electrodeionization

Electrodeionization (EDI) is a water treatment technology that utilizes DC power, ion exchange membranes, and ion exchange resin to deionize water, thereby removing trace minerals that function as anions and cations. By itself, it does not remove other contaminants, including pathogens, organic compounds, or dissolved gases. EDI is typically employed as a polishing treatment following reverse osmosis (RO), and is used in the production of ultrapure water. It differs from other RO polishing methods, such as chemically regenerated mixed beds, by operating continuously without chemical regeneration. Electrodeionization can be used to produce high purity water, reaching electrical resistivity values as high as 18.2 MΩ/cm. Electrodeionization (EDI) integrates three distinct processes: # Electrolysis: A continuous DC current directs positive and negative ions toward electrodes with opposing electrical charges. The electrical potential draws anions and cations from diluting chambers, through cation or anion exchange membranes, into concentrating chambers. # Ion exchange: An ion exchange resin fills the diluting chambers. As water flows through the resin bed, cations and anions become affixed to resin sites. # Electrochemical regeneration: Unlike chemically regenerated mixed beds, EDI accomplishes regeneration through water splitting induced by the continuous electric current.…

Electrodeionization (EDI) is a water treatment technology that utilizes DC power, ion exchange membranes, and ion exchange resin to deionize water, thereby removing trace minerals that function as anions and cations. By itself, it does not remove other contaminants, including pathogens, organic compounds, or dissolved gases. EDI is typically employed as a polishing treatment following reverse osmosis (RO), and is used in the production of ultrapure water. It differs from other RO polishing methods, such as chemically regenerated mixed beds, by operating continuously without chemical regeneration. Electrodeionization can be used to produce high purity water, reaching electrical resistivity values as high as 18.2 MΩ/cm. Electrodeionization (EDI) integrates three distinct processes: Electrolysis: A continuous DC current directs positive and negative ions toward electrodes with opposing electrical charges. The electrical potential draws anions and cations from diluting chambers, through cation or anion exchange membranes, into concentrating chambers. Ion exchange: An ion exchange resin fills the diluting chambers. As water flows through the resin bed, cations and anions become affixed to resin sites. Electrochemical regeneration: Unlike chemically regenerated mixed beds, EDI accomplishes regeneration through water splitting induced by the continuous electric current. Water splits from H 2 O into H + and OH − to effectively regenerate the resin without the need for external chemical additives. EDI is sometimes labeled "continuous electrodeionization" (CEDI) because the electric current continually regenerates the ion exchange resin mass. ==Theory== The electrodes in an electrochemical cell are each classified as either an anode or a cathode. An anode is an electrode at which electrons leave the cell and oxidation occurs, while a cathode is an electrode at which electrons enter the cell and reduction occurs. Each electrode may become either an anode or a cathode depending on the voltage applied to the cell. Each deionization cell consists of an electrode and an electrolyte with ions that undergo either oxidation or reduction. Because they commonly consist of ions in solution, the electrolytes are often known as "ionic solutions", but molten and solid electrolytes are also possible. Water passes between an anode and a cathode. Ion-selective membranes allow positive ions to separate from the water toward the negative electrode and negative ions toward the positive electrode. As a result, the ions cannot escape the cell and deionized water is produced. When using a current that is higher than necessary for the movement of the ions, a portion of the incident water will be split, forming hydroxide (OH − ) anions and hydrogen (H + ) cations. These species will replace the impurity anions and cations in the resin. This process is called "in situ regeneration" of the resin. Because this replacement occurs alongside the deionization process it allows for continuous purification, as opposed to deionization techniques that require a pause in operation to chemically regenerate ion exchange resins. The purpose of the ion exchange resin is to maintain a stable conductance across the feedwater. Without the resin, ions could be removed initially, but the conductance would drop dramatically as the concentration of ions decreases. With lower conductance, the electrodes would become less able to efficiently direct the flow of electrons across the cell, whereas with the addition of resin and thus a steady conductance, electron flow remains steady and ensures a steady rate of ion removal. With a resin, therefore, the final remaining ion concentrations in the processed water can be lower by orders of magnitude. ==See also== Electrodialysis Ionization Purified water Water purification Water treatment ==References== ==External links== video. Electrodeionzation Systems. Advanced Electrodeionization Technology for Product Desalting , Argonne National Laboratory Understanding the working principle of electrodeionization. How Does EDI Work?

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