STUDY OF ADSORPTION OF CrО42- AND Cr2О72- BY POLYANILINE FROM AQUEOUS SOLUTIONS

The optical properties of aqueous solutions of chromate CrО42- and dichromate Cr2О72- ions were studied. Optical spectra were used to study the adsorption of chromate CrО42- and dichromate Cr2О72- ions by a sample of polyaniline (PAn) from aqueous solutions of different concentrations. It was established that the removal and adsorption of CrО42- and Cr2О72- by the PAn sample depends on the concentration of oxyanions in the initial solutions. Adsorption studies of PAn sample with respect to oxyanions CrО42- and Cr2О72- were carried out from solutions with concentrations of 50, 100, 150, 200 and 250 mg/L. Examination of the samples after the adsorption tests revealed that the polyaniline sample retains adsorbed chromium, apparently in the Cr(III) state. The analysis of SEM-images, EDX-spectra and maps of elements proves that the distribution of adsorbed chromium is practically uniform over the surface of the adsorbent, and the intensity of its signal on the elemental maps depends on the initial concentrations of solutions of oxyanions CrО42- and Cr2О72-. Examination of the PAn sample using SEM-EDX spectra before and after adsorption revealed that the morphologies of the samples differ. The analysis of the EDX spectra of the elemental composition of the samples after adsorption of CrО42- and Cr2О72- confirmed that they contain, in addition to the PAn elements, also chromium. The distribution of chemical elements in the samples after adsorption revealed that they are almost uniformly distributed surfaces, and the intensity of its signal on EDX spectra depends on the initial concentrations of oxyanion solutions CrО42- and Cr2О72-. The value of CrО42- adsorption by the PAn sample is almost twice as small as the value of Cr2О72- adsorption. By comparing the contents of atoms of elements, in particular sulfur (S) and oxygen (O), before and after adsorption, it was found that S is replaced by Cr, and the content of O slightly increases with an increase in the initial concentration of Cr(VI) in the solutions.