A comparative study of removal of Cu(II) from aqueous solutions by locally low-cost materials: marine macroalgae and agricultural by-products

In this study, adsorption of Cu(II) onto the five locally abundantly low-cost biosorbents (Laminaria japonica, P. yezoensis Ueda, rice bran, wheat bran and walnut hull) was investigated depending on initial solution pH, contact time, adsorbent concentration and reaction temperature. Cu(II) removal was pH-dependent for various biosorbents investigated. For P. yezoensis Ueda, rice bran, wheat bran and walnut hull, the batch equilibrium data were correlated to Langmuir and Freundlich isotherms and the data fitted better to the Langmuir isotherm equation and yielded Langmuir monolayer capacity of 5.04, 10.41, 6.85 and 3.52 mg/g at the temperature of 20°C, respectively. In the case of Laminaria japonica, the equilibrium data obeyed the Hill-der Boer equation for the whole initial concentration ranges of 0–200 mg/L examined, but only to Langmuir and Freundlich equations for the initial concentration less than 120 mg/L at various temperatures. The apparent thermodynamic parameters were calculated for each of the five biosorbents (ΔH = 9.25–40.04 kJ/mol; ΔG = –17.60 to –24.16 kJ/mol and ΔS = 85.81–228 J/mol K). The numerical values obtained showed that Cu(II) adsorption is a spontaneous, entropy-driven and endothermic process. The batch kinetic data were correlated to the pseudo-first order and pseudo-second order models and the data fitted better to the pseudo-second order equation (the pseudo-second order rate constants, k_2,e = 0.1059–0.9453 g/(mg min); the correlation coefficients, r = 0.9816–0.9993).