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Section 9. Chemistry
https://doi.org/10.29013/ESR-20-7.8-63-67
Erkayev Aktam Ulashevich, doctor of technical sciences, professor of TCTI, Tashkent Reimov Karjawbay Dauletbaevich, doctor of technical sciences (PHd), associate professor, of Ajiniyaz Institute, Nukus Kaipbergenov Atabek Tulepbergenovich, doctor of technical sciences, associate professor of Ajiniyaz Institute, Nukus
E-mail: atabek2004@mail.ru
PROBLEMS OF UTILIZATION OF DISTILLED SUSPENSION OF SODA PLANTS AND WAYS TO SOLVE THEM
Abstract. The existing methods of utilization of the distilled liquid of the enterprises for the production of soda ash are analyzed. The possibility of processing a distilled suspension of the LLC Kungrad Soda Plant by processing it with sulfate-containing salts of Karakalpakstan to obtain sodium chloride is shown.
The optimal technological parameters of the process have been determined and the kinetics of precipitation of calcium sulfate has been studied.
Keywords: Soda ash, sodium hydroxide, ammonia process, industrial waste, distilled liquid, solid sludge, calcium and sodium chloride, lime, calcium sulfate, magnesium hydroxide.
Soda ash is a traditional product with a long his- sodium hydroxide. On LLC "Kungrads Soda Plant"
tory of production and use. There are currently over soda ash production is based on the ammonia meth-
75 soda plants in the world located in 34 countries. od. The ammonia soda method, however, has serious
An increase in output can be achieved by improv- drawbacks, the main of which are: the low degree of
ing the technological processes of existing industries, utilization of the feedstock (sodium uses approxi-
saving material resources, introducing progressive mately 2/3, and chlorine and calcium is not used at
consumption rates per unit of output. The soda in- all); a large amount ofliquid and solid waste requiring
dustry also faces important challenges. It is planned disposal, discharge and long-term storage; significant
to further increase production of soda ash, the inten- consumption of energy resources; large specific in-
sification of technological processes in existing soda vestment for the creation of soda production.
plants, searches rational ways of using and manufac- Therefore, in this production, simultaneously
turing equipment [1-4]. with the receipt of valuable products, a huge amount
At present, the production of soda in the world is of industrial waste accumulates. The most volumibased on four methods of its production: ammonia, nous waste from the production of soda ash by the from natural soda, from nepheline and carbonation of ammonia method is the distilled suspension, which
is formed in the amount of 8-10 m3 per 1 ton of soda. The distilled slurry can be separated into clarified liquid and solid sludge. Clarified distilled liquid and solid sludge must be processed into products useful for human economic activity.
The main way to reduce the amount of chloride waste of soda production is their processing to obtain marketable products. Currently, there are the following directions for solving the problem of waste disposal: obtaining from a distilled suspension of calcium and sodium chlorides; its application in the oil and gas industry, to obtain ameliorant, calcium hydroxide, cementless binder and other products [5-15].
The use of the distilled slurry on an industrial scale is very low and therefore it is usually sent to sludge ponds or the so-called "white seas".
Sludge ponds are specially prepared areas of the earth's surface, surrounded by dams up to 20 m high. Sludge ponds occupy significant land areas; in addition, they are sources of intensive pollution of ground and surface waters with sodium and calcium chlorides. Soda production wastes generated in large quantities restrict the further development ofexisting soda plants and impede the rational geographic location of new plants.
One of the real ways of using distilled liquid is waterflooding of oil reservoirs [5-6]. This method is used in the Shlapovskiy oil field, where a distilled suspension is used instead of fresh water for pumping into oil wells. In this case, the following requirements are imposed on the liquid: it must be free of CaO, not supersaturated with respect to CaSO4, the MPC of suspended particles in it must be no more than 20 mg/l. The preparation of the liquid consists of the following operations: settling in a sludge storage, dilution with water to the content of Cl - 89 g/l (liquid: water = 4:1), carbonization of the solution to remove Ca(OH)2; supply of return sludge to the carbonization column, thickening of the liquid containing 10 g/l of CaCO3 in the thickener and final clarification to a suspension content of 0.02 g/l in a section of 31 hectares.
The clarified liquid is fed through a 140 km pipeline to the oil fields of the Shlapovskiy field. The displacement coefficient of this liquid is not lower than that of fresh water.
For other soda plants, the distilled liquid can be used for pumping into absorbing horizons [5-6]. When injected into absorbing horizons, the effluent should not contain mechanical impurities that can reduce the permeability of the formation, and chemical components that may interact with it, and should not be supersaturated with any of the salts that may precipitate. One of the methods for eliminating cuttings from the "White Seas" is their disposal in salt workings of NaCl leaching wells. Preparation of the slurry consists of the following steps: sedimentation of e and filtration, e; mixing e precipitate supersaturated with NaCl brine to the ratio of T: L of from 1:4 to 1:10 and feeds a pulp pump at a speed of 2 m/s in the leaching chamber. In order to reduce the amount ofwaste wastes, it is proposed to separate insoluble impurities of sand, calcium carbonate, lime, calcium sulfate, magnesium hydroxide from the distiller suspension and use them in the production of cement or to neutralize acidic soils. For this, the distilled suspension, brine purification sludge and limestone roasting waste are mixed and thickened in the presence of flocculants to a solids content of 8-12 wt%. Then precipitate with 70-90 °C is subjected to multi-stage filtration centrifuge or disc filters, washing the precipitate during filtration fluid containing no ions Cl. The filtrate is then mixed with the original waste, and the sludge containing 50 wt.% Solids can be used in agriculture for liming soils and in the production of cement.
The use of solid precipitates obtained from filtering a distilled suspension is possible at a low NaCl content (~20-25 wt.%). To reduce the chloride content, the precipitate is washed or mixed with chalk waste. The choice of waste preparation method depends on the location of the plant.
Employees of NIOCHIM and the Kharkov Agricultural Institute named after V. V. Dokuchaev jointly
developed a technology for the preparation of solid waste of soda production for reclamation of acidic and alkaline soils [7]. The method is based on thickening the distilled liquid to t: w=1:10, filtering it on a FPAKM-50 filter press, followed by partial washing of the precipitate from chlorides on filters with a weak distiller suspension. Next, the sediment containing 50% moisture is mixed with chalk waste in a ratio of 1:(2-3), the resulting product is crushed and dried.
It is necessary to note the work of NIOCHIM [8] on the use of filter fluid from soda plants to obtain complex mineral fertilizers used for rice and sugar beets. The scheme provides for the extraction of P205 from simple superphosphate with a filter liquid and a two-stage filtration of phosphogypsum. A fertilizer containing 35-38% of nutrients is obtained.
Experiments on magnetic processing of a distilled suspension in order to reduce the amount of scale formation during its evaporation were carried out on a flow-type stand of the Slavic Soda Plant. To reduce deposits in the tubes of evaporators in the production of CaCl2, it is advisable to use magnetic treatment of the distiller liquid [9].
To obtain calcium chloride from a distiller suspension containing calcium sulfate, a significant part of CaSO4 is removed during decantation of CaCO3, as a result of which its concentration in the CaCl2 solution decreases, which makes it possible to evaporate without intensive formation of incrustations on the horizontal surface of the heat exchanger. At the first stage of evaporation, a plate heat exchanger should be used, since it is easily freed from incrustations [10].
In the method of purification of the distilled liquid of soda production from calcium sulfate in order to increase the degree of purification, the distilled liquid is preliminarily saturated with carbon dioxide, and the treatment with gypsum and carbonization is carried out simultaneously to pH 7.5-8 [11].
Waste of soda production with a high content of CaC12 and other salts is decanted to separate solids, the clarified solution (5 m3) is subjected to saturation to reduce the content of Ca(OH)2, then
concentrated by evaporation in multi-shell evaporators, separating crystallizing NaCl (0.4 t). A solution of CaCl2 in an amount of 1.2 m3 with a density of ~ 1.4 kg/m3 at 70 °C is pumped into subsoil cavities, initially filled with NaCl brine, which is then displaced by CaCl 2 and sent for reuse. For 1 ton of produced soda, 0.372 ton of NaCl is recovered [12].
Thus, the analysis of the materials available in the scientific and technical literature testifies to the scientific and practical, economic and environmental significance of research aimed at the development and creation of a waste-free technology for processing a distilled liquid to obtain purified water.
Generalization literature data related to disposal issues of waste soda production and methods of their processing into commercial products and their industrial implementation show that it is acceptable to process distilled liquid to obtain purified water, returned back to the soda ash production cycle [13-15].
However, there are no systematic studies in the literature on the following issues: the reactivity of the components that make up the waste; influence of various parameters on the process of purification of distilled liquid; the influence of the rate of sodium sulfate, brine and lime milk on the process of separating the solid phase from the suspension.
The purpose of this work is to develop a technology for the utilization of the distilled liquid of KSZ LLC, as a result of which the sodium chloride solution is returned to the technological cycle with the simultaneous production of such useful products as gypsum, chalk and magnesium hydroxide.
The essence of the technology lies in the fact that the distilled suspension is treated with sulfate-containing components and subsequently, after the gypsum is separated from the system, magnesium hydroxide and calcium carbonate (chalk) are sequentially precipitated, and the purified distilled suspension is returned back to the technological cycle of soda ash production, which is especially important in such a region as Karakalpakstan, where water is an expensive raw material.
The raw materials used were brine and solid salts rabilite of the Tumryuk deposit, the chemical com-of lakes Barsakelmes and Karaumbet, as well as mi- position of which is given in (table 1).
Table 1.-The chemical composition of the starting components
Samples Mass fractions,%
Anions Cations
Cl- SO 2- Ca2+ Mg 2+ Na+calc
Rapa lake Barsakelmes 16.14 1.94 0.029 1.87 7.7-4
Rapa lake Karaumbet 13.72 7.07 - 3.98 4.53
Self-precipitated salt of Lake Barsa kelmes 60.32 0.06 0.088 0.06 38.95
Salt of Karaumbet Lake No. 1 52.89 3.33 1.0 0.37 34.04
Distiller liquid KSZ LLC 9.62 0.25 3.49 0.031 -
Mirabilite of the Tumryuk field - 42.6 0.21 - 20.17
To study the effect of sodium sulfate on the degree of purification of the distilled liquid, the concentration of sodium sulfate was varied within 80; one hundred; 120% of stoichiometry with respect to calcium chloride, comprising: a first camping in
distiller liquid.
The process temperature varied from 40 to 80 °C. The duration of the process was 30; 60; 90 minutes The experiment used mirabilite Tumryuk deposit. Before mixing with the distilled liquid, mirabilite was ground to a particle size of 0.03 mm.
A certain amount of distillation liquid and sodium sulfate (mirabilite) were introduced into a round bottom flask equipped with a mechanical stirrer. Precipitation of calcium sulfate proceeded at room temperature. After stirring the suspension for a given temperature and time, a sample was taken, which was filtered through a dense paper filter.
It can be seen from the data that under the conditions prevailing in the experiments, calcium does not completely precipitate even with an excess of the precipitant of 20% and turbulent stirring of the suspension for 90 minutes. Along with the purification of the distiller suspension, we studied the kinetics of the settling properties of the resulting calcium sulfate. For this, the suspension was placed in a cylinder and the height of the clarified layer was noted every 5-10 minutes. The process took place at room temperature.
The data obtained show that under the conditions prevailing in the experiments, the settling rate of the solid phase is 0.006-0.012 m/h, and the final volume of the cuttings is 37-82% of the initial one.
The highest sedimentation rate is possessed by a suspension obtained at 100% normal Na2SO4 at a temperature of 40 °C and the mixing time 60 min. In this experiment, the sedimentation process lasts 95 minutes and the final volume of sludge is 37% of the total. The temperature and mixing time have little effect on the precipitation process. Thus, with a mixing time of 90 minutes, the amount of solid phase is 38.7%, which settles within 140 minutes, and a reduction in the mixing process to 30 minutes leads to an acceleration of the deposition process to 135 minutes. With an increase in the process temperature to 80 °C, the rate of the deposition process decreased and the duration of the deposition process reached 145 min.
Thus, the optimal conditions for the purification process of a distiller suspension using mirabilite from the Tumryuk deposit are: the rate of sulfate salts is 100% relative to calcium, the interaction time of the components is 1.5-2 hours, and the process temperature is not more than 60 °C.
As a result of implementation, there is practically no waste - distilled liquid. The water demand is reduced by 50-92%, the NaCl utilization rate reaches 90-95%.
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