www.aluminiumtoday.com BAUXITE 1 This paper was previously published in the ICSOBA Newsletter Volume 14, December 2015 Management and use of bauxite residue By Ken Evans* This paper serves as a brief overview of especially true of the early European sites the mud washing circuit is pumped, the history and trends in the management including: Bergheim (Germany) - on site with a solids content of 20 to 30%, into and use of bauxite residue, outlining: The storage then in a former lignite mines; storage areas created by dams and other dimensions of the problem; how methods Burntisland (UK) - disposal into an estuary, earthworks for secure containment. In of storage and disposal have developed then behind a sea wall, see Figure 1, then many instances valleys were dammed for over time and the implications for bauxite an old shale mine; see Figure 2, Gardanne example, Ewarton (Jamaica), see Figures residue use; characteristics of bauxite (France) - storage in a dammed valley 3 and 4, Gardanne, Salindres, Saint Cyr residue; the technically successful uses; then disposal by pipeline to the sea; La (France), Ouro Preto (Brazil). Examples the challenges to implementation – real Barasse (France) - storage on site then of old mine storage were: bauxite mines and perceived; a review of large scale/ nearby dammed valley then disposal to (Kirkvine (Jamaica), Bauxite (USA)), lignite industrial scale successes; and some hopes mines (Bergheim), and oil shale quarries for the future. (Burntisland). Annual production of smelter grade In the case with sites constructed and chemical grade alumina in 2015 was in the past three or four decades, the some 115 million tonnes1 which, with storage areas have normally been sealed the exception of some plants in Russia, to minimise leakage to the underlying Iran and China, is all produced using the ground and ground-water, however, this Bayer process. The global average for the tended not to be the practice in earlier production of bauxite residue per tonne years. Sealing approaches cover a range of of alumina is between 1 and 1.5 tonnes, materials including compacted clay and/or though the range is much broader, so it the use of plastic and other membrane is estimated that some of the 150 million materials. tonnes of bauxite residue is produced The supernatant liquor above the annually. This is generated at some 60 residue was normally returned to the active Bayer plants. In addition there are plant for reuse thereby recovering some at least another 50 closed legacy sites, so of the caustic soda value and avoiding the combined stockpile of bauxite residue contaminating the environment. Various at active and legacy sites is estimated at drainage and seepage collection systems three thousand million tonnes. have been incorporated into the design and construction of the facilities. The History and trends in disposal and construction of the storage area was often storage methods Fig 1. Bauxite disposasl into an estuary to recover land dictated by the type of bauxite residue and Management of and the methods of the differed for clay like muds compared to storage of bauxite residue has evolved sea via a pipeline; Larne (UK) - disposal more sandy residues. At Gramercy (USA), progressively over the decades2. In the into sea water lagoons; Ludwigshafen sand-bed filtration was used and “French early Bayer alumina plants, the residue (Germany) - storage on site; Newport (UK) Drains” were used with drainage pipes and generated was often merely piled up on – disposal into estuary from barges then covering layers of sand of different size site or an area adjoining the alumina plant. sea water lagoons; Salindres (France) – on and gravel to give permeability through Occasionally nearby depleted mine or site storage then in a dammed valley and the base of the lake. This was termed the quarry sites, were used. In other situations Schwandorf (Germany) – on site storage.. Decantation, Drainage and Evaporation of nearby estuaries or sea lagoons were used Prior to 1980, most of the inventory Water (DREW) system. and then later as the closest convenient of bauxite residue was stored in lagoon- There are many examples of this storage areas were filled, valleys were dammed type impoundments and the practice is method but they include Stade (Germany), to contain the ever-growing volume of still carried out at some facilities. In this Burnside (USA) and Vaudreuil (Canada). In residue. These methods of storage were method, the bauxite residue slurry from some cases, low dykes or levees were built *Consultant, International Aluminium Institute Aluminium International Today March/April 2016 2 BAUXITE www.aluminiumtoday.com of valuable soda and alumina to the Bayer process plants and to minimise the potential for leakage to the surrounding environment. The current trend in residue storage practice is towards increasing use of dry stacking as the preferred technology, and further research to optimise this technology is appropriate. Very many plants now use equipment such as Amphirols to aid dewatering of the mud in order to compact and consolidate the Fig 2. Bauxite residue disposal into a former oil shale mine residue. See Figure 6. Partial neutralisation using seawater is practiced at a number of to the final expected height at the start discharge is no longer undertaken at Australian plants close to the sea (Yarwun and a new area constructed when more any alumina refining facilities and all sea and QAL); carbonation by using waste volume was required whilst in others the discharge will be completely phased out carbon dioxide from ammonia production dam walls were successively increased by the end of 2015. has been used (Kwinana (Australia)); and when the space was filled. The area of As land for lagoon storage became accelerated carbonation using intensive suitable land readily available dictated the scarce for many plants, “Dry stacking” farming methods, Aughinish (Ireland), approach. methods were used. A dry stacking regime Kwinana, Worsley (Australia)) is showing If the residue material is not neutralised was adopted nearly 75 years ago in the considerable benefits. before discharge to the storage lagoon, UK3 and about 50 years ago in Germany4 Filtration using drum filters and plate it becomes a highly alkaline, poorly and since the 1980s the trend has been and frame filter presses to recover caustic compacted mud area covered by a highly increasingly towards dry stacking to reduce soda, produce a lower moisture and alkaline lake, see for example the lake in more handleable bauxite residue have Figure 4 which had a pH >12 and a soda been employed for some 80 years but is level in excess of 2,000 mg/L many years now growing in usage. Plate and frame after pumping had stopped. filter presses were adopted in Vaudreuil This creates safety and environmental in 1936 when the plant was constructed hazards including the potential for contact and in Burntisland in 1941 as the lagoons of humans and wildlife with alkaline adjacent to the site were full. In the case liquor and mud, and contamination of of Burntisland the bauxite residue needed surface and ground waters by leaching to be transported on public roads through of caustic liquor and other contaminants. the town to a nearby old oil shale mine Regrettably in many cases these early so a high solids content mud was a ponds have proved of limited efficacy and Fig 3. Bauxite residue disposal into a dammed valley key requirement. In the mid 1960s at caustic liquor, plus other contaminants, has to create a lagoon, early stages Ludwigshafen, vacuum drum filters were subsequently seeped into the surrounding adopted. Figure 7 shows a press filter. environment. Ongoing remediation of In addition to helping recover more these situations is proving to be a costly the potential for leakage of caustic liquor caustic, this trend opens up considerable exercise. Addressing the risk and to to the surrounding environment, reduce benefits in terms of reuse as the material eliminate the potential for catastrophic the land area required, and maximise is normally produced as a friable cake, failure of the dam/impoundment and the recoveries of soda and alumina. with typically less than 28% moisture, and consequent environmental hazard to Considerable work was undertaken in lower soda thereby dramatically reducing the surrounding area/communities Jamaica on the Robinsky5 sloped thickened transport issues and costs. Alunorte introduces high monitoring, maintenance tailing disposal system and Ewarton (Brazil), Distomon (Greece), Gardanne, and remediation costs. Under some adopted the practice in the mid-1980s6. Kwinana, Seydisehir (Turkey) and many circumstances, this has created the See Figure 5. Additionally, improved plants in China have already adopted prospect of an indefinite legacy. methods for thickening and washing of or plan to adopt plate and frame filter Another disposal technique adopted the residues prior to storage, and recovery presses. Hyper Baric filters are reported to by some plants was sea or river disposal of decant water during storage, have achieve particularly low moisture content particularly in the 1940s to 1960s. In at been developed to increase the recovery material with the performance of the least six plants, two located in France (Gardanne and La Barasse), one in Greece (Distomon) and three in Japan (Shimizu, Ehime, Yokohama), bauxite residue was discharged into the sea either via pipelines or from ocean going vessels. Other alumina plants disposed of the residue into rivers or estuaries, for example into the Mississippi River (Gramercy), and Severn Estuary (Newport). In other cases in Ireland (Larne), Wales (Newport) and Scotland (Burntisland), land was reclaimed from the sea by disposing of the residue Fig 4. Bauxite residue disposal into dammed valley, later stages in tidal lagoons or behind sea walls. River March/April 2016 Aluminium International Today www.aluminiumtoday.com BAUXITE 3 press being enhanced when steam is particle size distribution, morphology and used; moisture contents lower than 25% Component Typical range (%) nature of the residue emanating from a have been reported.