Separation of the Alkaline Earth Elements from Liquid Media

Among the alkaline earth elements, calcium and magnesium receive the most attention due to their common occurrence in ground water. Water with a high concentration of these minerals is said to be “hard water” and it poses challenges as it forms scale in equipment and piping. A variety of separation techniques can be employed to remove calcium and magnesium (and other alkaline earth elements).

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Sodium Na+ Cycle Softening

Sodium cycle ion exchange is the most widely practiced technology for industrial water softening, such as water conditioning for low pressure boilers and pretreatment for reverse osmosis to protect the membranes and improve overall water recovery. It is also widely practiced for applications such as hotels and residential installations to protect hot water pipes and decrease the use of detergents. In this process, water is contacted with a strong acid cation (SAC) exchange resin in the sodium (Na+) form where the harness ions of calcium (Ca2+) and magnesium (Mg2+) are exchanged for more soluble sodium ions.

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Hydrogen H+ Cycle Softening/Dealkalization

When source waters have a high level of carbonate (CO32-) or bicarbonate (HCO3-) alkalinity that is associated with the hardness ions of calcium (Ca22+) and magnesium (Mg2+), a very efficient hydrogen (H+) cycle ion exchange process can be employed to soften the water. This process is also called dealkalization since it removes the alkalinity along with the hardness ions. The process is especially well-suited for use prior to reverse osmosis or two-bed ion exchange demineralization systems.

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Nanofiltration (Membrane Softening)

The term membrane softening applies to a water treatment process that uses nanofiltration (NF) membrane technology to reduce hardness. Like reverse osmosis (RO), NF is a pressure driven separation process that employs a semi-permeable membrane and the principles of cross-flow filtration. Membrane softening using NF membranes is an option when very high level salt rejection is not necessary or even desirable. NF membranes preferentially reject hardness ions while partially demineralizing water, removing 10-90% of dissolved salts. Hardness removal with NF processes can range from 50-97% depending on the membrane selected. NF processes operate in the range of 75-150 psig making them an economical option for softening operations.

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Deashing of Syrup

Inorganic and proteinaceous impurities are found in starch-based sweeteners from both natural sources and as added processing aids. These impurities must be removed for quality purposes and to optimize downstream processing.

Deashing of glucose syrups helps improve the quality of products and is necessary for the isomerization of glucose to fructose when manufacturing high fructose corn syrup (HFCS). Although essential for the enzymatic conversion of starch to glucose, calcium (Ca) also deactivates the glucose isomerase enzyme during isomerization, making the deashing of glucose vital during the production of HFCS. Fructose syrups must be deashed for similar reasons—while magnesium (Mg) is essential to the isomerization process, it can foul downstream chromatographic enrichment media.

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Decalcification of Beet Sugar Thin Juice

The dilute sucrose solution, also called thin juice, derived from sugar beets contains natural minerals. The calcium (Ca) ions, or lime salts, in this thin juice can create scale on the heat transfer surfaces of the evaporation and crystallization equipment—increasing energy and maintenance costs and decreasing asset utilization. Decalcification of this thin juice with ion exchange has proven to be a successful solution. Additionally, a decalcified molasses improves sugar recovery through chromatographic processes.

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Brine Softening for Chlor-alkali Electrolysis

The use of functionalized membranes, consisting of fluorinated polymeric substrate with carboxylic or sulfonic acid functional groups, for chlor-alkali electrolysis has introduced much stricter requirements for brine purity. The membrane selectively allows the migration of sodium and hydrated sodium ions from the anode chamber to the cathode chamber. The presence of impurities such as calcium, magnesium, strontium, barium, alumina, silicon dioxide, sulfate, and iodine brought into the system by salt, dilution water, and chemicals used in the process can shorten the lifetime of the membranes or damage the electrodes. This results in a higher consumption of energy and higher membrane replacement cost. Dow Water & Process Solutions provide selective ion exchange resins to facilitate high purity brines, protecting sensitive and expensive electrolytic membranes.

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Heavy Oil Recovery (Softening for Steam Injection)

 Low pressure steam is injected into formations to reduce viscosity and improve oil recovery for heavy oils and bitumen. Typical injection quantities are 2 bbl steam/bbl oil. Water treatment is required to protect the boilers and once-through steam generators and for discharge of produced waters. Softening produced water that contains high solids (TDS) is widely practiced for this steam production. Dow Water & Process Solutions offers a range of ion exchange products to assist in this process as well as the UPCORE™ and AMBERPACK™ Packed Bed Technologies to meet your thermal EOR water treatment needs.

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Shale Gas & Oil (Hydraulic Fracturing)

The most widely practiced technology for industrial water softening, sodium-cycle ion exchange, can be used for low pressure boiler applications or as a pretreatment to reverse osmosis (RO) to help protect the membranes and improve overall water recovery. In this process, water is contacted with a strong acid cation (SAC) exchange resin in the sodium (Na+) form where the harness ions of calcium (Ca2+) and magnesium (Mg2+) are exchanged for more soluble sodium ions.

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Alkaline earths are di-valent cations. Calcium and magnesium are common in ground water caused by water percolating through deposits of calcium and magnesium-containing minerals such as limestone, chalk, and dolomite.