Resin regeneration, requirement

The batch contactor is limited to use with reactions that go to completion in a single stage or in relatively few stages. Difficulties may also arise with batch contactors if resin regeneration requires a greater number of equilibrium stages than the service portion of the cycle. 

Exchange resins may have an affinity for other ionic contaminants such as sulfates. Waste streams with these competing ionic contaminants may have lower removal efficiencies and these treatment systems may require more frequent resin regeneration or disposal. Ion exchange treatment does not destroy targeted contaminants. In some cases, waste disposal costs may render the technology cost prohibitive. 

Pilot plant studies (flow rates, 1 cm/s) with the SB-1 anion exchange resin (column diameter, 0.3-0.7 cm) yielded distribution coefficients of the order D = 400 cmVg. The boron sorption process was shown to be film diffusion controlled. The equilibrium values of boron loading were reached in 6-8 hr [280]. Boron elution and resin regeneration were carried out with 0.1 M NaOH. The complete elution of boron required 10 column volumes at 10 BV and yielded concentrates of 100 mg/L. This facilitated the eventual reduction to solid concentrates of alkali metal borates [281]. 

The configuration of most ion exchange plants involve one or several fixed resin beds contained in cylindrical pressure vessels interconnected by pipework. Valves control and direct pumped or gravity fed liquid flows in a strictly controlled sequence, and safely designed regenerant measuring plus dilution systems are required to handle resin regeneration chemicals. Finally, instrumentation is required to monitor liquid levels, flows, pressures, volumes, and product quality. 

However, for an industrial-scale installation, an economic evaluation has to be made not only considering the water quality but also taking into accoimt regeneration costs. The performance of an adsorption process is dependent on NOM and other surrounding conditions. Synthetic resins have to be considered since their overall performance is comparable to GAG if regeneration requirements are strict, they might even be the better choice. 

Therefore, concurrently with work on the Wlnfrith SGHWR system, a more attractive system requiring less plant and a lower heavy water inventory has been developed, based on the principle of recycling the resin, regenerants and heavy water in closed circuits. 

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