Rückgewinnung zweiwertiger Kationen aus Komplexmedien durch prozessintegrierte Nanofiltration

In the present work, the nanofiltration for effective wastewater treatment of process bath wastewater from surface treatment plants contaminated with heavy metals was studied. The primary aim was to recover divalent ions from complex solutions and to reuse the nanofiltration permeat. A mathematical model for describing the nanofiltration was used and in a simulation model for the entire rinsing process involved. Since the separation behavior of nanofiltration membranes depends on the solution composition and its concentration as well as on the alkaline-acidic conditions, several mono- and divalent aqueous electrolyte solutions at different pH values were investigated. The most important parameter for the separating capacity is the membrane charge that changes strongly depending on the solution properties. The use of nanofiltration in the acidic pH range allowed even with an effective pressure of 5 bar the retention till 98 - 99R0of valuable process bath components and at the same time environmentally hazardous heavy metal ions such as nickel and zinc as it was shown in good agreement between simulation and experiment. The validated nanofiltration model was integrated in a rinsing cascade and so allowed the simulation of a circulating the nanofiltration permeat. The permeate quality was found to be sufficiently good to reduce the drag-out from the last rinsing bath so that the heavy metal concentrations were below the limits of direct discharge.