Comparative solvent extraction study of silver(I) by MEHPA and Cyanex 302 as acidic extractants in a new industrial diluent (MIPS)

• Silver extraction with MEHPA was performed for the first time.
• A new industrial solvent was used for the first time.
• Extraction parameters were calculated for Cyanex-302 and MEHPA as extractants.
• Silver extraction with MEHPA was more feasible than that with Cyanex-302.

The experimental results for the solvent extraction of silver ions from acidic aqueous media with bis(2,4,4-trimethylpentyl) monothiophosphonic acid (Cyanex 302) and a mixture of mono and di(2-ethylhexyl) phosphoric acid and di(2-ethylhexyl)phosphoric acid (MEHPA) as the ligand, diluted with an industrial paraffinic solvent are presented. The effects of the influential parameters such as pH, contact time, extractant type, extractant concentration and temperature were investigated. The results of the solvent extraction of silver ions from the solutions showed that extraction of the silver ions increased with increasing pH, extractant concentration and temperature. The stoichiometry of the extracted metal species by Cyanex 302 and MEHPA with silver ions was 1.0:1.5 and 1.0:4.0, respectively. The results of solvent extraction showed that a quantitative extraction of silver ions was feasible in a single stage within 3 min only at the condition of O/A = 1, silver ions concentration of 0.035 mol L− 1, pHeq = 7.0 for [MEHPA] = 0.4 M and pHeq = 6.5 for [Cyanex 302] = 0.05 M, respectively. The stripping of silver from the loaded organic carried out with nitric acid showed quantitative stripping for MEHPA (97.2%).The composition of the extracted species in the organic phase was proposed to be AgL(HL)(4x − 1)(org) and AgL(HL)(1.5x − 1)(org), for MEHPA and Cyanex 302, respectively. The thermodynamic analysis of the temperature effects showed that the extraction processes were endothermic and standard enthalpy change for both extractants were positive.