Ion Exchange

Fact Sheet - Ion Exchange

   
 
PWMIS Home
Intro to Produced Water
Technology Descriptions
Fed & State Regulations
Technology Identification
   

Salt is the key parameter that determines how produced water is managed onshore. A separate fact sheet describes membrane processes for removing salt. This fact sheet describes ion exchange, another common process that removes salt and other inorganic chemicals from produced water.

Photo of home water softener column. 
Home water softener column with salt tank for regenerating the column and sodium hydroxide tank for neutralizing low pH; Source: J. Veil, Argonne National Laboratory.

Many consumers are familiar with home water softeners that remove iron and manganese from tap water. Water softeners use ion exchange columns filled with a specific type of resin. The resin is charged with sodium ions by passing a concentrated salt solution through the column. As water loaded with iron and manganese moves through the column, those ions are attracted to the resins, which prefer to bind with the iron and manganese. Sodium is released when the resin attaches to the iron and manganese. Once stripped of the undesirable iron and manganese, the water is piped into the home water supply. Periodically, the resin-exchange sites are all used. Then, the column is backwashed and regenerated with fresh salt solution.

The water softener example is provided to explain the principle of ion exchange. Exchange resins can be designed to selectively remove different types of chemicals. IOGCC and ALL (2006) provide a description of the different types and applications of ion exchange resins.

Photo of Ion exchange equipment at Argonne National Laboratory.
Ion exchange equipment at Argonne National Laboratory; Source: D&D - Nuclear Engineering Division of Argonne National Laboratory

In the case of produced water, the most common use of ion exchange is to preferentially remove sodium. For that application, resins are chosen that are regenerated with hydrogen ions. As the produced water passes through the column, sodium ions are removed from the water. They replace the hydrogen on the resin's exchange sites. The treated water contains more hydrogen ions, and therefore its pH drops. Often the pH is raised by contact with calcium carbonate, which in turn helps to control the sodium adsorption ratio or SAR (for more discussion of the SAR, see the fact sheet describing agricultural use).

However, ion exchange can be used to remove other contaminants too. At one treatment plant in the Powder River Basin, ion exchange is used to preferentially remove divalent cations which would otherwise form scale on the reverse osmosis membranes that do the bulk of the sodium removal. Further, special ion exchange resins have been developed to remove radium (NORM) from produced water.


Photo of Higgins Loop water treatment system
Higgins Loop water treatment system; Source: Severn Trent Services

One version of ion exchange for treatment of coal bed methane produced water in the Rocky Mountain region is the "Higgins Loop." Dennis (2006) and IOGCC and ALL (2006) describe the process. The Higgins Loop uses a continuous countercurrent ion exchange contactor for liquid phase separations of ionic components. The contactor consists of a vertical cylindrical loop, which contains a packed bed of resin separated into four operating zones by butterfly or "loop" valves. These operating zones - adsorption, regeneration, backwashing, and pulsing - function like four separate vessels.

Produced water containing high sodium levels is fed to the adsorption zone within the Higgins Loop. There, it contacts strong acid cation resin, which accepts sodium ions in exchange for hydrogen ions. Treated water containing less than 10 mg/L sodium then exits the loop. In the lower section of the Higgins Loop, resin filled with sodium is regenerated with either hydrochloric or sulfuric acid. This generates a small, concentrated spent brine stream. Regenerated resin is rinsed with water prior to reentry into the adsorption zone to remove acid from its pores. As resin in the upper layer of the adsorption zone becomes loaded with sodium, the flows to the Higgins Loop are momentarily interrupted. This allows advancement of the resin bed (pulsing) through the loop in the opposite direction of liquid flow. Liquid flows are restarted after resin pulsing is complete.

Beagle (2006) reports that 17 ion exchange units are operating in Montana and Wyoming to treat produced water. Emit Water Discharge Technology uses a Higgins Loop as part of an overall treatment system to treat produced water for subsequent reuse or discharge. The volume of water treated in this fashion has steadily increased from a few hundred thousand bbl (barrel = 42 gal) in August 2003, to nearly 5 million bbl in August 2006.

The backwash stream from ion exchange treatment of produced water will contain high levels of sodium. Therefore, disposal requirements for the concentrated brine should be considered when selecting ion exchange treatment technologies.

Other Versions of Ion Exchange Technologies
Other companies offer technologies that use ion exchange in different configurations. However, only a few have actually treated produced water. Descriptions of these technologies can be found in CSM (2009). Examples include:

  • the Drake Process, a continous ion exchange process that targets sodium bicarbonate.
  • the Eco-Tec: Recoflo® compressed-bed ion exchange process

Additional versions of ion exchange technology may be part of combined treatment systems.

References
Beagle, D., and R. Dennis, 2007, Continuous Countercurrent Ion Exchange Applied to CBM Produced Water Treatment in the Powder River Basin of Wyoming and Montana," presented at the 14th International Petroleum Environmental Conference, Houston, November 5-9. Available at http://ipec.utulsa.edu/Conf2007/Abstracts%202007/Beagle_40.pdf [PDF].

CSM, 2009, “Technical Assessment of Produced Water Treatment Technologies,” prepared by the Colorado School of Mines as part of RPSEA Project 07122-12, November. Available at http://aqwatec.mines.edu/produced_water/treat/docs/Tech_Assessment_PW_Treatment_Tech.pdf [PDF}

Dennis, R., 2006, "Coal Industry Turns to Ion Exchange Technology for Wastewater Minimization," Industrial WaterWorld, PennWell Corporation, Tulsa, OK, Sept. Available at http://ww.pennnet.com/Articles/Article_Display.cfm?Section=ARTCL&PUBLICATION_ID=41&ARTICLE_ID=276178&C=colmn .

IOGCC and ALL, 2006, "A Guide to Practical Management of Produced Water from Onshore Oil and Gas Operations in the United States," prepared for U.S. Department of Energy, National Energy Technology Laboratory, by the Interstate Oil and Gas Compact Commission and ALL Consulting, Oct. Available at http://www.all-llc.com/IOGCC/ProdWtr/ProjInfo.htm.

StayConnected Facebook Twitter LinkedIn RssFeed YouTube