RU2558896C1 - Method of producing sorbent for removing heavy metals from waste water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing a sorbent for cleaning waste water includes reacting elementary sulphur and sodium hydroxide in an aqueous solution in the presence of hydrazine hydrate. Further, chlorinated lignin and organochloride wastes from production of epichlorohydrin are fed for reaction, followed by polycondensation at 40-45°C.

EFFECT: obtained sorbent demonstrates nickel, zinc, cadmium, lead, mercury, copper and cobalt sorption of 330-450 mg/g.

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Description

The invention relates to the field of industrial ecology and specifically relates to a method for producing a sorbent for the extraction of heavy metals from wastewater generated at the enterprises of the chemical, metallurgical, engineering, electrical and other industries and containing zinc, cadmium, mercury, copper, lead compounds, nickel, cobalt and other toxic metals. Due to the fact that modern production is characterized by high metal consumption, these metals and many of their compounds are produced and used in large quantities. However, their production and use is associated with the formation of wastewater that contains heavy metals in dissolved form; therefore, wastewater treatment from heavy metals is an important environmental engineering problem [1, 2]. Heavy metals have a negative impact on the environment and are highly toxic to humans [3]. A particularly large amount of metal-containing wastewater is formed during electroplating, in hydrometallurgical processes, and in the production of chemical current sources, catalysts, pigments, and other practically important products.

There are several approaches for the extraction of heavy metals from wastewater [1]: reagent treatment, electrochemical methods, extraction, etc., most of which are applicable only to wastewater with a high concentration of toxic metal, while they do not provide the desired cleaning efficiency, leading to additional “salinization” of effluents due to the introduction of reagents, coagulants, flocculants or extractants. The most acceptable method for the removal of small, but much higher than the permissible concentrations of heavy metals is adsorption cleaning [1, 2, 4]. Using adsorption, the cleaning process can be easily automated; it is insensitive to changes in wastewater flow rate or a change in metal concentration.

Activated carbon, ion-exchange resins, zeolites, clays, and many other materials are used as adsorbents [1, 4]. However, many of them do not have sufficient sorption efficiency, have a high cost, low strength, tendency to caking, are difficult to dispose of after use and have other disadvantages. Therefore, an important task of promoting adsorption technologies in production is the creation of highly effective cheap sorbents convenient in technological applications.

Reducing the cost of synthetic sorbents can be achieved by using waste from other industries as raw materials. Considering the high affinity of heavy metal ions to sulfur atoms of organic molecules [5] (the formation of stable complexes), it is promising to create sorbents that contain sulfide or polysulfide groups in their composition. However, most of the available polymers of this type have the properties of rubbers (thiocols) and cannot be used as sorbents [6]. A known method of obtaining a solid powder product is polyethylene monosulfide [7], which is capable of adsorbing silver and mercury ions. However, the finely dispersed composition of the resulting sorbent makes it difficult to use it for wastewater treatment (ease of entrainment with the flow of water, high hydraulic resistance, caking, etc.).

There is a method of producing granular sulfur-containing sorbents that are formed during polycondensation of sodium polysulfide with organochlorine wastes of epichlorohydrin production containing 76.6% of 1,2,3-trichloropropane in the presence of ash and slag material (waste from TPP operation) [8]. Obtaining a sorbent is based on the use of organochlorine waste, the disposal of which is also an important task of industrial ecology [9]. The maximum sorption capacity of the obtained sorbent for zinc is 57 mg / g. However, the presence of ash and slag material in the sorbent may complicate its application in practice, since ash and slag always themselves contain toxic metals, which with prolonged contact of the sorbent with waste water can pass into the solution.

A known method of producing a sulfur-containing sorbent for wastewater treatment from heavy metals, based on the interaction of sodium polysulfide obtained in the reaction of elemental sulfur, sodium hydroxide and hydrazine hydrate, with trichloropropane fraction of waste products of the production of epichlorohydrin in the presence of oil coke particles acting as polycondensation centers [10] ( prototype). However, in this method, the polycondensation centers are associated with the polymer formed only by adsorption forces, which leads to the irrational use of petroleum coke, a small excess of which can lead to the formation of an inhomogeneous sorbent with lower technological parameters. In addition, this sorbent has low activity with respect to certain metals.

An important waste of the chemical industry is the natural network polymer lignin, which currently finds limited use as a filler for polymer materials, additives to solid fuels, raw materials for the production of activated carbon and some chemical products [11].

Using a lignin, a sulfur-containing sorbent was obtained by polycondensation of 1,2,3-trichloropropane with sodium polysulfide while thiourea (4-50%) and lignin (10-20%) were added to the reaction mixture at a temperature of 60 ° C [12]. The resulting sorbent effectively extracts gold, palladium, platinum and mercury from aqueous solutions at low concentrations of these metals. The disadvantages of this method of obtaining the sorbent are: the use of thiourea, an expensive and toxic reagent, the presence of lignin only in the form of a component of the mechanical mixture, because it does not contain reaction centers capable of interacting with thiourea, sodium polysulfides or trichloropropane.

The present invention provides a method for producing a sulfur-containing sorbent for wastewater treatment from heavy metal compounds based on the use of wastes from the production of epichlorohydrin, chlorinated lignin, easily obtained from lignin [13], and sodium polysulfides, which are also obtained from elemental sulfur and sodium hydroxide in aqueous solution in the presence of hydrazine hydrate.

An essential distinguishing feature of the proposed method is that the solid particles of chlorinated lignin, acting as polycondensation centers, are simultaneously a comonomer in the formation of a sulfur-containing polymer, which ensures the production of a product in the spatial macromolecule of which lignin fragments bound by a covalent chemical bond are included. The use of waste wood chemistry - lignin, is an important advantage of the proposed method.

Obtaining a sorbent includes the following stages, which are carried out in a single reaction vessel without isolation of intermediate products:

1. Obtaining sodium polysulfide

This process is similar to the preparation of sodium polysulfide in the prototype method and is carried out at a molar ratio of NaOH: S = 2: 2-3 and a molar ratio of NaOH: N ₂ H ₄ · H ₂ O = 1: 4.

2. Obtaining a sorbent

In the course of polycondensation, a brown polymer network with a particle size of 1-2 mm is formed.

We used a product containing 5.7% chlorine as chlorinated lignin. The yield of the resulting sorbent and its characteristics depend on the value of n in the sodium polysulfide used (NaOH: S ratio). The highest yield of sorbent with high efficiency in respect to the absorption of metals is observed when using the ratio of NaOH: S = 2: 2-3 (obtaining Na ₂ S _n with a value of n = 2-3). A decrease in this ratio, i.e., obtaining sodium polysulfide n> 3, results in a heterogeneous product, a decrease in the yield of the product, and an increase in the amount of residual chlorine in it. An increase in the ratio of NaOH: S to 2: 1.5 (obtaining a mixture of Na ₂ S ₂ and Na ₂ S) also leads to a decrease in the yield of the target product and to a significant increase in the content of residual chlorine.

An important factor affecting the yield and quality of the resulting sorbent is the ratio of monomers used for polycondensation (chloro lignin and trichloropropane fraction of organochlorine wastes from epichlorohydrin production). The most optimal ratio of chloro lignin: organochlorine waste is 5-4: 4 (by weight). An increase in the proportion of chloro lignin in the monomer mixture used is greater than 5: 4 leads to a decrease in the sulfur content in the resulting product, which is heterogeneous in composition. A decrease in the fraction of chloro lignin leads to a significant decrease in the yield of the product, which is also heterogeneous in composition, and to an increase in the content of residual chlorine. The polycondensation process is most appropriate to conduct at a temperature of 40-45 ° C. A decrease in temperature leads to the need to increase the duration of the process and to increase the residual chlorine content in the product. An increase in temperature above 40-45 ° C leads to a product of a heterogeneous composition. It is possible that in this case polycondensation processes with the participation of components of organochlorine waste proceed more rapidly, and the resulting polymer is released as a separate phase.

The developed method is illustrated by the following examples:

Example 1. In a solution containing 6.24 g (0.0156 mol) of NaOH, 60 ml of H ₂ O and 8 ml of hydrazine hydrate, 5.0 g (0.0156 mol) of powdered sulfur are sprinkled in portions at a temperature of 45 ° C (preparation Na ₂ S ₂ ). The mixture is stirred at this temperature for 3 hours, then 10 g of chloro lignin are sprinkled on and 8.0 g of a waste fraction of epichlorohydrin production are added dropwise (composition, mass%: 1,2,3-trichloropropane 86.2%, epichlorohydrin 6.5%, dichloropropanol 6, 4%, the rest is 0.9%). The reaction mass is stirred for 6 hours at a temperature of 45 ° C, cooled to room temperature and a dark brown precipitate is filtered off. The precipitate is washed with water and dried, yield 20.0 g. Sulfur content - 26%, residual chlorine - 4.8%.

The sorption activity of the obtained product was investigated by shaking for three hours 0.5 g of sorbent with 50 ml of a model solution of salts of nickel, zinc, cadmium, mercury, lead, cobalt and copper (C _O = 5.0 g / l) at room temperature. The residual concentration of metal ions in solutions is determined photometrically. Sorbent activity was calculated by the formula:

C _O and C _K - the initial and final concentration of the metal in the solution;

V is the volume of the solution (50 ml);

m is a sample of the used sorbent.

For the sorbent synthesized in example 1, the following data on the sorption value were obtained:

Example 2. Under the conditions of example 1, but when 7.5 g (0.234 mol) of powdered sulfur was added to a water-alkaline solution of hydrazine (production of Na ₂ S ₃ ), at the end of the process, 19.3 g of sorbent (sulfur content of 39%, residual chlorine 3.6%). Sorption data:

Example 3. Under the conditions of example 1, but when hydrazine 10.0 g (0.312 mol) of powdered sulfur was added to an aqueous alkaline solution (preparation of Na ₂ S ₄ ), 18 g of a product with a sulfur content of 65%, residual chlorine 7 was obtained upon completion of the process , 2%. The product is a dark brown powder with flat, rounded granules of greenish color.

Example 4. Under the conditions of example 1, but upon dissolution of 3.75 g (0.117 mol) of powdered sulfur (obtaining a mixture of Na ₂ S and Na ₂ S ₂ ), at the end of the process, 16.6 g of product with a sulfur content of 18%, residual chlorine 13.5%.

Example 5. Under the conditions of example 1, but when 12.0 g of chloro lignin was added to the polysulfide solution, at the end of the process, 21 g of product was obtained with a sulfur content of 19% and a residual chlorine of 4.6%.

Example 6. Under the conditions of example 5, but when 8.0 g of chloro lignin was added to the polysulfide solution, 18.2 g of product was obtained with a sulfur content of 29% and a residual chlorine of 4.8% at the end of the process.

Example 7. Under the conditions of example 5, but when 6.0 g of chloro lignin was added to the polysulfide solution, at the end of the process, 14.2 g of product was obtained, which was heterogeneous in composition with an average sulfur content of 28%, residual chlorine of 5.6%.

Example 8. Under the conditions of example 1, but with the addition of chloro lignin and organochlorine waste at a temperature of 25 ° C, stirring was continued for 12 hours (while the solution remained colored), and 16.6 g of a product were obtained with a sulfur content of 23% and a residual chlorine of 9.7% .

Example 9. Under the conditions of example 1, but with the addition of chloro lignin and organochlorine waste at a temperature of 60 ° C after 6 hours of stirring, 22 g of product was obtained that was heterogeneous in composition, the average sulfur content was 24.6%, and the residual chlorine was 5.3%.

Thus, a method for producing a sorbent for wastewater treatment from heavy metal compounds is proposed, which is based on the use of elemental sulfur (waste from the petrochemical and gas industries), alkali, lignin - waste from chemical chemistry and organochlorine waste from the production of epichlorohydrin. The sorbent has high efficiency for the extraction of ions of nickel, zinc, cadmium, mercury, cobalt, copper and lead from aqueous solutions.

References

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Claims (1)

A method of producing a sorbent for wastewater treatment from heavy metal compounds, based on the use of sodium polysulfide obtained from elemental sulfur and alkali in an aqueous solution of hydrazine, which is introduced into interaction with organochlorine wastes of epichlorohydrin production, characterized in that the alkali and sulfur are taken in a molar ratio 2: 2-3, and additionally, chloralignin is introduced into the reaction as a comonomer in a mass ratio of chloro lignin: organochlorine waste 5-4: 4, and the process is carried out at a temperature of 40-45 ° C.