Thermodynamics of strontium extraction using substituted crown ethers in mixtures of aliphatic alcohols

Abstract

The extraction of Sr(II) from 4 M nitric acid was carried out employing two substituted crown ethers, viz. dicyclohexano 18crown6 (DCH18C6) and di-t-butyl cyclohexano 18crown6 (DTBuCH18C6) in n-octanol and n-butanol-n-octanol mixtures. The extracted species conformed to SrL2+ · 2(NO3 -) · xH2O where L = DCH18C6/DTBuCH18C6 and x = no. of water molecules associated with the extracted complex. The log DSr vs. log[L] plots yielded straight lines with unity slope for DTBuCH18C6 as well as DCH18C6. Thermodynamics of Sr(II) extraction for the mixed diluent system employing these crown ethers has been investigated (in the temperature range of 10° to 50°C). The negative enthalpy as well as negative entropy values suggest ion-association type species getting extracted into the organic phase which are stabilised by solvation in the water rich alcohol phase.