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Iskandarova Mastura Iskandarovna, doctor of technical Sciences, Professor, head of the scientific-research and test center "Strom" Institute of General and inorganic chemistry of Academy of Sciences of the Republic of Uzbekistan E-mail: mastura-iskandarova@rambler.ru Atabaev Farrukh Bakhtiyarovich, doctor of philosophy (Ph. D.) in technics, senior scientific research, research and test center «Strom» Institute of General and inorganic chemistry of Academy of Sciences of the Republic of Uzbekistan
E-mail: atabaev-farruh@mail.ru
RATIONAL WAY OF DISPOSAL OF CHRYSOTILCEMENT WASTE IN THE MANUFACTURE OF THE PORTLANDCEMENT
Abstract: An efficient method of utilizing wet chrysotile cement wastes for Portland cement production has been developed and proposed for industrial application. The expediency of their thermal activation by supplying hot clinker to the layer leaving the rotary kiln of clinker production with a temperature of1000-1100 oC, followed by milling of the cooled clinker with additive - additive in the presence of gypsum stone. Portland cement from such clinker is used for the production of chrysotile cement products.
Keywords: chrysotile cement waste, secondary raw materials, utilization, thermal activation, additive to clinker, additional cement for chrysotile cement products, physical and mechanical properties, pilot-industrial tests.
Formulation of the problem. The intensive accumulation of a large amount of chrysotile cement waste during the filtration of the chrysotile cement mass on the sheet-forming machine leads to environmental contamination. Neutralization and disposal of these wastes are associated with great labor and financial costs, which negatively affects the cost of the main products. Taking into account the above, the solution of the problem of developing the technology of utilization of CCW by obtaining on their basis building materials and products of a wide range of purposes is topical.
The composition of "wet" chrysotile cement wastes is mainly represented by hydrated minerals of Portland cement clinker and fine chrysotile fibers that, when properly processed, exhibit astringent properties and can be a high-quality raw material for the manufacture ofbuilding materials and products, since they have high potential hydraulic activity [2]. An effective way to open it is a correctly selected heat treatment of solid waste. In this case, hydrate neoplasms and tiny particles of chrysotile will be
subjected to destructuring, and anhydrous products with hydraulic activity accumulate in the chrysotile-cement mixture [2-4]. Therefore, it becomes urgent to develop rational methods for processing chrysotile cement waste and their use in the production ofbuilding materials and products. With this in mind, the present work is devoted to the development of a method for utilization of chrysotile cement waste in relation to the production conditions ofJSC "Kizilkumcement" taking into account the technical and technological capabilities of the enterprise.
Materials research methods, equipment and instruments. In the work, clinker, two-water gypsum and wet chrysotile cement waste (CCW) ofJSC "Kizilkum-cement" were used as raw materials. They were submitted by two samples with an average moisture content of 80 and 35%, respectively. From dried to constant mass components (clinker and chrysotile cement waste at a temperature of 105-110 °C, gypsum - at 40 °C, medium samples were taken by quarting, which after grinding until complete passage through a No. 008 sieve according to
GOST (State Standard) 6613 was subjected to chemical 5382-91 "Cements and materials of cement production, analysis in compliance with the requirements of GOST methods of chemical analysis" (Table 1).
Table 1. - Chemical composition of raw materials
Material loss on ignition SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O SO3
Clinker* 0.75 20.54 5.19 3.56 62.04 3.60 0.97 1.07 2.62
Gypsum 2.2 1.52 0.13 0.14 33.04 0.20 0.10 0.10 43.5
Chrysoti e cement waste
Sample 1 1.90 23.41 5.90 4.93 55.71 7.12 - - 1.32
Sample 2 1.77 24.41 6.03 5.21 54.27 6.80 - - 1.38
* Calculated mineralogical composition of clinker,%: C S = 56.52; C2S = 17.12; C A = 7.74; C4AF = 10.82.
The essence of the method of activation of chrysotile cement wastes was their heat treatment by contact method according to which a dosage portion of waste with natural moisture is supplied to a layer of hot Portland cement clinker leaving the furnace and going to the refrigerator for cooling. In laboratory conditions, this scheme was simulated in this way: the bowl with clinker was placed in an electric muffle furnace in which, at a temperature of 1000 °C, it was kept for 30 minutes, after which the bowl with a hot clinker was extracted from the furnace, and the clinker was poured into a metal container into which the dosed 3, 5, 10% of the chrysotile cement waste, and the waste was thoroughly mixed with the hot clinker. After cooling under natural conditions, the charge "Portland cement clinker + chrysotile cement waste" was milled in the presence of 5% double-water gypsum. The fineness of grinding the obtained cements was characterized by the remainder on the screen No. 008 (12-14)%. Cement with additive (3, 5, 10)% of thermally activated (TCCW) chrysotile cement wastes were tested for compliance with the requirements of GOST (State Standard) 10178-85 "Portland cement and slag Portland cement. Technical specifications" and O'z DSt (State Standard ofthe Republic ofUzbekistan) 913-98 "Portland cement for the production of asbestos-cement
products. Technical conditions", according to the methods of GOST 310.1-310.4 "Cements. Methods of testing".
Results and its discussion. t was established that the experimental Portland cement with an addition of 3, 5, 10% heat-treated chrysotile cement waste after 60 min. The grinds had a residue on a No. 008 screen of 10, 9, 13%, respectively. Experimental cements at 28 days of age of normal hardening have compressive strength in the range of34.6-43.2 MPa. For the comparative analysis of the test results, the tensile strength of the additive cement was determined, which at the age of 28 amounted to 41.2 MPa at compression, which was assumed to be 100%. Experimental cements with the addition of 3, 5% of chrysotile cement waste, according to the requirements of GOST 10178-85, are marked 400. n increase in the content of the additive to 10% leads to a sharp decrease to 15% of the strength of cement (Table 2). It is noted that cements with thermally activated additives have an increased water demand (0.45-0.46). Therefore, the scope of such cements may be somewhat limited, that is, these cements can be recommended for the production of chrysotile cement products, the molding of which involves the preparation of a chrysotile-cement slurry with a large amount of water (60-92)%.
Table 2. - Physical and mechanical properties of Portland cement and their compliance with the requirements of GOST 10178 "Portland cement and slag Portlandcement. Specifications"
Cements Composition of cement,% Fineness of cement grinding on the remainder on a sieve No. 008,% Strength limit at 28 d, MPa, at:
Clinker Gypsum Thermal-ly activated cement waste bending compres-sion
PC D0 95 5 - 15 6.28 41.2
TPC D3 90 5 3 10 5.99 41.6
TPC D5 85 5 5 9 6.05 43.2
TPC D10 80 5 10 13 5.82 35.0
According to the requirements of Oz DSt 913-98, the strength indices of cement during bending and compression of 3-and 7-day normal hardening should have
a value not less than, MPa: for bending - R3 = 3.2 MPa; R7 = 4.2 MPa; for compression - R3 = 20.0 MPa; R7 = 27.0 MPa.
Table 3. - Physico-mechanical properties of experienced Portland cement and their compliance with O'z DSt 913 requirements
Cements Composition of cement,% Setting time, h - min Strength limit, MPa, aged, d
Clinker Gyp-sum Thermally activated cement waste Start End bending compression
3 7 3 7
PC D0 95 5 - 2-30 4-00 4.33 4.90 20.2 27.8
TPC D3 90 5 3 2-05 3-40 2.68 4.20 20.8 28.0
TPC D5 85 5 5 2-15 3-30 2.98 4.24 21.8 30.0
TPC D10 80 5 10 2-25 3-10 2.65 4.13 17.9 24.8
It is established that the values of the strength limit for bending and compression, as well as the setting time, cements with an addition of 3-5% of thermally activated waste meet the requirements of Oz DSt 913-98. The highest strength parameters of cements are also provided at a dosage of 3-5% of a thermoacti-vated chrysotile cement additive.
Pilot-industrial tests for the production of batch of clinker with additive-additive of chrysotile cement waste and Portland cement from modified clinker were carried out at JSC "Kizilkumcement". Heat treatment of wet chrysotile cement wastes occurred in contact with a heated Portland cement clinker having a temperature of 1000-1100 oC at the exit from the rotary kiln. Then clinkers with additives of thermally activated chryso-tile cement waste are fed to the grid of the grate cooler and cooled to a temperature of20-40 °C, moving along the refrigerator, fed to the grate screen and then to the clinker warehouse or through the bunker to the cement mill. Proceeding from positive test results, JSC "Kizilkumcement" under this scheme has constructed a technological line providing supply and dosing of chrysotile cement waste to the hot clinker layer for clinker production with a thermally activated additive.
In the conditions of JSC "Kizilkumcement" with the use of a pilot batch of cement with thermally activated chrysotile cement waste, an experimental-industrial batch of eight-wave chrysotile cement sheets of profile 40/150 was produced. In the process of their manufacture deviations from the established technological regime were not observed. The physical and
mechanical tests showed their compliance with the requirements of GOST 30340. The development includes a technological instruction for the process of thermal activation of chrysotile cement waste and their use for the production of Portland cement for chrysotile cement products, a technological scheme for the production of portland cement with the addition of chrysotile cement waste, the standard of organization (Ts) for clinker with additive- a thermally activated additive. The proposed method does not require large investments for the installation of additional equipment and will reduce the consumption of clinker part in the Portland cement, which will lead to a decrease in the cost of production.
Conclusion. An energy-efficient method of thermal activation of chrysotile cement waste by contact method was developed by feeding them to a layer of hot Portland cement clinker leaving the rotating furnace. Heat treatment of chrysotile cement waste in this way increases the grindability of the clinker, and Portland cement is obtained with improved physical and mechanical properties. Experimental cements with additives (3, 5)% of thermoactivated chryso-tile cement waste for construction and technical properties comply with the requirements of GOST 10178-85 and Oz DSt 913-98, therefore they are recommended for serial production of portland cement intended for the production of chrysotile cement products at JSC "Kizilkumcement" which in the future will be directed to the production of chrysotile cement products.
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