skip to main content


Title: A review of phosphate adsorption on Mg-containing materials: kinetics, equilibrium, and mechanistic insights
Significant efforts have been made to remove excess nutrient phosphorus in the form of aqueous phosphate ions from various wastewater streams to mitigate adverse environmental consequences to the watershed, such as eutrophication. Adsorption has long been a low-cost and highly effective method of phosphate removal which chiefly relied on immobilizing this valuable nutrient in low solubility solids. Magnesium-based adsorbents are emerging as an economically feasible solution to the phosphate removal problem that have the added benefit of facilitating nutrient recycling via the production of slow-release fertilizer. The current scientific literature on Mg-based adsorbents for phosphate has focused on a diverse range of techniques for the resulting material characterization, adsorption equilibrium and the observed kinetics making direct comparison between the diverse Mg-based adsorbents difficult. This tutorial review aims (a) to provide an overview of the state of the art in Mg-based phosphate adsorbents and (b) to propose a generalized data interpretation roadmap necessary to bridge the gap between the observed fundamental kinetics and mechanistic insights reported in the literature.  more » « less
Award ID(s):
1710120
NSF-PAR ID:
10292511
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Environmental Science: Water Research & Technology
Volume:
6
Issue:
12
ISSN:
2053-1400
Page Range / eLocation ID:
3178 to 3194
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    Heavy metal ions are highly toxic and widely spread as environmental pollutants. This work reports the development of two novel chelating adsorbents, based on the chemical modifications of graphene oxide and zirconium phosphate by functionalization with melamine-based chelating ligands for the effective and selective extraction of Hg( ii ) and Pb( ii ) from contaminated water sources. The first adsorbent melamine, thiourea-partially reduced graphene oxide (MT-PRGO) combines the heavier donor atom sulfur with the amine and triazine nitrogen's functional groups attached to the partially reduced GO nanosheets to effectively capture Hg( ii ) ions from water. The MT-PRGO adsorbent shows high efficiency for the extraction of Hg( ii ) with a capacity of 651 mg g −1 and very fast kinetics resulting in a 100% removal of Hg( ii ) from 500 ppb and 50 ppm concentrations in 15 second and 30 min, respectively. The second adsorbent, melamine zirconium phosphate (M-ZrP), is designed to combine the amine and triazine nitrogen's functional groups of melamine with the hydroxyl active sites of zirconium phosphate to effectively capture Pb( ii ) ions from water. The M-ZrP adsorbent shows exceptionally high adsorption affinity for Pb( ii ) with a capacity of 681 mg g −1 and 1000 mg g −1 using an adsorbent dose of 1 g L −1 and 2 g L −1 , respectively. The high adsorption capacity is also coupled with fast kinetics where the equilibrium time required for the 100% removal of Pb( ii ) from 1 ppm, 100 ppm and 1000 ppm concentrations is 40 seconds, 5 min and 30 min, respectively using an adsorbent dose of 1 g L −1 . In a mixture of six heavy metal ions at a concentration of 10 ppm, the removal efficiency is 100% for Pb( ii ), 99% for Hg( ii ), Cd( ii ) and Zn( ii ), 94% for Cu( ii ), and 90% for Ni( ii ) while at a higher concentration of 250 ppm the removal efficiency for Pb( ii ) is 95% compared to 23% for Hg( ii ) and less than 10% for the other ions. Because of the fast adsorption kinetics, high removal capacity, excellent regeneration, stability and reusability, the MT-PRGO and M-ZrP are proposed as top performing remediation adsorbents for the solid phase extraction of Hg( ii ) and Pb( ii ), respectively from contaminated water. 
    more » « less
  2. null (Ed.)
    Nutrient nitrogen (N) and phosphorus (P) recovery from wastewater is an important challenge for enhanced environmental sustainability. Herein we report the synthesis and properties of mesoporous MgO nanoparticles doped with copper (Cu), iron (Fe), and zinc (Zn) as an alternative low-solubility high-abundance magnesium (Mg) source for crystalline struvite precipitation from nutrient-laden wastewater. Undoped MgO was shown to have the fastest phosphate (PO 4 3− ) adsorption kinetics with a k 2 value of 0.9 g g −1 min −1 at room temperature. The corresponding rate constant decreased for Cu–MgO (0.175 g g −1 min −1 ), Zn–MgO (0.145 g g −1 min −1 ), and Fe–MgO (0.02 g g −1 min −1 ). Undoped MgO resulted in the highest PO 4 3− removal at 94%, while Cu–MgO, Fe–MgO, and Zn–MgO resulted in 90%, 66% and 66%, respectively, under equivalent reaction conditions. All dopants resulted in the production of struvite as the main product with the incorporation of the transition metals into the struvite crystal lattice. X-ray absorption spectroscopy (XAS) showed that the majority of the Cu, Fe, and Zn were primarily in the +2, +3, and +2 oxidation states, respectively. XAS also showed that the Cu atoms exist in elongated octahedral coordination, while Fe was shown to be in octahedral coordination. Zn was shown to be in a complex disordered environment with octahedral sites coexisting with the majority of the tetrahedral sites. Finally, X-ray photoelectron spectroscopy data suggest a two-fold struvite surface enrichment with dopant metals, with Cu exhibiting an interesting new local binding structure. The dopant concentrations utilized were consistent with those found in natural Mg minerals, suggesting that (a) utilizing natural mineral periclase as the Mg source for struvite production can result in struvite formation, albeit at the expense of the reaction kinetics and overall yields, while also (b) supplying essential micronutrients, such as Zn and Cu, necessary for balanced nutrient uptake. 
    more » « less
  3. Slag and Al/Mg oxide modified Douglas fir biochar (AMOB) were compared for their phosphate adsorbing abilities for use individually or in combination for simulated agriculture run-off remediation in wetlands. Aqueous batch and column sorption experiments were performed for both low-cost materials. AMOB was prepared in bulk using a novel green method. Material analyses included XRD, elemental analysis, SEM, EDX, and BET. Biochar and slag have different phosphate removal mechanisms. In short residence times (≤2 h), adsorption phenomena dominate for both adsorbents. Surface area likely plays a role in adsorption performance; slag was measured to be 4.1 m2/g while biochar’s surface area was 364.1 m2/g. In longer residence times (>2 h), the slow leaching of metals (Ca, Al, and Mg) from slag continue to remove phosphate through the precipitation of metal phosphates. In 24 h, slag removed more free phosphate from the solution than AMOB. Preliminary fixed bed column adsorption of slag or AMOB alone and in tandem was performed adopting a scaled-up model that can be used to remediate agricultural runoff with high phosphate content. Additionally, a desorption study was performed to analyze the efficiency of material regeneration. While AMOB does not release any adsorbed phosphates, slag slowly releases 5.7% adsorbed phosphate over seven days. 
    more » « less
  4. Abstract Practitioner points

    Existing reversible phosphate (Pi) adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity in their chemical structure.

    Co‐recovery of As(V) with Pican reduce the recovered product's reuse as a fertilizer.

    An immobilized phosphate‐binding protein (PBP)‐based system can be highly selective for Pieven in the presence of As(V).

    Piconstituted more than 97% of the recovered product, even when As(V) was present at 2‐fold higher concentrations than Pi.

    Immobilized PBP offers advantages over existing Piadsorbents by providing high‐purity Piproducts free of As(V) contamination for reuse.

     
    more » « less
  5. In this study, a suite of natural wastewater sources is tested to understand the effects of wastewater composition and source on electrochemically driven nitrogen and phosphorus nutrient removal. Kinetics, electrode behavior, and removal efficiency were evaluated during electrochemical precipitation, whereby a sacrificial magnesium (Mg) anode was used to drive precipitation of ammonium and phosphate. The electrochemical reactor demonstrated fast kinetics in the natural wastewater matrices, removing up to 54% of the phosphate present in natural wastewater within 1 min, with an energy input of only 0.04 kWh.m−3. After 1 min, phosphate removal followed a zero-order rate law in the 1 min - 30 min range. The zero-order rate constant (k) appears to depend upon differences in wastewater composition, where a faster rate constant is associated with higher Cl− and NH4+ concentrations, lower Ca2+ concentrations, and higher organic carbon content. The sacrificial Mg anode showed the lowest corrosion resistance in the natural industrial wastewater source, with an increased corrosion rate (vcorr) of 15.8 mm.y−1 compared to 1.9–3.5 mm.y−1 in municipal wastewater sources, while the Tafel slopes (β) showed a direct correlation with the natural wastewater composition and origin. An overall improvement of water quality was observed where important water quality parameters such as total organic carbon (TOC), total suspended solids (TSS), and turbidity showed a significant decrease. An economic analysis revealed costs based upon experimental Mg consumption are estimated to range from 0.19 $.m−3 to 0.30 $.m−3, but costs based upon theoretical Mg consumption range from 0.09 $.m−3 to 0.18 $.m−3. Overall, this study highlights that water chemistry parameters control nutrient recovery, while electrochemical treatment does not directly produce potable water, and that economic analysis should be based upon experimentally-determined Mg consumption data. 
    more » « less