The influence of physico-chemistry on the retention of chromium ions during nanofiltration

In the present work, we were interested in the treatment by nanofiltration of synthetic solutions containing chromium salts. Two types of solutions (CrCl 3  K 2Cr 2O 7) were treated according to the experimental parameters such as pH, pressure and concentration. With the aim of studying the influence of possible ionic interactions, we have carried out tests on solutions containing the trivalent and hexavalent chromium ions in the presence of various salts (NaCl, KCl, NaNO 3, Na 2SO 4, K 2SO 4) for different concentrations. The results have shown a total chromium retention which varies from 38 to 99% relating to the composition of the solution and operating conditions. For Cr(III), a better retention was obtained in acid medium and for an optimal pressure of 5 bar. The influence of the ionic strength as well as the concentration were found weak. The retention of the Cr(III) ions was not affected by the presence of salts solution. The results for bichromate solutions were strongly dependant of the form in which the Cr(VI) ions were present. The form of HCrO 4 − has given a better retention at low concentrations. When the concentration increases, the phenomenon of repulsion becomes less significant and consequently the ions were less and less retained. The influence of the salt addition on the retention of the Cr(VI) ions have revealed the effect of the interactions of the membrane/solute and solute/solute on the selectivity of the membrane.