Host–Guest Extraction of Heavy Metal Ions with p-t-Butylcalix[8]arene from Ammonia or Amine Solutions

The capacities of the p-t-butylcalix[8]arene (abbreviated as H(8)L) host to extract toxic divalent heavy metal ions and silver from aqueous solution phases containing ammonia or ethylene diamine to an organic phase (nitrobenzene, dichloromethane, or chloroform) were carried out. When the metal ions were extracted from an aqueous ammonia solution, the metal ion selectivity for extraction was found to decrease in the order Cd(2+)> Ni(2+)> Cu(2+)> Ag(+)> Co(2+)> Zn(2+). When the aqueous phase contained ethylene diamine, excellent extraction efficiencies of 97% and 90% were observed for the heavy metal ions Cu(2+) and Cd(2+), respectively. Under the same conditions the extraction of octahedral type metal ions, namely, Co(2+) and Ni(2+), was suppressed. The extraction of transition metal cations by H(8)L in ammonia and/or amine was found to be pH dependent. Detailed analysis of extraction behavior was investigated by slope analysis, the continuous variation method, and by loading tests.