REMOVAL OF PB(II), HG(II), CR(VI), AND NI(II) FROM WASTEWATER VIA COMPLEXATION-ASSISTED ADSORPTION ONTO MESOPOROUS ADSORBENT: EFFECTS OF PH, TEMPERATURE, AND PORE STRUCTURE

Abstract

Eluting the toxic heavy metals in wastewater is also a highly important environmental challenge because they are persistent and bioaccumulative as well as have detrimental health impacts. A functionalized mesoporous adsorbent was prepared in this research through amine grafting on a mesoporous silica structure and tested in adsorbing Pb(II), Hg(II), Cr(VI), and Ni(II) on aqueous solutions using complexation-based adsorption. Successful functionalization and maintenance of the mesoporosity of the structure was confirmed by structural characterization with the BET surface area of 412 m² g⁻¹ a high surface area and an average pore diameter of 6.7 nm. Experiments involving batch adsorption were carried out under different conditions of pH (2-10), temperature (20-60⁰C) and metal concentration (10-200 mg L⁻¹) in order to ascertain the conditions of optimal behavior and adsorption. The removal was also very dependent on solution pH and metal speciation with the best results being a pH of 5 with Pb(II) and Hg(II), pH of 6 with Ni(II), and pH of 3 with Cr(VI). The temperature raised the adsorption capacity and this is a sign of an endothermic process. Langmuir and Freundlich models provided a good characterization of the equilibrium data, implying that the adsorption took place on homogeneous adsorbing amine sites with a small portion of heterogeneity. The maximum adsorption capacities were 182.4, 165.7, 138.6 and 121.3 mg g⁻¹ of Pb(II), Hg(II), Cr(VI), and Ni(II), respectively. Spontaneous chemisorption was proved by means of thermodynamic parameters (ΔH° = 19-28 kJ mol⁻¹; ΔG° < 0). Enhanced adsorption behavior is probably explained by the synergistic activity of mesoporous diffus[]ion channels, large surface area, and an effective coordination interaction between amine functionalities and metal ions. The results indicate that the functionalized mesoporous adsorbents are valuable materials to be utilized effectively and selectively in the removal of various heavy metals in wastewater and justify their possible use in modern installations of water purification.