RU2329948C1 - Method of oxidised coal preparation from phytogenic raw materials for treatment of sewage water from copper ions - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention is related to preparation of sorbents. Method of oxidised coal production from shells of cedar nuts consists in shell incineration at air at temperature of 290-300°C until carbon material is obtained. Prepared material is oxidised by nitric acid or hydrogen peroxide. Sorbent capacity by copper amounts to 0.25 mg-eq/g.

EFFECT: sorbent is affordable and may be used at the stage of sewage water re-treatment from copper ions.

3 cl, 4 tbl, 3 ex

Description

The invention relates to a technology for producing sorbents, specifically to methods for producing sorbents from waste plant materials, in particular, from the shell of pine nuts, which can be used to treat wastewater from heavy metals, in particular copper.

A known method of producing activated carbon from waste plant material // A method of preparing activated carbon from plant material. Pat. RF 2237013, authors: Timofeev B.C., Temkin O.N., Gafarov I.G. // The method includes pre-processing of raw materials in water tanks for up to 2 months, carbonization without air in the nitrogen stream at a temperature of 300-350 degrees for 2-3 hours and activation in the presence of water vapor with nitrogen at 750- 850 degrees. Coconut shells, sugarcane, birch, pine, fruit and berry seeds are used as plant materials. Such a sorbent is not selective with respect to heavy metal ions. The iron sorbent capacity was determined; it is 97-99 mmol / l.

There is also known a method for producing activated carbon from pine nutshells by selecting the operating parameters of carbonization and steam activation processes, which provide porous carbon materials of various structures from pineal shells [G.V. Plaksin, O. N. Baklanova, V. A. Drozdov , V.K. Duplyakin et al. Carbon sorbents from pine nutshell. // Chemistry for sustainable development. 2000. No8. S.715-721]. By carbonization of a cedar shell, porous carbon materials with a molecular sieve structure have been synthesized, which can be used to separate air into O ₂ and N ₂ . Dependencies are established that link the yield of porous carbon materials with the conditions for the activation of the carbonized shell of pine nuts. It is shown that the optimal composition of the activating agent from the point of view of yield and texture characteristics of carbon products is 25-80% water vapor and 0-2% oxygen. Obtained under these conditions, activated carbons from cedar shells have a developed system of micro- and mesopores. No sorption capacity data for heavy metal ions are available. The method requires high energy consumption, because the process of carbonization and steam activation is carried out at a temperature of 600-700 degrees.

Closest to the claimed is a method for producing oxidized coals, which are obtained by oxidizing the surface of carbonizates with various oxidizing agents, as a result of which they acquire the ability to sorb heavy metal ions. So in the work // Tarkovskaya I.A., Goba V.E. et al. Surface chemistry, sorption, ion and electron exchange properties of oxidized coals. - In the book: Carbon adsorbents and their use in industry. M .: Nauka, 1983, 2005–220 // It was shown that charcoal (non-activated wood carbonizates) can be oxidized to deposit oxygen-containing functional groups on the surface of the sorbent. The technology for producing carbon ion exchangers (TU 81-05-06-80) has been developed. For example, DOU-74 has a dynamic exchange capacity (DOE) for sorption of copper from a solution of sodium chloride - 1000 mg / g. As oxidizing agents, nitric acid, sodium hypochlorite, and hydrogen peroxide can be used. The shell of pine nuts was not used to produce oxidized coal. The studies were carried out using specially prepared series of sorbents based on phenol-formaldehyde resin, stone coal, and charcoal.

The disadvantage of this method is that to obtain charcoal (carbonizates) use high temperatures of 600-700 degrees, carbonization is carried out in an inert atmosphere. This leads to high cost of the method, which limits its use for processing large volumes of waste plant materials.

The objective of the invention is to develop a method for producing an oxidized sorbent from a pine nut shell for extracting heavy metals from wastewater, in particular copper ions, in a less energy-intensive way than producing oxidized coal from carbonizates.

A less energy-intensive and affordable method for processing large volumes of plant waste is the processing of plant waste in air at lower temperatures and the subsequent oxidation of the surface of the obtained carbonized material. Oxidized coals are multifunctional cation exchangers with a wide range of changes in acidic properties, have sorption activity with respect to heavy metals due to the fact that they contain carboxyl, lactone, phenolic groups on the surface. Carbonization of plant materials in the air eliminates the use of sophisticated equipment.

The specified technical result is achieved by the fact that in the method of producing oxidized coal from plant materials for wastewater treatment from copper ions, based on high-temperature processing of plant materials and subsequent oxidation with nitric acid or hydrogen peroxide, pine nutshells are used as plant materials, which are calcined on air at a temperature of 290-300 ° C to obtain a carbon material. Hydrogen peroxide oxidation is carried out chemically using a solution or electrochemically in an electrolytic bath at the time of the formation of hydrogen peroxide.

To obtain a sorbent in the form of oxidized coals and to select the optimal method of heat treatment and oxidation, the shells of pine nuts were processed as follows: the shells of pine nuts were calcined in a muffle furnace with air access in the temperature range 290-300 ° С. At this temperature, carbonization of the shell occurs. When annealing occurs at temperatures above 300 ° C, the shelling of the nuts already occurs, therefore, in the study, a sorbent was used; the sorbent obtained at 300 ° C was oxidized by chemical or electrochemical methods.

First, the calcined sorbent was oxidized with HNO ₃ solutions. The concentration of nitric acid was varied from 10% to concentrated. After oxidation, oxygen-containing functional groups (carboxyl, lactone, phenolic) were determined by titration with solutions of bases of different strengths (NaHCO ₃ , Na ₂ CO ₃ , NaOH). The results of the oxidation of the calcined sorbent are presented in table 1.

Table 1
The results of the oxidation of the sorbent with nitric acid concentrate HNO ₃ % oxidation time, h number of functional groups, mEq / g ΣN -COOH Lact. -IT original absorbent 0.40 0.14 0,070 0.19 one 0.41 0.12 0,090 0.20 four 0.43 0.14 0.12 0.17 24 0.46 0.16 0,080 0.22 thirty one 0.44 0.19 0,040 0.21 four 0.46 0.16 0,080 0.22 8 0.50 0.15 0,060 0.29 24 0.54 0.25 0,050 0.24 concentrated 56 one 0.42 0.31 0,040 0,07 four 0.47 0.32 0,030 0.12 8 0.54 0.34 0,060 0.14

On the initial sorbent obtained by calcination, the number of CPH was 0.40 mEq / g, -COOH - 0.14 mEq / g. The highest number of CPH was achieved by oxidation with concentrated nitric acid in 8 hours (the total number of groups after oxidation was 0.54 mEq / g, -COOH 0.34 mEq / g. Oxidation of HNO ₃ when heated increases the amount of CPH. So when heated to 80 ° C for 3-5 hours, the total number of groups increases to 0.64 mEq / g.

table 2
Oxidation of the sorbent HNO _{3 conc} at t = 80 ° C oxidation time, h number of functional groups, mEq / g ΣN -COOH Lact. -IT 0.3 0.53 0.45 0.010 0,07 one 0.60 0.40 0,040 0.16 3 0.62 0.50 0.10 0.02 5 0.64 0.52 0.10 0.02

Another way of applying oxygen-containing functional groups to the surface of a carbonized material is to oxidize with a solution of hydrogen peroxide a concentration of from 5% to 30%. During the oxidation of the calcined sorbent, the highest number of CPH (0.68 mEq / g) is achieved with the oxidation of 15% H ₂ O ₂ . A further increase in the concentration of hydrogen peroxide practically does not lead to an increase in the number of functional groups on the surface.

Table 3
The results of the oxidation of H ₂ O ₂ calcined sorbent H ₂ O ₂ ,% number of functional groups, mEq / g ΣN -COOH Lact. -IT ref. sorbent 0.40 0.14 0,07 0.19 5 0.50 0.15 0.17 0.18 10 0.54 0.25 0.12 0.17 fifteen 0.68 0.43 0.11 0.14 thirty 0.69 0.42 0.11 0.16

To increase the number of CPH on the surface of sorbents obtained by calcination at 300 ° С, electrochemical oxidation with hydrogen peroxide was carried out.

For the oxidation of carbon materials by the electrochemical method, the conditions for producing hydrogen peroxide in industry were taken.

Electrolyte H ₂ SO ₄ , 5 m; V electrolyte 95 ml; m sorbent 2.0 g; i _a = 14 mA / cm ² .

Electrodes: anode - platinum mesh, cathode - Pb.

Electrolysis was carried out in an electrochemical cell without a diaphragm.

Oxidation of sorbents is carried out at different contact times of the oxidizing agent and carbon materials. After electrochemical oxidation, the sorbent is separated from the oxidizing agent and washed with distilled water until the washings are neutral. Next, the sorbent is dried in an oven at 105 ° C to constant weight. Then, oxygen-containing functional groups are determined by neutralization using solutions of bases of different strengths (NaHCO ₃ , Na ₂ CO ₃ , NaOH).

The results of the electrochemical oxidation of hydrogen peroxide by a calcined sorbent are shown in table 4.

Table 4
Electrochemical oxidation of the sorbent by hydrogen peroxide e / x oxidation time t, min number of functional groups, mEq / g ΣN -COOH Lact. -IT ref. sorbent 0.40 0.14 0,07 0.19 twenty 0.80 0.50 0.15 0.15 40 0.78 0.48 0.14 0.16 60 0.75 0.44 0.16 0.15 120 0.75 0.40 0.19 0.16

On a calcined sorbent, the largest number of oxygen-containing functional groups forms within 20 minutes and amounts to 0.80 mEq / g, carboxyl groups - 0.50 mEq / g, lactone groups - 0.15 mEq / g, phenolic groups 0.15 mEq / g.

We determined the characteristics of the oxidized sorbent: ash - 1.7%, total porosity - 0.39 cm ³ / g, specific surface area according to BET - 70 m ² / g, sorption capacity for copper ions - 0.25 mEq / g . Thus, from the studies conducted by the authors, a method was found for producing a sorbent from the shell of pine nuts with oxygen-containing functional groups on the surface, which ensure the sorption of heavy metals on the surface, including copper ions.

Obtaining a sorbent can be demonstrated by examples.

Example 1. The shell of a pine nut weighing 2 g is ground to 0.14 mm, calcined in a muffle furnace at a temperature of 300 ° C for 30 minutes. Then the sorbent is poured with concentrated nitric acid and kept at a temperature of 80 ° C for 5 hours, the sorbent is separated and washed with distilled water until neutral. The number of carboxyl functional groups on the surface of the sorbent is determined - 0.52 mEq / g. Place 1.0 g of sorbent in 20 ml of a solution of copper chloride with a copper content of 0.8 mg / l, incubated for 6 hours. The sorbent capacity for copper ions was 0.26 mEq / g.

Example 2. The shell of a pine nut weighing 2 g is ground to 0.14 mm, calcined in a muffle furnace at a temperature of 300 ° C for 30 minutes. Then the sorbent is poured with a 30% hydrogen peroxide solution, kept for 6 hours, the sorbent is separated from the solution, washed with distilled water, the number of carboxyl groups on the surface of the sorbent is determined - 0.42 mEq / g. Place 1.0 g of sorbent in 20 ml of a solution of copper chloride with a copper content of 0.8 mg / l, incubated for 6 hours. The sorbent capacity for copper ions was 0.25 mEq / g.

Example 3. Prepare a sorbent, as in examples 1, 2. A portion of coal with a particle size of ≤0.14 mm is placed in the electrolysis. During electrolysis, the suspension was maintained in suspension with constant mechanical stirring. Sorbent oxidation conditions: electrolyte H ₂ SO ₄ , 5 m; V electrolyte 95 ml; m sorbent 2.0 g;

i _a = 14 mA / cm ² , electrodes: anode - platinum mesh, cathode - Pb. The oxidation time is 20 minutes. Then the sorbent is separated from the electrolyte, washed with distilled water, the number of carboxyl groups on the surface of the sorbent is determined - 0.50 mEq / g.

The sorbent is placed in the wastewater of the Radio Plant "Relero" OJSC in Omsk after treatment facilities. The effluents were cleaned at the plant by the neutralization method. In wastewater, the concentration of copper ions was 0.041 mg / L (MPC - 0.003 mg / L). That is, the MPC value is exceeded by about an order of magnitude. The ratio of oxidized sorbent to the volume of wastewater was 1:20. Sorption was carried out with stirring for 6 hours. After the wastewater treatment from copper ions, the copper concentration decreased to 0.20 mg / l, i.e. 2 times. After repeated purification by a new batch of sorbent, the copper content in purified water was 0.002 mg / L. That is, the sorbent extracts copper ions at the stage of post-treatment to MPC for 2 stages.

Thus, the studies showed that an oxidized sorbent can be obtained from pine nutshells to extract heavy metals from wastewater after treatment plants, in particular copper ions, while providing a sufficiently good sorption capacity of 8 mg / g (0.25-0.26 mEq / g). In addition, using sorbent of vegetable origin — pine nutshells, which annually produces about 6 million tons per year in Siberia and which accounts for 51-59% of the weight of the nut itself — can simultaneously solve the problem of shell disposal and prevent environmental pollution by waste. processing plant materials.

Claims (3)

1. A method of producing oxidized coal from plant materials for the treatment of wastewater from copper ions, based on high-temperature processing of plant materials and subsequent oxidation with nitric acid or hydrogen peroxide, characterized in that cedar shells are used as plant materials, and the temperature treatment is carried out by calcination in air at a temperature of 290-300 ° C for 30 minutes 2. The method according to claim 1, characterized in that the oxidation with hydrogen peroxide is carried out chemically using a 15% solution or electrochemically in an electrochemical cell with an anode - a platinum grid, an electrolyte with a 5 M solution of sulfuric acid, at a current density of 14 ± 1 mA / cm ² for 20 minutes 3. The method according to claim 1, characterized in that the calcined pine nutshell is treated with concentrated nitric acid for 3 hours at a temperature of 75-85 ° C.