Modeling of Cu(II) and Cr(VI) ions PEUF separation from the bi-ionic mixtures containing sulfates

Application of nonlinear regression methods for modeling of the polymer enhanced ultrafiltration (PEUF) effectiveness was proposed. Separation of Cu(II) and Cr(VI) ions (bi-ionic mixtures) in the sulfates environment was experimentally tested. Polyethyleneimine (PEI) was chosen as a polymer aiding the ultrafiltration process. Selection of PEI resulted of the amine groups presence within its structure. In effect, the polymer is well water soluble, demonstrates the ability of binding metal cations, as well as it has weak anion exchange properties. Experimental analysis of the PEUF process covered 3 bi-ionic Cu(II)/Cr(VI) mixtures of different metals mole fractions, pH within 2–10 range and polymer/metals molar ratio C_PEI/C_M from 0.5 to 10. Based on measurement data, the nonlinear empirical models were elaborated for prediction of Cu(II) and Cr(VI) retention coefficients, as well as their selective separation effectiveness. The largest differences in retention coefficients of chromium(VI) and copper(II) were reported for their bi-ionic mixtures with prevailing chromium molar fraction, at high pH and relatively small PEI dose. Concentration of the bi-ionic mixture initially of 0.9 mmol dm^–3 Cr(VI) and 0.1 mmol dm^–3 Cu(II) at pH 10 with molar ratio C_PEI/C_M = 0.5 resulted in 9.5-time growth of copper concentration in retentate and 1.5-time chromium concentration raise.