Chemical remediation techniques can be effective in reducing or removing heavy metals from contaminated soil at a former industrial site. Some of the common methods include:1. Soil washing: This technique involves the use of water-based, chemical, or physical processes to separate contaminants from soil particles. Soil washing can be done using chelating agents, such as ethylenediaminetetraacetic acid EDTA , which form stable complexes with heavy metals, making them more soluble and easier to remove. The soil is then washed with water, and the heavy metal-chelate complexes are separated from the soil particles.2. Electrokinetic remediation: This method uses an electric field to move heavy metals through the soil matrix towards electrodes. The heavy metals are then collected at the electrodes and removed from the soil. This technique can be combined with other methods, such as the addition of chelating agents, to enhance the mobility of heavy metals.3. Chemical stabilization/immobilization: This technique involves the addition of chemicals to the contaminated soil to form stable, insoluble compounds with the heavy metals, thereby reducing their mobility and bioavailability. Commonly used chemicals include lime, phosphate, and various types of clay minerals. This method does not remove the heavy metals from the soil but makes them less harmful to the environment.4. Redox manipulation: This method involves altering the redox potential of the soil to change the chemical form of the heavy metals, making them less mobile and less bioavailable. For example, the addition of oxidizing agents can convert mobile forms of heavy metals, such as hexavalent chromium Cr VI , to less mobile and less toxic forms, such as trivalent chromium Cr III .5. Phytoremediation: This technique uses plants to extract, stabilize, or degrade heavy metals from contaminated soil. Some plants, known as hyperaccumulators, can take up and store large amounts of heavy metals in their tissues. The plants can then be harvested and disposed of safely, effectively removing the heavy metals from the soil. This method can be combined with the use of chelating agents to enhance the uptake of heavy metals by the plants.6. Bioremediation: This method uses microorganisms to transform heavy metals into less toxic forms or to immobilize them in the soil matrix. Some bacteria and fungi can produce compounds that bind to heavy metals, reducing their mobility and bioavailability. Bioremediation can be enhanced by adding nutrients or other amendments to stimulate microbial activity.It is important to note that the choice of remediation technique depends on the specific site conditions, the type and concentration of heavy metals present, and the desired end use of the site. In some cases, a combination of techniques may be necessary to achieve the desired level of remediation.