Abstract
Kinetics of phosphate adsorption by Ca/Cr layered double hydroxide (LDH) in a batch reactor was investigated in this study. The kinetic experiments indicated that the sorption of phosphate from the synthetic feed solution by the synthesised LDH was very fast, with over 98% removal being achieved within 5 min of contact. Kinetic modeling of the sorption process to different kinetic models (pseudo first order, pseudo second order, Elovich and intraparticle diffusion) showed that the pseudo-second order model best described the process. Studies of effect of hydrochemistry on the sorption process such as initial solution pH, ionic strength and organic load contamination interference, indicated nominal effect on the amount of phosphate removed by the LDH. Overall, the study indicated that chemisorption and precipitation are active contributory mechanisms to the sorption of phosphate by Ca/Cr LDH from solution. Key words: Adsorption kinetics, chemisorption, layered double hydroxide, phosphate removal, precipitation.
Highlights
With large quantities of phosphates being used for various industrial processes, most especially fertilizer production, which invariably generates large volumes of phosphate-bearing waste effluents, its removal from waste effluents is of prime importance to prevent inherent problems associated with its discharge in the environment
Layered double hydroxides (LDHs) called anionic clays are widely used as adsorbents and anion exchangers with huge selectivity for phosphate removal from aqueous system (Novillo et al, 2014)
Due to the high ion-exchange properties of LDHs for the selective uptake of polyatomic anions including phosphate from aqueous system, this study was carried out to assess the kinetics of phosphate removal from a synthetic feed phosphate wastewater in a batch sorption process by CaCr LDH
Summary
With large quantities of phosphates being used for various industrial processes, most especially fertilizer production, which invariably generates large volumes of phosphate-bearing waste effluents, its removal from waste effluents is of prime importance to prevent inherent problems associated with its discharge in the environment. Adsorptive treatment is more appealing because of cost effectiveness, simplicity of design, ease of operation and a remarkable high possibility of phosphate recovery for reuse. Layered double hydroxides (LDHs) called anionic clays are widely used as adsorbents and anion exchangers with huge selectivity for phosphate removal from aqueous system (Novillo et al, 2014). Due to the high ion-exchange properties of LDHs for the selective uptake of polyatomic anions including phosphate from aqueous system, this study was carried out to assess the kinetics of phosphate removal from a synthetic feed phosphate wastewater in a batch sorption process by CaCr LDH. Kinetic studies are usually undertaken by evaluating the effect of initial sorbate concentration, sorbent dosage, sorbent particle size, agitation speed, pH and/or temperature on the adsorption process. Effects of process variables (pH, ionic strength and organics contamination) on the sorption process were investigated and reported
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