Rapid oxidative removal of Fe2+ and Mn2+ from acidic mining wastewater by a new-type biofilter system: application and mechanism.

Aimed at the problem of excessive concentration of Fe2+ and Mn2+ in acidic mining wastewater during mining and utilization, a new rapid oxidative removal technology of Fe2+ and Mn2+ by a new-type biofilter system was designed and tested. The new-type biofilter system was constructed using a bioreactor filled with special mature bioceramic pellets after continuous biofilm cultivation as the filter layers. The results indicated that the biofilter system could efficiently treat five times its volume of wastewater per hour. The Fe2+ concentration of the influent wastewater was about 500 mg/L, and its Mn2+ concentration was about 20 mg/L. The average Fe2+ and Mn2+ removal rates could reach 99.7% and 90.8%, respectively. In addition, scanning electron microscopy and energy dispersive spectroscopy-energy dispersive spectroscopy and X-ray photoelectron spectroscopy were applied to analyze the migration distribution and valence change of Fe and Mn ions to clarify the removal mechanism of Fe2+ and Mn2+ using the biofilter system. The results showed that iron oxidation products were mainly coated at the surface of the mature bioceramic pellets and could be easily washed out from the filter layer with flowing water, while manganese oxidation products tended to accumulate between the pores of the mature bioceramic pellets. Furthermore, the final filtration products were multivalent complex oxides, indicating that the high-valent oxidation products could adsorb Fe and Mn ions, which were mainly removed by the oxidation effect.

Effect of Surface Heterogeneities on Interactions between Air Bubbles and Heterogeneous Surfaces.

The effects of surface heterogeneities on bubble-particle interactions have received little attention although heterogeneities are common for varieties of substance surfaces. In this work, heterogeneous surfaces consisting of discrete hydrophilic dots on a hydrophobic background were fabricated. The interactions between air bubbles and heterogeneous surfaces with different hydrophilic area fractions were investigated using a high-sensitivity microbalance coupled with a high-speed video camera. It was found that the snap-in, maximum adhesion, and pull-off forces increased as the hydrophilic area fraction decreased. These experimental results were compared with the calculated interaction forces. The comparison between experimental results and the calculated interaction forces showed that the normalized contact line length (δ) should be considered in the calculation of the snap-in force, and its value was between 1 and the δ value corresponding to the maximum pinning strength. In contrast, δ = 1 is more appropriate for the calculation of maximum adhesion force, indicating that the corrugations in the three-phase contact line could be neglected. These findings demonstrate that discrete hydrophilic defects make bubble-surface attachment difficult but have nearly no effect on bubble-surface detachment. Better understanding of the interactions between air bubbles and heterogeneous surfaces potential offers a new thought to control the bubble-particle interactions using appropriately design of particle surfaces.

Synthesizing slow-release fertilizers via mechanochemical processing for potentially recycling the waste ferrous sulfate from titanium dioxide production.

The goal of this study is aimed to develop a novel process to recycle the ferrous sulfate, the by-product of titanium dioxide industry. Zinc sulfate was added in the process of milling ferrous sulfate with calcium carbonate (CaCO3). The sulfates were transformed into carbonates to serve as slow-release fertilizers by co-grinding the starting materials of FeSO4·7H2O, ZnSO4·7H2O, and CaCO3 with small amounts of water in a planetary ball mill. The prepared samples were characterized by X-ray diffraction (XRD) analysis and quantitative measurements of the soluble ratios in water and 2% citric acid solution. It was found that Fe and Zn ions as sulfates were successfully combined with CaCO3 to form the corresponding Fe and Zn carbonates respectively. After milling, the release ratios of Fe and Zn nutrients in distilled water could be controlled at 0.1% and 0.7% respectively. Meanwhile, the release ratios of them in 2% citric acid solution were almost 98% and 100%. Milling speed was the critical parameter to facilitate the transformation reaction. The proposed process, as an easy and economical route, exhibits evident advantages, namely allowing the use of widely available and low-cost CaCO3 as well as industrial wastes of heavy metal sulfates as starting samples to prepare applicable products.

Polyvinyl alcohol/phytic acid/phosphorylated chitosan hydrogel electrode highly efficient electroadsorption of low concentration uranium from uranium tailings leachate.

In order to improve the removal rate of uranium and reduce the harm of radioactive pollution, a physically crosslinked polyvinyl alcohol/phosphorylated chitosan (PPP) hydrogel electrode was designed by freezing thawing method. The results show that PPP hydrogel has a good adsorption effect on uranium, and 200 mL of uranium tailings leachate is absorbed, and the treatment efficiency reaches 100 % within 15 min. PPP hydrogel can adapt to a wide range of pH conditions and exhibit excellent adsorption efficiency in the range of 3-9. At the same time, PPP hydrogel maintains an adsorption efficiency of over 85 % for 950 mg/L uranium solution. This lays the foundation for the practical application of PPP hydrogel. In addition, PPP hydrogel also exhibits good repeatability, after 7 cycles, the material still retains 95 % of its initial performance. The synergistic effect of various functional groups such as phosphate, hydroxyl, and ammonium in the material is the main mechanism of PPP's adsorption capacity for uranium. Furthermore, electrochemical adsorption method significantly enhances the adsorption performance of PPP hydrogel.

Preparation of novel polyvinyl alcohol-carbon nanotubes containing imidazolyl ionic liquid/chitosan hydrogel for highly efficient uranium extraction from seawater.

A novel polyvinyl alcohol-carbon nanotube containing an imidazolyl ionic liquid/chitosan composite hydrogel (termed CBCS) was prepared for highly selective uranium adsorption from seawater. The results show that CBCS has good adsorption properties for uranium within the pH range of 5.0-8.0. Kinetics and thermodynamics experiments show that the theoretical maximum adsorption capacity of CBCS to U(VI) is 496.049 mg/g (288 K, pH = 6.0), indicating a spontaneous exothermic reaction. Mechanism analysis shows that the hydroxyl group, amino group, and CN bond on the surface of CBCS directly participate in uranium adsorption and that the dense pores on the surface of CBCS play an important role in uranium adsorption. The competitive adsorption experiment shows that CBCS has excellent uranium adsorption selectivity. In addition, CBCS exhibits good reusability. After five adsorption-desorption cycles, the uranium adsorption rate of CBCS can still reach >98 %. Hence, CBCS has excellent potential for uranium extraction from seawater.

An eco-friendly porous hydrogel adsorbent based on dextran/phosphate/amino for efficient removal of Be(II) from aqueous solution.

A novel environmentally-friendly porous hydrogel adsorbent (GHPN) is firstly designed and prepared using dextran, phosphate, and calcium hydroxide for the adsorption of Be(II). GHPN shows good adsorption selectivity for Be(II) (Kd = 1.53 × 104 mL/g). According the adsorption kinetics and thermodynamics, the theoretical adsorption capacity of GHPN to Be(II) is 43.75 mg/g (35 °C, pH = 6.5), indicating a spontaneous exothermic reaction. After being reused for 5 cycles, the adsorption and desorption efficiencies of Be(II) with GHPN are obtained to be more than 80 %, showing acceptable recycling performance. Both of the characterizations and theoretical calculations indicate that the phosphate group, hydroxyl group, and amino group own the affinity to form stable complexes with Be(II). Benefiting from the introduction of phosphate and amino, the adsorption effect of the hydrogel adsorbent on Be(II) can be greatly improved, and surface precipitation, complexation, and ligand exchange are the dominant mechanisms of beryllium adsorption. The results suggest that GHPN has great potential to be utilized as an eco-friendly and useful adsorbent of Be(II) from aqueous solution.

Enhanced performance in uranium extraction by the synergistic effect of functional groups on chitosan-based adsorbent.

In this study, a novel sponge phosphoric acid functionalized porous composite adsorbent (named SPCCHC) was prepared from chitosan and chlorella hydrothermal charcoal. Kinetics and thermodynamics experiments showed that the theoretical maximum adsorption capacity of SPCCHC to U(VI) is 579.27 mg/g (288 K, pH = 6.5), indicating a spontaneous exothermic reaction. SPCCHC showed good adsorption selectivity for uranium in the adsorption studies of simulated seawater and a mixed solution of uranium-vanadium. The characterization of SPCCHC before and after U(VI) adsorption proves that the introduction of the phosphate group can greatly improve the adsorption effect of the adsorbent on uranium, particularly the distribution coefficients of uranium and vanadium differ by up to 89.5 times. At the same time, SPCCHC has good recycling performance, which is expected to be used in natural seawater uranium extraction.

Selective adsorption of uranium (VI) from wastewater using a UiO-66/calcium alginate/hydrothermal carbon composite material.

Uranium mining, smelting, and nuclear industries generate a considerable amount of wastewater containing uranium. To treat this wastewater effectively and inexpensively, a novel hydrogel material (cUiO-66/CA) was developed by co-immobilizing UiO-66 with calcium alginate and hydrothermal carbon. Batch tests were conducted to determine the optimal adsorption conditions for uranium using cUiO-66/CA, and the adsorption behavior was spontaneous and endothermic, confirming the quasi-second-order dynamics model and the Langmuir model. At a temperature of 308.15 K and pH = 4, the maximum adsorption capacity of uranium was 337.77 mg g-1. The surface appearance and interior structure of the material were analyzed using SEM, FTIR, XPS, BET, and XRD techniques. The results indicated two possible uranium adsorption processes of cUiO-66/CA: (1) Ca2+ and UO22+ ion exchange process and (2) coordination of uranyl ions with hydroxyl and carboxyl ions to form complexes. cUiO-66/CA exhibited strong selectivity for U (VI) in a multicomponent mixed solution and uranium-containing wastewater, with uranium removal rates of 99.03 % and 81.45 %, respectively. The hydrogel material demonstrated excellent acid resistance, and the uranium adsorption rate exceeded 98 % in the pH range of 3-8. Therefore, this study suggests that cUiO-66/CA has the potential to treat uranium-containing wastewater in a broad pH range.

Phosphorylation improved the competitive U/V adsorption on chitosan-based adsorbent containing amidoxime for rapid uranium extraction from seawater.

A novel chitosan-based porous composite adsorbent with multifunctional groups, such as phosphoric acid, amidoxime, and quaternary ammonium groups, was prepared to improve the adsorption rate and competitive uranium­vanadium adsorption of amidoxime group adsorbents. The maximum uranium adsorption capacity of PACNC was 962.226 mg g-1 at 308 K and pH = 7. The maximum adsorption rate constant of PACNC for uranium was 2.83E-2 g mg-1 min-1, which is 2.38 times that of ACNC (1.19E-2 g mg-1 min-1). Moreover, the adsorption equilibrium time was shortened from 300 (ACNC) to 50 (PACNC) min. In simulated and real seawater, the Kd and adsorption capacity of PACNC for uranium were approximately 8 and 6.62 times those for vanadium, respectively. These results suggest that phosphorylation significantly improved the competitive adsorption of uranium­vanadium and uranium adsorption rate. PACNC also exhibited good recycling performance and maintained stable adsorption capacity after five cycles. DFT calculations were used to analyze and calculate the possible co-complex structure of PACNC and uranium. The binding structure of phosphate and amidoxime is the most stable, and its synergistic effect effectively improves the competitive adsorption of uranium-vanadium of amidoxime. All the results demonstrated that PACNC has substantial application potential for uranium extraction from seawater.

Adsorptive removal of beryllium by Fe-modified activated carbon prepared from lotus leaf.

Lotus leaf was used as raw material to prepare HNO3-activated carbon with 1.5:1 (HNO3:lotus leaf) (wt:wt) impregnation. Then, the activated carbon was modified by Fe(NO3)3 to obtain Fe-activated carbon (Fe-AC). The adsorption test results show that Fe-AC maximum saturated adsorption capacity (Qm) is 45.68 mg/g when the Fe(NO3)3 loading is 5% of the total activated carbon, pH = 6, and the temperature is 35 ℃. The adsorption effect of Fe-AC under neutral conditions is better than that under alkaline and acidic conditions. The modified activated carbon has better adsorption selectivity. The obtained material (Fe-AC) was characterized by N2 adsorption-desorption isotherm, SEM, FT-IR, BET, XRD, XPS, and pHpzc. The total pore volume, specific surface area, and zero charges of modified activated carbon were increased. The types of modified functional groups were reduced, and the iron reacted with the functional groups, providing ion exchange sites for the adsorption of beryllium. The adsorption thermodynamics showed that the adsorption process was spontaneous and endothermic. The adsorption mechanism of Fe-AC to beryllium is mainly chemical adsorption.

Effect of mechanical-chemical modification on adsorption of beryllium by calcite.

The treatment of beryllium wastewater has become a major problem in industry. In this paper, CaCO3 is creatively proposed to treat beryllium-containing wastewater. Calcite was modified by an omnidirectional planetary ball mill by a mechanical-chemical method. The results show that the maximum adsorption capacity of CaCO3 for beryllium is up to 45 mg/g. The optimum treatment conditions were pH = 7 and the amount of adsorbent was 1 g/L, and the best removal rate was 99%. The concentration of beryllium in the CaCO3-treated solution is less than 5 µg/L, which meets the international emission standard. The results show that the surface co-precipitation reaction between CaCO3 and Be (II) mainly occurs. Two different precipitates are generated on the used-CaCO3 surface; one is the tightly connected Be (OH)2 precipitation, and the other is the loose Be2(OH)2CO3 precipitation. When the pH of the solution exceeds 5.5, Be2+ in the solution is first precipitated by Be (OH)2. After CaCO3 is added, CO32- will further react with Be3(OH)33+ to form Be2(OH)2CO3 precipitation. CaCO3 can be considered as an adsorbent with great potential to remove beryllium from industrial wastewater.

Adsorption of uranium by chitosan/Chlorella pyrenoidosa composite adsorbent bearing phosphate ligand.

In order to remove and recover uranium from acidic uranium-bearing wastewater in uranium mining and metallurgy. Herein, a novel chitosan/Chlorella pyrenoidosa composite adsorbent bearing phosphate ligand (CSP/CP) was designed and synthesized, demonstrating a high uranium adsorption capacity at a pH of 5 and excellent selectivity in an aqueous solution with eight coexisting ions. The CSP/CP exhibits a maximum adsorption capacity (1393.338 mg g-1) and selectivity (Su = 80.53%) for uranium, which is higher than many reported adsorbents. Mechanism analysis shows that the surface of CSP/CP is rich in hydroxyl, amino, phosphate and carboxyl groups, resulting in an excellent three-dimensional structure with active sites for high-performance uranium adsorption; U(VI) is selectively bound via ion exchanges with -COOH and -OH and through surface complexation with NH2 and PO. Furthermore, by desorption with 0.1 M Na2CO3 + 2% H2O2 at 318 K, CSP/CP can be recycled more than five times. It provides a new scientific basis for the preparation of high selectivity composite adsorbent by chitosan.

Cotransport of uranyl carbonate loaded on amorphous colloidal silica and strip-shaped humic acid in saturated porous media: Behavior and mechanism.

Uranyl carbonate (UC(VI)) is a stable form of uranyl (U(VI)) that widely coexists with amorphous colloidal silica (ACSi) and humic acid (HA) in carbonate-rich U-contaminated areas. In this context, the cotransport behavior and mechanism of UC(VI) with ACSi (100 mg L-1) and HA colloids in saturated porous media were systematically investigated. It was found that the ACSi and strip-shaped HA have a strong adsorption capacity for UC(VI), and their adsorption distribution coefficient (Kd) is 4-5 orders of magnitude higher than that of quartz sand (QS). In the ternary system, UC(VI) was mainly existing in the colloid-associated form at low UC(VI) concentration (4.2 × 10-6 M). Compared with the individual transport of UC(VI), the presence of ACSi and strip-shaped HA in the binary system promotes the transport of low-concentration UC(VI) (4.2 × 10-6 M) but shows a hindering effect when UC(VI) = 2.1 × 10-5 M. When ionic strength (IS) increased from 0 to 100 mM, the individual transport of UC(VI) and ACSi was weakened owing to the masking effect and the compression of the electrical double layer, respectively; this weakening effect is more pronounced in the binary (UC(VI)-ACSi) system. Notably, the transport of UC(VI) and ACSi in the ternary system is independent of the changes in IS due to the surface charge homogeneity strengthening the electrostatic repulsion between HA and QS. The Derjaguin-Landau-Verwey-Overbeek theory and retention profiles reveal the co-deposition mechanism of ACSi and UC(VI) in the column under different hydrochemical conditions. The nonequilibrium two-site model and the mathematical colloidal model successfully described the breakthrough data of UC(VI) and ACSi, respectively. These results are helpful for evaluating the pollution caused by UC(VI) migration in an environment rich in HA and formulating corresponding effective control strategies.

Co-transport of uranyl carbonate and silica colloids in saturated quartz sand under different hydrochemical conditions.

Uranyl carbonate (UC) and silica colloids (cSiO2) are widely distributed in carbonate-rich subsurface environments associated with uranium pollution. Mobile colloids such as cSiO2 can affect uranium's transport efficiency in the groundwater environment. Therefore, elucidating the mechanism of UC and cSiO2 co-transport in a saturated porous medium with different ionic strength (IS), pH, and UC concentration is essential for the prevention and control of groundwater radioactive pollution. At low UC concentrations (<2.1 × 10-5 M), cSiO2 is more prone to be deposited on the surfaces of quartz sand (QS) than UC, resulting in cSiO2 preventing UC transport. Compared to pH 7 and 9, at pH 5 the adsorption of uranium [in the form of 81.5% UO2CO3(aq), 8.6% UO22+, and 5.2% UO2OH+] on cSiO2 renders cSiO2 more prone to aggregate, causing smaller amounts of cSiO2 (86.6%) and UC (55.8%) to be recovered. Mechanisms responsible for the evolution of the pH and zeta potential in effluents have been proposed. Chemical reactions (ligand-exchange reactions and deprotonation) that occur in the QS column between UC and cSiO2/QS cause the pH of the suspension to varying, which in turn causes changes in the zeta potential and particle size of cSiO2. Eventually, the recovery rates of cSiO2 and UC are changed, depending upon the colloid particle size. Changes in ionic strength can seriously affect the stability of cSiO2 particles, and that effect is more significant when UC is present. Moreover, colloidal filtration theory, a non-equilibrium two-site model, and the Derjaguin-Landau-Verwey-Overbeek theory successfully describe the individual-transport and co-transport of cSiO2 and UC in the column. This study provides a strong basis for investigating UC pollution control in porous media.