Mercury(Ⅱ) Adsorption From Aqueous Solutions And Wastewaters Using Surface Modified Clay And Metal Oxide Gel

摘要

Surface modified and functionalized kaolinite clay and metal oxide gel (boehmite) have been developed as adsorbents for assessing the removal efficiency of Hg(Ⅱ) from aqueous solution and industrial wastewaters. We immobilized humic acid (HA) onto clay and boehmite and 2-mercaptobenzimidazole (MBI) onto clay; the adsorbents thereafter referred to as HA-clay, HA-boehmite and MBI-clay respectively, by batch equilibration technique. Adsorption experiments were conducted to evaluate the pH effects, kinetics, concentration effects and sorption isotherm of Hg(Ⅱ) adsorption onto different adsorbents. The adsorption of Hg(Ⅱ) increases with increasing pH and reached a plateau value. The optimum pH value for the removal of Hg(Ⅱ) was found to be 4.0-8.0 for MBI-clay and 5.0 to 8.0 for HA-clay and HA-boehmite. The highest Hg(Ⅱ) uptake values (24.53, 23.03 and 21.88 mg/g, respectively for MBI-clay , HA-clay and HA-boehmite) were achieved at pH 6.0 from an initial concentration of 50 mg/L. The kinetics of sorption of Hg(Ⅱ) were best described by a reversible-first-order model for HA-clay and HA-boehmite and pseudo-second-order model for MBI-clay. By increasing the metal concentration from 50 to 250 mg/L, the percentage adsorption of Hg(Ⅱ) decreased from 98.1 to 70.2 % for MBI-clay and 92.1 to 64.7 % for HA-clay and 87.5 to 61.3 % for HA-boehmite. The order of efficiencies for the removal of Hg(Ⅱ) ions is MBI-clay > HA-clay > HA-boehmite. The applicability of Langmuir isotherm equation for Hg(Ⅱ) removal has been tested. Chlor-alkali industrial wastewater was also treated by adsorbents to demonstrate their efficiencies in removing Hg(Ⅱ) from wastewaters. About 83.1 %, 94.0 % and 95.0 % of Hg(Ⅱ) can be removed respectively for the spent MBI-clay, HA-clay and HA-boehmite by controlling the pH at 2.0. The results obtained point towards viable adsorbents, which are both effective as well as economically attractive for Hg(Ⅱ) removal from wastewaters.