Experimental and theoretical characterization of commercial nanofiltration membranes for the treatment of ion exchange spent regenerant

Abstract

This work presents a joint experimental and simulation campaign aimed at characterizing two nanofiltration membranes (TS80 and NF270) in the presence of a multi-ionic water solution simulating the spent regenerant of cationic ion exchange resins employed for water softening. We identified the membrane parameters, which allowed for predicting the performances through the Donnan Steric Pore Model with Dielectric Exclusion. A good agreement between model and experimental trends of rejection as a function of the applied pressure was observed (error < 15%). The analysis of trans-membrane fluxes and exclusion coefficients showed that dielectric exclusion was the crucial mechanism for the ionic partition. In fact, the lower pore dielectric constant found for TS80 justified the higher rejections to divalent cations with respect to NF270. Moreover, negative charge densities were found for both membranes, because of the high concentration of chloride ions in the feed, which likely adsorbed onto the membrane. However, it was observed that the experimental rejections did not change significantly with the feed pH. This result, in line with the minor role of the Donnan exclusion resulting from the model, suggested that the membrane performances were not much affected by the charge density at high feed ionic strengths (~1 M).

Characterization of Selected Polymeric Membranes Used in the Separation and Recovery of Palladium-Based Catalyst Systems

“…From Equation (3), the effective membrane pore radius will increase proportionally with pure water permeability. This is in line with the literature; NF90 and NF270 are classified as “tight” and “loose” membranes, respectively [ 35 ]. The results show that BW30 and XLE are similar in terms of pore sizes; however, Nghiem and Coleman [ 36 ] proposed the absence of pores in BW30.…”

Removal of Copper, Nickel, and Zinc Ions from an Aqueous Solution through Electrochemical and Nanofiltration Membrane Processes

“…Thus, the total negative charge of the membrane decreases, and the repulsion between membrane and anion decreases. As a result, the co-ions (ions with the same charge as the membrane) quickly escape through the membrane and due to electro-neutrality, the rejection of counter-ions is reduced [8,43]. Figure 3d-f shows a slight decrease in the rejection of Ni and Zn ions with an increase in feed solution concentration, whereas the rejection of the Cu ions was not much affected.…”

Limits of High Recovery Inland Desalination: Closed‐Circuit Reverse Osmosis – a Viable Option?

“…Suitable further treatment of the IEX wastewater might be nanofiltration (NF) to separate Na + from the divalent Ca 2+ and Mg 2+ . The feasibility of NF treatment for IEX wastewaters was reported in [32], where NF270 (DuPont) membranes were used, with rejections of approx. -2 %, 60 % and 75 % for Na + , Ca 2+ and Mg 2+ , respectively.…”