EDTA modified LDHs as Cu2+ scavengers: Removal kinetics and sorbent stability

Abstract

EDTA modified layered double hydroxides (LDHs) were investigated as potential sorbents to remediate heavy metals pollution. The polidentate ligand was introduced by an exchange method in a Zn-Al-LDH, which takes place with partial erosion of the layers, causing the intercalation of [Zn(EDTA)]2- complex instead of the ligand. [Cu(H2O)6]2+ cation was selected as a model cation to study the uptake mechanism, exploring the elimination kinetics from the first minutes up to the steady state. A flow injection analysis system coupled to an amperometric detector (FIA-AM) was applied to perform fast and reliable [Cu(H2O)6]2+ determinations in monodisperse solid-aqueous solution systems. Furthermore, the sorbent stability was determined as a function of the pH and the nitrate concentration. The [Cu(H2O)6]2+ elimination is produced by an exchange reaction with [Zn(EDTA)]2- anions placed either in the solid interlayer or in the aqueous solution, this last being released from the sorbent. Additional [Cu(H2O)6]2+ removal is produced by Cu(OH)2 precipitation at high copper concentrations due to the LDHs high pH buffering capacity. The sorbent removes [Cu(H2O)6]2+ with high affinity in a wide concentration range. The elimination process reaches equilibrium in less than 30 min and leaves metal cation concentrations lower than 0.05 ppm in the supernatants.