Pretreatment of bauxite with hydrogen
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      "As part of a U.S. Bureau of Mines program seeking improvements to the Bayer process, a typical Jamaican bauxite was heated at temperatures up to 500 deg C in hydrogen, its leachability under Bayer process conditions was measured, and properties of its leached residue were observed. The objectives were to find ways to decrease the amount of organic carbon in bauxite or in leach liquor derived from it without impairing its leachability, and to improve the leached residue's filterability. Techniques employed included heating bauxite under pressure in an autoclave with hydrogen, and in flowing hydrogen at ambient pressure in a tube furnace. Leaching tests were done with a 600-ml stirred reactor. In some of the leaching tests, ferrous sulfate (FeSO4) was introduced before leaching to produce a partially magnetic product. Results showed that exposure to hydrogen at temperatures from 160 deg to 360 deg C progressively diminished the bauxite's content of organic carbon and decreased the ratio of organic carbon to aluminum in leach liquor, an improvement that would allow a process using hydrogen-treated bauxite to be operated at a smaller recycle ratio, thereby consuming less energy and allowing greater throughput for a plant of given capacity. The bauxite's leachability was not impaired by high- temperature pretreatments, except at temperatures higher than 280 deg C. Pretreatments in hydrogen produced black, partially reduced bauxite, which upon leaching gave a residue that was attracted to a magnetic field and was amenable to separation from green liquor by a magnetic filtra" - NIOSHTIC-2 NIOSHTIC no. 10008559
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