Hydrolytic Removal of Cured Urea–Formaldehyde Resins in Medium-Density Fiberboard for Recycling

This study focused on the removal of cured urea–formaldehyde (UF) resins by hydrolysis of medium-density fiberboard (MDF) at different temperatures and times for MDF recycling. Five aqueous solutions, i.e., two acids, two alkalis, and water, were used for MDF hydrolysis to obtain extract solutions and solid residues for the analysis of mass balance, nitrogen content, and resin removal. As expected, acidic solutions removed the greatest amount of cured resins, followed by water and alkaline. Moreover, temperature had a greater impact on hydrolysis than time. Fourier transform infrared spectra of MDF fibers before and after hydrolysis clearly showed the change in intensity of the amide group in UF resins. Reduction of the amide group was greater with increase in hydrolysis temperature than in time. Statistical analysis results suggested that the hydrolysis of MDF at 80°C for 2 h using oxalic acid solution was optimum condition for the removal of cured UF resins. However, water could be used as hydrolysis agent for the practice of MDF hydrolysis in the future.     

Applications of the Biosorption Process for Nickel Removal from Aqueous Solutions – A Review

Wastewaters and contaminants released to the aqueous environment increase due to developing industrialization and technology. These wastewaters should be treated before being discharged to water bodies. Also, reusable materials in wastewaters must be recovered by appropriate techniques. Discharge limits required by the authorities become more stringent with updated legislations. Nickel ions can be reusable by recovering it after the biosorption process. So, this will prevent the loss of raw materials in industries and it also affects the economy in a positive way. Conventional heavy metal removal processes may be costly and inadequate to meet the desired discharge limits and they exhibit low efficiencies. Eco-friendly and economical treatment technologies gain great importance in the removal and recovery of nickel from wastewaters. In this study, biosorption which is the subject of numerous studies and one of the heavy metal removal methods will be investigated, and nickel removal by this technique and the biosorption mechanism will also be elaborated with data from literature studies.     

Effectiveness in the Removal of Organic Compounds from Municipal Landfill Leachate in Integrated Membrane Systems: Coagulation – NF/RO

The article presents the results of studies concerning the hydraulic permeability of integrated membrane systems during the treatment of municipal landfill leachate. The laboratory-scale experiments were conducted to determine the effectiveness of coagulation as a pretreatment option for treating stabilized landfill leachate and effectiveness of nanofiltration (NF) and reverse osmosis (RO) processes. The municipal landfill leachates were analyzed for the concentration of the following: polycyclic aromatic hydrocarbons (PAHs), nitrate nitrogen, ammonium nitrogen, chemical oxygen demand (COD), total organic carbon (TOC), total carbon (TC), suspended soils (SS), turbidity, pH. The commercially available coagulant – aluminum sulfate Al₂(SO₄)₃·18H₂O (alum) was used as a coagulant. The NF process was carried out at the transmembrane pressure of 1.5 MPa. The membrane separation process was based on a thin film membrane (DK). The transmembrane pressure of the RO stood at 2 MPa and for this process one polyamide membrane (AG) was used. The level of leachate treatment was defined for raw and cleaned wastewater indicators. Both NF and RO membranes allowed obtaining the high level of pollutants removal. In the coagulation–NF system, the removal efficiency was equal to 77% for PAHs, 88% for COD, 72% for ammonium nitrogen, 80% for nitrate nitrogen, 67% for TOC, 80% for TC, 96% for SS and during the RO – 86% for PAHs, 98% for COD, 93% for ammonium nitrogen, 87% for nitrate nitrogen, 89% for TOC, 100% for TC, 98% for SS. The calculations based on the assumptions of the mathematical filtration model (relaxation) made it possible to predict the efficiency of commercial filtration membranes used for leachate treatment.     

Optimization of the Sodium Hydroxide–Assisted Hydrogen Sulfide Selective Removal from Natural Gas

Scrubbing of hydrocarbon-based gases such as natural gas or biogas is essential prior to its use. These gas mixtures when contaminated with hydrogen sulfide cause safety, environmental, and corrosion problems in pipelines. There are several methods of reducing the content of hydrogen sulfide in sour gases, but few of these are selective as well. Selectivity is important to avoid unnecessary chemical usage. Chemisorption in sodium hydroxide solution by applying a special spray technique appears to be an efficient and selective method for hydrogen sulfide removal. This study aims to determine the characteristic of system and thereby facilitating the design of gas-cleaning parameters. The studied parameters include the contact time, concentration of sodium hydroxide, absorbent volumetric flow rate, and gas composition. Model gas mixtures of hydrogen sulfide, carbon dioxide, and nitrogen were used for experiments. To define the optimal experiment setup, the Box–Behnken design (BBD) method was applied. Based on the method, the number and the condition of necessary absorption experiments were constructed. To rank the operating parameters of the absorption process from the point of view of which effect is more significant on the scrubbing performance, statistical analysis of variance (ANOVA) was done. The analysis shows contact time and concentration of sodium hydroxide as the two most influential factors in the absorption process. Carbon dioxide content of sour gas as influencing factor was examined for efficiency and order of priority parameters of process. An extended model has been created to support the optimization of operating conditions in the investigated removal system.     

Resins containing α-hydroxyphosphonic acid groups used for adsorption of dyes from wastewater

The synthesis of styrene–divinylbenzene copolymers functionalized with α-hydroxyphosphonic acid groups is presented. The phosphorus content was determined in order to calculate the degree of functionalization with pendant α-hydroxyphosphonic group, with values of 0.66 for St–1%DVB_HOPHOS and 3.14 for St–6.7%DVB_HOPHOS. Their characterization by IR, thermogravimetry is reported. The kinetics of adsorption of three dyes on St–6.7%DVB_HOPHOS polymer was studied.     

Molecular Imprinted Polymer of Methacrylic Acid Functionalised β-Cyclodextrin for Selective Removal of 2,4-Dichlorophenol

This work describes methacrylic acid functionalized β-cyclodextrin (MAA-βCD) as a novel functional monomer in the preparation of molecular imprinted polymer (MIP MAA-βCD) for the selective removal of 2,4-dichlorophenol (2,4-DCP). The polymer was characterized using Fourier Transform Infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The influence of parameters such as solution pH, contact time, temperature and initial concentrations towards removal of 2,4-DCP using MIP MAA-βCD have been evaluated. The imprinted material shows fast kinetics and the optimum pH for removal of 2,4-DCP is pH 7. Compared with the corresponding non-imprinted polymer (NIP MAA-βCD), the MIP MAA-βCD exhibited higher adsorption capacity and outstanding selectivity towards 2,4-DCP. Freundlich isotherm best fitted the adsorption equilibrium data of MIP MAA-βCD and the kinetics followed a pseudo-second-order model. The calculated thermodynamic parameters showed that adsorption of 2,4-DCP was spontaneous and exothermic under the examined conditions.     

Selective Removal of Low-Density Lipoproteins from Blood by Induced Precipitation with AAS in Vitro(Ⅰ)

1 INTRODUCTION It's evident that high level of cholesterol in blood is associated with the formation and devel-opment of familial hypercholestrolemia(FH)and atherosclerosis(AS).In general,choles-terol in blood is mainly combined with low-density lipoproteins(LDL),very low-densitylipoproteins(VLDL)and high density lipoproteins(HDL).About 60%-80% cholesterolexists in LDL and VLDL.LDL and VLDL have been recognized as the principal pathologic     

Ion‐selective Imprinted Superporous Monolith for Cadmium Removal from Human Plasma

Abstract

Molecular recognition based separation systems have received much attention because of their high selectivity for target molecules. Molecular imprinting has been recognized as a promising technique for the development of affinity adsorbents. Molecularly imprinted polymers (MIP) are easy to prepare, stable, inexpensive, and capable of molecular recognition. Cadmium is a carcinogenic and mutagenic element. The limit value of cadmium in blood should be no higher than 50 pg/L when exposure to cadmium is unavoidable in industry. There is no specific treatment available for acute or chronic metal poisoning. Besides supportive therapy and hemodialysis, metal poisoning is often treated with commercially available chelating agents including EDTA and dimercaprol. However, there is histopathological evidence for increased toxicity in animals when these agents are utilized. The aim of this study is to prepare superporous ion‐imprinted polymer monolith which can be used for the selective removal of Cd²⁺ ions from Cd²⁺‐overdosed human plasma. N‐methacryloly‐(L)‐cysteinemethylester (MAC) was chosen as the complexing monomer. In the first step, MAC synthesized by using methacryloyl chloride and cysteine. Cd²⁺ was complexed with MAC monomer and the Cd²⁺‐imprinted poly(HEMA‐MAC) monoliths were synthesized by bulk polymerization. After that, Cd²⁺ ions were removed by 0.1 M thiourea and 0.1 M HNO₃ solutions, respectively. Cd²⁺‐imprinted poly(HEMA‐MAC) monoliths had a specific surface area of 226.8 m²/g and the swelling ratio was determined to be 76%. According to the elemental analysis results, monoliths contain approximately 58.3 µmol/g of MAC. The maximum adsorption capacity for Cd²⁺ ions was 26.6 µmol/g of the dry weight of monolith. The adsorption capacity decreased significantly from 23.25 µmol/g to 3.08 µmol/g polymer with the increase of the flow‐rate from 1 mL/min to 4 mL/min. The Cd²⁺‐imprinted poly(HEMA‐MAC) monolith could be used many times without decreasing their adsorption capacities significantly.     

Physicochemical Aspects on Fluoride Adsorption for Removal from Water by Synthetic Hydrous Iron(III) – Chromium(III) Mixed Oxide

Fluoride removal with varying different parameters at 303 ± 1.6 K and pH 6.5 ± 0.2 was investigated by hydrous iron(III)-chromium(III) bimetal oxide. The kinetic and equilibrium data fitted with the pseudo-second order and Langmuir isotherm equations very well (R² = 0.99?1.00), respectively. The Langmuir capacity (θ) and free energy (E_DR) of adsorption evaluated were 16.34 (±0.50) mg·g^?1 and 15.81 kJ·mol^?1, respectively. The estimated thermodynamic parameters viz. ΔH⁰, ΔG⁰, and ΔS⁰ indicated that the reaction was endothermic but spontaneous for entropy increase. The small-scale column filtration of high fluoride (C₀ = 7.37 mg·L^?1) water gave encouraging results.     

Weak Base Anion Exchanger Amberlite FPA51 as Effective Adsorbent for Acid Blue 74 Removal from Aqueous Medium – Kinetic and Equilibrium Studies

In this work, the macroporous anion exchange resin – Amberlite FPA51, is proposed as the effective adsorbent for the removal of Acid Blue 74 from aqueous solutions. The sorption mechanism was investigated under static conditions taking into account the phase contact time, solution pH, initial dye concentration, and temperature. The equilibrium data were fitted to the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. The maximum monolayer capacity Q ₀ was 123.8 mg/g. The adsorption kinetics was found to follow the pseudo-second order model. The sorption energy was equal to 14.5 kJ/mol and indicated that the adsorption process of the dye may be described via a chemical anion-exchange mechanism.     

Modification of Malonamide Ion-Exchange/Chelating Resins Using the Fields–Kabatschnik Reaction and Their Application to Metal Ion Removal from Aqueous Solutions

A resin containing 2-aminoethyl-substituted amides of malonic acid was modified in the Fields–Kabatschnik reaction using diethyl phosphite. The resultant ion-exchange/chelating resins have aminomethylphosphonate groups. Modification proceeds almost quantitatively, giving a resin with P=1.97 mmol/g, N=4.20 mmol/g, and water regain of 0.44 g/g. It can be selectively hydrolyzed by treatment with trimethylchlorosilane/potassium bromide in dry acetonitrile. Both acidic and ester forms of the resin were used in the removal of Cu(II), Cd(II), Ni(II), and Zn(II) from their diluted 1×10^–4 N solutions in 0.2 M acetate buffer at pH 3.7 and 5.6. The affinity of the resin in an acid form toward divalent metal cations is high, and at pH 5.6 the log K _d is 7.54, 3.97, 3.41, and 3.98, respectively. The resins are selective and the presence of an excess of sodium ions does not influence the uptake of metal ions. The type of complexes formed between the resins and Cu(II) ions was studied using EPR spectroscopy. The ester form of the resin was used in the removal of tetrachloroaurate anions from hydrochloric acid solution. It has been found that the log K _d is in the range of 3.14–3.94 for the uptake of AuCl^– ₄ from 5.0–0.5 M HCl solutions.     

Selective Removal of Uranium from High‐Level Waste Solution Employing Tri‐n‐Butyl Phosphate as the Extractant

Abstract

Conditions for the selective removal of uranium from high‐level waste solution have been optimized using tri‐n‐butyl phosphate (TBP) as the extractant. Various aqueous soluble reducing agents viz. hydroxylamine nitrate (HAN), hydrazine nitrate (HN), and diethyl hydroxylamine nitrate (DEHAN) as well as n‐dodecane soluble reductant viz. tert‐butyl hydroquinone (TBH) have been evaluated for the separation of U with respect to Pu and Np. The combination of DEHAN and TBH has been found to be most promising for the selective extraction of U from HLW. Extraction data of a few other metal ions expected to be present in high‐level waste solutions viz. Am(III), Eu(III), Zr(IV), Sr(II), and Cs(I) are also obtained.     

Experimental Verification of Caustic‐Side Solvent Extraction for Removal of Cesium from Tank Waste

Abstract

A caustic‐side solvent extraction (CSSX) process was developed to remove Cs from Savannah River Site (SRS) high‐level waste. The CSSX process was verified in a series of flowsheet tests at Argonne National Laboratory (ANL) in a minicontactor (2‐cm centrifugal contactor) using simulant. The CSSX solvent, which was developed at Oak Ridge National Laboratory (ORNL), consists of a calixarene‐crown ether as the extractant, an alkyl aryl polyether as the modifier, trioctylamine as the suppressant, and Isopar®L as the diluent. For Cs removal from the SRS tank waste, the key process goals are that: (1) Cs is removed from the waste with a decontamination factor greater than 40,000 and (2) the recovered Cs is concentrated by a factor of 15 in dilute nitric acid. In the flowsheet verification tests, the objectives were to: (1) prove that these process goals could be met; (2) demonstrate that they could be maintained over a period of several days as the CSSX solvent is recycled; and (3) verify that the process goals could still be met after the solvent composition was adjusted. The change in composition eliminated the possibility that the calixarene‐crown ether could precipitate from the solvent. The process goals were met for each of the verification tests. The results of these tests, which are summarized here, show that the CSSX process is a very effective way to remove Cs from caustic‐side waste.     

Removal of heavy metal ions from water by an combined sorption–crystallization process using activated clays

The degree of comminution of materials in an ultrasonic field has been theoretically estimated by calculating the maximum and minimum energy inputs necessary for this process (upper and lower estimates have been obtained). The degree of comminution of kaolin in an ultrasonic bath determined by light and electron microscopy is in satisfactory agreement with the theoretical estimates. The efficiencies of heavy metal ion (Cu²⁺, Ni²⁺) removal from aqueous solutions in the following processes have been compared: adsorption on natural materials (kaolin and bentonite), chemical precipitation in homogeneous crystallization, and integrated sorption–crystallization process using activated clays. The highest purification efficiency has been attained in the integrated process preceded by ultrasonication of the clay slurry and alkaline reagent. Use of these sonochemically activated additives has shortened the duration of the integrated process and has increased the degree of removal of toxic metals to 10²–10³. Clays have been demonstrated to act as a sorbent, a heterogeneous crystallization stimulator, and a coagulant accelerating the sedimentation of the solid phase.     

Grafting of High α-Cellulose Pulp Extracted from Sunflower Stalks for Removal of Hg (II) from Aqueous Solution

Dissolving pulp containing 95.5% α-cellulose was extracted from sunflower stalks. The pulped sunflower stalks (PSFS) were used as starting material for grafting with acrylamide (Aam). All factors affecting the grafting reaction were examined. These factors include liquor ratio (LR), ceric ammonium nitrate (CAN) concentration as a catalyst, Aam concentration, as well as reaction time and temperature. The grafted PSFS (GPSFS) samples were characterized by estimation of nitrogen %. The GPSFS was utilized as adsorbent material to remove Hg (II) ions from aqueous solutions. All factors affecting adsorption process were examined. These factors include pH, adsorbent concentration, temperature, and agitation time. The adsorption data show that the maximum adsorption capacity, q_e, of Hg (II) onto GPSFS is 625 mg/g. The adsorption data also showed that the adsorption of Hg (II) onto GPSFS obeys Langmuir and Freundlich isotherms.     

Integrated ozone–photo–Fenton process for the removal of pollutant from industrial wastewater

The use of hybrid advanced oxidation processes(AOPs) for the removal of pollutants from industrial effluents has been extensively studied in recent literature. The aim of this study is to compare the performance of the photo,Fenton, photo-Fenton and ozone–photo–Fenton processes in terms of color removal and chemical oxygen demand(COD) removal of distillery industrial effluent together with the associated electrical energy per order. It was observed from the experimental results that the O_3/UV/Fe~(2 +)/H_2O_2 process yielded a 100% color and95.50% COD removals with electrical energy per order of 0.015 k W·h·m~(-3) compared to all other combinations of the AOPs. The effects of various operating parameters such as H_2O_2 and Fe~(2+) concentration, effluent pH, COD concentration and UV power on the removal of color, COD and electrical energy per order for the ozone–photo–Fenton process was critically studied and reported. The color and COD removals were analyzed using a UV/Vis spectrometer and closed reflux method.     

Hybrid Properties of Alginate‐PEI Adsorbent for Chromium (VI) Removal from Aqueous Solutions

Abstract

An adsorbent consisting of polyethyleneimine (PEI) immobilized in calcium alginate gel beads was synthesized and evaluated for Cr⁶⁺ removal. An evaluation of the synthesis process showed the importance of the PEI molecular weight on the immobilization efficiency. Polyethyleneimine of 70,000 Da molecular weight displayed the highest immobilization percentage at 52%. Batch kinetics and equilibrium tests showed that alginate‐PEI (APEI) resin displayed considerable affinity for negatively charged Cr⁶⁺ complexes at low pH conditions ranging from pH 1.5‐pH 3. The results also indicated the reduction of Cr⁶⁺ to less toxic Cr³⁺ species by the APEI adsorbent. The column adsorption experiments showed the ability of APEI resin to treat a 10 mg/L Cr⁶⁺ solution with pH influent adjustment from pH 1.5 to pH 3 to concentrations that satisfy effluent standards for Cr⁶⁺ (<0.1 mg/L) and total Cr (<0.5 mg/L). Finally, comparisons with a highly aminated commercial resin Chitopearl CS‐03 highlighted the unique ability of the hybrid APEI beads with its amine and carboxylic groups for the adsorption of Cr⁶⁺ as well as the retention of generated Cr³⁺ ions.     

Is the Coagulation-Filtration Process with Fe(III) Efficient for As(III) Removal from Groundwaters?

The coagulation–filtration process using Fe(III) salts is the most frequently practiced technology for As(V) removal in full scale water treatment plants. The co-existing As(III) is usually oxidized to As(V) prior to removal. Nonetheless, research studies applying high As(III) initial concentrations showed significant As(III) removal capacities, however, the efficiency of the process for initial As(III) concentrations commonly encountered in drinking water, i.e., 10-100 μg/L is not sufficiently investigated. The experimental results of this study indicated that the coagulation–filtration process using Fe(III) can safely meet the drinking water regulation limit of 10 μg/L, only when the initial As(III) concentration is < 25 μg/L and the Fe(III) dose ≥ 5 mg/L, for experiments performed with NSF challenge water. The limitations for efficient As(III) removal are attributed to the fact that As(III), under circumneutral pH values is mostly present with the uncharged H₃AsO₃ form, which is not efficiently adsorbed onto iron oxy hydroxides (FeOOH), the product of Fe(III) hydrolysis. Adsorption isotherms data were best fitted to BET model, indicating multi-layer adsorption and low affinity of As(III) for Fe(III) hydroxides.