Adsorbents Lab Report

The adsorption surfaces have the same affinity for molecules of the adsorbate and there is no trans-migration of adsorbate on the plane of the surface. The Freundlich equation is mostly used for data description whereas Langmuir isotherm is valid for single-layer adsorption. Adsorption is the process considered to be efficient to defluoridate the water. To defluoridize, there are many techniques but when compared to the physical and chemical methods of defluoridization, the physical method is the most suitable and economic. In physical method, various adsorbents are used to remove fluoride from water. Different adsorbents are derived from different materials and objects. Till now there is no method to defluoridize water which is

Chemical adsorption.

Physical Adsorption

In physical adsorption, the molecules adsorbed can be easily removed, or desorbed, by a change in the solution concentration of the adsorbate.This case of the molecular attractive forces that pulls the adsorbent on the surface are physical and are called as Vander Walls forces (17). Due to this reason the process is said to be reversible which is useful for the reuse of adsorbents in certain cases. Adsorption of this type is sometimes are referred to as adsorption.

Chemical Adsorption

Chemical adsorption occurs as a result of chemical reaction between the adsorbent and the adsorbate molecules. This type of adsorption is noticed to occur on the sides and corners of the micro-crystallites that comprise the adsorbent. The bonds formed in the chemisorption are strong and the process is almost always irreversible.

Factors influencing adsorption

Many factors that influence the rate of adsorption reaction occurs and the amount to which a material can be adsorbed is determined on some of the following factors (18): Surface

The above equation can be represented in a linear form as log⁡〖q_e=log⁡K+ 1/n*log⁡C 〗

The coefficients k and n can be estimated from slopes and by substituting values from a line fitted to a graph of log (X/M) versus log C.

Langmuir Isotherm

The simplest proposed model for characterizing adsorption is the Langmuir isotherm (20). The Langmuir isotherm assumes that each unit of surface area consists of n sites, which can adsorb one molecule, and all of the sites are energetically equivalent. Surface contains uniform energies of adsorption. Maximum adsorption corresponds to a saturated monolayer of solute molecules on the adsorbent surface, that the energy of adsorption is constant, and that there is no transmigration of adsorbate in the plane of the surface. This model is an adequate approximation for uniform surfaces. However, it is inaccurate for inorganic solids commonly used in catalytic materials. In addition, the model does not account for the interaction of adsorbed species and multi layer adsorbate growth. The Langmuir isotherm is developed by assuming that a fixed number of adsorption sites are available, and that the adsorption is reversible. The Langmuir isotherm may be used when the adsorbent surface is homogeneous. The Langmuir isotherm is expressed as