Laboratory study of boron removal by Mg/Al double-layered hydroxides

This paper is concerned with the preparation and use of Mg/Al double-layered hydroxides for boron removal from waste liquor. The structure of the DLHs synthesized is proposed to be Mg2AlNa1.4(OH)(7.57)Cl-0.03(NO3)(0.8)center dot x(H2O) which does not contain any carbonate anions. For treating model waters with various starting boron concentrations (5-500 mg/L), the maximum boron percentage removal was > 80% for DLH-60 and > 90% for DLH-450. The boron removal capacity is 5.4-17.3 mg of B/g for DLH-450 and 1.2-13 mg of B/g for DLH-60, respectively. The raw water's pH does not affect the boron removal performance. After six cumulative regenerations, boron percentage removal with regenerated DLHs decreased to about 40%. Overall, DLH-450 has a greater boron removal capacity than DLH-60 for both freshly prepared and regenerated materials. For the treatment of industrial effluent ([B](0) = 17 mg/L), 86.6% boron removal was achieved at the dose of 36 g/L for DLH-60 and 93.5% at the dose of 16 g/L for DLH-450. Arsenic can be completely removed by both DLHs. The main mechanism of boron removal with DLH-60 is proposed to be anion exchange while that with DLH-450 is adsorption. For DLH-450, both Langmuir and Freundlich isotherm models fit well for the experimental results.