**2. Mercury poisoning treatment**

As known, even a small amount of mercury can affect the digestive, nervous, and immune systems. Also, it can be a threat to the development and growth of a child in early life. Mercury products are hazardous waste. When this waste is placed in the trash, it does not decompose. Instead, they find their way into lakes, rivers, or soil [35].

#### **Figure 8.**

Mercury like other heavy metals, cannot be degraded in ecosystems, thus treatment should be based on removals or installations. Removal techniques include adsorption mechanism, Adsorption, oxidation, and reduction [36]. The main objective of these techniques is the separation or conversion of mercury from contaminated media toxic mercury species to less toxic species. The most widely adopted installation techniques are stabilization and containment, Which prevents the transfer of mercury by chemical complexity or physical baiting, respectively [37].

Novel materials, especially materials that possess high Surface area, large porosity as well as adsorption active sites It has been extensively examined in recent studies Regardless of the absorption capacity which is the main determinant of these materials, and other issues such as the method of generation, Stability, and reusability should also be seriously considered compared to traditional processing techniques such as heat absorbent or activated carbon adsorption, innovative [38].

The methods have proven to be more cost-effective and environmentally friendly. Interestingly, most of these techniques treat contaminated mercury Soil, water, and air can depend on the emerging materials or metabolizing organisms, i.e. plants, algae, and bacteria. **Figure 8** [15] shows the main mechanisms involved in Hg treatment.

Major mechanisms involved in Hg treatment from the air, water, and soil can be explained as follows:

a.The catalyst oxidation method is commonly used for gaseous phase mercury removal. Oxidation is a more cost-effective method to remove Hg0 from the flue gas. Several studies have focused on new oxidation, regardless of the oxidation method of the catalyst, the advanced free radical oxidation of Hg0 is also sometimes used, but the removal capacity of Hg0 using this technology is still limited [39].

The synthesis of a functional covalent thioether of triazine nanoparticles for Hg2+ and Hg0 is absorbed by water studies and the results show an excellent adsorption capacity (1253 and 813 mg/g for mercury Hg2+ and Hg0 , respectively). The maximum adsorption capacity was reached 172.6 mg/g by using silica-coated magnetron nanoparticles for Hg(II) extraction from wastewater and adsorption of mercury ions on imine groups (C-NH-) on the surface of nanoparticles [40].

b.Reduction of Hg2+ to Hg0 is often applied to prevent the formation of Methyl mercury (MeHg). Methyl mercury is the most bioavailable form of Mercury. Oxidation-reduction conditions in wetland sediments enhance formation From MeHg. The high concentration of mercury (II) species results in production from MeHg. Therefore, an effective way to control the production of methyl mercury is to reduce the Hg(II) concentration. Zerovalent iron (ZVI) or Fe (II) is often used. To reduce Hg(II) to Hg(0), thus inhibiting the production of MeHg [41].

Adsorption methods by using adsorbents usually possess high surface area and high porosity and the formation of chelates is the major approach to removing Hg(II) from water solution [42].

c.Stabilization approaches freeze the movement of mercury into contaminated sites. Through chemical complexity to reduce solubility for Reduce exposure to mercury in the environment During chemical fixation Sulfur-containing reagents such as elemental sulfur and pyrite (FeS2) or thiosulfate are commonly used to react with Hg(0) in pollutants oil to form HgS, which is very insoluble [43].

Soil can be dealt with either on-site or off-site, the former requires less energy and labor cost. However, fine mixing is still very difficult on-site stability. The basic defect in stability is that mercury is not removed from contaminated media, Thus it requires permanent prospective monitoring of contaminants on site. Similar to installation, pollution is left on site during containment treatment. Low permeability physical barriers (eg clay plaster walls, coverings, or curtains) around contaminated soil To isolate and contain the soil, thus preventing the migration of mercury to the surrounding environment. These material Barriers can be divided into three types: barricades, vertical barricades, and horizontal barriers [44].

Nano-materials are gaining more and more attention in mercury remediation of soil, water, and flue gas, owing to their high adsorption capacity, small dimension, and another unique electrical, mechanical and chemical properties. There are several major types of nanoparticles and nanocomposites such as carbon nanotubes (CNT) [45], Zinc oxide (ZnO) [46], and Ferro ferric oxide (Fe3O4), [47] nanoparticles can be used for Hg remediation in the wastewater.
