Production of micro- and mesoporous activated carbon from paper mill sludge: I. Effect of zinc chloride activation Original Research Article

A series of micro- and mesoporous activated carbons were produced from paper mill sludge using a modified carbonization methodology. N2-adsorption isotherm data and mathematical models such as the D–R equation, αs-plot, and MP and BJH methods were used to characterize the surface properties of the produced carbons. Results of the surface analysis showed that paper mill sludge can be economically and successfully converted to micro- and mesoporous activated carbons with surface areas higher than 1000 m2/g. Activated carbons with a prescribed micro- or mesoporous structure were produced by controlling the amount of zinc chloride (ZnCl2) used during chemical activation. Pore evolvement was shown to be most affected by the incremental addition of ZnCl2. Increasing the ZnCl2 to sludge ratio from 0.75 to 2.5 resulted in a 600% increase in the mesopore volume. ZnCl2 to sludge ratios less than 1 and greater than 1.5 resulted in the production of micro- and mesoporous carbons, respectively. At a ZnCl2 to sludge ratio of 3.5, an activated carbon with a predominantly (80%) mesoporous structure was produced. The calculated D–R micropore volumes for activated carbons with the suggested microporous structure were in good agreement with those obtained from the αs method, while estimated micropore volumes from the αs method deviated markedly from those obtained from the D–R equation for carbons with a predominantly mesoporous structure.