Development of novel sand binder to address treatment challenges in sodium silicate bonded waste foundry sands containing cristobalite polymorph
摘要
A novel geopolymeric binder system overcoming the irreversible cristobalite-induced polymorphic change of sodium silicate bonded waste foundry sands is presented. Attempts to treat the sand through conventional treatment methods such as thermal shock, ultra sonication, and acid or alkali treatments have proven to be ineffective in restoring binding properties. X-ray diffraction analysis (peak at 2θ value of 22.00°) and Fourier Transform Infrared Spectroscopy analysis (absorption band at 621 cm−1) showed that the cristobalite phase remained stable even after treatment, limiting the sand’s reusability with sodium silicate binders and failing to improve its binding properties. The novel binder system used sodium aluminate in combination with alkali activators like sodium silicate and sodium hydroxide to effectively bind sodium silicate bonded waste foundry sand. Laboratory-scale sand moulds made with this geopolymeric binder system were thermally cured at 100 °C for 2 h, achieving a Core Hardness of 60–85. X-ray Diffraction analysis of the moulds revealed peaks of sodium aluminium silicate, a geopolymeric mineral responsible for the mould’s strength. The new binder system allowed the sand moulds to be reused multiple times, with each batch meeting the required Grain Fineness Numbers in the range of 40–51 and Core Hardness standards (minimum 60) through multiple reuse cycles.