The terminology like retention, fixation, sorption, and adsorption are used in soil chemistry and material sciences. These terminologies always confusing. For example, the using this term in P nutrient, we found some scientists think the retention or fixation of phosphorus involves both adsorption and precipitation reactions. And they define the adsorption as the fixation of solutes from a solution on the surface of a solid. Other think, P fixation or sorption, retention (the three terms are frequently used interchangeably). The differentiate between phosphate retention and fixation some authors think retention is easy to remove even by dilute acid, while the fixation phosphate anion held by the soil clay cannot be removed by the treatment of the soil clay with the same acid. Therefore, the distinct between fixation and retention need more explanation.
Therefore, we are looking more detail and explanations of these issue, lecture note, e-book, literature review, articles, and technical report explanting these issue, also are needed.
The meanings are not synonymous, even if some do not understand or confuse them. It is sometimes important to be able to make these distinctions. Certainly in soil P chemistry retention may involve adsorption and precipitation, especially at high P loads. That is when one needs to use the broader terms, unless there is a solid phase speciation measurement.
Sorption or absorption is a physical and chemical process by which one substance become attached to another, it involves the whole volume of the material ; while adsorption is a surface based process .
The retention is the action of absorbing and continuing to hold a substance. It is control of something. On the other hand fixation is the action or process of fixing at the status. It is the state of being fixed.
*The retention is the presence of ions on the surfaces of ion exchange complexes called the image available.
*The fixation is the capture of ions between the inner layers of clay minerals or other soil particles or enters into the chemical formula of the crystal structure called an image that is not available.
*Adsorption is the retention of ions on the surfaces of the ion exchange complexes in a readily available form.
*Absorption is the process of penetration of ions into the structural structure of clay minerals, especially montmorillonite.
While they all represent somewhat similar molecular interactions, an exact and precise terminology is highly recommended to avoid any misconception that may arise in your study. Adsorption can be written off as a subset to sorption which also includes precipitation and absorption. Retention can be understood as an opposing factor to desorption while fixation deal with ionically bounded layers of soil minerals.
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