Synergy of Boron Containing Solid Wastes and Fructose for the Production of Lightweight Aggregates: Microstructure and Properties

Abstract

In Turkey 400,000 t/year of boron containing solid wastes are produced. The production of lightweight aggregates is a promising way to valorise these wastes. In the development of a suitable process the main disadvantage is borate migration towards the surface of the green pellets that causes excessive liquid phase formation during firing and subsequent sticking of the aggregates together or with the refractory lining of the kiln. In order to address this problem, fructose was added in the raw mix as a migration inhibitor, in 0.5 and 3.0 wt% respectively. The results have shown that 3.0 wt% of fructose lead to a sticky plastic mass whereas the pellets present no volume expansion during firing. The optimal results were obtained for 0.5 wt% of fructose addition, which inhibited the salt formation and a glassy impervious layer was formed after firing. For abrupt heating at 720 and 760 °C for 2 min, pellets were produced with porosity varying from 58 to 63 % and bulk density from 0.8 to 0.9 g/cm3. The individual compressive strength value of these samples was measured at 0.18 and 0.39 MPa, for 720 and 760 °C, respectively. The microstructure is comprised predominantly of a matrix with extended vitrified regions with both open and closed pores. Taking into account the relative low compressive strength values and the high water absorption, the possible applications of the boron containing lightweight aggregates could be insulation, geotechnical application, gardening and/or horticulture.