*2.2.1 Immobilization techniques*

This technique, also known as Solidification and Stabilization. Immobilization is the process of adding immobilizing chemicals to polluted soils to reduce the mobility, bioavailability, and bioaccessibility of heavy metal(loid)s in the soil [29]. The immobilization of heavy metals in soil can be achieved through complexation, precipitation, and adsorption. By redistributing heavy metal(loid)s from soil solution to solid particles, these processes limit heavy metal(loid) transport and bioavailability in soil [30]. Binders, cement, clay, zeolites, phosphates, alkaline materials, termitaria, industrial eggshell, red-mud, chemical compounds, and more recently nanomaterials are a few of the mixing ingredients employed in the imobilization procedure [31].

*New Advancements in the Field of Pollution Treatment, Including Contamination of the Soil… DOI: http://dx.doi.org/10.5772/intechopen.109955*

### *2.2.2 Encapsulation*

Encapsulation of contaminated soil stops the pollutants from spreading by covering the contaminant source with layers of concrete, lime, clay caps, or synthetic textiles, to limit the leaching and migration of contaminants away from the isolated zone [12]. By becoming immobile, the polluted soil avoids contaminating the nearby materials [32]. Several binding materials are used in the production of solid blocks, but cement is chosen due to its accessibility, adaptability, and affordability [33]. Encapsulated soil can never be used to grow anything, hence this method of soil cleanup is only used as a last resort. Various immobilization agents are utilized during encapsulation, including polyvinyl alcohol, chitosan, alginate, agar, polyacrylamide, and polyurethanes [3]. The leaching of organic materials may be prevented effectively by encapsulation. Various immobilization agents, such as polyvinyl alcohol, chitosan, alginate, agar, polyacrylamide, and polyurethanes, are employed during encapsulation. While asphalt encapsulation is utilized for soils contaminated with hydrocarbons, encapsulation by lime and concrete has been used concurrently in the efficient treatment of soil contaminated with heavy metals and oil [34].

### *2.2.3 Soil washing*

A technique known as soil washing uses two processes to remove pollutants from soil: physical separation and chemical leaching by aqueous solutions. This method starts with a homogenization step in which the coarse particles are divided based on their densities [35]. Depending on the type of metal and soil, the contaminated soil is dug up and combined with an appropriate extractant solution during soil washing [36]. For a predetermined amount of time, the extractant solution and dirt are fully blended. The heavy metals in soil are transported from soil to liquid phase and then removed from the leachate through precipitation, ions exchange, chelation, or adsorption [37]. If the contaminated soil passes regulatory tests for heavy metals after the washing process is complete, it will be returned to its original location. It is very common to use soil washing to purify heavy metals from contaminated soils, because it completely removes heavy metals. In addition, soil washing is a rapid method which can easily meet the researchers' criteria [38, 39]. A variety of chemicals, such as synthetic chelating agents (EDTA, EDDS), organic acids, humic compounds, surfactants, and cyclodextrins, have been employed to mobilize and remove heavy metals from soil [40, 41]. The capacity of the extractant to dissolve the heavy metal in soils determines the effectiveness of soil cleaning [42].
