A Study on the Removal of Chromium(VI) Oxanions from Acid Solutions by Using Oxonium Ion-Crown Ether Complexes as Mobile Carrier Agents

Crown ethers ۱۲-crown-۴ (۱۲C۴), benzo-۱۵-crown-۵ (B۱۵C۵), ۱۸-crown-۶ (۱۸C۶), nitrobenzo-۱۸-crown-۶ (NB۱۸C۶) dibenzo-۱۸-crown-۶ (DB۱۸C۶) and dicyclohexyl-۱۸-crown-۶ (DC۱۸C۶), dissolved in dichloromethane, are able to form oxonium-ion complexes in contact with aqueous sulfuric and hydrochloric acid solutions. This ability allows the transfer of Cr(VI) oxanions from the acid media, through an organic liquid membrane, into a distilled water receiving phase. Among the studied crown ethers, DC۱۸C۶ shows the highest transport efficiency.The effect of parameters influencing the process such as the crown ether concentration in the membrane, types of the organic diluent, acid concentration in the feed phase and time is investigated and discussed. Four replicate experiments show that an average of ۹۵.۶ (±۱.۳)% of the initial chromium in the source phase (۱۰-۳ M Cr(VI), ۶ M H۲SO۴, ۱۰ ml) is extracted into the distilled water(۱۰ ml) through the membrane (DC۱۸C۶ ۰.۰۵ M in CH۲Cl۲, ۲۰ ml) after ۸ h. The corresponding result, under similar conditions, in the presence of hydrochloric acid solution (۴ M) was found to be ۹۵.۰ (±۱.۲)%. The selectivity of the process was assessed by performing the competitive transport experiments on a solution containing Cr(VI), Ni(II), Co(II), Pb(II), Mn(II), Zn(II) and Fe(III) ions. The method was used for the recovery of chromium from two real samples provided by chromium-electroplating industries.

کلیدواژه ها:

Cr(VI) ions ، Recovery ، Electroplating waste ، Liquid membrane ، Crown Ethers