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Improving Membrane Filtration for Copper Speciation: Optimal Salt Pretreatments of Polyethersulfone Membranes to Prevent Analyte Retention.

Tonya GräfKatharina GummiJuliane FilserJorg ThömingJan Köser
Published in: ACS omega (2023)
Membrane filtration has been increasingly used to separate dissolved metal ions from dispersed particles, commonly using ultrafiltration membranes, for example, polyethersulfone (PES) membranes with a molecular weight cut-off of 3 kDa. The disadvantage of this technique is an undesired retention of ions, resulting from Coulomb interactions with sulfonic acid groups of the membrane. Therefore, such a membrane acts similar to a cation exchanger column. We solved this drawback by a pretreatment of the PES membrane by other cations. Using CuSO 4 as a model compound, we compared the effectiveness of five cations using their salt solutions (Ca 2+ , Mg 2+ , Fe 2+ , Ag + , Ba 2+ ) as pretreatment agents and identified the most effective pretreatment component for a high recovery of copper ions. After membrane filtration without pretreatment, only 52 ± 10%, 64 ± 5%, 75 ± 8%, and 89 ± 7% of nominal Cu concentrations were obtained using initial concentrations of 0.2, 0.5, 1.0, and 4.0 mg L -1 , respectively. The efficiency of the investigated cations increased in the order Fe < Ag < Mg < Ca < Ba. Furthermore, we analyzed the most efficient concentration of the pretreatment agent. The best performance was achieved using 0.1 mol L -1 CaCl 2 which increased copper recovery to slightly below 100%, even at the lowest tested Cu concentration (recovery 93 ± 10% at 0.2 mg L -1 ). In the environmentally relevant Cu concentration range of 0.2 mg L -1 , 0.1 mol L -1 BaCl 2 was identified as the most efficient pretreatment (103 ± 11%).
Keyphrases
  • aqueous solution
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