Mechanisms of Cu2+, triethylenetetramine (TETA), and Cu-TETA sorption on rectorite and its use for metal removal via metal-TETA complexation

Uptake of metals, organics, and formation of metal-organic complexes on the surface or in the interlayer of clay minerals had been studied extensively over the last half century. In this study, we investigated the uptake mechanisms of Cu2+, triethylenetetramine (TETA), and Cu-TETA on rectorite and its use for metal removal via metal-TETA complexation. The uptake of Cu2+, TETA, and Cu-TETA by rectorite occurred on the external as well as in the interlayer space, resulting in a change of d(001)-spacing due to differences in sizes of interlayer cations or complexes. Although the uptake of Cu2+ and Cu-TETA by rectorite was via a cation exchange process as evidenced by the stoichiometric desorption of dominant interlayer cation Ca2+, the uptake of TETA alone on rectorite was via complexation with interlayer cation Ca2+. Due to strong affinity of TETA for Cu2+, significant amounts of Cu2+ uptake occurred on TETA-rectorite. Desorption of Ca2+ from TETA-rectorite confirmed the replacement of interlayer cation Ca2+ by Cu2+. However, the replacement of Ca2+ by Cu2+ in TETA-rectorite did not involved in removal of TETA. As such, TETA-modified clay minerals may serve as a type of sorbents for the removal of selected heavy metals via surface or interlayer via complexation.