Sorption of lead by chemically modified rice bran

In this work, the effectiveness of native and chemically modified rice bran to remove heavy metal Pb(II) ions from aqueous solution was examined. Chemical modifications with some simple and low-cost chemicals resulted in enhancement of the adsorption capacities and had faster kinetics than native rice bran. Experiments were conducted in shake flasks to monitor the upshot of parameters over a range of pH, initial Pb(II) concentrations and contact times using a batch model study. The sorption capacities q (mg g^?1) increased in the following order: NaOH (147.78), Ca(OH)₂ (139.08), Al(OH)₃ (127.24), esterification (124.28), NaHCO₃ (118.08), methylation (118.88), Na₂CO₃ (117.12) and native (80.24). The utmost uptake capacity q (mg g^?1) was shown by NaOH-pretreated rice bran. The results showed that, using NaOH-modified rice bran, the chief removal of Pb(II) was 74.54 % at pH 5, primary Pb(II) concentration 100 mg L^?1 and contact time 240 min. Equilibrium isotherms for the Pb(II) adsorption were analyzed by Langmuir and Freundlich isotherm models. The Langmuir isotherm model, showing Pb(II) sorption as accessible through the high value of the correlation coefficient (R ² = 0.993), showed a q _max value of 416.61 mg g^?1. The kinetic model illustrated adsorption rates well, depicted by a second order, which gives an indication concerning the rate-limiting step. Thermodynamic evaluation of the metal ion ?G ^o was carried out and led to the observation that the adsorption reaction is spontaneous and endothermic in nature. NaOH chemically modified rice bran was a superb biosorbent for exclusion of Pb(II) and proved to be excellent for industrial applications.     

Removal of lead(II) from aqueous stream by hydrophilic modified kapok fiber using the Fenton reaction

A hydrophilic kapok fiber was prepared by a chemical process of the Fenton reaction and used as an adsorbent to remove Pb(II) from aqueous solution. The effects of experimental parameters including pH, contact time, Pb(II) concentration, and coexisting heavy metals were estimated as well as evaluated. The optimum concentrations of FeSO₄ and H₂O₂ for the Fenton reaction-modified kapok fiber (FRKF) were 0.5 mol L^?1 and 1 mol L^?1, respectively. The adsorption kinetic models and isotherm equations of Langmuir and Freundlich were conducted to identify the most optimum adsorption rate and adsorption capacity of Pb(II) on FRKF. The FRKF displayed an excellent adsorption rate for Pb(II) in single metal solution with the maximum adsorption capacity of 94.41?±?7.56 mg g^?1 at pH 6.0. Moreover, the FRKE still maintained its adsorption advantage of Pb(II) in the mixed metal solution. The FRKF exhibited a considerable potential in removal of metal content in wastewater streams.     

Lead removal from aqueous solution by basaltic scoria: adsorption equilibrium and kinetics

Pb-contaminated water is a dangerous threat occurring near metallurgic and mining industries. This circumstance produces serious environment concern, due to Pb(II) high toxic effects. Several reactive materials have been reported for Pb(II) adsorption, but not all reached final Pb(II) suitable concentrations, or they are expensive and rejected in massive remediation technologies; hence, natural materials are good options. The adsorption behavior of a volcanic scoria (two sieved fractions 1425 and <425 µm) was studied toward synthetic Pb(II) water solutions in batch experiments (170.4–912.3 mg L^?1) with high removal efficiencies (97%). The Langmuir model fits both fractions with high linear correlation coefficients (0.9988 and 0.9949) with high maximum capacity values (588.23 and 555.55 mg g^?1). Separation factor R _L parameter varies with initial concentration, and the empirical equation predicts the limits of the material usefulness, a criterion proposed in this paper for conditions’ selection. The Lagergren pseudo-second-order analysis demonstrates chemisorption; calculated rate constant (416.66 mg g^?1 min^?1). Weber–Morris intraparticle model proves that the adsorption phenomena occur fast on the material surface (k _inst = 72 g mg^?1 min^?0.5). The characterization of the volcanic material afforded the elemental composition (X-ray fluorescence), and the empirical formula was proposed. X-ray diffraction patterns verify the material structure as basalt, with a plagioclase structure that matches anorthite and albite, mostly composed of quartz. The presence of oxides on the material surface explain the high Pb(II) adsorption capacity, observed on the surface by scanning electronic microscopy. The studied volcanic scoria has potential use as a Pb(II) adsorbent in water remediation technologies.     

Effective removal of zinc from an aqueous solution using Turkish leonardite–clinoptilolite mixture as a sorbent

In this study, the feasibility of using a low-cost adsorbent mixture composed of leonardite (L) and clinoptilolite (C) was evaluated by batch adsorption method using different parameters such as mixing ratio, contact time, pH, temperature, and adsorbent amount for the removal of Zn (II) ions from an aqueous solution. The adsorbents were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Additionally, leonardite–clinoptilolite mixture was analyzed by scanning electron microscopy coupled with energy dispersive X-ray. The Zn (II) adsorption along with an unprecedented adsorption capacity of 454.55 mg g^?1 for unmodified natural sorbents was obtained by mixing leonardite and clinoptilolite (LC) without any pretreatment at a ratio of 3:1, using 0.1 g of sorbent at a pH 6, for 2 h of contact time. The experimental data showed a good fit for the Langmuir isotherm model. The thermodynamic parameters revealed that the present adsorption process was spontaneous and exothermic in nature (25–50 °C). The kinetic results of the adsorption showed that the Zn (II) adsorption onto the LC follows pseudo-second-order model. The resultant LC mixture has an excellent adsorption capacity of a Zn (II) aqueous solution, and data obtained may form the basis for utilization of LC as an unpretreated low-cost adsorbent for treatment of metalliferous industrial wastewater.     

Utilization of ochre as an adsorbent to remove Pb(II) and Cu(II) from contaminated aqueous media

The ability of ochre to remove Pb(II) and Cu(II) from aqueous media has been studied by batch sorption studies varying the contact time, initial metal concentration, initial solution pH and temperature to understand the adsorption behaviour of these metals through adsorption kinetics and isotherms. The pH of the solution and the temperature controlled the adsorption of metal ions by ochre and rapid uptake occurred in the first 30 min of reaction. The kinetics of adsorption followed a pseudo-second-order rate equation (R ² > 0.99) and the isotherms are well described by the Freundlich model. Adsorption of metals onto ochre is endothermic in nature. Between the two metals, Pb(II) showed more preference towards the exchangeable sites on ochre than Cu(II). This study indicates that ochre is a very effective adsorbent in removing Pb(II) and Cu(II) from the aqueous environment with an adsorptive capacity of 0.996 and 0.628 mg g^?1 and removal efficiency of 99.68 and 62.80 %, respectively.     

Efficient removal of hexavalent chromium from aqueous solutions using autohydrolyzed Scots Pine (Pinus Sylvestris) sawdust as adsorbent

In this work, a low-cost lignocellulosic adsorbent with high biosorption capacity is proposed, suitable for the efficient removal of hexavalent chromium from water and wastewater media. The adsorbent was produced by autohydrolyzing Scots Pine (Pinus Sylvestris) sawdust. The effect of the autohydrolysis conditions, i.e., pretreatment time and temperature, on hexavalent chromium biosorption was investigated using energy-dispersive X-ray spectroscopy (EDS) and UV–visible spectrophotometry. The Freundlich, Langmuir, Sips, Radke-Prausnitz, Modified Radke-Prausnitz, Tóth, UNILAN, Temkin and Dubinin-Radushkevich adsorption capacities and the rate constant values for pseudo-first- and pseudo-second-order kinetics indicated that the autohydrolyzed material exhibits significantly enhanced hexavalent chromium adsorption properties comparing with the untreated sawdust. The Freundlich’s adsorption capacity K _F increased from 2.276 to 8.928 (mg g^?1)(L mg^?1)^1/n , and the amount of hexavalent chromium adsorbed at saturation (Langmuir constant q _m) increased from 87.4 to 345.9 mg g^?1, indicating that autohydrolysis treatment at 240 °C for 50 min optimizes the adsorption behavior of the lignocellulosic material.     

Uptake of Indosol Dark-blue GL dye from aqueous solution by water hyacinth roots powder: adsorption and desorption study

Adsorption characteristics of water hyacinth roots powder for the removal of Indosol Dark-blue GL dye were investigated in batch mode. Operating variables, such as initial solution pH, presence of detergent, adsorbent dosage, initial concentration and contact time, were studied. The results showed that the adsorption of dye increased with increasing the initial concentration and contact time. The adsorption is highly pH dependent and adsorption capacity increased with decrease in pH. Kinetic study revealed that the uptake of Indosol Dark-blue GL was very rapid within the first 15 min and equilibrium time was independent of initial concentration. Batch equilibrium experiments were carried out at different pH and found that equilibrium data fitted well to Langmuir isotherm model. The maximum sorption capacity of the adsorbent was found as 86 mg g^?1 at pH 3 which reduced to 64 mg g^?1 at pH 5. The presence of detergent reduced the sorption capacity of the adsorbent significantly. Using equilibrium and kinetic data, the forward and backward rate constants were determined from the unified approach model. Desorption study revealed that the dye can be recovered by swing the pH from low to high.     

Kinetic and equilibrium studies on the removal of <Superscript>14</Superscript>C-ethion residues from wastewater by copper-based metal–organic framework

There are compelling economic and environmental reasons to remove pesticides from wastewater because they are toxic and carcinogenic. The effectiveness of copper-based metal–organic framework (Cu-BTC) for adsorbing the insecticide ¹⁴C-ethion from wastewater has been studied as function of contact time, adsorbent dosage, temperature and pH. ¹⁴C-ethion/Cu-BTC isotherms exhibit two plateaus (BET type IV) and are reliably represented by Brunauer–Deming–Deming–Teller and Zhu–Gu models, with deviations of only 1.99 and 3.95%, respectively. The removal curve measured under batch operation is well represented by a pseudo-first-order equation, yielding results equivalent to the theoretical linear driving force model of Glueckauf. At pH 7, 75 mg L^?1 ethion concentration, 150 min, 25 °C and 0.425 g L^?1 Cu-BTC dose, the sorbent capacity is ca. 122 mg g^?1. Moreover, Cu-BTC has a good stability after six adsorptions cycles. Finally, our results disclose the fundamental understanding of the adsorption mechanism: the ethion molecule coordinates to two copper(II) atoms across the metal–organic framework channel via the phosphoryl (P–O) group.     

Removal of cationic dye methylene blue (MB) from aqueous solution by ground raw and base modified pine cone powder

The adsorption capacity of raw and sodium hydroxide-treated pine cone powder in the removal of methylene blue (MB) from aqueous solution was investigated in a batch system. It was found that the base modified pine cone exhibits large adsorption capacity compared with raw pine cone. The extent of adsorption capacity was increased with the increase in NaOH concentration. Overall, the extent of MB dye adsorption increased with increase in initial dye concentration, contact time, and solution pH but decreased with increase in salt concentration and temperature for both the systems. Surface characteristics of pine cone and base modified pine cone were investigated using Fourier transform infrared spectrophotometer and scanning electron microscope. Equilibrium data were best described by both Langmuir isotherm and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity was found to be 129.87 mg g^?1 at solution pH of 9.02 for an initial dye concentration of 10 ppm by raw pine cone. The base modified pine cone showed the higher monolayer adsorption capacity of 142.25 mg g^?1 compared with raw pine cone biomass. The value of separation factor, R _L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. The various kinetic models, such as pseudo-first-order model, pseudo-second-order model, intraparticle diffusion model, double-exponential model, and liquid film diffusion model, were used to describe the kinetic and mechanism of adsorption process. Overall, kinetic studies showed that the dye adsorption process followed pseudo-second-order kinetics based on other models. The different kinetic parameters, including rate constant, half-adsorption time and diffusion coefficient, were determined at different physicochemical conditions. A single-stage bath adsorber design for the MB adsorption onto pine cone and modified pine cone has been presented based on the Langmuir isotherm model equation. Thermodynamic parameters, such as standard Gibbs free energy (ΔG ⁰), standard enthalpy (ΔH ⁰) and standard entropy (ΔS ⁰), were also calculated.     

Immobilization of copper under an acid leach of colloidal pyrite waste rocks by a fixed-bed column

Colloidal pyrite waste rocks (CPWR) which are mainly composed of colloidal pyrite and siderite widely deposit in sulfide mines in the middle and lower reaches of the Yangtze River belt, China, especially in Tongling City, Anhui Province, China. In this paper, a fixed-bed column was used to investigate the weathering and oxidation of CPWR and its role in immobilizing low-concentration Cu (10 mg L^?1) under weakly acidic leach (pH = 5.0). The experimental results indicated that the breakthrough capacity was around 14.0 mg Cu g^?1 CPWR when Cu²⁺ breakthrough concentration was 0.5 mg L^?1. Sequential extraction of Cu and dithionite–citrate–bicarbonate extraction of free iron in the used CPWR after the column breakthrough indicated that Cu removal by CPWR consisted of the following processes: oxidation of pyrite and dissolution of siderite in CPWR, ferrous oxidation, and adsorption of Cu on ferric (hydr)oxides. This study shows the potential application of CPWR as an effective sorbent for the removal of low-concentration Cu from acid mine drainage.     

Effect of phosphorus on the attenuation of lead and chromium transport in soils

This study analyses the adsorption of Pb(II) and Cr(III) in soils. These metals are commonly found together in nature in urban wastes or industrial spillages, and the theoretical approach of the work was to evaluate the response of the soil to continuous Cr and Pb spillages to soil in terms of several physicochemical parameters. The influence of an anthropogenic input of phosphorus was evaluated. Continuous flow experiments were run in duplicates in acrylic columns (25 cm × 3.2 cm). The influent Cr(III) and Pb(II) solutions of 10 mg l^?1 and 25 mg l^?1 at pH 5 were pumped upward through the bottom of the columns to ensure saturation flow conditions. Also, successive experiments were run with the above concentrations of Cr(III) and Pb(II) and NaH₂PO₄, keeping metal to phosphorus ratio of 1:0, 1:0.1 and 1:1. Modelling parameters included Freundlich and Langmuir equations, together with the Two-site adsorption model using CXTFIT code. Results obtained allowed concluding that Pb(II) adsorption presents a certain degree of irreversibility and the continued spillages over soil increment the fraction which is not easily desorbed. Cr(III) desorption was almost complete, evidencing its high mobility in nature. The presence of an anthropogenic input of phosphorus leads to a marked increase of both Pb(II) and Cr(III) adsorption in soils. Z-potential measurements allow to discard the electrostatic attraction of Cr(III) and Pb(II) with the surface charged soil as the dominant process of metal sorption. Instead, CheaqsPro simulation allows to identify PbH₂PO₄ ⁺, PbHPO₄ (aq) and CrHPO₄ ⁺ as the dominant species which regulate Cr(III) and Pb(II) transport in soils.     

Separation of Cu<Superscript>2+</Superscript> and Pb<Superscript>2+</Superscript> by tetraethylenepentamine-modified sugarcane bagasse fixed-bed column: selective adsorption and kinetics

Tetraethylenepentamine-modified sugarcane bagasse (SCB) was prepared to improve its adsorption capacity and selectivity toward Cu²⁺. Adsorption performances of the modified sorbent for Cu²⁺ were studied in batch system. Separation of Cu²⁺ from Pb²⁺ by the modified sorbent fixed-bed column were studied under dynamic system with initial molar concentration ratio \(\left( {C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}} } \right)\) ranging from 1:1 to 1:100. The amount of Cu²⁺ and Pb²⁺ adsorbed on the saturated column was calculated by the elution curve. Batch experimental results showed that the adsorption capacity of the sorbent for Cu²⁺ increased from 0.12 to 0.21 mmol g^?1 after modification. Dynamic adsorption results showed that the modified SCB had higher adsorption affinity toward Cu²⁺ than Pb²⁺. 0.07 mmol g^?1 of adsorbed Pb²⁺ was pushed off by Cu²⁺ during the competitive adsorption process at \(C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}} = {\text{1:1}}.\) The breakthrough curves and adsorption kinetics of Cu²⁺ in the column could be fitted well by the Yoon–Nelson and modified Yoon–Nelson model, respectively. According to the elution curve, the amount of Cu²⁺ adsorbed on the fixed-bed column were 0.16, 0.16 and 0.15 mmol g^?1, while that of Pb²⁺ were 0.0016, 0.0051 and 0.0094 mmol g^?1 when \(C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}}\) increased from 1:1 to 1:10 and 1:100. Cu²⁺ could be selectively adsorbed and separated from Pb²⁺ by using the modified sorbent fixed-bed column.     

Ionic solid-impregnated sulphate-crosslinked chitosan for effective adsorption of hexavalent chromium from effluents

Microwave-assisted tetrabutyl ammonium-impregnated sulphate-crosslinked chitosan was synthesized for enhanced adsorption of hexavalent chromium. The adsorbent obtained was extensively characterized using Fourier transform infrared, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray studies. Various isotherm models such as Langmuir, Freundlich and Dubinin–Radushkevich were studied to comprehend the adsorption mechanism of hexavalent chromium by the adsorbent. Maximum adsorption capacity of 225.9 mg g^?1 was observed at pH 3.0 in accordance with Langmuir isotherm model. The sorption kinetics and thermodynamic studies revealed that adsorption of hexavalent chromium followed pseudo-second-order kinetics with exothermic and spontaneous behaviour. A column packed with 1 g of adsorbent was found to give complete adsorption of Cr(VI) up to 900 mL of 200 mg L^?1 solution which discerns the applicability of the adsorbent material for higher sample volumes in column studies. The effective adsorption results were obtained due to both ion exchange and ion pair interaction of adsorbent with hexavalent chromium. Greener aspect of overall adsorption was regeneration of the adsorbent which was carried out using sodium hydroxide solution. In the present study, the regenerated adsorbent was effectively reused up to ten adsorption–desorption cycles with no loss in adsorption efficiency.     

Biosorption of heavy metals by organic carbon from spent mushroom substrates and their raw materials

The use of agricultural wastes as biosorbents is gaining importance in bioremediation of heavy metal-polluted water and soils, due to their effectiveness and low cost. This work assesses the Cd, Pb and Cu adsorption capacity of the raw materials used in the production of substrates for mushroom production (Agaricus bisporus and Pleurotus ostreatus) and the spent mushroom composted (SMC), based on the functional groups of their organic carbon. The raw materials studied included agricultural wastes (wheat straw, wheat and rice poultry litter, grape pomace) and inorganic substances (gypsum and calcareous sand). Organic carbon from wastes and their composting products were characterized by CP-MAS ¹³C NMR. Langmuir adsorption isotherms of metals were plotted for each raw material, composting step, spent A. bisporus and P. ostreatus substrates and the final SMC. The maximum adsorption capacities of SMC were 40.43, 15.16 and 36.2 mg g^?1 for Cd, Pb and Cu, respectively. The composting process modified the adsorption properties of raw materials because of the enhanced adsorption of Cd and Cu and decreased adsorption capacity of Pb. CP-MAS ¹³C NMR and potentiometric titration were used to identify the functional groups of the organic carbon responsible for the metal adsorption. The content of cellulose was correlated with Pb adsorption (p < 0.001), alkyl and carboxyl carbon with Cd adsorption (p < 0.001), and N-alkyl (p < 0.001) and carboxyl (p < 0.010) groups with Cu adsorption. These results are valuable to develop new biosorbents based on agricultural wastes and demonstrate the high potential of SMC to adsorb heavy metals from polluted environments.     

Adsorption of diethyl and dibutyl phthalates onto activated carbon produced from <Emphasis Type="Italic">Albizia julibrissin pods:</Emphasis> kinetics and isotherms

The adsorption behavior study of diethyl and dibutyl phthalates was investigated onto a new activated carbon prepared from an abundant biomass “Albizia julibrissin pods,” treated chemically by H₃PO₄. A series of experiments were conducted in a batch system to estimate the effect of operating conditions such as the adsorbent nature, the dose of adsorbent, the contact time, the initial concentration and the temperature on the adsorption efficiency. The optimum operating conditions were found to be 0.1 and 0.05 g of adsorbent for diethyl and dibutyl phthalates, respectively, at 30 min equilibrium time, 150 mg g^?1 and 293 K. The adsorption isotherms for both phthalates were fit at different temperatures using the nonlinear regression of Langmuir, Freundlich, Dubinin–Radushkevich and Redlich–Peterson. The pseudo-first order, pseudo-second order by nonlinear regression and intraparticle diffusion models were used to describe the adsorption kinetic. The results show that the intraparticle diffusion model is not the limiting step governing the adsorption mechanism. The structural and textural characteristics of adsorbent surface were investigated. FTIR analysis of unloaded and phthalates-loaded adsorbent revealed that the aliphatic groups attached to phthalate esters are involved in adsorption mechanism.     

Comparative study of the absorptive potential of raw and activated carbon <Emphasis Type="Italic">Acacia nilotica</Emphasis> for Reactive Black 5 dye

Acacia nilotica was used for the adsorption of Reactive Black 5 (RB5) dye from an aqueous solution. Both the raw and activated (with H₃PO₄) carbon forms of Acacia nilotica (RAN and ANAC, respectively) were used for comparison. Various parameters (including dye concentration, contact time, temperature, and pH) were optimized to obtain the maximum adsorption capacity. RAN and ANAC were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The maximum experimental adsorption capacities for RAN and ANAC were 34.79 and 41.01 mg g^?1, respectively, which agreed with the maximum adsorption capacities predicted by the Langmuir, Freundlich, and Dubinin–Radushkevich equilibrium isotherm models. The adsorption data of ANAC showed a good fit to the isotherm models based on the coefficient of determination (R ²): Langmuir type II (R ² = 0.99) > Freundlich (R ² = 0.9853) > Dubinin–Radushkevich (R ² = 0.9659). This result suggested monolayer adsorption of RB5 dye. The adsorption of RB5 dye followed pseudo-second-order kinetics. The RAN adsorbent reflected an exothermic reaction (enthalpy change, ΔH = ?0.006 kJ mol^?1) and increased randomness (standard entropy change, ΔS = 0.038 kJ mol^?1) at the solid–solution interface. In contrast, ANAC reflected both exothermic [?0.011 kJ mol^?1 (303–313 K)] and endothermic [0.003 kJ mol^?1 (313–323 K)] reactions. However, the ΔS value of ANAC was lower when the RB5 adsorption increased from 313 to 323 K. The negative values for the Gibbs free energy change at all temperatures indicated that the adsorption of RB5 dye onto RAN and ANAC was spontaneous in the forward direction.     

Removal of diazinon pesticide from aqueous solutions using MCM-41 type materials: isotherms,kinetics and thermodynamics

In this research, ordered mesoporous silica, including MCM-41, was synthesized via sol–gel process and a propyl methacrylate-modified ordered mesoporous silica (MPS-MCM-41) was successfully synthesized via a postsynthesis grafting process. Then both MCM-41 and MPS-MCM-41 were characterized using FTIR, XRD, SEM and BET techniques. The synthesized materials were utilized as adsorbent for removal of diazinon pesticide from aqueous solutions. The effects of pH, contact time, adsorbent dose, initial concentration and temperature have been evaluated using removal efficiencies. Also, the kinetic, thermodynamic and isotherm models of diazinon adsorption were studied for the both MCM-41 and MPS-MCM-41. The results showed that the maximum adsorption capacities are 142 and 254 mg g^?1 for the MCM-41 and MPS-MCM-41, respectively, at the initial concentration of 50 mg L^?1, temperature of 298 K and adsorbent dose of 0.1 g L^?1. The highest percentages of diazinon removal are 56.4 and 87.2 (at adsorbent dose of 2 g L^?1 and the temperature of 318 K) for the MCM-41 and MPS-MCM-41, respectively. The Freundlich and Langmuir models are more compatible for describing equilibrium data of the diazinon adsorption capacity on the MCM-41 and MPS-MCM-41, respectively. Thermodynamic study indicated that the adsorption process of diazinon onto MCM-41 and MPS-MCM-41 is exothermic and has a spontaneous nature. The higher adsorption capacity and higher spontaneous nature of MPS-MCM-41 in comparison with MCM-41 might be due to the presence of the both hydrogen bonding and hydrophobic interaction between surface functional groups of MPS-MCM-41 (hydroxyl and propyl methacrylate) and diazinon functional groups.     

Lanthanides removal from mine water using banana peels nanosorbent

This study focuses on the performance of nanostructured banana peels in lanthanide-laden mine water treatment. Specifically, nanostructure formation via mechanical milling, characterization in detail and application of this sorbent media in rare earth elements (REEs) removal from synthetic and real mine water are thoroughly investigated. The sorbent samples were characterized by transmission electron microscopy, Brunauer–Emmett–Teller, X-ray diffraction and Fourier transform infrared analyses, while the amount of REEs adsorbed was analysed using inductively coupled plasma optical emission spectroscopy. Results revealed that the particle and crystallite sizes were reduced from <65,000 to <25 nm and 108 to 12 nm, respectively, as the milling progressed. Furthermore, the fracture of particles resulted in a surface area increment from 1.07 to 4.55 m² g^?1. Through Fourier transform infrared analysis, the functional groups responsible for the coordination and removal of metal ions were found to be carboxylic group (at absorption bands of 1730 cm^?1) and amine groups (889 cm^?1). The Langmuir maximum adsorption capacity was 47.8 mg g^?1 for lanthanum and 52.6 mg g^?1 for gadolinium. Meanwhile, results revealed that banana peels have a high affinity for Sm, Eu, Nd, Pr, Gd, Tb and Lu compared to other lanthanides present in the mine water samples. The results obtained so far indicate that nanostructured banana peel is a potential adsorbent for REEs removal from mine water. However, for any application, the water matrix to be treated substantially influences the choice of the sorbent material.     

Uptake of hazardous elements by spring onion (<Emphasis Type="Italic">Allium fistulosum</Emphasis> L.) from soil irrigated with different types of water and possible health risk

Bio-concentration of elements such as Mo, As, Se, Fe, Cu, Zn, Ni and Pb was analyzed in spring onion (Allium fistulosum L.) in three different locations of central Punjab, Pakistan. At location GW, relatively low level of hazardous elements was found in spring onion, suggesting that groundwater is a safe source of water for irrigating food crops. The pH of soil at wastewater irrigation was found less acidic (pH 7.4) than the other sites. The range of concentration in the different samples of spring onion was as follows: 6.15–8.16 mg kg^?1 for Mo, 2.77–4.28 mg kg^?1 for As, 0.395–0.705 mg kg^?1 for Se, 36.73–48.17 mg kg^?1 for Fe, 10.58–16.26 mg kg^?1 for Cu, 28.87–39.79 mg kg^?1 for Zn, 6.66–8.75 mg kg^?1 for Ni and 4.33–6.09 mg kg^?1 for Pb, respectively. High bio-concentration of Zn (15.37) from soil to spring onion was found at canal water irrigated location. The estimated daily intake of metal for spring onion was less, but the health risk index was higher than 1 for Mo, As, Cu, Pb and Ni, respectively. This was due to higher proportion of spring onion in diet, which consequently increased the health risk index for metals. Therefore, it is recommended to avoid growing vegetables in untreated urban and rural wastewater containing elevated amounts of metals.     

Characterization and evaluation of a tropical peat for the removal of Cr(VI) from solution

Tropical peat soils present higher ash content than those generated at temperate climate areas. Therefore, this study evaluated the characteristics of a Brazilian organic soil (OS), commercialized as peat, as well as its capacity in removing Cr(VI) from contaminated waters. The OS is composed of 35.5 wt% of organic matter and 56 wt% of inorganic fraction (ash), which is formed by minerals and phytoliths rich in silica (29.2 wt%) and alumina (23.6 wt%). The Cr(VI) removal tests were carried out in batch and column systems using OS and solutions of Cr(VI) prepared with distilled water and groundwater. Batch tests revealed that the organic substances in the OS caused the reduction of Cr(VI) to Cr(III), with an efficiency depending on solution pH. At pH 5.0 the Cr(VI) removal was 0.45 mg g^?1 in 24 h; whereas at pH 2.0, this removal increased to 1.10 mg g^?1. Since this redox reaction is very slow, the removal of Cr(VI) at pH 5.0 increased to around 2 mg g^?1 after 5 days. The removal of Cr(VI) was more effective in the column tests than in the batch test due to the greater solid/solution ratio, and their half-lives were 4.4 and 26.2 h, respectively. Chemical analysis indicated that Cr(VI) was reduced by the humic substances of OS, followed by the precipitation and/or adsorption of Cr(III) into the organic and inorganic components, as anatase. The presence of Cr(III) increased the stability of anatase structure, avoiding its transformation into rutile, even after being heated at 800 °C/2 h.