A Novel Approach for Continuous Uptake of Phosphate Using Feooh Hydrogel Beads with Phosphorus Accumulation for Recovery

Abstract

Due to the rapid depletion of global phosphorus reserve and widespread eutrophication of waterbodies caused by excessive phosphorus discharge, efficient removal and recovery of phosphorus from aquatic systems become urgent. Although various materials have been developed with satisfactory capacities of phosphorus adsorption, the high adsorbent-adsorbate affinity often increases the difficulty of desorption and consequently the cyclic operation. In this study, a desorption-independent regeneration method for a FeOOH-loaded hydrogel beads (FOH-HB), as an efficient phosphorus adsorbent, was developed to improve its long-term efficacy and thereby the economic feasibility in real application. The results show that FOH-HB exhibited a maximum adsorption capacity of 24.2 mg/g at 25 °C, being 1.4-fold higher than that of commercialized granular FeOOH. At an initial phosphorus concentration of 1.5 mg/L, the adsorption capacity at equilibrium remained stable for 10 adsorption-regeneration cycles. The improved stability of adsorption within the cycles is attributed to the regeneration method, using alkali and calcium solutions, that continuously produced new adsorption sites because the desorbed phosphate by the alkali treatment (as a conventional desorption method) was marginal. The increase in calcium content and the enhanced Ca-P interactions on the FOH-HB surface reveals that the loaded Ca2+ during the regeneration and the subsequent formation of Ca-PO4 and Fe-PO4-Ca minerals played an important role in the phosphorus adsorption cycles. As such, the developed regeneration method in this study enables continuous phosphate removal without degradation of its adsorption capacity, providing a promising solution for the treatment of agricultural runoff and remediation of phosphorus-contaminated water bodies.

Keywords: Phosphate, Adsorption, amorphous FeOOH, regeneration, calcium, layered precipitation