~ Pergamon P l h S0043-1354(97)00071-7 Wat. Res. Vol. 31, No. 9, pp. 2327 2339, 1997 :i~ 1997 ElsevierScience Ltd. All rights reserved Printed in Great Britain 0043-1354/97 $17.00 + 0.00 OPTIMIZING Cu REMOVAL/RECOVERY IN A BIOSORPTION COLUMN DAVID KRATOCHVIL t, BOHUMIL VOLESKY I* and GEORGE DEMOPOULOS" 'Department of Chemical Engineering, -'Department of Mining and Metallurgical Engineering, McGill University, 3480 University Street, Montreal, Qu6bec, Canada H3A 2A7 (First received June 1996; accepted in revised form February 1997) Abstraet--Biosorption of Cu 2 + by Sargassum fluitans seaweed biomass protonated by an acidic wash or loaded with Ca -'+ is based on ion exchange. The uptake of Cu 2+ is respectively accompanied by a release of either H + or Ca -'+ into the solution phase. The effects of Ca-, H- and H/Ca-cycles on the performance of a continuous-flow biosorption fixed-bed were established. The Ca-cycle applied to Sargassum biomass in a packed bed led to a high degree of a column utilization but did not allow an effective Cu recovery. The H-cycle permitted 100% Cu recovery but also shortened the sorption column service time. The combined Ca/H-cycle was shown to be inefficient due to the time consuming regeneration of biomass from the H-form to the Ca-form. Biomass pretreatment with 1% (w) solution of CaCI2 and with 0.1 M HCI resulted in the same Cu uptake of 75 mg/g. The Ca-pretreated biomass lost approximately 30% of its Cu capacity with subsequent acidic wash. The equilibrium aspects of Cu removal and recovery in a biosorption column were analyzed through the concept of ion-exchange isotherms. The dynamics of Cu sorption and of biomass regeneration in a fixed-bed column was predicted by numerically solving the equations of a proposed ion-exchange model. © 1997 Elsevier Science Ltd Key words--biosorption, ion-exchange, Cu removal, Cu recovery, fixed-bed column, regeneration NOMENCLATURE a, b = stoichiometric coefficients in the ion- exchange reaction equation (5) A, B = species in the resin phase A, B = species in the liquid C0 = normality of the solution (meq/liter) CeNT =equivalent fraction of counterion in liquid phase CcNlo = equivalent fraction of counterion in the feed to a column C~ = equilibrium final concentration of species M in liquid phase (meq/liter) CM = XM= equivalent fraction of species M in liquid phase CMo= equivalent fraction of species M in the feed to a column CML = concentration of species M in liquid phase (meq/liter) C = concentration of binding sites in biomass (meq/g) Dz = axial dispersion coefficient (cma/s) KAB= ion-exchange equilibrium constant K~ = overall mass transfer coefficient of species M (rain -I) KH, KM,, KM2 = equilibrium constants of biosorption equilibrium model /= vertical distance from the top of a column L0 = length of the column (cm) MWCNT = molecular weight of the counterion MwM = molecular weight of the sorbing metal *Author to whom all correspondence should be addressed [E-mail: boya (a chemeng.lan.mcgiU.ca]. NEP = number of experimental points for a given binary biosorption system qM = yM = equivalent fraction of species M in solid phase qM* = dimensionless equilibrium uptake of species M at CM qMS= uptake of species M (meq/g) Q = equilibrium uptake of species M at CMt = Cuo'C0 (meq/g) rA. -- ion-exchange separation factor t = dimensionless time V = interstitial velocity of the fluid (cm/min) Greek symbols E = column void fraction v = stoichiometric coefficient of the ex- change reaction pb = packing density (g/liter) = time (min) Dimensionless groups DBM = pbQ/CoE = solute distribution parameter Pe¢ = Lov/Dz = column Peclet number ShM = KrmLo/v = modified Sherwood number INTRODUCTION Aqueous heavy-metal pollution represents an import- ant environmental issue. Although the removal of toxic heavy metals from industrial waste-waters has been addressed for many years, the effectiveness of the commonly employed treatment of metal-bearing effluents remains limited. Chemical precipitation leads to the production of toxic sludges. Due to the 2327