Recovery of heavy metals by means of ultrafiltration with water-soluble polymers:: calculation of design parameters

A process for recovery heavy metals - Cu(II), Ni(II), Pb(II) and Cd(II) - from industrial wastewaters has been studied. This process is called PSU (Polymer Supported Ultrafiltration), and includes complexation of metallic ions with polymers (polyethyleneimine - PEI, or poly(acrylic) acid - PAA), in order to make this solution flow through an ultrafiltration ceramic membrane and to obtain two different streams: permeate (nearly free of metal) and retentate (with high complex concentration). In a previous stage, complex stoichiometries and stabilities have been exhaustively studied by UV/visible absorbance spectrophotometry and potentiometric measures. Next, optimum operating conditions and best pH values affecting to permeate flux, complex formation, further polymer regeneration and polymer capacities have been achieved by means of ultrafiltration experiments. Flux and concentration values measured with these processes have been modeled with concentration polarization model, and mass transfer coefficients (k) and polarization concentrations (c(m)) have been obtained for different operation conditions. These data are not commonly reported in previous literature, although they are important for scale-up to an industrial process.