Arsenic Removal Using Mesoporous Alumina Prepared via a Templating Method

Abstract

The health threat of arsenic is well-known, and the U.S. EPA recommends the maximum contaminant level to be 0.01 ppm or less for arsenic in drinking water. Therefore, advanced treatment processes are needed for finished water to meet the required regulations. Adsorption is considered to be a less expensive procedure that is safer to handle than precipitation, ion exchange, and membrane filtration. Activated alumina (AA) is the most commonly used adsorbent for the removal of arsenic from aqueous solutions. However, conventional porous solids including AA have ill-defined pore structures and, typically, low adsorption capacities and act in a kinetically slow manner. An ideal adsorbent should have uniformly accessible pores, an interlinked pore system, a high surface area, and physical and/or chemical stability. To meet this requirement, mesoprous alumina (MA) with a wide surface area (307 m2/g) and uniform pore size (3.5 nm) was prepared, and a spongelike interlinked pore system was developed through a post-hydrolysis method. The resulting MA was insoluble and stable within the range of pH 3-7. The maximum uptake of As(V) by MA was found to be 7 times higher [121 mg of As(V)/g and 47 mg of As(III)/ g] than that of conventional AA, and the kinetics of adsorption were also rapid with complete adsorption in less than 5 h as compared to the conventional AA (about 2 d to reach half of the equilibrium value). A desorption study using sodium hydroxide solutions (0.01-1 M) was conducted, and 0.05 M NaOH was found to be the most suitable desorption agent. More than 85% of the arsenic adsorbed to the MA was desorbed in less than 1 h. Several other activated aluminas with different pore properties were also tested. The results show that the surface area of the adsorbents does not greatly influence on the adsorption capacity. In fact, the key factor is a uniform pore size and an interlinked pore system. These studies show that MA with a wide surface area, uniform pore size, and interlinked pore system can be used as an efficient adsorbent for the removal of arsenic.

Arsenate Adsorption on an Fe−Ce Bimetal Oxide Adsorbent: Role of Surface Properties

“…coefft (R 2 ), b, and Q0 of 0.99, 18.59 L mmol -1 , and 2.00 mmol g -1 , respectively, indicating that adsorption of As(V) onto Fe-Ce08 obeys the Langmuir isotherm model at the given range of As(V) concentration. It is clear that the Q0 (2.00 mmol g -1 ) of FeCe08 was significantly higher than those of the two referenced materials (0.35 mmol g -1 for the Fe oxide and 0.45 mmol g -1 for the Ce oxide), the iron hydroxides, and some other arsenate adsorbents reported recently (24)(25)(26)(27)(28)(29)(30). In the next section, the differences in adsorption performance will be discussed in relation to the differences in structures between the Fe-Ce adsorbent and its referenced oxide materials.…”

A novel approach for arsenic adsorbents regeneration using MgO

“…The determination of surface morphological characteristics of the used MgO by the BET method showed a specific surface area of 59 m 2 /g, a pore volume 0.14 mL/g and a mean pore diameter 156Å. The large pore size of MgO allows arsenate ions to diffuse into the pore channel of the mesoporous material with relevant convenience, since their radius is significantly smaller (H 2 AsO 4 − : 4.16Å, HAsO 4 2− : 3.97Å) [35] than the corresponding of MgO. Therefore, arsenic can potentially be initially adsorbed onto the surface of the MgO and when the exterior surface reached saturation it can enter into the pores and bind to the interior surfaces of the particles.…”

Adsorption behavior of arsenic onto protonated titanate nanotubes prepared via hydrothermal method

“…Arsenic exists in natural water predominantly as inorganic arsenate, As (V) and arsenite, As (III) [3][4][5][6][7]. Elevated concentrations of arsenic are found in groundwater in many regions around the world, which are caused by the release of arsenic from As-bearing sediments or anthropogenic sources [8][9][10].…”

“…Natural materials such as zeolite [11], natural iron ores [7,12,13], siderite [14] and red mud [15] have been examined intensively for arsenic removal. Although these materials are regarded as cheap and effective adsorbents, there are several problems (their impurities, unknown stability and regeneration, low adsorption capacity and slow kinetics) associated with their use [4,13,16]. An ideal adsorbent should have suitable particle size or uniformly accessible pores, high surface area, and physical and/or chemical stability [4].…”

“…Although these materials are regarded as cheap and effective adsorbents, there are several problems (their impurities, unknown stability and regeneration, low adsorption capacity and slow kinetics) associated with their use [4,13,16]. An ideal adsorbent should have suitable particle size or uniformly accessible pores, high surface area, and physical and/or chemical stability [4]. Recently, nanoscale metal oxides such as mesoporous alumina [4], TiO 2 [8], and zero-valent iron [5] have attracted the attention of researchers, and they have shown great advantage towards arsenic removal.…”