title: Adsorption of phosphonate antiscalant from reverse osmosis membrane concentrate onto granular ferric hydroxide.
abstract: Adsorptive removal of antiscalants offers a promising way to improve current reverse osmosis (RO) concentrate treatment processes and enables the reuse of the antiscalant in the RO desalination process. This work investigates the adsorption and desorption of the phosphonate antiscalant nitrilotris(methylenephosphonic acid) (NTMP) from RO membrane concentrate onto granular ferric hydroxide (GFH), a material that consists predominantly of akaganéite. The kinetics of the adsorption of NTMP onto GFH was predicted fairly well with two models that consider either combined film-pore or combined film-surface diffusion as the main mechanism for mass transport. It is also demonstrated that NTMP is preferentially adsorbed over sulfate by GFH at pH 7.85. The presence of calcium causes a transformation in the equilibrium adsorption isotherm from a Langmuir type to a Freundlich type with much higher adsorption capacities. Furthermore, calcium also increases the rate of adsorption substantially. GFH is reusable after regeneration with sodium hydroxide solution, indicating that NTMP can be potentially recovered from the RO concentrate. This work shows that GFH is a promising adsorbent for the removal and recovery of NTMP antiscalant from RO membrane concentrates.
authors.affiliation: Wetsus, Centre of Excellence for Sustainable Water Technology, Leeuwarden, The Netherlands. luciaan.boels@wetsus.nl
authors.forename: Luciaan
authors.initials: L
authors.lastname: Boels
authors.forename: Karel J
authors.initials: KJ
authors.lastname: Keesman
authors.forename: Geert-Jan
authors.initials: GJ
authors.lastname: Witkamp
mesh_terms: D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D008958:Models, Molecular; D009943:Organophosphorus Compounds / Q000302:isolation & purification*; D009995:Osmosis; D054712:Salinity; D018508:Water Purification
chemical_list: D005290:Ferric Compounds; D009943:Organophosphorus Compounds; C041182:(nitrilotris(methylene))triphosphonic acid; C021024:ferric hydroxide