Regulating the Performance of Calcium Aluminate Produced from Secondary Aluminum Dross Based on Quaternary Basicity: Broadening the Range of Raw Materials for Water Treatment Chemicals

Abstract

As wastewater treatment expands and discharge standards tighten, water environmental management faces growing pressure. A novel method for regulating the performance of calcium aluminate produced from secondary aluminum dross (SAD) for water treatment chemicals based on quaternary basicity (R4) was proposed in this study. The results indicated that CaO played a double-edged role in the performance of calcium aluminate. While CaO could improve the solubility of calcium aluminate, it also diluted the Al2O3 content. CaO·2Al2O3 and CaO·Al2O3 exhibited the best filtration and dissolution properties. CaO/Al2O3 molar ratio (C/A) was the key determining the calcium aluminate phases, but MgO and SiO2 would interfere with it. They would preferentially form MgAl2O4 and Ca2Al2SiO7 during roasting. The formation of MgAl2O4 and Ca2Al2SiO7 would alter the effective C/A. This would shift the products from CaO·2Al2O3 and CaO·Al2O3 to CaO·6Al2O3 and 12CaO·7Al2O3, reducing product performance. By controlling R4 at 0.84–1.04, MgO/Al2O3 molar ratio (M/A) < 0.08, calcium aluminate products meeting the requirements of a filtration time <3 min, soluble Al2O3 content >47%, and acid-insoluble content <15% could be produced using various types of SAD. This study provided a reliable formulation and low-cost aluminum source for preparing calcium aluminate used in water treatment chemicals.