Cu(II), Pb(II) and Cr(VI) Adsorption on the Modified Activated Carbon

In this study, the sorptions of Cu(II), Pb(II), and Cr(VI) on amine-functionalized activated carbon were investigated. Coal from the Tavantolgoi deposit of Mongolia was used as a precursor for the modification. After the coal carbonization, the char was activated with heated steam at different times (120, 180, and 240 min) and several temperatures (800oC and 850oC). The activated carbon at 850oC for 240 min was used for the treatment with 3-aminopropyltriethoxysilane (APTES). The interactions between metal ions and functional groups on the sorbent surface were confirmed by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDS). The influence of various parameters such as pH (2-7), contact time (0.5-6 h), temperature (25oC, 35oC, 45oC, and 55oC), initial concentration of heavy metals ions (10, 25, and 50 mg/L), and common cations (Na, K, Ca, Mg) was investigated. The optimum pH for Cu(II), Pb(II), and Cr(VI) sorption on the modified activated carbon was chosen as 4, 3, and 3, respectively. The sorption capacity was increased from 6.15 to 9.88 mg/g and 17.1 mg/g to 19.0 mg/g when increased the temperature from 25oC to 55oC for Cu(II) and Cr(VI) adsorption, respectively (initial concentration of metal ions were 50 mg/L). But the sorption capacity was decreased from 3.13 mg/g to 2.69 mg/g when increased the temperature from 25oC to 55oC for Pb(II) adsorption. The thermodynamic parameters such as enthalpy (ΔHo), entropy (ΔSo), and Gibb’s free energy (ΔGo) were estimated, and the results confirmed that all sorption processes are spontaneous and thermodynamically favorable. The sorption capacity was decreased when the amount of Na, K, Ca, or Mg increased from 0 to 200 mg/L, and a remarkable decrease in sorption capacity was observed for Pb(II) adsorption. The order of adsorption capacity of modified activated carbon for metal ions was Cr(VI) Cu(II) Pb(II). The sorption mechanism was discussed for the