Common chromium salts and compounds in water
“Chromium salts in water” can refer to added industrial compounds or to dissolved chromium species formed after a salt dissolves. The forms that matter depend chiefly on oxidation state, pH, redox conditions, concentration and other dissolved constituents. Cr(III) is generally less soluble and mobile than Cr(VI); the table below distinguishes representative compounds from the aqueous species actually present.
Chromium species in natural and industrial waters
| Water or process stream | Chromium forms that may be relevant | Context |
|---|---|---|
| Groundwater and surface water | Usually Cr(III) complexes, hydroxide solids or chromium associated with mineral surfaces; Cr(VI) as hydrogen chromate (HCrO4−) or chromate (CrO42−) where oxidation conditions or contamination support it | Natural levels are commonly low, but local concentrations and the Cr(III)/Cr(VI) ratio vary. The result depends on pH, redox chemistry, minerals and organic matter. |
| Leather tanning and some metal-finishing streams | Cr(III) sulfate, basic chromium(III) sulfate and related Cr(III) complexes | Chromium is used in tanning and other industrial processes. After dissolution, the original salt does not remain as an intact molecule in water. |
| Chrome plating, chromate conversion and oxidising process liquors | Cr(VI) from chromic acid/chromium trioxide, sodium chromate or dichromate, and potassium chromate or dichromate | High-strength process solutions may contain Cr(VI). The particular compound depends on the process; it should not be assumed from a total-chromium result alone. |
| Chromite ore processing and alkaline leaching | Soluble sodium chromate in alkaline leach liquors; Cr(III)-bearing mineral solids in residues | Chromium speciation and residual salts depend on the roasting, leaching and water-treatment steps. |
Cr(VI) salts are generally more soluble than Cr(III) salts. In water, however, the dissolved ions and complexes re-equilibrate; a compound name identifies a source or reagent, not necessarily the final species in the stream.
Representative chromium salts and compounds
Solubility values below describe the named solid in water at the stated conditions. Hydration state, temperature and data source matter, so these figures are comparative reference values rather than process design limits. Chromium compounds—especially Cr(VI) compounds—require appropriate occupational and environmental controls.
| Compound | Formula | Oxidation state | Reported water solubility | Where it may be encountered |
|---|---|---|---|---|
| Chromium(III) chloride | CrCl3 (anhydrous) | Cr(III) | Slightly soluble; hydrated forms and solution conditions differ | Reagent or process chemical; not a typical natural-water salt |
| Chromium(III) sulfate hydrate / basic chromium sulfate | Cr2(SO4)3·xH2O; variable for basic sulfate | Cr(III) | Soluble; exact value depends on hydration and product composition | Leather tanning and chromium-bearing process liquors |
| Chromium(III) nitrate nonahydrate | Cr(NO3)3·9H2O | Cr(III) | Very soluble in water | Specialty reagent or process solution |
| Sodium chromate | Na2CrO4 | Cr(VI) | 53 g/100 mL at 20 °C | Chromite processing, chemical manufacture and selected chromate processes |
| Potassium chromate | K2CrO4 | Cr(VI) | 62.9 g/100 mL at 20 °C | Specialty reagent and chromate process solutions |
| Sodium dichromate | Na2Cr2O7 (hydration state matters) | Cr(VI) | Highly soluble; a published value for the anhydrous compound is 73.18% by mass at 20 °C | Oxidising reagent and industrial process chemical |
| Potassium dichromate | K2Cr2O7 | Cr(VI) | 12 g/100 mL at 20 °C | Oxidising reagent and selected industrial processes |
| Chromium trioxide (chromic acid anhydride) | CrO3 | Cr(VI) | 624 g/L (reported); reacts with water to form chromic-acid species | Chromic-acid plating and other strongly oxidising process solutions; not a salt |
| Chromium(III) hydroxide | Cr(OH)3 | Cr(III) | Low solubility; forms a precipitated solid over suitable pH conditions | Product of Cr(VI) reduction followed by Cr(III) precipitation |
Soluble sodium and potassium chromates or dichromates can produce mobile Cr(VI) oxyanions. Lead chromate and barium chromate are sparingly soluble solids and are not representative of the usual dissolved chromium species in natural water; they may be relevant to specific pigment or waste residues.
Chromium removal, recovery and concentration
Treatment must be selected for the chromium oxidation state and the full water matrix. Total chromium alone may not show whether an anion-exchange step, a cation-exchange step or reduction is needed. Analysis should distinguish Cr(VI) where it is relevant and account for pH, competing ions, suspended solids and the intended reuse or discharge quality.
| Challenge | Potential treatment approach | Key considerations |
|---|---|---|
| Dissolved Cr(VI) in plating, metal-finishing or mine water | Chemically reduce Cr(VI) to Cr(III), then adjust pH to precipitate chromium hydroxide and separate the solids | Commonly used for industrial wastewater. Reducing-agent dose, pH, reaction time and solids separation require process control; chromium-bearing sludge needs suitable management. |
| Low-level chromate in rinse water or polishing streams | Anion exchange or suitable chromate-selective adsorptive media | Performance depends on competing anions and loading. Regeneration produces a smaller, concentrated residual that still requires treatment or recovery. |
| Dissolved Cr(III) | Hydroxide precipitation and solids separation; cation exchange may be considered for polishing or recovery | Complexing agents and pH affect removal. A representative test should confirm residual chromium and sludge properties. |
| Water reuse or dissolved-salt concentration | Nanofiltration or reverse osmosis as part of a treatment train | Membranes can reduce dissolved chromium and concentrate the reject, but do not destroy chromium. Pretreatment, scaling/fouling control and concentrate management are essential. |
| Concentrated, segregated process rinse or recovery liquor | Segregation, ion exchange, evaporation or other concentration steps may support chemical reuse or metal recovery | Recovery depends on stream purity, chromium speciation, process compatibility and product requirements; it should be demonstrated for the specific stream. |
For background on ion exchange, nanofiltration and reverse osmosis, see Lenntech’s technology pages. Treatment residuals and Cr(VI)-bearing materials must be managed under the applicable safety and environmental requirements.
Discuss a chromium-bearing water-treatment challenge
Tell Lenntech about the chromium form, concentration, water composition and treatment objective.
Discuss a water-treatment challenge
For a treatment discussion, contact Lenntech at info@lenntech.com.
Last reviewed: 8 November 2026 by Lenntech.
Sources and further reading
- WHO: Chromium in drinking-water — background document.
- WHO: Chromium chemical fact sheet.
- ILO/WHO International Chemical Safety Card 1370: Sodium chromate.
- ILO/WHO International Chemical Safety Card 1770: Potassium chromate.
- ILO/WHO International Chemical Safety Card 1371: Potassium dichromate.
- PubChem / HSDB: Sodium dichromate physical and chemical data.
- ILO/WHO International Chemical Safety Card 1530: Chromium(III) nitrate nonahydrate.
- U.S. EPA: Treatment options for chromium-6 in drinking water.
- U.S. EPA: Chromium waste treatment — reduction, precipitation, filtration and ion exchange.