Facile fabrication of dolomite-doped biochar/bentonite for effective removal of phosphate from complex wastewaters

The removal of phosphate from wastewater using traditional biological or precipitation methods is a huge challenge.The use of high-performance adsorbents has been shown to address this problem.In this study,a novel composite adsorbent,composed of dolomite-doped biochar and bentonite(DO/BB),was first synthesized via co-pyrolysis.The combination of initial phosphate concentration of 100 mg/L and 1.6 g/L of DO/BB exhibited a high phosphate-adsorption capacity of 62 mg/g with a removal efficiency of 99.8%.It was also stable in complex water environments with various levels of solution pH,coexisting anions,high salinity,and humic acid.With this new composite,the phosphate concentration of the actual domestic sewage decreased from 9 mg/L to less than 1 mg/L,and the total nitrogen and chemical oxygen demand also decreased effectively.Further,the cross-flow treatment using a PVC membrane loaded with DO/BB(PVC-DO/BB),decreased the phosphate concentration from 1 to 0.08 mg/L,suggesting outstanding separation of phosphate pollutants via a combination of adsorption and separation.In addition,the removal of phosphate by the PVC-DO/BB membrane using NaOH solution as an eluent was almost 90%after 5 cycles.The kinetic,isotherm and XPS analysis before and after adsorption suggested that adsorption via a combination of electrostatic interaction,complexation and precipitation contributed to the excellent separation by the as-obtained membranes.

Fabrication of recyclable Fe^(3+) chelated aminated polypropylene fiber for efficient clean-up of phosphate wastewater

Herein,a Fe^(3+)-loaded aminated polypropylene fiber has been reported as an efficient phosphate adsorbent.The remarkable phosphate removal ability of the fiber is due to Fe^(3+)immobilization,and it demonstrates a maximum adsorption capacity of 33.94 mg·P·g^(–1).Adsorption experiments showed that the fiber is applicable over a wide pH range from 2 to 9.Furthermore,the adsorption kinetics and isotherm data were consistent with the pseudo-second-order and Langmuir adsorption models,respectively.The adsorption equilibrium of the fiber for phosphate was reached within 60 min,indicating an efficient monolayer chemisorption process.Moreover,the adsorbent maintained prominent phosphate removal in the presence of competitive ions such as NO_(3)^(–)and Cl^(–),exhibiting high selectivity.More importantly,the fiber demonstrated excellent reusability(5 times)and low adsorption limit below 0.02 mg·P·g^(–1).In addition,the phosphate removal efficiency of the fiber can exceed 99%under continuous flow conditions.The adsorption mechanism was studied by X-ray photoelectron spectroscopy,showing that the adsorption of phosphate on the fiber mainly depended on the chemical adsorption of the modified Fe^(3+).Overall,this study proves that the fiber possesses many advantages for phosphate removal,including high adsorption efficiency,lower treatment limit,good recyclability,and environmental friendliness.

Phosphate removal by a La(OH)_(3) loaded magnetic MAPTAC-based cationic hydrogel:Enhanced surface charge density and Donnan membrane effect

Cationic hydrogels have received great attention to control eutrophication and recycle phosphate.In this study,a type of La(OH)_(3) loaded magnetic MAPTAC-based cationic hydrogel(La(OH)_(3)@MMCH)was developed as a potential adsorbent for enhanced phosphate removal from aqueous environment.La(OH)_(3)@MMCH exhibited high adsorption capacity of 105.72±5.99 mg P/g,and reached equilibrium within 2 hr.La(OH)_(3)@MMCH could perform effectively in a wide pH range from 3.0 to 9.0 and in the presence of coexisting ions(including SO_(4)^(2-),Cl^(-),NO_(3)^(-),HCO_(3)^(-),SiO_(4)^(4-) and HA).The adsorption-desorption experiment indicated that La(OH)_(3)@MMCH could be easily regenerated by using NaOH-NaCl as the desorption agent,and 73.3%adsorption capacity remained after five cycles.Moreover,La(OH)_(3)@MMCH was employed to treat surface water with phosphate concentration of 1.90 mg/L and showed great removal efficiency of 95.21%.Actually,MMCH showed high surface charge density of 34.38-59.38 meq/kg in the pH range from 3.0 to 11.0 and great swelling ratio of 3014.57%within 24 h,indicating that MMCH could produce the enhanced Donnan membrane effect to pre-permeate phosphate.Furthermore,the bifunctional structure of La(OH)_(3)@MMCH enabled it to capture phosphate through electrostatic attraction and ligand exchange.All the results prove that La(OH)_(3)@MMCH is a promising adsorbent for eutrophication control and phosphate recovery.

Improved utilization of active sites for phosphorus adsorption in FeOOH/anion exchanger nanocomposites via a glycol-solvothermal synthesis strategy

Metal oxide/hydroxide-based nanocomposite adsorbents with porous supporting matrices have been recognized as efficient adsorbents for phosphorus recovery.Aiming at satisfying increasingly restrictive environmental requirements involving improving metal site utilization and lowering metal leakage risk,a glycol-solvothermal confined-space synthesis strategy was proposed for the fabrication of Fe OOH/anion exchanger nanocomposites(Fe/900s)with enhanced metal site utilization and reduced metal leakage risk.Compared to composites prepared using alkaline precipitation methods,Fe/900s performed comparably,with a high adsorption capacity of 19.05 mg-P/g with an initial concentration of 10 mg-P/L,a high adsorption selectivity of 8.2 mg-P/g in the presence of 500 mg-SO_(4)^(2-)/L,and high long-term resilience(with a capacity loss of~14%after five cycles),along with substantially lower Fe loading amount(4.11 wt.%)and Fe leakage percentage.Mechanistic investigation demonstrated that contribution of the specific Fe OOH sites to phosphate adsorption increased substantially(up to 50.97%under the optimal conditions),in which Fe(Ⅲ)-OH was the dominant efficient species.The side effects of an excessively long reaction time,which included quaternary ammonium decomposition,Fe OOH aggregation,and Fe(Ⅲ)reduction,were discussed as guidance for optimizing the synthesis strategy.The glycol-solvothermal strategy provides a facile solution to environmental problems through nanocrystal growth engineering in a confined space.

Highly efficient P uptake by Fe3O4 loaded amorphous Zr-La (carbonate) oxides: Electrostatic attraction, inner-sphere complexation and oxygen vacancies acceleration effect

Bimetallic oxides composites have received an increasing attention as promising adsorbents for aqueous phosphate (P) removal in recent years. In this study, a novel magnetic composite MZLCO was prepared by hybridizing amorphous Zr-La (carbonate) oxides (ZLCO) with nano-FeOthrough a one-pot solvothermal method for efficient phosphate adsorption. Our optimum sample of MZLCO-45 exhibited a high Langmuir maximum adsorption capacity of 96.16 mg P/g and performed well even at low phosphate concentration. The phosphate adsorption kinetics by MZLCO-45 fitted well with the pseudo-second-order model, and the adsorption capacity could reach 79% of the ultimate value within the first 60 min. The phosphate adsorption process was highly p H-dependent, and MZLCO-45 performed well over a wide p H range of 2.0-8.0. Moreover, MZLCO-45 showed a strong selectivity to phosphate in the presence of competing ions (Cl^(-), NO_(3)^(-), SO_(4)^(2-), HCO_(3)^(-), Ca^(2+), and Mg^(2+)) and a good reusability using the eluent of Na OH/Na Cl mixture, then 64% adsorption capacity remained after ten recycles. The initial 2.0 mg P/L in municipal wastewater and surface water could be efficiently reduced to below 0.1mg P/L by 0.07 g/L MZLCO-45, and the phosphate removal efficiencies were 95.7% and 96.21%, respectively. Phosphate adsorption mechanisms by MZLCO-45 could be attributed to electrostatic attraction and the inner-sphere complexation via ligand exchange forming Zr/La-O-P, -OH and CO_(3)^(2-)groups on MZLCO-45 surface played important roles in the ligand exchange process. The existence of oxygen vacancies could accelerate the phosphate absorption rate of the MZLCO-45 composites.