Removal of copper on composite sewage sludge/industrial sludge-based adsorbents: The role of surface chemistry

Sewage sludge and industrial waste oil sludge were pyrolyzed in an inert atmosphere at 650 or 950 °C, either as single components or as 50:50 mixtures. Composite materials were used as adsorbents of copper ions from aqueous solution. The capacity for copper removal was comparable to that of commercial activated carbon. To relate the performance of materials to their properties, the surface features were characterized using adsorption of nitrogen, thermal analysis, XRF, potentiometric titration, and elemental analysis. The results indicated that a high copper removal capacity could be linked to basic surface pH and specific compounds present on the surface. The high removal ability of materials obtained at 650 °C is attributed to cation exchange reactions between calcium and magnesium in aluminosilicates, formed on their surface during heat treatment, and copper. On the other hand, the high degree of mineralization of the surface of the materials obtained at 950 °C promotes copper complexation and its surface precipitation as hydroxides or hydroxylcarbonate entities.

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