Speciation of copper–humic acid in zeolite Y during extraction with a RTIL

Abstract

Chemical structure of copper chelated with humic acid (Cu–HA) in the micro-pores of zeolite Y (to simulate micropores in copper contaminated soils) and extracted with a room temperature ionic liquid (RTIL) ([C 4mim][PF 6], 1-butyl-3-methylimidazolium hexafluorophosphate) has been studied by X-ray absorption (near edge structure (XANES) and Fourier transformed extended X-ray absorption fine structure (EXAFS)) spectroscopy. At the temperature of 298 K, within 30 min, about 84% of Cu–HA in Y can be extracted by the RTIL. The XANES spectra reveal that a small amount of Cu(II)–HA (7%), adsorbed Cu(II) ( Cu ( ads ) 2 + ) (5%) and Cu [ mim ] 4 2 + (4%), which are not extracted, are found in Y. In the copper extracted RTIL, 75% of Cu(II)–HA in Y are converted to Cu [ mim ] 4 2 + during extraction. About 17% of Cu(II)–HA is also found in the RTIL. Therefore, at least three reaction paths may be involved in the extraction process: (1) extraction of Cu(II)–HA in the RTIL, (2) Cu 2+ (formed from dissociation of Cu(II)–HA in the RTIL) adsorbed on Y, and (3) inter-conversion of Cu(II)–HA to Cu [ mim ] 4 2 + in the RTIL. The refined EXAFS data indicate that the Cu–O bond distance in the Y and RTIL phases is 1.94 Å with an average coordination number (CN) of 3.4. Note that Cu [ mim ] 4 2 + in the RTIL processes a Cu–N bond distance of 1.96 Å and a CN of 4.1.