Erbium salts in water: solubility, removal and concentration
Erbium chloride and nitrate are water-soluble sources of Er(III), while carbonate, oxalate and fluoride are poorly soluble compounds. The chemical form present after mixing with water determines treatment behaviour; the name of the original salt is not enough.
For sources and environmental pathways, see erbium in water.
Common erbium salts and solubility
These qualitative descriptions are not saturation concentrations or dosing specifications. Check data for the exact hydrate, temperature and solution composition. Acidity, complexing substances and other ions can change how much erbium remains dissolved.
| Salt | Representative formula | Behaviour in water | Practical relevance |
|---|---|---|---|
| Erbium(III) chloride, anhydrous | ErCl3 | Water-soluble. | Supplies dissolved Er(III). Check whether the product is anhydrous or hydrated before calculating a dose. |
| Erbium(III) nitrate pentahydrate | Er(NO3)3·5H2O | Water-soluble. | Both erbium and nitrate enter solution. Verify hydrate and assay on the product certificate. |
| Erbium(III) sulfate octahydrate | Er2(SO4)3·8H2O | Water-soluble according to supplier information. | Check hydrate, temperature and sulfate composition before preparing or concentrating a solution. |
| Erbium(III) carbonate hydrate | Er2(CO3)3·xH2O | Poorly soluble in water. | A suspension is not a dissolved solution. Variable hydration affects mass calculations. |
| Erbium(III) oxalate hydrate | Er2(C2O4)3·xH2O | Poorly soluble in water. | A possible precipitation product; measure residual dissolved erbium rather than assuming complete capture. |
| Erbium(III) fluoride | ErF3 | Poorly soluble in water. | Include fluoride as well as erbium in the assessment of water quality and residues. |
What happens after dissolution?
These compounds contain trivalent erbium, Er(III). Changes in acidity or complexing substances can alter dissolved species and the tendency to form particles or bind to surfaces. A solution prepared from a soluble salt can therefore change after mixing with another stream.
Measure total erbium and, where relevant, the dissolved fraction defined by a specified sampling and filtration method. Fine particles and colloids can affect this distinction. Record preparation methods so that before-and-after treatment results are comparable.
Removing erbium from water
Solids separation and precipitation
Settling and filtration can remove erbium-bearing particles if those particles can be separated effectively. They do not by themselves establish removal of dissolved Er(III). Precipitation can transfer dissolved erbium into a poorly soluble solid when the solution chemistry permits.
For any proposed precipitation step, check acidity, complexing substances, competing ions, residual dissolved erbium and the filterability of the solids. There is no universal dose or operating pH established by a qualitative solubility label. Account for added reagents and sludge as part of the treatment balance.
Adsorption and ion exchange
Research on D113-III resin examined erbium adsorption and desorption in batch and column systems. A separate study of crosslinked sericin-alginate beads examined capture, desorption, reuse and selectivity. These results support testing adsorption and ion-exchange mechanisms with the actual water, including the effects of competing metals and complexing substances.
Ion exchange is used in rare-earth separation, but practical selection requires testing the actual mixture. Evaluate capacity, contact time, breakthrough, competing-ion effects and regeneration. A simple erbium salt solution may behave differently from a mixed rare-earth liquor or a water containing organic ligands.
Concentration: mg/L as Er versus mg/L of salt
A value expressed as elemental erbium excludes counterions and water of crystallisation. Using an erbium atomic mass of 167.259 g/mol:
mg/L as Er = mg/L of salt × (number of Er atoms per formula unit × 167.259) / molar mass of the salt.
| Pure salt | Formula | Approximate molar mass | Er from 100 mg/L of salt |
|---|---|---|---|
| Anhydrous erbium chloride | ErCl3 | 273.62 g/mol | 61.1 mg/L as Er |
| Erbium chloride hexahydrate | ErCl3·6H2O | 381.71 g/mol | 43.8 mg/L as Er |
| Erbium nitrate pentahydrate | Er(NO3)3·5H2O | 443.35 g/mol | 37.7 mg/L as Er |
These examples assume the stated pure compound and complete dissolution; they are not solubility limits. Correct for product assay, moisture, the actual hydrate and undissolved material. A concentration of 1 mmol/L of erbium corresponds to 167.259 mg/L as Er. Total elemental analysis alone cannot identify the original salt.
Concentrating and recovering erbium
Adsorption followed by desorption or ion exchange followed by elution can move captured erbium into another liquid stream. A smaller final volume can increase its concentration. A concentrate may also contain other rare earths, salts and impurities, so recovery and purity need separate measurements.
For an illustrative mass balance, 1 m3 of water at 10 mg/L as Er contains 10 g of erbium. Recovering 90% of that mass into a final liquid volume of 10 L would give 900 mg/L as Er, a concentration factor of 90. This is a calculation, not an expected treatment yield. Include all liquid outlets, residual solids and losses in an actual balance.
Useful process inputs include flow, temperature, pH, total and dissolved erbium, other rare-earth elements, major ions, suspended solids and known complexing substances. Define both the treated-water target and any recovery objective before establishing performance through laboratory or pilot testing.
Sources
- Thermo Scientific Chemicals: anhydrous erbium chloride, erbium nitrate pentahydrate and erbium sulfate octahydrate.
- Inorganic Ventures: Periodic Table Guide, erbium solution chemistry.
- Adsorption of erbium(III) on D113-III resin from aqueous solutions: batch and column studies.
- Biosorption of europium and erbium from aqueous solutions using crosslinked sericin-alginate beads.
- Royal Society of Chemistry: erbium atomic data and separation.