Phosphorus desorption and recovery from aqueous solution using amorphous zirconium hydroxide/MgFe layered double hydroxides composite

Global phosphorus scarcity implies the importance of phosphorus recovery. Desorption is an essential process in phosphate removal by adsorption technique by enabling two crucial aspects: the reusability of adsorbent and the recovery of phosphorus. In this study, phosphate desorption by NaOH for composite reusability and phosphorus recovery by CaCl2 were investigated. Based on the cost analysis, the uncalcined amorphous zirconium hydroxide/MgFe layered double hydroxides composite (am-Zr/MgFe-LDH) with Zr to Fe molar ratio of 1.5 was effective in reducing cost for phosphate adsorption compared to amorphous zirconium hydroxide (am-Zr) and MgFe layered double hydroxide (LDH). The XRD analysis indicated that phosphate desorption was preferably performed by stripping adsorbed phosphate on the composite surface using NaOH solution. The reuse of 2 N NaOH for composite regeneration could effectively maintain a higher adsorption ability (86%) than 1 N NaOH, and additionally, could be considered as an economic regeneration agent. The composite was chemically stable in maintaining its structure during eight adsorption-desorption cycles. The mechanisms involved during phosphate desorption by NaOH were mainly ligand exchange and electrostatic repulsion. The phosphorus recovery showed that the optimum recovery (~95%) was obtained by adding CaCl2 at pH 13 and calcium to phosphorus molar ratio of 3.5.

Preparation of Synthetic Clays to Remove Phosphates and Ibuprofen in Water

The main objective of this study consists in the synthesis of a layered double hydroxide (LDH) clay doped with magnesium and aluminum in order to test the removal of phosphates and ibuprofen in water. Two different LDH composites are assessed: oven-dried (LDHD) and calcined (LDHC). Single adsorptions of phosphate and ibuprofen showed up to 70% and 58% removal in water, when LDHC was used. A poorer performance was observed for LDHD, which presented adsorption efficiencies of 52% and 35%, respectively. The simultaneous removal of phosphate and ibuprofen in water showed that LDHC allows a greater reduction in the concentration of both compounds than LDHD. Phosphate adsorption showed a close agreement between the experimental and theoretical capacities predicted by the pseudo-second-order model, whereas ibuprofen fitted to a first-order model. In addition, phosphate adsorption showed a good fit to an intraparticle diffusion model and to Bangham model suggesting that diffusion into pores controls the adsorption process. No other mechanisms may be involved in ibuprofen adsorption, apart from intraparticle diffusion. Finally, phosphate desorption could recover up to 59% of the initial concentration, showing the feasibility of the recuperation of this compound in the LDH.

Novel Application of Hybrid Anion Exchange Resin for Phosphate Desorption Kinetics in Soils: Minimizing Re-Adsorption of Desorbed Ions

The process of phosphate desorption from soils is difficult to measure using stirred batch techniques because of the accumulation of desorbed ions in a bathing solution. To accurately measure the apparent rate coefficient of phosphate desorption from soils, it is necessary to remove the desorbed ions. In this study, a novel hybrid (i.e., iron oxide coated) anion exchange resin was used as a sink to study long-term (seven days) P desorption kinetics in intensively managed agricultural soils in the Midwestern U.S. (total phosphorus (TP): 196–419 mg/kg). The phosphate desorption kinetics in the hybrid anion exchange resin method were compared with those in the other conventional batch desorption method with pure anion exchange resins or without any sink. The extent of P desorption in the hybrid resin methods was >50% of total desorbed phosphate in the other methods. The initial kinetic rate estimated in the pseudo-second-order kinetic model was also highest (3.03–31.35 mg/(g·hr)) in the hybrid resin method when the same soil system was compared. This is because adsorbed P in the hybrid resins was nearly irreversible. The hybrid anion exchange resin might be a new and ideal sink in measuring the P desorption process in soils and sediments.

Removal and Recovery of Phosphate from Water and Wastewater Using Metal-Loaded Agricultural Waste-Based Adsorbents: A Review

There is a growing research interest in the development of adsorbents based on agricultural wastes (AWs) for the removal of phosphate from waste water sources, which otherwise can cause eutrophication. Nevertheless, due to the lack of active exposed surface sites, raw AWs-based adsorbents are usually inefficient for the adsorption of phosphate from aquatic environment. Consequently, modification of raw adsorbents has been frequently used to improve their phosphate adsorption capacity. Of the various methods of modification, this review paper focused on most widely used chemical modification method. It presents a critical and comprehensive review of the literature on the effectiveness of metal-loaded agricultural wastes (MLAWs)-based adsorbents in removing and recovering of phosphate from waste waters. Mechanisms and factors affecting phosphate adsorption as well as phosphate desorption and regeneration from MLAW adsorbents are critically evaluates. If phosphate from waste waters can be of economical value, regeneration may partly overcome the future shortage of global phosphate rock reserves. It is evident from the literature survey presented herein that MLAWs-based adsorbents exhibited as potential adsorbent for the removal/recovery of phosphate from waste waters. However, there still needs a refined practical utility of these adsorbents on a commercial scale, which may serve as the novel, cost effective and environmentally benign methods of modification.