Interactions of Cd(II) with waste-derived 11 Å tobermorites

Paper recycling gives rise to significant volumes of secondary waste materials which undermine its economic and environmental sustainability. In response to this problem, a waste combustion ash arising from newsprint recycling has been evaluated as a feedstock material for the hydrothermal synthesis of Al-substituted 11 Å tobermorites. Highly crystalline tobermorite (NRR-H2O) was obtained from a stoichiometrically optimised mixture of newsprint recycling residue, sodium silicate and calcium oxide, whereas a less well-ordered product (NRR-NaOH) was acquired when sodium hydroxide was also incorporated into the reagent mixture.Structural disorder within the tobermorite lattice was found to accelerate the kinetics of Cd2+ for Ca2+ ion exchange although had little impact on the total number of available exchange sites per unit formula. The Langmuir isotherm model provided a suitable description for the steady state uptake of Cd2+ by both tobermorite specimens under single metal ion batch sorption conditions, from which, maximum adsorption capacities of 167 and 179 mg g−1 were obtained for NRR-NaOH and NRR-H2O, respectively.