RU2592525C2 - Sorbent for cleaning aqueous media from heavy metals and preparation method thereof - Google Patents

Abstract

FIELD: environmental protection.

SUBSTANCE: invention relates to sorption materials for removal of compounds of heavy metals and arsenic from water. Method of producing sorbent comprises soaking porous support with aqueous solution of iron compounds while stirring, adding alkali solution or concentrated ammonia, washing and drying sorbent at 120-150 °C. Support used is vermiculite concrete milled to particle size of 0.25-8 mm, which contains (wt%): vermiculite from 6 to 20, cement from 24 to 40, sand from 50 to 70. Obtained sorbent contains iron oxyhydroxide in amount of 47-69 % on support.

EFFECT: invention enables to obtain a sorbent with high adsorption capacity and mechanical strength.

3 cl, 2 tbl

Description

The invention relates to the field of environmental protection, and in particular to methods and sorption materials for removing compounds of heavy metals and arsenic, petroleum products, polar organic substances, organic and inorganic acids from groundwater, surface water systems and wastewater of various enterprises. The claimed invention can find application in local water intakes, enterprises of the chemical and metallurgical industries, in the use of pickling and galvanic technologies, as well as in individual drinking water purification systems.

A known method of producing a sorbent for collecting oil from the surface of the water (AS USSR 1378913, dated 07.03.1988), including hydrophobization of the surface of expanded vermiculite with colloidal solutions of polyvalent metal hydroxides to their content from 0.1 to 3.0% by weight sorbent followed by impregnation with aliphatic hydrocarbons. Hydrophobization of vermiculite with colloidal solutions is carried out by circulating them at a speed of 8 to 18 m / h, and impregnation with aliphatic hydrocarbons by passing oil-containing wastewater through a hydrophobized sorbent to an oil content of at least 0.1% by weight of the sorbent. However, this method has low productivity, which is associated with the use of polyvalent metal hydroxides for the treatment of expanded vermiculite with colloidal solutions. In addition, these colloidal solutions must be disposed of.

A known method of producing sorbents for water purification (RU 2277013 dated 05/27/2006), including processing natural aluminosilicate (zeolite, expanded vermiculite or a mixture thereof) with a solution of chitosan in dilute acetic acid with a mass ratio of aluminosilicate and chitosan solution equal to 1: 1, and the final pH of the solution above the precipitate, equal to from 8 to 9. The formed plastic mass is granulated by extrusion through dies of a given size, the obtained granules are dried, and then treated with a solution of humic acids taken in quantities ie, providing a complete binding of the amino groups of chitosan. Then the granules of the sorbent are separated from the solution and give hardness to the polymer layer formed on the surface of the granules.

However, the implementation of this method of producing sorbents due to its multi-stage requires the use of sophisticated equipment. In addition, in the synthesis process, the pores of the aluminosilicate are blocked by the molecules of the active component, which reduces the total active area of the sorbent.

Known sorbent that purifies water from arsenic ions with different valencies (US patent No. 6921732 from 07/26/2005). The sorbent is a zeolite coated with nanophase oxides of iron and manganese, and the sorbent contains from 0.25 to 10% iron oxide with a molar ratio of Mn / (Mn + Fe) equal to 0.10. The sorbent is obtained by adding zeolite to an iron-manganese solution prepared by mixing a solution of iron oxide with a manganese-containing compound. This mixture is filtered and the sorbent in the form of a zeolite coated with nanophase hydroxides of iron and manganese is obtained from the filtered product by drying.

However, this material allows you to remove only arsenic ions from water and is not used to purify water from ions of other heavy metals. Moreover, the highest concentration of water pollution at which a high degree of purification is achieved is relatively small: 1.57 mg / dm ³ (ppm). In addition, in the process of purification of As (III) arsenic ions, which is widely distributed under natural conditions, manganese ions Mn (II) are released, which are also water pollutants.

A known method of producing a sorbent (RU 2343973 dated 01/20/2009), comprising supplying carrier particles to the working chamber, which is used as expanded vermiculite, and an organosilicon compound, supplying a stream of heated air to the working chamber, as a result of which the carrier particles interact with sprayed organosilicon compound, subsequent drying of the carrier with a layer of organosilicon compound.

However, this sorbent purifies water environments only from oil products. In addition, the implementation of this method requires a complex production line consisting of a working chamber, which includes the application zone and the drying zone, as well as three supply lines of the corresponding reagents, which affects the productivity and efficiency of the process.

Known sorbent for removing oil and oil products from the surface of the water (SU No. 1062340 dated 12/23/1983), which is used as granular expanded clay expanded clay.

However, this sorbent does not purify water from arsenic ions and heavy metals. In addition, this sorbent is not used for the purification of drinking water.

A known product for water treatment (RU 2225251 dated 03/10/2004), which is a particulate material having a specific surface area of 10.0 m ² / g, or an article obtained by bonding such a particulate material and having an insoluble hydrated ferric oxide coating. Preferably, the particulate material is alumina based material. The product is effective in treating water to remove organic substances, cations or anions, especially As arsenic ions, Se selenium, or fluorine F. In this case, ferric oxide is deposited on particles having sizes from 5 μm to 5000 μm with a maximum specific surface area of at least 100 m ² / g.

The support used is a porous material obtained by heating alumina particulate matter and consists of particles of a size of 5 to 10 μm and has a specific surface area of 100-150-200 m ² / g. However, the surface of such particles, especially in closed pores, is not accessible for the deposition of metals. This limits the sorption capacity of the material and reduces the adsorption rate under dynamic operating conditions of the sorption material. The method of applying iron oxide does not allow to obtain a sorption layer having high sorption characteristics.

Known sorbent (RU 2328341 from 07/10/2008) for water purification from heavy metal ions, which consists of crushed zeolite, nanophase iron hydroxide and nanophase boehmite in the following ratio of components, wt.%: Nanophase iron hydroxide from 12 to 18, nanophase boehmite from 5 to 13, zeolite - the rest. The sorbent allows trapping of arsenic ions of different valencies, cadmium, copper, lead and chromium from ground and surface waters and during wastewater treatment.

The disadvantages of this sorbent are the small size of the cross section of the pores of the carrier, which prevents the penetration of iron and aluminum compounds into them and the formation of iron and aluminum hydroxides on the zeolite’s inner surface. As a result of this, the active components settle on the outer surface of the zeolite, which reduces the effective surface area of the sorbent. In addition, the carrier pores are blocked by particles of boehmite and iron hydroxide, which prevents the release of exchange ions contained in the zeolite. In addition, at a given content of boehmite and iron hydroxide, a significant amount of them is not deposited on the surface of the carrier and is contained in the reaction medium in the form of individual nanoparticles or small agglomerates, which makes it difficult to extract them from the solution when the finished product is isolated from the reaction mass. In addition, the presence in the sorbent of nanoparticles in a free state, although it increases the effective surface area, significantly degrades the hydrodynamic characteristics of the cleaning process. There is also a risk of leaching free particles during the water treatment process.

Also known is a sorbent of heavy metals, a method for its preparation and a method for water purification (RU No. 2336946 dated 02.21.2006). This method of producing a sorbent of heavy metals and preferably arsenic involves impregnating a porous base with an aqueous solution of an iron compound, then adding an alkali solution, using granules of highly porous alumina with a pore volume of at least 0.55 cm ³ / g and a specific surface area of less than 200 m ² / g, which are wetted with water before being impregnated with an aqueous solution of the iron compound.

The heavy metal sorbent obtained by this method contains alumina modified with nanosized particles of iron oxides, made in the form of granules of highly porous alumina with a pore volume of at least 0.55 cm ³ / g, a specific surface area of at least 200 m ² / g, which are the assembly of nanofibers interconnected into a rigid sponge structure, while nanosized particles of iron oxides are formed as a layer on the surface of said granules in an amount of 2 to 10% by weight of the granules. This is a sorbent of heavy metals and the method of its production is selected as a prototype of the proposed solution.

However, this method does not allow to obtain a sufficient amount of the active component (nanosized particles of iron oxides from 2 to 10% by weight of the granules), which leads to a lower sorption ability of the material. In addition, the implementation of the method requires the use of an expensive carrier to obtain sorption material.

As a prototype of the proposed solution, a method for producing sorbents of heavy metals and sorbents of heavy metals (options) was chosen (application for invention No. 20111148497 dated 11/30/2011). This method of producing sorbents of heavy metals consists in impregnating a porous carrier with an aqueous solution of iron compounds and the subsequent addition of an alkali solution. An aqueous solution of iron compounds is mixed by supplying compressed air to the reaction medium, and crushed vermiculite or expanded clay is chosen as carriers.

The disadvantages of this material include the low hardness of one of the carriers (vermiculite), which will deform and contract under the influence of a water stream. And another carrier (expanded clay) has a closed pore system that can not take a sufficient amount of iron hydroxide. In addition, to obtain a prototype sorbent, an aqueous solution of iron compounds uses a solution of iron ammonium alum, which is a very expensive reagent. Stirring the carrier in an iron solution is at least 3 hours, which is a long process. And the air supply to the reaction medium during the heating process leads to its cooling, which requires more time for the process and, accordingly, additional energy costs. The sorbent prototype has an insufficiently wide range of granule sizes (fraction size from 0.2 to 5 mm). And the drying of this sorbent is carried out at a temperature of from 180 to 220 ° C, which is a very high temperature. Moreover, under various conditions, iron hydroxide begins to pass into iron oxide at a temperature of from 180 to 250 ° C, which can drastically reduce the sorption capacity of the material. In addition, when preparing the material of the prototype, the reaction medium is washed (before drying) with distilled water, which is not economically feasible.

The aim of the invention is the creation of a new sorbent material (sorbent) that can effectively purify water at high concentrations, remove contamination of any charge from petroleum products, polar organic substances, organic and inorganic acids at pH values from 4 to 9 by changing the surface charge depending on conditions of the cleaned environment.

The technical result of the invention is to increase the capacity of the sorbent with respect to heavy metals, reduce the hydrodynamic resistance, increase the effective adsorption surface and increase the mechanical strength.

The specified technical result is achieved in that in a method for producing a sorbent of heavy metals, comprising impregnating a porous carrier with an aqueous solution of iron compounds and the subsequent addition of an alkali solution, the aqueous solution of iron compounds is mixed by installing a container with a solution of the reaction medium on an orbital shaker where the vessel is shaken.

There is an option in which a solution of ferric chloride with a concentration of from 70 to 130 g / dm ³ in a volume of 230 cm ³ per 3 g of support is used as an aqueous solution of iron compounds.

There is also an option in which vermiculite concrete is pre-crushed to a size of fractions from 1.5 to 2.5 mm.

A variant is possible where the mixing of vermiculite concrete in an aqueous solution of iron compounds is carried out using an orbital shaker for at least 1 hour.

It is also possible that the resulting sorbent is washed, filtered, and then dried to completely remove moisture at a temperature of from 120 to 150 ° C.

The technical result is also achieved by the fact that the sorbent of heavy metals contains a porous carrier and iron oxohydroxide, the porous carrier is vermiculite concrete, and the sorbent has the following ratio of components, wt.%: Iron oxohydroxide from 47 to 69; vermiculite concrete from 31 to 53.

It is possible that vermiculite concrete is used as a porous carrier in the following ratios of components, wt.%: Vermiculite from 6 to 20; cement from 24 to 40; sand from 50 to 70.

The claimed invention allows to provide a technical result, which consists in increasing the efficiency of water purification from heavy metal ions by expanding the effective surface area.

Due to the use of a carrier with a large pore diameter in the form of crushed vermiculite concrete, the sorbent of heavy metals is able to take a large content of the active component in its structure, which increases its sorption ability. Through the use of mixing by installing a container with a carrier in a solution of ferric chloride on an orbital shaker, uniform saturation of the porous structure of the carrier with iron compounds is achieved to the entire depth. Subsequent introduction into the medium of an alkali solution of NaOH or concentrated ammonia causes the transition of iron compounds into the form of oxohydroxide with their fixation on the surface and in the pores of the support and initiates the formation of a polymolecular structure of iron oxohydroxide in the form of fibers. Due to the large pores with a developed active surface of the sorbents with the presence of iron oxohydroxide in the porous structure of the support in a larger quantity, a shorter contact time with the medium to be cleaned is required in comparison with the prototype when treating water with high concentrations of contaminants (Cd ²⁺ is 5 mg / dm ³ ; Cu ²⁺ is 5 mg / dm ³ ; Pb ²⁺ is 10 mg / dm ³ ; Zn ²⁺ is 5 mg / dm ³ ; Fe ³⁺ is 30 mg / dm ³ ; Mn ²⁺ is 6 mg / dm ³ ) A more durable carrier reduces the hydrodynamic resistance of the inventive sorbent in comparison with the prototype.

The result is a sorbent containing iron oxohydroxide both on the surface and in the pores of the carrier, which significantly increases the active surface area of the product and allows you to increase the amount of active component in the porous structure of the material in contrast to the sorbent of the prototype.

Sorbent based on crushed vermiculite concrete allows trapping heavy metal ions of different valencies, for example, iron, chromium, cadmium, lead, nickel, zinc, copper, molybdenum.

A method of producing a sorbent of heavy metals is implemented as follows.

A carrier in the form of porous vermiculite concrete is selected, which is ground in an agate mortar. Next, the crushed vermiculite concrete is sieved to the required size fractions on the sieves in the range from 0.25 to 8 mm. Then, a weighed portion of the carrier of ground vermiculite concrete in an amount of 3 g is placed in a glass beaker into which a solution of ferric chloride of ferric FeCl ₃ · 6H ₂ O is added in an amount of 230 cm ³ with a concentration ranging from 70 to 130 g / dm ³ . The glass is installed on an orbital shaker and the process is shaken for at least 1 hour. Thanks to this operation, the carrier is very effectively mixed in the solution, due to which its pores are saturated with an iron-containing reagent. After the necessary mixing time of at least 1 hour, the lower part of the glass is wrapped in asbestos cloth and mounted on an electric stove, where the temperature of the reaction medium is brought to a process temperature of 30 to 75 ° C, which provides optimal synthesis conditions.

Concentrated ammonia or a solution of sodium hydroxide in a concentration of at least 30 g / dm ³ in the required volumes is added to the reaction medium to bring the pH of the reaction medium from 11 to 12. A reaction is carried out with periodic stirring with a glass rod. The temperature of the process is controlled using a thermometer. After the synthesis process, the electric stove is turned off and the reaction medium is cooled to room temperature.

Rinse the reaction medium with tap water to lower the pH of the reaction medium to a neutral reaction with further decantation (in a beaker) and filtering on a Buchner funnel using a vacuum pump.

The resulting mass is placed in an oven, and dried at a temperature of 120 to 150 ° C until moisture is removed from the finished sorbent.

Determination of the sorption properties of the proposed sorbent is carried out in the following way.

Prepare in volumetric flasks a solution containing ions of the determined elements with concentrations: Cd ²⁺ is 5 mg / dm ³ ; Cu ²⁺ is 5 mg / dm ³ , Pb ²⁺ is 10 mg / dm ³ , Zn ²⁺ is 5 mg / dm ³ , Fe ³⁺ is 30 mg / dm ³ , Mn ²⁺ is 6 mg / dm ³ . For this, a weighed portion of a sorbent weighing 200 mg is placed in a glass cup with a volume of 100 cm ³ . 20 cm ^{3 of} solution are poured from the measuring cylinder. Fix the glass on a magnetic stirrer, turn it on at low revolutions up to 200 rpm and carry out the sorption process for at least 150 minutes.

After the sorption process is carried out, remove the beaker from the mixer and filter the solution with the sorbent in a vacuum filtration unit through a blue ribbon paper filter. Filtered from the sorbent solution - the filtrate is analyzed for contamination. Determination of the content of cadmium ions Cd ²⁺ , copper ions Cu ²⁺ , lead ions Pb ²⁺ , zinc ions Zn ^{2+ is} carried out by the method of inverse voltammetry on an analyzer, for example, TA-07 (LLC Tekhnoanalit, Tomsk) . The content of Fe ³⁺ iron ions and Mn ²⁺ manganese ions in solutions is determined photocolorimetrically using a KFK-2 photocolorimeter.

The arithmetic mean of the results of three parallel determinations is taken as the test result, the permissible discrepancy between them should not exceed 5%.

Examples of practical implementation of the method for producing sorbents and their adsorption activity are given below.

Example 1

To obtain the claimed sorbent for one load take crushed vermiculite concrete GOST 11050-64 with a ratio of components, wt.%: Iron oxohydroxide from 47 to 57; vermiculite concrete from 43 to 53.

A portion of vermiculite concrete is crushed in an agate mortar, then sieved to the desired fraction on sieves. Then, a sample of crushed vermiculite concrete weighing 3 g is selected and the carrier is saturated with an iron-containing component. To do this, crushed vermiculite concrete in an amount of 3 g is placed in a reaction vessel, a solution of ferric chloride of FeCl ₃ · 6H ₂ O with a concentration of 70 g / dm ³ in an amount of 230 cm ^{3 is} added, the reaction vessel is placed on an orbital shaker and held for at least 1 hour. At the end of the saturation process, the reaction vessel with a suspension of the carrier in a solution of iron chloride is placed on an electric stove and heated to a temperature of 30 to 75 ° C. With periodic stirring with a glass rod, add 40.3 cm ^{3 of a} 25% solution of NH ₄ OH or NaOH solution with a concentration of from 30 g / dm ³ to a pH of the medium, from 11 to 12.

The synthesis of the sorbent is carried out with periodic stirring for from 20 to 30 minutes at a temperature of from 30 to 75 ° C. Then the suspension is cooled to ambient temperature and subjected to repeated washing with tap water until a neutral pH of the washing water medium is reached. Next, the precipitate is filtered on a Buchner funnel using a vacuum pump. The filtered precipitate is dried at a temperature of from 120 to 150 ° C until dry.

Example 2

To obtain the claimed sorbent for one load is taken vermiculite concrete, GOST 11050-64, with a ratio of components, wt.%: Iron oxohydroxide from 53 to 63; vermiculite concrete from 37 to 47.

A portion of vermiculite concrete is crushed in an agate mortar, then sieved to the desired fraction on sieves. Then, a weighed sample of crushed vermiculite concrete weighing 3 g is taken and the carrier is saturated with an iron-containing component, for which crushed vermiculite concrete in an amount of 3 g is placed in a reaction vessel, a solution of ferric chloride FeCl ₃ · 6H ₂ O with a concentration of 95 g / dm ³ in an amount is added 230 cm ³ , place the reaction vessel on an orbital shaker and incubate for at least 1 hour. At the end of the saturation process, the reaction vessel with a suspension of the carrier in a solution of iron chloride is placed on an electric stove and heated to a temperature of 30 to 75 ° C. With periodic stirring with a glass rod add 58.7 cm ^{3 of a} 25% solution of NH ₄ OH or NaOH solution with a concentration of from 30 g / dm ³ to a pH of 11 to 12.

The synthesis of the sorbent, washing, filtering, drying and activation is carried out, as in example 1.

Example 3

To obtain the claimed sorbent for one load is taken vermiculite concrete, GOST 11050-64, with a ratio of components, wt.%: Iron oxohydroxide from 59 to 69; vermiculite concrete from 31 to 41.

A portion of vermiculite concrete is crushed in an agate mortar, then sieved to the desired fraction on sieves. Then, a weighed sample of crushed vermiculite concrete weighing 3 g is selected and the carrier is saturated with an iron-containing component, for which crushed vermiculite concrete in an amount of 3 g is placed in a reaction vessel, a solution of ferric chloride ferric FeCl ₃ · 6Н ₂ О with a concentration of 130 g / dm ³ in an amount is added 230 cm ³ , place the reaction vessel on an orbital shaker and incubate for at least 1 hour. At the end of the saturation process, the reaction vessel with a suspension of the carrier in a solution of iron chloride is placed on an electric stove and heated to a temperature of 30 to 75 ° C. With periodic stirring with a glass rod add 82.4 cm ^{3 of a} 25% solution of NH ₄ OH or NaOH solution with a concentration of from 30 g / dm ³ to a pH of 11 to 12.

The synthesis of the sorbent, washing, filtering, drying and activation is carried out, as in example 1.

Sorbent studies were carried out on three samples obtained with a fractional composition from 1.5 to 2.5 mm. The specific surface area of the powders was measured by thermal desorption of nitrogen on a SORBTOMETER M instrument. The specific pore volume was also determined on a SORBTOMETER M instrument. Data on the specific surface and specific pore volume of the sorbent with different contents of iron oxohydroxide are given in table 1.

As can be seen from table 1, sample No. 3, which contains iron oxo-hydroxide in the following ratio of components, wt.%: Iron oxo-hydroxide from 59 to 69, vermiculite concrete from 31 to 41, has the largest specific surface area and specific pore volume. that with an increase in the amount of iron oxohydroxide in the sample, an increase in the specific surface and specific pore volume of the sorbent is observed.

Tests of the obtained sorbent samples for adsorption ability with respect to heavy metal ions were carried out as follows.

The study of the absorption of heavy metal ions was carried out on model solutions with various concentrations, which were prepared using state standard samples in distilled water. For this, a 200 mg sample of the sorbent is placed in 20 cm ^{3 of a} model solution located in a glass beaker with a volume of 100 cm ³ and mixed on a magnetic stirrer for 150 minutes. Then the solution on the funnel is filtered through a blue ribbon paper filter and the filtrate is analyzed by inversion voltammetry and photocolorimetric for the residual ion content of the metals being determined. Similarly, samples of the sorbent are tested for adsorption of heavy metal ions at values many times higher than the maximum permissible concentrations: Cd ²⁺ is 5 mg / dm ³ ; Cu ²⁺ is 5 mg / dm ³ ; Pb ²⁺ is 10 mg / dm ³ ; Zn ²⁺ is 5 mg / dm ³ ; Fe ³⁺ is 30 mg / dm ³ ; Mn ²⁺ is 6 mg / dm ³ . Sorption studies were carried out on three samples with a fractional composition from 1.5 to 2.5 mm. Data on the sorption ability of the inventive sorbent with different contents of iron hydroxide are shown in table 2.

As can be seen from table 2, with an increase in the content of iron oxohydroxide in the sorbent sample, there is an increase in the sorption ability of the material. The best sorption characteristics with respect to all elements except manganese ions Mn ²⁺ are possessed by sample No. 3 containing iron oxohydroxide in the following ratio of components, wt.%: Iron oxohydroxide from 59 to 69, vermiculite concrete from 31 to 41. According to manganese ions, Mn ²⁺ values for all samples are approximately the same.

Claims (3)

1. A method of producing a sorbent of heavy metals, comprising impregnating a porous carrier with an aqueous solution of iron compounds with stirring, followed by adding an alkali solution or concentrated ammonia, washing and drying the sorbent at a temperature of 120-150 ° C, characterized in that the carrier is ground to fraction size 0.25-8 mm vermiculite concrete, which contains (wt.%): vermiculite from 6 to 20, cement from 24 to 40, sand from 50 to 70, while vermiculite concrete is impregnated with an iron-containing solution agitating with an orbital shaker for at least 1 hour. 2. The method according to p. 1, characterized in that as an aqueous solution of iron compounds use a solution of ferric chloride of Fe _{III 3} · 6H ₂ O with a concentration of 70-130 g / DM ³ in a volume of 230 cm ³ . 3. A heavy metal sorbent obtained by the method described in paragraph 1, containing (wt.%): Iron oxohydroxide from 47 to 69; vermiculite concrete from 31 to 53.