Fluoride removal in water is an important step in reducing the potential hazards of drinking water. It is a complex process that involves the application of different sorbents and filters to remove fluoride and other heavy metals from the water. One of the most common sorbents is a lanthanum-impregnated bauxite (LIB) filter, which is a highly effective and inexpensive method for removing fluoride. But it can be difficult to determine how well this method performs in real-world applications.
Lanthanum-Impregnated Bauxite (LIB)
Bauxite is an abundant mineral that is widely used to produce aluminum. It is a macroporous mineral and has a good affinity for fluoride. Various studies have been done to test the feasibility of using bauxite to remove fluoride from water.
Bauxite is a very low-cost material. Therefore, it is likely that it would be a suitable choice for fluoride removal in water. However, it is important to note that a sorbent’s adsorption capacity is affected by a variety of factors. In particular, the specific composition of the ore and minor minerals in the ore affect its sorption behavior.
The adsorption characteristics of bauxite depend on the type of adsorbent and its pretreatment methods. Some samples need surface modification to enhance their adsorption properties.
Bauxite was impregnated with lanthanum by thermally heating it. This pretreatment method increases the surface area of the adsorbent and promotes the solid binding of metallic ions to its surface. Moreover, it helps to activate the original sorption sites.
Langmuir isotherm
The Langmuir isotherm is an equation for adsorption processes of multilayers of adsorbate on adsorbents with a finite number of adsorption sites. It can be expressed in a linear form. However, the adsorption behavior is determined by equilibrium isotherms such as the Freundlich and the Redlich-Peterson isotherms.
These two isotherms are used to measure fluoride adsorbed per unit mass of adsorbent. A non-linear method was used for this experiment to eliminate bias from linearization. For this study, the adsorbent was quaternized with N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHMAC). This treatment increases surface area and chelating functional groups.
Fluoride removal efficiency was evaluated at three different pH values and at varying contact times. Maximum fluoride uptake was achieved at pH 3 and 4 h of contact time.
Among the nanomaterials, ferrihydrite showed the highest fluoride removal efficiency. However, quaternized lignocellulosic fiber showed higher adsorption capacity towards anionic substrates.
The adsorption kinetics was also investigated by evaluating pseudo-first order and pseudo-second order kinetics. Pseudo-second order kinetics is a better fit to adsorption than the pseudo-first order.
Freundlich isotherm
The Freundlich isotherm is a model for adsorption on heterogeneous surfaces. The isotherm is used to describe adsorption processes, ranging from simple monolayer adsorption to multilayer sorption.
A variety of adsorption technologies, such as reverse osmosis, flocculation, and filtration, have been studied to remove fluoride from water. The most important characteristic of adsorption is the kinetics of the process.
The Langmuir and the Freundlich isotherms are the two most common isotherms. Typically, the Langmuir isotherm describes monolayer adsorption, while the Freundlich isotherm describes equilibrium adsorption on a heterogeneous surface. Both isotherms are used to measure the adsorption of a particular substance in solution.
The Redlich-Peterson isotherm is another commonly used isotherm. It is a graphical representation of the concentration of fluoride adsorbed per unit mass of a QPKS at a given pH and temperature.
To assess the adsorption behavior of magnesite, a series of experiments were conducted. These included adsorption experiments, kinetics studies, and equilibrium isotherms. Each experiment was performed in a batch system using 250 mL Erlenmeyer flasks. In order to minimize leakage, all samples were shaken mechanically at 150 rpm.
Re-applicability of spent sorbent
Adsorption is an effective method for the removal of fluoride from water. There are many different adsorbent materials available. The most commonly used are natural and carbon-based materials. These adsorbents are easy to use and environmentally benign. They can be reused and recycled. Consequently, they are considered to be suitable for household applications.
Various studies have been conducted to determine the re-applicability of spent sorbents for fluoride removal. A number of real groundwater samples were analyzed. Some of the results showed that the regenerated sorbent could be used up to 4 times without significant loss. Among these, ferrihydrite was found to be an effective material for fluoride removal. It showed higher removal efficiency compared to other nanomaterials.
Several investigations were also carried out to determine the optimum pH for fluoride removal. Higher adsorption occurred at lower pH values because the surface charge of adsorbent increased. This indicates that the surface area of adsorbent increases, increasing the availability of more active sites for fluoride adsorption.