Layered double hydroxides as potential chromate scavengers

Abstract

The LDH of Ni with Fe, having the formula Ni(1-x)Fe(x)(OH)2(A(n-))(x/n)yH2O (A = NO3-, Cl-; x = 0.25, 0.33), scavenges CrO4(2-) ions from solution throughout the concentration range examined (0.00625-0.25 N). The CrO4(2-) uptake capacity is independent of the anion in the starting LDH but is higher when x = 0.25 (3.60 meq g(-1)) as compared to x = 0.33 (2.40 meq g(-1)). These values are higher than those observed for control compounds beta-Ni(OH)2 (1.86 meq g(-1)) and FeO(OH) (1.26 meq g(-1)), which do not have any interlayer chemistry, showing that chromate uptake takes place by its incorporation in the interlayer region by a stoichiometric anion-exchange reaction, rather than by adsorption. Nevertheless, the interaction between the LDH and the chromate ions is weak. The weak interaction is due to the mismatch between the symmetry of the chromate ions and the symmetry of the interlayer site, which introduces turbostratic disorder in the chromate-intercalated LDHs. The chromate ions can be completely leached out by soaking the LDH in a sodium carbonate solution.

Synthesis and characterization of arsenate-intercalated layered double hydroxides (LDHs): Prospects for arsenic mineralization

“…To illustrate the plausible mechanism of anion exchange and reflect upon the relative stability of the intermediate phases, if any, two related phases, Mg(OH) 2 and Al(OH) 3 , were aged in arsenate solution at the natural pH of the latter (pH 8.5) as controls. Both these compounds compose charge-neutral layers and do not posses any interlayer chemistry.…”

“…Layered double hydroxides (LDHs) are widely used for catalysis and sorption and are sinks for the mineralization of insidious anions such as chromates [2,3], selenates [4], fluorides [5], radioactive anions [6], and various organic pollutants [7]. LDHs exhibit anion exchange properties, which make them candidate materials for the immobilization of arsenate in the interlayer region of the LDHs.…”

“…Brucite comprises a close packing of hydroxyl ions in which Mg 2+ ions occupy alternative layers of octahedral sites, leading to a stacking of charge-neutral metal hydroxide layers of composition [Mg(OH) 2 ]. When a fraction x of Mg 2+ ions is replaced by a trivalent ion such as Al 3+ or Fe 3+ , the positive charge, x+, generated on the metal hydroxide layer is compensated for by the inclusion of hydrated anions, A n− , in the interlayer region to * Corresponding author.…”

Interlayer Structures and Dynamics of Arsenate and Arsenite Intercalated Layered Double Hydroxides: A First Principles Study

“…Layered double hydroxides (LDHs) have the potential to remove oxyanion water contaminants such as arsenate [8,[28][29][30][31], chromate [32][33][34], and phosphate [3,[35][36][37][38][39] due to its large specific surface areas and high anion exchange capacity. LDHs, also known as hydrotalcite-like compounds or anionic clays, are a class of layered minerals with exchangeable anions in the gallery spaces [40].…”

Synthesis and Characterization of LDHs (Layered Double Hydroxides) Intercalated with EDTA (Ethylenediaminetetracetic Acid) or EDDS (N, N'-1, 2-Ethanediylbis-1-Aspartic Acid)

“…The capacity of LDHs as adsorbents of pollutant has been extensively reported both for inorganic [7] and organic [8,9] anions. LDHs also can be intercalated with different polydentate ligands as scavengers of these solids to metal cations and lanthanides [10][11][12].…”