Surface Modification of Amberlite XAD‐4 Resin with D2EHPA by a Two‐Step, Solvent–Nonsolvent Procedure and the Application on the Selective Separation of Lead and Copper Ions

Abstract

Di(2‐ethylhexyl)phosphoric acid (D2EHPA) has the tendency to adsorb at interfaces in an oriented fashion due to the amphiphilic structure. The study of the surface tension shows that the adsorption of D2EHPA at interface can lower the surface tension of ethanol solution. The amount of adsorption is affected by the pH and ionic strength of the solution. Being a small surface‐active molecule, a monolayer of D2EHPA molecules can be immobilized on the surface of nonpolar Amberlite XAD‐4 resin by a two‐step, organic solvent–nonorganic solvent process. The amount of immobilized D2EHPA is as high as 1.02 (mol/kg of resin). The electron spectroscopy for chemical analysis (ESCA) results show that the immobilized D2EHPA undergoes reorientation by further exposing the phosphoric acid group to the water phase. Since the hydrophobic alkyl chains of D2EHPA physically entangle with the surface polymer chains of Amberlite XAD‐4, the immobilized extractant has good stability on the resin surface. This D2EHPA‐modified Amberlite XAD‐4 can be used for the separation of lead and copper ions as an ion‐exchange resin. Ion‐exchange isotherm experiments show that D2EHPA‐modified resin has higher Pb ion affinity than Cu ion. This new type of D2EHPA‐modified resin shows better Pb and Cu ions separation than analogous D2EHPA‐impregnated resin [extractant‐impregnated resin (EIR)] and solvent extraction system. The selective separation results using series contacts of solution mixtures with resins further demonstrated the feasibility of using D2EHPA‐modified Amberlite XAD‐4 resin for the separation of Pb/Cu mixed ion solution. After only six batches of contacts, the relative ion concentration of Cu ion increases from 50% to more than 99%, while the relative ion concentration of Pb ion decreases from 50% to less than 1%. The Cu recovery rate is more than 75%, comparing to 54% in the EIR system.