Recovery of copper by biopolymer gel and polymer vegetation by electrowinning and ion exchange technologies

Abstract

Biopolymer gel beads of calcium alginate and alginic acid have high affinities for divalent metal ions such as Cu 2+. Hence they may be useful materials for recovering copper from aqueous solutions. The copper sorbed by the calcium alginate gel beads could be completely eluted and the metal recovered in a salable metallic form by using a combination of ion-exchange and electrowinning technologies. In such processes, the calcium alginate gel beads are fully regenerated. The resorption capacity of the gel beads did not decrease significantly during up to three sorption-desorption-electrowinning cycles. Distribution ratios of copper between the gel and liquid phases were measured using a batch method. Distribution ratios of copper for gel beads of calcium alginate ranged from 0.3 to 0.9 liter solution/gram dry sodium alginate [(mg Cu 2+ / gram dry sodium alginate)/(mg Cu 2+ / liter solution)]. Distribution ratios of copper for gel beads of alginic acid ranged from 0.47 to 0.84 liter solution/gram dry sodium alginate [(mg Cu 2+ / gram dry sodium alginate)/(mg Cu 2+ / liter solution)]. The equilibrium data were consistent with the ion-exchange reaction between cupric ions and calcium alginate/alginic acid. Maximum sorption capacities of the gel beads of calcium alginate and alginic acid were determined by comparing the experimental data with theoretical predictions. Maximum sorption capacities of the gel beads were found to be 5.21 X 10 -3 kmol/ kg dry sodium alginate and 4.11 X 10 -3 kmol/ kg dry sodium alginate for calcium alginate and alginic acid respectively. 3.2% sodium alginate in water was used to make the gel beads of calcium alginate and alginic acid. Scale up of the technology was studied in a fluidized bed reactor and electrowinning cell designed for this purpose. Calcium alginate gel beads were reused up to three times for absorption of copper after regeneration using ion exchange and electrowinning technologies. This technology reduced the influent copper concentration by 63%.