Co-existing Ions Research Articles

Highly selective removal of thallous ions from wastewater using Prussian Blue biochar composite

Thallium, a highly toxic pollutant, shows greater toxicity to human than other common heavy metals such as mercury, lead, cadmium and its effective removal from wastewater gains great attention. The main restriction for the Tl+ removal is the interference of a high concentration of co-existing ions in wastewater. Therefore, the goal of the current work was to synthesis adsorbent with high selectivity for the Tl+ removal. Herein, the pore size sieving strategy was proposed and Prussian blue-impregnated biochar (BC@PB) particles was synthesized. More than 95% Tl+ can be removed even the concentrations of the coexistence ions (Na+, Cd2+, and Zn2+) 1,000 higher than the initial concentration of Tl+ (500 μg/L). BC@PB also showed large adsorption capacity (9365 μg/g) and more than 99% Tl+ (initial concentration, 500 μg/L) were removed in just 1 min. The BC@PB had excellent and stable Tl+ removal ability (> 99%) over a range of pH from 3 to 9, which covered the pH range of common thallium-containing wastewater. The density functional theory (DFT) calculation confirmed that not only hydrated volume but also the hydration free energy of ions, which governed the energy barrier for ions entering into narrow channels of BC@PB, played essential roles on the selectivity removal of Tl+. Overall, due to its high selectivity, high adsorption capacity and easy preparation process, the synthesized BC@PB particles based on the pore sizing sieving strategy, can be a promising candidate for the removal of thallium from wastewater.

The redistribution process of As(Ⅲ) and Fe(Ⅱ) caused by As/Fe ratio, organic matter, and co-existing ions: Co-precipitation and co-oxidation

The contamination of arsenic (As) in aqueous environments has drawn widespread attention, and iron compounds may largely alter the migration ability of As. However, the stability of As(III) in Fe-As system with the intervention of organic matter (OM) remains unclear. Herein, we had explored the co-precipitation and co-oxidation processes of As-Fe system by using batch experiments combined with Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) in this research. The precipitation quantity of As(III) increased (28.85–92.41 %) when the As/Fe ratio decreased, and increased (24.20–64.20 %) with pH increased. The main active substance for oxidizing As(III) was H2O2, which was produced in the As-Fe system. FTIR and XPS revealed that As(III) was first oxidized in neutral, and then absorbed and enteredthe interior of Fe(OH)3 colloids. But under alkaline conditions, As(III) was adsorbed by Fe (Oxyhydr) oxides firstly, and then oxidized. The intervention of OM would inhibit the redistribution process of As(III) in aqueous environments. Functional groups and unsaturation of the carbon chain were the dominant factors that affected the precipitation and oxidation processes of As(III), respectively. Co-existing ions (especially PO43-) also signally affected the precipitation quantity of As(Ⅲ) in the system and, when coexisting with OM, could exacerbate this process. The influence of co-existing ions on the redistributive process of As(III) in the As-Fe system with/without OM were as follows: PO43- > SO42- > mixed ions > SiO32-. Moreover, high concentration of OM and PO43- might lead to morphological alterations of As, acting as a threat to aqueous environments. In summary, the present findings were to further understand and appreciate the changes of As toxicity in the aqueous environments. Particularly, the coexistence of OM and As can potentially increase the risk to drinking water safety.

Comparing the abiotic removal of glyphosate by β-MnO2 and δ-MnO2 colloids: Insights into kinetics and mechanisms

Glyphosate as an effective broad-spectrum herbicide is frequently detected in various water and soil resources. Given the ubiquity of β-MnO2 and δ-MnO2 colloids in groundwater and soil, the abiotic removal of glyphosate by MnO2 colloids was investigated. β-MnO2 colloids exhibited superior glyphosate removal efficiency, up to 37%, compared to 21% for δ-MnO2 colloids at a pH of 4.0. Glyphosate removal involved simultaneous adsorption and oxidation process, identified by HRTEM, NH3-TPD, XPS, LC-MS, FTIR analyses and the occurrence of aminomethylphosphonic acid (AMPA) and Mn2+. Moreover, adsorption dominated the removal of glyphosate by two MnO2 colloids. The solution pH had a substantial effect on glyphosate removal. Co-existing ions in the solution, such as carbonate (CO32−), phosphate (Na2HPO4, NaH2PO4) and humic acid (HA), were also found to impede glyphosate removal. Phosphate, in particular, exhibited a strong competitive effect for adsorption sites on both MnO2 colloids. Of them, the removal of glyphosate by β-MnO2 colloids was more prone to occur due to its higher specific surface area, abundant oxygen vacancies, and moderate acid sites. However, δ-MnO2 colloids presented a stronger oxidation capacity than that of β-MnO2 colloids due to the quicker generation rate of Mn2+. Finally, AMPA was the same products by two MnO2 colloids in the oxidation process, revealing the degradation pathway based on the cleavage of C–N bond. Therefore, by comparing kinetics and mechanisms of glyphosate removal by β- and δ-MnO2 colloids, this study improves us better understanding for the behavior of glyphosate in the environment.

Nano-zerovalent copper biochar composite for treating selenium oxyanions in water: synthesis, evaluation, removal mechanism, density functional theory, and molecular dynamics simulations

This study focused on the synthesis and applicability of nano-zerovalent copper biochar composite (nCu0-BC) for treating selenium oxyanions in water. In batch experiments, 2 g/L of nCu0-BC efficiently removed 98.96 % of selenite [Se(IV)] and 98.78 % of selenate [Se(VI)] in 10 mL of water (10 mg/L for each Se oxyanion) in 12 h. Both Se(IV) and Se(VI) removal followed the pseudo-second-order kinetic model, and their removal rates increased by 3.02 and 7.44-folds, respectively, by increasing the nCu0-BC dose from 2 to 3 g/L. Co-existing ions had minimal effect on Se(VI) removal except PO43- which significantly reduced the Se(VI) removal; while the presence of calcium, sodium, nitrate, and bicarbonate lowered Se(IV) removal by 7–10 %. Spectroscopic analyses were employed to characterize virgin and spent nCu0-BC. XRD analysis revealed that nCu0-BC contains copper in two crystalline phases, i.e., zerovalent copper (Cu0) and cuprous oxide. XPS analysis showed that Cu0 was the main source of electrons for the reduction of Se oxyanions; Se(IV) was reduced to Se(0) while Se(VI) was reduced to Se(IV) and Se(0). The density functional theory simulation indicated that both Se(VI) and Se(IV) form stable complexes with nCu0-BC with the calculated adsorption energies of −3,657 kcal/mol and −3,669 kcal/mol, respectively. The molecular dynamic simulation revealed a high adsorption affinity of Se oxyanions towards nCu0-BC owing to the presence of Cu0 on its surface, resulting in stable bidentate binuclear complexes formation between Se oxyanions and Cu0.

Zirconium-loaded zeolite composites for selective sorption of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) from water: Performance and mechanism

Three zirconium-loaded zeolite (Zr-Z) composites—namely, Zr4+-Z, ZrO2-Z, and ZrMo2O8-Z—were prepared by co-precipitation of Zr4+, ZrO2, and ZrMo2O8, respectively, with artificial zeolite, and these composites were used for the efficient removal of a representative phosphonate, i.e., 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). The adsorption efficiency of the three composites for HEDP at an initial concentration of 2 mg/L was more than double that of artificial zeolite. Pseudo-second-order kinetics could fit the adsorption process of the three composites well. The heterogeneous adsorption by Zr4+-Z, ZrO2-Z, and ZrMo2O8-Z was determined by using the Sips model. And the theoretical maximum HEDP-adsorption capacities of Zr4+-Z, ZrO2-Z and ZrMo2O8-Z were 3.52 mg P/g, 3.38 mg P/g and 3.77 mg P/g, respectively, at 308 K. At pH 4–9, the three Zr-Z composites could achieve efficient and stable HEDP adsorption. Among Co-existing ions (Cl−, HCO3−, NO3−, SO42−, Ca2+, Mg2+), 50 mM HCO3− hindered adsorption due to its competition with HEDP. The characterization results show that the adsorption mechanism involved hydrogen bonds, electrostatic attraction, and ligand exchange. In addition, the reusability and column adsorption performance of the Zr-Z composites were explored for the efficient removal of the organic phosphonate HEDP from wastewater in practical applications.

Copper-doping induced hierarchically porous metal-organic framework for enhanced adsorption of cefradine antibiotic

Development of hierarchically porous materials is important for adsorptive removal of antibiotic with large molecular size. Herein, we proposed a novel strategy for constructing hierarchically porous metal-organic frameworks (MOFs), via introducing low-coordination-number copper in zirconium-oxygen clusters. Compared with UiO-66 (UiO, University of Oslo), the Cu-doped sample exhibits larger specific surface area and importantly, abundant defects and large rhombus-like window. Benefited from that, cefradine is easily diffused into the cages of UiO-66. The resultant UiO-66-Cu owns much higher adsorption capacity (325.1 mg g−1) for this antibiotic than Cu-absence sample does (102.0 mg g−1), which is also superior to those reported adsorbents. Besides, adsorption equilibrium was obtained at ∼600 min. It is found that the adsorption behavior can be well described by Langmuir isotherm model and pseudo-second-order model. The adsorption is gradually enhanced along with the increasing pH (2.0–8.0). Co-existing ions including Na+, K+, Ca2+, Mg2+, Cl-, NO3- and SO42- commonly have negligible effects on the adsorption. Finally, the adsorbent can be well regenerated by using ethanol as the eluent. Mechanism investigation indicates that cefradine adsorption in UiO-66-Cu is driven by electrostatic, hydrogen bond and coordination interactions. Thus, our work provides an effective adsorbent for cefradine and meanwhile proposes a new approach to construct hierarchically porous MOFs.

Heterogeneous activation of permonosulfate by biochar supporting CuCoFe layered double hydroxide for rapid degradation of phenanthrene

In this study, a ternary layered double hydroxide (CuCoFe-LDH) coated on corn straw-based biochar (BC@LDH) was synthesized and characterized using various approaches. Application in heterogeneous activation of permonosulfate (PMS) for the degradation of phenanthrene (PHE) suggested that the higher Co content in the material, the higher the catalytic activity, maximum of which was 96.5% reached at catalytic dosage of 0.2 g/L, PMS concentration of 2.0 mmol/L, pH 7 and temperature of 45 ℃ within 15 min in BC1 @LDH1 (BC to mass ratio of 1:1)/PMS system. Improved PHE degradation and wide pH application range supported that BC not only acted as CuCoFe-LDH carrier, but also probably participated in the activation of PMS due to abundant functional groups, like hydroxyl as FT-IR revealed. Co-existing ions (NO3-, CO32-) and humic acid (HA), but not Cl-, significantly inhibited PHE degradation. Moreover，the removal of PHE was mainly attributed to SO4·- and ·OH, while O2·− and 1O2 contributed less. It was proposed that Cu (I), Co (II) and Fe (II) were responsible for the PMS activation and produced Co (III) can be reduced by HSO5- and Fe (II) to achieve Cu (I)/Co (III) cycle, thereby maintaining high catalytic activity and structural stability of BC1 @LDH1. Remarkably, Consecutive runs (>80.0% PHE removal after 4 cycles) and low level of leaching metal concentration (0.053 mg/L of Co and 0.077 mg/L of Cu at pH 7) all implied that BC1 @LDH1 possesses much greater potential in activating PMS for practical application.

Polytetrafluoroethylene supported polyphenol-functionalized metal–organic framework as a bio-based membrane for efficient mercury extraction from aqueous samples

In this study, we have designed and synthesized a porous membrane by functionalizing the polytetrafluoroethylene (PTEF) support with natural biomass polyphenols (tannins) grafted on amino-functionalized UiO-66 metal–organic framework to give a robust, environmentally friendly polyphenol/metal–organic framework/PTFE membrane, namely PPG-UiO-66@PTFE. Then, the nominal solid was used for the efficient extraction of mercury ions from water samples before ICP-Mass measurements. The effects of some parameters such as pH, type, and volume of eluent, eluent, sample flow rate, and co-existent ions were explored and optimized. Under optimum conditions, the limit of detection was obtained at 1.5 ng/L. The results exhibited that the presence of the co-existing ions does not affect the experimental results. The PPG-UiO-66@PTFE demonstrated superior performance compared to individual materials. This bio-based porous membrane had benefits such as a wide linear range, selectivity, renewability, and real applications in laboratory settings.

Nitrogen-doped Fe-MOFs derived carbon as PMS activator for efficient degradation of tetracycline

BackgroundTetracycline (TC) poses a significant threat to ecosystems and human health. Advanced oxidation techniques based on persulfates are increasingly investigated for their environmental friendliness and efficiency. Co-pyrolysis of melamine (MA) and Fe-MOFs can avoid the accumulation of MOFs and produce structural nitrogen and defective structures, thus enhancing the catalytic activity of the catalyst. MethodsFe-NPC was prepared by co-pyrolysis using MIL-101-Fe and MA. The effects of MA/MIL-101-Fe ratio, dosages of catalyst and PMS, initial pH and co-existing ions were discussed. The catalysts were characterized by XRD, SEM, BET, and VSM, and the degradation mechanism was analyzed using EPR, LC-MS, and XPS characterization of the catalysts before and after use. Significant findingsResults showed that approximately 90% of TC was removed within 20 min using 15 mg Fe-NPC, 30 mg PMS at 25℃. Co-existing ions and humic acid had no apparent effect on TC degradation efficiency in the Fe-NPC-600/PMS system. The Fe species and pyridinic N played significant roles in activating PMS and therefore achieving high efficiency of TC degradation. 1O2 was identified as the dominant reactive species in the Fe-NPC-600 system. Four possible TC degradation pathways were confirmed. The catalyst maintains a good circulation effect after five cycles.

Effect of Co-Existing Ions on Salinity Gradient Power Generation by Reverse Electrodialysis Using Different Ion Exchange Membrane Pairs.

This study investigates the influence of co-existing ions on the salinity gradient power generation performance of the reverse electrodialysis (RED) using three different commercial ion exchange membrane pairs. The feed solutions, including the mixture of two different salts, were prepared with 90 wt.% of NaCl and 10 wt.% of LiCl, KCl, CaCl2, MgCl2 or Na2SO4 by keeping the salt ratio between high concentrate solution and low concentrate solution constant as 1:30 (g/g) at various flow velocities (50, 125 and 200 mL/min). It was observed that the divalent ions exhibited a negative impact on the performance of the RED system due to their high valence and low ionic mobility depending on their high hydrated radius and low diffusion coefficients compared to those of the monovalent ions. On the other hand, the effect of the monovalent ions differed according to the properties of ion exchange membranes used in the RED stack. When the power generation performances of ion exchange membrane pairs employed in the RED stack were compared, it was considered that Neosepta AMX and CMX membranes provided the highest power density due to their low membrane thicknesses, low electrical resistances, and relatively high ion exchange capacities compared to other two commercial ion exchange membrane pairs.

Magnetic porous carbons derived from metal-organic frameworks for effective adsorption of tetracycline

Recovery of adsorbent from solid-liquid adsorption system is important for the application of adsorption technique. Due to high efficiency and low cost, separation induced by external magnetic field has attracted large attentions. In this work, we prepared a series of cobalt-doped magnetic porous carbons (Co-PC) via using Co-benzimidazole (Co-PhIm) as the precursor. In the green synthesis of Co-PhIm, water was used to partly substitute the organic solvent that was applied in previous reports. Interestingly, upon the addition of water, the porosity was boosted and the magnetism was not weakened obviously. Among the prepared porous carbons, the optimized Co-PC-C exhibited a large adsorption capacity (998.3 ​mg ​g−1) for tetracycline (TC) and rapid equilibrium time (30 ​min) at low concentrations. Co-existing ions had almost ignorable interferences and the optimized pH was found near the neutral environment. Furthermore, this material can be well regenerated through a simple elution method. Therefore, our work provides an effective adsorbent for TC antibiotic and proposes a guideline to enhance the porosity of adsorbent.

Adsorption of Pb(II) in Water by Niobate/Titanate Nanoflakes

A niobate/titanat nanoflakes (Nb/TiNFs) composite was synthesized via the hydrothermal method and used to remove Pb(II) from water. XRD, TEM, and SEM results indicate that Nb/TiNFs appear as nanoflakes, of which the primary crystal phase is tri-titanate. Nb/TiNFs show rapid adsorption kinetics and the result fits well with the pseudo-second order model. The key mechanism of adsorption is ion-exchange between metal and -ONa/H. According to the Langmuir isotherm model, the maximum capacity of Pb(II) is 488.323 mg·g−1. The relatively low RL values indicate that Nb/TiNFs exhibit favorable adsorption of Pb(II). Nb/TiNFs indicate high adsorption capacity over a broad pH range. Co-existing inorganic ions (Na+ and Ca2+) have a slight inhibition effect on adsorption, and HA moderately inhibits the adsorption of Pb(II) on Nb/TiNFs. Because of the simple method of synthesis and high removal efficiency for heavy metals, Nb/TiNFs are a promising material in remediation of heavy metal polluted water.

A facile microwave-assisted synthesis of mesoporous hydroxyapatite as an efficient adsorbent for Pb2+ adsorption

This study investigated the potential adsorption ability of microwave-assisted hydroxyapatite (MHAP) for the removal of metal ions (Pb2+) polluted water. The hydroxyapatite composite was synthesized by using CaCl2 and (NH4)2HPO4 powders as raw material through simple grinding, and then being assisted with microwave. Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses were applied to characterize the adsorbent sample. Pb2+ adsorption was performed by discussing the effects of various factors, such as initial pH, initial Pb2+ concentration, adsorbent dosage, and contact time. Co-existing ions (Na+ and Ca2+) showed little influence on Pb2+ adsorption, and were absorbed onto MHAP on the contrary. The adsorption kinetics of MHAP was well described by the pseudo-second-order model, and the equilibrium adsorption data showed a high correlation coefficient with the Langmuir isotherm model. Thermodynamically, the adsorption process of Pb2+ onto MHAP was spontaneous, endothermic and favorable in nature as ΔG° < 0, ΔH° > 0, and ΔS° > 0. The maximum adsorption capacity of synthesized MHAP for Pb2+ was 1438.85 ​mg/g according to the Langmuir adsorption model, significantly higher than many other adsorbents. It suggested that the mesoporous MHAP synthesized in this study was an effective and promising material for Pb2+ removal from aqueous solution.

Hydrated zirconia-loaded resin for adsorptive removal of phosphate from wastewater

Adsorption of phosphorus by Zr-based materials has attracted more and more attention. However, the use of these materials was still limited due to the influence of coexisting ions and poor regeneration ability. In this study, hydrated zirconia was loaded into anion exchange resin (D280) to develop phosphorus adsorption material (D280-Zr). As a contrast, the phosphorus adsorption material HZO-201 was prepared by hydrating zirconia with large pore diameter anion resin D201. The samples were characterized by scanning electron microscope (SEM) with an EDX (energy dispersive X-ray), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Zirconium was successfully loaded onto the D280 and surface hydroxyl groups on D280-Zr played a significant role. Through batch adsorption experiments, the maximum adsorption amount of D280-Zr was 47.2198 mg P/g at temperature of 30 °C and pH 6−7. Adsorption isotherms could be described by the Langmuir model, and the adsorption kinetics were well described by the pseudo-first-order and pseudo-second-order model. Co-existing ions (Cl−, NO3−, HCO3−) had minimum effect on adsorption performance with efficiency above 80%. Through six cycles of regeneration, the adsorption efficiency was still above 80%. After treatment with D280-Zr packed bed column, the effluent could meet the A discharge standard in China of P < 0.5 mg/L in wastewater, and the treated water volume reached about 3500 times the bad volume (3500 BV). The results illustrated that D280-Zr was an effective phosphorus adsorption material.

Ni-based layered metal-organic frameworks with palladium for electrochemical dechlorination

Electrocatalytic hydrogenolysis (ECH) appears to be an effective method for remediation of toxic contaminants in natural water. In this work, metallic palladium was loaded on Ni-based layered metal-organic frameworks (NiMOF) using adsorption followed by an electroreduction method. Benefiting from high dispersion of palladium and enhanced adsorption of NiMOF towards 2,4-dichlorophenoxyacetic acid (2,4-D), the as-obtained electrode (Pd-NiMOF/Ni) offers large amounts of active hydrogen and high surface concentration of 2,4-D in the ECH process. Consequently, Pd-NiMOF/Ni displays enhanced activity and selectivity compared to traditional electrodes. In addition, the Pd-NiMOF/Ni cathode was extremely stable, as verified by six successive cycling tests. Co-existing ions, including NO3−, HCO3−, CO32− and Ca2+ exert a negative impact on the electrocatalytic dechlorination, whereas no effect of Cl− on the process. Nonetheless, the electrochemical dechlorination of 2,4-D in Evian water remained effective, demonstrating the potential application of this electrode in efficient dechlorination of chlorinated aromatic compounds.

Promotional effect of Mn(II)/K2FeO4 applying onto Se(IV) removal

Promotional effect of Mn(II)/K2FeO4 [Fe(VI)] applying onto Se(IV) removal was determined for the first time, with description of reaction mechanisms. Four different combinations of water treatment agents [K2FeO4 alone, K2FeO4 with Al(III) ions, K2FeO4 with Fe(III) ions, and K2FeO4 with Mn(II) ions] were used for Se removal in spiked deionized water, and K2FeO4 in combination with Mn(II) ions showed great removal efficiency. Over 90% of Se(IV) (200 μg/L) was removed within 2 min by using 1 mg/L of K2FeO4 and 9 mg/L of Mn(II) ions (pH 7.0, 23 °C). XPS analysis identified that in the reaction process, Se(0) formed on the settlement. It was speculated that Se(IV) was oxidized to Se(VI) by K2FeO4, and the Se(VI) species was reduced to insoluble Se(0) by γ-Fe2O3-Mn(II) nanocomplex. Insoluble Se(0) adsorbed on the surface of Fe-Mn particle and coprecipitated, thus removed from aqueous solution. As solution pH varied from 4.0 to 8.0, Se(IV) removal ratio ranged from 89% to 98% in the system. Co-existing ions such as Na+, Ca2+ and SO42− had no intense effect on Se removal, while PO43- and humic acid (HA) inhibited Se removal in Mn(II)/K2FeO4 system. Mn(II)/K2FeO4 was an effective and convenient way for Se(IV) removal from polluted water.

The influence of pH, co-existing ions, ionic strength, and temperature on the adsorption and reduction of hexavalent chromium by undissolved humic acid

The retention of Cr(VI) in subsurface environment is highly dependent on humic acid (HA), however, the undissolved form is poorly investigated, the amount of which can be of two magnitude higher compared with the dissolved one in soils and sediments. In this study, the effects of time, initial concentration, pH, ionic strength, ion species and temperature on the adsorption and reduction respective processes by undissolved self-extracted peat soil HA from Northeast China (EHA) and from Sigma Aldrich (CHA) were investigated by batch experiments. Cr(VI) removal rates by EHA were higher than CHA and the maximum Cr(VI) removal amount for EHA and CHA were 0.77 (±0.01) and 0.61 (±0.02) mmol/g. Of these, 98% and 54% were reduced to Cr(III) by EHA and CHA respectively, which were related to the phenolic group content of HA. With time, the adsorbed Cr(VI) on HA increased to a maximum level (equilibrium) beyond which Cr(VI) reduction dominated the removal process. Cr(VI) adsorption and reduction by undissolved HA increased as pH decreased. Co-existing ion species had varying effect on Cr(VI) adsorption and indirectly on reduction especially divalent cations which was suggestive of cation bridging between Cr anions and ionized carboxyl group of HA. The positive effect of ionic strength (Ca2+) on Cr(VI) adsorption through complexation corroborated the cation bridge effect of divalent cations. Temperature increased both Cr(VI) adsorption (complexation) and reduction with enhancing reduction rate constants and partitioning. ΔHo, ΔSo, and ΔG⁰ parameters showed that Cr(VI) adsorption and reduction processes were endothermic, irreversible and spontaneous.

Effects of Co-Existing Ions on the Phosphorus Potassium Ratio of the Precipitate Formed in the Potassium Phosphate Crystallization Process

Livestock wastewater is mainly treated with activated sludge, but ions such as phosphorus, potassium, ammonium, nitrate and sulfate remain in the effluent. In this study, the effects of residual ions on phosphorus recovery using the magnesium potassium phosphate crystallization method were investigated when magnesium was added to increase the pH. If co-existing ions affect the products, the phosphorus to potassium molar ratio (K/P ratio) of the precipitate will deviate from being equimolar. Artificial wastewater test solutions containing 5.6 - 20.3 mM ammonium, 25.6 mM potassium, 6.5 mM phosphorus, 0 - 7.35 mM nitrate, and 0 - 3.06 mM sulfate were used. First, the optimum operating pH and amount of magnesium added to give a high phosphorus removal rate and recovery rate were determined. The experimental setup was a 10 L aerated and stirred reactor, and a 5 L settling tank. The K/P ratio in precipitate was approximately 1 using the optimum conditions. Continuous 2 h treatment allowed a white precipitate containing about 30 g of needle-like crystals to be obtained. Next, the effects of varying the ammonium, nitrate, and sulfate ion concentrations in the artificial effluent were investigated. Ammonium and sulfate ion concentrations of 8 mM or more and 3 mM or more, respectively, caused the K/P ratio to decrease to about 0.7 and 0.5, respectively. Varying the nitrate concentration did not affect the K/P ratio, even at a nitrate concentration of 7.35 mM.

Removal of strontium(II) and cobalt(II) from acidic solution by manganese antimonate

Radioactive strontium and cobalt are two major contaminants in the low-level radioactive wastewaters (LLRWs). In this study, a manganese-antimony composite oxide (MnSb) were prepared to study the sorption behavior and the removal of Sr(II) and Co(II) from acidic wastewaters. The as-prepared MnSb was identified and characterized by X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), Transmission Electron Microscope (TEM), zeta potential, and surface analysis, and its sorption performance was tested by batch experiments. Our results suggest that the MnSb oxides, with their microcrystal rutile structures and high specific surface areas, are promising candidate for the removal of Co (KdCo=2.3×106mL/g) and Sr (KdSr=8.3×105mL/g) in aqueous solutions at pH>2. Co-existing ions, like Na+, Mg2+ and Ca2+, affect the adsorption of Co and Sr to a limited degree. Adsorption of Co and Sr onto MnSb is fast and increases with elevating operating temperature. The equilibrium isotherms of Sr and Co could be best fitted by the Freundlich model with KF values up to 1.98 and 0.54mmol/g for Co and Sr at 323K, respectively. Co ions were found to be more competitive than Sr ions onto MnSb with a selectivity ratio of S(Co/Sr)=1.8. The kinetic performance of Co and Sr could be described well by the pseudo-second order equation, and film diffusion was the rate-controlling step under our experimental conditions.

Equilibrium and Kinetics of Silver Uptake by Multinuclear Alginate Microcapsules Comprising an Ion Exchanger Matrix and Cyanex 302 Organophosphinic Acid Extractant

Uptake characteristics of alginate microcapsules containing bis(2,4,4-trimethylpentyl)monothiophosphinic acid for adsorption of Ag(I) ions were examined using batch methods. Under a definite initial Ag+ concentration (Cb), at equilibrium, all the Ag(I) ions are adsorbed by extractant, while above Cb, ion exchange by the alginate matrix becomes the dominating mechanism. The kinetic mechanism varies depending on the presence of coexisting ions (CI). If the concentration of CI is low, the kinetics is controlled by a combination of slow adsorption of Ag(I) ions by Cyanex 302 (HA) microdroplets and shielding of inner microdroplets by the outer reacting ones (physical−chemical shielding mechanism). At higher concentrations of CI, intrapore diffusion controls the kinetics. Different types of the shrinking core model remarkably fitted the kinetics experiments. The microcapsules were able to selectively adsorbed 90% of the Ag(I) ions from a 10 ppm Ag(I) + 3 mol·dm-3 Na+ solution. In addition, the uptake percentage was constantly high in wide range of pH values and Ag+ concentrations.