Removal of copper(II) from aqueous solution using chemically modified fruit peels as efficient low-cost biosorbents

Fruit peels, which are common agricultural byproducts, have been extensively used as abandoned or low-cost biosorbents to remove heavy metals. In this study, dragon fruit peel (DFP), rambutan peel (RP), and passion fruit peel (PFP) were used to remove Cu(II) ions from an aqueous solution. Concentrations of the adsorbed metal ions were determined using the atomic absorption spectroscopic method. Adsorption experiments were performed with different adsorbent dosages, pH values, contact times, and initial copper concentrations. The optimum set of conditions for biosorption of Cu(II) ions was found to be an adsorbent dosage of 0.25 g, a contact time of 180 min, an initial concentration of 100 mg/L, a pH value of 4 for RP and PFP, and a pH value of 5 for DFP. The adsorption conformed with the pseudo-second-order kinetic model. The adsorption data were consistent with the Langmuir and Freundlich isotherm models, but the best fit was with the Langmuir model. The Langmuir monolayer adsorption capacity values of DFP, RP, and PFP were calculated to be 92.593, 192.308, and 121.951 mg/g, respectively. RP showed a higher adsorption capacity of Cu(II) ions than PFP and DFP for all parameters. The results indicate that these biosorbents might be used to effectively adsorb Cu(II) ions from wastewater treatment plants.     

砂样钢渣对酸性Cr(Ⅵ)的吸附动力学与机理研究

以砂样钢渣作为吸附剂,研究了去除废水中Cr6+的工艺条件和机理。结果表明,最佳工艺条件分别为：pH值0.8~1.5,温度为20℃~25℃,钢渣投放量为5 g,废水初始体积以150~200 mL为宜。铬去除量与钢渣水溶液静置时间呈线性关系,且颗粒内扩散模型、准一级和二级速率方程、Langmuir和Freundlich吸附等温模型拟合曲线的相关系数较大,属于单分子层的吸附方式并具有较好的吸附性。通过机理分析可知,砂样钢渣对Cr6+的吸附过程分为还原（降毒）、水化、沉淀、吸附等4个阶段,钢渣最大吸附量为45.872 mg/g,占砂样钢渣的比例较小。钢渣完成吸附铬后,仍可用来配制砂浆、混凝土等。     

Removal of Cr(VI) by magnetite nanoparticle.

Magnetite nanoparticles were synthesized by sol-gel method. The highly crystalline nature of the magnetite structure with diameter of around 10 nm was characterized with transmission electron microscopy and X-ray diffractometry. The surface area was determined to be 198 m2/g. Batch experiments were carried out to determine the adsorption kinetics and mechanism of Cr(VI) by these magnetite nanoparticles. The Cr(VI) uptake was mainly governed by physico-chemical adsorption. The adsorption process was found to be pH and temperature dependent. The adsorption data fit well with the Freundlich isotherm equation. The Freundlich constants were calculated at different temperatures. The adsorption capacity increased with rising temperature. Preliminary results indicate that magnetite nanoparticles may be used as an adsorbent for removal of Cr(VI) from wastewater.     

Adsorption of Cr(VI) in wastewater using magnetic multi-wall carbon nanotubes

Magnetic multi-wall carbon nanotubes were prepared with wet chemical treatments and characterized by a transmission electron microscope (TEM) and X-ray diffraction (XRD). They were used as adsorbents for the removal of Cr(VI) in aqueous solutions. The effects of adsorbent dosage, the concentration of Cr(VI) in aqueous solution, temperature, and pH value on the removal efficiency were studied. Results showed that the adsorption capacity of the magnetic multi-wall carbon nanotubes increased with the initial Cr(VI) concentration, but decreased with the increase of adsorbent dosage. The adsorption amount increased with contact time. The adsorption kinetics were best represented by the pseudo second-order kinetic model, and the adsorption isotherms indicated that the Langmuir model better reflected the adsorption process. The obtained calculation results for the Gibbs free energy revealed that the adsorption was a spontaneous and endothermic process. The enthalpy deviation was 3.835 kJ·mol⁻¹. The magnetic multi-wall carbon nanotubes showed significant potential for application in adsorption of heavy metal ions.     

Investigation of Pb(II) bioremediation potential of algae and cyanobacteria strains isolated from polluted water

Algae and cyanobacteria are known to be able to remove a variety of pollutants from water, including toxic metal ions. In this study, algal and cyanobacterial species growing in two polluted water bodies were identified, and the Pb(II) removal ability of these isolated species was investigated. Based on microscopic observations, 27 species were identified, and nine species were isolated as pure cultures. Pb(II) bioremediation of five selected species (Anacystis sp., Chlorella sp. 1, Monoraphidium sp., Phormidium sp., and Uronema sp.) was studied in detail. The mean Pb(II) removal abilities varied among these five species: Phormidium sp. > Monoraphidium sp. > Uronema sp. > Chlorella sp. 1 > Anacystis sp. The Pb(II) tolerance of each species was determined based on the live cell percentage and biofilm formation capacity. Within a period of 3 d, Phormidium sp., Monoraphidium sp., and Uronema sp. showed nearly 90% of survival, and all five species demonstrated biofilm formation capacities exceeding 50%. Furthermore, the Pb(II) removal ability of the five species exhibited a strong positive correlation with the live cell percentage and showed a strong negative correlation with the biofilm formation capacity. In conclusion, Phormidium sp., Monoraphidium sp., and Uronema sp. exhibited high tolerances towards Pb(II) and presented high removal abilities. Thus, these species can be identified as potential sorbents for development of suitable adsorption systems to remove Pb(II) from aqueous solutions.     

The sorption of lead, cadmium, copper and zinc ions from aqueous solutions on a raw diatomite from Algeria

The adsorption of Cu(2+), Zn(2+), Cd(2+) and Pb(2+) ions from aqueous solution by Algerian raw diatomite was studied. The influences of different sorption parameters such as contact pH solution, contact time and initial metal ions concentration were studied to optimize the reaction conditions. The metals ions adsorption was strictly pH dependent. The maximum adsorption capacities towards Cu(2+), Zn(2+), Cd(2+) and Pb(2+) were 0.319, 0.311, 0.18 and 0.096 mmol g(-1), respectively. The kinetic data were modelled using the pseudo-first-order and pseudo-second-order kinetic equations. Among the kinetic models studied, the pseudo-second-order equation was the best applicable model to describe the sorption process. Equilibrium isotherm data were analysed using the Langmuir and the Freundlich isotherms; the results showed that the adsorption equilibrium was well described by both model isotherms. The negative value of free energy change ΔG indicates feasible and spontaneous adsorption of four metal ions on raw diatomite. According to these results, the high exchange capacities of different metal ions at high and low concentration levels, and given the low cost of the investigated adsorbent in this work, Algerian diatomite was considered to be an excellent adsorbent.     

Poly(acrylic acid) modifying bentonite with in-situ polymerization for removing lead ions

In this paper, a new kind of poly(acrylic acid) modified clay adsorbent, the poly(acrylic acid)/bentonite composite (PAA/HB) was prepared by in-situ polymerization, and utilized to remove lead(II) ions from solutions. The maximum adsorption of adsorbent is at pH 5 for metal ions, whereas the adsorption starts at pH 2. The effects of contact time (5-60 min), initial concentration of metal ions (200-1,000 mg/L) and adsorbent dosage (0.04-0.12 g/100 mL) have been reported in this article. The experimental data were investigated by means of kinetic and equilibrium adsorption isotherms. The kinetic data were analyzed by the pseudo-first-order and pseudo-second-order equation. The experimental data fitted the pseudo-second-order kinetic model very well. Langmuir and Freundlich isotherms were tried for the system to better understand the adsorption isotherm process. The maximal adsorption capacity of the lead(II) ions on the PAA/HB, as calculated from the Langmuir model, was 769.2 mg/g. The results in this study indicated that PAA/HB was an attractive candidate for removing lead(II) (99%).     

Adsorption of Cd(II), Zn(II) by extracellular polymeric substances extracted from waste activated sludge

Adsorption of Cd(II) and Zn(II) ions in single solutions using extracellular polymeric substances (EPS) from activated sludge was investigated. Langmuir and Freundlich models were applied to describe metal adsorption. The results showed that EPS was an effective adsorbent for the zinc and cadmium ions from aqueous solution. The equilibrium metal uptake was increased with increasing the initial concentration of metal ion. Constants calculated from isotherms model showed that the maximum uptake capacity of cadmium was estimated to be 45 mg/g of Cd(II) and 80 mg/g of Zn(II). Both Langmuir and Freundlich isotherms were suitable for describing adsorption of Cd(II) by EPS, while the Langmuir isotherm equation fit the date of Zn(II) adsorption better, indicating that EPS adsorb Cd(II) and Zn(II) by different mechanisms.Analysis of FTIR spectra demonstrated that C-O-C of polysaccharides at 1,150-1,030 cm(-1), group of the amide(I), CH(2) group of the lipids, carboxyl and -OH groups of proteins and polysaccharides were involved in cadmium and zinc binding, of which the -OH groups and the C-O-C group of polysaccharides.     

生物炭/铁酸锰对Zn^2+和Cu^2+的吸附性能试验

为探求吸附效果好、回收方便的吸附剂以解决重金属污染废水的处理难题,以玉米秸秆和铁酸锰为原料,通过溶胶-凝胶法以蛋清为络合剂经热解制备了一种生物炭/铁酸锰(BC/FM)复合材料,在对该复合材料扫描电子显微镜(SEM)和磁滞回线分析的基础上,进行了去除废水中Zn^2+、Cu^2+的吸附试验。结果表明,铁酸锰可有效地负载到生物炭上,形成官能团丰富、磁性良好的复合材料;BC/FM对Zn^2+、Cu^2+的吸附最佳pH值分别为5和6,并均在90 min达到吸附平衡,准二级模型能更好地描述BC/FM对Zn^2+、Cu^2+吸附过程;Langmuir模型拟合曲线和Freundlich模型拟合曲线分别适用于描述BC/FM对Zn^2+、Cu^2+的等温吸附过程,且均为自发吸热反应;BC/FM对Zn^2+、Cu^2+吸附机制主要为络合反应。     

Comparison of surface functional groups and metal uptake efficiency of rice husk harvested from different climatic zones

Rice husk (RH) is a very effective natural adsorbent for fast removal of heavy metal cations from water solutions. Application of RH for removal of some heavy metal ions, such as Ni, Zn, Mn, Co, Cu, Pb and Cd from water solutions has been studied and different maximum adsorption capacities and a variety of optimized conditions were reported in the literature. In this work, the efficiency of RH harvested from different climatic regions was studied. For this proposal, different RH samples were collected from three different climatic regions of Iran (nominated as RH1 to RH3); their removal efficiencies of heavy metal cations of Ni(2+), Cu(2+) and Cd(2+) were investigated and compared. The adsorption data at optimum conditions could be assessed well by both Langmuir and Freundlich models. Statistical analysis of the results of adsorption isotherms showed that different RH samples have different efficiencies in uptake of these heavy metal ions. The RH samples were characterized using Fourier transform infrared spectroscopy and Boehm titration, which indicated that amounts of functional groups differed between RHs that are grown in different climatic conditions.     

Chromium adsorption on surface activated biochar made from tannery liming sludge: A waste-to-wealth approach

In a beamhouse, liming plays a key role in the removal of hair/wool and epidermis, but problems are created when waste liming sludge is discharged to the environment. The treatment of tannery wastewater is another major challenge to the industry. In this study, thermally-activated biochars derived from liming sludge were studied for their effective adsorption of chromium (Cr) from the tannery wastewater. The thermally activated biochars (B500, B550, B600, and B650) were prepared at different temperatures from the liming sludge. Their characteristics before and after the treatment were investigated using Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, Brunauer–Emmett–Teller, and scanning electron microscopy analyses. The related functional groups (C–H, O–H, C–N, and =C–O) and chromium adsorption capacity were determined according to the surface morphology, element contents (C, O, Ca, Na, Al, Mg, and Si), surface area (5.8–9.2 m²/g), pore size (5.22–5.53 nm), and particle size (652–1 034 nm) of the experimental biochars. The biochar originated at 600°C from the tannery liming sludge (B600) had a greater surface area with a chromium adsorption capacity of 99.8% in comparison to B500, B550, and B650 biochars. This study developed an innovative way of utilizing liming sludge waste to minimize the pollution load and wastewater treatment cost in the tannery industry.     

Phosphonated cross-linked polyethylenimine for selective removal of uranium ions from aqueous solutions

Among many remediation techniques for metal ion removal, polymeric adsorbents are efficient and widely applied. This has made them comparable with other remediation techniques in terms of technical and economic efficiency, feasibility as well as green technology. This study was dedicated to the development of an insoluble modified chelating polymer for use as an adsorbent for abstraction of uranium from wastewaters. Cross-linked polyethylenimine (CPEI) was phosphonated by phosphorous acid for selective removal of uranium ions. The binding affinity of the phosphonated cross-linked polyethylenimine (PCPEI) to uranium ions was assessed as well as its ability to be regenerated for reuse. It exhibited high removal percentage for uranium ions up to 99% with high selectivity even in the presence of competing ions (Mn, Ni, As). The Freundlich isotherm was found to be the best fit describing the adsorption process of uranyl ions onto the PCPEI. The pseudo-second-order equation was found to better explain the adsorption kinetics, implying chemisorption. The thermodynamic study of the adsorption revealed high activation energies which confirmed the chemisorption as the mechanism of adsorption.     

改性陶土颗粒吸附砷的实验研究

以赤玉土为骨料烧制陶土材料,经FeCl3溶液浸渍及热处理改性后制备成新型的改性陶土颗粒吸附剂,对其表面特征及除砷性能进行初步研究:BET测定得出该吸附剂比表面积为36.493m2/g,孔容量为0.070mL/g;SEM EDX显示吸附剂表面有大量铁、氧元素分布;对比该吸附剂和HCl溶液改性吸附剂表面的微观数码照片及3D影像图,表明该吸附剂表面存在大量铁氧化物;该吸附剂在中性pH范围内有良好吸附除砷能力,共存的氟离子、磷酸根离子对除砷效果有不同程度的竞争影响,碳酸根离子对除砷效果无显著影响;Freundlich等温线方程能较好地拟合As(V)的吸附过程(R2=0.9927),吸附平衡时的饱和吸附容量可达43.491mg/g。低成本高效的改性陶土颗粒应用于实际的砷吸附处理,具有较好的应用前景。     

Fabrication of graphene oxide-keratin-chitosan nanocomposite as an adsorbent to remove turbidity from tannery wastewater

Excessive turbidity in water is aesthetically unappealing and severely malfunctions the photosynthesis process of aquatic ecosystems. This study aimed to evaluate the effectiveness of a nanocomposite adsorbent made of graphene oxide-keratin-chitosan for removing turbidity from tannery influent. The nanocomposite was fabricated with simple solution casting methods. Material dispersibility, bonding between composite materials (amide linkage), and the surface morphology of the nanocomposite were analyzed with the ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. At pH of 6, 2 g/L of adsorbent and a 25-min contact time resulted in about 88% of turbidity elimination. After the adsorption process, the total suspended solids, total dissolved solids, salinity, biochemical oxygen demand, and chemical oxygen demand of the tannery wastewater were reduced by 55%, 29%, 12%, 58%, and 75%, respectively. The optimum dosage of the nanocomposite with the maximum turbidity removal capacity was 12.62 mg/g. According the adsorption kinetic and isotherm models, the graphene oxide-keratin-chitosan nanocomposite played a key role in the turbidity removal process with chemisorption and electrostatic multilayer adsorption. This study provided methodological and mechanistic insights into the procedures of investigating the removal of turbidity from tannery wastewater with a novel composite material.     

Removal of lead(II) and copper(II) from aqueous solution using foitite from Linshou mine in Hebei, China

Foitite from Linshou mine in China's Hebei province was investigated as an adsorbent to remove Pb(II) and Cu(II) from aqueous solution. The results showed that foitite can readily remove heavy metal ions from aqueous solution. The data shows that the metal uptake for Pb(II) increases rapidly, accounting for 74.47% when contact time was 2 min. In contrast to Pb(ll), there was a worse capability for adsorption of Cu(II). In the first 4 min, the metal uptake accounted for 34.7%. According to the analytical results obtained from X-ray diffraction, laser Raman spectrum, X-ray energy dispersive spectrometer, and Zeta potential, the removal mechanism of Pb(II) and Cu(II) by using foitite can be explained as following: firstly, the existence of an electrostatic field around foitite particles can attract heavy metal ions and consequently combine heavy metal ions with OH; secondly, heavy metal ions in the solution are exchanged with the Fe3+ and Al3+ in the foitite.     

Use of sesame stalk biomass for the removal of Ni(II) and Zn(II) from aqueous solutions

In this study an agricultural residue, sesame stalk, was evaluated for the removal of Ni(II) and Zn(II) metal ions from aqueous solutions. Biosorption studies were carried out at different pH, biosorbent dosage, initial metal ion concentrations, contact time, and solution temperature to determine the optimum conditions. The experimental data were modeled by Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherm models. Langmuir model resulted in the best fit of the biosorption data. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data and to evaluate rate constants. The best correlation was provided by the second-order kinetic model. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated for predicting the nature of adsorption. The experimental results showed that sesame stalk can be used as an effective and low-cost biosorbent precursor for the removal of heavy metal ions from aqueous solutions.     

Removal of hexavalent chromium from wastewater by Fe0-nanoparticles-chitosan composite beads: characterization, kinetics and thermodynamics

Fe0-nanoparticles-chitosan composite beads (CS-NZVI beads) were prepared and used to remove hexavalent chromium (Cr (VI)) from wastewater. Characterization with a scanning electron microscopy (SEM) demonstrated that with the increase of the concentration of CS from 5.0 to 20.0 g/L and NaOH from 0.5 to 2.0 mol/L, the average aperture size of the CS-NZVI beads decreased from 26.8 to 10.6 μm and 42.6 to 0.8 μm, respectively. Batch experiments revealed that the removal of Cr (VI) using CS-NZVI beads was consistent with pseudo first-order reaction kinetics. The rate constant increased with increasing NZVI dosage but decreased with the increase in pH values. The Freundlich isotherm described the adsorption process better, suggesting that the CS-NZVI beads were heterogeneous in the surface properties. At equilibrium qmax was 35.97 mg/g. The thermodynamics study suggested that Cr (VI) removal by CS-NZVI beads was an endothermic and spontaneous process, reflecting good affinity of the sorbent for Cr (VI) ions and increasing randomness at the solid-solution interface during the adsorption process. This result will be very useful to understand the effects of NZVI on heavy metal Cr (VI) removal from wastewater in the successful application.     

Phosphorus removal by adsorbent based on poly-aluminum chloride sludge

Phosphorus adsorption tests were carried out using poly-aluminum chloride sludge (PACS), which was collected from a water treatment plant in Nanjing. The amount of phosphorus adsorbed by PACS increased quickly within the first hour and reached equilibrium after about 48 h. The adsorption behavior of PACS for phosphorus is consistent with the Langmuir adsorption isotherm equation (R² > 0.99) and parallel first-order kinetic equation (R² > 0.98). With the increase of the PACS concentration, the adsorption capacity of PACS for phosphorus decreased, and the removal rate increased. The results of batch tests showed that the adsorption capacities of PACS for phosphorus ranged from 1.64 to 1.13 mg/g when the pH value varied from 4 to 10. However, the adsorption capacity of PACS was not evidently influenced by temperature. In comparison with the ion exchange resin, the adsorption capacity of PACS was barely inhibited by competitive ions, such as ${\text{SO}}_4^{2-}$, ${\text{NO}}_3^{-}$, and Cl⁻. The PACS surface after adsorption became smooth, and the vibration peaks of Al–O and Al–OH shifted. Both HCl and NaOH have a strong desorption effect on PACS after adsorption saturation, and with higher concentrations of HCl and NaOH, the desorption effect was stronger. Results of column adsorption experiments showed that with lower phosphorus and hydraulic loads, the adsorption column took longer to reach saturation. This indicated that PACS could be used as an efficient material for removal of phosphorus from water. This study provides a new treatment method with PACS.     

壳聚糖基印迹水凝微球对Cr (VI)的选择性吸附研究

目前水环境污染物成分复杂,常用的化学沉淀法已很难将重金属污染物分类去除并资源化利用,由此产生了大范围的危废污染环境,需要进行二次处理。利用离子印迹技术对壳聚糖基水凝微球进行改性,制备具有对Cr (VI)特异识别性能的吸附材料(CTS-IGB）,对其在单一Cr (VI)溶液和模拟电镀废水中的吸附行为特征进行研究。研究结果表明:在20 ℃、pH值为3时,CTS-IGB在单一Cr (VI)溶液和模拟电镀废水中Cr (VI)的吸附量在180 min内分别达到37.4 和44.3 mg/g,半饱和吸附时间仅分别为5.8和23.5 min;吸附行为符合准二级动力学。吸附等温线拟合表明吸附过程符合Freundlich模型;热力学参数表明吸附过程是放热反应,且吸附后无序度减小;相比于未改性壳聚糖水凝微球,CTS-IGB在共存离子（模拟电镀废液及其他双组份溶液）工况下对Cr (VI)的选择性提高32%~74%。该材料可作为潜在的吸附材料用于污染水环境中Cr (VI)的分离及回收。     

Removal of hexavalent chromium in aquatic solutions by pomelo peel

This study investigated the removal of hexavalent chromium(Cr(VI)) in aqueous solutions using pomelo peel(PP) and FeCl_3-modified pomelo peel(FPP) as novel biomass adsorbents.Batch adsorption experiments were performed to evaluate the effects of pH,time,temperature,initial concentration,and adsorbent dose on Cr(VI) removal by PP and FPP.The results show that the maximum adsorption capacity of Cr(VI)was 21.55 mg/g for FPP and 0.57 mg/g for PP at a pH of 2.0 and a temperature of 40℃.The surface shape,microstructure,and chemical composition of FPP were analyzed with scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and energy dispersive spectroscopy(EDS),and compared with those of PP.The results show that the adsorption performance of FPP was much better than that of PP,indicating that FPP can be an alternative high-efficiency adsorbent for Cr(VI) removal.