Laboratory Study of Boron Removal by Mg/Al Double-Layered Hydroxides

Abstract

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 Mg 2 AlNa 1.4 (OH) 7.57 Cl 0.03 (NO 3 ) 0.8 · x (H 2 O) 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.