Preparation Of Nano-sized Iron-oxyhydroxide-modified Macroporous Ion Exchange Resins For The Removal Of Heavy Metals

Ion exchange resins are widely used to remove heavy metal ions in water due to their high adsorption capacity,stabilization,and reusable characteristics.But its selective adsorption ability is weak,and it needs to be regenerated with strong acid or strong alkali which will affect the effluent water quality.In this study,the macroporous strong acid cation exchange resin?D001?and strong basic anion exchange resin?D201?were modified by nano-sized iron oxyhydroxides?n Fe OOH?with ethanol dispersion and impregnation method to improve their selectivity to lead and chromium and simplify the regeneration process.The characterization showed that the n Fe OOH?20-120 nm and 20-150 nm?were evenly distributed on the D001 and D201 surfaces.The experimental results showed that n Fe OOH can improve the adsorption performance of D001 resin for Pb?II?and D201 resin for Cr?VI?.The maximum adsorption capacities of n Fe OOH@D001 for Pb?II?and n Fe OOH@D201 for Cr?VI?were 476.2 mg/g and 219.3 mg/g,respectively,which were 6.7%and 11.0%higher than the original resins D001 and D201.The adsorption process conforms to the pseudo-first-order,pseudo-first-order kinetic and Langmuir model,indicating that the adsorption process was a single layer adsorption,and physical adsorption and chemical adsorption exists simultaneously in the adsorption process.The adsorption of n Fe OOH@D001 to Pb?II?mainly depends on the ion exchange by-SO₃H and the complexation by Fe-O,while the adsorption of n Fe OOH@D201 to Cr?VI?was simultaneously controlled by the electrostatic adsorption?>Fe OH₂⁺?,ion exchange?-N+?CH₃?₃?and complexation?>Fe OH?.Moreover,both n Fe OOH@D001 and n Fe OOH@D201 had stronger anti-interference performance than the original resin.When the concentrations of co-existent Ca²⁺and Mg²⁺were 0.8 m M,the n Fe OOH@D001 had a 31.5%and 23.8%higher Pb?II?removal efficiency than D001,respectively.For n Fe OOH@D201,when the concentration of co-existent NO₃^-and SO₄^2-were 2 and 4 m M,respectively,it had a 32.5%and 18.9%higher Cr?VI?removal efficiency than D201,respectively.In addition,the adsorbed n Fe OOH@D001 and n Fe OOH@D201 could be desorbed with 0.1 M acetic acid.And the used n Fe OOH@D001and n Fe OOH@D201 could be eluted by 0.1 M HCl to remove n Fe OOH,and the renewed D001 and D201 could be recoated by n Fe OOH and achieved an efficiency of 97.6%and90.9%,respectively.According to the dynamic adsorption study,the removal capacity of the n Fe OOH@D001column for Pb?II?was 988.1 mg/g at the flow rate of 12.5 cm/min and the Pb?II?concentration of 5 mg/L,its removal capacity and life-span were 23.5%and 25.8%higher than D001 column,respectively.For the n Fe OOH@D201 column,the Cr?VI?removal capacity was 401.3 mg/g at the flow rate of 12.5 cm/min and the Cr?VI?concentration of 2.5mg/L,its removal capacity and life-span were 25.3%and 12.6%higher than D201 column,respectively.The above results indicated that the modified D001 and D201 by nano-sized Fe OOH had a better performance for Pb?II?and Cr?VI?removal,and it enhanced the its anti-interference performance,desorption and regeneration performance and life-span,so that n Fe OOH@D001and n Fe OOH@D201 would be an effective adsorbent materials for removing heavy metals in drinking water.