GYPSUM-BASED BINDERS DERIVED FROM PORCELAIN AND DECORATIVE FINISHING INDUSTRY WASTE

УДК 691.335.5:628.477.6

Abstract

The accumulation of gypsum-containing waste at porcelain manufacturing enterprises and decorative finishing production workshops in the Rishton district of the Fergana region, Uzbekistan, presents both an environmental problem and an untapped raw-material resource for the construction industry. The aim of this study was to develop calcium-based binders from such industrial waste and to evaluate their physical, mechanical, and chemical properties in comparison with standard construction gypsum of grade G-6. To achieve this aim, gypsum waste was purified, crushed to a dispersion of 0.2 mm in accordance with OʻzR DSt 125-2018, and dehydrated at various temperatures; the optimal heating regime was identified, and the setting times of samples prepared at different gypsum-to-water ratios were determined. The mechanical strength of the samples was tested using an AlfaTest device, while the chemical composition of the resulting hemihydrate (CaSO₄·0.5H₂O) was confirmed by IR spectroscopy. The results showed that the optimal gypsum-to-water ratio was 1.0:1.0, with a mass loss of 20–25% upon heating at 220°C, and that the compressive strength of the waste-derived binder reached 79.55% of that of G-6 grade gypsum. A material balance analysis further confirmed the economic and environmental feasibility of the proposed technology, with an overall product yield of 80.1% from the initial raw material. These findings indicate that gypsum-based binders obtained from porcelain and decorative finishing industry waste can serve as competitive, cost-effective, and environmentally sound construction materials, particularly in applications where ecological requirements are prioritized.

Аннотация

Накопление гипсосодержащих отходов на предприятиях по производству фарфоровых изделий и в цехах производства декоративной отделки, действующих в Риштанском районе Ферганской области, Узбекистан, представляет собой как экологическую проблему, так и невостребованный сырьевой ресурс для строительной отрасли. Целью данного исследования являлась разработка кальциевых вяжущих материалов на основе указанных промышленных отходов и оценка их физических, механических и химических свойств в сравнении со стандартным строительным гипсом марки G-6. Для достижения этой цели гипсовые отходы были очищены, измельчены до дисперсности 0,2 мм в соответствии с OʻzR DSt 125-2018 и подвергнуты дегидратации при различных температурах; был определён оптимальный температурный режим, а также сроки схватывания образцов, приготовленных при разных соотношениях гипс:вода. Механическая прочность образцов была испытана с использованием прибора AlfaTest, а химический состав полученного полугидрата (CaSO₄·0,5H₂O) был подтверждён методом ИК-спектроскопии. Результаты показали, что оптимальное соотношение гипс:вода составляет 1,0:1,0, потеря массы при нагревании до 220°C составляет 20–25%, а прочность на сжатие вяжущего, полученного из отходов, достигает 79,55% от прочности гипса марки G-6. Анализ материального баланса подтвердил экономическую и экологическую целесообразность предложенной технологии при общем выходе готового продукта 80,1% от исходного сырья. Полученные результаты свидетельствуют о том, что гипсовые вяжущие, полученные из отходов фарфорового производства и декоративной отделки, могут использоваться как конкурентоспособные, экономически выгодные и экологически безопасные строительные материалы, особенно в областях, где предъявляются повышенные экологические требования.

Keywords: gypsum waste, porcelain and ceramic production waste, calcium binder, mechanical strength, compressive strength, IR spectroscopy analysis.

Ключевые слова: гипсовые отходы, отходы фарфоровых и керамических изделий, кальциевое вяжущее, механическая прочность, прочность на сжатие, анализ ИК-спектроскопии.

Introduction

At present, the Republic of Uzbekistan has developed major strategic programs for producing modern construction materials from industrial waste with the aim of protecting the environment. The purpose of these programs is to ensure efficient use of natural resources while sustaining the further development of the Uzbek economy. Maintaining a balance between the production and consumption of renewable natural resources, rational use of non-renewable resources, efficient utilization of waste, and improving the capacity for natural regeneration at the regional and local levels are all among the principal measures envisaged.

In this regard, reducing the cost of construction materials and developing energy-efficient technologies through the use of industrial waste are among the key directions of this work. Accordingly, Resolution PQ-4335 of the President of the Republic of Uzbekistan, dated May 23, 2019, encompasses objectives related to the development and expansion of new, modern types of wall-cladding materials in the construction sector [1].

Today, more than 50 types of gypsum-containing waste are generated in the national economy, the largest in volume being phosphogypsum. Currently, more than 100 million tons of accumulated phosphogypsum waste exists in Uzbekistan. In the field of utilizing chemical-industry waste as secondary resources, the innovative technologies developed by Professor T.A. Otakuziyev and his research school — including modified phosphogypsum, sulphomineral cements, and other binder-production methods — are particularly noteworthy [2].

Worldwide, and in Russia in particular, extensive scientific and experimental work exists on the use of industrial waste in the production of construction materials [3]. A.P. Merkin and A.S. Bagdasarov demonstrated the effectiveness of utilizing phosphogypsum without pre-treatment [4, p. 303; 5, p. 96]. Yu.M. Bazhenov, P.F. Shubenkin, and L.I. Dvorkin [6, p. 54] confirmed the efficiency of producing construction materials from industrial waste. Technologies for obtaining products from unwashed phosphogypsum by extrusion in Bulgaria, and for producing polymer-phosphogypsum in Belarus, are also noteworthy [7].

Globally, 35–40 million tons of gypsum binders are produced annually, of which 90% are used in construction. In Uzbekistan, the production of gypsum binders is well developed in the Bukhara and Fergana regions. In the Republic, reserves of 25 different types of gypsum-suitable raw material, totaling close to 12 million tons, have been identified [8, p. 512].

Gypsum forms from the deposition of sulfate salts in drying lakes and sea basins. Gypsum deposits have been found in the Fergana (Kuvasoy), Bukhara (Kogon), and Surkhandarya regions of Uzbekistan. Construction gypsum (CaSO₄·2H₂O) is a binder that sets and hardens rapidly in air; it is obtained by calcining natural gypsum at a temperature of 140–190°C [9, p. 70-74].

Calcined gypsum (CaSO₄·0.5H₂O) is one of the most ecologically clean and stable construction binders. The energy expenditure required for gypsum production is considerably lower than that for cement and lime production. Gypsum can also be produced from industrial waste — phosphogypsum, or by-products formed during the desulfurization of flue gases from coal-fired power plants [10].

Materials and methods

Gypsum-based molds used in the porcelain casting process at porcelain and ceramic manufacturing enterprises, as well as gypsum waste generated at decorative finishing production workshops, were subjected to preliminary purification for the purpose of further processing. The degree of dispersion was established in accordance with the requirements of OʻzR DSt 125-2018, and the crushed gypsum samples were passed through a sieve with a mesh size of 0.2 mm.

The crushed gypsum waste was heated at various temperatures, and the optimal temperature regime for dehydration was determined. The parameters for converting the gypsum waste into a primary product through the addition of modifying agents were established. The preparation and testing of samples were carried out in accordance with the requirements of the state standards OʻzR DSt 125-2018 and OʻzR DSt 23789-2018.

The mechanical strength of the samples was examined using an AlfaTest device on samples prepared in standard 4×4×16 cm molds. In accordance with GOST requirements, the mechanical strength of each sample was tested at two stages after casting — 2 hours and 48 hours — in order to evaluate the development of strength over the curing period. The chemical composition was analyzed using IR spectroscopy. Construction gypsum of grade G-6 was used as the control sample.

Results and discussion

According to the experimental results, at a constant temperature (220°C) and varying heating times, the mass reduction amounted to 20–25%. The sample heated at 220°C for 60 minutes hardened in the shortest time. The setting rate at a 1.0:1.0 ratio proved considerably more effective than that of technical gypsum used in construction (Table 1).

Table 1. Setting indicators of samples heated for different durations, mixed with water in various ratios

Figure 1. Gypsum samples tested at various ratios (1:2, 1:1, 1:1.5, 1:1.25, 1:1.75)

The amount of water used in preparing the gypsum mixture was tested in several ratios in accordance with the requirements of OʻzR DSt 125-2018. The results showed that the optimal gypsum-to-water ratio is 1:1.

Table 2. Compressive strength results of the samples

After 48 hours, the mechanical strength of the gypsum samples obtained from the waste of porcelain and ceramic manufacturing enterprises amounted to 79.55% of the mechanical strength of G-6 grade construction gypsum.

The IR spectroscopy analysis of the gypsum samples obtained from porcelain casting waste was carried out as follows.

Figure 2. IR spectrum of porcelain and ceramic manufacturing waste (unheated sample)

Figure 3. IR spectrum of porcelain and ceramic waste heated at 220°C

As shown in Figure 2, characteristic peaks for CaSO₄·2H₂O (gypsum) are observed in the unheated sample. As shown in Figure 3, after heating at 220°C, the release of water molecules and the formation of CaSO₄·0.5H₂O (hemihydrate) are clearly visible in the spectrum. This process confirms the dehydration stage essential for use as a calcium-based binder.

Figure 4. IR spectrum of decorative finishing production waste for buildings and structures (unheated sample)

As shown in Figure 4, characteristic peaks for CaSO₄·2H₂O (gypsum dihydrate) are observed in the unheated decorative finishing waste sample in the 1100–1150 cm⁻¹ region. In addition, peaks indicating the presence of SiO₂ (silica) were identified in the sample, which is associated with the mineral additives present in decorative materials. Compared with the reference sample (D_CaSO₄), the spectrum of the sample confirms its gypsum nature.

Figure 5. IR spectrum of decorative finishing production waste for buildings and structures, heated at 220°C

As shown in Figure 5, the IR spectrum of the decorative finishing waste heated at 220°C clearly shows the formation of CaSO₄·0.5H₂O (hemihydrate) as a result of the release of water molecules. The silica (SiO₂) peaks are preserved, indicating the stability of the material's composition. As a result of the dehydration process, the binding properties were improved, rendering the material suitable for use as a calcium-based binder.

Table 3. Material balance and cost of the gypsum production process

The material balance results showed that the technology for obtaining gypsum from enterprise waste is efficient both economically and environmentally. From 1250 g of initial raw material, 1001 g of finished product was obtained — an overall yield of 80.1%.

Conclusion

In the production of gypsum binders from waste, the secondary product differs significantly from natural gypsum raw material. The presence of various impurities requires additional processing, such as neutralization, enrichment, and drying. However, the compiled material balance results showed that the technology of obtaining gypsum from enterprise waste proved to be efficient both economically and environmentally.

The compressive strength of the samples obtained, relative to the standard, amounted to 79.55%. It was established that, in accordance with GOST testing requirements, the mechanical strength of the calcium-based binder increases between the 2-hour and 48-hour test points after casting. IR spectroscopy analysis confirmed that, when heated at 220°C, the gypsum waste transforms into the hemihydrate state (CaSO₄·0.5H₂O).

Thus, gypsum-based binders obtained from porcelain and decorative finishing industry waste can be used as competitive construction materials in certain fields — particularly in cases where environmental requirements are high and the compressive strength indicator exceeds 79% of the standard.

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