Composition for detoxification of soils contaminated mainly with arsenic

FIELD: agriculture.

SUBSTANCE: composition for detoxification of soils contaminated mainly with arsenic includes diatomite treated with Fe3+, and blue clay in the following ratio of components, wt % weight: diatomite treated with Fe3+ - 50-60, blue clay - 40-50.

EFFECT: composition reduces the content of mobile forms of arsenic in the soil and maintains the optimum pH in the soil.

2 tbl

 

The present invention relates to the field of land reclamation and can be used for reclamation of land contaminated by arsenic and other elements with variable oxidation state, manifesting in the soil both oxidizing and reducing properties and easy turning of the cationic form of anionic and back.

Known compositions for the amelioration of soils that absorb or cationic form elements - heavy metals (U.S. Pat. Of the Russian Federation No. 20491207, IPC C09K 17/00, 1992), or anionic sulfates, nitrates and the like (for example, organic substances sapropel) or compounds molecular structure without the Express charges on the particles - petroleum products and other organic compounds (U.S. Pat. Of the Russian Federation No. 2198987, IPC E02B 15/04, C02F 1/28, 2003).

A disadvantage of the known compounds is their low efficiency in the presence of soil elements with valence transition, existing both in cationic and anionic form.

Closest to the present invention is a composition for soil reclamation "Sorbex" (U.S. Pat. Of the Russian Federation No. 2049107, IPC C09K 17/00, 1992) based on sapropel, including mineral components, such as zeolite and alumina. Has a high sorption activity in respect of mobile forms of heavy metals, particularly copper and zinc, but much less effective against the elements with a valence transition, in private the ti arsenic.

To remedy this allows the proposed composition for detoxification of soils contaminated primarily with arsenic, including diatomite treated Fe3+and blue clay in the following ratio, wt.%:

diatomite treated Fe3+50-60
blue clay40-50.

Components for a given sorbent were selected on the basis of the performed laboratory experiments.

Ferric iron Fe3+an active sorbent anionic forms of arsenic (,and the like) due to the formation of arsenate iron:

However, these salts are unstable, and as a result of hydrolysis in aqueous solution arsenic is converted back to a soluble state:

Therefore, trivalent iron should be mounted at the silicates, diatomaceous earth, resulting in arsenate iron remain immobilized.

Similar action has Al3+in the composition of aluminum oxide (Al2O3) - mineral blue clay:

However, in this case, the anionic form of arsenic easily restored to their cationic forms under the influence of soil organic matter:

(e organic compounds soil) = N2About + As3+

Cationic forms of arsenic can be absorbed only anionic sorbents (e.g., organic matter sapropel), so as to prevent the recovery process of arsenic in the composition should be a strong oxidant, which moves the arsenic in the oxidized anionic form. Trivalent iron meets these requirements, as is easily restored to divalent and thus hinders the process of recovery of arsenic.

Fe3++e (e organic compounds soil) = Fe2+

Thus, the composition on the basis of diatomite and blue clay should contain as sorbents anionic forms of arsenic, and the oxidant, preventing the recovery of arsenic, in this case the ferric ions.

The experiments confirm this theory.

The proposed structure for detoxification of soils contaminated primarily with arsenic containing diatomite treated Fe3+and blue clay, was prepared as follows.

Natural diatomite was crushed to the size of the cha is TIC no more than 2 mm to increase the total area of the sorbent. Chloride iron (III) was dissolved in distilled water to obtain a saturated solution. Crushed diatomite was placed in the solution for 24 hours, and then the supernatant solution was decanted and the treated iron particles were dried to air-dry state.

Blue clay was ground to particle size of not more than 2 mm, dried to 10-15% moisture content. Then the components were mixed in different proportions.

To study the action of this mixture was performed the following laboratory experiment.

Alluvial soil with background arsenic content 0 mg/kg was artificially contaminated with a solution of sodium arsenate Na3AsO4. The sample was kept in a dark place at a temperature of 22-25C for four weeks. Then determined the mobile form of arsenic. A week later, the analysis was repeated. After the establishment of equilibrium in the system, the sample was treated with different sorbents (7 options, 3-fold repetition). The amount of sorbent was determined from dose calculation made 10 t/ha as sorbents used:

- diatomaceous earth,

- diatomite treated with trivalent iron,

blue clay,

- a mixture of diatomaceous earth treated with trivalent iron, and blue clay

- SORBEX (sapropel, zeolite, alumina),

- sapropel,

zeolite.

All samples were brought to 65% moisture and withstand without access of light at a temperature of 22-25 C during 4 weeks then made the determination in the soil of mobile forms of arsenic. A week later, the analysis was repeated to establish equilibrium in the system. The results are shown in table 1.

7,3
Table 1
The content of mobile forms of arsenic in the soil sample after treatment with adsorbents of different composition
SorbentThe decrease in the content of mobile forms of arsenic, %pH(H2O)
Diatomite treated Fe3+, + blue clay877,4
Sapropel637,3
Diatomite treated Fe3+457,5
Blue clay377,8
ZORBAX307,5
Diatomite197,3
Zeolite-14

From the obtained results we can make the following conclusions.

The most effective, immovable greatest amount of arsenic, is a composition containing diatomite treated with trivalent iron, and blue clay. The pH values after making various compounds remain within the normal range (5,6-7,5), except for the option when I made the blue clay in its purest form (7,8).

A similar test was carried out with the composition with different percentages of components of diatomite treated with trivalent iron, and blue clay. The results are shown in table 2.

Table 2
The content of mobile forms of arsenic in the soil after interaction with compounds with different percentages of components
The composition of the sorbent% reduction of mobile forms of arsenic
Diatomite treated Fe3+100%45
Diatomite treated Fe3+80-90%58
Blue clay 10-20%
Diatomite treated Fe3+50-60% 87
Blue clay 40-50%
Diatomite treated Fe3+30-40%63
Blue clay 60-70%
Diatomite treated Fe3+10-20%42
Blue clay 80-90%
Blue clay 100%37

Thus, the optimum composition ratio of the components 50-60% of diatomite treated Fe3+and 40-50% of blue clay, which reduces the content of mobile forms of arsenic in soil at 87% and the supporting soil, the optimum pH of 7.4.

Composition for detoxification of soils contaminated primarily with arsenic, including diatomite treated Fe3+and blue clay in the following ratio, wt.%:

diatomite treated Fe3+50-60
blue clay40-50



 

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