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 d₀₀₁-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.