effect of hydrochloric acid on leaching behavior of calcareous phosphorites

the bulk of the world's phosphate reserves is located in sedimentary horizons that contain appreciable amounts of carbonate. during beneficiation of phosphate rocks, huge amounts of oversize phosphate rocks are rejected from crushers. this reject also mostly contains low tricalcium phosphate and high carbonate content. in this study, experiments have been carried out to reduce/eliminate carbonate content by leaching the ground phosphate rock with dilute hydrochloric acid solution. effects of hydrochloric acid concentration, reaction time, temperature and liquid/solid ratio (vol./wt. basis) on the process have been studied. under the reaction conditions, some of the apatite may be dissolved to form soluble monocalcium phosphate during the selective leaching. however, by specifying the ph of the process the lime milk can be used to recover the dissolved apatite. it has been observed that upon treatment of the ground rock with dilute hydrochloric acid, the p2o5 percent can be raised up to the industrially acceptable level due to the selective reduction/elimination of calcium carbonate content of the sample, depending on the reaction conditions as well as nature and size of the raw phosphate particles used for analysis.