Synthetic Iron Oxides for Adsorptive Removal of Arsenic

Removal of arsenic from water reservoirs is the issue of great concern in many places around the globe. As adsorption is one of the most efficient techniques for treatment of As-containing media, thus the present study concerns application of iron oxides-hydroxides (akaganeite) as adsorbents for removal of this harmful metal from aqueous solution. Two types of akaganeite were tested: synthetic one (A) and the same modified using hexadecyltrimethylammonium bromide (A_M). Removal of As was tested in batch studies in function of pH, adsorbent dosage, contact time, and initial arsenic concentration. The adsorption isotherms obey Langmuir mathematical model. Adsorption kinetics complies with pseudo-second-order kinetic model, and the constant rates were defined as 2.07?×?10^?3and 0.92?×?10^?3 g mg^?1 min^?1 for the samples (A) and (A_M), respectively. The difference was caused by significant decrease in adsorption rate in initial state of the process carried out for the sample A_M. The maximum adsorption capacity achieved for (A) and (A_M) akaganeite taken from Langmuir isotherm was 148.7 and 170.9 mg g^?1, respectively. The results suggest that iron oxides-hydroxides can be used for As removal from aqueous solutions.     

Fluoride Removal from Aqueous Solutions by Boehmite

Boehmite was used for the removal of fluoride ions from aqueous solutions in a batch system. The pH, contact time, and fluoride concentration in the removal of fluoride ions by boehmite were evaluated. The removal of fluoride ions by boehmite was the highest between the pH values of 4.5 and 7.5. The kinetic fluoride sorption from aqueous solutions by boehmite was best described by the pseudo-second-order model, and equilibrium was reached in about 24 h. The Freundlich model described the isotherm sorption process; the results indicate that the sorption mechanism is chemisorption on a heterogeneous material.     

Fluoride Removal from Water Using Combined Moringa oleifera/Ultrafiltration Process

The occurrence of fluoride in groundwater has been reported in many countries, mainly because the excess fluoride in drinking water can lead to dental or skeletal fluorosis. Fluoride removal by coagulation with Moringa oleifera seeds, followed by separation with membranes, was investigated in this work. Artificially fluoridated water, at a starting fluoride concentration of 10?mg?L^?1, was submitted to a coagulation process with aqueous extracts of M. oleifera seeds. The coagulation process was followed by ultrafiltration with membranes at different pressures. The coagulation process with 2.5?g?L^?1 of M. oleifera promoted a reduction of 90.90?% in the fluoride content of the treated water, making it possible for poor communities to consume this water. It is noteworthy that the combined coagulation/filtration process using raw coagulant showed the highest values of colour and turbidity, which, however, were still below the limits set for drinking water by Brazilian legislation. The advantage of proposing a sequential process using membrane separation is that it removes colour and turbidity, caused by the use of M. oleifera as a coagulant, resulting in water that meets potability standards.     

Modification Effects of Hematite with Aluminum Hydroxide on the Removal of Fluoride Ions from Water

The modification effects of hematite with aluminum hydroxide were investigated on the removal of fluoride ions from water using batch experiments. The effects of pH, contact time, fluoride concentration, and the dose of sorbent on the sorption of fluoride ions by a modified hematite were studied. Characterization of hematite before and after the modification with aluminum hydroxide was studied by X-ray diffraction, scanning electron microscope, and Brunauer–Emmett–Teller. Equilibrium was reached in 48 h of contact time and the maximum sorption of fluoride was found in the pH_eq range between 2.34 and 6.26. The Elovich model described the kinetic sorption processes and the Langmuir–Freundlich model, the sorption isotherm process. These results indicated that the sorption mechanism was chemisorption on a heterogeneous material.     

Removal of Dyes from Water Using a TiO2 Photocatalyst Supported on Black Sand

A TiO₂ photocatalyst was prepared by depositing silica and titanium dioxide on the surface of black sand that made the photocatalyst recoverable using a magnetic field. The magnetic photocatalyst was used to remove six aqueous dyes from water and the removal was attributed to both adsorption and photocatalytic oxidation. Removal by adsorption was more noticeable with the cationic dyes than with the anionic dyes. The difference was related to the electrostatic interaction between the charged dye molecular and the silica-occupied surface of the photocatalyst. Removal by photocatalytic oxidation occurred with anionic dyes, while it was not appreciable with cationic dyes. It was postulated that photocatalytic oxidation might have happened with cationic dyes as well, but the strong adsorption made the photocatalytic oxidation undetectable.     

动态条件下壳聚糖稳定纳米铁去除水体中Cr（Ⅵ）的研究

以重金属Cr（Ⅵ）为目标污染物,在两种实验条件下（实验柱Ⅰ为模拟污染水样,实验柱Ⅱ为实际污染水样）考察了壳聚糖稳定纳米铁对Cr（Ⅵ）的去除能力。实验柱Ⅰ和实验柱Ⅱ分别在第160PV和127PV时发生了击穿效应。与实验柱Ⅰ相比,实验柱Ⅱ中壳聚糖稳定纳米铁对Cr（VI）的去除能力降低了25％。SEM表征显示,实验柱Ⅱ中壳聚糖稳定纳米铁的表面形成了许多葡萄状晶体,它们的存在导致实验柱Ⅱ中纳米铁的去除能力明显低于实验柱Ⅰ。XPS表征显示,由于Ca和Mg的氢氧化物替代了部分铁氢氧化物,导致实验柱Ⅱ中壳聚糖稳定纳米铁表面Fe原子的相对含量低于实验柱Ⅰ。Cr元素高分辨率XPS能谱分析显示,在实验柱Ⅰ的条件下CKVI）被还原得更充分,而且在两种实验条件下都有部分Cr（VI）被吸附在纳米铁表面最终没有被零价铁所还原。     

The Remobilization of Metals from Iron Oxides and Sediments by Metal-EDTA Complexes

Synthetic chelating agents such as EDTA form strong complexes with heavy metals and therefore have the potential to remobilize metals from sediments and aquifers. In natural waters EDTA is present almost exclusively in the form of metal-complexes. Therefore, remobilization of metals is always a metal-metal-EDTA exchange reaction. We have investigated, to our knowledge for the first time, the remobilization of metals from the surface of synthetic iron oxides and from a river sediment by different metal-EDTA complexes. The metals are exchanged as follows:MeEDTA_dissolved + Me^ast _adsorbed Me^astEDTA_dissolved + Me_adsorbed The order of the remobilization rate of Zn²⁺ from goethite is CaEDTA > Fe(III)EDTA, reflecting the slow exchange reaction of Fe(III)EDTA. For the remobilization of Pb²⁺ from goethite, the rate was found to be Fe(III)EDTA > CaEDTA > ZnEDTA. Here, Fe(III)EDTA has surprisingly the fastest exchange rate. Only very limited remobilization of Pb²⁺ is possible from hydrous ferric oxide at pH 8 due to the very strong adsorption of Pb²⁺. The order of remobilization of Zn²⁺ from a natural river sediment was found to be CaEDTA > CuEDTA > Fe(III)EDTA. The remobilization rate of Zn²⁺ with Fe(III)EDTA is only 12% of the rate with CaEDTA, illustrating the importance of EDTA speciation for assessing remobilization.     

Removal of Iron and Manganese from Water with a High Organic Carbon Loading. Part I: The Effect of Various Coagulants

Iron and manganese removal from water is considered a routine operation in most potable water treatment plants. However, when there is dissolved organic carbon (DOC) present in the water source, it can significantly influence the success of iron and manganese removal. This investigation focused on the use of two different coagulants, alum and ferrichloride, used in conjunction with hydrogen peroxide as an oxidant, to reduce dissolved iron and manganese in water with a high DOC loading. The two coagulants behaved in a totally different manner during the treatment process, with alum being successful in reducing the iron content in the treated water, and ferrichloride yielding a good removal of the dissolved manganese present. Since these results were only possible in cases where hydrogen peroxide concentrations were also present, it was concluded that treatment with a single reagent would not yield the desired removal of contaminants from this specific water. Both treatment options significantly reduced the DOC levels in the water to below the desired concentration after treatment.     

Zinc Removal from the Aqueous Solutions by the Chemically Modified Biosorbents

Biosorbents are the natural origin adsorbents, which popularity in environmental engineering is steadily increasing due to their low price, ease of acquisition, and lack of the toxic properties. Presented research aimed to analyze the possibility of chemical modification of the straw, which is a characteristic waste in the Polish agriculture, to improve its biosorption properties with respect to removal of selected metals from aquatic solutions. Biosorbents used during the tests was a barley straw that was shredded to a size in the range of 0.2–1.0 mm. The biosorption process was performed for aqueous solutions of zinc at a pH 5. Two different modifications of straw were analyzed: esterification with methanol and modification using the citric acid at elevated temperature. The results, obtained during the research, show a clear improvement in sorption capacity of the straw modified by the citric acid. In the case of straw modified with methanol, it has been shown that the effectiveness of zinc biosorption process was even a twice lower with respect to the unmodified straw. Moreover, it was concluded that the removal of analyzed metals was based mainly on the ion-exchange adsorption mechanism by releasing a calcium and magnesium ions from the straw surface to the solution.

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Graphical Abstract ?

     

Removal of Iron and Manganese from Water with a High Organic Carbon Loading. Part II: The Effect of Various Adsorbents and Nanofiltration Membranes

This paper describes the second part of an investigation into the removal of iron and manganese from water with a high dissolved organic carbon (DOC) loading. This investigation focused on the use of ferrichloride as coagulant in conjunction with hydrogen peroxide as an oxidant and different physical treatment processes, such as adsorption and nanofiltration, to reduce dissolved iron and manganese in water with a high DOC loading. It was found that nanofiltration employing H₂O₂ is the only treatment capable of producing drinking water within the set requirements of the treatment facility. Both fly ash and powdered activated carbon (PAC) used as adsorbents yielded a low percentage removal of DOC, while all the treatment methods evaluated accomplished high removals of the metallic ions Fe(II) and Mn(II). From the results a staggered treatment approach is recommended to obtain the best results at the lowest cost.     

Study of Phosphorus Removal by Using Sponge Iron Adsorption

Phosphorus is one of the key elements causing lake eutrophication. This paper deals with phosphate removal by Sponge iron in batch and fixed-bed operation. Isotherm and kinetic studies are conducted. The isotherm data is described by the Freundlich and Langmuir model, while the kinetic data of adsorption is fitted by the pseudo-second-order kinetic model. The saturated adsorption capacity of Langmuir isothermal equation is about 3.25 mg/g. The concomitant anions have adverse effect on phosphate adsorption and the effects follow the order: NO₃^??>?Cl^??>?SO₄^2?. The phosphate adsorption capacities of SI were improved significantly under the acidic condition. The results of the fixed-bed operation show that, with the increase of the influent phosphate concentrations, the breakthrough curve becomes steeper while the break point time decrease. According to the Adams–Bohart model, the critical height of the column decrease from 0.135 to 0.105 m when the contact time increased from 10 to 30 min with the influent concentration of 1.0 mg/L. According to BDST model, the critical bed depth is 0.15 m when the influent concentration of phosphate is 1.0 mg/L and the contact time (h) is 20 min.     

Investigation of Arsenic Removal from Water by Iron-Mixed Mesoporous Pellet in a Continuous Fixed-Bed Column

Natural clay combing with iron oxide and iron particle was developed to be iron-mixed mesoporous pellet that was packed in a fixed-bed column for removing arsenic from water. The performance of the column in terms of breakthrough curve analysis was investigated with the variations of influent flow rate, adsorbent bed height, initial solution pH, and initial adsorbate concentration. The results indicated that increasing in the flow rate decreased the removal capacities of the adsorbent. A relatively low bed height provided a better and beneficial performance. Higher adsorption capacity was observed with an increase of initial adsorbate concentration. At higher initial solution pH, the repulsive process occurred between adsorbate species and the surface charge of the adsorbent, resulting in a poor performance of the column. The Thomas model fitted very well to the experimental data for all cases. Estimated from the model, the highest adsorption capacity for arsenite and arsenate was found to be about 509 and 430 μg/g, respectively. The Adam-Bohart model provided only a relatively satisfactory fit to the initial part of the experimental data. From a practical view, the new developed pellet could be used as the effective and efficient adsorbent to treat elevated arsenic contaminated groundwater.     

Mechanistic Consideration of Zinc Ion Removal by Zero-Valent Iron

Mechanism of zinc iron removal by zero-valent iron was discussed through zinc removal responses to several operational conditions of a packed column reactor with zero-valent iron powder. The adsorption isotherm observed implied that a kind of chemisorption was responsible for zinc removal. Zinc removal by zero-valent iron was enhanced by dissolved oxygen and ferric ion addition. However, it was deteriorated under acidic pH. In addition, zinc adsorbed on zero-valent iron was eluted by a reducing agent such as citric acid, whereas the zinc was not eluted by diluted sulfuric acid. Consequently, the zinc removal mechanism by zero-valent iron was inferred to be as follows: Zero-valent iron was firstly corroded and oxidized into ferric ion by dissolved oxygen. The ferric ion was precipitated as iron hydroxide onto the surface of the zero-valent iron powder. Zinc ion was adsorbed on and/or coprecipitated with the iron hydroxide. The iron hydroxide was finally oxidized and transformed into iron oxides.     

改性沸石吸附柱去除和回收脱磷尿液废水中氨氮试验研究

经鸟粪石沉淀法回收尿液中磷后的废水中仍含有高浓度的氨氮,若直接排放,不仅会造成水体污染,也导致氮资源浪费。本文在5％HCl浸提,400℃焙烧,结合微波处理改性沸石以提高氨氮吸附能力的基础上,研究了改性沸石吸附柱高度（H）、吸附柱串联数量（N）以及水力停留时间（T）对脱磷尿液废水中氨氮去除效果的影响,评价了HCl溶液、NaCl溶液及其组合对吸附氨氮饱和的沸石的再生效果。结果表明：HCl-焙烧-微波改性沸石对氨氮的平衡吸附量为17．9mg·g-1,是天然沸石对氨氮平衡吸附量（6．9mg·g^-1）的2．6倍。当柱高H=35cm,水力停留时间亚2．0h,吸附柱串联个数N=3时,改性沸石对脱磷尿液废水中氨氮的去除效果最佳。当吸附柱内氨氮负荷小于6370mg时,吸附柱出水中氨氮浓度低于30mg·L-1。10％HCI＋5g·L-1 NaCl混合液作为沸石再生剂时,氨氮洗脱率达到88．3％,再生沸石的平衡吸附量可达16．4mg·g-1,为改性沸石的91．6％。可见,改性沸石吸附柱可有效去除脱磷尿液废、水中氨氮,同时10％HCI＋5g·L-1 NaCl混合溶液能够有效实现沸石再生和氨氮回收。研究结果为脱磷尿液废水中氨氮处理与回收中试试验奠定了基础。     

Removal of Zinc from Tidal Water by Sediments of a Mangrove Ecosystem: A Radiotracer Study

The removal of ⁶⁵Zn from tidal water by underlaying sediment cores collected in a mangrove forest and a tidal creek that drains this forest in Sepetiba Bay (SE Brazil) was investigated. After 30-h experiments in laboratory microcosms, the ⁶⁵Zn half-removal times from tidal creek and mangrove forest sediments were 8.7?±?1.8 and 9.2?±?0.9 h respectively. Depth penetration of ⁶⁵Zn was mainly restricted to the upper 3 cm in mangrove forest cores, while detectable ⁶⁵Zn activities were found in all layers (0–7 cm depth) of tidal creek cores. An unexpected ⁶⁵Zn release back to the overlaying water was observed for one of the tidal creek experiments in the 12–18 h interval (corresponding to a return of 17% of the initial ⁶⁵Zn activity in overlaying water), suggesting a reversibility of the ⁶⁵Zn removal process (e.g., by adsorption) in tidal creek sediments. The results indicate that mangrove-vegetated sediments allowed a lower vertical mobility of Zn than observed in creek sediments and mangrove sediments appear to be less susceptible to a reversion in the process of zinc removal from overlaying water, suggesting a greater capacity to retain this metal near the water–sediment interface. This first radiotracer approach on the mangrove sediments removal of Zn from tidal waters supports earlier experimental studies employing stable Zn, contributing for a better understanding of the metal uptake kinetics by such sediments and suggesting that these sediments act as active sinks for trace metals.     

柠檬酸对三种人工合成氧化铁磷吸附特性的影响

试验采用了3种人工合成的氧化铁为材料,研究了氧化铁对磷的吸附以及柠檬酸对氧化铁磷吸附特性的影响。结果表明:3种人工合成的氧化铁对磷的吸附特性及柠檬酸对氧化铁吸附磷的影响都可用Langumir方程来描述,都达到了极显著水平。从磷的最大吸附量(Sm)、吸附反应常数(K)和最大缓冲容量(MBC)来看,未加入柠檬酸时,水铁矿对磷的吸附在容量和强度方面均为最高;而在加入柠檬酸时,3种人工合成的氧化铁对磷的吸附能力的顺序并无差别,水铁矿和针铁矿的磷Sm和MBC要比赤铁矿大很多。     

耐冷菌强化去除农田径流污染水体中氮磷的模拟研究

通过室内模拟实验研究1株土著反硝化菌(Acinetobacter johnsonii DBP-3)对农田径流污染水体中氮磷的低温生物强化去除特征。结果表明:10℃下避光好氧培养时菌株对水样中的硝酸盐氮和溶解性正磷酸盐具有较强的去除能力,培养8d后灭菌水样和原水样中硝酸盐氮的浓度分别下降了78.5%和70.2%,溶解性正磷酸盐的浓度分别下降了82.4%和74.6%,与未投加菌的对照组相比差异显著。菌株在低温模拟系统中具有较强的适应能力,实验周期内能够保持数量上的优势。与10℃相比,培养温度为25℃时,菌株的脱氮除磷能力明显增强,5℃时菌株的氮磷代谢能力明显降低,但与对照相比,菌株对氮磷仍然保持一定的代谢活性。菌株在模拟系统中对盐度具有较强的抗性,当盐度为10%时,其氮磷代谢能力才受到明显的抑制。多菌灵和毒死蜱的浓度分别为80.0,60.0mg/L时才对菌株的生长代谢产生明显的抑制作用,表明菌株对这2种农药的耐性较强。研究结果说明,实验用菌株在低温条件下不仅具有明显的脱氮除磷能力,而且对盐度和常见的农药具有较强的抗性,在面源污染的治理方面具有广阔的应用前景。     

Hydrous Ferric Oxide (HFO)—a Scavenger for Fluoride from Contaminated Water

Groundwaters contaminated with excess fluoride (above 1.5 mg/L) posed some risks to the public health in India. Methods available for fluoride contaminated water treatment are cogaulation–filtration using alum + lime + bleaching powder (Nalgonda technique) and adsorption using activated alumina. Use of aluminium compounds for water treatment purpose needs replacement on neurological health problem. Objective to this, the synthesis and fluoride adsorption behavior of hydrous ferric oxide (HFO) are reported here. It is seen that fluoride adsorption density varies as a function of pH, contact time, aging time, drying temperature and particle size of HFO. Highest adsorption density for fluoride is found to be at pH 4.0. Effects of competing anions in removing fluoride from solution were tested. Arsenite, arsenate, phosphate and sulfate show strong interfering effect at high anions to fluoride molar ratio in solution. Adsorption of fluoride on HFO follows the Freundlich isotherm and the Lagergren first-order kinetic model. It was also determined that HFO is a better adsorbent in removing fluoride from high fluoride groundwater than some other adsorbents. Regeneration of fluoride-rich HFO results showed that 1.0 M NaOH solution could be used up to a maximum of 75% regeneration.