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Exploration of easily produced visible light photocatalysts is still necessary. Thus, this study investigated the catalytic performance of a mixed metal oxide-titanium dioxide (MMO-TiO2) to remove perfluorooctanoic acid (PFOA), a typical and harmful perfluoroalkyl substance, under visible light conditions. Analysis of degradation efficiencies revealed that MMO-TiO2 exhibited a remarkable removal efficiency of 95.99 ± 1.49 %, surpassing other catalysts, including TiO2, ZnAl, MMO, and ZnAl-TiO2. MMO-TiO2, derived from ZnAl-TiO2 calcination, displayed a 5.66-fold higher apparent degradation rate constant (1.07 × 10−2 min−1) compared to ZnAl-TiO2 (1.89 × 10−3 min−1). These materials were characterized via X-ray powder diffractometry, Fourier transform infrared-attenuated total reflectance, N2 adsorption-desorption analysis, and field emission-scanning electron microscopy. Results revealed that O2•- radicals play a pivotal role as the predominant species that mediate PFOA removal. Comparative experiments using probe compounds confirmed increased O2•- production during MMO-TiO2 photoreaction under visible light. In addition, this study explored the effect of operational parameters, such as catalyst dose, initial PFOA concentration, solution pH, and water matrices on the photocatalytic removal process. These findings provide insight into the removal of PFOA using MMO-TiO2, highlighting the potential of this visible light catalyst for the eco-friendly removal of persistent organic pollutants in aquatic systems.

In a photocatalytic Cr(VI) reduction system, a hole scavenger (electron donor) is required to enhance the performance of photocatalytic reaction. In this study, mandarin peel extract (ME) was used as a natural sacrificing agent to enhance the photocatalytic Cr(VI) removal performance. The use of ME increased the Cr(VI) reduction rate (0.0286 min−1), and a Cr(VI) removal efficiency of 99.1% was achieved within 150 min. Hole scavenging by antioxidants contained in ME on TiO2 surface contributed to the enhancement of the photocatalytic Cr(VI) removal. Under the optimal conditions (ME volume = 5 mL, TiO2 dose = 0.2 g L−1, and pH = 2), the Cr(VI) reduction rate constant was about 1.2–7.3 times higher than the values reported in the literature. Furthermore, experiments on Cr(VI) treatment in real wastewater and H2O2 production showed the suitability of ME for other reaction systems. The photocatalytic Cr(VI) reduction efficiency achieved in 150 min in real wastewater increased from 58.6% to 83.6% after ME addition. This study employed a waste material as a reagent to improve the photocatalytic Cr(VI) removal performance for the photoreduction of a water pollutant, namely Cr(VI), which can be employed as a strategy for simultaneous waste and water treatment.

Material science is an interdisciplinary research field that includes interrelationships between the composition, structure, process, and performance of various materials and is widely integrated with other disciplines to form many interdisciplinary subjects [...]

Bioleaching has been regarded as a green alternative to chemical leaching in metal extraction processes. In this study, the bioleaching properties of indigenous acidophilic bacteria for various sulfide minerals were compared and evaluated in terms of pH reduction and metal leaching. The primary minerals in the samples were sphalerite (ZnS) (SP), galena (PbS) (GN1 and GN2), pyrite (FeS2) (PY), and chalcopyrite (CuFeS2) (CCP), and an indigenous acidophilic bacterium, Acidiphilium cryptum (99.56%), was applied for bioleaching experiments. The metal extraction in bioleaching differed according to the mineral content. The leached metal concentration of Zn was higher than that of Pb for the SP sample with a high ZnS content, whereas the concentration of Pb was higher than that of Zn for the GN1 and GN2 samples with a high PbS content. Meanwhile, the leaching rate of Zn was faster than that of Pb for all samples. Corrosion action was observed on the surface of bacterial residues in SP and GN1 samples. These results show that the bioleaching mechanism based on sulfide minerals proceeds through indirect biological oxidation, chemical oxidation, and direct bacterial oxidation. The results of this study can provide basic research data for process optimization when employing bioleaching to extract valuable metals.

Oxytetracycline (OTC) is a tetracycline antibiotic that is widely used in the drug therapy and livestock industry and may threaten human health and ecosystems when released into the environment. In this study, a catalyst was prepared from hand-warmer waste using a simple magnetic separation method. The prepared hand-warmer waste catalyst (HWWC) was used as a persulfate (PS) activator for OTC removal. Characterization methods, such as X-ray diffraction and scanning electron microscopy–energy dispersive X-ray spectrometry, were used to investigate the crystal structure, surface morphology, and weight ratios of the elements in the HWWC. The degradation efficiency of OTC in the presence of the catalyst and PS was studied, and the radical generation mechanism of the catalyst was investigated. The removal ratio of OTC by PS activation was greater than 99% for a reaction time of 24 min at a pH of 6. The effects of the HWWC dosage, PS concentration, and solution pH on OTC degradation were also investigated. The reuse test revealed that HWWC can be reused for eight cycles with great stability. These results suggest that PS activation using hand-warmer waste can be an efficient strategy for the degradation of antibiotics.

This study assessed the applicability of Fe-impregnated biochar derived from cattle manure (Fe-CMB) as an adsorbent for removing Sb(V) from aqueous solutions and investigated the Sb(V) adsorption mechanism. Fe-CMB was mainly composed of C, O, Cl, Fe, Ca, and P, and the adsorption of Sb(V) onto Fe-CMB was identified using an energy dispersive spectrometer and Fourier transform infrared spectroscopy. Sb(V) adsorption reached equilibrium within 6 h, and the Sb(V) adsorption data as a function of time were well described by the pseudo-second-order model. The Langmuir isotherm model fit the equilibrium data better than the Freundlich model. The maximum adsorption capacity of Fe-CMB for Sb(V) obtained from the Langmuir model was 58.3 mg/g. Thermodynamic analysis of Sb(V) adsorption by Fe-CMB indicated that the adsorption process was exothermic and spontaneous. The Sb(V) removal percentage increased with the Fe-CMB dose, which achieved a removal of 98.5% at 10.0 g/L Fe-CMB. Increasing the solution pH from 3 to 11 slightly reduced Sb(V) adsorption by 6.5%. The inhibitory effect of anions on Sb(V) adsorption followed the order: Cl− ≈ NO3− < SO42− < HCO3− < PO43−.

This study investigated the applicability of algae (Hizikia fusiformis, Green gracilaria, and Codium fragile) for removing heavy metals (Cd2+, Cu2+, Ni2+, and Pb2+) from aqueous solutions. Among the algae, H. fusiformis was chosen as a bioadsorbent and modified with NaOH and HCl. The results showed that the biosorption capacity of H. fusiformis improved significantly after treatment with NaOH; however, H. fusiformis modified with HCl did not achieve the expected value. The NaOH treatment enhanced the biosorption of metals on the treated H. fusiformis because of the hydrolysis reaction producing carboxylic (–COOH) and hydroxyl groups (–OH). The kinetics for Cd2+, Cu2+, Ni2+, and Pb2+ biosorption well fitted to pseudo-first-order, pseudo-second-order, and Elovich models, with R2 of >0.994. The Freundlich model provided a good fit for the equilibrium biosorption of Cd2+, Cu2+, and Ni2+ by both algae and the Langmuir model for Pb2+. The maximum biosorption of metals was in the order Pb2+ >> Cu2+ ≈ Ni2+ > Cd2+, with qmax of 167.73, 45.09, 44.38, and 42.08 mg/g, respectively. With an increase in the solution pH, metal biosorption was enhanced, and considerable enhancement was observed in the pH range of 2–4. Thus, H. fusiformis is expected to be considered a superior candidate for metal biosorption.

A mechanized thermo-chemical treatment system was developed to treat the undecomposed carcass and remediate livestock burial sites. Animal carcasses were thus processed via crushing, mixing, and treatment with quicklime treatment, heat treatment (200–500 °C), and mixing with sawdust. The machinery was applied to two sites where 16,000 chickens and 418 pigs had previously been buried in fiber-reinforced plastic storage bins. No dioxins were detected in the gas discharged during processing, and the concentration of total volatile organic compound, toluene, ethylbenzene, xylene, and styrene were 430.3, 139.0, 18.3, 21.4, and 10.4 μg/m3, respectively, which were below the air pollutant emission standards issued by the Korean Ministry of Environment. Korean standards stipulating the use of treated carcasses as compost (C, N, and P content, heavy metal concentration, Escherichia coli, and Salmonella) were met, but the germination index value was less than 70, not satisfying the criteria. Plant height, leaf length, leaf width, and dry weight of lettuce grown in soil amended with treated carcass product were significantly lower than those grown in low nutrient soil due to the poor germination index of the treated carcass. These results indicate that a composting process is required before the use of the treated carcass as a fertilizer. The addition of zeolite retarded the elution of ammonia from the carcasses and its efficiency was about 87.9%. It is expected that the mechanized thermo-chemical treatment process developed in this study could replace other technologies for the remediation of livestock burial sites.

Polyaniline (PANI) is a promising conducting polymer for surface modification of TiO2 to achieve extended photoresponse to visible light and increased photocatalytic efficiency. In this study, we report the synthesis of a PANI/TiO2 composite with different weight ratios of PANI, which was subsequently employed for photocatalytic degradation of methylene blue (MB), bisphenol A (BPA), and bacteriophage MS2 under visible-light irradiation. The functional groups, morphology, and light response of the composite were characterized by Fourier-transform infrared spectroscopy, field-emission transmission electron microscopy, and diffuse reflectance UV–visible spectroscopy, respectively. The PANI/TiO2 composite containing 4% by weight ratio of PANI was most suitable for MB degradation, and this photocatalyst was very stable even after repeated use (four cycles). The degradation of BPA and bacteriophage MS2 by PANI/TiO2 composite reached 80% in 360 min and 96.2% in 120 min, respectively, under visible-light irradiation. Therefore, the PANI/TiO2 composite with enhanced visible-light photocatalytic efficiency and stability can be widely used for the degradation of water contaminants.

We assessed the applicability of rice husk (RH) to remove cationic dyes, i.e., methylene blue (MB) and crystal violet (CV), from water. RH thermally treated at 75 °C showed a higher adsorption capacity than that at high temperatures (300–700 °C). For a suitable CV-adsorption model, a pseudo-first-order model for MB adsorption was followed by the kinetics adsorption process; however, a pseudo-second-order model was then suggested. In the qt versus t1/2 plot, the MB line passed through the origin, but that of CV did not. The Langmuir isotherm model was better than the Freundlich model for both dye adsorptions; furthermore, the adsorption capacity for MB and CV was 24.48 mg/g and 25.46 mg/g, respectively. Thermodynamically, the adsorption of both MB and CV onto the RH was found to be spontaneous and endothermic. This adsorption increased insignificantly on increasing the solution pH from 4 to 10. With an increasing dosage of the RH, there was an increase in the removal percentages of MB and CV; however, adsorption capacity per unit mass of the RH was observed to decrease. Therefore, we conclude that utilizing RH as an available and affordable adsorbent is feasible to remove MB and CV from wastewater.

Ceramic membranes and ion exchangers are effective at removing turbidity and ionic contaminants from water, respectively. In this study, we demonstrate the performance of a hybrid ion-exchange fabric/ceramic membrane system to treat metal ions and turbidity at the same time in synthetic wastewater. The removal rate of As(V) and Zn(II) by the ceramic membrane increased with solution pH, while turbidity was completely removed regardless of the solution pH. The main reaction of As(V) removal was adsorption at solution pH 6 and precipitation at solution pH 8, whereas phase-change was the predominant reaction for Zn(II) removal at both solution pH values. The removal efficiency of the ion-exchange fabric was affected by the solution pH, with the maximum removal capacity of As(V) occurring at solution pH 4. The As(V) adsorption capacity of the ion-exchange fabric reached equilibrium within 120 min. The ion-exchange capacity of the ion-exchange fabric was compared with commercial ion-exchange fibers. The regeneration efficiency of the ion-exchange fabric using 0.1 M NaCl solution was around 95% on average and decreased slightly as the number of regeneration cycles was increased. Over 80% of As(V) and Zn(II) were steadily removed at solution pH 6 by the hybrid ion-exchange fabric/ceramic membrane system. Reduced flow rate and removal capacity were recovered through a backwashing process during continuous treatment with the hybrid ion-exchange fabric/ceramic membrane system.

In this study, we explored the adsorption potential of biochar derived from palm kernel shell (BC-PKS) as an affordable adsorbent for the removal of crystal violet from wastewater. Kinetics, equilibrium, and thermodynamics studies were carried out to evaluate the adsorption of crystal violet onto BC-PKS. The kinetics adsorption process followed the pseudo-second-order model, indicating that the rate of adsorption is principally controlled by chemisorption. The adsorption equilibrium data were better fitted by the Langmuir isotherm model with a determination coefficient of 0.954 and a maximum adsorption of 24.45 mg/g. Thermodynamics studies found the adsorption of crystal violet by BC-PKS to be endothermic with increasing randomness at the BC-PKS/crystal violet interface. The percentage removal and adsorption capacity increased with the pH of the solution, as the negative charges on the biochar surface at high pH enhance the electrostatic attraction between crystal violet molecules and BC-PKS. Increasing the BC-PKS dosage from 0.1 to 1.0 g increased percent removal and decreased the adsorption capacity of crystal violet onto BC-PKS. Therefore, biochar from agricultural by-products, i.e., palm kernel shell, can be cost-effective adsorbents for the removal of crystal violet from textile wastewater.

Polyacrylonitrile (PAN) fibers were prepared via electrospinning and were modified with diethylenetriamine (DETA) to fabricate surface-modified PAN fibers. The surface-modified PAN fibers were used to evaluate their adsorption capacity for the removal of Cu(II) from aqueous solutions. Batch adsorption experiments were performed to examine the effects of the modification process, initial concentration, initial pH, and adsorbent dose on the adsorption of Cu(II). Kinetic analysis revealed that the experimental data fitted the pseudo-second-order kinetic model better than the pseudo-first-order model. Adsorption equilibrium studies were conducted using the Freundlich and Langmuir isotherm models, and the findings indicated that the PAN fibers modified with 85% DETA presented the highest adsorption capacity for Cu(II) of all analyzed samples. Moreover, the results revealed that the Freundlich model was more appropriate than the Langmuir one for describing the adsorption of Cu(II) onto the modified fibers at various initial Cu(II) concentrations. The maximum adsorption capacity was determined to be 87.77 mg/g at pH 4, and the percent removal of Cu(II) increased as the amount of adsorbent increased. Furthermore, the surface-modified PAN fibers could be easily regenerated using NaOH solution. Therefore, surface-modified PAN fibers could be used as adsorbents for the removal of Cu(II) from aqueous solutions.

UV/H2O2 is a commonly used advanced oxidation process for removing non-biodegradable organic compounds. However, additional efforts are needed to understand the relative significance of operational factors during the UV/H2O2. Here, we investigated the effect and specific contribution of crucial factors such as H2O2 concentration, UV intensity, and reaction time on the color and total organic carbon (TOC) removal efficiency in textile wastewater using the one-factor-at-a-time method and multi-layer perceptron (MLP) analysis. The results showed that color removal was enhanced with high H2O2 concentration, high UV intensity, and long reaction time. Overall, more than 99% removal of color was achieved by the UV/H2O2, utilizing the following parameters: H2O2 concentration of 5 mM, UV intensity of 26.6 W/m², and reaction time of 180 min. On the other hand, the removal of TOC was increased by high H2O2 concentration and long reaction time, but not by high UV intensity. In the MLP analysis, the H2O2 concentration was identified as the primary factor affecting both color and TOC removal, accounting for 43% and 50% reduction of the color and TOC, respectively. Overall, this study helps to understand the relative importance of the most critical operating factors in treating actual textile wastewater by the UV/H2O2. [ABSTRACT FROM AUTHOR]

This study assessed the applicability of seafood waste, Patinopecten yessoensis shells (PY), for fluoride removal. PY was modified by calcination to improve its fluoride removal capacity, and 800°C was the optimum calcination temperature its modification as a fluoride adsorbent. Fluoride adsorption by PY-800 was confirmed due to the formation of fluorite (CaF2) through X-ray diffraction analysis. The fluorine adsorption to PY-800 reached equilibrium within 2 h at an initial fluoride concentration of 50 mg/L, and a reaction time of 36 h was required to reach equilibrium at 200 mg/L. Both the pseudo-first-order and pseudo-second-order models described the kinetic adsorption data well. In isotherm studies, the fluoride adsorption of PY-800 was best suited to the Langmuir model. The enthalpy change of fluoride adsorption was 45.49 kJ/mol, ranging in the boundary between physical and chemical adsorption. Fluoride adsorption decreased from 113.13 to 86.01 mg/g as the pH increased from 3 to 11. Anions in the solution inhibited fluoride adsorption, and impacted other ions in the following order: chloride < sulfate < carbonate < phosphate. PY-800 has a higher adsorption capacity than other reported adsorbents, with a maximum of 159.62 mg/g. These results show that PY-800 recycled from food waste is highly efficient for fluoride removal. [ABSTRACT FROM AUTHOR]

Surface-modified activated carbon (AC) was fabricated using different concentration of HCl or NH4OH to enhance its adsorption capacity for the removal of Cr(VI) from aqueous solution. Surface-modified ACs were also characterized by analyzing their morphologies, specific surface area, zeta potential, elemental composition, and functional groups. Batch adsorption experiments revealed that the modification of AC with HCl was more effective for increasing Cr(VI) removal by AC than NH4OH. Cr(VI) adsorption onto AC treated with 20% HCl (20H-AC) under different contact times followed the pseudo-second-order model, indicating that chemisorption limited the rate of Cr(VI) adsorption. The determination coefficient of the Langmuir model fit was higher than that of the Freundlich model. The maximum adsorption capacity of 20H-AC for Cr(VI) was 177.9 mg/g, which was comparable to adsorbents listed in other literatures. A thermodynamic study showed that Cr(VI) adsorption onto 20H-AC is an endothermic and spontaneous reaction and chemisorption. An increase in solution pH from 2 to 10 resulted in a significant decrease in the adsorption amount of Cr(VI), that is from 78.37 to 28.40 mg/g. The negative influence of HCO3 - on the Cr(VI) adsorption was higher than that of SO4 2- and NO3 -. Therefore, this study reveals that the modification of AC using HCl is effective in enhancing the removal efficiency of Cr(VI). [ABSTRACT FROM AUTHOR]

This study investigated triclosan removal using rice husks thermally treated at 100°C, 300°C, and 500°C. Rice husks were characterized by analyzing their surface morphologies, pore size, pore diameter, specific surface area, elemental composition, and chemical functional groups. The rice husks thermally treated at 300°C (RH-300) displayed higher triclosan removal efficiency than those treated at other temperatures. Adsorption of triclosan onto RH-300 was achieved within 4 h, and the kinetic adsorption data were well described by a pseudo-first-order model. The Langmuir model described the equilibrium adsorption of triclosan to RH-300 more suitably than the Freundlich model did, indicating that triclosan was adsorbed on RH-300 as a monolayer. Positive enthalpy changes and negative free energy change obtained from thermodynamic experiments indicated that triclosan adsorption by RH-300 was endothermic and spontaneous under these experimental conditions. A decrease in triclosan adsorption with an increase in solution pH was more obvious in the RH-300 dosage of 3.33 than 6.67 g/L. As fulvic acid increased from 0-10 mg/L, triclosan adsorption onto RH-300 decreased by 25.3%; changes in triclosan adsorption were not distinct above 10 mg/L. In conclusion, RH-300 is a low-cost and effective material for the removal of triclosan from aqueous solutions. [ABSTRACT FROM AUTHOR]

Phosphate, which can cause eutrophication of the aquatic environment, can be effectively removed by an adsorption process using calcium-containing adsorbents. In this study, Ca-carbon foam was prepared by a simple method that entailed addition of Ca during the manufacturing process of carbon foam, and the phosphate removal characteristics of the prepared foam were analyzed using kinetic, equilibrium isotherm, and artificial neural network (ANN) models. The phosphate adsorption capacity decreased with an increase in the solution pH from 3.05 to 6.99. Furthermore, phosphate adsorption increased with increasing time, and the kinetic data were found to be well described by a pseudo-second- order model. The Freundlich isotherm provided the best fit of the equilibrium data, which indicates multilayer adsorption of phosphate on the Ca-carbon foam. The phosphate adsorption capacity as a function of three operational parameters—solution pH, initial phosphate concentration, and time—was well predicted by an ANN model (R² > 0.993), and the optimal ANN for the process of phosphate adsorption on Ca-carbon foam had a 3–20–1 structure with 20 hidden layers. The solution pH was the most influential operational parameter out of all the examined parameters. The results of these analyses are expected to be useful in designing the process of phosphate adsorption from aqueous solutions. [ABSTRACT FROM AUTHOR]

The use of illite for the removal of microorganisms from water has not been studied by other researchers. We assessed the applicability of illite for bacterial removal from water and compared it with commercially available filter media. Column experiments were performed to evaluate the bacterial removal efficiency of filter media under different pH conditions and with chlorine-free tap water. The removal percentage of illite was higher than 90% and its sticking efficiency was greater than 0.85 under all experimental conditions. The removal percentage and sticking efficiency of illite were far superior to that of the other filter media. The high bacterial removal efficiency of illite may be a result of bacterial adhesion enhancement by the Al and Fe eluted from illite. A response surface methodology was employed to optimize experimental conditions including pH, filter depth, and flow rate and to elucidate the effects and interactions of these variables. All these parameters significantly influenced the bacterial removal of illite. From the optimization study, the highest removal percentage of 99.9% was obtained under conditions of a pH of 4.02, a filter depth of 18.49 cm, and a flow rate of 0.86 mL/min. Illite is a potential filter medium for purifying water and preventing groundwater pollution from septic tanks and carcass disposal. [ABSTRACT FROM AUTHOR]

This study was performed to identify an economical but highly effective adsorbent for the removal of fluoride. Dolomite was thermally treated to improve its adsorption capacity for fluoride; dolomite thermally treated at 800°C (DTT-800) was superior to that treated at other temperatures. The maximum fluoride adsorption capacity of DTT-800 was 163.7 mg g-1, which was superior to that of other adsorbents reported in the literature. Fluoride adsorption onto DTT-800 was characterized by chemisorption, multi-layer adsorption, and an endothermic reaction. Response surface methodology was employed to investigate the influence pH, ionic strength, reaction temperature, and time on fluoride adsorption; these parameters were optimized to maximize the adsorption process. pH and ionic strength had a negative effect, while reaction temperature and time had a positive effect on fluoride adsorption. The influence of all four parameters was significant (p <0.001). Highest fluoride adsorption (165.91 mg g-1), was obtained under the following conditions: pH 4.57, ionic strength 7.45 mM, temperature 28.30°C, and contact time 58.33 h. This study demonstrated that DTT-800 is a low-cost, natural, and abundant material for the removal of fluoride from aqueous solutions. [ABSTRACT FROM AUTHOR]

Water and soil properties in paddy fields subjected to organic and conventional farming were characterized over the rice cycle in South Korea. To achieve the goals of this study, we sampled and analyzed soil and water from 24 organic paddy plots and 11 conventional paddy plots in March, May, August, and October 2016. The results were analyzed using statistical analyses, including analysis of variance (ANOVA), cluster analysis, and principal component analysis. The ANOVA results showed that water content (WC), electrical conductivity (EC), organic matter (OM), and available phosphorus (P2O5) in soil varied significantly (p < 0.01) depending on the farming method. Higher OM, EC, and P2O5 of soil were observed in the conventional paddies than in the organic paddies. All soil properties, except pH and ammonium, depended on seasonal variation. Cluster analysis revealed that soil properties in May were distinctly separated from those in other seasons mainly due to basal fertilization. The principal component analysis distinguished the soil properties in different seasons, but such a distinction was not observed between the soil properties in organic and conventional paddies. Low contents of WC, OM, and total N were observed in March. High concentrations of nitrate and total P were observed in May, but these were low in August and October. The soils from October were also characterized by high concentrations of EC and P2O5. These results indicate that the sampling time for soil and water can significantly influence the evaluation of soil properties with different farming methods. [ABSTRACT FROM AUTHOR]

In this study, a modacrylic anion exchange fiber (KaracaronTM SA2) made from acrylonitrile and vinyl chloride was used for the removal of Cr(VI) and As(V) in aqueous solutions. This study focused on the two parts: (i) investigate the simultaneous removal of Cr(VI) and As(V) present in mineral processing wastewater by the SA2, and (ii) examine the protonated amine sites available on the SA2 in response to pH change using X-ray photo electron spectroscopy (XPS) analysis. Batch experiments indicated that the maximum removal capacities for Cr(VI) and As(V) were 2.350 and 0.346 mmol/g, respectively. The SA2 was successfully regenerated by 0.1 M NaCl solution and reused for five adsorption-desorption experiments. The removal of Cr(VI) and As(V) was influenced by the solution pH. The pH dependency of Cr(VI) and As(V) removal was closely related to both the number of protonated amines available for anion exchange and speciation of Cr(VI) and As(V) in response to the pH change. XPS analysis demonstrated that the C-N+ peak (401.5 eV) was prominent at pH 2. As pH increased to 4 and 10, the C-N+ peak gradually decreased due to partial deprotonation of the anion exchange sites. At pH 12, the C-N+ peak disappeared because nearly all of the exchange sites were deprotonated. Simultaneous removal experiments in mineral processing wastewater (pH = 2.9; Cr(VI) concentration = 60.2 mmol/L; As(V) concentration = 67.5 mmol/L) demonstrated that Cr(VI) removal by the SA2 tended to be greater than that of As(V). The Cr(VI) and As(V) removal capacities in the wastewater were 1.587–3.098 and 0.042–2.124 mmol/g, respectively, at fiber dosages of 2–20 g/L. [ABSTRACT FROM AUTHOR]

Attapulgite was used for the removal of phosphate in aqueous solution and was thermally treated to improve its phosphate adsorption capacity. Attapulgite treated at different temperatures was analyzed to characterize its physical and chemical properties and quantify its phosphate removal efficiency. Attapulgite treated at 700°C (700-ATP) was found to remove phosphate more efficiently than the attapulgite treated at the other temperatures did. The pseudo-second-order and Freundlich models were appropriate for describing phosphate adsorption onto 700-ATP for various reaction times and initial phosphate concentrations, respectively. Both enthalpy and entropy increased during phosphate adsorption onto 700-ATP. An increase in solution pH from 3 to 11 led to a decrease in the adsorption amount of phosphate from 51.53 to 42.43 mg/g. The influence of competitive anions on the phosphate adsorption was as follows: HCO3 – > SO42– > NO3– . Attempts to reutilize the 700-ATP with deionized water were not successful. Phosphorus fractionation experimentation showed that most of the phosphate in 700-ATP was present in residual form. Phosphorus was strongly adsorbed onto 700-ATP. This study demonstrated that thermal treatment is a simple but effective way to improve the phosphorus removal efficiency of attapulgite and 700-ATP is a low-cost, natural, and abundant material for the removal of phosphate from aqueous solution. [ABSTRACT FROM AUTHOR]