RU2471849C1 - Composition for detoxification of soils contaminated mainly with arsenic - Google Patents

Abstract

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.

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Description

The present invention relates to the field of soil reclamation and can be used in the reclamation of lands contaminated with arsenic and other elements with a variable degree of oxidation, exhibiting both oxidizing and reducing properties in the soil and easily transforming from cationic to anionic form and vice versa.

Compositions for soil reclamation are known that sorb either cationic forms of elements - heavy metals (US Pat. RF No. 20491207, IPC C09K 17/00, 1992), or anionic - sulfates, nitrates, etc. (for example, organic substances of sapropel) or compounds of molecular structure without pronounced charges on the particles of the substance - oil products and other organic compounds (US Pat. RF No. 2198987, IPC E02B 15/04, C02F 1/28, 2003).

A disadvantage of the known compositions is their low efficiency in the presence of transitional valence elements in the soil that exist both in cationic and anionic forms.

Closest to the proposed is a composition for land reclamation "Sorbex" (US Pat. RF No. 2049107, IPC C09K 17/00, 1992) based on sapropel, including mineral components such as zeolite and alumina. It has high sorption activity in relation to mobile forms of heavy metals, in particular copper and zinc, but is much less effective in relation to transition valence elements, in particular arsenic.

To eliminate this drawback allows the proposed composition for detoxification of soils, mainly contaminated with arsenic, including diatomite treated with Fe ³⁺ , and blue clay in the following ratio, wt.%:

di ³ treated with Fe ³⁺ 50-60 blue clay 40-50.

The components for this sorbent were selected based on laboratory experiments.

,

и т.п.) в результате образования арсенатов железа:Trivalent iron Fe ³⁺ is an active sorbent of the anionic form of arsenic (

,

etc.) as a result of the formation of iron arsenates:

However, these salts are unstable, and as a result of hydrolysis in an aqueous solution, arsenic again passes into a soluble state:

Therefore, ferric iron must be fixed on diatomite silicates, as a result of which the obtained iron arsenates remain immobilized.

Al ³⁺ in the composition of aluminum oxide (Al ₂ O ₃ ) - the mineral blue clay has a similar effect:

However, in this case, the anionic forms of arsenic are easily reduced to cationic forms under the influence of soil organic matter:

(электронные органических соединений почвы) = Н₂О + As³⁺

(electronic organic soil compounds) = H ₂ O + As ³⁺

Cationic forms of arsenic can only be sorbed by anionic sorbents (for example, organic substances of sapropel), therefore, to prevent the recovery of arsenic, a strong oxidizing agent must be present in the composition, converting arsenic into an oxidized anionic form. Ferric iron meets these requirements, as it is easily reduced to ferrous and thereby interferes with the recovery of arsenic.

Fe ³⁺ + e (electronic organic soil compounds) = Fe ²⁺

Thus, the composition based on diatomite and blue clay should contain both sorbents of anionic forms of arsenic proper and an oxidizing agent that impedes the recovery of arsenic, in this case ferric ions.

The conducted experiments confirm this theory.

The proposed composition for the detoxification of soils contaminated mainly with arsenic, containing diatomite treated with Fe ³⁺ and blue clay, was prepared as follows.

Natural diatomite was crushed to a particle size of not more than 2 mm to increase the total area of the sorbent. Iron (III) chloride was dissolved in distilled water to obtain a saturated solution. The crushed diatomaceous earth was placed in the solution for 24 hours, then the supernatant was decanted, and the iron-treated particles were dried to an air-dry state.

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

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

Alluvial soil with a background content of arsenic of 0 mg / kg was artificially contaminated with a solution of sodium arsenate Na ₃ AsO ₄ . The sample was kept in a dark place at a temperature of 22-25 ° C for four weeks. Then the mobile forms of arsenic were determined. After a week, the analysis was repeated. After establishing the equilibrium state in the system, the sample was treated with various sorbents (7 options, 3-fold repetition). The amount of sorbent was determined from the calculation of the dose of 10 t / ha. As sorbents used:

- diatomite,

- diatomaceous earth treated with ferric iron,

- blue clay,

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

- SORBEX (sapropel, zeolite, alumina),

- sapropel

- zeolite.

All samples were brought to 65% moisture and kept without light at a temperature of 22-25 ° C for 4 weeks, then the mobile forms of arsenic were determined in the soil. After a week, the analysis was repeated until the equilibrium in the system was established. The results are shown in table 1.

Table 1 The content of mobile forms of arsenic in the soil sample after treatment with sorbents of various compositions Sorbent The decrease in the content of mobile forms of arsenic,% pH (H ₂ O) Fe ³⁺ treated diatomite + blue clay 87 7.4 Sapropel 63 7.3 Di ³ treated with Fe ³⁺ 45 7.5 Blue clay 37 7.8 SORBEX thirty 7.5 Diatomite 19 7.3 Zeolite -fourteen 7.3

From the results obtained, the following conclusions can be drawn.

The most effective, immobilizing the largest amount of arsenic, is a composition containing diatomaceous earth treated with ferric iron and blue clay. The pH values after application of various compositions remain within the normal range (5.6-7.5), with the exception of the option when pure blue clay was applied (7.8).

A similar experiment was carried out with a composition with different percentages of components — diatomite treated with ferric 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 in mobile forms of arsenic Diatomite treated with Fe ³⁺ 100% 45 Diatomite treated with Fe ³⁺ 80-90% 58 Blue clay 10-20% Diatomite treated with Fe ³⁺ 50-60% 87 Blue clay 40-50% Diatomite treated with Fe ³⁺ 30-40% 63 Blue clay 60-70% Diatomite treated with Fe ³⁺ 10-20% 42 Blue clay 80-90% Blue clay 100% 37

Thus, the optimal composition is with a component ratio of 50-60% of diatomite treated with Fe ³⁺ and 40-50% of blue clay, which reduces the content of mobile forms of arsenic in the soil by 87% and maintains an optimum pH of 7.4 in the soil.

Claims (1)

Composition for detoxifying soils, mainly contaminated with arsenic, including diatomite treated with Fe ³⁺ and blue clay in the following ratio, wt.%:
di ³ treated with Fe ³⁺ 50-60 blue clay 40-50