Pyrolyzed Ca-impregnated lignite for aqueous phosphate removal: Batch and column studies. Issue 5 (October 2021)

• Record Type: Journal Article
• Authors: Samaraweera, Hasara; Edwards, John; Reid, Claudia; Perera, S. Sameera; Thirumalai, Rooban Venkatesh K.G.; Pittman, Charles U.; Mlsna, Todd
• Is Part Of: Journal of environmental chemical engineering. Volume 9:Issue 5(2021)
• Publication Date: 2021-10
• Subjects: Lignite coal -- Phosphate ions -- Adsorption -- Breakthrough curve -- Desorption -- Selectivity; Chemical engineering -- Environmental aspects -- Periodicals; Environmental engineering -- Periodicals; Chemical engineering -- Environmental aspects; Environmental engineering; Periodicals; 660.0286
• DOI: 10.1016/j.jece.2021.106077
• Languages: English
• ISSNs: 2213-2929

Abstract

Abstract: 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 of lignite. In this study, activated lignite (A−L), Ca 2+ −modified lignite (Ca−L), and Ca 2+ −modified activated lignite (Ca−A−L) were synthesized to remove aqueous phosphate. Lignite was first activated (KOH: lignite, mass ratio, 3:1) at 750 ºC to prepare A−L, improving its surface area by ~984-fold. Ca−L (27 wt% Ca) showed a large phosphate uptake (227.3 mg/g) (adsorbent dose 50 mg, 25 mL of 10–1500 ppm phosphate, 24 h, 25 °C, initial pH 6), due to the large amounts of micro-sized CaCO3, Ca(OH)2, and CaO particles in Ca−L. These particles actively precipitate phosphate/hydrophosphate as CaHPO4 /Ca3 (PO4 )2 . The breakthrough capacity of a 2.0 g Ca−L bed column (bed height 2.5 cm, diameter 1 cm) was 58.2 mg/g (flow rate 1.5 mL/min, 25 ºC, initial [PO4 3- ] = 46.6 mg/L, particle size, 125–150 µm), ~4 fold lower than the maximum Langmuir sorption capacity. An interference study indicated that Ca−L is highly selective for phosphate. Spent Ca−L may improve soil fertility as it retains more phosphate species for later slow-release to the soil. Unit weight of phosphate can be removed by Ca−L more inexpensively than Norit ROW and Darco KB (two commercial activated carbon carbons). Precipitated Ca 2+ phosphates/hydrophosphates in exhausted Ca−L can be recovered using HCl and Ca−L recycled. Moreover, low-cost lignite is a promising carbon support for the future synthesis of different value-added products. Graphical Abstract: ga1 Highlights: KOH activation at 750 ºC produced a highly porous lignite carbon (A−L). Micro CaCO3, Ca(OH)2, and CaO particles on Ca−L gave a high PO4 3- uptake. Ca−L removed PO4 3- by stoichiometric precipitation of CaHPO4 /Ca3 (PO4 )2. Low unit weight of phosphate removal cost reported by Ca−L. Phosphate column capacity of Ca−L is 4-times less than its Langmuir capacity.