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phenyl]thiourea (=MEPT) was synthesized to examine the extraction properties of metal ions. MEPT selectively extractedd copper (II), palladium (II), gold (III) and silver (I) over base metals in 1 mol dm-3 aqueous ammonium nitrate solution. The extraction of copper (II), palladium (II) and gold (III) was dependent on pH. The stoichiometry of the extraction of copper (II) with MEPT was elucidated by examining the effects of hydrogen ion, extractant and nitrate ion concentrations on its extractability. It was found that copper (II) was extracted as a complex of copper (II): MEPT with a mole ratio of 1:3. The copper (II) extraction with MEPT (=HR) was represented by the following reaction:The extraction equilibrium constant was determined to be K=0.60(mol dm-3)-1 1 Introduction Solvent extraction has attracted much attention as an effective and energy-saving type of separation technique for metal ions.[ 1 ] This technique has been now widely accepted as a process for the recovery of metal ions in hydrometallurgical and environmental applications. The separation and purification of various metals by solvent extraction has been conducted using various types of extraction. Thus, many extractants have been developed with high selectivity and high extraction rate.[2J Recently, derivatives of thiourea have gained serious interest far the extraction and separation of precious metals from hydrochloric acid.[3] It was considered that the high selectivity for precious metals over base metals was attributed to the difference of complex formation

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