Adsorptive treatment via simultaneous removal of copper, lead and zinc from soil washing wastewater using spent coffee grounds

In the present work, the performance of spent coffee grounds (SCG) as an adsorbent in the treatment of real soil washing wastewater (SWW) was evaluated. Scanning electron microscopy, Fourier transform infrared spectroscopy, zeta potential measurement and Brunauer–Emmett–Teller analysis were utilized to determine the physicochemical characteristics of SCG. Maximum removal efficiency of 68.73% for Cu(II), 57.23% for Pb(II) and 84.55% for Zn(II) was attained at 2.5 g SCG, 300 min and 328 K. Error analysis was performed using root mean square error (RMSE) and sum of square error (SSE). Equilibrium data correlated well with the Langmuir isotherm for Pb(II) adsorption and Freundlich model for the removal of Cu(II) and Zn(II). The kinetic study shows that adsorption of the heavy metals using SCG can be satisfactorily described using the pseudo-second order equation (R2 ≥ 0.9901; RMSE ≤ 15.0539; SSE ≤ 145.1461). Activation parameters including activation energy, change in free energy of activation, activation entropy change (ΔS*) and activation enthalpy change (ΔH*) were determined using Arrhenius and Eyring equations. Thermodynamic studies show that adsorption of the heavy metals using SCG is spontaneous, endothermic (ΔH° ≥ 9.80 kJ/mol·K) and results in increased randomness at the solid/solution interface (ΔS° ≥ 2.28 J/mol).