Selected Platinum Salts in Water: Speciation and Treatment
Selected platinum salts are relevant to industrial water engineers assessing specialist process streams and wastewater. The examples below identify compounds that may be handled in such settings; they do not indicate that these salts are prevalent in natural waters. For broader context on the element, see platinum.
For the broader chemistry, sampling and treatment context, see platinum in water.
Selected salts and platinum oxidation states
| Salt | Formula | Platinum in the named complex |
|---|---|---|
| Potassium tetrachloroplatinate(II) | K2[PtCl4] | Pt(II) in the anionic [PtCl4]2− complex |
| Potassium hexachloroplatinate(IV) | K2[PtCl6] | Pt(IV) in the anionic [PtCl6]2− complex |
Manufacturer product information identifies potassium tetrachloroplatinate(II) and potassium hexachloroplatinate(IV), the latter described as a precursor. These product identities establish the names of the starting salts, not the platinum species that will remain in a particular water sample.
Solubility in water
| Salt | Reported water solubility | Source and interpretation |
|---|---|---|
| Potassium tetrachloroplatinate(II) | 10 g/L at 20 °C | Thermo Scientific product information for the named salt. |
| Potassium hexachloroplatinate(IV) | 50 g/L at 95 °C | Thermo Scientific product information; this hot-water value must not be used as a room-temperature limit. |
These values refer to the mass of the named salt, not to elemental platinum. They are product reference values for the stated temperatures, not guaranteed limits in wastewater. They do not provide a direct comparison at a common temperature. Use data for the exact product and solution conditions when assessing dissolution or crystallization.
Speciation and analytical reporting
Solubility must be evaluated for the specific salt and conditions. Temperature and the composition of the water matrix can affect dissolution and the forms present. After dilution, chloride concentration, pH, oxidation–reduction conditions and other ligands may influence platinum speciation. The Pt(II) and Pt(IV) complexes shown in the table should therefore not be treated as a complete description of a process stream without suitable analysis.
Concentration units also need to be explicit. A result in mg/L as Pt reports the mass of platinum, not the mass of K2[PtCl4] or K2[PtCl6]. Converting from compound mass requires the correct material identity and composition, including hydrate form and assay where applicable. Total and filtered platinum results can help distinguish material retained by the chosen filter from platinum passing through it, but neither result identifies individual dissolved species.
Treatment assessment
Where platinum is associated with particles, solids removal can address that fraction. Platinum passing through a filter requires separate assessment of its dissolved forms and potential treatment routes. Ion exchange and membrane processes may be considered, but their performance cannot be assumed from a salt name: matrix-specific testing is needed to assess removal and operating behavior. Any process mass balance should include platinum captured in solids as well as platinum transferred to concentrates or other residual streams.
For a defensible treatment assessment, distinguish the supplied salt from measured platinum in the water, specify the reporting basis and evaluate the relevant fractions under the actual matrix conditions.
Concentration: mg/L as Pt versus mg/L of salt
The CIAAW standard atomic weight of platinum is 195.084. Therefore, 1 mmol/L of platinum corresponds to 195.084 mg/L as Pt. For a salt of known composition, multiply its concentration in mg/L by the number of Pt atoms per formula unit and by 195.084, then divide by the salt's molar mass in g/mol.
For pure anhydrous K2[PtCl4], the molar mass is approximately 415.08 g/mol and the platinum mass fraction is approximately 0.4700, or 47.00%. Thus, 100 mg/L of this salt corresponds to approximately 47.00 mg/L as Pt, assuming complete dissolution. This is a composition calculation, not a measured dissolved concentration. Correct for the actual assay and any water of crystallization; a purity stated on a metals basis is not automatically the platinum mass fraction of the entire reagent.
Removal and concentration for recovery
Separate the objective of reducing platinum in treated water from that of producing a useful recovery stream. Solids separation, adsorption, ion exchange and membranes transfer platinum into different residual streams; test the relevant species, capacity and separation performance in representative water. Account for platinum in the feed, treated water, captured solids, spent media and liquid concentrates.
As an illustrative mass balance, 1,000 L of feed containing 1 mg/L as Pt holds 1,000 mg of platinum. Transferring 90% of that mass into 10 L of concentrate gives 900 mg in the concentrate, equivalent to 90 mg/L as Pt and a concentration factor of 90. This is not a predicted removal efficiency or recovery yield. Actual performance and the suitability of the concentrate for further recovery depend on the process and the water composition.