Engineering & Mining Journal

JUN 2013

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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ORBITE Cleaning Up the Red Mud Canadian scientists hook up with worldwide waste management specialists to introduce a technology breakthrough that will reclaim the scourge of bauxite beneficiation By Steve Fiscor, Editor-in-Chief ments. In early February, Orbite announced it was teaming up with Veolia Environmental Services, a worldwide waste management firm whose specialties include wastewater treatment processes, to treat and recycle red mud worldwide. Together they will build the first of many plants to treat red mud using the Orbite Aluminae process. A Different Approach Orbite Aluminae recently transformed its commercial-scale demonstration plant into a high-purity alumina plant. Estimates indicate that more than 4 billion tons of red mud will have accumulated in piles of various sizes around the world by 2015-2018. The Bayer process, which refines bauxite to produce alumina (aluminum oxide), generates a significant waste stream. Since its inception in the late-1800s, the only option was to impound the caustic red mud. On occasion, red mud discharges have created environmental calamities, such as the Ajka sludge spill in western Hungary during 2010. On average, bauxite contains about 40% to 50% alumina. The Bayer process uses a hot solution of sodium hydroxide to digest the ore. It converts the alumina into sodium aluminate. The other solid impurities do not dissolve and are filtered off. As the alkaline solution cools, aluminum hydroxide precipitates. The solid impurities are mostly a mixture of silica (sand), iron oxides (red color) and titanium dioxides. The amount of silica in bauxite can range from a few percentage points to as much as 10%. The ratio of alumina to silica is what really determines the quality of bauxite ore. The best bauxite ores have the highest ratio of alumina to silica and the lowest quality bauxite, vice versa. As a general rule of thumb, processing the best bauxite generates about 2 tons of red mud per ton of alumina. As the percentage of silica increases so does the amount of red mud. At more than 10% silica, the Bayer process becomes uneconomical because of red mud. A Canadian company, Orbite Aluminae Inc., has found a way to not only refine alumina without producing red mud, it can also extract smelter-grade alumina, as well as other products such as rare earth metals, from existing red mud impound88 E&MJ • JUNE 2013 "The Bayer process is an inefficient, caustic process," said Richard Boudreault, president and CEO of Orbite Aluminae. "The digestive system only captures about half the alumina and the remaining alumina and iron attaches itself to the atoms into red mud compounds. Nearly all of the iron ore is then locked into the silica. So, a lot of the metal is lost to the red mud. Our approach is much different as we recover most of what is in the ore." The Orbite Aluminae process also digests the metals, but it uses an acid instead of a base. "We use the same acid found in the human stomach, hydrochloric acid (HCl)," Boudreault said. "The human stomach avoids digesting the silica found in food. Likewise, in our process, silica is never put into the solution and the red mud never forms." The process of using an acid to digest bauxite, however, has historically been difficult to manipulate. HCl will try to eat away at everything, including the container. Orbite Aluminae has used a process where it sprays glass on the walls of the container (or digester). It's a new technology that did not exist until a few years ago. The glass lining allows the use of an acid-based process without destroying the equipment.

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