Химия и химические технологии/6. Органическая химия

d.t.n. Anarbayev A.A., c.t.n. Kabylbekova B.N., Seitmagzimova G.M., c.t.n. Assibekova A.D.

International Kazakh-Turkish University named after H.A. Yassaui

ECOLOGICAL PROBLEMS OF SODA ASH PRODUCTION

Nowadays much attention is devoted to environmental protection and production technogenic waste processing. The research of methods of waste liquid processing in soda ash production is one of the methods of ecological problem solving. The waste liquid represents a suspension of non-soluble impurities and it contains (g/l): СаСІ₂ - 85-95; NaCІ - 45-50; CaCO₃ - 5-6; CaSO₄ - 3-5; Mg(OH)₂ - 3-10; СаО - 3-4; (Fe₂O₃ + AІ₂O₃) - l-3; SіO₂ - 1-4.

To bury this liquid is pumped into sludge collectors, which during long-term preservation undergo significant changes under influence of natural factors and occupy significant ground areas. They are sources of intensive pollution of underground and surface water with sodium and calcium chlorides and damage the environment. It should be solved problems of waste reduction in soda ash production by Solvay method in two directions: the technology improvement by using all components of raw materials and processing preaccumulated waste ("white seas ") /1/. There are such methods as regeneration of waste liquid by means of MgO with subsequent hydrogen chloride using. Herewith it is possible to obtain the following products: soda ash, table salt, calcium chloride and fertilizer or fodder precipitate /2/. There is also method of complex oil sludge processing with obtaining soda ash, potash, Portland cement and alumina. The method of waste liquid recycling for oil measures flooding as well as for its pumping into underground horizons is used.

A number of efforts of scientists to bring into wasteless soda ash production and to form waste processing into calcium chloride, table salt, construction materials, mineral feedings etc. have not been still successful.

To our opinion waste liquid processing by means of phosphoric acid and sodium and calcium phosphates NaH₂PO₄, Са(Н₂РО₄)₂ and, СаНРО₄×2Н₂О and hydrochloric acid is one of rational methods.

Therefore we performed preliminary thermodynamic calculation of Gibbs energy change for Са(Н₂РО₄)₂, NaH₂PO₄ and НСІ formation according to the following chemical reaction:

NaCІ+ СаСІ₂ + ЗН₃РО₄ ® NaH₂PO₄ + Са(Н₂РО₄)₂ + ЗНСІ

in temperature interval 298-423К.

The calculations have shown, that in this temperature interval G⁰_т potential has negative value and shows probability of reaction course to the side of target products formation.

To determine process optimal parameters for chloride salts decomposition the kinetic research was carried out in the next parameters: the process temperature interval - 120-150⁰С, duration – 2-4 hours and phosphoric acid concentration - 45% Н₃РО₄. The results of laboratory research are given in the table 2.

As it follows from the table 2, temperature increasing from 120⁰С to 150⁰С at dwell time 2-4 hours causes chlorine extraction degree into gaseous phase increasing. Thus, extraction degree equals to 92.05-98.81% at temperature 120⁰С and time 2-4 hrs, 98.96-99.99% at temperatures 140⁰С and 150⁰С in match. Thereat optimal process parameters are 140⁰С temperature and process duration 4 hrs, when extraction degree 99.68% is attained.

The table 2 - The temperature and process duration influence on NaCІ and СаCІ₂ decomposition degree

#	T, ^0C	τ, min	NaCІ mass, g	СаСІ2 mass, g	45%-solution of Н3РО4 consumption,g	СІ residual content, g	СІ extraction degree, %
1	120	2.0	5.8	12.0	64.66	1.67	92.05
2		3.0	5.8	12,0	64,66	1.01	96.90
3		4.0	5.8	12,0	64,66	0.62	98.81
4	140	2.0	5.8	12.0	64.66	0.58	98.96
5		3.0	5,8	12,0	64.66	0.31	99.12
6		4.0	5.8	12,0	64.66	0.28	99.68
7	150	2.0	5,8	12,0	64,66	0.30	99.26
8		3.0	5,8	12.0	64.66	0.10	99.92
9		4.0	5,8	12.0	64.66	0.01	99.99

Hydrogen chloride, emitting into gaseous phase, is subjected to absorption with water for hydrochloric acid preparation. After absorption 27-30% hydrochloric acid is formed which corresponds to the SS requirements. HCl absorption degree equals to 99,0-99.9%, hydrogen chloride MPC in exhaust gas equals to 0,01 mg/m³.

Then solution containing 5% of NaH₂PO₄, circulates in the system, and solution medium рН=4,4. The solution is subjected to evaporation at temperature 60-80⁰С to concentration increasing up to 50-55% NaH₂PO₄. Then it is cooled at temperature 25-30⁰С and crystallized as crystalline hydrate NaH₂PO₄•2Н₂О. After centrifuging sodium dihydrophosphate is dried, and filtrate containing 20-30% of NaH₂PO₄, is reversed into the initial stage of the process. Sodium dihydrophosphate is used as a product or it is processed into sodium pyrophosphate using heating to 250⁰С. Formed product Na₄P₂O₇•10Н₂О can be used in food industry.

On the basis of obtained data we have developed principal-technological scheme of processing of soda ash production waste, which consists of the next stages:

- calcium and sodium chlorides decomposition;

- obtaining calcium hydrophosphate from salts mixture;

- calcium hydrophosphate precipitate filtration;

- sodium dihydrophosphate crystallization and filtration;

- hydrogen chloride absorption and hydrochloric acid production.

Technical-economic calculation of proposed technology of chlorine-containing waste processing in soda ash production by phosphoric acid shows profitability of the given manufacture.

The literature

1. Наркевич И.П., Печковский В.В. Recycling and liquidation отходов in technology inorganic

Substances. M.: chemistry, 1984, -.240с.

2. Крашенинников С.А. Technology of soda. M.: chemistry, 1988. -340с.