Terbium salts in water: solubility, removal and concentration
Terbium chloride, nitrate and sulfate can supply dissolved terbium to water. Carbonate, oxalate and fluoride are poorly soluble compounds. Treatment depends on the chemical form present, not just the name of the salt originally added.
This guide covers common commercially available terbium salts, treatment considerations and concentration calculations. For sources and environmental pathways, see terbium in water.
Common terbium salts and water solubility
The following descriptions are qualitative. They are not saturation concentrations or dosing specifications. Use solubility data for the exact hydrate, temperature and solution composition; acidity and complexing substances can change the dissolved concentration.
| Salt | Representative formula | Behaviour in water | Practical relevance |
|---|---|---|---|
| Terbium(III) chloride hexahydrate | TbCl3·6H2O | Water-soluble. | A source of dissolved Tb(III). Hydration affects the terbium mass fraction. |
| Terbium(III) nitrate hexahydrate | Tb(NO3)3·6H2O | Water-soluble. | Both terbium and nitrate enter the solution. Verify the hydrate and assay on the product certificate. |
| Terbium(III) sulfate octahydrate | Tb2(SO4)3·8H2O | Water-soluble. | Check temperature and sulfate composition when preparing or concentrating solutions. |
| Terbium(III) carbonate hydrate | Tb2(CO3)3·xH2O | Poorly soluble in water. | A suspension is different from a dissolved solution. Variable hydration changes mass calculations. |
| Terbium(III) oxalate hydrate | Tb2(C2O4)3·xH2O | Poorly soluble in water. | Relevant to precipitation and recovery; measure residual dissolved terbium rather than assuming complete capture. |
| Terbium(III) fluoride | TbF3 | Poorly soluble in water. | Account for fluoride as well as terbium when assessing water quality and residues. |
What happens after a salt dissolves?
These salts contain trivalent terbium, Tb(III). Dissolved terbium can occur as hydrated ions or complexes, and hydrolysis becomes relevant as pH changes. A solution prepared from a soluble salt can subsequently form particles or bind terbium to other surfaces. Organic ligands and other ions can change that behaviour.
Distinguish total terbium from the operationally defined dissolved fraction obtained using a specified filtration method. Fine particles and colloids can complicate this distinction. Record the sampling and preparation method so that before-and-after treatment measurements can be compared.
Removing terbium from water
Solids separation and precipitation
Settling and filtration remove particles containing terbium, provided that the solids can be separated effectively. They do not by themselves demonstrate removal of dissolved Tb(III). Precipitation can transfer dissolved terbium into a poorly soluble solid when the solution chemistry permits it.
Terbium oxalate formation has been used in recovery processes. This does not establish a universal reagent dose or operating pH for wastewater. Check acidity, complexing substances, competing metals, residual dissolved terbium and the filterability of the precipitate. Added reagents and the resulting sludge must be included in the process assessment.
Adsorption and ion exchange
Primary research has examined terbium capture using cellulose-based adsorbents, functionalized magnetic particles and natural clinoptilolite. A study of clinoptilolite investigated trace Tb(III) under flow conditions and subsequent desorption. These studies provide examples of possible capture and recovery mechanisms, rather than guaranteed performance for a different water.
For a practical design, test media capacity, contact time, breakthrough, competing-ion effects and regeneration using the actual feed. Results from a simple terbium salt solution may differ from those for a mixed rare-earth leachate or water containing organic ligands. Evaluate the treated water and the spent media or regeneration liquid together.
Concentration: mg/L as Tb versus mg/L of salt
A concentration expressed as elemental terbium excludes counterions and water of crystallisation. Using an atomic mass of 158.925 g/mol:
mg/L as Tb = mg/L of salt × (number of Tb atoms per formula unit × 158.925) / molar mass of the salt.
| Pure salt weighed | Approximate molar mass | Terbium from 100 mg/L of salt |
|---|---|---|
| Anhydrous TbCl3 | 265.28 g/mol | 59.9 mg/L as Tb |
| TbCl3·6H2O | 373.37 g/mol | 42.6 mg/L as Tb |
| Tb(NO3)3·6H2O | 453.03 g/mol | 35.1 mg/L as Tb |
These calculations assume the stated pure compound and complete dissolution. Correct for product assay, moisture and undissolved material. A concentration of 1 mmol/L of terbium corresponds to 158.925 mg/L as Tb. Total elemental analysis cannot identify the original salt from this concentration alone.
Concentrating and recovering terbium
Removal from the main water stream and recovery as a useful product are distinct objectives. Adsorption followed by desorption can transfer terbium into a smaller liquid volume. A cellulose-based study demonstrated acid desorption from a loaded adsorbent, while research on scrap-recovery wastewater examined capture at low terbium concentrations.
A concentrate may also contain other rare-earth elements, dissolved salts and impurities. Assess selectivity and product purity separately from the percentage removed. Neither concentration nor successful adsorption alone establishes the commercial value of a recovered material.
For an illustrative mass balance, 1 m3 of water at 10 mg/L as Tb contains 10 g of terbium. Recovering 90% of that mass into a final liquid volume of 10 L would produce 900 mg/L as Tb, a concentration factor of 90. This is a calculation, not an expected treatment yield. Include all liquid outlets, residual solids and losses in a real balance.
Information useful for process selection
Useful inputs include flow, temperature, pH, total and dissolved terbium, other rare-earth elements, major ions, suspended solids and known complexing substances. Define both the treated-water target and any recovery objective, then use laboratory or pilot results to establish achievable performance.
Sources
- Thermo Scientific Chemicals: terbium chloride hexahydrate and terbium nitrate hydrate.
- Stanford Materials: terbium sulfate octahydrate and terbium carbonate.
- Inorganic Ventures: Periodic Table Guide, terbium solution chemistry.
- American Elements: terbium compounds, including fluoride.
- Methods of recovering terbium oxide from a glass, patent describing oxalate precipitation.
- Cellulose-based bioadsorbent for recovery of terbium ions.
- Sorption of terbium on Transcarpathian clinoptilolite.
- Terbium adsorption using functionalized magnetic nanoparticles.
- Terbium adsorption from Nd-Fe-B scrap-recovery wastewater.
- Royal Society of Chemistry: terbium atomic data.