This study investigates Hg(II) and Cu(II) sorption in single and binary systems by alginate/polyethylenimine membranes. Batch experiments are conducted to assess the metal sorption performance and complementary. FTIR and SEM-EDX analyses are used to identify metal binding. The sorption kinetics are better fitted by the pseudo-second-order-equation compared to the pseudo-first-order-equation. Three isotherms are compared for fitting the sorption in mono-component solutions and the Sips model gives the best simulation of experimental data. The competitive-Sips model fits well sorption data in Hg-Cu binary solutions and finds that the Cu uptake is drastically reduced by Hg competition. Copper(II) uptake remains negligible at low pH whereas it increases with pH up to 6 because of material deprotonation. Mercury(II) sorption behaves differently, it slightly changes from pH 1 (qeq: 0.76 mmol g-1) to pH 6 (qeq: 0.84 mmol g-1) due to chloro-anion formation. Therefore, playing with the pH allows separating Hg(II) from Cu(II).