A Comparison among Synthetic Layered Double Hydroxides (LDHs) as Effective Adsorbents of Inorganic Arsenic from Contaminated Soil–Water Systems

Abstract

The need for cost-effective adsorbents of inorganic arsenic (As(III) and As(V)) stimulates the academia to synthesize and test novel materials that can be profitably applied at large-scale in most affected areas worldwide. In this study, four different layered double hydroxides (Cu-Al-, Mg-Al-, Mg-Fe- and Zn-Al-LDH), previously synthesized and studied for As(III) removal capacity, were evaluated as potential adsorbents of As(V) from contaminated systems, in absence or presence of common inorganic anions (Cl−, F−, SO42−, HCO3− and H2PO4−). The As(V) desorption by H2PO4− was also assessed. Lastly, the As(V) adsorption capacities of the four layered double hydroxides (LDHs) were compared with those observed with As(III) in a complementary paper. All the LDHs adsorbed higher amounts of As(V) than As(III). Fe-Mg-LDH and Cu-Al-LDH showed higher adsorption capacities in comparison to Mg-Al-LDH and Zn-Al-LDH. The presence of competing anions inhibited the adsorption of two toxic anions according to the sequence: Cl− < F− < SO42− < HCO3− < < H2PO4−, in particular on Mg-Al-LDH and Zn-Al-LDH. The kinetics of As(V) desorption by H2PO4− indicated a higher occurrence of more easily desorbable As(V) on Zn-Al-LDH vs. Cu-Al-LDH. In conclusion, synthetic Cu- and Fe-based LDHs can be good candidates for an efficient removal of inorganic As, however, further studies are necessary to prove their real feasibility and safety.

Elevated Urinary Arsenic Level among Residents of an Arsenic-Endemic Area of Southern Thailand and its Related Factors: Three Decades after Mitigation Attempts

“…Arsenic (As) is one of the most toxic elements and also known as "the king of poisons" [1]. The occurrence of As in nature can be found in a 3 variety of different mineral forms in which around 60% are presented as arsenates, 20% are sulfies and sulfosalts, and the 20% remaining As are also in the form of arsenides, arsenites, oxides, silicates, and elemental As [2]. Generally, it is well known that the toxicity of inorganic As (iAs) forms are higher than the organic ones.…”