Abstract
The U.S. Bureau of Mines conducted investigations on extracting phosphate values from fine-particle wastes generated during the mining and beneficiation of phosphate ore by leaching dried wastes using an h2so4-methanol mixture. Although phosphatic clay waste contains up to a third of the phosphate originally present in the ore, recovery of these values represents a significant challenge due to the fine grain size of the material, the particles averaging less than 1 um in diameter. Waste samples obtained from two Florida producers yeilded phosphate extractions of 71 and 84 pct, respectively, when leached under ambient conditions and at a stoichiometric acid ratio of 1.4:1. Elevated temperatures did not improve the amount of phosphate extracted. Undersirable al2o3, fe2o3, and mgo impurities were largely rejected; higher grade wastes gave acids that met established industry impurity standards, and lower grade samples yielded acids that marginally fell short of the standard. Separation of the crude acids from the insoluble residues was accomplished via vacuum filtration through either filter paper or commercial filter cloths. Both filtration rates and solids 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.
