Adsorption of Cu(II) ions from aqueous solutions on waste coffee residues: sorption kinetics, equilibrium isotherms, and thermodynamic parameters

Water polluted with metal ion is a serious environmental problem worldwide in recent years. Among various metal ions commonly found in wastewater, copper (II) is a priority toxic pollutant and needs to be removed Cu(II) from aquifers to mitigate water pollution. One possible way to clean Cu(II)-polluted water is the use of agricultural based low-cost adsorbent. Therefore, in this study, waste coffee residue (WCR) with four different morphologies has been used as adsorbents to adsorb Cu(II) from aqueous solutions. These adsorbents have been characterized using Fourier-Transform Infrared Spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) specific surface area (SSA), and point of zero charge (pHPZC) using zeta potential measurement. Batch Cu(II) adsorption data were evaluated in terms of adsorption edges, kinetics, isotherms, and thermodynamic calculations. Cu(II) adsorption was rapid and reached equilibrium within 60 min and strongly depended on solution pH. Adsorption data correlated with pseudo-second-order kinetic and Langmuir model satisfactorily. The maximum adsorption capacities for these adsorbents defined as WCR1, WCR2, WCR3, and WCR4 were 4.79, 8.04, 12.34, and 13.33 mg/g, respectively, at pH 5 and 25 degrees C. Thermodynamic calculations with WCR2 substrate revealed that Cu(II) adsorption was spontaneous and endothermic in nature. The result of this study shows that these adsorbents are efficient in removing Cu(II) and could be used to adsorb other pollutants from large scale environmental samples. This study could be a good contribution of the cleanup waste water and represents an active research in the area of waste water treatment by bio-adsorbent.