Abstract
The objective of this work was to synthesize and characterize Layered Double Hydroxides (MgAl-LDHs, MgFe-LDHs, and MgAlFe-LDHs) containing phosphate anions and study P release kinetics was conducted with the prepared materials. The release kinetics tests were performed in water by the stirred-flow method to verify the P release profile from LDHs materials. Results showed LDHs have similar characteristics to those of reactive sources of P, such as thermophosphates. The LDHs presented gradual P release and the LDH prepared with the molar ratio of cations Mg:Al = 2:1 showed a more sustained profile of P release compared to other produced materials. Thus, the chemical and structural characteristics of the LDHs make them potential materials for the use and storage of slow P release fertilizer.
Highlights
Layered Double Hydroxides (LDHs), known as hydrotalcite like compounds, are materials with a bidimensional (2D) structure[1]
Because of the need to develop new technologies to increase the efficiency of phosphate fertilizers, the objectives of this work were as follows: (i) synthesis and characterization of MgAl-LDHs, MgFe-LDHs and MgAlFe-LDHs containing phosphate ions; and (ii) evaluation of P release kinetics in the prepared materials
The values of molar ratio of M2+/M3+ cations present in the layers were close to those added during the synthesis: Mg2Al-LDH (Mg/Al = 2.2); Mg3Al-LDH (Mg/Al = 3.3); Mg2Fe-LDH (Mg/Fe = 1.9); Mg3Fe-LDH (Mg/Fe = 2.8), and Mg2Fe0.5Al0.5-LDH (Mg/FeAl) = 2.1)
Summary
Layered Double Hydroxides (LDHs), known as hydrotalcite like compounds, are materials with a bidimensional (2D) structure[1]. LDHs can be represented by the chemical formula [M2+(1-x) M3+x(OH)2](An-)x/n ·zH2O, where M2+ refers to bivalent metallic cations, such as Mg2+, Cr2+, Ca2+, Fe2+, Mn2+, Co2+; M3+ refers to trivalent metallic cations, such as Al3+, Co3+, Fe3+, Cr3+, and An- refers to interlayer anions, commonly nitrate, phosphate, carbonate or chloride. In these materials, divalent cations are partially replaced by trivalent cations, generating positive charges that are neutralized by anions and water molecules[2,3]. When LDHs were compared with pure herbicides, leaching test results showed that the release is slow when the molecules are intercalated. Results showed that herbicide molecules intercalated in LDH presented the same pre-emergence control efficiency on Lepidium sativum as the pure herbicide molecules
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