What are the binding forms of heavy metals in soil and briefly describe their environmental effects

The existence form of heavy metals in soil is affected by their composition and physical and chemical properties, so their existence forms are particularly complex and can be divided into the following forms:

1. Commutative state:

Ion exchange and obligate adsorption are the characteristics of this form of heavy metal. This form of heavy metal can be released in a cationic solution and can be bioabsorbed directly in the soil.

2. Carbonate bound state:

The precipitated or co-precipitated active form of heavy metals released by milder acids can also be called bioavailable heavy metals;

3. Manganese-iron bound state:

It is co-precipitated or obligate adsorbed in soil oxides, but can be released into the soil in the reduced state.

4. Residue state:

The forms of heavy metals contained in the mineral lattice are difficult to migrate and be bioused, and are relatively safe for the environment, and will only be released into the environment when they encounter acids, chelating agents or microorganisms, which will have an impact on the ecology.

5. Organically bound state:

The content of heavy metals in this form is affected by the content of organic matter in the soil, as well as the content of coordination groups, and the morphology of the outer electron orbitals of metal ions can also affect it.

Environmental effects of heavy metals in soil:

The existence and chemical properties of heavy metals formed through various reactions such as dissolution, condensation, and sedimentation determine the migration of heavy metals in the soil and the degree of harm to the human body, and the existence of heavy metals determines the migration and transformation characteristics, the degree of harm and the nature of pollution.

Most of the heavy metals belong to transition elements with unique variable valence, which can undergo redox reactions under certain conditions. Heavy metals have different valence states, and so do their toxicity and activity.

1.It exists in ionic form and is very harmful. Soluble in water, easy to diffuse, large pollution area, after binding with protein, protein inactivation, resulting in heavy metal poisoning.

2.Poorly soluble compounds are generated. It is not easy to diffuse and does not easily bind to proteins. Virtually non-polluting.

1.commutable state; 2.carbonate-bound state; iron-manganese oxide bound state; 3.organically bound state; 5.Residue state.

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Analysis: The morphology of heavy metals in soil is mainly affected by soil pH value, redox potential (EH) and other types of compounds. The availability of heavy metals in soil is only a relative indicator and cannot reflect the absolute amount that objectively exists.

At present, it is generally believed that the exchangeable state (including the water-soluble state) is relatively easy for plants to absorb and utilize, which is of great significance in plant nutrition, and is also the main form of heavy metal pollution to plants. The effectiveness of organic complexes on plants is very complex, because the organic complex heavy metals formed in the soil are not only easy to be used by plants, but also have relatively low solubility (macromolecular organic complex heavy metals such as humic acid) that cannot be absorbed by plants. Therefore, the low molecular weight organic compounds produced during the over-elimination process of animal and plant decomposition can also increase the effectiveness of heavy metals on plants.

The speciation analysis of heavy metals in soil can be divided into exchange state, carbonate state, iron and manganese oxidation state, organic state and residue state.

1 Universal characteristics With the development of industrial production, heavy metal pollution is becoming more and more common, threatening almost every country, in the 50s of the last century, Japan's Toyama Tsukawa River Basin "bone pain" is caused by cadmium pollution in brown rice excessive cadmium. In 1997, two agricultural areas in Montana, USA, were also contaminated with cadmium, making local wheat inedible. Many of our cities have been affected by the suburbs and irrigation districts.

There are different degrees of heavy metal pollution. Such as the Zhangtu irrigation area in Shenyang.

2.Concealment Characteristics The soil polluted by heavy metals is colorless and odorless, and it is difficult to detect by human sensory organs, and it can only be reflected when plants enter the food chain to accumulate to a certain extent.

3 Characteristics of surface polymerization Most of the heavy metal pollutants in the soil remain in the soil tillage layer and rarely move to the lower layer of the soil. This is due to the existence of organic colloids, inorganic colloids and organic-inorganic composite colloids in the soil, which have strong adsorption and chelation ability for heavy metals, which limits the migration ability of heavy metals in the soil.

4 Irreversibility Characteristics Because heavy metals accumulate in the soil to a certain extent, it leads to changes in soil structure and function, and because heavy metals are difficult to degrade, it is difficult to recover once the soil is polluted.

Soil types;

land-use patterns;

oxidation-reduction conditions of soils;

the pH of the soil;

soil colloidal adsorption;

Complexation-chelation of heavy metals in soil.

soil colloidal adsorption;

oxidation-reduction conditions of soils;

Soil types; The factors influencing the migration and transformation of heavy metals in soil are as follows:

the pH of the soil;

Complexation-chelation of heavy metals in soil.