Valorisation of different types of boron-containing wastes for the production of lightweight aggregates.

Four boron-containing wastes (BW), named as Sieve (SBW), Dewatering (DBW), Thickener (TBW) and Mixture (MBW) waste, from Kirka Boron plant in west Turkey were investigated for the formation of artificial lightweight aggregates (LWA). The characterisation involved chemical, mineralogical and thermal analyses as well as testing of their bloating behaviour by means of heating microscopy. It was found that SBW and DBW present bloating behaviour whereas TBW and MBW do not. Following the above results two mixtures M1 and M2 were prepared with (in wt.%): 20 clay mixture, 40 SBW, 40 DBW and 20 clay mixture, 35 SBW, 35 DBW, 10 quartz sand, respectively. Two different firing modes were applied: (a) from room temperature till 760 °C and (b) abrupt heating at 760 °C. The obtained bulk density for M1 and M2 pellets is 1.2g/cm(3) and 0.9 g/cm(3), respectively. The analysis of microstructure with electron microscopy revealed a glassy phase matrix and an extended formation of both interconnected and isolated, closed pores. The results indicate that SBW and DBW boron-containing wastes combined with a clay mixture and quartz sand can be valorised for the manufacturing of lightweight aggregates.