Electroregeneration Technology for Mixed-Bed Ion Exchange Resins — Electroregeneration of Mixed-Bed Resins

Based on a brief overview of mixed-bed ion exchange resin electroregeneration technology, this paper focuses on the characteristics, principles, experimental results, and structure of the electroregeneration device for multi-bed ion exchange resins. The multi-bed resin electroregenerator invented by the author can simultaneously regenerate both the failed cation and anion bed resins in a multi-bed system, achieving excellent regeneration results. It operates without consuming acid or alkali chemicals, produces no waste, and does not pollute water bodies or the environment. It consumes only a small amount of electricity and pure water, resulting in excellent economic benefits. Operation is simple and convenient.

Mixed-bed Resin Electroregeneration

In the EDI process, the H+ and OH- ions generated by water dissociation continuously regenerate the resin filling the desalination chamber. This self-regeneration is a key factor in the continuous and high-quality water output of EDI water purification equipment. Therefore, if an electroregenerator with a structure similar to EDI water purification equipment but without mixed-bed resin filling the desalination chamber is manufactured, then by introducing failed mixed-bed resin into it and energizing and circulating pure water, the failed mixed-bed resin will inevitably be completely regenerated after a period of operation.

In the regeneration chamber of this electro-regenerator, H+ and OH- ions generated by water dissociation continuously electro-regenerate the exhausted mixed-bed resin. Salt ions displaced from the resin are then continuously migrated to the concentrate chamber and discharged under the influence of the electric field. The exhausted mixed-bed anion and cation resins transform from basic type to H+/OH- type resins, completing the regeneration process. Because the exhausted resin does not flow, this method is called static external electro-regeneration. Correspondingly, as long as exhausted mixed-bed resin is continuously fed into the external electro-regenerator, regenerated mixed-bed resin slowly flows out, thus achieving dynamic external electro-regeneration of the mixed-bed resin.

External electro-regeneration of mixed-bed resin uses water as a regenerant under the action of a DC electric field, replacing acid and alkali to regenerate the exhausted mixed-bed resin. Regeneration eliminates the need for complex regeneration steps such as separation, regeneration, mixing, and washing. Only hydraulic conveying is required to send the exhausted mixed-bed resin into the external electro-regenerator for regeneration. No acid or alkali chemicals are used, resulting in no environmental pollution. It consumes only a small amount of electricity, is convenient to use, and is inexpensive, fundamentally changing traditional ion exchange water treatment processes.

Besides ordinary mixed beds, there are also high-speed mixed beds for condensate polishing. These mixed beds typically operate at a high flow rate of 120 m/h. After the resin becomes degraded, it is hydraulically transported to a specialized resin regeneration unit for acid-base chemical regeneration. After regeneration, it is then returned to the original high-speed mixed bed for reuse. In this case, it is convenient to replace the acid-base chemical regeneration with external regeneration, as the delivery system is readily available. Only an external electro-regenerator needs to be connected in series with the resin delivery system. Since the anion and cation resins do not need to be separated during electro-regeneration, there is no concern about cross-contamination common in acid-base chemical regeneration.

To obtain theoretically pure water with a conductivity of 0.055 μS/cm (resistivity of 18.2 MΩ·cm) for use in the electronics, pharmaceutical, or other industries, a polishing mixed bed is usually installed after the ordinary mixed bed or EDI water purification equipment for final polishing. The resin used in this polishing mixed bed is a mixture of anion and cation resins with very similar relative densities. Because the anion and cation resins cannot be separated in this type of resin, they cannot be regenerated separately with acid or alkali. Therefore, this polishing resin is discarded after it becomes degraded. If electroregeneration is used to regenerate this waste anion and cation resins, they can be mixed and electroregenerated together into usable new recycled resin, turning waste into treasure with extremely high economic benefits.

Tsinghua University, Tianjin University, Wuhan University, and North China Electric Power University, among other universities, collaborated with enterprises to form five research teams to verify the feasibility of resin electroregeneration. Experiments showed that the degree of regeneration of spent resin after electroregeneration can reach a level comparable to that of chemical regeneration.