Common lutetium salts in water: solubility, removal and concentration
Lutetium salts differ in their behaviour in water. Chloride, nitrate and sulfate reagents can supply dissolved lutetium, while carbonate, oxalate and fluoride are poorly soluble. Treatment depends on the chemical form present after mixing, not just the name of the starting salt.
For sources and general aqueous chemistry, see lutetium in water.
Common lutetium salts and solubility in water
| Salt | Formula | Behaviour in water | Practical consideration |
|---|---|---|---|
| Lutetium(III) chloride hexahydrate | LuCl3·6H2O | Soluble | Hydration changes the mass of reagent needed for a given Lu concentration. |
| Lutetium(III) nitrate hydrate | Lu(NO3)3·xH2O | Soluble | Use the stated hydration or certified Lu content; an unspecified hydrate has no single formula mass. |
| Lutetium(III) sulfate octahydrate | Lu2(SO4)3·8H2O | Soluble | Temperature and the other dissolved salts affect the applicable solubility. |
| Lutetium(III) carbonate hydrate | Lu2(CO3)3·xH2O | Poorly soluble | Acid addition can change dissolution and speciation. |
| Lutetium(III) oxalate hydrate | Lu2(C2O4)3·xH2O | Poorly soluble | Precipitation requires subsequent solids separation. |
| Lutetium(III) fluoride | LuF3 | Poorly soluble | Fluoride can interfere with keeping lutetium in an analytical solution. |
These are qualitative descriptions, not saturation concentrations or treatment guarantees. Use solubility data for the exact product, temperature and solution composition when designing a preparation or process. Poorly soluble does not mean that dissolved lutetium is absent.
What happens after a salt dissolves?
Lutetium is commonly present in the +3 oxidation state. Its distribution between dissolved species and solids depends on pH, complexing substances and competing ions. A soluble reagent can form a precipitate after mixing with another stream. Conversely, acid or a complexing substance can change the dissolution of a solid.
Measure total and dissolved lutetium using clearly defined sample preparation. Colloids and fine particles can affect the operationally defined dissolved fraction. The salt formula alone does not identify every species in the treated water.
Removing lutetium from water
Settling and filtration can remove separable particles. They do not by themselves establish removal of dissolved Lu(III). Precipitation converts dissolved lutetium into a solid for separation; test pH, reagent dose, residual dissolved lutetium and sludge behaviour in the actual water.
Ion exchange and adsorption can capture dissolved lutetium. Research with activated cation and anion exchangers has investigated uptake from nitrate solutions. Competing rare earths, acidity and complexing substances can change performance, so laboratory results should not be transferred directly to another stream.
Specialised membrane processes may also be assessed. Research on a polymer inclusion membrane examined Lu(III) transport and membrane regeneration. This is a different mechanism from ordinary particle filtration. Assess selectivity, recovery and the composition of all outlet streams before choosing a process.
Concentration: mg/L as Lu versus mg/L of salt
A concentration expressed as elemental Lu counts only the lutetium mass. A salt concentration also includes counterions and any water of crystallisation. For a pure salt of known composition:
mg/L as Lu = mg/L of salt × (number of Lu atoms in the formula × 174.9668) / molar mass of the salt.
| Reagent basis | Approximate molar mass (g/mol) | Lu mass fraction | Lu supplied by 100 mg/L of salt |
|---|---|---|---|
| Anhydrous LuCl3 | 281.32 | 62.2% | 62.2 mg/L as Lu |
| LuCl3·6H2O | 389.41 | 44.9% | 44.9 mg/L as Lu |
One mmol/L of lutetium corresponds to approximately 174.97 mg/L as Lu. For nitrate hydrate with unspecified x, calculate from the certified Lu content or a verified hydration state. Correct reagent calculations for purity and the assay basis stated on the certificate.
Concentrating and recovering lutetium
After capture, desorption or elution can transfer lutetium into a smaller liquid volume. Removal from the feed, recovery into that liquid and purity of the recovered product are separate measures. Co-captured rare earths and salts may reduce product purity even when the Lu concentration increases.
For an illustrative mass balance, 1 m³ of feed containing 10 mg/L as Lu contains 10 g of Lu. If 90% of that mass is recovered in 10 L of final solution, the solution contains 9 g of Lu, or 900 mg/L as Lu: a concentration factor of 90 relative to the feed. This is a calculation, not a predicted process yield.
Account for lutetium in treated water, solids, spent media, rinses and regeneration liquids. Include added water and reagents in the volume balance, and verify the final product by analysis.
Sources
- Royal Society of Chemistry: lutetium properties and atomic weight.
- Inorganic Ventures: Periodic Table Guide, lutetium solution chemistry.
- Thermo Scientific Chemicals: lutetium(III) chloride hexahydrate specification; nitrate hydrate; sulfate octahydrate.
- Enhanced Lutetium Ion Sorption from Aqueous Solutions Using Activated Ion Exchangers.
- A preliminary study of polymer inclusion membrane for lutetium(III) separation and membrane regeneration.