Performance modeling of layered double hydroxide incorporated mixed matrix beads for fluoride removal from contaminated groundwater with the scale up study

Abstract

In this study, calcium aluminium based layered double hydroxide (LDH) was synthesized in a controlled manner and its efficiency as a potential adsorbent in fluoride removal was explored. The LDH basal spacing of 8.2°A confirmed the planar orientation of the intercalated NO₃^-. The maximum adsorption capacity of LDH was 247.1 mg/g (at 308 K) and the adsorption was facilitated by the lower crystal radius and higher electro-negativity of F- compared to NO₃^-. For practical application in adsorption column, the LDH was incorporated in polysulfone to form spherical mixed matrix beads (MMB) of average diameter 2.8 mm. The elongated macrovoids inside the MMB promoted the diffusion of fluoride to the adsorption sites. The maximum adsorption capacity of the MMB was 90 mg/g (at 308 K). A fundamental mass transfer-pore diffusion-adsorption model linking convection, diffusion and adsorption was used to predict the adsorption kinetics and the breakthrough behaviour in the batch and continuous column mode experiments with the synthetic solution and contaminated groundwater. Different model-estimated transport parameters, like, effective pore diffusivity, mass transfer coefficient and the axial dispersion coefficient were used for scaling up of the column filters. The spent adsorbent was regenerated using 0.1(M) NaOH and 1(M) NaNO3.