International Research Journal of Engineering and Technology (IRJET) Volume: 10 Issue: 05 | May 2023
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e-ISSN: 2395-0056 p-ISSN: 2395-0072
PROSPECTS FOR THE USE OF GYPSUM WASTE FOR THE PRODUCTION OF BUILDING GREEN CERAMICS Verónica González Molina, Jesús Agüero López, Abigail Parra Parra, Pedro Antonio Márquez Aguilar, Marina Vlasova Centro de Investigación en Ingeniería y Ciencias Aplicadas de la Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos, México. --------------------------------------------------------------------------***-----------------------------------------------------------------------Abstract The study considers the prospects of using large-scale wastes of gypsum molds from the ceramic industry and phosphogypsum to produce blocks/bricks for the construction industry. The technology was based on the principle of obtaining gypsum concrete. To initiate the binding properties of gypsum wastes, they were subjected to low-temperature treatment in the range of 200-300 oC. Additionally, phosphogypsum was subjected to neutralization without subsequent washing from newly formed compounds. Compressive strength tests of samples showed that for mixtures of Portland cementgypsum molds Fcomp. varies from 170 to 90 kg/cm2 at a cement content of 90-10 wt%. For mixtures of Portland cementphosphogypsum Fcomp. varies from 150 to 100 kg/cm2 at a content of 90-60 wt% cement. For comparison, similar mixtures of Portland cement and commercial semi-aqueous gypsum were prepared.
Keywords: Portland cement, waste gypsum molds, phosphogypsum, glass fibers, concrete, green ceramics 1.
Introduction
Gypsum in the form of CaSO4‧0.5H2O and CaSO4 is widely used both in construction [1-4] and in the production of fine ceramics (porcelain, semi-porcelain, faience, etc.) [5], when slip is poured into gypsum molds. As a result, the production and use of gypsum products is accompanied by the accumulation of large volumes of waste. As a rule, gypsum wastes are represented by CaSO4‧2H2O. One of the most important properties of such gypsum wastes is the relative ease of obtaining new (secondary) binders from them, namely, CaSO4‧0.5H2O [4, 6, 7]. It is known that primary dihydrate calcium sulfate (CaSO4‧ 2H2O) when heated in the temperature range of 140–170 °C turns into hemihydrate calcium sulfate (CaSO4‧0.5H2O). However, for waste from spent gypsum molds, as established in [4], the transition temperature (CaSO4‧2H2O) → (CaSO4‧0.5H2O) can reach 300 oC due to the accumulation of electrolyte solutions introduced into the clay to liquefy it by the gypsum matrix. This feature of gypsum waste should be taken into account for the complete conversion of CaSO4‧2H2O into CaSO4‧0.5H2O. Phosphogypsum is a by-product of the production of phosphorus-containing mineral fertilizers and phosphoric acid [8]. These large-tonnage wastes are removed from the territories of enterprises to sludge storages, which turn out to be environmental pollutants. Phosphogypsum contains from 80 to 98% gypsum and can be classified as a gypsum raw material, so the most promising areas for the utilization of phosphogypsum is its use in the production of gypsum binders. However, the presence in their composition of acidic fluorine- and phosphorus-containing impurities, which pass into the gaseous phase during heat treatment, significantly complicates the direct use of phosphogypsum as a high-temperature or low-temperature binder. To overcome the negative impact of steam and gas emissions on the environment in the technological process of obtaining "pure gypsum", as a rule, procedures are used to neutralize and wash off waste phosphogypsum [9, 10]. This leads to significant capital and energy costs and hinders the large-scale processing of this type of waste. Phosphogypsum can be used in the cement industry to produce Portland cement, as well as a mineralizer during firing and an additive in clinker grinding [11]. Phosphogypsum can be used as an additive and filler in mixed binders without the use of heat treatment to obtain phospho concrete [12, 13].
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