Next-Level Alumina Production
A recent project has established a facility in Gardanne, France, for the production of high-purity Bayer-type aluminas.
Setting the bar higher is the stimulus for so much that can be positive inside and outside of business. We push ourselves to our limits, and we exceed our customers’ expectations. For a company such as Alteo, with origins from the start of the alumina refining industry, this has meant quite a number of process developments, including double-digestion extraction and specialized low-soda technologies. One recent project has established a facility for the production of high-purity Bayer-type aluminas that were previously limited to pilot-scale availability.
High-purity alumina (HPA) is a well-established raw material for demanding applications such as synthetic sapphire used for phone and watch covers, substrates for LED lighting, and special polishes. HPA is often defined in terms of 4N, 5N or even 6N purity, which translates to alumina contents of 99.99%, 99.999%, and 99.9999%, respectively. Such very high purity levels require alternative process routes, typically through aluminum salts, but they also come at a very high price. The challenge for Bayer alumina producers is to provide the purest alumina possible in order to give HPA users an attractive cost/performance alternative.
The improvements that can be achieved over classic low-soda aluminas, in terms of electrical, mechanical and corrosion functionality, for example (particularly at high temperatures), also closes the performance gap in applications where HPA is often the sole option. Components for semiconductor manufacturing and special wear parts are examples where being able to achieve very high sintering density (> 3.9 gcm-3), with very controlled chemistry, can challenge the ≥ 4N grades in terms of value for money.
Beyond Very Low Soda
Specialty alumina suppliers have specialized in high-quality low-soda aluminas for many years. These products are the backbone of the advanced or technical ceramics industry, finding multiple applications in industries such as electronics and semiconductor manufacturing, electrical insulation such as spark plugs, ceramic filters, armor protection, catalyst supports, and a range of structural components—generally, where toughness and wear resistance are needed and where corrosive environments are encountered at elevated temperatures. As each of these industries is continuously developing, improving and innovating with new applications, suppliers must also raise the bar.
Following feasibility studies in mid-2018, construction began in late 2018 for a new Alteo Gardanne facility that will take alumina purity levels to between 99.9 and 99.95% (3N5); a commissioning date was set for March 2019. Site clearance and preparation, equipment selection, purchasing, and delivery began in earnest in the second quarter of last year. Throughout the year, discussions took place with existing customers and prospects to refine targets and approval processes. Following startup, initial capacity will ramp up substantially as the year progresses, with the capability for further expansion built in as demand grows.
Starting with low-soda alumina, a controlled and proprietary cleaning process follows. Soda levels that begin at around 0.05% or less will be reduced to less than 0.01% (or < 100 ppm). After the step to minimize impurities, the material can be ground, typically by batch ball milling. Strict process control is adhered to, employing special grinding media and equipment, as well as appropriate handling measures, to ensure that purity is maintained. Table 1 presents typical properties and purities of some Bayer aluminas.
Specialty aluminas are produced by the so-called Bayer process, which enables the extraction of alumina from bauxite ore. Bauxite is digested with caustic soda, and aluminum trihydroxide (ATH) is precipitated from the sodium aluminate solution. The ATH is calcined in rotary kilns to produce alumina, which can be further processed to reduce the size of the particles. During the calcination process, it is also possible to remove the impurities inherent by this extraction method, particularly soda.
The normal-soda grade is an example of a typical “untreated” and unground alumina. The low-soda grade is one that is ground in a batch ball mill to break down the particles into their individual crystals, but has also been calcined using the Reynolds soda removal process (of course, other methods to do this also exist). As described previously, the high-purity grade involves additional steps.
Many people and functions within the Gardanne site were involved as the material evolved through lab scale, pilot testing and supply, and now full industrialization. An R&D team, business development engineers and production specialists have been heavily involved in ensuring that Alteo can provide the product at the volume and quality that are in line with customers’ needs. With portfolio development a continual business driver, we now set our sights on where to move the bar up to next.
For additional information, visit www.alteo-alumina.com.