Nitric acid adsorption by a phosphonic acid ester type adsorbent

A novel adsorbent was prepared and its adsorption properties for nitric acid were studied. The adsorbent with a phosphonic acid dibutyl ester-type active group was prepared by chloromethylating styrene/divinylbenzene copolymer of different divinylbenzene content following phosphorylation. Column method was used for the adsorption experiment. The adsorbent adsorbed nitric acid preferentially in acidic solution and adsorbed nitric acid was desorbed by rinsing the adsorbent with water. The amount of nitric acid adsorbed increased almost linearly with nitric acid concentration in solution up to approx. 2 M. The adsorbent apparently did not adsorb nitric acid in dilute solution less than approx. 0.1 M, since the isotherm did not pass through the origin. Maximum amount of nitric acid was nearly equal to the active group content of the adsorbent. Coions of nitric acid enhanced nitric acid adsorption though sodium chloride without coions of nitric acid was not adsorbed and had no effect on nitric acid adsorption. The product of total acid concentration and total nitrate concentration ([H] • [NO3]) demonstrated the effects of both ions simultaneously on nitric acid adsorption and accounted for the adsorption. A plot of nitric acid adsorbed vs [H] • [NO3] gave a single curve under various experimental conditions. Nitric acid adsorbed increased linearly with [H] • [NO3] up to 0.4, the slope of the curve subsequently became gradual, and a plateau was observed when [H] • [NO3] exceeded 30. Divinylbenzene content of starting gel adversely affected nitric acid adsorption, and adsorbed nitric acid decreased with increase in DVB content. The novel adsorbent proved useful for the removal, recovery and purification of nitric acid or nitrate ion in effluent treatment or manufacturing processes.