Insights into the mechanism involved by electric double layer on phosphate removal of metal-bearing environmental remediation agent: Taking tricalcium aluminate as representative.

Metal-bearing materials are known to be desirable environmental captures for phosphate removal, yet few studies focus on understanding the reaction process, especially formed a special phenomenon, i.e., electric double layer (EDL), which might influence the phosphate removal. To fill in this gap, we fabricated metal-bearing tricalcium aluminate (C3A, Ca3Al2O6) as representative, to remove phosphate and unveil the impact by electric double layer (EDL). Specifically, a preeminent removal capacity of 142.2 mg·g-1 was achieved at the initial phosphate concentration below 300 mg·L-1. Following thorough the characterizations, the process was that the released Ca2+ or Al3+ of C3A formed positive charged stern layer attracted phosphate to generate Ca or Al-precipitation. At high phosphate concentration (>300 mg·L-1), C3A exhibited inferior removal capability for phosphate (<45 mg·g-1), due to the aggregation of C3A particles with low water permeability under the EDL effect, obstructing Ca2+ and Al3+ to release for phosphate removal. In addition, the feasibility application of C3A was evaluated based on response surface methodology (RSM), highlighting its prospective phosphate treatment. This work not only provides a theoretical guidance for the application of C3A to remove phosphate, but also deepens the understand of phosphate removal mechanism by metal-bearing materials, shedding light on environmental remediation.

A novel magnesium-rich tricalcium aluminate for simultaneous removal of ammonium and phosphorus: Response surface methodology and mechanism investigation.

Coexisting ammonium (NH4+-N) and phosphate (PO43--P) in wastewater is one of the main causes of eutrophication, which poses severe risks to aquatic ecosystem and human health worldwide. Herein, magnesium-rich tricalcium aluminate (Mg/C3A), which was constructed by incorporating Mg into cement-based material C3A via solid-state reaction, was employed in the simultaneous removal of NH4+-N and PO43--P. Considering the wastewater with unbalanced N/P ratio and fluctuant pH, the effect of multiple factors (Mg/C3A dosage, pH, initial contaminant concentration, and temperature) on the removal of both ions were systematically investigated by employing response surface methodology technique. The results demonstrated that the impact order of the factors on the NH4+ removal by Mg/C3A was: temperature > Mg/C3A dosage > initial NH4+ concentration > pH > initial PO43- concentration; the impact order on the PO43- removal was: initial PO43- concentration > Mg/C3A dosage > temperature > pH > initial NH4+ concentration. The maximum removal amount of NH4+ (54.13 mg g-1) and PO43- (56.47 mg g-1) were obtained at: Mg/C3A dosage = 3 g L-1, initial NH4+ concentration = 160 mg L-1, initial PO43- concentration = 160 mg L-1, temperature = 308 K, and pH = 7. In addition, the possible interactive influence mechanisms were elucidated in depth. Mg2+ played a major role in the PO43- removal by forming struvite (MgNH4PO4·6H2O) and newberyite (MgHPO4·3H2O). OH- released from Mg/C3A hydration mainly contributed to NH4+ removal. This work showed that Mg-rich C3A is a promising candidate for simultaneous removal of NH4+ and PO43-, shedding light on practical water remediation.

The enhancement roles of sulfate on the adsorption of sodium dodecylsulfate by calcium-based layered double hydroxide: microstructure and thermal behaviors.

As a commonly used surfactant, sodium dodecyl sulfate (SDS) usually coexists with inorganic anions in the industrial wastewater. These anions have a significant influence on SDS removal, indirectly threatening the environment. It is important to understand the relationship between the adsorption of SDS and inorganic anions. In this study, calcium-based layered double hydroxide (CaAl-LDH-Cl) as an efficient adsorbent was synthesized for investigating the effect of SO42- on SDS removal. The SDS adsorption capacities were enhanced to 3.21 and 4.21 mmol g-1 in the presence of SO42- with low/high SDS concentration, respectively. The phenomenon and mechanism were confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Scanning electron microscopy (SEM). Anionic exchange played a dominant role in the adsorption of SDS onto CaAl-LDH-Cl at DS-/SO42- < 2, while both anion exchange and precipitation occurred when DS-/SO42- exceeded 2. Moreover, the thermal analysis (TG-DTA) was employed to further reveal the interaction mechanism. The results showed the highest total mass loss and the lowest loss temperature of interlayer water in the sulfate coexist system, confirming the enhancement of SDS adsorption amount in the presence of SO42-.

Effect of anion co-existence on ionic organic pollutants removal over Ca based layered double hydroxide.

The effects of co-existing anions (NO3- or SO42-) on the removal of sodium dodecylsulfate (SDS), representing anionic organic pollutants, by Ca-based layered double hydroxide (CaAl-LDH-Cl) are investigated to provide fundamental insights on the ionic surfactant removal in the presence of co-existing anions, and facilitate the establishment of a practical and advanced water treatment for environmental remediation. The SO42- system shows higher adsorption capacity (4.43 mmol·g-1) and larger d-spacing of adsorption resultant (3.4 nm) than the control system with no co-existing anion (3.64 mmol·g-1, 3.25 nm) and the NO3- system (3.82 mmol·g-1, 3.27 nm). The macroscopic and microscopic analyses reveal that, NO3- had a little influence on the SDS removal due to strong electrolysis, while SO42- could significantly promote the SDS removal. Moreover, the reaction mechanism varies under different molar ratios of DS-/SO42-.