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.

Chemical treatment of wastewater from flue gas desulphurisation

“…Preparatics of original DLH substance, prepared using magnesium nitrate(V), aluminium chloride and sodium hydroxide, is described in detail in literature [19]. Detailed research performed with the preparation mentioned above led to some appropriate modifications of original DLH preparation, and in consequence obtaining stable preparation, efficiently removing boron and avoiding significant saltness of solution, denoted as DLH/NO3-Cl/M in subsequent text [24].…”

“…Numerous difficulties and economical disadvantages of processes mentioned above were the impulse for new research works oriented on establishing effective and economically reasonable methods of boron removal, since according to the World Health Organization [18], boron is an element that cannot be removed using conventional methods of water and wastewater processing. One of recently tested technologies of boron removal are doublelayered hydroxides [19]. Double-layered hydroxides (DLH) are a kind of synthetic silty materials with a structure described by the formula M(II)1-xM(III)x(OH)2(A n-)x/n•mH2O, where both bivalent M(II) and trivalent M(III) cations form positively charged layers.…”

“…Double-layered hydroxides (DLH) are a kind of synthetic silty materials with a structure described by the formula M(II)1-xM(III)x(OH)2(A n-)x/n•mH2O, where both bivalent M(II) and trivalent M(III) cations form positively charged layers. These layers remain in equilibrium with A n-anions in hydrated interlayer areas [19]. Removal of boron/borates or arsenate ions may be done by exchange with ions from the hydrated layer or by complexation of hydroxyl groups on the surface of DLH layers.…”

Removal of boron species by layered double hydroxides: A review

“…Powder XRD showed that the interlayer space increased from 3.8 to 4.8Å to accommodate borate ions indicating that the mechanism of boron uptake for the uncalcined LDH was anion exchange [3]. Jiang et al [55] investigated the removal of boron from aqueous solutions using Mg/Al Finally, the possibility of regenerating the LDH sorbents was investigated. A 5M solution of sodium nitrate (NaNO 3 ) was chosen for regenerating the LDHs as it was expected to result in the highest boron uptake capacity.…”

“…Boron removal decreased with the increasing number of regenerations with the Mg/Al LDH still removing 69% of boron present. The thermally activated LDH removed only around 54% of boron present after three regenerations indicating that a significant decomposition of the adsorbent must have occurred during the repeated regeneration cycles [55]. and aluminium nitrate (2.93g) into a fine paste.…”