•Lanthanum modified zeolite (LMZ) was prepared from coal fly ash.•LMZ greatly reduced P levels in water overlying sediment within 212 day period.•Release of P from sediment under high pH or anoxic conditions was impeded by LMZ.•Releasable P species in sediment was converted to stable species by adding LMZ.•LMZ was shown to be a promising material to control internal P loading in lakes.Tackling the release of phosphorus (P) from sediments remains a challenge to mitigating the eutrophication of lakes. The current study investigated the efficacy of lanthanum-modified zeolite (LMZ), which was developed from coal fly ash via a one-pot process, to reduce P levels in a simulated water–sediment system. LMZ was dosed to bind releasable P fractions (i.e., labile P, reductant-soluble P, NaOH-P, and organic P fractions) in sediment of shallow lakes. LMZ treatment was found to be effective at decreasing the P concentration in water overlying sediment. On average, total P and soluble-reactive P were reduced by 81.1% and 86.9% in a 28-day sediment core incubation experiment and by 57.1% and 72.8% in a 212-day mesocosm experiment, respectively. LMZ decreased P release from sediment under high pH value (∼10.0) and anoxic conditions by 45.8% and 87.4% for total P and by 52.9% and 94.0% for soluble-reactive P, respectively. Adding LMZ induced a change of P in sediment from releasable P fractions to refractory P forms. Although aquatic parameters interfered with P binding, increasing the LMZ dosage enhanced the effect of LMZ. The control of internal phosphorus loading by LMZ was explained as follows: (i) capture of P from water; (ii) inhibition of P release from sediment; (iii) enhancement of P retention capacity of sediment; and (iv) inactivation of sediment P via the formation of stable P forms.Download high-res image (164KB)Download full-size image

•The composite of zeolite and hydrous zirconia was prepared from coal fly ash.•Surfactant was successfully loaded onto the composite creating a patchy bilayer.•The surfactant modified composite (SMZFA/HZ) was investigated as a new adsorbent.•SMZFA/HZ was able to adsorb cationic, anionic, and organic pollutants from water.•SMZFA/HZ was a better versatile adsorbent than previously developed SMZFA.Surfactant modified zeolite from coal fly ash (SMZFA) was previously developed as a multi-functional adsorbent. But its ability to capture anionic pollutants depends on the type and composition of coal fly ash and the synthesis process of zeolite (ZFA), the precursor of SMZFA, produces waste alkaline solution. To tackle these problems, the composite of zeolite and hydrous zirconia (ZFA/HZ) was synthesized by neutralizing waste alkaline solution with zirconium salt and was then modified with the surfactant of hexadecyltrimethylammonium to develop a new type of multi-functional adsorbent, SMZFA/HZ. The obtained materials were evaluated for their performances to sequester multiple classes of pollutants from water. The target pollutants include cationic pollutant (ammonium), anionic pollutant (phosphate) and organic pollutants (humic acid and bisphenol A). Results showed that, when compared with ZFA, ZFA/HZ had 3 times higher adsorption capacity for phosphate, and more negative charges on both external (by 16.9%) and internal surfaces (by 12.3%). For both ZFA and ZFA/HZ, modification with surfactant reduced the capacity for uptake of ammonium by less than 10% and the reduction was trivial for phosphate. However, surfactant modification greatly augmented the adsorption performances for humic acid and bisphenol A. Compared with SMZFA, SMZFA/HZ was found to have higher potential for the retention of each pollutant and is thus a more excellent versatile adsorbent.

•Zeolite/hydrous zirconia composite material (ZHZ) was prepared from coal fly ash.•SRP concentration in pond water was efficiently decreased by adding ZHZ.•Capping of sediment with ZHZ caused enduring P inactivation in the 28 day period.•ZHZ stabilized sediment and reduced turbidity, TP and SRP after resuspension.A unique sediment-capping agent consisting of a zeolite/hydrous zirconia composite (ZHZ) was developed and tested for P-immobilization in the overlying water and sediment cores from a freshwater pond. In the ZHZ, NaP1 zeolite was covered with hydrous zirconia, which existed as an amorphous phase. Experimental results in pond water indicated that ZHZ could efficiently remove soluble reactive phosphorus. The 28-day sediment incubation experiments showed that capping sediment with ZHZ resulted in a more efficient, rapid and sustained decrease in P concentration when compared with the traditional alum treatment method. Furthermore, ZHZ increased the sediment stability, resulting in the lowest turbidity, total phosphorus and soluble reactive phosphorus concentrations in overlying water following artificially induced resuspension of sediment. Phosphorus fractionation of sediment showed that the dominant P form transferred from HCl-extractable P to residual P, and the most release-sensitive P (labile P and reductant reactive P) was decreased after ZHZ application. Overall, ZHZ is a highly effective P-immobilization material. ZHZ has high potential as a sediment capping material to control internal P loading in eutrophic water bodies.Download high-res image (92KB)Download full-size image

Hydrous lanthanum oxide was loaded onto the surface of Fe3O4@SiO2 core/shell magnetic nanoparticles to obtain an easily separable adsorbent (abbreviated as Fe–Si–La) for efficient separation of phosphate from water. Fe–Si–La was characterized with XRF, XRD, TEM, specific surface area and magnetization and their performance for phosphate removal was investigated. The Fe3O4@SiO2 core/shell structure was confirmed and the hydrous lanthanum oxide was successfully loaded onto its surface. The newly developed adsorbent had magnetization of 51.27 emu/g. The Langmuir adsorption capacity of phosphate by Fe–Si–La reached 27.8 mg/g by loading only 1 mmol lanthanum per gram of magnetite. The adsorption was fast; nearly 99% of phosphate could be removed within 10 min. The removal of phosphate was favored within the pH range 5.0–9.0. The adsorption on Fe–Si–La was not significantly influenced by ionic strength and by the coexistence of the anions of chloride and nitrate but sulfate, bicarbonate and humic acid showed slightly greater negative effects. Phosphate removal efficiency of higher than 95% was attained for real effluent of a wastewater treatment plant when the dose of adsorbent was >0.2 kg/ton. The results showed that adsorbed phosphate could be nearly completely desorbed with NaOH solution for further use. In conclusion, Fe–Si–La is a promising adsorbent for the removal and recovery of phosphate from water.

•Zeolite/hydrous lanthanum oxide composite was synthesized from coal fly ash.•The material was highly efficient to capture phosphate from lake water.•The performance of phosphate removal was correlated with properties of lake water.•pH effect and pH reversibility of phosphate adsorption was investigated.•The material showed additional ability to retain cationic pollutants.We investigated the use of coal fly ash as a raw material for the production of a zeolite/hydrous lanthanum oxide hybrid material (ZHLO) and as a means of controlling internal phosphorus loading in lakes. We found that the use of ZHLO, as a method for capturing phosphate from five lake water samples, was considerably more efficient than the existing alum-treatment method. There was some variability in the performance of the ZHLO-method in different lake waters but we noted that, within the La/P molar ratio range of between 2:1 and 4:1, we were able to attain an almost-complete removal of phosphate. Correlation analysis indicated that high alkalinity reduced the performance of phosphate binding. Phosphate adsorption by ZHLO was found to decrease with increasing pH. The phosphate adsorbed at acidic pH levels was partly released with increasing pH, while phosphate that was in equilibrium solution at high pH was adsorbed when the pH declined. The extent of reversibility when using the ZHLO method was much lower than that observed when using the alum treatment method. FTIR measurements showed that the monodentate surface species of ≡La-OPO3 was formed via a ligand exchange mechanism. Moreover, ZHLO could also function as a means of removing cationic pollutants. This has important implications in terms of preventing the release of toxic substances (such as manganese and ammonium) from sediments in eutrophic lakes.

•Spinel zinc ferrite was prepared with a facile solvothermal technique.•The saturation magnetization was 34.95 emu/g, allowing easy magnetic separation.•Zinc ferrite showed good performance for phosphate removal from water.•The adsorption was shown to be an endothermic and spontaneous process.To develop a phosphate adsorbent in powder form that is easily separated from water, we prepared magnetic spinel zinc ferrite using a facile solvothermal technique. Characterization of zinc ferrite was done by VSM, XRD, TEM, and FTIR measurements. We found that zinc ferrite crystallized as a cubic ZnFe2O4 phase (JCPDS card no. 89-1010). It had a saturation magnetization of 34.95 emu/g, which allowed easy separation using a magnet. Phosphate adsorption under different initial phosphate concentrations, solution pH values, ionic strengths, temperatures, contact times, as well as in the presence of competitive ions, was investigated. Data from kinetic experiments fit well the pseudo-second-order model. The maximum adsorption capacity obtained by fitting adsorption isotherm data to the Langmuir model ranged within 5.23–6.28 mg/g at different temperatures. Thermodynamic parameters indicate that phosphate adsorption by zinc ferrite is an endothermic and spontaneous process. The amount of phosphate adsorbed increased with decreasing pH and increasing ionic strength. Zinc ferrite showed good selectivity for phosphate. Results suggest that phosphate adsorbed onto the zinc ferrite surface via formation of an inner-sphere complex.

•Activated aluminum oxide (AAO) and lanthanum oxide (LO) had high P removal ability.•P adsorption capacity was 20.88 mg/g for the former and 46.95 mg/g for the latter.•Efficient phosphate removal was achieved at pH <~ 5.0 for AAO and pH <~ 10.5 for LO.•The adsorption by the oxides was interpreted by the ligand exchange mechanism.•Adsorbed P could be recovered by acid treatment or basic treatment.Phosphorus is a non-renewable resource for food production in modern agriculture and a leading cause of eutrophication in water bodies. Both the removal and recovery of phosphorus from water/wastewater are important. The phosphate adsorption performances of activated aluminum oxide (AAO) and lanthanum oxide (LO) have been investigated. Langmuir adsorption capacities for AAO and LO of 20.88 mg/g and 46.95 mg/g, respectively, were attained. Efficient phosphate removal by AAO could only be achieved under acidic pH conditions (<~ 5.0), whereas that by LO was not greatly influenced at pH < 10.5. The adsorption mechanism is interpreted as a ligand-exchange process, and a surface complex of monodentate nonprotonated species (≡ La–OPO3) has been identified by FTIR for LO. The adsorption of phosphate is quite selective, especially for LO. The dosages required to lower a phosphate concentration level of around 5.0 mg P/L to < 0.5 mg P/L were determined as 0.08–0.1 g/L for LO and 1.2 g/L for AAO, respectively. The adsorbed phosphate could be completely desorbed by treatment with 0.1 M NaOH for AAO, while for LO both acid treatment (0.5 M HCl) and basic treatment (12.5 M NaOH) were viable.

Highlights•A natural zeolite was modified by surfactants with varying carbon chain length.•Adsorption of organic pollutants by modified zeolite was investigated.•Adsorption increased with increasing surfactant chain length.•The chain length, amount and conformation of surfactant are crucial in adsorption.•More hydrophobic compounds were preferably adsorbed by surfactant modified zeolite.Surfactant modified zeolites are promising for decontamination of organic pollutants from water. However, the influence of chain length of surfactants on decontamination process has not been clarified to our knowledge. In this study, a natural zeolite was modified with surfactants of varying chain length (from one carbon to 22 carbons) and the adsorption of organic contaminants, including anionic (sodium form of humic acid), ionizable (phenol, p-chlorophenol and bisphenol A), and non-ionizable compounds (naphthalene) was investigated. Results showed that the amount of surfactant loaded increased with increasing chain length. Measurement of FTIR spectroscopy indicated that the surfactant chains adopted a more disordered conformation as the chain length decreases. In general, the adsorption of the organic pollutants increases as the chain length increases. We noted that long chain length, high surfactant coverage, and ordered chain conformation are driving forces for the retention of organic chemicals. The pH dependency of adsorption suggested that negatively charged groups of anionic or ionizable organic solutes interacted with positively charged head of surfactant. Furthermore, adsorption increased with increasing kow value for organic pollutants, indicating that hydrophobic interaction of the benzene ring(s) of organic compounds with the carbon chain of surfactant contributes to adsorption.

Since the first successful synthesis of zeolite from coal fly ash (ZFA) in 1985, the preparation and application of ZFA has been intensively investigated to recycle the solid waste. However, problems arising from the waste alkaline solution have rarely been addressed to date. This study initiated a novel method to synthesize ZFA/Al2O3 hybrid material by introducing a reaction step involving the neutralization of the waste alkaline solution with soluble Al salts into the traditional ZFA synthesis route. When compared with ZFA, ZFA/Al2O3 was found to have a significantly higher CEC. The increases of the BET surface area and phosphate-immobilization capacity were even more dramatic, with the former increasing by 2–4 times and the latter increasing by 2–3 times. The hybrid material had a significantly lower alkalinity than ZFA. The results also showed that the effluent from the production of the hybrid material could be much more environmentally friendly.

A zeolite (ZFA) was synthesized from coal fly ash and then modified using hexadecyltrimethylammonium. The surfactant modified ZFA (SMZFA) was evaluated for its versatility to sequester multiple classes of pollutants from water. The target pollutants include ionic inorganic pollutants (ammonium and phosphate), ionic organic pollutants (methylene blue and humic acid), ionizable organic pollutants (bisphenol A, ρ-chlorophenol and phenol, with different pKa), and electrically neutral organic pollutants (aniline, nitrobenzene, and naphthalene, with different hydrophobicity). The SMZFA showed high potential for the retention of ammonium and phosphate, being comparable with ZFA. While the negative charge in the internal pores of zeolite was responsible for the retention of ammonium, the oxides of CaO, Al2O3 and Fe2O3 in the non-zeolite fraction, which originated from coal fly ash but received modification during zeolite synthesis, accounted for the removal of phosphate. Results also showed that while ZFA had little affinity for humic acid, the ionizable, and the electrically neutral organic compounds, SMZFA exhibited greatly enhanced adsorption capacity. Thus, the surfactant modified external surface, which formed a bilayer micelle of zeolite, imparts a hydrophobic characteristic that enables the uptake of the organic pollutants. We showed that SMZFA is a promising versatile sorbent for water treatment.

Zeolite synthesized from coal fly ash (ZFA) was modified with hexadecyltrimethylammonium (HDTMA) and was examined for the adsorption of bisphenol A (BPA) from water. Two ZFAs were prepared in our laboratory and were characterized to obtain chemical and mineralogical composition, surface area, and total and external cation-exchange capacity among other parameters. HDTMA was confirmed to form bilayer micelles on external surfaces of zeolites. Results indicate that, while ZFA had no affinity for BPA, the surfactant-modified ZFA (SMZFA) showed greatly enhanced adsorption capacity. Uptake of BPA was greatly influenced by pH, increasing at alkaline pH conditions which enable the deprotonation of BPA to form organic anions. The SMZFA with higher BET area and higher amount of loaded HDTMA showed greater retention for BPA. Uptake of BPA by SMZFA was improved slightly in the presence of NaCl, and was enhanced at a low temperature. We propose that BPA anions interact strongly with the positively charged heads of HDTMA, with the two hydrophobic benzene rings of BPA pointing to the inside of HDTMA bilayers. The adsorption of uncharged BPA probably involved hydrophobic partitioning into HDTMA bilayers and the coordination of the oxygen atoms of BPA with positively charged heads of HDTMA.Modification of zeolite with surfactant greatly enhanced the retention of bisphenol A from water. This figure shows the possible interaction mechanisms of bisphenol A with surfactant-modified zeolite.

This research was initiated to determine the effects of different constituents and properties of zeolite synthesized from fly ash (ZFA) on Cr(III) sorption. The uptake of Cr(III) by ZFA was influenced greatly by pH, increasing with the increase in pH. The pH was controlled mainly by calcium-related components (especially CaCO3 and free CaO) and zeolite components in ZFAs. Sorption maximum of Cr(III) (QmQm), determined by a repeated batch equilibration method, ranged from 22.29 to 99.91 mg/g for the 14 ZFAs. The QmQm value correlated significantly with Ca-related components. The correlation coefficients were 0.9467, 0.5469, 0.7521, and 0.9195 for total Ca, CaCO3, CaSO4, and f.CaO, respectively. The QmQm value was also closely related to cation-exchange capacity (r=0.6872r=0.6872) and specific surface area (r=0.7249r=0.7249). Correlation coefficients of QmQm with dissociated Fe2O3 and Al2O3 were much higher than those of total Fe and total Al contents, respectively. It was suggested that, in ZFAs, zeolite and iron oxide acted as ion exchanger and adsorbent for Cr(III), respectively, while Ca components elevated the pH of the reaction system and consequently promoted ion exchange and adsorption and caused the surface precipitation of chromium hydroxide.Both the zeolite component and the nonzeolite component in zeolites synthesized from fly ashes contributed to sorption of Cr(III). The figure shows that the calcium component could increase pH and thus enhance sorption.

Discharge of wastewater containing nitrogen and phosphate can cause eutrophication. Therefore, the development of an efficient material for the immobilization of the nutrients is important. In this study, a low calcium fly ash and high calcium fly ash were converted into zeolite using the hydrothermal method. The removal of ammonium and phosphate that coexist in aqueous solution by the synthesized zeolites were studied. The results showed that zeolitized fly ash could efficiently eliminate ammonium and phosphate at the same time. Saturation of zeolite with Ca2+ rather than Na+ favored the removal of both ammonium and phosphate because the cation exchange reaction by the NH4+ resulted in the release of Ca2+ into the solution and precipitation of Ca2+ with PO43− followed. An increase in the temperature elevated the immobilization of phosphate whereas it abated the removal of ammonium. Nearly 60% removal efficiency for ammonium was achieved in the neutral pH range from 5.5 to 10.5, while the increase or decrease in pH out of the neutral range lowered the adsorption. In contrast, the removal of phosphate approached 100% at a pH lower than 5.0 or higher than 9.0, and less phosphate was immobilized at neutral pH. However, there was still a narrow pH range from 9.0 to 10.5 favoring the removal of both ammonium and phosphate. It was concluded that the removal of ammonium was caused by cation exchange; the contribution of NH3 volatilization to immobilization at alkaline conditions (up to pH level of 11.4) was limited. With respect to phosphate immobilization, the mechanism was mainly the formation of precipitate as Ca3(PO4)2 within the basic pH range or as FePO4 and AlPO4 within acidic pH range.

•Hydrous zirconia–coated magnetite was used for phosphate capture.•Regulation of pH was able to enhance P removal in the presence of coexisting ions.•Phosphate was coordinated onto zirconium by replacement of hydroxyl groups.•The material could be easily separated from water for reuse by a magnet.•Desorption of phosphate from the material could be achieved with NaOH treatment.Owing to the easy magnetic separation from water for reuse, magnetic nanoparticles have drawn great interest as adsorbents. Herein hydrous zirconia-coated magnetite nanoparticles (Fe3O4@ZrO2) were created by a facile method and a bench–scale study was undertaken to evaluate its effectiveness and mechanism to remove phosphate at low concentrations. Results indicated that phosphate removal by Fe3O4@ZrO2 was fast (95% of phosphate removal within 10 min) and nearly complete removal could be achieved at the adsorbent dosage >0.6 g/L. In tap water or wastewater where competitive anions coexist, regulation of pH was found to be quite effective to augment the performance of phosphate removal. In pH–lowered adsorption systems, phosphate removal followed a good pattern similarly to pure water, i.e., a continuous high efficiency removal followed by a rapid saturation. Adsorption–desorption–regeneration studies showed that Fe3O4@ZrO2 could be repeatedly used for phosphate removal and adsorbed phosphate could be stripped for recovery. The fractionation of adsorbed phosphorus suggested that NaOH-P fraction was dominant. We also found that the adsorption reaction of phosphate with Fe3O4@ZrO2 shifted the isoelectric point of Fe3O4@ZrO2 from ~9.0 to ~3.0. FTIR measurements further showed the direct coordination of phosphate onto zirconium by replacement of hydroxyl groups. The formation of the monodentate (ZrO)PO2(OH) complex was proposed.Download high-res image (142KB)Download full-size image

•Hybrid materials of zeolite/hydrous metal oxides were prepared from coal fly ash.•The materials showed high adsorption ability for the removal of methylene blue.•Adsorption of methylene blue increased with increasing pH.•Adsorption was very fast and removal efficiency reached ~ 100% at suitable doses.•Heating plus pH adjustment was viable to regenerate the materials for further use.Zeolites are useful crystalline aluminosilicate minerals, and zeolite synthesis from coal fly ash (ZFA) has been investigated widely to recycle solid waste. This synthesis process produces waste alkaline solution as a by-product. To date, research has focused mainly on ZFA synthesis and use; the problematic waste alkaline solution has rarely been addressed. In this study, we developed two composites of zeolite/hydrous iron oxide (ZFA/HIO) and zeolite/hydrous zirconia (ZFA/HZ) by adding, after zeolite synthesis, a step in which waste alkaline solutions are neutralized with an iron or zirconium salt. The composites were characterized by X-ray fluorescence, X-ray diffractometry, scanning electron microscopy, acid–base neutralizing ability, specific surface area and pore size distribution, and their performance as adsorbents for the removal of methylene blue (MB) from water was investigated. MB adsorption by ZFA/HIO and ZFA/HZ was much higher than that by ZFA, and increased with increasing pH. This behavior was explained by the increased variable charge on the metal oxides. The adsorption was rapid, and nearly complete removal could be achieved at a sufficiently high dose. Material heating resulted in a decrease in pH and adsorption, but heating with pH adjustment could regenerate adsorbents for repeated use in MB removal. Zeolite/hydrous metal oxide synthesis from coal fly ash was environmentally friendly and products exhibit a high potential as reusable adsorbents for MB removal from water.