Adsorption and recovery of immobilized coffee ground beads for silver ions from industrial wastewater

To efficiently adsorb silver ions from industrial wastewater, powdered coffee grounds were immobilized as a bead form by modified polyvinyl alcohol and boric acid method. The beads with 2.0 mm of diameter have the 9.87 m(2)/g of surface area and were stable in the range of similar to 45 degrees C and to all pH range in wastewater without untangling. In addition, the beads have excellent mechanical strength and low swelling ratio. The adsorption capacity of immobilized coffee ground beads for silver ion was achieved as about 36.3 mg/g at the pH 6.0 in wastewater solution when the beads containing 3.0 g of coffee grounds was used. The surface condition and the existence of silver ions onto the immobilized coffee ground beads were confirmed by the SEM image and EDX spectrum. The Langmuir isotherm model showed significant fit to the equilibrium adsorption data and maximum adsorption capacity of 39.583 mg/g of silver ions was achieved at the pH 6.0 of wastewater. The breakthrough point was appeared around 180 (1.0 mL/min) and 340 bed volumes (0.5 mL/min), respectively, and 6 bed volumes of 1.0 M HNO3 solution was required to get desorption efficiency of 95% in continuous process. And, the bed volumes can be still maintained as 310 even though secondary reused immobilized coffee ground beads were used. (C) 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.