Adsorption behaviors of ETS-10 and its variant, ETAS-10 on the removal of heavy metals, Cu2+, Co2+, Mn2+ and Zn2+ from a waste water

Nano-sized large pored titanium silicate zeolitic materials, ETS-10 and ETAS-10 with different Al2O3/TiO2 ratio were successfully applied to the removal of heavy metal ions, in particular, Cu2+, Co2+, Mn2+ and Zn2+. The study of equilibrium and adsorption isotherm at 298 K and 323 K for Cu2+, Co2+, Mn2+ and Zn2+ were conducted using batch mode.The uptake rates for Cu2+, Co2+, Mn2+ and Zn2+ were extremely rapid and fitted to the pseudo-second order equation well. The equilibrium capacities by the pseudo-second order equation on ETS-10 and ETAS-10 synthesized by titanium oxysulfate as the titanium source were determined to be 1.31 mmol/g and 1.13 mmol/g for Cu2+, 1.05 mmol/g and 1.08 mmol/g for Zn2+, 0.96 mmol/g and 0.99 mmol/g for Mn2+, 0.93 mmol/g and 1.01 mmol/g for Co2+ at 30 mmol/l of initial concentration.Adsorption isotherms for Cu2+, Co2+, Mn2+ and Zn2+ were fitted to Langmuir, Freundlich and Langmuir–Freundlich isotherms. The results show that Langmuir–Freundlich isotherm has fitted best to the current system. The selectivity of heavy metal ions both on ETS-10 and ETAS-10 at 298 K is in the order of Cu2+ > Zn2+ > Mn2+ > Co2+ while it is in the order of Cu2+ > Mn2+ > Zn2+ > Co2+ at 323 K. The monolayer capacities on ETS-10 and ETAS-10 synthesized by titanium oxysulfate as the titanium source at 298 K were determined to be 1.55 mmol/g and 1.62 mmol/g for Cu2+, 1.30 mmol/g and 1.32 mmol/g for Zn2+, 0.98 mmol/g and 1.11 mmol/g for Mn2+, 0.91 mmol/g and 0.89 mmol/g for Co2+, respectively. However, at 323 K, the monolayer capacity of Mn2+ ion on ETS-10 and ETAS-10 was determined rather larger than that of Zn2+ ion.Finally, thermodynamic parameters suggest that the adsorption process of Cu2+, Co2+, Mn2+ and Zn2+ on ETS-10 and ETAS-10 is endothermic and spontaneous process, being indicated by positive ΔH0 and negative ΔG0. In addition, positive ΔS0 suggests that heavy metal ions are not stable on the adsorption sites of ETS-10 and ETAS-10 probably due to the increase in translation energy of heavy metal ions displaced from the adsorption sites.