Resume Abstract

Abstract

Content

Introduction

In the conditions of active urban processes in industrial cities, the level of pollution of natural water with technogenic pollutants is especially increasing. A huge number of pollutants enter the reservoirs with wastewater enterprises of ferrous and nonferrous metallurgy, chemical, petrochemical, gas, coal industry, agriculture enterprises and public utilities, as well as surface runoff from adjacent areas.

The most dangerous pollutants of the aquatic environment are organic substances: phenols, formaldehyde, aromatic hydrocarbons, oils, resins, petroleum products, and heavy metal compounds: copper, zinc, chromium.

A lot of technogenic organic pollutants have a toxic effect on aquatic organisms. Insoluble hydrocarbons form a film on the water surface, which prevents the dissolution of atmospheric oxygen in water. Heavy metals have cumulative and additive properties and cause mutagenic and carcinogenic processes in organisms.

1 Theme urgency

The existing methods of purification of industrial wastewater do not reach a satisfactory level of water quality at minimal cost. Therefore, the actual task is to improve such processes.

Application of adsorption technologies for the removal of pollutants is of particular importance.

Search and investigation of sorbents that based on available materials with low cost is of considerable interest. Thermally expanded graphite (TEG), obtained from natural graphite, can be used as such material.

Thermally expanded graphite is a promising sorbent material. Its advantage over other sorbents is large porosity, large specific surface area and low cost.

2 Goal and tasks of the research

The purpose of the study is to develop a method for obtaining a sorbent from natural graphite for the purification of wastewater from organic pollutants and heavy metals.

Objectives of the study:

• development of a method for processing graphite to produce thermally expandable graphite compounds;
• examination of the structure and physicochemical properties of the obtainedcompounds;
• investigation of the sorption properties of the sorbent based on thermally expanded graphite.

The object of the study is natural graphite and a sorbent obtained as a result of its processing.

The subject of the study are the structural features, physicochemical properties of graphite intercalation compounds (GIC) and thermally expanded graphite obtained on the basis of synthesized GIC.

The work is expected to produce the following results:

• determination of the optimal way of processing graphite to produce a sorbent based on it;
• investigation of the sorption capacity of the resulting thermally expanded graphite in relation to aquatic environmental pollutants;
• development of a method of using the developed sorbent in technological processes of water purification.

3 Development of sorbent based on expanded graphite

The graphite used was a purified natural graphite GT-1 from Zavalie Graphite Works, Ukraine. Nitric acid (98 wt%) was chosen as the main intercalant. To improve the stability of graphite nitrate, it was modified (co-intercalated) with organic compounds: 1,4-dioxane, ethyl formate, acetic acid, ethyl acetate, dimethylacetamide or a mixture of substances in a ratio of 1 : 1 by volume. These substances showed a good ability to stabilize graphite nitrate [19]. Graphite nitrate cointercalation compounds were synthesized in the thermostatic reactor at 20 °C. Nitric acid was added to the sample of natural graphite. The mixture was stirred for 10 min. Cointercalant (an organic compound or two compounds in equal amounts) was then added, and the mixture was stirred again for 10 min. Nitric acid and cointercalants were used at 0.6 and 6 cm3 per 1 g of graphite, respectively. Then product was separated by filtration and dried at 20 °C until the sample mass became constant. Sheme of production of TEG is present on Fig. 1

Figure 1 – TEG production scheme

The thermal expansion coefficients (K_v) of graphite nitrate and its cointercalation compounds were determined by the thermal shock mode of heating. A stainless cuvette was placed into a muffle furnace preheated up to 900 °C. About 0.2 – 0.25 g of the product was inserted into the heated cuvette and kept in the furnace for 120 s. Then the cuvette with expanded graphite was removed from the furnace, the contents were gently transferred to a graduated cylinder and obtained graphite foam volume was measured.

The thermal expansion coefficient for all samples was determined from the equation:



where K_v – the thermal expansion coefficient, cm³/g;

V – the graphite foam volume, cm³;

m – the initial mass of the sample before heating, g.

The obtained values of K_v for the test samples shown in Table 1.

Table 1 - The thermal expansion coefficients of test compounds

Intercalants			Kv, cm3/g
1	2	3
HNO3	-	-	249
HNO3	Acetic acid	-	354
HNO3	1,4-dioxane	-	260
HNO3	Ethyl acetate	-	273
HNO3	Dimethylacetamide	-	125
HNO3	Ethyl formate	-	318
HNO3	Ethyl formate	Acetic acid	378
HNO3	Ethyl formate	1,4-dioxane	357
HNO3	Ethyl formate	Ethyl acetate	340
HNO3	Ethyl formate	Dimethylacetamide	242

On the basis of the obtained values of the expansion coefficient, the method for treating graphite nitrate with ethyl formate and acetic acid, which makes it possible to achieve the greatest expansion volume of graphite crystals (378 cm³/g) was chosen.

The microstructure of the expanded graphite was investigated with scanning electron microscopy (SEM). SEM image of the expanded graphite is present on Fig. 2



Figure 2 - SEM images of initial graphite (a), graphite nitrate cointercalated with acetic acid and ethyl formate (б), and of expanded graphite (в)

The sorption capacity of the expanded graphite to benzene, engine oil and heavy oil was determined. Our results along with those for expanded graphite from the bisulfate graphite modified with H₂O₂ [20] are listed in Table 2.

Table 2 - The sorption capacity of the expanded graphite

Pollutant	Sorption capacity, g per 1 g of the expanded graphite
	expanded graphite from the bisulfate graphite modified with H2O2	expanded graphite from the nitrate graphite modified with ethyl formate and acetic acid
Heavy oil	55	62
Engine oil	50	43
Benzene	35	71

Thus, there is an increase in the sorption capacity of the investigated TEG relatively to heavy oil and benzene, in comparison with the TEG that is traditionally used for water purification. From the data obtained it can be concluded that it is expedient to use the developed sorbent for purification of industrial wastewater and reservoirs in case of emergency hydrocarbon spills.

Conclusions

It can be concluded that the studies on improving the methods of sorption water purification are relevant. Thermally expanded graphite is an easily accessible material with a high sorption capacity and the ability to regenerate. The listed characteristics make relevant further studies on the use of TRH as a sorbent.

This master's work is not completed yet. Final completion: July 2018. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

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