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.

Keywords:

• Surface modification
• Separation technology
• Pb and Cu ions
• Hydrometallurgy
• D₂EHPA
• Amberlite XAD‐4 resin

Acknowledgment

The authors thank the National Science Council of R.O.C. for the financial support (Project No. NSC91‐2214‐E‐027‐005).