Water-soluble polymer ultrafiltration process at pilot scale: Study of hydrodynamics and factors limiting flux

Municipal Solid Waste as Secondary Resource: Selectively Separating Cu(II) from Highly Saline Fly Ash Extracts by Polymer-Assisted Ultrafiltration

Urban mining from fly ash resulting from municipal solid waste incineration (MSWI) is becoming more and more important due to the increasing scarcity of supply-critical metals. Metal extraction from acid fly ash leaching has already been established. In this context selective Cu recovery is still a challenge. Therefore, our purpose was the separation of Cu(II) from MSWI fly ash extracts by polymer-assisted ultrafiltration (PAUF). We investigated three polyethyleneimines (PEIs) with regard to metal retention, Cu(II) selectivity, Cu(II) loading capacity, and the viscosity of the PEI containing solutions. A demanding challenge was the highly complex matrix of the fly ash extracts, which contain up to 16 interfering metal ions in high concentrations and a chloride content of 60 g L−1. Overcoming that, Cu(II) was selectively enriched and separated from real fly ash extract at pH 3.0. At pH 1.0, a PEI-free Cu(II) concentrate was obtained and PEIs could be regenerated for reuse in further separation cycles. The PAUF conditions developed at laboratory scale were successfully transferred to pilot scale, and hyperbranched PEI (HB-PEI) was found to be the most suitable reagent for PAUF in a technical scale. Moreover, HB-PEI enables photometric control of the Cu(II) enrichment.

Characterization of a ceramic ultrafiltration membrane in different operational states after its use in a heavy-metal ion removal process

In the present study, the atomic force microscopy (AFM) technique has been used to characterize a Carbosep M5 ceramic membrane (MWCO=10kDa, TiO(2)-ZrO(2) active layer). This membrane was previously used in a polymer supported ultrafiltration (PSU) process to recover copper, using partially ethoxylated polyethylenimine as the water-soluble polymer. The membrane was characterized in four different operational states: new, new and cleaned, fouled in a PSU stage and cleaned after a PSU process. The influence of the membrane state on pore opening size distribution and roughness was studied, finding a 16% decrease in the former and a 20% increase in the latter due to foulant deposition upon the membrane active layer. Phase angle distribution was also analyzed to indicate the foulant spreading on the membrane surface. These phase angle measurements can be related to pore opening size and roughness, concluding that the cleaning procedure is not totally effective and that foulant presence on the membrane active layer is not remarkable. Finally, AFM was used to measure the influence of pH on adhesion forces between a silica probe and the membrane active layer. These results can be related to the flux evolution vs pH in PSU experiments, finding both lowest adhesion and highest flux at pH 6.