Investigation of experimental results andD-optimal design of hafnium ion extraction from aqueous system using emulsion liquid membrane technique

Hafnium metal is used in a wide range of industries such as microprocessor manufacturing, nuclear reactors and special alloys due to its physical, chemical and radiation properties. Emulsion liquid membrane (ELM) is an effective and efficient alternative for heavy metal separation compared to conventional methods due to high selectivity, energy-saving, high mass transfer and low operating capital. In this study, Cyanex 572 as a carrier, Span 85 as a surfactant, hydrochloric acid as an internal phase and kerosene as a diluent were used. In the first part of the study, the stability of the emulsions was investigated. The most stable emulsions were obtained by adding PIB polymer (3% w/v), Span 85 surfactant (3% w/v) and stirring for 15 min. In the second part, the separation of hafnium metal ions from aqueous solutions was investigated using ELM technique. The highest separation was obtained at 4% (v/v) as carrier concentration, 4% (w/v) as surfactant concentration, the membrane-to-feed volume ratio of 20/100 and W/O/W emulsion stirring rate and time equal to 400 rpm and 5 min, respectively. Moreover, to optimize the factors influencing the tests, the design of experiment (DOE) was performed usingD-optimal method via Design Expert 10 software. Based on DOE results, the maximum extraction (> 99%) was achieved when the carrier concentration, the surfactant concentration, W/O/W emulsion stirring time, W/O/W emulsion stirring rate and emulsion volume/feed phase ratio were 4.49% v/v, 3.90% w/v, 11.49 min, 310.54 rpm and 2:1, respectively.