Study of arsenic(V) adsorption on bone char from aqueous solution

Arsenic is a toxic element and may be found in natural waters as well as in industrial waters. Leaching of arsenic from industrial wastewater into groundwater may cause significant contamination, which requires proper treatment before its use as drinking water. The present study described the removal of As(V) on bone char in batch studies conducted as a function of pH, dosage of adsorbent, and contact time. Kinetics revealed that uptake of As(V) ion by bone char was very rapid in the first 30min and equilibrium time was independent of initial As(V) concentration. And the adsorption process followed a first-order kinetics equation. The arsenic removal was strongly dependent on pH and dosage of adsorbent. Fourier transform infrared spectra of bone char before and after As(V) adsorption demonstrated that Ca-OH functional group plays an important role for As(V) ions removal, and the mechanisms of the removal of As(V) on bone char was complex mechanism where both co-precipitation and ion exchange. The results suggested that bone char can be used effectively for the removal of As(V) ion from aqueous solution.     

The effect of nanocrystalline magnetite size on arsenic removal

Higher environmental standards have made the removal of arsenic from water an important problem for environmental engineering. Iron oxide is a particularly interesting sorbent to consider for this application. Its magnetic properties allow relatively routine dispersal and recovery of the adsorbent into and from groundwater or industrial processing facilities; in addition, iron oxide has strong and specific interactions with both As(III) and As(V). Finally, this material can be produced with nanoscale dimensions, which enhance both its capacity and removal. The objective of this study is to evaluate the potential arsenic adsorption by nanoscale iron oxides, specifically magnetite (Fe₃O₄) nanoparticles. We focus on the effect of Fe₃O₄ particle size on the adsorption and desorption behavior of As(III) and As(V). The results show that the nanoparticle size has a dramatic effect on the adsorption and desorption of arsenic. As particle size is decreased from 300 to 12 nm the adsorption capacities for both As(III) and As(V) increase nearly 200 times. Interestingly, such an increase is more than expected from simple considerations of surface area and suggests that nanoscale iron oxide materials sorb arsenic through different means than bulk systems. The desorption process, however, exhibits some hysteresis with the effect becoming more pronounced with small nanoparticles. This hysteresis most likely results from a higher arsenic affinity for Fe₃O₄ nanoparticles. This work suggests that Fe₃O₄ nanocrystals and magnetic separations offer a promising method for arsenic removal.     

Removal of As(V) and As(III) by reclaimed iron-oxide coated sands

This paper aims at the feasibility of arsenate and arsenite removal by reclaimed iron-oxide coated sands (IOCS). Batch experiments were performed to examine the adsorption isotherm and removal performance of arsenic systems by using the IOCS. The results show that the pH(zpc) of IOCS was about 7.0 +/- 0.4, favoring the adsorption of As(V) of anion form onto the IOCS surface. As the adsorbent dosage and initial arsenic concentration were fixed, both the As(V) and As(III) removals decrease with increasing initial solution pH. Under the same initial solution pH and adsorbent dosage, the removal efficiencies of total arsenic (As(V) and As(III)) were in the order as follows: As(V)>As(V)+As(III)>As(III). Moreover, adsorption isotherms of As(V) and As(III) fit the Langmuir model satisfactorily for the four different initial pH conditions as well as for the studied range of initial arsenic concentrations. It is concluded that the reclaimed IOCS can be considered as a feasible and economical adsorbent for arsenic removal.     

Adsorption of fluoride on gas concrete materials

In this study, gas concrete waste materials were used to remove F(-) from aqueous solutions. The influence of pH, temperature, agitation rate and gas concrete dosage on F(-) removal was investigated by conducting a series of batch adsorption experiments. In addition, the yield and mechanisms of F(-) removal were explained on the basis of the results of X-ray spectroscopy and images of scanning electron microscopy (SEM) of the particles before and after adsorption. The values of zeta potential and BET-N(2) specific surface area of gas concrete particles were defined. In this study, F(-) removal in excess of 96% was obtained. It was thought that the removal of fluoride by gas concrete took place both adsorption and precipitation of Al(3+) and Ca(2+) salts (F(-)). As a result of this study, it was concluded that wastes of gas concrete were an efficient adsorbent for the removal of F(-).     

Adsorptive desulfurization by zinc-impregnated activated carbon: characterization,kinetics, isotherms,and thermodynamic modeling

Sulfur oxides emission because of burning of liquid fuels has become a global environmental challenge. Refineries need to meet ever-stringent liquid fuel standards by using newer desulfurization methods. Present paper reports the results of the studies on adsorptive removal of sulfur compounds from model fuel by zinc-impregnated granular activated carbon (GAC). Zn-loaded adsorbent (Zn-GAC) prepared by wet impregnation method was characterized for its textural, morphological, and structural characteristics by different techniques like liquid nitrogen adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The adsorbent was further used for the removal of dibenzothiophene (DBT), a sulfur compound, from iso-octane. Equilibrium adsorption was obtained in 6 h. The equilibrium adsorption data were well represented by the Redlich–Peterson isotherm. Thermodynamic parameters were calculated by applying the van’t Hoff and Clausius–Clapeyron equations. Values of change in enthalpy and entropy were found to be 4.89 kJ/mol and 30 J/mol K, respectively. Isosteric heat of adsorption was correlated with surface coverage and heterogeneous nature of the Zn-GAC.     

Carbonate effects and pH-dependence of uranium sorption onto bacteriogenic iron oxides: kinetic and equilibrium studies

The removal of U(VI) from groundwaters by adsorption onto bacteriogenic iron oxides (BIOS) has been investigated under batch mode. The adsorbent dosage, the uranium concentration, the concentration of carbonate and the use of a real groundwater spiked with uranium comprised the examined parameters. In addition, the effect of pH was examined in two different water matrixes, i.e., in distilled water and in real groundwater. Equilibrium studies were carried out to determine the maximum adsorption capacity of BIOS and the data correlated well with the Langmuir and Freundlich models. The presence of carbonate affected adversely the adsorption of U(VI) onto BIOS. The maximum adsorption capacity of BIOS was 9.25 mg g(-1) at 0.1mM carbonate concentration and decreased to 6.93 mg g(-1) at 0.5mM carbonate concentration, whereas at carbonate concentration of 2mM practically no adsorption occurred. The data were further analyzed using the pseudo-second order kinetic equation, which fitted best the experimental results. The initial adsorption rate (h) was found to increase with decreasing the concentration of carbonate in all cases. When experiments were accomplished in the absence of carbonate, the pH values did not have an effect on the adsorption of U(VI). However, the extent of U(VI) adsorption was strongly pH-dependent when the experiments were carried out in the real groundwater. The maximum adsorption capacity increased sharply as the pH decreased and optimum removal was obtained in the pH range 3.2-4.0, thus bacteriogenic iron oxides can found application in the removal of U(VI) by adsorption from low pH or low carbonate waters.     

Synthesis of different nanostructured flower-like iron oxides and study of their performance as adsorbent

Iron oxides with different flower-like nanostructures have been successfully synthesized by decomposition of the iron alkoxide precursor at different conditions. The effect of reaction time (reflux time) and the calcination conditions on the morphology and composition of prepared iron oxides were investigated. Characterizations of the prepared powders were performed by scanning electronic microscopy, X-ray diffraction and N₂ adsorption/desorption isotherm. The results show that the prepared nanostructured iron oxides can be used as adsorbent for rapid removal of dye pollutants from water.     

The synthesis,activation and characterization of charcoal powder for the removal of methylene blue and cadmium from wastewater

Charcoal prepared from biomass, wastes of the local forest (tree branches), activated with NaOH solution and with Degussa P25 (TiO₂) was used as adsorbent and photocatalyst for the removal of cadmium cations and methylene blue from wastewater. These materials were characterized by using atomic force microscopy for roughness surface. The energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis indicate the existence of nano TiO₂ on the charcoal surface. Additionally, the FT-IR spectroscopy measurements indicate that the alkali treatment develops hydroxyl groups on charcoal surface which could adsorb methylene blue, heavy metals and other pollutants via the synergistic effect. The activities of the charcoal (BC), activated charcoal (BCA) and BCA/TiO₂ mixture (BCA-D) depend on the contact time, adsorbent dosage and pH. The adsorption kinetic data were tested using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The kinetic studies showed that the adsorption is followed by the pseudo-second-order reaction with regard to the intraparticle diffusion rate kinetics.     

Kinetics and mechanism of arsenate removal by nanosized iron oxide-coated perlite

This study discussed the adsorption kinetics of As(V) onto nanosized iron oxide-coated perlite. The effects of pH, initial concentration of As(V) and common anions on the adsorption efficiency were also investigated. It was observed that a 100% As(V) adsorption was achieved at pH value of 4-8 from the initial concentration containing 1.0 mg-As(V)L(-1) and the adsorption percentage depended on the initial concentration; the phosphate and silicate ions would not interfere with the adsorption efficiency. Furthermore, nanosized iron oxide-coated perlite (IOCP) has been shown to be an effective adsorbent for the removal of arsenate from water. The adsorption kinetics were studied using pseudo-first- and pseudo-second-order models, and the experimental data fitted well with the pseudo-second-order model. Moreover, it suggests that the Langmuir isotherm is more adequate than the Freundlich isotherm in simulating the adsorption isotherm of As(V). The adsorption rate constant is 44.84 L mg(-1) and the maximum adsorption capacity is 0.39 mg g(-1). These findings indicate that the adsorption property of IOCP gives the compound a great potential for applications in environmental remediation.     

MnCl2-NaOH改性硅藻精土吸附剂的制备及其对As(V)的吸附机制

以硅藻精土为基体,MnCl₂和NaOH为复合改性剂制备了针对As（V）离子的吸附剂。研究了MnCl₂-NaOH/硅藻土吸附剂用量对As（V）去除率的影响,通过SEM、FT-IR、XRD、XPS对改性前后及吸附后的样品进行了微观分析。结果表明：随着吸附剂投量的增加,溶液中As（V）的去除率从44.9%增加到93.9%。改性后硅藻基体未发生改变,MnCl₂-NaOH/硅藻土吸附剂平均孔径变大,比表面积增大近7倍。硅藻土经改性后红外活性羟基峰消失,表面新生成Mn-O-Si吸收峰,在XRD数据上显示新生成含有MnO₂的物相,表面Mn得到电子,通过氧化与硅藻表面形成复合接枝,吸附剂吸附溶液中含As（V）的离子后,出现Mn₃（AsO₄）（OH）₄等物相,吸附过程中As得电子,Mn失电子,O、Si表面电子向As偏移,As在吸附剂表面的吸附方式有配位吸附、电荷吸附等。     

Adsorption and removal of arsenic(V) from drinking water by aluminum-loaded Shirasu-zeolite

The demand for effective and inexpensive adsorbents is to increase in response to the widespread recognition of the deleterious health effects of arsenic exposure through drinking water. A novel adsorbent, aluminum-loaded Shirasu-zeolite P1 (Al-SZP1), was prepared and employed for the adsorption and removal of arsenic(V) (As(V)) ion from aqueous system. The process of adsorption follows first-order kinetics and the adsorption behavior is fitted with a Freundlich isotherm. The adsorption of As(V) is slightly dependent on the initial pH over a wide range (3-10). Al-SZP1 was found with a high As(V) adsorption ability, equivalent to that of activated alumina, and seems to be especially suitable for removal of As(V) in low concentration. The addition of arsenite, chloride, nitrate, sulfate, chromate, and acetate ions hardly affected the As(V) adsorption, whereas the coexisting phosphate greatly interfered with the adsorption. The adsorption mechanism is supposed as a ligand-exchange process between As(V) ions and the hydroxide groups present on the surface of Al-SZP1. The adsorbed As(V) ions were desorbed effectively by a 40 mM NaOH solution. Continuous operation was demonstrated in a column packed with Al-SZP1. The feasibility of this technique to practical utilization was also assessed by adsorption/desorption multiple cycles with in situ desorption/regeneration operation.     

Synthesis and thermoanalytical study of SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> composites modified with macrocyclic endoreceptors

We have developed processes for the fabrication of SiO₂–TiO₂ composites containing crown ethers (CEs) with composite: CE weight ratios from 1: 0.06 to 1: 1. As oxide sources, we used titania and silica sols. The composites were characterized by differential thermal analysis, X-ray diffraction, and adsorption gravimetry. The results demonstrate that most of the water and the solvent are bound into a complex with the CE, which decomposes at temperatures from 170 to 230°C. The temperature range of CE removal depends on the SiO₂: TiO₂ and oxide: CE ratios in the composite. Our results demonstrate effectiveness of strontium cation imprint formation in an adsorbent in the sol–gel processing step, which ensures an increase in the amount of strontium cation adsorption by 20%. We have identified conditions for quantitative lanthanum, strontium, and barium adsorption on the synthesized composites.     

Removal of As(V) and Cr(VI) from aqueous solutions using solid waste from leather industry

This study evaluated the feasibility of using a solid waste from the leather industry as an adsorbent for removal of Cr(VI) and As(V) from aqueous media. The adsorbent material was characterized by chemical analyses, infrared spectroscopy, and scanning electronic microscopy (SEM) prior to reaction in order to assess its surface properties. Langmuir and Freundlich equations were used for analyzing the experimental data, which showed a better fit to the Langmuir model, thus suggesting a monolayer adsorption process in the surface of the adsorbent. The high amounts of Cr(VI)-133 mg g(-1) and As(V)-26 mg g(-1) adsorbed demonstrates the great potential for using this solid waste from the leather industry as a low-cost alternative to the traditionally used adsorbent materials.     

Adsorption behavior of phosphate on lanthanum(III)-coordinated diamino-functionalized 3D hybrid mesoporous silicates material

An inorganic/organic hybrid adsorbent for phosphate adsorption was synthesized by introducing lanthanum (La) onto diamino modified MCM-41. The adsorbent was characterized by XRD, SEM, BET, TGA, and FTIR spectroscopy. A series of batch tests were conducted to investigate the influence of contact time, initial phosphate concentration, pH of the solution, and competitive ions on the phosphate adsorption capacity. The Langmuir and Freundlich models were used to simulate the sorption equilibrium, and the results indicated that the Langmuir model fitted the experiment data better than the Freundlich model. The maximum adsorption capacity calculated from the Langmuir model is 54.3 mg/g. For kinetic study, phosphate adsorption followed the pseudo-second-order equation well with a correlation coefficient greater than 0.99. Optimum pH value for the removal of phosphate was between 3.0 and 7.0. The presence of Cl(-) and NO(3)(-) has neglectable influence on the phosphate adsorption. F(-)and SO(4)(2-) have negative effects on the adsorption of phosphate. Phosphate on the spent adsorbent can be almost released by 0.01 M NaOH solution in 12 min.     

Adsorption characteristics of As(III) from aqueous solution on iron oxide coated cement (IOCC)

Contamination of potable groundwater with arsenic is a serious health hazard, which calls for proper treatment before its use as drinking water. The objective of the present study is to assess the effectiveness of iron oxide coated cement (IOCC) for As(III) adsorption from aqueous solution. Batch studies were conducted to study As(III) adsorption onto IOCC at ambient temperature as a function of adsorbent dose, pH, contact time, initial arsenic concentration and temperature. Kinetics reveal that the uptake of As(III) ion is very rapid and most of fixation occurs within the first 20 min of contact. The pseudo-second order rate equation successfully described the adsorption kinetics. Langmuir, Freundlich, Redlich-Peterson (R-P), and Dubinin-Radushkevich (D-R) models were used to describe the adsorption isotherms at different initial As(III) concentrations and at 30 g l(-1) fixed adsorbent dose. The maximum adsorption capacity of IOCC for As(III) determined from the Langmuir isotherm was 0.69 mg g(-1). The mean free energy of adsorption (E) calculated from the D-R isotherm was found to be 2.86 kJ mol(-1) which suggests physisorption. Thermodynamic parameters indicate an exothermic nature of adsorption and a spontaneous and favourable process. The results suggest that IOCC can be suitably used for As(III) removal from aqueous solutions.     

Combined use of photocatalyst and adsorbent for the removal of inorganic arsenic(III) and organoarsenic compounds from aqueous media

A novel method for the removal of inorganic arsenic(III) (As(III)), monomethylarsonate (MMA), and dimethylarsinate (DMA) from aqueous media, was proposed and investigated. This method involves the combined use of TiO₂-photocatalyst and an adsorbent, which has a high ability of As(V) adsorption, under photo-irradiation. When an aqueous solution of As(III) was stirred and irradiated by sunlight or xenon lamp in the presence of TiO₂ suspension, the oxidation of As(III) into As(V) was effectively attained. By use of the same photocatalytic reaction, MMA and DMA were also degraded into As(V), while the total organic carbon (TOC) in the aqueous phase was decreased. When an aqueous solution of As(III) was stirred with a mixed suspension of TiO₂ and an adsorbent for As(V) (activated alumina) under sunlight irradiation, the arsenic removal reached 89% after 24 h. By use of the same photocatalyst–adsorbent system, 98% of MMA and 97% of DMA were removed. The mechanism of the removal of arsenic species by the photocatalyst–adsorbent system was discussed.     

Removal of arsenite from water by synthetic siderite: behaviors and mechanisms

Synthetic siderite has been used as adsorbent for As(III) removal in this study. Effects of contact time, temperature, pH, co-existing anions on As(III) adsorption were intensively investigated. Adsorption mechanisms were also studied using the X-ray absorption technique. Results show that the maximum adsorption capacity is up to 9.98 mg g(-1) at 25°C at a siderite dosage of 2 g L(-1). Adsorption kinetics agrees with the Lagergren pseudo-second order model. Arsenic(III) adsorption can be better described by Langmuir isotherm model for As(III) adsorption at 55°C, indicating that the coverage of the adsorption sites is in the form of monolayer, although Freundlich isotherm yields a better fit to the experimental data at 25, 35 and 45°C. Thermodynamic study indicates that As(III) adsorption on the synthetic siderite is spontaneous and endothermic in nature. The adsorption capacity is enhanced with the increase in reaction temperature. The adsorption is independent on solution pH between 3.0 and 9.6. The presence of NO(3)(-), SO(4)(2-), PO(4)(3-) or SiO(3)(2-) with element concentrations less than 20 mg L(-1) does not have adverse effect on As(III) adsorption. XANES spectra indicate that As mainly occurs as As(V) in the As adsorbed-materials, and the fraction of oxidized As(III) increases with the decrease in As(III) concentration. The formation of Fe hydroxide minerals (such as lepidocrocite and goethite) followed by As(III) oxidation and adsorption is shown to be the main mechanism of As(III) removal by the synthetic siderite.     

Arsenic removal from groundwater by MnO2-modified natural clinoptilolite zeolite: effects of pH and initial feed concentration

Adsorption of arsenic (As(5+)) on natural and MnO(2)-modified clinoptilolite-Ca zeolite adsorbents was investigated to explore the feasibility of removing arsenic from groundwater using natural zeolite adsorbents. The natural and MnO(2)-modified clinoptilolite-Ca zeolite adsorbents were characterized with nitrogen adsorption at 77K for pore textural properties, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray fluorescence for morphology, elemental composition and distribution. Batch adsorption equilibrium experiments were conducted to study the effects of pH and initial feed concentration on arsenic removal efficiency. It was found that the amphoteric properties and arsenic removal efficiency of the natural clinoptilolite-Ca zeolite were significantly improved after modification with MnO(2). The MnO(2)-modified zeolite could effectively remove arsenic from water at a wide pH range, and the arsenic removal efficiency that is basically independent of the pH of feed solutions varies slightly with the initial arsenic concentration in the feed solutions. The removal efficiency obtained on the modified zeolite was doubled as compared to that obtained on the unmodified zeolite. The MnO(2)-modified clinoptilolite-Ca zeolite appears to be a promising adsorbent for removing trace arsenic amounts from water.     

碳纳米管的表征和重金属阴离子吸附性能

通过化学修饰使碳纳米管表面富含各种氧功能团,利用XPS和TPD方法表征了碳纳米管表面氧功能团的化学物理特性.研究发现:对比于未修饰的碳纳米管,化学修饰后的碳纳米管对高毒性的铬酸根阴离子有很强的吸附能力;其优异的吸附能力归结于金属阴离子与纳米管表面氧功能团的相互作用.研究指出碳纳米管可以作为替代吸附材料用于处理废水中重金...     

Removal of phosphate from aqueous solution with blast furnace slag

Blast furnace slag was used to remove phosphate from aqueous solutions. The influence of pH, temperature, agitation rate, and blast furnace slag dosage on phosphate removal was investigated by conducting a series of batch adsorption experiments. In addition, the yield and mechanisms of phosphate removal were explained on the basis of the results of X-ray spectroscopy, measurements of zeta potential of particles, specific surface area, and images of scanning electron microscopy (SEM) of the particles before and after adsorption. The specific surface area of the blast furnace slag was 0.4m(2)g(-1). The removal of phosphate predominantly has taken place by a precipitation mechanism and weak physical interactions between the surface of adsorbent and the metallic salts of phosphate. In this study, phosphate removal in excess of 99% was obtained, and it was concluded that blast furnace slag is an efficient adsorbent for the removal of phosphate from solution.