RU2125914C1 - Method of cleaning solid materials from contaminated substances - Google Patents

Abstract

FIELD: chemical methods of cleaning the solid materials; may be used in cleaning of soils from contaminating substances, mainly, from oil products. SUBSTANCE: method includes crushing of solid materials, mixing of ground material with solution of reagents, stirring of mixture, settling and separation of mixture into liquid and solid fractions. Reagent is used in the form of aqueous solution of water glass with concentration of 0.5-2.0 vol.% and solid material-reagent solution volumetric ratio of 1:(1-3). Then mixture is stirred for 5-15 min, settled for 5-15 min and solid fraction is washed after separation 3-5 times by water. The merits of the method cover cleaning without water heating, use of water glass - inorganic substance, ecologically safe, fire- and explosion-proof and featuring higher cleaning efficiency as compared with other alkali reagents and associated with the presence in its composition of silicate anions which are hydrolyzed in aqueous solutions and capable of sorption of contaminating matter. EFFECT: higher efficiency. 5 tbl

Description

 The present invention relates to chemical technology, and in particular to methods for cleaning solid materials, such as soils, from harmful substances, mainly from petroleum products.

 Soil pollution by products of human production is a major environmental problem. An example of a negative impact on the environment is the penetration of various substances into the soil, including oil products, in the territories of locomotive-car repair plants, depots, oil refineries, in enterprises manufacturing greases, warehouses for fuel and lubricants, etc. The presence of a huge amount of contaminated soils necessitates the use of various methods for the removal of harmful substances.

 The known "Method, installation and emulsifying substance for the separation of materials containing harmful substances" (see the list of sources of information used for the examination, at the end of the description, I).

 According to the known method, for microdispersed emulsification of harmful substances, the contaminated material is mixed with at least one emulsifying substance, if necessary with water, and then the emulsion with the addition of water is separated from the material. As an emulsifier, a substance is used containing at least one nonionic and / or anionic tenside, especially a fatty alcohol polyglycol ether and / or a salt, for example, an alkali metal salt of one of such sulfates.

 In this method, mixtures are used to clean the soil from contamination, the components of which are organic compounds, very complex in composition and unsafe in the environmental aspect. The description says that finely dispersed emulsified particles are well perceived by microorganisms and thereby become harmless. However, there is no data on the residual content of emulsifying agent components in the purified material, and their complete absence seems doubtful. The described technology is carried out when heated, which increases the cost of cleaning.

 Also known is the "Improved method of removing harmful substances from the soil" (II), mainly oil and its derivatives, using aqueous extractants.

According to this method, an extractant containing sodium pyrophosphate or sodium oxalate with a concentration of 0.1-1.0% is used to extract harmful impurities. Contaminated soil is isolated with watertight partitions, and the extractant is piped into the soil. The volume of extractant 50-100 l / m ² soil per day. Then carry out the removal of the extractant by pumping. In another embodiment, the extractant is applied to the surface of the soil by spraying. Over time, the extractant seeps into the lower layers of the isolated area, and then is pumped out as an extract. The choice of method depends on the type of harmful substance being removed.

 This method of removing harmful substances from the soil requires equipment for pumping and pumping mortar, pipes, partitions to isolate the contaminated area, etc. All this significantly increases the cost of cleaning. In addition, the consumption of extractant for tillage is very high. In the description of the patent, as an example, the results of processing the soil with a low degree of pollution - 1 g / kg of soil (0.1%) are presented, so the question arises about the insufficient effectiveness of this method with a large initial soil contamination.

 The closest to the claimed object in technical essence is, in our opinion, the "Method of removing contaminants from solid materials" [III], according to which the material to be purified is crushed to a particle size of less than 15 cm and mixed with a cleaning agent containing alkali or alkaline earth metal hydroxide alcohol and a liquid sulfoxide catalyst. After stirring, the dirty light fraction is separated by sedimentation or centrifugation from the less soiled fraction at the bottom. The bottom fraction is cleaned to the desired level by washing.

 This contaminant removal method is effective only for the purification of halogenated organic pollutants, such as polychlorobiphenyl. Petroleum products are non-halogenated pollutants and are poorly removed from the soil by this method, which we tested in practice. According to our data, the degree of soil purification from oil products by this method is not more than 42% with an initial soil contamination with oil products of 10.63% (see table 5).

 The patent specification does not contain information on the residual content of the components of the reaction mixture (alkali metal hydroxide, sulfoxide, organic alcohol) in the purified material, although at least the last two of them are environmentally unsafe.

 The aim of the invention is to increase the degree of purification of solid materials using cheap and non-toxic reagents.

 To achieve this goal, in a method for purifying solid materials from pollutants, mainly oil products, including crushing the material, mixing the crushed material with a reagent solution, mixing the mixture and separating fractions, according to the invention, an aqueous solution of liquid glass with a concentration of 0.5 - 2 is used as a reagent, 0 volume percent with a volume ratio of solid material and a reagent solution of 1: (1-3). Then the mixture is stirred for 5-15 minutes, defended for 5-15 minutes and after separation of the solid fraction, it is washed with water 3-4 times.

Liquid glass is an aqueous solution of alkali metal silicates of the general formula A ₂ O • mSiO ₂ , where A = Na, K or Li; m - siliceous module (from 1.5 to 3.5 for sodium liquid glass and up to 4.0-4.5 for potassium). This is a thick yellow or gray liquid with a density of 1.36-1.50 g / cm ³ . Due to the alkaline nature of liquid glass, oil and oil pollution are saponified, emulsified and transferred from the surface of the material particles to the volume of the aqueous phase. We found that the highest degree of purification from petroleum products is achieved when using a reagent with a liquid glass content of 0.5-2.0 volume percent, and the optimal content of liquid glass is 1.0 volume percent. At this concentration, the efficiency of removing contaminants from the soil is maximum and reaches 97%.

 A big advantage of the proposed method is the ability to clean without heating the water, which gives a certain economic benefit, although in principle the treatment of contaminated material can be carried out at elevated water temperatures.

 Liquid glass is an inorganic substance, environmentally friendly, fire and explosion safe and relatively cheap. Its more effective cleaning action compared to other alkaline reagents is associated with the presence of silicate anions in the composition, which are hydrolyzed in aqueous solutions and are capable of absorbing impurities.

 The method is as follows.

 A solid material contaminated with oil products, for example, soil, is crushed into pieces no larger than 15 cm, then placed in a reactor and poured with an aqueous solution of liquid glass with a concentration of 0.5-2.0 volume percent (see Table 1). The ratio of volumes of soil-solution is 1: (1-3) (see table. 2). Then the mixture is stirred for such a time that is necessary to remove pollutants from the surface of the particles, namely, for 5-15 minutes. With a mixing time of less than 5 minutes, the degree of purification is insufficient, and a time of more than 15 minutes does not increase the efficiency of cleaning (see table 3). After this, the solution settles for 5-15 minutes in the same mixing device (see table 3). The sedimentation is necessary for the separation of phases: solid, aqueous with dissolved pollutants and organic in the form of oil products that float to the surface. After settling, the aqueous and organic phases are separated from the solid. An aqueous solution with oil and oil products is sent for purification, water is supplied to the mixing device for washing solid material from residues of pollutants and reagent in an amount of 1 to 5 volumes per 1 volume of material. The number of washes depends on the degree of contamination of the material. Washing is carried out 3-4 times, as a result of which soil is obtained, purified from oil products.

Examples of the method
Example 1

 Samples of soil contaminated with oil products were crushed to obtain fractions with piece sizes of not more than 15 cm. Next, these samples were poured with aqueous solutions of water glass with a concentration of 0.1%, 0.5%, 0.8%, 1.0%, 1, 5%, 2.0%, 2.3%, 2.5% by volume with a soil-solution volume ratio of 1: 1. Then the mixture was stirred for 10 minutes at a rotational speed of the mixing device shaft of 10 r / sec, defended for 10 minutes, after which the liquid fraction was drained for subsequent processing, and the solid was washed 3 times with water, each time with a new portion.

 The cleaning results are presented in table. 1.

 Example 2

 Soil samples were treated according to the method described in example 1, with a liquid glass solution, with a concentration of 1% by volume, and the treatment was carried out at volumetric soil-solution ratios: 1: 0.5; eleven; 1: 1.5; 12; 13; fourteen.

 The cleaning results are presented in table. 2.

 Example 3

 Soil samples with a petroleum product content of 7.95% by weight were treated according to the method described in Examples 1-2 with a liquid glass solution with a concentration of 1% by volume at a soil-solution ratio of 1: 1 (by volume), the mixture being mixed for 1, 5, 7, 10, 15, 25 minutes and subsequent sedimentation for 3, 5, 7, 10, 15, 25 minutes.

 The cleaning results are presented in table.3.

 Example 4

 Soil samples were processed according to the method described in examples 1-3, except that after separation of the solid fraction it was washed with water, followed by determination of the oil content and the degree of soil purification.

 The research results are presented in table. 4.

 According to the research results presented in table. 1-4, we can conclude that for the cleaning of soils from oil products, the most suitable is the method of treating the soil with an aqueous solution of liquid glass at concentrations of 0.5 - 2.0 volume percent with a volume ratio of solid material and solution of 1: (1-3). The optimal values for the concentration of liquid glass is its content - 1% by volume, and for the volume ratio of solid material and solution - 1: 1.

 Mixing and settling of the mixture should be carried out for 5-15 minutes, and the best time is 10 minutes for both processes. After separation of the solid fraction, to ensure the most effective cleaning, the soil should be washed with water 3-4 times.

 We conducted studies to compare the degree of soil purification after treatment with water and various reagents, including the method described in the description of US patent N 5228921 (prototype).

 The research results are presented in table. 5.

According to the table. 5, a comparison of different cleaning methods shows the greatest effectiveness of our proposed method, because the degree of soil cleaning by this method is at least 95%. This technology allows you to conduct the process in a wide temperature range of aqueous solutions from +5 ^o C to + 80 ^o C.

 Known chemical agents previously used are typically artificially synthesized complex organic compounds such as alkylbenzenesulfonates, alkyl sulfates, alkyl ethoxysulfates, ethoxylated alcohols, ethoxylated alkyl phenols, and the like. Their use during cleaning leads to the fact that a certain amount of these compounds gets into the purified material. Their biodegradability is difficult, and it takes a long time for complete decomposition. On the contrary, trace amounts of water glass remaining after cleaning the soil do not harm the environment due to the wide distribution in nature of the components that make up water glass (sodium cations and silicate anions). The proposed method makes it possible to remove contaminants relatively inexpensively due to the lower cost of water glass in comparison with synthetic organic compounds.

Sources of information used in the preliminary examination:
I. German application N 3815309; A1 "M cl. A 62 D 3/00, B 09 B 3/00, C 02 F 3/34, C 02 F 3/12 II B 01 D 17/025, B 01 F 17/00, 17/42 , 17/04 "published on November 17, 88

II. German patent N 3738264 C1 M. cl ⁴ A 62 D 3/00, B 01 D 1/02, published March 30, 89.

III. U.S. Patent No. 5,228,921 M.cl ⁴ B 08 B 3/08; B 08 B 7/00 published July 20, 1993 (prototype)

Claims (1)

 The method of purification of solid materials from pollutants, mainly oil products, including crushing the material, mixing the crushed material with a reagent solution, mixing the mixture and separating fractions, characterized in that an aqueous solution of liquid glass with a concentration of 0.5-2.0 vol. % when the volume ratio of the solid material and the reagent solution is 1: 1–3, then the mixture is stirred for 5–15 minutes, sedimented for 5–15 minutes, and after separation of the solid fraction, it is washed with water 3-4 times.

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