DIFFERENT CONCENTRATIONS OF SODIUM HYDROXIDE CAUSTIC LEACHING OF CR6+ FOR REFINEMENT OF CALCIUM SOURCE FROM DENTAL MOULD WASTE
Dental mould is a component used in making the model structures of patient-specific dentures in treating tooth defects. It will be disposed once the patient obtains their dentures. Dumping these non-biodegradable wastes into the landfills, particularly the green dental mould waste (DMW-type 3) which is characterized as calcium sulphate dihydrate (CaSO4.2H2O) containing-chromium. CaSO4.2H2O can produce odorous hydrogen sulfide gas as well as introducing toxic chromium into soil. The current study aimed to process DMW via alkaline roasting followed by caustic leaching to remove chromium and subsequently converting it into high purity calcium hydroxide (Ca(OH)2). The ground DMW powder was mixed with sodium carbonate (Na2CO3) and roasted at 1000°C for an hour. The roasted samples were then proceeded with caustic leaching using 5, 7 and 10M of sodium hydroxide (NaOH). The effect of different concentrations of NaOH on chromium removal were investigated. Our finding showed that chromium could be efficiently leached out up to 94% using 7M NaOH. The white residue powder was an indication of the efficiency of chromium removal, which was then confirmed by X-ray Fluorescence (XRF) analysis. This is supported by X-ray Diffraction (XRD) analysis, demonstrating the formation of portlandite (Ca(OH)2) phase. The synthesized Ca(OH)2 powder observed under Field Emission Scanning Electron Microscopy (FESEM) showed highly agglomerated with presence of needle-shape or fibrous-like particles. Transforming this calcium-rich DMW into Ca(OH)2, which then can be used as a source of raw material in making bone substitute material is thought to be one of the sustainable approaches in preserving our environment.