Kinetics of 1,8-dihydroxy-2-(pyrazol-5-ylazo)-naphthalene-3,6-disulphonic acid immobilization on anion exchangers

The sorption of 1,8-dihydroxy-2-(pyrazol-5-ylazo)-naphthalene-3,6-disulphonic acid (PACA) onto the anion exchange resins, Dowex 1-X8 and Dowex 2-X8, from aqueous solutions with pH between 1 and 10 was studied spectrophotometrically. Conditions for obtaining modified sorbents with a given capacity for the azo compound were determined. The absorption and reflectance spectra of the sorbed dye were recorded. The immobilized reagent retained similar chromic characteristics as in the solution. The sorption mechanism was investigated under static conditions in the temperature range from 0 to 25 °C, by determining the amount of sorbed dye as a function of contact time. The sorption was a first order process in all cases. The pore diffusion was found to be a rate-limiting step in the sorption process. The diffusion coefficient values from 6.0 to 7.4×10−7 cm2 s−1 were calculated from the experimental results. The activation energy of PACA sorption is −8.56 and −8.05 kJ mol−1 for Dowex 1-X8 and Dowex 2-X8, respectively.