Production of Lightweight Aggregates from Different Types of Boron Wastes

Abstract

Four boron wastes (BW), named as Sieve (SBW), Dewatering (DBW), Thickener (TBW) and Mixture (MBW) waste, from Kirka plant (Turkey) were investigated for the formation of Artificial Lightweight Aggregates (LWA). The characterization involved chemical, mineralogical and thermal analyses. The bloating behavior was examined by heating microscopy. SBW and DBW expanded in two stages, at 300°C approximately and subsequently at 550°C with concurrent formation of liquid phase. However, at 650-700°C there is excessive liquid phase formed resulting in large, non uniform porosity of irregular shape. On the contrary, in the case of TBW and MBW no noticeable expansion or glassy surface was formed. An optimization route, involved the formation of a mixture with 20wt% clay, 40wt% SBW, 40wt% DBW and one with 20wt% clay, 35wt% SBW, 35wt% DBW, 10wt% quartz sand. The raw aggregates were fired in a rotating crucible at 650°C, 700°C, 710°C and 760°C for 2-5 min. It was observed that the clay addition leads to better plasticity and cohesion between the particles whereas the quartz addition shifts the softening point 50°C higher. Water absorption was 56.8-60.5%, apparent specific gravity 2.3-2.4g/cm and bulk density 0.9-1.1g/cm3. The analysis of microstructure with electron microscopy revealed a glassy phase matrix and an extended formation of both open and closed pores. The results indicate that SBW and DBW boron wastes can be utilized in LWA production.