Adsorption removal of heavy metal ions from multi-component aqueous system by clay-supported nanoscale zero-valent iron

Abstract

The peculiarities of adsorption removal of the mixture of heavy metal ions Cu, Cd, Co, Zn, and Cr from an aqueous solution using clay-supported nanoscale zero-valent iron (nZVI) composite materials were investigated. As an inorganic matrix for stabilizing nZVI the aluminosilicates kaolinite (K) (1:1), montmorillonite (MMT) (2:1) and palygorskite (Pg) (2:1) were used. Powder X-ray diffraction (XRD), N2 adsorption-desorption, electrochemical methods, and inductively coupled plasma atomic emission spectroscopy were used to characterize the samples. Adsorption experiments were investigated in a wide range рН. The obtained results show that at pH 6, the adsorption of heavy metal ions for modified samples is two to four times higher than for natural clay minerals. The experimental results were analyzed using Freundlich and Langmuir models of adsorption isotherms. The selectivity coefficients for all pairs of heavy metals (HM) were calculated. It shows that the adsorption centers on the surfaces of layer silicates form strong complexes with heavy metal ions, which correspond to the Irving-Williams series of stability of the corresponding complexes in solutions: Cu > Zn > Co > Cd > Cr. The role of the dispersed matrix as a stabilizing component of highly reactive nano-dispersed iron in the composite adsorbent is determined. According to the efficiency of removal of heavy metals from aqueous solutions, composite materials form a sequence: nZVI-montmorillonite ≥ nZVI-palygorskite > nZVI-kaolinite. The results indicated that clay-supported nanoscale zero-valent iron might be an effective material for water purification from the mixture of heavy metal ions.