Adsorption of Copper (II) onto activated carbons from sewage sludge by microwave-induced phosphoric acid and zinc chloride activation

Sewage sludge-based activated carbons were prepared with microwave-induced activation process using phosphoric (SP) or zinc chloride (SZ) as the chemical activating agents. The physicochemical properties of the carbons were carried out. The effectiveness of the carbons prepared in adsorption of Cu(II) has been studied as a function of pH, agitation time and temperature. The results showed that the adsorption of Cu(II) onto SP and SZ was maximal at about pH 5.0. The rates of adsorption were found to conform to the pseudo-second-order kinetic model. The intra-particle diffusion was identified to be the rate-limiting step. Langmuir isotherm showed better fit than Freundlich isotherm for all activated carbon samples and the maximum adsorption capacities of Cu(II) were 7.73 and 10.56 mg/g for SP and SZ, respectively. The thermodynamics parameters such as △G0, △H0, △S0 were also evaluated. The SZ carbon was found to be both effective and economically viable.

Research highlights
► Sewage sludge-based carbons are prepared with microwave-induced activation process using H3PO4 and ZnCl2 as the chemical activating agents.
► The pore structure of the microwave activated carbon is better developed than that of the thermally activated carbon.
► The SZ is an alternative adsorbent for the removal of Cu2+ from water due to its considerable adsorption capacity and economically available.