Metal Adsorption and Desorption Characteristics of Surfactant-Modified Clay Complexes

Abstract

Several modified clays have been designed and created for selective removal and recovery of heavy metals such as Cd, Cu, Cr, etc. These surfactant−clay complexes were prepared using hectorite or montmorillonite as the base clay. A simple two-step approach has been developed to synthesize these modified-clay complexes through ion exchange and hydrophobic anchoring of several surfactants such as long-chain alkyldiamines, long-chain dialkylamines, and long-chain carboxylic acids onto the clay matrices. The adsorption capacities and affinity constants of the modified clays can be found to approach those of commercial chelating resin (Chelex 100, Bio-Rad). Using cadmium as a model metal and montmorillonite−cetylbenzyldimethylammonium−palmitic acid (M−CBDA−PA) as a model modified-clay complex, the maximum adsorption capacity of the modified clay is found to be 42 ± 0.8 mg/g of clay and the affinity constant is 3.0 ± 0.1 mg/L. The metal adsorption has been shown to be mainly through chemical complexation rather than ion exchange. The immobilization of the metal ions is pH dependent, and thus, pH can act as a molecular switch to regenerate the modified-clay complexes.

Organically modified clay with potassium copper hexacyanoferrate for enhanced Cs+ adsorption capacity and selective recovery by flotation

“…The intercalated EHDA molecules provided sites to anchor the metal ligand alkyldiamine (DT) through hydrophobic interactions. Without the inclusion of EHDA, DT molecules were unable to bind to the clay particles as evidenced by previous research 23 . Immobilization of DT onto clay particles promotes both the hydrophobic modification of the clay particles and generates binding sites for the chelation of transition metals via a metal-diamine coordination mechanism, see Figure 1a.…”

“…EH surfactant molecules were intercalated into the montmorillonite (as confirmed by TGA analysis, shown in Figure S2 of the Supporting Information), with the metal ligand DT anchored to the EH through hydrophobic interaction 23 to form an organo-clay of Mont-EH-DT. As is known, alkyldiamine chelates to a wide assortment of transition metal cations 19 , making the ligand a useful chelating agent to build different metal-ferrocyanides.…”

“…the strong broad adsorption band with a peak at ~1000 cm -1 corresponds to the Si-O vibration of the tetrahedral silica sheet 27 . In the sample of organo-clay (Mont-EH-DT), the C-H stretching vibration peaks between 2750 cm -1 and 3000 cm -1 , and the CH2 bending vibration at 1470 cm -1 are assigned to the methylene moiety 15,23 Figure 3b). From the C 1s deconvolution spectrum in Figure 3c, two peaks centered at 283.92 eV and 285.69 eV were identifiable, which corresponded to the matrix C-C/C-H peaks and a C N group respectively 28 .…”

Removal of Nickel (II) ion from aqueous solution onto H2SO4 Activated carbon prepared from Erythrina Indica Bark

“…Industrial processes have greatly enhanced the mobilization of heavy metals. The presence of heavy metals in the environment is of major concern because of their extreme toxicity and tendency for bioaccumulation in the food chain even in relatively low concentrations [1], [2] . They are highly toxic as ions or in compound forms; they are soluble in water and may be readily absorbed into living organisms.…”

“…In recent years, a number of adsorptive materials, such as aquatic plants [10] , agricultural by-products [11] , industry by-product [4] , sawdust [12] , clay [13] , zeolite [14] , and microorganisms [15] were used in heavy metal removal from wastewaters. 1 Rate constant of adsorption (l/min) k 2 Second-order constants h Initial adsorption rate (mg/g min) N Number of data points…”