Adsorption of Arsenic on Layered Double Hydroxides:  Effect of the Particle Size

Abstract

This paper describes a study of arsenic(V) adsorption on appropriately conditioned calcined layered double hydroxide (LDH) adsorbents. Conditioning the adsorbent significantly reduced the dissolution previously observed with uncalcined and calcined LDH. The adsorption rates and isotherms have been investigated in batch experiments. As(V) adsorption is shown to follow a Sips-type adsorption isotherm. The As(V) adsorption rate on conditioned LDH increases with decreasing adsorbent particle size; the adsorption capacity of As(V) on conditioned LDH, on the other hand, is independent of the particle size. When a homogeneous surface diffusion model was used to fit the experimental kinetic data, the estimated diffusivity values were shown to depend on the particle size. On the other hand, when a bidisperse pore model, which considers the adsorbent particles to be agglomerates of microparticles with a porous region present between them, is applied to the same data, it predicts an intracrystalline diffusivity, which is fairly invariable with the particle size.

Characteristics, Preparation Routes and Metallurgical Applications of LDHs: An Overview

“…Those pollutants include: oxyanions [70][71][72][73][74][75], monoatomic anions [76][77][78] cations [79][80][81], organics [82][83][84], and gas [85,86]. For example, Kovanda et al [87] demonstrated the capabilities of Co:Mn:Al LDH (calcined at 500°C) in the total oxidation of ethanol (Figure 4).…”

Comparison of adsorption equilibrium and kinetic models for a case study of pharmaceutical active ingredient adsorption from fermentation broths: parameter determination, simulation, sensitivity analysis and optimization

“…At equilibrium, the adsorption equilibrium isotherm can be represented by the Sips model (Equation (3)), which was previously reported to describe the arsenic adsorption process in batch and continuous adsorption (Dadwhal et al, 2009;Yang et al 2006). There are numerous other adsorption equilibrium models, e.g.…”

“…Assuming homogeneous spherical adsorbent particles, a concentration-independent diffusivity (this assumption was relaxed by Yang et al (2006) without offering any particular advantage in the model fit), the intra-particle transport and solute uptake is described by the following equation (Yang et al, 2006):…”

Synthesis and characterization of arsenate-intercalated layered double hydroxides (LDHs): Prospects for arsenic mineralization

“…Anions contribute to the thermodynamic stability of the LDH by affecting both enthalpy and entropy [10]. For a given pair of metal ions, the affinity of the LDH for different anions varies in the order CO ions by a mineral acid (HCl or HNO 3 ) at pH 4.5 [14] and (b) calcination of the pristine LDH to yield a defect oxide phase and subsequent reconstruction of the LDH by soaking the oxide residue in As(V) solution [15]. The uptake by the former method is essentially through anion exchange at a pH close to the dissolution pH of the LDH, while the latter is based on the memory-effect of LDHs.…”