Dysprosium removal from water using active carbons obtained from spent coffee ground

This paper describes the physicochemical study of the adsorption of dysprosium (Dy^(3+)) in aqueous solution onto two types of activated carbons synthesized from spent coffee ground. Potassium hydroxide (KOH)-activated carbon is a microporous material with a specific Brunauer-Emmett-Teller (BET) surface area of 2330 m^2.g^-1 and pores with a diameter of 3.2 nm. Carbon activated with water vapor and N_2 is a solid mesoporous, with pores of 5.7 nm in diameter and a specific surface of 982 m^2.g^-1. A significant dependence of the adsorption capacity on the solution pH was found, but it does not significantly depend on the dysprosium concentration nor on the temperature. A maximum adsorption capacity of 31.26 mg.g^-1 and 33.52 mg.g^-1 for the chemically and physically activated carbons, respectively, were found. In both cases, the results obtained from adsorption isotherms and kinetic study were better a fit to the Langmuir model and pseudo-second-order kinetics. In addition, thermodynamic results indicate that dysprosium adsorption onto both activated carbons is an exothermic, spontaneous, and favorable process