early 1990s, experimental work was done to identify an additive for the direct filtration of digester blow-off. The developed chemistry is largely unknown across the alumina industry since there were only 1 or 2 plants that operated, at that time, by directly filtering blow-off slurry. Research efforts resulted in a filter aid that increased plant filtration rate by 25–30%, along with other benefits such as: increased A/C ratio, increased precipitation yield, improved product quality, reduced energy consumption, increased filter cloth life, and easier cleaning of the presses. The product was used continuously in plant scale operations for approximately 10 years. In recent years, the topic of ‘returning’ to direct filtration has been discussed as it offers some benefits over mud removal via gravity sedimentation in CCD circuits. This paper provides an overview of the application and performance of this filter aid in the direct filtration of digester blow-off.

Introduction of new chemical additives into the Bayer circuit or the replacement of an existing one is required from time to time to support security of supply, cost reduction, better performance, or to align with new technologies. If the steps taken to select a new product are not carefully considered, introduction of these additives could change the liquor characteristics and result in adverse effects on particle sizing, oxalate control, settling, and/or filtration. To mitigate this, Al Taweelah alumina refinery has developed a comprehensive poisoning test methodology to screen and qualify chemical additives prior to field trials and permanent use. This methodology looks at the refinery as a whole, and not the area of use in isolation. Additives are evaluated in the lab for their impacts on agglomeration, growth, and settler/washer circuit, aiming to identify potential changes in nucleation, agglomeration, oxalate imbalance or settling and filtration. This paper provides a comprehensive evaluation of the results obtained from laboratory tests, offering insights into the importance of a careful evaluation before experimenting new chemicals in the plant. The findings have significant implications for alumina refinery operations.

This paper explores how alumina refineries can benefit from Nalco Water's FilterMax Technology to enhance product hydrate filter performance. Traditionally, alumina refineries have strived to improve filter performance to achieve full production capacity and reduce energy use. FilterMax offers a comprehensive solution for the alumina industry. The technology centers around improving the permeability of the hydrate cake, which reduces cake resistance and leads to faster filtration rates. Refineries that have adopted FilterMax have reported better de-liquoring and improved filter efficiency through lower hydrate cake moisture and washable soda levels. This reduction in moisture content also translates to optimized energy consumption within the refinery. This paper will delve into specific examples of how refineries around the world have benefited from implementing FilterMax Technology.

Alumina is generally produced from bauxites through the Bayer process and is the main raw material for the production of aluminium metal. In addition to this, chemical grade alumina is used for the production of adsorbents, abrasives, polishing agents, refractory materials, etc. In the Bayer process, bauxite is digested with caustic at temperatures ranging from 140 C to more than 240 C, depending on the bauxite characteristics, mainly tri hydrate alumina (THA) and Mono hydrate alumina (MHA) which determine the digestion technology viz. low or high temperature, or a combination of both (i.e. double digestion). During bauxite digestion, some other impurity bearing minerals also react with caustic. One of the undesirable ones is iron which enters the liquor during high temperature digestion. This iron is present in the liquor in colloidal, suspended, and dissolved forms, and tends to co-precipitate with gibbsite (or THA) during agglomeration and growth stages. Beyond a certain concentration, this iron in THA is an undesirable impurity when the alumina is converted to aluminium metal, impacting its physical properties. Therefore, it is important to control the iron in liquor which involves studying its dissolution in liquor and its incorporation into THA. Several methods, such as the use of lime, some inorganic compounds to precipitate the iron in liquor and also operating at a higher charging A/C have been suggested to control the iron concentration in liquor to acceptable levels. Sand filtration and addition of bauxite residue also represent cost effective methods for controlling iron in liquor. This paper presents the study of iron dissolution and its incorporation into THA and also reviews the various methods available for reducing the iron in liquor to achieve acceptable product quality.

In the process of alumina production, vanadium is co-extracted in the caustic solution and can have detrimental effects on the extraction of target ions, such as aluminum and gallium. Removal of vanadium is an important process, accounting for about 50% of the production cost in the gallium extraction. However, the species of vanadium ion in the caustic solution vary and no clear explanation of its binding mechanism has yet been proposed. At present, precipitation, extraction and ion exchange have been applied for removal of vanadium from caustic solution. The present paper summarizes the findings of recent studies for vanadium removal, discussing the interaction mechanisms from batch experiments, spectroscopy analysis and theoretical calculations. The advantages and disadvantages of the three proposed ways to remove V and prospects for the development of an optimum V removal method are presented.