The requirements for the quality of ultra pure water (UPW) used in the semiconductor industry and the grounds for criteria for respective quality parameters are summarized. Examples of the UPW systems are shown, and how the ion exchange resins (IER) are used in such systems is described with relation to particles, TOC (Total Organic Carbon), resistivity, and dissolved oxygen of the UPW.
It is possible to reduce the particle throw from IER by proper pre-conditioning. Reducing TOC in UPW calls for minimining organic leachables from IER. In the way of maintaining a high resistivity of UPW, the optimum pretreatment (coagulaion) and employing reverse osmosois membrane are effective. When the catalytic resins are used to reduce dissolved oxygen, it is necessary to collect more data on the trace metal leachable from the catalytic resins.
In the future UPW production systems, IER must be “ultra”-cleaned, especially with regard to TOC.

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The inside of ion-exchanger has conventionally assumed to be a kind of homogeneous electrolyte solution. This assumption may inevitably lead to the result that the complexes UO₂Cl₅^3- and UO₂Cl₆^4- exist as sorbed species in the present uranyl-chloride system, which can hardly be considered from the potential energy calculation of coordination. We considered that an ion-exchanger phase can be divided into two parts, one being a region around the exchange sites and the other a Donnan invasion region. By the equilibrium analysis besed on this model, we reached a reasonable conclusion that main uranyl chloride complexes are UO₂Cl₃^- and UO₂Cl₄^2- in the anion-exchange resin phase.

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Adsorption characteristics of La (III) -loaded chelating resin containing phosphono-methylamino groups for fluoride ion and application to the selective removal of fluoride ion have been studied. The adsorption of fluride ion depends on the pH of the solution i. e., the capacity and the adsorption rate increase with decrease of the pH. But when the pH is less than 3.5, gradual leaking of La (III) inevitably takes place. Therefore, pH 3.5 is chosen as the optimal adsorption condition of the solution. Fluoride ion is effectively adsobed on the column packed with La (III) -loaded resin at pH 3.5. No significant interference from Cl^-, NO₃^- and SO₄^2- were observed. The retained fluoride ion has been released from the column by elution with 1mol⋅dm^-3 sodium hydroxide solution without any leakage of the metal ion. The column can be used repeatedly after regeneration.

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