Bauxite mines typically employ to people. The bauxite ore contains aluminum trihydrate Al OH 3. Alumina refining produces alumina Al 2 O 3 from the bauxite ore, by exploiting the reversible reaction of the Bayer process 1—3 :. The reaction is firstly driven in the sodium aluminate NaAlO 2 direction by the addition of caustic soda NaOH to bauxite.
The major steps in alumina refining are as follows 1—3 :. Wet grinding of the bauxite ore in rod mills, ball mills, or semiautogenous grinding mills to produce fine slurry. Residues are stored in residue drying areas. Alumina refineries are generally located on or near the coastline to facilitate shipping of alumina to aluminum smelters. Refineries typically employ about people Figures 1 and 2. Traumatic injury in bauxite mining is relatively uncommon compared with underground metalliferous mining or underground coal mining.
Nevertheless, potential causes of injury include vehicle rollovers, mobile equipment collisions, being struck by falling trees, falls from height, entrapment, explosion, and electrocution. An emergency medical response capacity is therefore required. This always involves an on-site capacity, but may also include the provision of a substantial medical facility or access to aeromedical evacuation depending on the local conditions.
Minor trauma is still reasonably common in refineries—particularly hand and finger injuries. Major trauma is uncommon, but there is the potential for falls from height, mobile equipment collisions, entrapment, and electrocution.
Refineries usually have on-site medical centers with an emergency medical response capacity and provision to transfer patients to hospital. Noise is generated in mining by scraping, drilling, blasting, excavating, hauling, crushing, and conveying. Exposure to noise is controlled primarily by enclosing personnel within vehicle cabins. This is not entirely successful however with noise-induced hearing loss still occurring at contemporary operations.
Hearing conservation programs are essential and should include noise surveys, noise control initiatives, annual audiometry, and a range of hearing protection devices with fit testing and education. Noise is commonly encountered throughout refineries and can be very loud during tasks such as the descaling of tanks using impact tools.
Noise-induced hearing loss has been a significant problem in refineries. Heat and humidity are encountered in tropical locations. Although heat stroke has not been reported, heat exhaustion and miliaria rubra may occur.
Control measures are necessary and have been discussed in detail elsewhere. Whole-body vibration is commonly experienced while operating mobile equipment, such as scrapers, drilling rigs, excavators, and haulage trucks. This can cause or exacerbate spinal disorders. In some cases remote-controlled vehicles are used where the terrain is so rough that whole-body vibration could be excessive. Road and vehicle maintenance are important control measures. Hand-arm vibration syndrome seems to be rare in bauxite mining and alumina refining.
Vibrating hand tools are not an important part of the process at bauxite mines, but are common at alumina refineries. Nevertheless, most bauxite mines and alumina refineries are located in tropical climates, so cold-provoked vasospasm is less likely. Bauxite is a low-level naturally occurring radioactive material. It contains small quantities of uranium U , thorium Th , and potassium 40 K. The bauxite ore, Bayer process materials before precipitation, mud residue, and sand residue are therefore of radiological interest, whereas the alumina product is not.
Total incremental composite doses for individuals were all less than the public exposure limit of 1. In summary, this is an issue that requires some consideration and monitoring at bauxite mines and alumina refineries, but is unlikely to be of concern. Solar ultraviolet exposures in surface bauxite mining operations and alumina refineries are likely to contribute to the occurrence of squamous cell and basal cell carcinomas, although this is an inference drawn from studies of outdoor workers in other industries.
Occupations involving substantial outdoor work seem not to be associated with an increased risk of melanoma. Tropical cyclones hurricanes can impact bauxite mines and alumina refineries in tropical locations. Bauxite is generally regarded as being relatively biologically inert. More recently, epidemiological studies of employees exposed to bauxite dust have been conducted.
A cross-sectional study of employees at a US bauxite mine, alumina refinery, and alumina-based chemical products plant studied lung function in relation to cumulative total dust exposures. Because one third of the study cohort never smoked, the effects of dust exposure could be examined independent of the effects of smoking.
The study did not report forced vital capacity FVC results, so it is not known whether the results reflect an obstructive or restrictive lung defect. Nevertheless, industrial bronchitis in response to high dust exposures is a possible explanation.
Unfortunately, the exposure data did not distinguish between bauxite and other exposures such as alumina and caustic mist. It is therefore somewhat difficult to interpret the findings in relation to bauxite.
Also, the exposures were clearly much higher than those typically sustained during contemporary bauxite mining. The prevalence was statistically significantly increased among nonsmokers who had longer tenure and higher cumulative total dust exposures. After adjustment for age, height, and smoking, there was a small but statistically significant decline in FEV 1 7.
The association between FEV 1 and the duration of employment was independent of bauxite exposure, which the researchers found difficult to explain.
In summary, it seems that bauxite exposures in contemporary best-practice mining operations have not been demonstrated to be associated with clinically significant decrements in lung function or pneumoconiosis. These were thought unlikely to be clinically of note. A cancer incidence and mortality study has been undertaken for a cohort of employees working in three bauxite mines and three alumina refineries in Western Australia.
Mortality for all cancers combined was not significantly different from the comparison population. There were no statistically significant trends seen with the duration of employment for any of the causes of death. Nevertheless, an independent review by the Western Australian Mesothelioma Registry found that mesothelioma was associated with exposures outside the aluminum industry in all but one case—for example, five of the nine cases had exposure to crocidolite at Wittenoom, an asbestos mining location in Western Australia.
For melanoma there was no increase in risk with the duration of employment. Subsequent analysis at one of the studied refineries found no statistically significant increase in the incidence of melanoma when state rather than national comparison data were used unpublished data.
The researchers commented that there was no known exposure related to office work in this industry, and the finding may be an artifact of the large number of analyses performed in the study. An internal analysis of the same cohort looked at cancer incidence, circulatory mortality, and respiratory mortality in relation to bauxite dust exposure and alumina dust exposure.
In the Caribbean, as well as in Southern Europe, bauxite is found in smaller pocket deposits, while interlayered deposits occur in the United States, Suriname, Brazil, Guyana, Russia, China, Hungary and the Mediterranean. Bauxite is generally extracted by open cast mining, being almost always found near the surface, with processes that vary slightly depending on the location.
Before mining can commence the land needs to be cleared of timber and vegetation. Next the top soil is removed and is usually also stored for replacement during rehabilitation. On some surface deposits there is no overburden, and on others, the bauxite may be covered by up to 20 metres of rock and clay. Members Area. Home » Industries » Production » Bauxite. Buyer's Guide. Bauxite ore, refined through two processes, is the primary source of aluminum.
Land conservation is a key industry focus An average of 80 percent of the land mined for bauxite is returned to its native ecosystem. Topsoil from the mining site is stored so it can be replaced during the rehabilitation process. Reserves will last for centuries Although demand for aluminum is increasing rapidly, bauxite reserves, currently estimated at 40 to 75 billion metric tons, are projected to last for centuries.
Guinea and Australia have the two largest proven reserves. A wealth of bauxite reserves Vietnam may hold a wealth of bauxite. Mining bauxite Bauxite is usually found near the surface of terrain and can be strip-mined economically. Production and reserves More than million metric tons of bauxite are mined each year. Looking forward: Continued improvement in environmental restoration efforts Environmental restoration goals continue to advance.
Further separation of the pregnant liquor from the bauxite residue is performed utilising a series of security filters. The purpose of the security filters is to ensure that the final product is not contaminated with impurities present in the residue. In this stage, the alumina is recovered by crystallisation from the pregnant liquor, which is supersaturated in sodium aluminate.
The precipitation reaction is the reverse of the gibbsite dissolution reaction in the digestion stage:. The spent liquor is heated through a series of heat exchangers and subsequently cooled in a series of flash tanks. The condensate formed in the heaters is re-used in the process, for instance as boiler feed water or for washing bauxite residue.
The remaining caustic soda is washed and recycled back into the digestion process.
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