Pyrolyzed Ca-impregnated lignite for aqueous phosphate removal: Batch and column studies

Lignite is an abundant carbon material with a variable surface structure and low cation density The introduction of metal (hydr)oxide phases has improved the anionic binding potential lignite. In this study, activated lignite (A−L), Ca2+−modified (Ca−L), (Ca−A−L) were synthesized to remove aqueous phosphate. was first (KOH: lignite, mass ratio, 3:1) at 750 ºC prepare A−L, improving its area by ~984-fold. Ca−L (27 wt% Ca) showed large phosphate uptake (227.3 mg/g) (adsorbent dose 50 mg, 25 mL 10–1500 ppm phosphate, 24 h, °C, initial pH 6), due amounts micro-sized CaCO3, Ca(OH)2, CaO particles in Ca−L. These actively precipitate phosphate/hydrophosphate as CaHPO4/Ca3(PO4)2. breakthrough capacity 2.0 g bed column (bed height 2.5 cm, diameter 1 cm) 58.2 mg/g (flow rate 1.5 mL/min, ºC, [PO43-] = 46.6 mg/L, particle size, 125–150 µm), ~4 fold lower than maximum Langmuir sorption capacity. An interference study indicated that highly selective for Spent may improve soil fertility it retains more species later slow-release soil. Unit weight can be removed inexpensively Norit ROW Darco KB (two commercial carbons). Precipitated Ca2+ phosphates/hydrophosphates exhausted recovered using HCl recycled. Moreover, low-cost promising support future synthesis different value-added products.