IMPROVING THE TECHNOLOGY FOR PRODUCTION OF ENERGY-EFFICIENT EXPANDED CLAY AGGREGATE BASED ON BENTONITE CLAY AND SECONDARY WASTE

ABSTRACT

This article investigates the chemical-mineralogical compositions and technological properties of clay-based raw materials and secondary resources for expanded clay aggregate production. Research results confirm that their composition and properties comply with the GOST standard requirements for raw materials used in expanded clay aggregate manufacturing. The physical and mechanical properties of expanded clay granules, based on bentonite clay and secondary resources, were studied in detail under both laboratory and industrial conditions. Additionally, recommendations are provided regarding the application areas for the produced expanded clay aggregate.

АННОТАЦИЯ

В данной статье исследованы химико-минералогические составы и технологические свойства глинистого сырья и вторичных ресурсов для производства керамзита. По результатам исследований установлено, что их состав и свойства соответствуют требованиям ГОСТа, предъявляемым к сырью для производства керамзита. Детально изучены физико-механические свойства гранул керамзита в лабораторных и промышленных условиях на основе бентонитовой глины и вторичных ресурсов. Также представлены рекомендации по областям применения производимого керамзита.

Keywords: bentonite, clay, vermiculite, soda waste, chemical analysis, physical and technical properties, electron microscope, X-ray diffraction pattern, swelling, expanded clay, granule

Kлючевые слова: бентонит, глина, вермикулит, содовый отход, химический анализ, физико-технические свойства, электрон микроскоп, рентгенограмма, вспучивание, керамзит, гранула

Introduction. Currently, in the construction industry, the effective use of local raw materials in the production of thermal insulation materials is of great importance. Simultaneously, the utilization of secondary waste to preserve the local raw material base and conserve natural resources is considered one of the urgent tasks. The use of secondary waste not only increases economic efficiency but also serves to protect the environment, promote rational use of waste, and reduce production costs. Therefore, the production of thermal insulation materials by processing existing waste under local conditions is one of the most critical challenges in building materials technology today.

Among thermal insulation building materials, expanded clay occupies a special place due to its multifunctional properties. Expanded clay is primarily obtained by burning bentonite clays. The requirements for raw materials in the production of expanded clay are governed by GOST 32026-2012 [1].

Objects and methods of research. Chemical-analytical, X-ray diffraction, and electron microscopic analyses were used to determine the properties of bentonite clay and secondary waste in the production of expanded clay. The chemical composition of bentonite clay and secondary waste was determined using chemical-analytical analysis. The mineralogical composition of this clay and secondary waste was determined by X-ray diffraction method. The mineral composition of bentonite clay and secondary waste was determined using a Shimadzu LABX XRD-6100 diffractometer with CuKα radiation and powder analysis technique. X-ray diffraction patterns were obtained with a step of 0.02, while the tube current and voltage were set at 30 mA and 30 kV, respectively. Scanning electron microscopic analysis of the sample was carried out using a SEM - EVO MA 10 (Zeiss, Germany) scanning electron microscope, utilizing backscattered electrons with Signal A=SE 1, under the following imaging conditions: voltage ENT-15.0 kV, working distance WD - 8.5 mm. The characterization of phase composition and determination of structural properties of raw materials and glass samples were performed using reference materials [2-3].

RESEARCH RESULTS AND DISCUSSION. In developing the composition for expanded clay, bentonite clays from the Uchsay deposit and waste from ‘Kungrad Soda Plant’ LLC JV were used, along with residual vermiculite waste generated during the enrichment process of Tebinbulak vermiculite. The results of the chemical composition analysis of the raw materials are presented in Tables 1-3.

Table 1.

Chemical composition of bentonite clay from the Uchsay deposit

Table 2.

Chemical composition of vermiculite enrichment waste

Table 3.

Chemical composition of soda production waste

Information about the experimental compositions developed using Uchsay bentonite clay, vermiculite enrichment waste, and soda production waste is presented in Table 4 [4-5].

Table 4.

Experimental compositions developed for the production of expanded clay

From the prepared charge, cylindrical experimental samples with a diameter of 22-26 mm and a length of 40-65 mm were produced in a continuous mode using a screw-type hydraulic press, which is a technological equipment in the production process. The experimental samples, with a moisture content of 20-23%, were then fired in rotary kilns [6-7].

For this purpose, after initial heat treatment, the experimental samples were transferred via a belt conveyor to a preheated rotary kiln at a temperature of 400-450°C. There, the samples underwent heat treatment for 20-25 minutes. Subsequently, the heat-treated samples were immediately transferred to the main rotary kiln at a temperature of 950-1000°C and held at the final temperature for 7 minutes. The characteristics of the experimental samples were determined in accordance with the methodologies of current standards (Table 5). It should be noted that the best results were obtained from the UchK-1 experimental batch mixture containing distillation waste from ‘Kungirot Soda Plant’ LLC JV and residual vermiculite waste formed during the enrichment process of Tebinbulak vermiculite. In this case, the expansion coefficient was 3.90%, the expansion temperature ranged from 1070 to 1100 °C, and the bulk density was 670-690 kg/m3 [8-9].

Table 5.

Physical and technical characteristics of experimental samples with various combustible expanded clay granules, both with and without additives.

In this X-ray diffraction pattern of the experimental expanded clay sample UchK-1, the presence of diffraction maxima corresponding to the following minerals was identified (Fig. 1): wollastonite (d=0.293, 0.228, 0.181 nm), mullite (d=0.369, 0.343, 0.293 nm), high-temperature quartz (d=0.425, 0.334, 0.245, 0.228, 0.223, 0.212, 0.197, 0.181, 0.167, 0.152, 0.137 nm), hematite (d=0.369, 0.265, 0.249, 0.181, 0.165 nm), and partially anorthite (d=0.321, 0.310, 0.283, 0.197 nm). 0.181 nm; mullite d = 0.369; 0.343; 0.293 nm, high-temperature quartz d= 0.425; 0.334; 0.245; 0.228; 0.223; 0.212; 0.197; 0.181; 0.167; 0.152; 0.137 nm, hematite d=0.369; 0.265; 0.249; 0.181; 0.165 nm and partially to anorthite minerals d=0.321; 0.310; 0.283;

Figure 1. X-ray diffraction pattern of an expanded clay aggregate sample with UchK-1 composition

The physicochemical, physical-mechanical, and technological properties of the samples in the UchK-1 composition were found to comply with the current standards of GOST 9759-83 and GOST 32026-2012. This composition was selected as optimal for the production of expanded clay granules that meet the standard requirements for expanded clay gravel and sand obtained from clay raw materials.

The results of electron microscopic analysis of the experimental expanded sample of UchK-1 expanded clay aggregate granules (Fig. 2) revealed that the expanded experimental samples possess a uniform fine-grained crystalline structure and are composed of grains of the above-mentioned aluminosilicate minerals [10-11].

CONCLUSION. Thus, based on the results of conducted tests and analysis of laboratory studies, it was determined that expanded clay granules prepared from UChK-1, among the above-mentioned optimal compositions, in both fine and coarse-grained forms, meet all necessary requirements for strength according to GOST 32496-2013 grade P-150 and for bulk density of porous aggregates according to grade M-700, respectively. Consequently, they are recommended for use as aggregates in the preparation of lightweight concrete mixtures.  

References:

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