Layered Double Hydroxides and the Environment: An Overview - Advanced Materials for Agriculture, Food and Environmental Safety - page 17

CO 3 2- > SO 4 2- . h e reconstruction process of the LDHs has been investi-
gated for the removal of environmentally undesirable anion. Parker et al.
[110] have pointed out that the high selectivity for carbonate anion pre-
vents LDHs to be used as an anion exchange material unless further treat-
ment is made. h ey measured anion exchange capacities of hydrotalcite
in single and mixed anion solutions by observing the amount of anion
adsorbed by freshly prepared hydrotalcite. h ey have compared the rela-
tive preference of anions at er 24 h as SO 4 2- > F - > HPO 4 2- >Cl - >B(OH) 4 -
>NO 3 - . h is application of layered double hydroxides can be explained by
the points shown below.

1.6.5.1 Removal of Heavy Metal Cations

Layered double hydroxides can be used as precipitating agents of heavy
metal cations for the decontamination of wastewater. h e Mn 2+ , Fe 2+ and
Cu 2+ cations were removed by synthetic hydrotalcite-like compounds; zac-
cagnaite [31] and hydrotalcite thin i lms were used for the remediation of
aqueous wastes containing hazardous metal ions [111].

1.6.5.2 Removal of Nuclear Wastes

Hydrocalumite or ettringite, the calcium form of hydrotalcite, have been
evidenced as earlier alteration products of cements or basaltic glasses [112,
113]. h ey have been studied for their adsorption properties of actinides
(h , U, Np, Pu, Se and Am) [114-116]. h e high ability of LDHs and their
calcined products to adsorb/exchange anions from solution was also used
for the removal of Tc, Re and Mo in their anionic form from radioactive
wastewater [117, 118]. Synthetic hydrotalcite has been investigated for the
sorption of iodine and iodine-containing anionic species [119-124].

1.6.5.3 Removal of Greenhouse Gases

Layered double hydroxides are ei cient scavengers for acid gases recovery
from hot gas streams due to their unique and strong basic properties. h e
recovery of CO 2 and SO x from power plant l ue gases is considered to be
the i rst step in reducing total carbon and sulfur oxide emissions. Many
papers and patents describe the use of calcined LDHs for the adsorption of
CO 2 [125-128] and sulfur oxide [129-131] gases.

1.6.5.4 Removal or Adsorption of Organic Compounds and Pesticides

Recently, LDHs and their oxides have been investigated as scavengers to
treat wastewater containing anionic organic contaminants. h e materials