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Leaching of Phosphate Values from Phosphate Wastes Using H2so4- methanol Mixtures.

Wilemon-GM; Swanton-RG; Davis-JG; Scheiner-BJ
Miner Met and Mater Soc Paper A89-4 1989 :17 pages
The U.S. Bureau of Mines conducted investigations on extracting phosphate from fine-particle wastes that are generated during the mining and beneficiation of phosphate rock. These wastes may contain up to one-third of the phosphate orginially present in the untreated ore. Samples of the dried waste were leached using sulfuric acid and methanol mixtures. The phosphate extractions in these experiments ranged from 60 to 85 pct when leached under ambient conditions and at stoichiometric ratios ranging from 1.2:1 to 1.4:1. Undersirable al2o3, fe2o3, and mgo impurities were largely rejected. Higher grade ores produced acids that met established industrial impurity standards. The presence of up to 24 pct water in the waste did not depress the extraction of phosphorus from the waste or adversely affect the impurity content of the acid product. Methanol was recovered via vacuum distillation and used in subsequent tests. No significant difference was observed between the tests using recycled methanol and those using fresh methanol. Crude acid products were separated from insoluble residues via vacuum filtration using either filter paper or commercial filter cloths. Filtration times and fines retention were improved by the addition of 0.5 Lb/ton of polyvinyl acetate (pvac) or polyethylene oxide (peo) to the methanol-acid slurries. These results show potential for substantially increasing the reserves of an important domestic resource.
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OP 74-89
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Miner., Met., and Mater. Soc. Paper A89-4, 1989, 17 PP.