A new approach to sustainable management of industrial phosphogypsum waste: mechanism exploration and industrial application

• MCA was prepared by mixed commercial CaO with Butanol and then used for curing PG • Fast curing speed, high curing efficiency and long stability were achieved • Soluble P and F in PG were transformed to fluorapatite with extremely low Ksp • MCA was practically applied to PG curing with an industrial scale of 0.79 Mt A novel inexpensive modified calcium oxide (MCA) was prepared using commercial calcium oxide (CCO) and n- butanol and applied to curing phosphogypsum (PG) waste. With the MCA, the soluble phosphorus (SP), soluble fluoride (SF) and pH of PG changed from 230.6 mg/L, 180.7 mg/L and 2.89 drastically to 0.46 mg/L, 8.3 mg/L and 8.58 after 3 days, meeting the GB8978-1996 (SP≤0.5 mg/L, SF≤10 mg/L, pH = 6∼9), remaining stable even after 90 days. Our mechanism study revealed that the MCA reacted with SP to form amorphous CaHPO 4 which further tranformed to Ca 5 (PO 4 ) 3 OH. Ca 5 (PO 4 ) 3 OH combined with SF to produce Ca 5 (PO 4 ) 3 F (K sp =2.1 × 10 -59 ). Compared to CaF 2 and CaHPO 4 , the K sp of Ca 5 (PO 4 ) 3 F decreased markedly by approximately 10 48 and 10 52 times. More importantly, in this work MCA has been industrially applied to cure 790,000-tons PG. Moritoring for more than 500 days showed that the SP, SF and pH values met the GB8976-1996 standard continuously. This study demonstrated a promising new approach to sustainable management of industrial PG waste by treating PG with the novel inexpensive MCA to solidify SF and SP into precipitates of Ca 5 (PO4) 3 F with greatly improved long-term stability.