Maximum Phosphate Adsorption Capacity Research Articles

Biochar produced from tobacco stalks, eggshells, and Mg for phosphate adsorption from a wide range of pH aqueous solutions

Preparing biochar from tobacco stalks modified with Mg is a feasible way to utilize tobacco stalks as a resource. However, the capacity of phosphate removal of Mg-biochar is affected greatly with increasing pH. In the present work, biochar produced from the tobacco stalks was modified via Mg addition and eggshells during the preparation for improving the phosphate adsorption performance at higher pH. The results revealed that the theoretical maximum adsorption capacity of phosphate for the biochar increased from 110.62 to 272.37 mg P/g when the mass ratio of Mg to tobacco stalk increased from 0.12:1 to 0.48:1 (M-C). The adsorption capacity of the biochar with a mass ratio of 0.3:1 (M-C2) was more than 200 mg P/g in the pH range of 3 to 7 but with further increase of pH from 7 to 12 the capacity decreased from 205 to 135.2 mg P g−1. Addition of eggshells with the magnesium solution during the dipping process can effectively improve the capacity of the modified biochar for phosphate in the alkaline condition. When the mass ratio of eggshell to tobacco stalk was ≥0.25:1, the phosphate adsorption capacities of the biochar can reach above 200 mg P/g within a wide pH range of 3 to 12, and the maximum adsorption capacity can reach more than 270 mg P g−1 for the mass ratio of 1:1 (EM-C24). The characterization results demonstrated that Ca and Mg were loaded on the biochar. The high adsorption performance provides reference values for the utilization of tobacco stalks and eggshells.

Facile design of UiO-66-NH2@La(OH)3 composite with enhanced efficiency for phosphate removal

Excessive phosphate in wastewater can cause eutrophication of water body, which will worsen the ecological environment and threaten human health and biological life safety. Adsorption of phosphate is the most effective way to remove phosphate, and efficient adsorbent is the key. Amorphous La(OH)3 has been deemed as a potential phosphate adsorbent on account of high adsorption capacity and environmentally friendly property. However, it also shows some disadvantages such as easy agglomeration, poor water dispersion. In this study, UiO-66-NH2 was used as carrier to load amorphous lanthanum hydroxide as an adsorbent for phosphate removal. The adsorbent (UiO-66-NH2@La(OH)3, ULCs) has good water dispersibility and it is easy to be separated and recovered. At the same time, the maximum phosphate adsorption capacity can reach 140.7 mg P/g. The adsorption process accords with pseudo second order kinetic model and Freundlich isotherm model. The thermodynamic results showed that the adsorption process was spontaneous and endothermic. In addition, in the presence of coexisting anions (such as Cl−, SO42−, NO3−), it also exhibited high selectivity and phosphate removal efficiency. Meanwhile, the adsorption capacity keeps at a high level in the range of pH 3–11. By the merit of above-mentioned properties, the prepared material is expected to be an ideal candidate for phosphate removal from contaminated water.

La(OH)3 nano-rods/polyacrylonitrile nanofibers: fabrication, characterization and application for phosphate removal.

In this study, an excellent phosphate adsorbent was prepared for removing phosphate to an extremely low concentration. The La(OH)3 nano-rods stabilizing in polyacrylonitrile (PAN) nanofibers (PLNFs) were prepared by electrospinning and a subsequent in situ precipitation. PAN nanofibers were employed as the matrix of the composite nanofibers, where the well-dispersed La(OH)3 nano-rods were encapsulated as the active species for highly efficient phosphate capture owing to the strong binding between phosphate and lanthanum. On account of the nano-structure, the maximum phosphate adsorption capacity was 151.98 mg P/g (La), much higher than the result of La(OH)3 nano-crystal, produced by precipitation without PAN or any organic surfactants. Moreover, the PLNFs could remove phosphate (2 mg P/L) to an extremely low concentration within 20 min, which could lead to a nutrient deficient condition to protect water quality and ecosystem. The optimization of PLNFs design was implemented through parameter adjustment of electrospinning. Lanthanum salt content, humidity, concentration of solution and applied voltage were chosen to analyze the influences on the composition, diameter and morphology of the nanofibers, giving the result that the most effective adsorbent was the PLNFs with spider-web-like nano-structures.

Influence of Ca2+ on phosphate removal from water using a non-core-shell Fe3O4@ZIF-67 composites

Excessive phosphate in surface water can spur the growth of organism, which put a threat on the bio-safety of drinking water. Different from previous study, sodium acetate (NaAc) was used as modification agent of Fe3O4, then the magnetic Fe3O4@ZIF-67 composites with a non-core-shell sturture were synthesized. According to ZIF-67 loading and phosphate adsorption of synthesized Fe3O4@ZIF-67, the Fe3O4@ZIF-67 composites with a Co2+/Fe3O4 molar ratio of 1:2 was taken into further evaluation. Fe3O4@ZIF-67 composites exhibited satisfactory adsorption performance and easy magnetic recovery, and the sorption capacity reached 116.59 mg P/g within 180 min (C0 = 20 mg P/L, 298 K). The maximum adsorption capacity of phosphate was obtained at the neutral pH, and not significantly interfered with ions of K+, Mg2+, NO3− and SO42-. Remarkably, Fe3O4@ZIF-67 described enhanced phosphate adsorption ability in the presence of Ca2+. To investigate the role of Ca2+, two modes (preloading and addition) of Ca2+ dosing were examined and the improved adsorptive performance could be owing to the synergistic eff ;ect of adsorption and Ca-P micro-precipitation on the surface of Fe3O4@ZIF-67. During the regeneration process, the performance of desorbent was evaluated by phosphate releasing and secondary adsorption, and the absence or presence of Ca2+ would have a significant impact on the selection of desorption solution.

Effect of bioslurry application on soil chemical properties and growth of maize (Zea mays L.) in an Alfisol in Maiduguri area, Nigeria

The use of biochar as a low-cost adsorbent to remove nutrients from aqueous solutions is getting great attention lately due to its many environmental applications and benefits. Although, biochar has been widely used to remove phosphate from aqueous solutions, inconsistencies still exist with regards to biochar properties responsible for the adsorption process. This research was therefore, carried out to determine the influence of some biochar properties on maximum phosphate adsorption capacity of biochar produced from four different feed-stocks. The biochars used for this study were prepared from two plant materials; (Maize cob and rice husk) and two animal wastes (cow dung and poultry litter) at 600 °C. The different biochars were subjected to a laboratory batch sorption experiment. Data obtained were fitted into the linear forms of the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) adsorption isotherms while least square regression analysis was used to test the goodness of fit using the coefficient of determination (R2). Similarly, stepwise regression analysis was carried out to determine the nature and extent of relationships between the biochar properties and maximum phosphate adsorption capacity using statistical analysis software (SAS 9.4). Results revealed higher R2 values for the D-R adsorption isotherm (> 0.97) across all the treatments suggest better fit of the D-R adsorption isotherm for phosphate adsorption onto the biochar materials. The maximum phosphate adsorption capacity of the biochar materials is in the order: maize cob biochar > poultry litter biochar > cow dung biochar > rice husk biochar. Stepwise regression analysis revealed that 99 % of the change in maximum phosphate adsorption is influenced by the combined effects of biochar EC, moisture content and specific surface area. Hence, modification of biochar EC, moisture content and specific surface area is essential for improving phosphate adsorption by biochar.

Benign zinc oxide betaine-modified biochar nanocomposites for phosphate removal from aqueous solutions

Phosphate is one of the most costly and complex environmental pollutants that leads to eutrophication, which decreases water quality and access to clean water. Among different adsorbents, biochar is one of the promising adsorbents for phosphate removal as well as heavy metal removal from an aqueous solution. In this study, biochar was impregnated with nano zinc oxide in the presence of glycine betaine. The Zinc Oxide Betaine-Modified Biochar Nanocomposites (ZnOBBNC) proved to be an excellent adsorbent for the removal of phosphate, exhibiting a maximum adsorption capacity of phosphate (265.5 mg. g−1) and fast adsorption kinetics (~100% removal at 15 min at 10 mg. L−1 phosphate and 3 g. L−1 nanocomposite dosage) in phosphate solution. The synthesis of these benign ZnOBBNC involves a process that is eco-friendly and economically feasible. From material characterization, we found that the ZnOBBNC has ~20–30 nm particle size, high surface area (100.01 m2. g−1), microporous (25.79 Å) structures, and 7.64% zinc content. The influence of pH (2–10), coexisting anions (Cl−, CO32−, NO3− and SO43−), initial phosphate concentration (10–500 mg. L−1), and ZnOBBNC dosage (0.5–5 g. L−1) were investigated in batch experiments. From the adsorption isotherms data, the adsorption of phosphate using ZnOBBNC followed Langmuir isotherm (R2 = 0.9616), confirming the mono-layered adsorption mechanism. The kinetic studies showed that the phosphate adsorption using ZnOBBNC followed the pseudo-second-order model (R2 = 1.0000), confirming the chemisorption adsorption mechanism with inner-sphere complexion. Our results demonstrated ZnOBBNC as a suitable, competitive candidate for phosphate removal from both mock lab-prepared and real field-collected wastewater samples when compared to commercial nanocomposites.

High adsorption capacity of Mg–Al-modified biochar for phosphate and its potential for phosphate interception in soil

In this study, Mg and/or Al modified biochars (MABC1, MBC2, ABC3) prepared by co-precipitation were to explore their phosphate adsorption capacity from aqueous solution and the potential for soil phosphate interception. The results revealed that MABC composites contained more functional groups than MBC and showed a higher surface area than ABC. The surface of MABC contained dispersed MgAl2O4, Mg(OH)2, AlOOH and Al2O3 crystals that were associated with its enhanced maximum phosphate adsorption capacity (153.40 mg g−1). According to Langmuir model, the maximum adsorption capacity of MABC was 15.91, 1.85, and 93.54 times the capacity of MBC, ABC, and raw biochar (BC4), respectively. The addition of MABC in red soil could significantly slow down the release of soil phosphorus, and MABC also had a stronger phosphate interception capacity (59.89%) than other BCs. In summary, MABC exhibits superior phosphate adsorption and interception capacity, making it ideal for treatment and prevention of phosphorus-polluted water.

Removal of phosphate from aqueous solution by ferrihydrite/bagasse composite prepared through in situ precipitation method

Ferrihydrite/bagasse composite adsorbent (FH/SCB) was prepared by in situ precipitation method to remove phosphate from aqueous solution. Effects of precipitation pH on adsorption performances of the composites were investigated and adsorption performances and mechanism of phosphate on the composite prepared at the optimum pH for phosphate were studied. Results showed that precipitation pH played a key role on the morphology and adsorption performances of the FH/SCB. SEM-EDX, TEM, XRD and Zeta potential illustrated that ferrihydrite was loaded uniformly on the bagasse surface at pH 4.5, and the obtained composite (FH/SCB4.5) with higher isoelectric point exhibited the maximum adsorption capacity for phosphate. pH and adsorption isotherm results depicted that FH/SCB4.5 showed higher adsorption capacity at lower solution pH. Obvious synergistic effects were observed in co-ions experiment, and both the common anions (NO3−, Cl−, SO42−) and cations (K+, Ca2+, Na+, Mg2+) could promote the phosphate adsorption. Adsorption mechanism analysis showed that electrostatic attraction and inner-sphere complexation involved in the phosphate adsorption. Furthermore, wastewater treatment results showed that more than 99.7 % of phosphate could be removed from wastewater by FH/SCB4.5, demonstrating that the as prepared sorbent had great potential in practical application.

Increasing phosphate sorption on barium slag by adding phosphogypsum for non-hazardous treatment

Barium slag (BS) is a waste residue in the barium salt industrial procedure. Due to its high leaching concentration of Ba2+, BS is classified as a kind of hazardous waste. Industrial waste phosphogypsum (PG) is effective to immobilize barium ion in BS owing to the slightly soluble sulfate included. In this study, two different proportions of PG were selected for mixing with BS to solidify soluble barium ion. The non-hazardous BS samples treated with the proportions of PG (BS-PG1, BS-PG3) were then functionally used for phosphate removal in solution. Batch experiments for removal of phosphate were performed to evaluate the adsorption efficiency of BS-PG1 and BS-PG3. The effect of various factors such as contact time, initial pH, and reaction temperature on sorption performance was investigated. BS-PG1 and BS-PG3 reached adsorption equilibrium in approximately 3h at the initial concentration of 15 mg/L, and BS-PG1 exhibited adsorption capacity of 12.47 mg P/g, higher than that of BS (11.49 mg P/g) under the condition of solid:liquid, 1g:1L, 25 °C, natural pH. The results show that the adsorption processes of phosphates ions onto both BS-PG1 and BS-PG3 fitted well with the pseudo-second-order kinetic model. The Langmuir isothermal model was considered as the appropriate equation for experimental data, showing a maximum adsorption capacity for phosphate up to 13.67 mg P/g and 11.59 mg P/g for BS-PG1 and BS-PG3. In comparison with other adsorbents, BS-PG1 and BS-PG3 could be considered as efficient materials for the removal of phosphate.

Phosphate adsorption performance and mechanisms by nanoporous biochar–iron oxides from aqueous solutions

To evaluate the adsorption mechanism and performance of phosphate onto the composite of low-cost biochar and iron oxide, four biochar-iron oxides, namely biochar-magnetite (BC-M), biochar-ferrihydrite (BC-F), biochar-goethite (BC-G), and biochar-hematite (BC-H), were prepared by fabricating iron oxide to porous biochar. The biochar-iron oxides had huge surface areas of 691-864m2/g and average pore diameters of 3.4-4.0nm. Based on the characterization analysis of FTIR, XRD, XPS, and zeta potential, the interactions of electrostatic attraction, ligand exchange, and deposition dominated the phosphate adsorption onto biochar-iron oxides. The maximum adsorption capacity of phosphate followed the order of BC-G > BC-F > BC-H > BC-M. The isotherm data of BC-M and BC-H were well fitted by the Langmuir and Freundlich models, while those of BC-G and BC-F followed the Langmuir model. In addition, BC-M, BC-F, BC-G, and BC-H owned excellent regeneration ability and adsorption performance in practical (simulated) wastewater environment. Then the biochar-iron oxides exerted extensive and satisfactory prospect in wastewater remediation and recycling application in soil.

Synthesis and evaluation of zirconia/magnetite/zeolite composite for controlling phosphorus release from sediment: A laboratory study

Although the conventional zirconium-based solid-phase phosphorus (P)-inactivating agents (ZrPIAs) have high potential for controlling P release from sediments in aquatic systems, they are difficultly retrieved from sediments after their application. Therefore, it is very necessary to develop new ZrPIAs that can be readily retrieved from sediments after their application. In this study, a novel magnetic ZrPIA, i.e., zirconia/magnetite/zeolite composite (ZMZ) was prepared, characterized and used as a sediment amendment to control the release of P from sediments. The adsorption performance and mechanism of phosphate on ZMZ were studied using batch experiments and XPS analysis. The impact of ZMZ addition on the releasing flux of P from sediments to the overlying water as well as on the fractionation and bioavailability of P in sediments was studied using microcosm incubation experiments. In addition, the stability of P captured by ZMZ was also investigated. Results showed that ZMZ exhibited high adsorption ability towards phosphate, with a maximum phosphate adsorption capacity of at least 4.1 mg P/g, and phosphate adsorption onto ZMZ was mainly controlled by inner-sphere complex formation mechanism. The ZMZ addition greatly decreased the releasing flux of P from sediments into the overlying water in anoxic environment, with a DTP (dissolved total P) reduction efficiency of 61.8–97.8%. Moreover, the added ZMZ could immobilize mobile P in sediments by changing P species from Na2S2O4/NaHCO3-extractable P (BD-P) to NaOH-extractable P (NaOH-rP) and residual P (ResP). Furthermore, the bioavailability of P in sediments could be reduced by the addition of ZMZ. The stability evaluation of P captured by ZMZ after its application showed that a majority of P adsorbed by ZMZ existed in the form of NaOH-rP and ResP, which were difficult to be re-released into the water column under common pH (5–9) and reducing condition. In summary, the above results demonstrate the high potential for the application of ZMZ as an amendment in the control of P release from sediments.

Strong adsorption of phosphate from aqueous solution by zirconium-loaded Ca-montmorillonite

Achieving ultralow levels of phosphorus (P) concentrations to prevent eutrophication is an important goal of surface water management. Hence, a highly efficient and economical adsorbent for phosphate removal is urgently required to meet the increasingly stringent water quality standards. This study investigated the phosphate adsorption performance of zirconium (Zr)-modified calcium-montmorillonite (Zr-CaMs). Batch experiments were conducted to obtain the adsorption isotherms, kinetics, and the influences of dosage, solution pH, and coexisting anions. The results demonstrated that Zr was successfully introduced to the surface and interlayer of raw CaM in the presence of the [SiO]…[HOZr] hydrogen bond and that it increased the specific surface area. The adsorption isotherms obeyed the Langmuir nonlinear model. The calculated maximum phosphate adsorption capacity was 22.37 mg/g, which was more than twice that of Phoslock. The Elovich model fit the kinetics data well, which was indicative of chemical adsorption. An optimum dosage of 100/1–150/1 and wide pH range (4–8.5) are recommended for practical applications. The coexistence of HCO3− slightly inhibited the adsorption capacity, whereas Cl− and SO42− had a positive impact. The adsorption mechanism was primarily the ligand exchange between the surface hydroxyl groups and phosphate resulting from the formation of inner-sphere coordination complexes. This study demonstrated that Zr-CaMs can serve as a prospective adsorbent for phosphate removal from contaminated surface water.

Fast and efficient phosphate removal on lanthanum-chitosan composite synthesized by controlling the amount of cross-linking agent

In the present study, non-crosslinked lanthanum-chitosan (La-CTS-0X) and crosslinked lanthanum-chitosan (La-CTS-1X/2X) composites were prepared as new complex biosorbents for effective phosphate removal from wastewater. Batch adsorption experiments were investigated by varying the influencing parameters, viz., pH, initial concentration of phosphate ions, contact time, temperature and co-existing anions. Experimental data were well fitted to the Langmuir isotherm model (R2 = 0.9998) as well as the pseudo-second-order model (R2 = 1.000), indicating that the phosphate adsorption process was homogeneous, mono-layered and chemisorption dominated. Besides, the maximum phosphate adsorption capacity for La-CTS-0X/1X/2X was 47.28, 57.84 and 31.01 mg g−1 at pH 6, respectively. Thermodynamic parameters including ΔH° (−43.7 kJ mol−1), ΔS° (−132 J mol−1 K−1) and ΔG° (−4.60 kJ mol−1) revealed that the essence of adsorption was spontaneous and exothermic. The regenerated materials could be repeatedly used for three cycles without obvious degradation of performance. Characterization of the adsorbent using FTIR, SEM, EDS and XPS techniques suggested that the possible adsorption mechanisms were electrostatic attraction as well as ligand exchange. More importantly, the La-CTS-1X had rapid removal rate for phosphate within 10 min and the remained P concentration met the permissible limit by the U.S. Environmental Protection Agency (EPA).

Competitive adsorption of phosphate and dissolved organic carbon on lanthanum modified zeolite

Lanthanum (hydr)oxide-based materials are attractive as highly efficient adsorbents for phosphate removal from both sewage and lake environment. However, dissolved organic carbon (DOC) coexists in the waters and exact information is still lacking on how DOC influence the phosphate adsorption process. In this study, competitive adsorption of phosphate and DOC on lanthanum modified zeolite (LMZ) was investigated using humic acid as the representative. In LMZ, lanthanum hydroxide was shown to be the active ingredient accounting for >98% of the binding sites of both phosphate and DOC. Without competition, the maximum adsorption capacity of phosphate and DOC estimated from the Langmuir isotherm model was 52.25 and 41.32 mg/g, respectively. When coexisted, DOC did not affect the adsorption of phosphate while phosphate reduced the adsorption of DOC by ~40%. In addition, preloading LMZ with DOC had little effect on phosphate adsorption while coating with phosphate substantially lowered DOC adsorption. Furthermore, phosphate can release most of the adsorbed DOC (>60%), while DOC can not replace adsorbed phosphate (<2%). The adsorption kinetics of both phosphate and DOC was best described by the psudo-second-order model (r2 > 0.999). The adsorption of both phosphate and DOC increased with decreasing pH or increasing ionic strength. We proposed that phosphate was competitive than DOC for the ligand exchange sites of singly-coordinated hydroxyls, but DOC can be solely adsorbed onto the uncharged hydroxyls via hydrogen bonding.

Designing ZIF-8/hydroxylated MWCNT nanocomposites for phosphate adsorption from water: Capability and mechanism

In this study, ZIF8@MWCNT nanocomposite has been designed throughout in-situ growth of zeolitic imidazolate framework-8 (ZIF8) polyhedron on hydroxylated multi-walled carbon nanotube (MWCNT). In detail, three types of nanocomposites harvesting different nanostructures are obtained by varying the dosages of MWCNTs. Such nanocomposites are assessed as phosphate adsorbents via batch experiments to determine the adsorption capacity, reusability and stability. Among the three types of composites, the ZIF8@MWCNT120 affords the maximum phosphate adsorption capacity of 203.0 mg g−1, which is 0.7–3.7 times higher than those of the other adsorbents at the same adsorption conditions. Experimental characterizations in combination with theoretical calculations reveal that the outstanding performance of ZIF8@MWCNT120 is mainly attributed to the enhanced Zn-O-P interaction and hydrogen bonding. In addition, high phosphate removal performance was observed in the real wastewater (residual effluent Conc. = 0.0–0.45 mg L−1) with initial concentrations of 0.63 mg L−1-6.32 mg L−1, which satisfied the A-level standard of phosphate effluent in China (0.5 mg L−1). This work offers a versatile solution to tailor the adsorption affinity of emerging metal-organic-frameworks (MOFs) toward phosphorous-based pollutants.

Biochar-loaded Ce3+-enriched ultra-fine ceria nanoparticles for phosphate adsorption

Biochar-loaded Ce3+-enriched ultra-fine ceria nanoparticles (Ce-BC) was prepared by a facile impregnation-precipitation-pyrolysis process and applied as adsorbents to adsorb phosphate from water. The crystal size of ceria nanoparticles in the Ce-BC was as small as 2−5 nm and the concentration of Ce3+ was high to 59.6 %, which was benefited from the rapid precipitation, N2 pyrolysis atmosphere and the presence of the biochar during preparation. Ce-BC exhibited a fast adsorption kinetics for phosphate and the adsorption equilibrium could be reached within 10 min. The maximum phosphate adsorption capacity was up to 77.7 mg P g−1 at pH 3.0. Based on Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analysis, Ce3+ of ceria was demonstrated playing the vital role on phosphate removal and the formation of CePO4 nanocrystals was the main adsorption mechanism. This work provides a facile strategy for preparing high Ce3+ contenting materials and shows a great potential application for the phosphate removal for its high-effective and high stability.

Assessment of urban river water quality and developing strategies for phosphate removal from water and wastewaters: Integrated monitoring and mitigation studies

In this work, the water quality status of the surface water that lies around the Karamana River basin, Trivandrum urban area, was studied on the basis of the water quality index (WQI) method. The eutrophic condition of the basin is revealed, and proper mitigation strategy was adopted for the removal of phosphate species using pillared clay materials. Proper sampling was carried out in the urban rivers, and various physico-chemical parameters for evaluating the quality of water were analysed. WQI values obtained for these riverine systems are in the range 317.7–3005.1, indicating that the water is not suitable without treatment for any domestic activities. Also, phosphate ions in the range 1.98–20.52 mg/L reflect the dominance of phosphate species in surface water. A proper mitigation strategy was adopted for the selective removal of phosphate ions using adsorption technique by using zirconium-pillared bentonite clay (ZPBC) prepared by the stirring–ageing technique. The batch adsorption experiment performed on simulated phosphate solution shows that for 2.0 g/L of ZPBC a maximum phosphate adsorption capacity of 35.71 mg/g was achieved in 30 min at pH 3.0. The data obtained were used to study models in kinetics and isotherm. The reusability of spent ZPBC for five continuous cycles without major loss in adsorption capacity using 0.025 M Na2CO3 extractant was proved from the desorption study. A single-stage reactor was also designed from the isotherm data and proved to be effective. The applicability of the adsorbent towards phosphate anions was successfully checked in the laboratory using surface water collected and found that the complete removal of phosphate was achieved using 6.0, 8.0 and 10.0 g/L of ZPBC.

Metal-Modified Mussel Shell for Efficient Binding of Phosphorus in Eutrophic Waters

As phosphorus (P) exceeds 0.1 mg P L−1, the water is usually considered high enough to cause eutrophication. Thermally treated mussel shell (TMS), a calcium-rich (36.76%) biological material, was an environmentally friendly and low-cost adsorbent for P removal. To achieve very low concentrations of P, composite agents of PAC–TMS, Fe–TMS and La–TMS were prepared with the optimum weight ratio of 0.4, 0.2 and 0.2 (g g−1) [polyaluminium chloride (PAC), Fe(OH)3 or La2O3 to TMS] with the lower cost and high P adsorption efficiency, respectively, all of which had more than 80% of P removal rate after 12-h treatment of 5 mg L−1 P solution, much higher than that of TMS alone (50%). Isotherm experiment showed that these composite agents have maximum phosphate adsorption capacities of 91.74 mg P g−1 (PAC–TMS), 101.42 mg P g−1 (Fe–TMS) and 56.50 mg P g−1 (La–TMS), respectively. Additionally, the metal-modified TMS was almost independent of pH. Long-term efficient removal of P (< 0.1 mg L−1) was achieved during a 3-month removal trial of P-contaminated water while using these metal-modified TMS. Since metal-modified TMS both had calcium and other multivalent metal (Al, La or Fe), the modification pathway was mainly dependent on both enhance adsorption/precipitation by a simultaneous effect of the calcium and other multivalent metal.

Removal of lead complexes by ferrous phosphate and iron phosphate: Unexpected favorable role of ferrous ions

The high chemical stability of lead complexes in solution precludes most traditional removal methods. Achieving the efficient, cost-effective, and environmentally friendly removal of metal complexes from wastewater is a challenge. In this study, ferrous phosphate and iron phosphate were used to treat wastewater containing EDTA-Pb, and the differences in their removal processes were compared. Both materials enabled efficient removal of the EDTA-Pb complex from 50 mg Pb/L to <1 mg Pb/L, and the leaching of Fe was <50 mg/L. More attractively, the maximum adsorption capacity of ferrous phosphate significantly increased from 80.44 mg Pb/g to 436.68 mg Pb/g as the reaction environment changed from aerobic to anoxic. The concentration of Pb was reduced to the sub-ppm level by ferrous phosphate even when the initial concentration of EDTA-Pb was 300 mg/L. In-depth exploration of the removal mechanism of EDTA-Pb demonstrated that the synergistic effect of Fe2+ and Fe3+ contributed to the high removal efficiency of EDTA-Pb by ferrous phosphate. Moreover, ferrous phosphate was minimally affected by salinity and organics, but the iron phosphate performance was significantly suppressed. The potential application of ferrous phosphate was further explored by processing explosive wastewater containing lead complexes. The results showed that the residual Pb content was 0.94 mg/L (lower than the discharge standard of China) and the removal performance of iron phosphate was suppressed. The results demonstrate that ferrous phosphate is a promising material for the decontamination of EDTA-Pb-contaminated water.

Phosphate Adsorption by Silver Nanoparticles-Loaded Activated Carbon derived from Tea Residue

This study presents the removal of phosphate from aqueous solution using a new silver nanoparticles-loaded tea activated carbon (AgNPs-TAC) material. In order to reduce costs, the tea activated carbon was produced from tea residue. Batch adsorption experiments were conducted to evaluate the effects of impregnation ratio of AgNPs and TAC, pH solution, contact time, initial phosphate concentration and dose of AgNPs-AC on removing phosphate from aqueous solution. Results show that the best conditions for phosphate adsorption occurred at the impregnation ratio AgNPs/TAC of 3% w/w, pH 3, and contact time lasting 150 min. The maximum adsorption capacity of phosphate on AgNPs-TAC determined by the Langmuir model was 13.62 mg/g at an initial phosphate concentration of 30 mg/L. The adsorption isotherm of phosphate on AgNPs-TAC fits well with both the Langmuir and Sips models. The adsorption kinetics data were also described well by the pseudo-first-order and pseudo-second-order models with high correlation coefficients of 0.978 and 0.966, respectively. The adsorption process was controlled by chemisorption through complexes and ligand exchange mechanisms. This study suggests that AgNPs-TAC is a promising, low cost adsorbent for phosphate removal from aqueous solution.