The most common adsorbents on the market today are activated carbon, silica gel, and alumina, because they have large surface areas per unit weight. Activated carbon is produced by roasting organic material to decompose it to granules of carbon – coconut shell, wood, and bone are common sources. Also activated carbon is the most commonly used adsorbent in wastewater treatment. As Silica gel is a matrix of hydrated silicon dioxide. Alumina is mined or precipitated aluminum oxide and hydroxide.
Adsorptions Isotherm equation is q=f(C) where q is the mass of the adsorbed species and C is the equilibrium concentration of absorbable species in the solution. Figure 1. This is an example of an Adsorption Isotherm. However absorption is different. Absorption is a process in which either liquid or light is absorbed. Between the two absorption is the least commonly used in environmental engineering. For example when a human being applies lotion on their skin and after a couple of minutes it disappears. What happened there was that their skin absorbed the lotion.
In addition absorption comes in many different context such as: Chemistry, skin , pharmacokinetics, CO2 scrubber , electromagnetic radiation and etc. However, when speaking about adsorption and absorption the clear difference should always be idenfited. The difference between adsorption and absorption is that absorption a process in which a substance, originally present in a certain phase, is removed from that phase by dissolution in another, on the other hand adsorption is sort of a build up on a surface of a specific object. However both absorption and absorption are all part of sorption as a whole.
Sorption is the combined process of adsorption of a solute at the interface and partitioning of solute into the organic that has coated the surface. During the sorption hydrophobic compounds partition onto surfaces in two phase systems containing liquid such as water or soil. Sorption is commonly used to remove toxins from waste streams and is a very important mechanism in controlling the rate at which contaminant movement in soil. In order for the partitioning of species between a fluid phase and the sorbed phase to be represented a sorption isotherm is created.
The three most common forms are: linear qe=KadsCe, Freundlich qe=KfCe1/n, and Langmuir qe=qmax(bCe)/(1+bCe). Sorbate is a substance being transferred from a liquid to a solid. Sorbent is a solid phase in which the absorbate accumulates. In addition sometimes while sorption occurs desorption does as well. Desorption is the complete opposite of adsorption and it involves the dissociation of a compounds from the solids. Another aspect of sorption that is important is chemisorption/chemical sorption. Chemical sorption is characterized by stronger, more permanent bond relative to physical sorption mechanisms.
Chemical sorption has a high enthalpy so it is favored by high tempture. Figure 2. This is a picture of a water vapor sorption isotherm Chitin is an excellent cosmetic product that is remarkably well tolerated by the skin. Chitin has a chemical make up a natural polymer that is very close to that of mucopolysaccarides, whoses biogocal tolerance has been show may times. In addition, chitin is a good hydrating agent. Many industries use this chemical in there creams, pack material, lotions, nail enamel, nail lacquers, foundation, eye shadow, lipstick, cleansing materials, and bath agents.
However it is also can also be used as a chelation agent and as a heavy metal trap. Figure 3. This is a picture of Chitin’s composition. When used as a chelation agent it treats drinking water by separting organic compounds and heavy metals, for treating sewage it breaks down certain anionic wastes and captures pollutants such as DDT and PCBs. Chitin has many uses as the EPA has approved this compound to treat water. Studies have shown that a product with this chemical has increase wound healing in animal and humans.