The influence of foundry wastes on the quality of autoclaved sand-lime materials

The paper presents the results of research on the possibility of reusing selected types of foundry waste, i.e. used molding and core sands and dust obtained in the process of their regeneration, as alternative or supplementary materials in relation to the quartz sand originally used in manufacturing of sand-lime bricks. In the production technology of sand-lime products, quartz sand is used as aggregate. A rational factor in favor of such a technological solution is the high content of crystalline silica in the waste molding and core sands, in which the mineral matrix is composed of good quality quartz sands. The research concept covers production of a series of samples of autoclaved silicate materials formed by pressing, from raw material mixtures involving the discussed waste materials. In the laboratory tests conducted for the preparation of autoclaved materials of the sand-lime brick type, apart from traditional raw materials in the form of natural quartz sand and burnt lime, different molding waste and/or core sand materials and post-regenerative dusts were used for composing raw material mixtures. Foundry industry wastes were introduced into the basic raw material based on the gradually increasing substitution of quartz sand, in the amount within the range of 0 - 100% (wt. %). The assessment of the possibility of using the discussed waste materials in the indicated direction was based on the result of a comparative analysis, covering the main functional characteristics of two types of materials, i.e. reference material, obtained from raw material mixture, containing no waste and series of experimental materials, produced with various quantitative and qualitative contributions of waste materials. The characteristics of the obtained autoclaved materials are also supplemented by the results of the leaching tests, for heavy metal elements and the analysis of selected aspects of the microstructure carried out by the SEM and EDAX method. The results of the research show that it is possible to use casting waste compounds after their processing, in the production of autoclaved sand-lime products. This processing of wastes is two-stage operation. The purpose of the first stage is to restore the primary graining of quartz sand used to obtain foundry moulds and cores, while the second stage is to remove the organic binder residues that appear on the quartz sand grains in the form of thin layers hindering the reaction with burnt lime.