Titration of chelating fibrous sorbent in the presence of complex-forming divalent cations

Abstract

Titration curves of H-forms of the fibrous chelating sorbent with iminodiacetic groups based on industrial polyacrylonitrile fiber Nitron with potassium hydroxide in 1M KCl solution in the presence of Ni²⁺, Co²⁺, Cu²⁺ and Ca²⁺ chlorides were obtained. The method used made it possible to simultaneously measure the pH of the solution and the concentration of the divalent cation at each point of the titration curve. From these data, the dependences of their sorption values on the pH of the equilibrium solution were calculated. The curves of direct and back titration practically coincided in all cases. As the pH changed during titration, precipitation was observed at pH values of precipitation of the corresponding hydroxides. In this case, the increase in pH was suspended or greatly slowed down by adding alkali to the titration cell. The formation of a precipitate occurred mainly in a solution for Co²⁺ and Ni²⁺ (pH 8), when the ion exchanger was saturated with a metal ion. In the case of Cu²⁺ (precipitate formation pH 4), Cu²⁺ sorption occurs at both lower and higher pH due to ionization of carboxyl groups and partial dissolution of the precipitate. In all cases, the maximum sorption of Ni²⁺, Co²⁺, Cu²⁺, Ca²⁺ corresponded to the formation of sorption complexes of the R–N(CH₂COO^-)₂Me²⁺ type.