UTILISATION OF INDUSTRIAL MINING BY-PRODUCTS FOR THE PRODUCTION OF HEAVY CLAY CERAMICS

摘要

In the present study, the valorisation of mining and industrial by-products, the solid boron-containing Wastes (BWs), which are created at various stages during the production process of concentrated and refined boron products, were investigated. The byproducts under consideration, existing in five types SBW, DBW, SSBW, TBW and MBW, were used as additives, as well as raw materials in clay mixtures for the production of heavy clay ceramics (bricks, tiles and artificial lightweight aggregates). The BW were characterised in means of chemical and mineralogical composition and studied for their thermal behaviour. Clay mixtures with different amounts of BWs (SBW and SSBW) were studied. A first approach was made on the formation of rectangular ceramic samples by dry pressing in order to minimize the borate migration towards the surface. The physical and mechanical properties, as well as the microstructure of the final products were studied. For 5 wt% SSBW addition and firing at 900-950°C, the sintered bodies presented comparable or improved physical and mechanical properties with respect to the reference formulation. Moreover, SBW or a commercial available borate solution (Evansite~R) were introduced in a clay-based mixture aiming to investigate their behaviour during a processing cycle comparable with that followed in the heavy clay industry. For firing at 1000°C, water absorption was reduced and bending strength increased for the samples with borates, compared to the reference samples. The addition of borates resulted in the formation of new crystalline phases during firing at high temperatures. BWs consist of important fluxing oxides as well as of gas producing minerals during firing.Tests were performed on the bloating behavior of BWs and mixes of them with other materials, by means of heating microscopy, aiming on the laboratory production of lightweight aggregates (LWA). A new mix was proposed, according to the obtained results, consisting of 70wt% BWs, 20wt% clay mixture and 10wt% quartz sand, for the formation of pellets. Abrupt heating of the dry pellets at 760°C, for 5min, resulted in porous LWA with bulk density