A strategy based on chelating agent addition was used to assist the in-situ growth of MgAl-layered double hydroxides (LDHs) films on magnesium alloy AZ31 in a relatively mild condition. The growth behavior of MgAl-LDH films was studied on the magnesium alloy AZ31 substrate as the sole source of Al 3+ and/or adding aluminum compounds as a supplementary source of respective ions. The composition, structure, corrosion resistance , and formation mechanism of LDH films were investigated and discussed. Results showed that the LDH-coated samples could effectively retard the corrosion of magnesium alloy. A thicker Mg (OH) 2 /MgAl-LDH composite film with larger flake size was formed without additional aluminum source. MgAl-LDH film fabricated with moderate additional Al 3+ concentrations showed better corrosion resistance and an interesting stable network structure on a flat surface both covered/consisting of very fine LDH flakes.
In order to facilitate recovery and enhance phosphate adsorption capacity of lanthanum (La)-based materials, magnetic Fe 3 O 4 @MgAl-LDH@La(OH) 3 (MMAL) composites with a hierarchical core-shell structure were synthesized. In the preparation process, citric acid played a vital role in the morphology control of La(OH) 3 , deciding the La content and phosphate adsorption capacity of materials. MMAL composites with a citric acid-to-La molar ratio of 0.375 (MMAL-0.375) exhibited a high adsorption capacity of 66.5 mg P/g, fast adsorption kinetics of 30 min, widely applicable pH range of 4.0–10.0, outstanding selective adsorption performance, and superior reusability in batch adsorption experiments. Moreover, the phosphate in the desorption solution could be concentrated by repeated use of desorption solution and recovered by using CaCl 2 . When the obtained composites were used for the sedimentary phosphorus sequestration and recovery, the results showed that the addition of MMAL-0.375 effectively reduced the concentration of soluble reactive phosphorus (SRP) in the overlying water. Accompanied by an evident increase in HCl-extractable phosphorus (HCl–P), mobile phosphorus (P mob ) in sediments was effectively reduced. This work indicates that the MMAL-0.375 composites can serve as an effective tool for the removal of phosphate from wastewater and the control of sedimentary phosphorus.
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