|
Step
|
Fe oxide extraction
(Na3C6H5O7·2H2O-NaHCO3-Na2S2O4) |
Sulfide-carbonate leach procedure
(aqua regia) |
Total digestion
(HNO3-HF) |
|---|---|---|---|
| 1 | Add 10 mL 0.3-M Na citrate solution + 1.25 mL 1-M Na bicarbonate solution | Add 1 mL 1-M HCl to consume carbonate | Add 2 mL conc. HNO3 + 5 mL conc. HF |
| 2 | Heat solution overnight at 70°–75°C | Add 3 mL 7-M HCl | Heat on hot plate at 125°C for 36 hr in closed Teflon vessel |
| 3 | Add 0.5 g Na dithionite and stir for 15 s | Add 1 mL HNO3 | Evaporate to dryness at 75°C |
| 4 | Maintain at constant temperature for 15 min and stir every 5 min | Heat on hot plate at 125°C for 24 hr in closed Teflon vessel | Redissolve in 2 mL conc. HNO3 |
| 5 | Centrifuge 30 min at 4000 rpm | Evaporate to dryness at 75°C | Evaporate to dryness at 75°C |
| 6 | Decant and rinse residue with H2O, centrifuge 30 min at 4000 rpm | Redissolve in 2 mL 7-M HCl | Redissolve in 6 mL 7-M HCl |
| 7 | Evaporate under air in closed Teflon chamber (Aliquot 1) | Repeat Steps 5 and 6 | Evaporate to dryness at 75°C |
| 8 | Repeat Steps 1–7 on residue (Aliquot 2) | Centrifuge 20 min at 4000 rpm | Redissolve in 2 mL 7-M HCl |
| 9 | Redissolve Aliquots 1 and 2 in 7-M HCl and combine |
|
Centrifuge 20 min at 4000 rpm |
| 10 | Centrifuge 30 min at 4000 rpm |
|
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