Synthesis, characterization and application of lanthanum-impregnated activated alumina for F removal

Abstract

Elevated fluoride (F) in groundwater presents an obvious environmental concern. Adsorption using activated alumina (AA) is currently the best available technology for F removal, despite its low efficiency, pH dependence, and aluminium (Al) release. The motivation for our study is to synthesise a new F adsorbent by impregnating commercially available granulated AA with lanthanum oxide (LAA), and to explore its F adsorption mechanism on the molecular scale. Five cycles of lanthanum impregnation on AA followed by calcination at 573 K increased the La content up to 19.1% and the F removal from 18.1% by pristine AA to 92.4% by LAA. The SEM, TEM, XRD, TGA, and EXAFS results demonstrated that the 5-20 nm thin flakes of LaOOH on LAA were in an amorphous form, with 7.6 oxygen atoms around each La. This LaOOH layer was uniformly distributed inside the micropores of the 1-3 mm AA granules.LAA exhibited four fold higher F adsorption capacity than AA in the pH range 3.9 to 9.6, with substantially reduced Al release. The ability to regenerate and reuse LAA makes it an attractive sustainable material. Multiple complementary spectroscopic analyses demonstrated that ligand exchange between F and surface hydroxyl groups is the mechanism for F adsorption on LAA. Our work improves the understanding of F interaction with metal oxides on the molecular scale and presents an alternative solution for elevated F water treatment.

Arsenic Adsorption on Lanthanum-Impregnated Activated Alumina: Spectroscopic and DFT Study

“…LAA and lanthanum oxyhydroxide (LaOOH) were prepared using the method described in our previous report. 13 Briefly, to impregnate La on AA, a mixture of 10 mL of La stock solution and 14.5 g of AA was sonicated for 4 h. The solid was separated, dried at 328 K, and then calcined at 573 K for 4 h. After the obtained material was cooled, it was washed with DI water until the conductivity of the wash water was below 100 μS/cm. The impregnation process was repeated five times.…”

“…7,10−12 Lanthanum (La)-impregnated activated alumina (LAA), an example of a REMA, has demonstrated advantages over activated alumina (AA) in F adsorption efficiency, applicable pH range, and Al leachability. 13 Meanwhile, a simple physical mixing of lanthanum oxide with AA was found to substantially enhance the As adsorption capacity. 14 These observations promote the hypothesis that the rare earth elements in REMAs, such as La in LAA, may provide additional adsorption sites with different adsorption mechanisms from those of its supporting materials.…”

Adsorption of arsenate on lanthanum-impregnated activated alumina: In situ ATR-FTIR and two-dimensional correlation analysis study

“…This nonspecific interaction is attributed to the adsorption trend as the As(V) adsorption capacity decreased with increasing pH from 6 to 9. The exceptional low adsorption capacity at pH 5 was due to the La leaching from LAA at pH < 6 as shown in our previous study [5] (Fig. 3).…”

“…Since lanthanum (La)-impregnated silica gel was first designed as an adsorbent for water treatment in 1996 [4], extensive La loading materials have been widely studied for hazardous anion removal, especially for fluoride [5], phosphate [6], and arsenate (As(V)) [7], due to their selectivity and high removal efficiency without producing harmful by-products. While many La-based materials were synthesized for adsorption, however, research efforts have primarily focused on the promotion of anion removal efficiency, while studies on the adsorption mechanisms at the liquid/solid interface are still scarce, which has seriously limited the development of the adsorbents.…”

Nanoscale lanthanum oxide catalysts for self-condensation of acetone: preparation via self-assembly on anodic aluminum oxide, structure, and properties

“…Mass loss in the temperature range from 583 K to 803 K is due to the formation of La 2 O 3 (1.74 mass %). Rosynek and Magnuson (1977) and Shi et al (2013) also found that the dehydration of La(OH) 3 to La 2 O 3 occurred in the temperature range from 502 K to 892 K. TGA results show that Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 10/8/15 10:08 AM the amount of La loading is small and support the XRD assumption of the presence of a critical point between 723 K and 823 K for lanthanum hydroxide dehydration, above which the amount of active ingredient La 2 O 3 with hexagonal structure is detectable for XRD, as well as the results of the catalytic behavior study to be commented below. Fig.…”