Adsorption/desorption of arsenite and arsenate on chitosan and nanochitosan

Equilibrium sorption studies of anionic species of arsenite, As(III) ions and arsenate As(V) ions onto two biosorbents, namely, chitosan and nanochitosan, have been investigated and compared. The results and trends in the sorption behavior are novel, and we have observed during the sorption process of the As(III) and As(V) on chitosan, a slow process of desorption occurred after an initial maximum adsorption capacity was achieved, before reaching a final but lower equilibrium adsorption capacity. The same desorption trend, however, is not observed on nanochitosan. The gradual desorption of As(III) and As(V) in the equilibrium sorption on chitosan is attributed to the different fractions of the dissociated forms of arsenic on the adsorbent surface and in solution and the extent of protonation of chitosan with the changing of solution pH during sorption. The change of solution pH during the sorption of arsenite ions on chitosan was also influenced by the interaction between the buffering effect of the arsenite species in the aqueous medium and the physical properties of chitosan. The final equilibrium adsorption capacity of chitosan for As(III) and As(V) was found to be around 500 and 8000 μg/g, respectively, whereas the capacities on nanochitosan are 6100 and 13,000 μg/g, respectively.

     

Organo-modified sericite in the remediation of an aquatic environment contaminated with As(III) or As(V)

The aim of this investigation was to obtain the hybrid material precursor to the naturally and abundantly available sericite, a mica-based clay; the materials were further employed in the remediation of arsenic from aqueous solutions. The study was intended to provide a cost-effective and environmentally benign treatment technology. The hybrid organo-modified sericite was obtained using hexadecyltrimethylammonium bromide (HDTMA) and alkyldimethylbenzylammonium chloride (AMBA) organic surfactants by introducing regulated doses of HDTMA or AMBA. The materials were characterized using infrared and X-ray diffraction analytical data, whereas the surface morphology was discussed by taking its SEM images. These materials were employed to assess the pre-concentration and speciation of As(III) and As(V) from aqueous solutions. The batch reactor data showed that increasing the sorptive concentration (from 1.0 to 15.0 mg/L) and pH (i.e., pH 2.0 to 10.0) caused the percent uptake of As(III) and As(V) to decrease significantly. The kinetic data showed that a sharp initial uptake of arsenic reached its equilibrium state within about 50 min of contact time, and the sorption kinetics followed a pseudo-second-order rate law both for As(III) and As(V) sorption. A 1,000 times increase in the background electrolyte concentration, i.e., NaNO₃, caused a significant decrease in As(III) removal, whereas As(V) was almost unaffected, which inferred that As(III) was adsorbed, mainly by the van der Waals or even by the electrostatic attraction, whereas As(V) was adsorbed chemically and formed “inner-sphere” complexes at the solid/solution interface. The equilibrium state modeling studies indicated that the sorption data fitted well the Freundlich and Langmuir adsorption isotherms. Henceforth, the removal capacity was calculated under these equilibrium conditions. It was noted that organo-modified sericite possessed a significantly higher removal capacity compared to its virgin sericite. Between these two organo-modified sericite, the HDTMA-modified sericite possessed a higher removal capacity compared to the AMBA-modified sericite.     

Flotation removal of As(V) onto goethite

Arsenic oxyanions, considered as priority pollutants, were removed from dilute aqueous solutions by sorption onto synthetic goethite, a typical inorganic adsorbent. Flotation was subsequently applied as an effective solid/liquid separation method. The combined process produced a foam concentrate, containing the arsenic-loaded goethite particles. The dispersed-air flotation technique was used for the generation of fine gas bubbles. The main parameters affecting the process were studied and promising results, in terms of arsenic removal and of goethite separation, were obtained.     

Removal processes for arsenic in constructed wetlands

Arsenic pollution in aquatic environments is a worldwide concern due to its toxicity and chronic effects on human health. This concern has generated increasing interest in the use of different treatment technologies to remove arsenic from contaminated water. Constructed wetlands are a cost-effective natural system successfully used for removing various pollutants, and they have shown capability for removing arsenic. This paper reviews current understanding of the removal processes for arsenic, discusses implications for treatment wetlands, and identifies critical knowledge gaps and areas worthy of future research. The reactivity of arsenic means that different arsenic species may be found in wetlands, influenced by vegetation, supporting medium and microorganisms. Despite the fact that sorption, precipitation and coprecipitation are the principal processes responsible for the removal of arsenic, bacteria can mediate these processes and can play a significant role under favourable environmental conditions. The most important factors affecting the speciation of arsenic are pH, alkalinity, temperature, dissolved oxygen, the presence of other chemical species - iron, sulphur, phosphate -, a source of carbon, and the wetland substrate. Studies of the microbial communities and the speciation of arsenic in the solid phase using advanced techniques could provide further insights on the removal of arsenic. Limited data and understanding of the interaction of the different processes involved in the removal of arsenic explain the rudimentary guidelines available for the design of wetlands systems.     

As(III) removal from groundwaters using fixed-bed upflow bioreactors

The application of biological oxidation of iron and manganese, as a potential treatment method for the removal of arsenic from contaminated groundwaters, was examined in this paper. This method was based on the growth of certain species of indigenous bacteria, which are capable of oxidizing the soluble iron and manganese ions; the oxidized forms can be subsequently removed from the aqueous stream by over 97%, through their transformation to insoluble oxides and separation by a suitable filter medium. Arsenic was removed by around 80%, under certain conditions, which were found to be sufficient for Fe(II) removal (dissolved oxygen 2.7 mg/l, redox 280-290 mV, pH 7.2, U 8.25 m/h). The specific treatment technique presents several advantages towards conventional physicochemical treatment methods, such as enhanced coagulation or direct adsorption since: (a) it does not require the addition of other chemicals for oxidizing and removing As(III), (b) it does not require close monitoring of a breakthrough point, as in conventional column adsorption processes and (c) it could find application for the removal of, at least, three groundwater contaminants (Fe, Mn, As).     

Sorption of arsenate and arsenite anions by iron(III)-poly(hydroxamic acid) complex

Iron(III)-poly(hydroxamic acid) resin complex has been studied for its sorption abilities with respect to arsenate and arsenite anions from an aqueous solution. The complex was found effective in removing the arsenate anion in the pH range of 2.0 to 5.5. The maximum sorption capacity was found to be 1.15 mmol/g. The sorption selectivity showed that arsenate sorption was not affected by chloride, nitrate and sulphate. The resin was tested and found effective for removal of arsenic ions from industrial wastewater samples.     

壳聚糖季铵盐的合成及其絮凝性能

对壳聚糖进行季铵化改性制得壳聚糖季铵盐,用于味精废水的絮凝实验证明了其絮凝性能较壳聚糖好,投药量低,ｐＨ值适用范围宽,絮体沉降快且含水率低,是一种具有良好反应活性的高分子絮凝剂。     

Thermodynamic and kinetic studies of As(V) removal from water by zirconium oxide-coated marine sand

Arsenic contamination of groundwater is a major threat to human beings globally. Among various methods available for arsenic removal, adsorption is fast, inexpensive, selective, accurate, reproducible and eco-friendly in nature. The present paper describes removal of arsenate from water on zirconium oxide-coated sand (novel adsorbent). In the present work, zirconium oxide-coated sand was prepared and characterised by infrared and X-ray diffraction techniques. Batch experiments were performed to optimise different adsorption parameters such as initial arsenate concentration (100–1,000 μg/L), dose (1–8 g/L), pH of the solution (2–14), contact time (15–150 min.), and temperature (20, 30, 35 and 40 °C). The experimental data were analysed by Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models. Furthermore, thermodynamic and kinetic parameters were evaluated to know the mode of adsorption between ZrOCMS and As(V). The maximum removal of arsenic, 97 %, was achieved at initial arsenic concentration of 200 μg/L, after 75 min at dosage of 5.0 g/L, pH?7.0 and 27?±?2 °C. For 600 μg/L concentration, the maximum Langmuir monolayer adsorption capacity was found to be 270 μg/g at 35 °C. Kinetic modelling data indicated that adsorption process followed pseudo-second-order kinetics. The mechanism is controlled by liquid film diffusion model. Thermodynamic parameter, ΔH°, was ?57.782, while the values of ΔG° were ?9.460, ?12.183, ?13.343 and ?13.905 kJ/mol at 20, 30, 35 and 40 °C, respectively, suggesting exothermic and spontaneous nature of the process. The change in entropy, ΔS°?=??0.23 kJ/mol indicated that the entropy decreased due to adsorption of arsenate ion onto the solid adsorbent. The results indicated that the reported zirconium oxide-coated marine sand (ZrOCMS) was good adsorbent with 97 % removal capacity at 200 μg/L concentration. It is interesting to note that the permissible limit of arsenic as per World Health Organization is 10 μg/L, and in real situation, this low concentration can be achieved through this adsorbent. Besides, the adsorption capacity showed that this adsorbent may be used for the removal of arsenic from any natural water resource.     

Equilibrium studies for the sorption of lead from effluents using chitosan

The sorption of lead ions from aqueous solution onto chitosan has been studied. Equilibrium studies have been carried out to determine the capacity of chitosan for lead ions. The effects of solution pH and chitosan particle size on the sorption capacity have been studied.The experimental data were analyzed using three equilibrium isotherm correlations, namely, Langmuir, Freundlich and Redlich-Peterson equations. The linear correlation coefficients were determined for each isotherm and the Freundlich provided the best fit. In addition, error functions have been used to determine the alternative single component equilibrium isotherm parameters by non-linear regression due to the inherent bias in using the correlation coefficient from the linearization. This technique enables the "best fit" isotherm parameters to be used in the equilibrium equations for the sorption of lead ions on chitosan within the limits and assumptions of the various error analysis methods.     

A new bacterial strain mediating As oxidation in the Fe-rich biofilm naturally growing in a groundwater Fe treatment pilot unit

A bacterial strain B2 that oxidizes arsenite into arsenate was isolated from the biofilm growing in a biological groundwater treatment process used for Fe removal. This strain is phylogenetically and morphologically different from the genus Leptothrix commonly encountered in biological iron oxidation processes. T-RFLP fingerprint of the biofilm revealed that this isolated strain B2 corresponds to the major population of the bacterial community in the biofilm. Therefore, it is probably one of the major contributors to arsenic removal in the treatment process.     

Biosorption and Biovolatilization of Arsenic by Heat-Resistant Fungi (5 pp)

Goal, Scope and Background

The aim of this work is to show the ability of several fungal species, isolated from arsenic polluted soils, to biosorb and volatilize arsenic from a liquid medium under laboratory conditions. Mechanisms of biosorption and biovolatilization play an important role in the biogeochemical cycle of arsenic in the environment. The quantification of production of volatile arsenicals is discussed in this article.

Methods

Heat-resistant filamentous fungi Neosartorya fischeri, Talaromyces wortmannii, T. flavus, Eupenicillium cinnamopurpureum, originally isolated from sediments highly contaminated with arsenic (more than 1403 mg.l-1 of arsenic), and the non-heat-resistant fungus Aspergillus niger were cultivated in 40 mL liquid Sabouraud medium (SAB) enriched by 0.05, 0.25, 1.0 or 2.5 mg of inorganic arsenic (H3AsO4). After 30-day and 90-day cultivation under laboratory conditions, the total arsenic content was determined in mycelium and SAB medium using the HG AAS analytical method. Production of volatile arsenic derivates by the Neosartorya fischeri strain was also determined directly by hourly sorption using the sorbent Anasorb CSC (USA).

Results

Filamentous fungi volatilized 0.025–0.321 mg of arsenic from the cultivation system, on average, depending on arsenic concentrations and fungal species. The loss of arsenic was calculated indirectly by determining the sum of arsenic content in the mycelium and culture medium. The amount of arsenic captured on sorption material was 35.7 ng of arsenic (22nd day of cultivation) and 56.4 ng of arsenic (29th day of cultivation) after one hour's sorption. Biosorption of arsenic by two types of fungal biomass was also discussed, and the biosorption capacity for arsenic of pelletized and compact biomass of Neosartorya fischeri was on average 0.388 mg and 0.783 mg of arsenic, respectively.

Discussion

The biosorption and amount of volatilized arsenic for each fungal species was evaluated and the effect of initial pH on the biovolatilization of arsenic was discussed.

Conclusions

The most effective biovolatilization of arsenic was observed in the heat-resistant Neosartorya fischeri strain, while biotransformation of arsenic into volatile derivates was approximately two times lower for the non-heat-resistant Aspergillus niger strain. Biovolatilization of arsenic by Talaromyces wortmannii, T. flavus, Eupenicillium cinnamopurpureum was negligible. Results from biosorption experiments indicate that nearly all of an uptaken arsenic by Neosartorya fischeri was transformed into volatile derivates.

Recommendations and Perspective

. Biovolatilization and biosorption have a great potential for bioremediation of contaminated localities. However, results showed that not all fungal species are effective in the removal of arsenic. Thus, more work in this research area is needed.

     

Removal of arsenic(V) from aqueous solutions using iron-oxide-coated modified activated carbon.

Removal of arsenic(V) from aqueous solutions was evaluated with the following three different sorption materials: coal-based activated carbon 12 x 40 (activated carbon), iron(II) oxide (FeO)/activated carbon-H, and iron oxide. The apparent characteristics and physical chemistry performances of these adsorbents were investigated by X-ray diffraction, nitrogen adsorption, and scanning electronic microscope. Also, batch experiments for arsenic removal were performed, and the effects of pH value on arsenic(V) removal were studied. The results suggest that the main phases of the iron oxide surface are magnetite, maghemite, hematite, and goethite; fine and uniform iron oxide particles can cover activated carbon surfaces and affect the surface area or pore structures of activated carbon; adsorption kinetics obey a pseudo-first-order rate equation; and adsorption capacities of adsorbents are affected by the values of pH. The optimum value of pH for iron oxide lies in a narrow range between 4.0 and 5.5, and arsenic(V) removal by FeO/activated carbon-H is ideal and stable in the pH range 3 to 7, while activated carbon has the lowest adsorption capacity in the entire pH range. Also, the adsorption characteristics of FeO/activated carbon-H composites and virgin activated carbon match well the Langmuir adsorption model, while those of iron oxide fit well the Freundlich adsorption model.     

Novel chitosan/PVA/zerovalent iron biopolymeric nanofibers with enhanced arsenic removal applications

Enhanced removal application of both forms of inorganic arsenic from arsenic-contaminated aquifers at near-neutral pH was studied using a novel electrospun chitosan/PVA/zerovalent iron (CPZ) nanofibrous mat. CPZ was carefully examined using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), atomic fluorescence spectroscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermal gravimetric analysis (TGA). Application of the adsorbent towards the removal of total inorganic arsenic in batch mode has also been studied. A suitable mechanism for the adsorption has also been discussed. CPZ nanofibers mat was found capable to remove 200.0?±?10.0 mg g^?1 of As(V) and 142.9?±?7.2 mg g^?1 of As(III) from aqueous solution of pH 7.0 at ambient condition. Addition of ethylenediaminetetraacetic acid (EDTA) enabled the stability of iron in zerovalent state (ZVI). Enhanced capacity of the fibrous mat could be attributed to the high surface area of the fibers, presence of ZVI, and presence of functional groups such as amino, carboxyl, and hydroxyl groups of the chitosan and EDTA. Both Langmuir and Freundlich adsorption isotherms were applicable to describe the removal process. The possible mechanism of adsorption has been explained in terms of electrostatic attraction between the protonated amino groups of chitosan/arsenate ions and oxidation of arsenite to arsenate by Fentons generated from ZVI and subsequent complexation of the arsenate with the oxidized iron. These CPZ nanofibrous mats has been prepared with environmentally benign naturally occurring biodegradable biopolymer chitosan, which offers unique advantage in the removal of arsenic from contaminated groundwater.     

Cr(VI) removal from synthetic wastewater using coconut shell charcoal and commercial activated carbon modified with oxidizing agents and/or chitosan

In this study, the technical feasibility of coconut shell charcoal (CSC) and commercial activated carbon (CAC) for Cr(VI) removal is investigated in batch studies using synthetic electroplating wastewater. Both granular adsorbents are made up of coconut shell (Cocos nucifera L.), an agricultural waste from local coconut industries. Surface modifications of CSC and CAC with chitosan and/or oxidizing agents, such as sulfuric acid and nitric acid, respectively, are also conducted to improve removal performance. The results of their Cr removal performances are statistically compared. It is evident that adsorbents chemically modified with an oxidizing agent demonstrate better Cr(VI) removal capabilities than as-received adsorbents in terms of adsorption rate. Both CSC and CAC, which have been oxidized with nitric acid, have higher Cr adsorption capacities (CSC: 10.88, CAC: 15.47 mg g(-1)) than those oxidized with sulfuric acid (CSC: 4.05, CAC: 8.94 mg g(-1)) and non-treated CSC coated with chitosan (CSCCC: 3.65 mg g(-1)), respectively, suggesting that surface modification of a carbon adsorbent with a strong oxidizing agent generates more adsorption sites on their solid surface for metal adsorption.     

Removal of As(III) and As(V) using iron-rich sludge produced from coal mine drainage treatment plant

To test the feasibility of the reuse of iron-rich sludge (IRS) produced from a coal mine drainage treatment plant for removing As(III) and As(V) from aqueous solutions, we investigated various parameters, such as contact time, pH, initial As concentration, and competing ions, based on the IRS characterization. The IRS consisted of goethite and calcite, and had large surface area and small particles. According to energy dispersive X-ray spectroscopy mapping results, As was mainly removed by adsorption onto iron oxides. The adsorption kinetic studies showed that nearly 70 % adsorption of As was achieved within 1 h, and the pseudo-second-order model well explained As sorption on the IRS. The adsorption isotherm results agreed with the Freundlich isotherm model, and the maximum adsorption capacities for As(III) and As(V) were 66.9 and 21.5 mg/g, respectively, at 293 K. In addition, the adsorption showed the endothermic character. At high pH or in the presence of phosphate, the adsorption of As was decreased. When the desorption experiment was conducted to reuse the IRS, 85 % As was desorbed with 1.0 N NaOH. In the column experiment, adsorbed As in real acid mine drainage was 43 % of the maximum adsorbed amount of As in the batch test. These results suggested that the IRS is an effective adsorbent for As and can be effectively applied for the removal of As in water and wastewater.     

Soil attenuation of As(III,V) and Se(IV,VI) seepage potential at ash disposal facilities

Leachate from ash landfills is frequently enriched with As and Se but their off-site movement is not well understood. The attenuation potential of As and Se by soils surrounding selected landfills during leachate seepage was investigated in laboratory column studies using simulated ash leachate. As(III, V) and Se(IV, VI) concentrations as well as pH, flow rate, and a tracer were monitored in influent and effluent for up to 800 pore volumes followed by sequential desorption, extraction, and digestion of column segments. Column breakthrough curves (BTCs) were compared to predictions based on previously measured sorption isotherms. Early As(V) breakthrough and retarded As(III) breakthrough relative to predicted BTCs are indicative of oxidative transformation during seepage. For Se(VI), which exhibits linear sorption and the lowest sorption propensity, measured BTCs were predicted fairly well by equilibrium sorption isotherms, except for the early arrival of Se(IV) in one site soil, which in part, may be due to higher column pH values compared to batch isotherms. Most of the As and Se retained by soils during leaching was found to be strongly sorbed (60–90%) or irreversibly bound (10–40%) with <5% readily desorbable. Redox potential favoring transformation to the more sorptive valence states of As(V) and Se(IV) will invoke additional attenuation beyond equilibrium sorption-based predictions. With the exception of Se(IV) on one site soil, results indicate that attenuation by down-gradient soils of As and Se in ash landfill seepage will often be no less than what is predicted by equilibrium sorption capacity with further attenuation expected due to favorable redox transformation processes, thus mitigating contaminant plumes and associated risks.     

Adsorption and removal of As(V) and As(III) using Zr-loaded lysine diacetic acid chelating resin

An adsorption process for the removal of As(V) and As(III) was evaluated under various conditions using zirconium(IV) loaded chelating resin (Zr-LDA) with lysine-Nalpha,Nalpha diacetic acid functional groups. Arsenate ions strongly adsorbed in the pH range from 2 to 5, while arsenite was adsorbed between pH 7 and 10.5. The sorption mechanism is an additional complexation between arsenate or arsenite and Zr complex of LDA. Adsorption isotherm data could be well interpreted by Langmuir equation for As(V) at pH 4 and As(III) at pH 9 with a binding constant 227.93 and 270.47 dm3 mol(-1) and capacity constant 0.656 and 1.1843 mmol g(-1), respectively. Regeneration of the resin was carried out for As(V) using 1 M NaOH. Six adsorption/desorption cycles were performed without significant decrease in the uptake performance. Column adsorption studies showed that the adsorption of As(V) is more favorable compared to As(III), due to the faster kinetics of As(V) compared to As(III). Influence of the coexisting ions on the adsorption of As(V) and As(III) was studied. The applicability of the method for practical water samples was studied.     

负载壳聚糖膨润土的制备及其吸附性能的影响

以天然膨润土和壳聚糖为原料，制得一种新型水处理剂——负载壳聚糖膨润土，研究了制备条件对酸性大红印染废水处理效果的影响。实验表明，当壳聚糖的浓度为30 g/L、膨润土质量与壳聚糖溶液体积之比为0.7、浸泡时间80 min、微烘时间15 min时，壳聚糖改性膨润土对酸性大红印染废水的脱色率可达97%。对改性土进行比表面积测定、电镜扫描及X-射线衍射等结构特性分析，证明壳聚糖的引入改变了膨润土在水中的分散状态，增强了其对污染物的吸附和离子交换能力。     

壳聚糖联合碱改性粉煤灰对重金属离子的吸附特性

采用浸渍法将壳聚糖负载在经NaOH改性的粉煤灰上，制备了联合改性的粉煤灰。随粉煤灰上壳聚糖负载量的增加，粉煤灰对Pb²⁺和Cd²⁺的吸附率均提高。当负载壳聚糖的质量分数为8%，吸附温度为30℃，吸附时间为120 min时，粉煤灰对Pb²⁺的吸附率最高（为98.9%），对Cd²⁺的吸附率也最高（为91.5%）。其吸附行为符合Freundlich等温吸附模型，但表现为2个线性区。粉煤灰负载壳聚糖的改性机理是粉煤灰与带正电荷的壳聚糖的化学键合作用。     

Sorption of Zn(II) in aqueous solutions by scoria

We conducted kinetic and equilibrium sorption experiments on removal of Zn(II) from aqueous solutions by scoria (a vesicular pyroclastic rock with basaltic composition) from Jeju Island, Korea, in order to examine its potential use as an efficient sorbent. The batch-type kinetic sorption tests under variable conditions indicated that the percentage of Zn(II) removal by scoria increases with decreasing initial Zn(II) concentration, particle size, and sorbate/sorbent ratio. However, the sorption capacity decreases with the decrease of the initial Zn(II) concentration and sorbate/sorbent ratio. Equilibrium sorption tests show that Jeju scoria has a larger capacity and affinity for Zn(II) sorption than commercial powdered activated carbon (PAC); at initial Zn(II) concentrations of more than 10mM, the sorption capacity of Jeju scoria is about 1.5 times higher than that of PAC. The acquired sorption data are better fitted to the Langmuir isotherm than the Freundlich isotherm. Careful examination of ionic concentrations in sorption batches suggests that the sorption behavior is mainly controlled by cation exchange and typically displays characteristics of 'cation sorption'. The Zn(II) removal capacity decreases when solution pH decreases because of the competition with hydrogen ions for sorption sites, while the Zn(II) removal capacity increases under higher pH conditions, likely due to hydroxide precipitation. At an initial Zn(II) concentration of 5.0mM, the removal increases from 70% to 96% with the increase of initial pH from 3.0 to 7.0. We recommend Jeju scoria as an economic and efficient sorbent for Zn(II) in contaminated water.