A study on removal characteristics of copper from aqueous solution by sewage sludge and pomace ashes

In the present work, the abilities of sewage sludge and pomace ashes to remove copper (Cu2+) ions from aqueous solutions are compared. Batch adsorption experiments were performed in order to evaluate the removal efficiency of these materials. Effect of contact time, solution pH, ash concentration and temperature on the removal of Cu2+ was investigated. The results of batch equilibrium studies showed that the solution pH was the key factor affecting the adsorption characteristics. In general, the amount of Cu removed increased as the solid concentration and pH increased, and then it remained constant over a wide pH region. The adsorption test of applying sewage sludge and pomace ashes into synthetic wastewater revealed that the adsorption data of these materials for copper ions were better fitted to the Langmuir isotherm since the correlation coefficients for the Langmuir isotherm were higher than that for the Freundlich isotherm. The estimated maximum capacities of copper adsorbed by sewage sludge and pomace ashes were 5.71 and 6.98 mg g−1, respectively. Experimental results indicated that the adsorption was favorable at higher pH and higher temperature. Values of ΔG° ranging from −4.64 to −5.13 kcal mol−1 for sewage sludge ash and from −4.97 to −5.53 kcal mol−1 for pomace ash suggest that the adsorption reaction is a physical process enhanced by the electrostatic effect. The values of ΔH° and ΔS° are, respectively, 4.27 kcal mol−1 and 30.6 cal K−1 mol−1 for sewage sludge ash and 4.33 kcal mol−1 and 31.3 cal K−1 mol−1 for pomace ash. The mechanisms of copper removal by these materials included adsorption and precipitation. The sewage sludge and pomace ashes are shown to be effective adsorbents for this metal.