**1.3 Chemical methods**

These methods include soil washing and immobilization technologies. Different chemicals or solvents (metallic oxides, clays, or biomaterials) are added into the soils to stabilize the pollutants and convert them into less toxic forms to living organisms, thus reducing their bioavailability, adsorption, or transformation [27]. The remediation chemical methods are faster than biological ones and could also be applied *in situ*. However, the harmful effects of the use of chemical methods should also be considered before its implementation.

*—Immobilization (8):* It is a sequence of precipitation-adsorption, ion exchange, humification, and other oxidation-reduction reactions by adding a fixative to the contaminated soil and changing the existing form. This process reduces the metal bioavailability in soil and its toxicity. The fixed repair technology has a short cycle and quick effect. Sometimes, this method does not completely remove the metal/ oids, only changes its occurrence state, and can cause secondary pollution.

*Scale-up of Mycorrhizal-Assisted Phytoremediation System from Technology Readiness… DOI: http://dx.doi.org/10.5772/intechopen.101584*

*—Soil washing (9):* Contaminated soil is repaired using injection wells to infiltrate the water or chemical auxiliary eluent under the action of gravity or external force, so the HMs present in the contaminated soil are fully combined with it and desorbed by the eluent. This method uses liquids that contain chelation agents, freshwater, and other solvents to wash the contaminated soil with mechanical processes [28, 29].
