Zinc Chloride Recovery from Textile Recycling Wastewater Using a Multi-stage Membrane Filtration Process

Sammanfattning

Textile waste presents significant harm to the environment, prompting the development of advanced textile recycling technologies. One such process recycles cellulosic fibers using zinc chloride (ZnCl2) at certain hydration levels to dissolve the cellulose, which is later precipitated by the addition of water and can be re-spun into new fibers. However, this process uses large amounts of zinc chloride and generates substantial volumes of zinc chloride wastewater due to the repeated cellulose washing steps. Zinc chloride is both corrosive and hazardous to aquatic life, and its recovery is critical for environmental protection and resource conservation. One possible method for recovery is membrane filtration. This study evaluated the use of a multi-stage membrane filtration process for the recovery of zinc chloride from textile recycling wastewater. The process involved sequential filtration using a 10-um mesh to remove larger particles, ultrafiltration (UF) for cellulose removal, and nanofiltration (NF) or reverse osmosis (RO) for zinc chloride concentration. The membranes were evaluated based on particle size distributions, flux, and zinc chloride concentrations. Pure water fluxes for the NF/RO membranes were also measured to assess fouling and cleaning efficiency. Membrane screening for the UF stage found the ETNA10PP membrane to be optimal, yielding in the permeate with the lowest particle size as determined by dynamic light scattering measure-ments as well as a relatively high flux (1683 L/m2h). In the subsequent NF/RO stage, all tested membranes exhibited larger particles in the permeates than in the feed, suggesting membrane degradation. The RO98 membrane achieved the highest concentration of zinc chloride (8.28%). However, because it exhibited signs of membrane degradation as well as a significantly lower flux (14 L/m2h), it is not suited for zinc chloride recovery. Overall, the multi-stage membrane filtration was found to be ineffective for concentrating zinc chloride. Instead, concentration of the ultrafiltration permeate using an evaporator is recommended.