The use of new methods for cleaning urbanized soils from heavy metals

IN AND. Savich, Doctor of Agricultural Sciences, Professor, S.L. Belopukhov, Doctor of Agricultural Sciences, Professor, D.N. Nikitochkin, Candidate of Agricultural Sciences, Russian State Agrarian University - Moscow Agricultural Academy. K.A. Timiryazev; A.V. Filippova, Doctor of Biological Sciences, Professor, Orenburg State Agrarian University

Pollution of urban soils reduces the quality of life of the population, as dust particles carried by the wind enter the human body, leading to health problems. Filtration of pollutants, or their cumulation, depends on the properties of the soil and its saturation with pollutants. The issues of cleaning urban soils were discussed by the scientific community, measures were proposed for the periodic change of urbanized soils, the use of micropreparations that bind heavy metals, etc. It should be noted that any studies that improve the quality of urban soils have a place to be.

Biological purification of urban soils from heavy metals has its own characteristics. Purification of urban soils from heavy metals can be carried out by alienating them from the soil by green plants. At the same time, for a more enhanced development of the process, it is necessary to select the growing conditions and plant species. Different plants have unequal resistance to certain types of pollution, which is determined by the characteristics of the metabolic processes occurring in them. So, according to E.M. Ivanova et al., when comparing the resistance to copper sulfate of three grasses - crystal grass, red clover and rapeseed - clover showed the greatest resistance. At the same time, the toxicity of copper for plants was largely determined by its ability to bind to the BN groups of proteins and easily change its redox state, generating active forms oxygen and causing a state of oxidative stress.

Purpose and methods of research. When studying the possibilities of phytoremidia, experiments were carried out to study the possibilities of the removal of heavy metals by plants.

In experiment No. 1, the purpose of the study was to identify the influence of the composition of the soil on the development of plants grown on it, the removal of certain elements (N, Fe, Mn, Mg) with plants, the assessment of plants that accumulate maximum and minimum accumulate various microelements. The components of the studied soils were quartz sand, peat, zeolite impregnated with NPK solution, soddy-podzolic soil (taken in a forest park in Moscow), soil contaminated with various toxicants (taken from the roadside). Plants of watercress, radish, bluegrass meadow and fescue were grown on the obtained soils.

red for 1-1.5 months. Then, the obtained seedlings were analyzed using chemical analysis data (the content of elements of manganese, zinc, magnesium, iron), as well as data on the length of the stems and roots of grown seedlings (the pH values ​​of the studied soils ranged from 6.4 to 7.1).

Research results. The maximum development of stems was noted in the variant containing 10 g of zeolite, 30 g of peat, 30 g of sand and 30 g of contaminated soil. The options most favorable for the formation of the mass, the length of the stems and roots are different. This, apparently, is associated both with the presence of different growth substances in the variants, and with the formation of a set of physicochemical, water-physical, and structural-chemical properties of soils that are favorable for various individual processes.

best development plants by their weight was noted in the variant containing 25 g of peat, 25 g of zeolite, 25 g of sand and 25 g of contaminated soil. At the same time, the optimum for the development of different plants is noted on different soils.

The removal of zinc from soils due to biological reclamation is shown in Table 1.

The removal of zinc from soils depends on the composition of the soil and the plants grown. More removal was in the culture, which has a higher vegetative mass. Obviously, feeding plants with nutrients will increase the removal of heavy metals by plants. At the same time, fescue and bluegrass showed the highest removal of mg of zinc per plant. The removal of zinc in soils with the addition of peat was 46.5 + 13.4 mg / vessel, and in soils without peat - 38.4 + 14.0.

The maximum removal of zinc from polluted soils (mg/vessel) was carried out by radish, the minimum - by lettuce (Table 2).

1. Removal of zinc from soils by individual crops (n = 8)

Culture Zinc removal

mg/vessel 100 mg/g plant 100

Watercress 16.5±4.7 50.0

Radish 109.2±28.7 67.0

Bluegrass 22.3±5.6 82.6

Fescue 32.6±8.5 90.5

2. Removal of zinc by plants, mg/vessel 102

Variant Plants

lettuce radish bluegrass fescue

zeolite > 10% (option 1) 7.7±6.4 75.5±3.7 18.9±2.2 42.3±26.9

zeolite< 10% (вариант 2 и 4) 15,4±6,5 112,8±39,9 20,9±6,8 22,0±4,7

The introduction of zeolite into the soil in more than 10% (25%) compared with the introduction of 10% zeolite led to the binding of zinc in the soil and to a lower removal of zinc by lettuce and radish plants (mg/vessel) (differences are not significant for bluegrass and fescue).

In experiment No. 2, we studied the removal of lead, cadmium, iron, and zinc from soils by vetch and oat seedlings. The objects of study were polluted soils. To increase the mobility of heavy metals in soils, the samples were poured with 0.001 m EDTA to 60% HP, then seedlings were grown on them for 10 days. At the end of the growing period, heavy metals were extracted from the seedlings with 0.1 N HCl and then determined on an atomic absorption spectrophotometer. According to the data obtained, the removal of heavy metals from soils by plants differed for soils different levels contamination, which can be seen from Table 3.

3. Removal of heavy metals by plants

Degree of contamination Removal, mg/100 g

Weak Increased 0.85±0.38 1.95±0.55 2.9±0.81 6.7±2.8 6.1±1.9 21.4±5.4 74±±63

4. Removal of heavy metals from soils by vetch and oat seedlings (mg/100 g of plants)

Seedlings Pb Cd Fe Zn

Vika 1.0±0.4 7.1±2.5 8.5±3.1 2.9±1.0

Oats 0.7±0.2 3.0±1.0 11.4±3.8 2.1±0.6

Vetch and oats differed in their ability to extract heavy metals from soils.

Judging by the data obtained, vetch took out more lead, cadmium, zinc from the soil, and oats - iron.

A series of experiments have shown that the purification of urban soils from mobile forms of heavy metals can be carried out not only with the use of sorbents, with the precipitation of heavy metals in the form of sparingly soluble sediments, with the use of soil electroreclamation, and very successfully with the help of phytoobjects. Obviously, the removal of heavy metals from soils by plants (or microorganisms, fungi) depends on the degree of mobility of toxicants in the soil and increases when conditions are created for the intensive development of plants. Since different plants withstand both a certain nature and degree of pollution, for the biological purification of urban soils from specific metals, selective conditions for their extraction should also be selected (including changes in the physicochemical properties of soils and the selection of ameliorant crops).

In one of the experiments, the development of seedlings was studied on soil samples taken in various districts of Moscow. In the samples, the pH value of the aqueous suspension was determined; the length of roots and stems of seedlings and their weight were evaluated. Growing plants at

optimal humidity lasted 10 days. The data obtained are shown in Table 5.

5. Development of seedlings on the soils of parks and heavily polluted areas

Area Mass Roots Stems

Moscow Ring Road, v. 1 Squares, v. 6, 8 0.8 1.7±0.1 2.7 5.2±1.2 7.3 11.6±1.5

As can be seen from the presented data, on heavily polluted soils near the Moscow Ring Road, plants developed much worse than in the city squares.

From a theoretical point of view, adding to the soil nutrient solution should improve the development of plants, and the introduction of lead into the soil, on the contrary, worsen their development. In the experiment, the nutrient solution and Pb(CH3COO)2 were added according to the variants.

The addition of lead to polluted soils led to the complete suppression of plants, and on the soils of public gardens it reduced their mass, reduced the length of roots and stems. At the same time, the introduction of a nutrient solution into the soil improved the development of plants on polluted soils and almost did not change the development on the soils of public gardens.

In the next experiment, the influence of vetch, ryegrass, and white mustard on the content of heavy metals in the soil was evaluated. Despite the fact that plants absorbed a certain amount of heavy metals from soils, the content of their mobile forms in soils did not decrease due to the excretion of complexones by plants through the root system and the influence of decomposition products of organic residues on the mobility of heavy metals.

Theoretically, when KNO3 is introduced into the soil (when watering the soil), the development of plants should improve, and, consequently, their removal of heavy metals from the soil should increase. However, this will also increase the ionic strength of the solution, and hence the solubility of the precipitates. The influence of plants on the solubility of sediments in the soil will also increase. In connection with the foregoing, the total content of heavy metals in soils during such biological reclamation should decrease, while the content of mobile forms may increase. Similar processes also occur when soils are irrigated with EDTA (complexone for polyvalent metals). However, this reagent is not a source of plant nutrition, and its effect on the solubility of precipitation is greater than that of KNO3, but less on plant development. The considered theoretical patterns are also illustrated by the data in Table 6.

Thus, there are various ways to remove mobile forms of heavy metals from the upper soil layer, the priority of which is determined by specific soil, lithological, hydrological conditions and economic opportunities. In addition

Fig. 6. Influence of the introduction of KNO, EDTA into soils and plant cultivation on the content of mobile forms of heavy metals in soils (n=10-30)

Options C<1 Си Ми

Vetch yugo3 EDTA Ryegrass White mustard KZh)3 + vetch + ryegrass + mustard EDTA + vetch + ryegrass + mustard 1.10±0.21 0.95±0.10 0.81±0D0 0.78±0D9 1.20± 0.18 1.08±0.21 0.28±0.13 0.0 0.51±0.16 0.0 0.0 0.90±0.11 0.55±0.06 3.60 ±0.4 0.79±0.16 1.17±0.53 0.70±0.16 3.90±1D 2.72±0.8 3.60±1.1 1.70±0.5 1 .10±0.2 323.5±47.5 167.7±18.3 332.1±38.9 230.7±43.2 237.5±36.5 212.7±35.1 113, 8±42.3 72.4±31.0 373.5±77.2 332.0±67.1 77.9±31.7

to the known methods, from our point of view, it is advisable to add the following:

1) leaching of heavy metals with complexion solutions to a certain depth and then their sedimentation there, followed by soil washing with solutions containing carbonates, phosphates, which have an alkaline environment;

2) removal from soils due to phytoremediation and absorption of heavy metals by fungi while creating conditions for their greater bioproductivity;

3) regulation of exchange constants in the soil-roots system; roots - the above-ground part of plants due to the nutritional regime;

4) application for phytoremediation of plant species and varieties with a higher sorption capacity of roots to heavy metals;

5) the use of long-acting sorbents for the sorption of heavy metals,

taking into account the equilibrium constants in the system soil - heavy metal and sorbent - heavy metal;

6) a decrease in the entry of heavy metals into plants when complexones are introduced into soils from agricultural waste, which form stable complexes of large molecular weight with metals;

7) electromelioration of soils when creating conditions for increasing the mobility of heavy metals;

8) creation of geochemical barriers in the soil profile that prevent their entry into plants, migration to groundwater, and evaporation from soils.

The choice of a strategy when using a set of measures to improve the condition of urban soils, sometimes called urban soils, is possible only when carrying out a physicochemical calculation and predicting ongoing processes for specific soils, plants and conditions. environment.

Literature

1. Kholodova V.P., Volkov K.S., Kuznetsov V.V. Adaptation to high concentrations of copper and zinc salts in crystal grass plants and the possibility of their use for phytoremediation // Plant Physiology. 2005. T. 52. C, 848-858.

2. Ivanova E.M., Volkov K.S., Kholodova V.P., Kuznetsov V.V. New promising plant vitts in phytoremediation of copper-contaminated territories // Bulletin of the Peoples' Friendship University of Russia. Series "Agronomy and animal husbandry". 2011. No. 2. S. 28-37.

3. Clemens D. Toxic metal accumulations. Responses to exposure and mechanisms of tolerance in plants, Biochem., 2006, v. 88, p. 1707-1719.

4. Kramer U. Metal hyper-accumulation in plants, Ann. Rev. Plant Biol., 2010, v. 10, p. 517-534.

5. Savich V.I., Belopukhov C.JI., Nikitochkin, Filippova A.V. New methods of soil purification from heavy metals / Proceedings of the Orenburg State Agrarian University. 2013. No. 4. S, 216-218.

The introduction of boric acid into the soil due to the participation of boron in the formation of complex compounds of metals with polysaccharide derivatives - pectin and rhamnogalacturonan II during the formation of a network in the cell wall matrix significantly increases the removal of plants by heavy metal remediants from the soil. There is a method of biological purification of the soil from heavy metals with the help of plant remediants. In the proposed method of phytoremediation, boric acid is introduced into the soil in low doses of 0110 kg ha, which makes it possible to increase the...

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The method of biological purification of soils from heavy metals.

1. Brief description of the development.

The introduction of boric acid into the soil, due to the participation of boron in the formation of complex compounds of metals with derivatives of polysaccharides - pectin and rhamnogalacturonan-II during the formation of a network in the cell wall matrix, significantly increases the removal of heavy metals from the soil by plants-remediants.This principle was used in the development of a method for phytoremediation of soils contaminated with heavy metals. The method is designed to protect and restore natural resources, is environmentally friendly, low-cost.

2. Advantages of development and comparison with analogues.

There is a method of biological purification of the soil from heavy metals with the help of remedial plants. In the proposed method of phytoremediation, boric acid is introduced into the soil in low doses (0.1-1.0 kg/ha), which makes it possible to increase the removal of heavy metals from polluted soil by remediant plants tenfold and regulate the removal of certain metals from the soil.

3. Areas of commercial use of the development.

Phytoremediation of soils contaminated with heavy metals using boric acid to target critical values: 1) in agriculture (for agriculture, horticulture, animal husbandry); 2) in landscape construction (for recreational land use); 3) in the municipal economy (for the organization of recreation areas in the restored territories); 4) in specially protected natural areas (to ensure the conditions for the existence of rare and endangered species).

4. Form of intellectual property protection.

Received Patent for invention No. 2342822 "Method of biological soil purification from heavy metals" dated 01/10/2010

Developer - FGBUN IL KarRC RAS.

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Short description

Pollutants are substances of anthropogenic origin that enter the environment in quantities exceeding the natural level of their intake.
Soil pollution is a type of anthropogenic degradation, in which the content chemical substances in soils subject to anthropogenic impact, exceeds the natural regional background level. The excess of the content of certain chemicals in the human environment due to their intake from anthropogenic sources is an environmental hazard.

Attached files: 1 file

With the expansion of environmental monitoring of the state of soils, methods for determining the content of acid-soluble (1 N HCI, 1 N HNO3) HM compounds began to be widely used. Often they are given the name “conditional gross content of HMs.” The use of diluted solutions of mineral acids as reagents does not ensure complete decomposition of the sample, but allows the main part of the compounds of chemical elements of technogenic origin to be transferred into the solution.

The mobile forms of HM include elements and compounds of the soil solution and the solid phase of the soil, which are in a state of dynamic equilibrium with the chemical elements of the soil solution. To determine mobile HMs in soils, weakly saline solutions are used as an extractant, with an ionic strength close to the ionic strength of natural soil solutions: (0.01–0.05M CaCI 2, Ca(NO 3) 2, KNO 3). The content of potentially mobile compounds of controlled elements in soils is determined in an extract of 1 N. NH4CH3COO at different pH values. This extractant is also used with the addition of complexing agents (0.02–1.0 M EDTA).

For analysis, the upper layers of the soil (0–10 cm) are most often selected, sometimes the distribution of pollutants in the soil profile is analyzed. The upper horizons play the role of a geochemical barrier to the flow of substances coming from the atmosphere. Under the conditions of the leaching water regime, pollutants can penetrate deep into and accumulate in illuvial horizons, which also serve as geochemical barriers.

The sanitary and hygienic criterion of environmental quality is the maximum permissible concentration (MPC) of chemicals in environmental objects. MPC corresponds to the maximum content of a chemical in natural objects that does not cause a negative (direct or indirect) impact on human health (including long-term consequences).

The toxic effect of various chemicals on living organisms is characterized by a general sanitary indicator, which is often used as the LD-50 indicator (lethal dose), which shows the mass of the substance that entered the body of experimental animals (mice, rats) and caused the death of 50% of them. The dimension of this indicator is mg of the substance/kg of the mass of the experimental animal. Direct contacts of a person with the soil are insignificant and occur indirectly through other components: soil - plant - person; soil - plant - animal - man; soil - air - man; soil - water - man. The determination of MPC in soils is reduced to the experimental determination of the ability of these substances to maintain the concentration of substances acceptable for living organisms in water, air, and plants in contact with the soil. That is why the MPC of chemicals for soils is set not only according to the general sanitary indicator, as is customary for other natural environments, but also according to three other indicators: translocation, migratory water and migratory air.

The translocation indicator is determined by the ability of soils to provide the content of chemicals at an acceptable level in plants (radish, lettuce, peas, beans, cabbage, etc. serve as test crops).

Accordingly, migratory water and migratory air are determined by the ability of soils to ensure the content of these substances in water and air is not higher than the MPC. However, sanitary and hygienic standards for soil quality are not without drawbacks; the main one is that the conditions of the model experiment for determining the MPC and the natural conditions are very different.

One of the steps in solving the problem of environmental regulation was an approach based on determining the permissible load on the soil, taking into account its buffer properties, which ensure the ability of the soil to limit the mobility of chemicals coming from outside, the ability to self-purify. Such approaches are being developed in Russia and other countries.

But it is very difficult to develop MPC for each type of soil. It is advisable to develop chemical standards for soil-geochemical associations, united by the commonality of the basic physical and chemical properties that determine their resistance to chemical pollution.

At the next stage, for a number of chemical elements, AECs (roughly permissible concentrations) of these elements were developed for soils that differ in the most important properties (acidity and granulometric composition). They were developed not on the basis of a standardized experimental method, but on a generalization of the available information on the relationship between the level of load on soils, the state of soils and adjacent environments.

Table 3

List of major soil polluting chemicals for which maximum allowable concentrations have been determined

Substances	MAC in soil, mg/kg	Hazard Class
Manganese
Formaldehyde
Benz(a)pyrene
Acetaldehyde

4 Methods for cleaning soil from heavy metals

The ability to convert metals into a mobile form is the basis for soil purification methods by washing, extraction, chemical leaching, electrodialysis, and electrokinetic treatment. Metals are removed from the soil in the form of solutions, which are processed by ion exchange, reagent precipitation, evaporation, membrane separation, electrochemical precipitation, electrodialysis to obtain solid residues with a small volume, suitable for disposal in landfills, places of disposal of harmful substances.

When choosing a method for extracting metals, their amount in the soil, the composition and dispersion of the solid phase are taken into account. Metals that are in the exchange form are extracted by salt solutions associated with carbonates-solutions of acids, with oxides of iron and manganese-chemical reducing agents, with organic matter-solutions of complexing agents, in the form of sulfides-chemical oxidizing agents.

In biological methods for increasing the mobility of heavy metals, microorganisms and plants are used to extract them from the soil. The mobility of metals increases:

• as a result of biomineralization of organic substances containing metals.
• in the course of oxidative reactions occurring with the participation of microorganisms in the processes of bioleaching;
• as a result of changes in pH, Еh of the soil environment during the course of biological processes;
• in the formation of soluble metal complexes with organic substances synthesized and excreted by microorganisms and plant roots;
• in the bioreduction of metals by organic substances under anoxygenic conditions;
• as a result of the transfer of metals into a volatile form during methylation and transalkylation.

The fixation of heavy metals in soil reduces their availability for plants and migration through food chains.

One of the options for reducing the bioavailability of heavy metals is the introduction of sorbents into the soil.

From various sorbents of natural and artificial origin, zeolites, bentonites, red clay, ash, phosphates, peat, manure, compost, pond sludge, biomass of microorganisms on various carriers, waste wool, silk, waste containing tannin and fiber are used. General requirements for sorbents: pH 6.0-7.5, available and relatively cheap.

One technology, called the Bio Metal Sludge Reactor (BMSR), designed to treat soil, sludge, solid waste, uses the bacteria Ralstonia metallidurans. Bacteria solubilize metals with synthesized siderophores and adsorb metals on the cell surface with metal-induced outer membrane proteins, cell wall polysaccharides, and peptidoglycans. Bacteria are resistant to heavy metals. Metals are removed from the cell by antiport with protons, which leads to the accumulation of OH - ions in the periplasmic space, alkalization of the external environment and the formation of carbonates and bicarbonates. Metal ions exported from the cytoplasm form carbonates and bicarbonates in supersaturated concentrations on the cell surface and around the cell and crystallize on cell-bound metals that serve as crystallization centers. This results in a high metal to biomass ratio (0.5 to 5.0). Such bacteria remove metals from solution in the late phase of exponential growth or in the stationary phase of growth, which is convenient for the extraction of metals from contaminated soils by ex situ methods. Bacteria have special properties that cause a low settling rate of bacterial cells compared to organic and clay soil particles. This makes it possible to separate soil particles and cells with absorbed metal by the precipitation method. Bacteria with adsorbed metals, which are in the aqueous phase after separation, are easily removed from the latter by flotation or flocculation.

5 General information about Ralstonia metallidurans

Fig.1 Image of Ralstonia metallidurans

Cell structure and metabolism

R. metallidurans is a gram-negative, rod-shaped bacterium. Thus, they share the structural features of Gram-negative bacteria, such as peptidoglycan-containing cell walls, lamella-containing outer membranes, and periplasmic spaces.

R. metallidurans has the ability to use various substrates as a source of carbon. It can grow autotrophically using molecular hydrogen as an energy source and carbon dioxide as a carbon source. In addition, in the presence of nitrate representatives, it can grow anaerobically. They do not grow on fructose and its optimum growth temperature is 30 C.

Ecology

Due to its ability to withstand the action of toxic metals, the use of this feature in the fields of biological restoration has been studied.

Pathology

It was found that R.metallidurans is not pathogenic for humans.

Application in biotechnology

R. metallidurans has been found to be able to produce enzymes that can be used to make fuel cells. These enzymes are able to oxidize hydrogen, which can eventually lead to electricity generation.

6 Technology for cleaning soil from heavy metals

When cleaning using BMSR technology, contaminated soil is introduced into a flow-type reactor with a stirrer, into which water and nutrients (acetate-5g/l, nitrogen-0.5g/l, phosphorus-0.05g/l) are supplied, bacteria are introduced ( in the amount of 10 8 cells/ml). The soil is pre-fractionated to remove large agglomerates, debris, etc. The particle size in the reactor should be no more than 2 mm. The pH is maintained at 7.2. The hydraulic residence time in the reactor is 10 to 20 hours.

During processing, contaminant metals are transferred from the soil particles to the bacterial walls. After treatment in the reactor, the sludge is deposited in a sump, into which water is added. In the presence of bacteria, soil particles have good sedimentation properties and settle in the sump within 1-2 hours. Bacteria containing metals remain in suspension, which from the sump enters the settling tank (decanter). A flocculant is added to it, after which the biomass sludge can be dehydrated and dried. The content of metals in the biomass of bacteria is: Zn-8-25, Pb-3-5, Cd-0.16-0.25. This biomass can be incinerated by pyrometallurgical treatment to produce ash with a high metal content that can be recovered by leaching, or with subsequent storage of the ash in a landfill. The content of heavy metals in the cleaned soil is reduced by 5-10 times. Soil treated with bacteria at neutral pH using BMSR technology can be reused. Waste water contains very low concentrations of metals and can be recycled.

Calculation of the process of soil bioremediation from heavy metals.

Soil samples were taken from a 6 ha site at a depth of 9 cm (0.09 m). The lead content is 50 mg/kg.

1. Determination of the volume of contaminated soil.

V p \u003d S p × H

V p \u003d 6000 m 2 × 0.09 \u003d 540 m 3

2.Weight of contaminated soil.

R n = V n × d

R p \u003d 540 m 3 × 1.2 t / m 3 \u003d 648 t

3.Total weight of heavy metals.

1 kg of soil - 2.5 g HM

1 ton of soil - 2500 kg HM

640 t soil - x kg HM

x = 640 t × 2.5 t = 320 t

The IBU of microorganisms Ralstonia metallidurans is 8 m 3 /t HM.

x m 3 - 640 t

Set the amount of amophos.

For 1 t HM - 24 kg AMF

R AMP = 320 × 24 = 7680 kg AMP

Solubility of AMP = 18 kg/m 3 .

Water volume.

1 m 3 H 2 O - 18 kg AMP

x m 3 H 2 O -104.8 kg

V in \u003d 104.8 / 18 \u003d 5.82 t

7680 t + 5.82 t = 7686 t

Site selection

Soil harrowing

Transportation for remediation

Grinding up to 2 mm

bacteria

Loading into the bioreactor

Nutrients

settling

flocculant

decanter

Dehydration

pyrometallurgical processing

Storage at burial sites

Fig.2 Technological scheme of soil bioremediation from heavy metals.

UDC 546.621.631

SOIL SOIL CLEANING FROM HEAVY METALS1

A.I. Vezentsev, M.A. Trubitsyn,

L.F. Goldovskaya-Piristaya, N.A. Volovicheva

Belgorod State University, 308015, Belgorod, st. Victory, 85

[email protected]

The results of studying the ability of clays in the Belgorod region to absorb Pb (II) and Cu (II) ions from water and buffer soil extracts are presented. During the experiment, the optimal ratio clay:soil was established, at which the removal of heavy metals from soil is most effective.

Keywords Key words: clay sorbents, soil, sorption activity, montmorillonite, heavy metals.

The industrial use of heavy metals is very diverse and widespread. That is why phytotoxicity and harmful accumulation in soils, as a rule, are observed near enterprises. Heavy metals accumulate in the upper humus horizons of the soil and are slowly removed during leaching, consumption by plants, and erosion. Humus and the alkaline environment of the soil contribute to the absorption of heavy metals. The toxicity of such heavy metals as copper, lead, zinc, cadmium, etc. for agricultural crops in natural conditions is expressed in a decrease in the yield of commercial crops in the fields.

There are several methods for reclamation of soils contaminated with heavy metals and other pollutants:

Removal of the contaminated layer and its burial;

Inactivation or reduction of the toxic effect of pollutants using ion-exchange resins, organic substances that form chelate compounds;

Liming, application of organic fertilizers that absorb pollutants and reduce their entry into plants.

The introduction of mineral fertilizers (for example, phosphate, reduces the toxic effect of lead, copper, zinc, cadmium);

Growing Pollution Tolerant Crops.

Currently in world practice for ecological refining fertile soils mineral aluminosilicate adsorbents are increasingly used: various clays, zeolites, zeolite-containing rocks, etc., which are characterized by high absorption capacity, resistance to environmental influences and can serve as excellent carriers for fixing various compounds on the surface during their modification.

Materials and methods of research

this work is a continuation of earlier studies of clays of the Gubkinsky district of the Belgorod region, as potential sorbents for cleaning fertile soils from heavy metals.

1 The work was supported by the Russian Foundation for Basic Research, project No. 06-03-96318.

In this work, clays from the Kyiv suite of the Sergievsky deposit in the Gubkinsky district were used as sorbents, which differed in material composition and properties: K-7-05 (middle layer) and K-7-05 YuZ (lower layer). Soil samples K-8-05 and No. 129, taken on the territory of the Gubkinsko-Starooskolsky industrial region, were used as cleaning objects. Preliminary studies have shown that the clays of the Sergievsky deposit absorb copper and lead ions well from model aqueous solutions. Therefore, further studies were carried out with water and buffer extracts from the soil.

The aqueous extract was prepared according to the standard procedure. The essence of the method lies in the extraction of water-soluble salts from the soil with distilled water at a ratio of soil to water of 1: 5. The concentration of metal ions was determined by the photocolorimetric method on a KFK-3-01 instrument according to the appropriate methods for each metal.

The buffer extract from the soil was prepared according to the standard method of the Central Institute of Agrochemical Services. Agriculture(CINAO) using an acetate-ammonium buffer solution with a pH of 4.8. This extractant is accepted by the agrochemical service for the extraction of trace elements available to plants. The initial concentration of mobile forms of copper and lead available to plants in the buffer extract was determined by atomic absorption spectrometry.

Sorption of copper and lead ions was carried out at a constant temperature (20°C), under static conditions for 90 minutes. The ratio of sorbent: sorbate was: 1: 250; 1:50; 1:25; 1:8 and 1:5.

The discussion of the results

A study of the aqueous extract, which was prepared for 4 hours, showed that the concentration of water-soluble copper compounds is insignificant and amounts to 0.0625 mg/kg (in terms of Cu2 ions). Water-soluble lead compounds were not detected.

The initial concentration of heavy metal ions in buffer extracts from soils was: for K-8-05 soil: Cu2+ 2.20 mg/kg, Pb2+ 1.20 mg/kg; for soil No. 129: Cu2+ 4.20 mg/kg, Pb2+ 8.30 mg/kg.

The results of determining the degree of purification of soil K-8-05 with clays K-7-05 (middle layer) and K-7-05 YuZ (lower layer) are presented in Table 1.

Table 1

The degree of purification of the buffer extract from the soil K-8-05, mass, %

Sorbent ratio: sorbate Clay K-7-05 (middle layer) Clay K-7-05 YuZ (lower layer)

Cu2+ Pb2+ Cu2+ Pb2+

1: 250 45,5 33,3 54,5 33,3

1: 50 70,5 45,8 68,2 58,3

1: 25 72,3 58,3 79,5 58,3

1: 8 86,4 75,0 87,3 83,3

1: 5 95,5 83,3 95,5 83,3

The results presented in Table 1 show that with an increase in the ratio of sorbent: sorbate from 1: 250 to 1: 5, the degree of purification of the buffer extract from copper ions with K-7-05 clay increases from 45.5 to 95.5%, and from lead ions - from 33.3 to 83.3%.

The degree of purification of the buffer extract with clay K-7-05 YuZ with the same increase in the ratio increased from 54.5 to 95.5% (for Cu2+) and from 33.3 to 83.3% (for Pb2+).

Note that the initial concentration of copper ions was higher than that of lead ions. Therefore, cleaning the buffer extract from copper ions with these clays is more effective than from lead ions.

table 2

The degree of purification of the buffer extract from soil No. 129 with K-7-05 clay (middle layer), wt. %

Ratio of sorbent: Cu2+ sorbate +

1: 250 39,3 66,7

Note: with clay K-7-05 YuZ, the experiment was not made, due to the lack of a sufficient amount of the sample.

The results presented in Table 2 show that the degree of purification of the buffer extract from soil No. 129 with clay K-7-05 with an increase in the ratio of sorbent: sorbate from 1: 250 to 1: 5 increases from 39.3 to 93.0% (for copper ions) and from 66.7 to 94.0% (for lead ions).

It should be noted that in this soil the initial concentration of copper ions was lower than that of lead ions. Therefore, we can assume that the efficiency of purification from copper ions of this soil is no worse than that of K-8-05 soils.

To clarify the mechanism of sorption of heavy metals, we assessed the composition and state of the ion-exchange complex of clayey rocks in the Belgorod region. It has been established that the cation-exchange capacity of the studied samples varies from 47.62 to 74.51 meq/100 g of clay.

A comprehensive study of the acid-base properties of clays has been carried out. Determination of active acidity confirmed that all clays have an alkaline character. At the same time, the pH of the salt extract of the same samples is in the range of 7.2-7.7, which indicates that these clays have a certain share of exchangeable acidity. Quantitatively, this value is 0.13-0.22 mmol-eq/100 g of clay and is due to the low content of sufficiently mobile exchangeable protons. The value of the sum of exchangeable bases fluctuates within a fairly wide range of 19.6 - 58.6 mmol-equiv / 100 g of clay. Taking into account the data obtained, a hypothesis was formulated that the sorption capacity of the studied clay samples with respect to heavy metals is largely determined by the processes of ion exchange.

From the work carried out, the following conclusions can be drawn.

With an increase in the ratio of sorbent: sorbate from 1: 250 to 1: 5, the degree of soil purification increases: from 40 to 95% (for copper ions) and from 33 to 94% (for lead ions) when using clay from the Sergievsky deposit (K-7- 05) as a sorbent.

The studied clays are a more effective sorbent for copper ions than for lead ions.

It has been established that the optimal ratio of clay: soil is 1: 5. With this ratio, the degree of soil purification is:

For copper ions, about 95% (wt.)

For lead ions, about 83% (wt.)

Bibliography

1. Bingham F.T., Costa M., Eichenberger E. Some questions of the toxicity of metal ions. - M.: Mir, 1993. - 368 p.

2. Galiulin R.V., Galiulina R.A. Phytoextraction of heavy metals from contaminated soils // Agrochemistry.- 2003.- №3. - S. 77 - 85.

3. Alekseev Yu.V., Lepkovich I.P. Cadmium and zinc in plants of meadow phytocenoses // Agrochemistry. - 2003. - No. 9. - P. 66 - 69.

4. Dayan U., Manusov N., Manusov E., Figovsky O. On lack of interdependency between the abiotic and antropeic factors/// International Scientific Journal for Alternative Energy and Ecology ISJAEE, 2006.-№ 3(35). - P. 34 - 40.

5. Vezentsev A.I., Goldovskaya L.F., Sidnina N.A., Dobrodomova E.V. Zelentsova E.S. Determination of the kinetic dependences of the sorption of copper and lead ions by the rocks of the Belgorod region. Nauchnye Vedomosti BelGU. Series Natural Sciences. - 2006. - No. 3 (30), issue 2. - P.85-88

6. Goldovskaya-Piristaya L.F., Vezentsev A.I., Sidnina N.A., Zelentsova E.S. Investigation of the total content and content of mobile forms of cadmium in the soils of the Gubkinsko-Starooskolsky industrial region. Nauchnye Vedomosti BelSU. Series "Natural Sciences". - 2006. - No. 3 (23), issue 4. - P.65-68.

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SORPTION PURIFICATION OF SOILS FROM HEAVY METALS A.I. Vesentsev, M.A. Troubitsin, L.F. Goldovskaya-Peristaya, N.A. Volovicheva

Belgorod State University, 85 Pobeda Str., Belgorod, 308015 [email protected] edu. en

Results of research of ability of clays of the Belgorod region to absorb ions Pb(II) and Cu(II) from water and buffer soil extracts are presented. During experiment of the optimum ratio clay: ground with most effective purification from heavy metals is established.

Key words: clay sorbents, soil, sorption activity, montmorillonite, heavy metals.

Deteriorating environmental conditions have a negative impact on the soil - due to pollution, yields are reduced and a toxic effect is manifested.

Due to soil self-purification, harmful substances are gradually removed, but this process takes quite a long time, and in addition, the rate of pollution processes in the technogenic environment significantly exceeds the rate of self-purification processes.

Therefore, methods of artificial purification of the soil are actively used.

To clean the soil from pollution, various technological methods have been developed, and new ones are regularly introduced. First of all, the most environmentally friendly and safe methods should be used to clean the soil, not forgetting the efficiency and financial costs.

Soil cleaning methods

If we consider methods of cleaning contaminated soil, then we can divide them according to the principle of action into the following categories:

• chemical cleaning methods.
• physical cleaning methods.
• biological cleaning methods.

Physical methods of soil cleaning

1) Electrochemical cleaning.

It is used to remove chlorine-containing hydrocarbons, various oil products, phenols from the soil. What is the basis of the electrochemical cleaning method? On the move electric current electrolysis of water, electrocoagulation, reactions of electrochemical oxidation and electroflotation are carried out through the soil. The oxidation state of phenol is in the range of 70 to 90 percent.

The qualitative level of soil disinfection during electrochemical cleaning approaches one hundred percent (the minimum figure is 95%). The method allows removing from the soil also such harmful elements as mercury, lead, arsenic, cadmium, cyanides, etc.

The disadvantages of the method include a rather high cost ($ 100-250 per 1 m³ of soil).

2) Electrokinetic cleaning.

It is used to clean the soil from cyanides, oil and oil derivatives, heavy metals, cyanides, organic chloride elements. Soil types to which electrokinetic cleaning can be successfully applied are clayey and loamy, partially or completely saturated with moisture.

The technology is based on the use of processes such as electrophoresis and electroosmosis. The level of control and impact on the processes of soil cleansing is quite high. The method requires the use of chemical reagents or surfactant solutions.

The efficiency of electrokinetic soil cleaning is from 80 to 99 percent. The cost is somewhat lower than with electrochemical cleaning ($100-170 per 1 m³ of soil).

Chemical methods of soil cleaning

1) Washing method.

Soil chemical cleaning technologies involve the use of surfactant solutions or strong oxidizing agents (active oxygen and chlorine, alkaline solutions). Basically, the method is used to clean the soil from oil. The efficiency of the washing method is up to 99%.

After the soil is cleared, it can be recultivated.

Of the minuses of chemical methods of soil purification, one can note long periods (1-4 years on average) and a significant amount of polluted water, which also has to be cleaned before being released into the environment.

Biological methods of soil cleaning

1) Phytoextraction.

The technology of cleaning soils contaminated with harmful substances by phytoextraction is the cultivation of certain types of plants on contaminated soil areas.

Phytoextraction demonstrates good results when cleaning the soil from copper, zinc and nickel compounds, as well as cobalt, lead, manganese, zinc and chromium. To remove the vast majority of these elements from the soil, it is necessary to provide several cycles of plant crops.

At the end of the phytoextraction process, the plants should be harvested and burned. The ash obtained after incineration is considered hazardous waste and must be disposed of.

Another biological method is the targeted increase in the activity of specific soil microflora, which is involved in the decomposition of oil. It is also acceptable to add certain microbial cultures to the soil.

As a result, favorable conditions are created for microorganisms that utilize petroleum products and oil.
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