**Figure 6.**

*XRD patterns of (a) L4 and (b) L5.*


#### **Table 2.**

*The basal spacing of L1, L2, L4, and L5 calculated from XRD by using Bragg's equation.*

which may be due to the hydrogen bonding on the layer. Hydrogen bonding makes soft agglomeration occur on the surface of the LDHs, and after the chelating agent, anion replaces the nitrate ions between the layers, the hydrogen bonding between the hydroxyl groups is reduced, and the aggregation is weakened to a certain extent.

The inhomogeneous surface of the adsorbent indicated that a large amount of metal salt attached to the surface of the hydrotalcite in an excessive state, its unique

**173**

*Adsorption of Heavy Metals on Layered Double Hydroxides (LDHs) Intercalated with Chelating…*

layered structure, resulting in removal of heavy metal ions in the aqueous solution not only by interlayer anion and heavy metal cation interaction but also rely on the

Element distribution analysis of L1, L2, L4, and L5 by EPMA is shown in **Figure 8**. After the ion exchange, the element distribution of N decreased obviously (by comparing red parts in these pictures), and this decrease is observed in both MgAl-LDHs (a, b) and ZnAl-LDHs (c, d). Furthermore, it is found that the moles of divalent metals are at least equal to or greater than that of the trivalent metals [34, 35], which

**Figure 9** has shown the specific surface area of the product. Specific surface area of L2 and L3 are bigger than that of L1, and that of L5 is bigger than L4, which may be attributed to intercalation of EDTA or EDDS. Specific surface area of L0 is bigger

The adsorption capacities of Cu(II) or Pb(II) onto L1, L2, L3, and L0 are compared in **Figure 10**. The adsorption efficiency of Cu2+ was larger than that of Pb2+ for the same absorbent, which could be attributed to their stability constant (EDTA-Cu, 18.7; EDDS-Cu, 18.4; EDTA-Pb, 18.0; EDDS-Pb, 12.7) [12, 26]. That is to say, it can be considered that the large adsorption capacity is obtained when the stability constant of chelate-metal is high. By comparing among adsorbents used in this work, the order of the adsorption capacity is L2 > L3 > L0 > L1. The higher adsorption efficiency of L0 than L1 may be attributable to its high specific surface area.

In order to confirm the effect of the intercalation with chelate agents on the adsorption capacity of metals, the adsorption experiments of some metallic elements

*DOI: http://dx.doi.org/10.5772/intechopen.80865*

role of surface adsorption and sedimentation.

*SEM image of (a) L1, (b) L2, (c) L3, (d) L4, and (e) L5.*

**3.5 Electron probe microanalyzer (EPMA)**

is consistent with the results of chemical analysis.

than that of L1; it is due to the difference of their particle size.

**3.7 Adsorption of Cu(II) or Pb(II) onto L1, L2, L3, and L0**

**3.8 Adsorption of Cu(II), Pb(II), and Cd(II) onto L4 and L5**

**3.6 Specific surface area**

**Figure 7.**

*Adsorption of Heavy Metals on Layered Double Hydroxides (LDHs) Intercalated with Chelating… DOI: http://dx.doi.org/10.5772/intechopen.80865*

**Figure 7.** *SEM image of (a) L1, (b) L2, (c) L3, (d) L4, and (e) L5.*

layered structure, resulting in removal of heavy metal ions in the aqueous solution not only by interlayer anion and heavy metal cation interaction but also rely on the role of surface adsorption and sedimentation.
