Separation of Chromium from Water

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Cr

Drinking Water Trace Contaminant Removal

Chromate is found in the effluent from chromium-plating operations and has been used in cooling tower water chemistry. Chromate is also found in ground water both as a natural contaminant and from man-made sources. While trivalent chromium (Cr3+) is not considered to be harmful, hexavalent chromium (Cr6+) is toxic. The World Health Organization (WHO) and many countries have established a maximum tolerable concentration of 50 µg/L (ppb).

Weak base anion resins have a strong affinity for chromate, making them a good choice to minimize leakage. The common practice today is to dispose of the resin after it is loaded with chromate, so a high-capacity resin is desirable. AMBERLITE™ PWA7 Resin is a unique phenol-formaldehyde weak base anion resin that has demonstrated significantly higher chromate loading capacity compared to other commercially-available ion exchange resins.

Filtration can also be used to remove chromate from drinking water. Ferrous sulfate is used to reduce hexavalent chrome to trivalent chrome. This material is then precipitated, coagulated, and filtered out of the water. DOW™ Ultrafiltration SFD Modules can facilitate low levels of chrome-containing particles in the final drinking water.

These ion exchange and ultrafiltration products may be subject to drinking water application restrictions in some countries. Please check the application status before use and sale. For more information see our regulatory information. (Even when ultrafiltration modules are certified, their use is not recommended for drinking water where dedicated operators are not available.)

Groundwater Remediation

The concentration of chromate in the groundwater, the required purity level, and the economics to meet those needs will determine if a regenerable or non-regenerable ion exchange resin system should be employed.

If a non-regenerable system is used, AMBERLITE™ PWA7 Resin is the best choice. This weak base anion resin has a strong affinity for chromate, minimizing leakage, and it also has demonstrated significantly higher chromate loading capacity compared to other commercially-available ion exchange resins.

If a regenerable system is used, then DOWEX™ SAR Resin should be selected. This strong base anion resin can capture the anionic chromate complex that forms, and since it is a Type II resin, it also benefits from improved regeneration efficiency.

Filtration can also be used to remove chromate from groundwater. Ferrous sulfate is used to reduce hexavalent chrome to trivalent chrome. This material is then precipitated, coagulated, and filtered out of the water. DOW™ Ultrafiltration Modules can facilitate low levels of chrome-containing particles in the treated water.

 

Plating

Ion exchange resins can be used in plating processes to both remove impurities from the rinse water so that it can be either recycled or discharged and to purify the plating bath solution.

To treat the rinse water so that it can be recycled or discharged, a series of resins can be used to achieve the desired outcome. A strong acid cation resin such as DOWEX™ G 26 (H) Resin is recommended for the removal of cationic metallic impurities. Following that, a strong base anion resin such as DOWEX 21K XLT Resin can then be used for the removal of anions or cyanide metallic complexes. In the cyanide alkaline rinse water, this same strong base anion resin can also remove all the weak acids, such as hydrogen cyanide.

Copper is often a problem metal in precious metal and trivalent chromium plating operations. Information on the specific removal of copper can be found in the Plating section of the Periodic Table - Copper Removal.

Wastewater

  • Chromate is found in the effluent from chromium-plating operations and has been used in cooling tower water chemistry, and from man-made sources. While trivalent chromium (Cr3+) is not considered to be harmful, hexavalent chromium (Cr6+) is toxic.
  • If the chromium ion to remove from the wastewater stream is in the +3 oxidation state, then it typically behaves as a cation, so a cation exchange resin such as DOWEX™ G 26 (H) Resin is recommended. However, if the chromium is in the +6 oxidation state, then it is likely in the form of an oxyanion such as chromate (CrO4)2- (above pH 6) or dichromate (Cr2O7)2- (between pH 2 and pH 6); these oxyanions can be removed by an anion exchange resin such as DOWEX 21K XLT Resin. More chromium can be removed by the resin per equivalent when the chromium is in the dichromate form (pH 2 – pH 6).
  • Filtration can also be used to remove chromate from wastewater. Ferrous sulfate is used to reduce hexavalent chrome to trivalent chrome. This material is then precipitated, coagulated, and filtered out of the water. DOW™ Ultrafiltration Modules can facilitate low levels of chrome-containing particles in the treated water.

 

Chromium is commonly found in process and waste solutions in either the Cr3+ or the Cr6+oxidation states. In general, the Cr6+ ionic forms are anionic in character, such as: HCrO4-, CrO42-, and Cr2O72-  chromate complexes.