Common neodymium salts and compounds: solubility and recovery
Neodymium is present in water mainly as dissolved Nd(III) species or in suspended solids, depending on the source and water chemistry. The compounds below include process salts and treatment precipitates; they should not be read as a list of minerals commonly found in natural water.
Solubility of neodymium salts and compounds
| Compound and formula | Solubility behavior and caveat | Where it may be encountered |
|---|---|---|
| Neodymium sulfate, Nd2(SO4)3, including hydrates | Measured solubility depends on pH, temperature and other sulfate salts. Published measurements cover pH 2–7 and 25–80 °C, including sodium- and ammonium-sulfate mixtures [1]. Hydrate form affects comparisons. | Sulfate leach liquors and rare-earth processing solutions. |
| Neodymium chloride, NdCl3, including hydrates | A water-soluble Nd(III) process salt. Its solubility in a simple system does not predict speciation or precipitation in a mixed liquor. | Chloride-based process solutions and reagents. |
| Neodymium nitrate, Nd(NO3)3, including hydrates | A water-soluble Nd(III) source; downstream precipitation depends on the full solution chemistry. | Nitrate process solutions and reagents. |
| Neodymium carbonate and basic carbonate | Carbonate can form solids, but aqueous carbonate complexes and double salts complicate simple solubility predictions [4]. Basic-carbonate composition may vary. | Carbonate-bearing liquors and precipitation products. |
| Neodymium hydroxide, Nd(OH)3 | May precipitate as pH rises; dissolved residuals depend on pH and complexing constituents. | Neutralization and treatment solids. |
| Neodymium oxalate, Nd2(C2O4)3, including hydrates | Forms low-solubility precipitates under suitable conditions; acidity, dose and competing species affect recovery and product composition [3]. | Oxalate precipitation and mixed rare-earth concentrates. |
| Neodymium phosphate, NdPO4 | A sparingly soluble phase may form where phosphate is available; actual formation depends on the water matrix. | Phosphate-bearing process waters and treatment solids. |
| Neodymium fluoride, NdF3 | A sparingly soluble phase may form under suitable fluoride conditions; complexes and competing precipitates affect behavior. | Fluoride-bearing process solutions and treatment solids. |
Why actual streams behave differently
A salt’s pure-water solubility is not a direct prediction of dissolved neodymium in mine water or a process liquor. pH affects hydrolysis and precipitation; sulfate and carbonate influence complexation and solid formation. Temperature, ionic strength, other metals and organic ligands also matter. Published sulfate results show why pH, temperature and background salts must be specified [1]. Neodymium carbonate can also form double salts under particular solution conditions [4].
Treatment and recovery options
Neutralization may transfer dissolved rare earths into solids and can promote co-precipitation with iron or aluminium. Freshly formed iron, aluminium or manganese oxides can sorb rare-earth elements; mine-drainage treatment solids may contain rare earths in several geochemical associations [2]. This removes material from the dissolved phase but does not destroy it, and the resulting solids require appropriate management.
Cation or chelating ion exchange can capture dissolved rare earths and elute them into a smaller-volume stream for further processing [6]. Staged precipitation, including oxalate crystallization, can be evaluated to recover a mixed rare-earth concentrate. Research on acid mine water reports that recovery varies with the element mix and operating conditions [3]; it does not guarantee selective recovery of neodymium as a pure product.
Nanofiltration or reverse osmosis may concentrate a suitable stream when osmotic pressure, scaling and fouling permit. These membranes are not inherently selective rare-earth recovery steps. Representative testing should assess dissolved residuals, concentrate or eluate quality, and management of treatment solids and residual streams.
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Last reviewed: 8 November 2026 by Lenntech.
Sources and further reading
- [1] Cunningham et al. (2024), neodymium and dysprosium sulfate solubility, Hydrometallurgy 224, DOI: 10.1016/j.hydromet.2023.106253. Study page.
- [2] Hedin et al. (2024), rare-earth-element associations in mine-drainage treatment wastes, USGS. Publication page.
- [3] Crespo et al. (2026), ion exchange followed by oxalic-acid precipitation from acid mine water. Study page.
- [4] Yang et al. (2019), neodymium carbonate solution behavior and double-salt precipitation, ACS Omega. Full text.
- [5] IUPAC Solubility Data Series, Dysprosium. Data series.
- [6] Lenntech, Ion exchange.