Phosphogypsum waste, originating from phosphoric acid production from apatite ores, is well known for its high production rate and possible release of sulphate-rich seepage waters. In addition to negative environmental impacts, phosphogypsum waste heaps are also remarkable secondary sources of rare earth elements (REE); in the phosphoric acid production process a majority of REE, occurring in apatite, are precipitated to the phosphogypsum waste. Therefore, a method treating both sulphate-rich waters and recovering REE from phosphogypsum heaps and seepage waters would offer both economic and environmental benefits. In this ongoing study, seepage waters from a phosphogypsum heap are treated with sulphate reducing bacteria (SRB) and ethanol as a substrate. Sulphate is first reduced to hydrogen sulphide, which is then assumed to precipitate REE as sulphides. The main challenge, low concentration of REE in seepage waters (e.g. 2.87 µg/l La, 5.13 µg/l Ce, 0.67 µg/l Y and 3.32 µg/l Nd), is overcome by utilizing continuous mode, semi-passive and cost effective column apparatus, requiring no agitation and performing both sulphate reduction and REE recovery in a single reactor. The SRB method results in a sulphate reduction rate of 40-80 % (from app. 1400 mg/l to 276-844 mg/l sulphate in the effluent) and efficient REE recovery from seepage water. The concentrate obtained from the column consists of a mixture of anaerobic sludge and precipitated REE, with respective REE concentrations of 202 mg/kg La, 477 mg/kg Ce, 49 mg/kg Y and 295 mg/kg Nd.
|Series||Solid State Phenomena|
|Conference||22nd International Biohydrometallurgy Symposium|
|Period||24/09/17 → 27/09/17|
- rare earth element
- sulphate reducing bacteria