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

Abstract

The arsenate-intercalated layered double hydroxide (LDH) of Mg and Al is synthesized by coprecipitation. The higher thermodynamic stability and the consequent lower solubility of the unitary arsenates preclude the formation of arsenate-intercalated LDHs of other metals directly from solution. However other M/AlAsO 4 (M = Co, Ni, Zn) LDHs could be prepared by anion exchange, showing that arsenate intercalation proceeds topotactically. The intercalation of various species of As(V) into the interlayer of LDHs and the subsequent arsenate carrying capacity are dependent upon the pH of the solution. Upon thermal decomposition, the intercalated arsenate ion undergoes reductive deintercalation to give a mixture of As(III) and As(V) oxides. The product oxides revert back to the LDH upon soaking in water on account of the compositional and morphological metastability of the former. This is in contrast with the phosphateintercalated LDHs, in which the reversibility is suppressed, consequent to the formation of stable metal phosphates.

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

“…The calculated basal spacings (i.e., 9.10 Å and 8.90 Å for H2AsO4 − and HAsO4 2− , respectively) are consistent with some of the reported experiments [31,80] that are conducted under initial pH around 7 and 8 (range from 8.71 Å to 9.21 Å, Figure 3) at a Mg/Al ratio of 2:1, while large differences are found between our simulations and the other experiments [8,76] conducted under pH of 5 or higher than 9 (<8.48 Å, Figure 3 [47]. This agreement validates our simulation set up.…”

“…H2AsO4 − and HAsO4 2− co-exist at near-neutral pH conditions and they both occurred in the experimental systems [31], so the basal spacings for As(V) are presented together in Figure 3. The calculated basal spacings (i.e., 9.10 Å and 8.90 Å for H2AsO4 − and HAsO4 2− , respectively) are consistent with some of the reported experiments [31,80] that are conducted under initial pH around 7 and 8 (range from 8.71 Å to 9.21 Å, Figure 3) at a Mg/Al ratio of 2:1, while large differences are found between our simulations and the other experiments [8,76] conducted under pH of 5 or higher than 9 (<8.48 Å, Figure 3 [47].…”

“…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].…”

Anion Exchange Kinetics of Nanodimensional Layered Metal Hydroxides: Use of Isoconversional Analysis

“…39 The reactions may involve multiple steps which include: accessed by following the link in the citation at the bottom of the page. …”

Interlayer structure of iodide intercalated layered double hydroxides (LDHs)

“…Given their structure, the LDHs are natural hosts for mineralization of a variety of anionic pollutants [4,5]. Radioactive iodine is one of the many hazardous elements discharged from nuclear reactors and is a serious health hazard.…”