Extraction of lanthanides from apatite concentrate by hemihydrate-dihydrate process via sulfuric acid

Dissolution of lanthanides present in apatite concentrate, by hemihydrate-dihydrate leaching process has been studied. At first apatite concentrate leached with pure sulfuric acid at high temperature. Phosphoric acid and calcium sulfate hemihydrate (phosphogypsum) was then produced which most of lanthanides were accumulated in it (PG). Apatite contains up to 1% rare earth elements or lanthanides. This process which is also the main process of phosphoric acid production was the first step of apatite concentrate leaching in order to recover the lanthanides. Besides phosphogypsum, concentrated phosphoric acid was produced and was in vicinity of remaining acid sulfuric. In second step, hemihydrate precipitates were dissolved in less concentrated sulfuric acid and at lower temperature and crystallized as calcium sulfate dihydrate. According to the results for extraction of lanthanides from apatite concentrate, a two-step leaching process is suggested; in first step, apatite concentrate is leached with pure sulfuric acid at 70°c with L/S ratio of 4 and for 2 hours, and in second step, calcium sulfate hemihydrate is leached with a diluted sulfuric acid (1M) at ambient temperature.

کلیدواژه ها:

apatite ، lanthanides ، two-step leaching ، phosphogypsum ، sulfuric acid