Chelation is defined as a reaction of a metal ion with an organic molecule. Chelates are normally negative in charge and are therefore not fixed to the soil surface. The reason being that the soil is negatively charged so the soil surface typically repels the chelates. Metals, on the other hand, are positively charged, so the positive ions of the metals are attracted to the soil surface. Chelating agents remove the metal ion from the soil, as illustrated below.
The Four Most Common Organic Structures Found in Chelation Processes.
Source: McBride, 1994
Soils with a high amount of organic matter will tend to have a minimal amount of free metal ions within the soil because of the chelating agents in the organic matter.
Not all metals are made nontoxic by chelation and complexation. Some are actually made more toxic.
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