Extraction of transition metals from wood pulp fibers using supercritical carbon dioxide (original) (raw)
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Dynamics of chelation-supercritical fluid extraction from wood fibers
Journal of Separation Science, 2004
The dynamics of supercritical fluid extraction (SFE) of the metal content of wood fibers chelated with lithium bis(trifluoroethyl) dithiocarbamate (FDDC) by supercritical (SF) CO2 was investigated experimentally by monitoring the spectra of the eluted metal complex as a function of time. The characteristic shape of the dynamic SFE curve was determined mainly by the flow conditions in the extraction vessel, the mass transfer resistance in the SF phase, and the solubility. High extraction yields of metal content were obtained in two-stage extraction including static (batch) and dynamic (semi-batch) stages. Increasing the length of the static stage increased the rate of dynamic elution of metal complex until it approached the dynamics of fluid displacement for a continuous stirred tank reactor (CSTR). In such cases, increasing the flow rate had no effect on the dynamic extraction curve when it was plotted using dimensionless time. Efficient chelation-SFE from wood fibers was obtained at a pressure of 20.3 MPa and with a static time of 30 min.
CLEAN - Soil, Air, Water, 2010
The effects of pressure, temperature, time, and ligand to metal ratio (50:1-200:1) on the extraction efficiency of metal ions with 4,4 0 -dimethyl-2,2 0 -bipyridyl (DMBP) as a chelating ligand were systematically investigated in supercritical carbon dioxide (sc-CO 2 ). Eight metal ions (Mn 2þ , Fe 3þ , Co 2þ , Ni 2þ , Cu 2þ , Zn 2þ , Cd 2þ , and Pb 2þ ) were tested, respectively, to be extracted from solid matrix into sc-CO 2 . The best extraction efficiency for Co 2þ (83.68%) was obtained in the optimized condition (DMBP and perfluoro-1octanesulfonic acid tetraethylammonium salt as a co-ligand used, 25 MPa, 323 K, 20 min, ligand to metal ratio of 200). Extraction from mixed metal ions with DMBP was also achieved and the results showed that selectivity for Co 2þ ion was notable (98.17%) in the above-mentioned conditions. Finally, the detailed calculation results exhibited that the extraction constants (K ex ) of the metal ions increased with the increase of the extraction efficiency in the same extraction system.
Analytical Letters, 2011
A preconcentration procedure using solid phase extraction of heavy metals in pulp wastewater is reported. The procedure was optimized by using model solutions of selected heavy metals to investigate the effect of matrix constituents. Equilibrium studies highlighted the bonding and adsorption characteristics. The metal recoveries after spiking pulp waste filtrate with Cu, Ni, and Pb each at 0.1 and 0.2 ppm was 120, 91, and 93%, respectively. The Freundlich adsorption isotherms with correlation coefficients (R 2) 0.612, 0.810, and 0.750, showed a better fit compared to Langmuir isotherm values of 0.277, 0.389, and 0.272 for Cu, Mn, and Fe, respectively.
Lignin and outer cell wall removal from aspen pulp fibres by using supercritical CO2 extraction
Abstract: Supercritical carbon dioxide extraction (scCO2) is chosen to a treatment to remove lignin and to peel off outer cell wall layers to expose S2 layer of aspen wood fibres. The aim is to find an effective and environmentally friendly method to advance the fibrillation of the BCTMP pulp. The effects of the treatment are analysed by using scanning electron microscopy (SEM). The chemicals used together with scCO2 extraction include 1:1 ethanol: water co-solvent, isopropyl alcohol, and dimethyl sulfoxide (DMSO) with urea. The results show that supercritical CO2 extraction helps to peel the fibres of mechanical pulp. Best results are gained with 1:1 ethanol: water co-solvent. Key words: Cellulose; Lignin; Super-critical CO2; Aspen; BCTMP, Microfibrils,
Extraction of Heavy Metals from Fly Ash and Sand with Ligands and Supercritical Carbon Dioxide
Industrial & Engineering Chemistry Research, 2000
This project further develops supercritical fluid extraction as an industrial remediation process for soil and other heavy-metal-contaminated solid materials. In this study, divalent metals such as Zn 2+ , Cu 2+ , Pb 2+ , Cd 2+ , and Cr 3+ are removed from sand and fly ash using CO 2. When the solvating power of supercritical CO 2 is combined with the metal ion complexing power and selectivity of organic ligands, a clean alternative to conventional liquid-liquid and liquid-solid extraction is obtained. Extraction technologies are required, which not only remove the mobile or total fraction of metals but also maintain the matrix's morphology and structure. In particular, the reuse of fly ash as construction or landfill material becomes possible with the application of supercritical fluid technology. In a study with spiked sand samples, the effect of pressure, the humidity of the contaminated material, and the use of methanol as the entrainer in CO 2 on the extraction efficiency is investigated. Influences of the type of complexing ligands is studied with both fly ash and sand samples. It is shown that the use of methanol as the entrainer and the humidity have strong effects on the metal extraction.
Bioresources
Desorption of metal ions from oxygen-bleached hardwood and softwood kraft pulps by different chelation treatments were studied. The main focus was on desorption of manganese, iron, and magnesium ions, but also on desorption of some other common metal ions. The metal ion concentrations were determined by the DCP-AES and ICP-MS techniques. Acid treatments with nitric and oxalic acids removed manganese and magnesium very effectively and partially iron as well. Some potential complexing agents such as triethanolamine (TEA), citric acid, oxalic acid, and formic acid were also tested. By using the concept of side reaction coefficients, a comparison of the chelating strengths between different chelating agents can be made. TEA is a strong chelant for iron and did remove part of iron at pH 10. The effect of chemical reduction simultaneously with EDTA was studied by using sodium borohydride, sodium dithionite, and sodium bisulfite as reducing agents. The reducing environment improved desorpt...
BioResources
Cellulose nanocrystals (CNC) and succinic anhydride-modified CNC from bleached soda bagasse pulp under different parameters were used to remove Cd+2 and Pb+2 heavy metal ions from aqueous solution. The aim was to modify the chemical structure of cellulose nanocrystal using succinic anhydride and to investigate the effect of CNC and succinic anhydride-modified CNC on the adsorption capacity of heavy metal ions. The adsorption parameters included pH (3, 5, 6, and 8), contact time (30, 60, and 90 min), and initial metal ion concentration (40, 120, 200, and 280 ppm). It was found at all pHs that the adsorption capacity of the succinic anhydride-modified CNC adsorbent was much higher than that of the default CNC adsorbent, and this difference was greater at higher pHs. The results showed that the maximum metal ion adsorption was obtained at pH 6 for Pb+2 and Cd+2 ions. Both types of CNC had a higher adsorption capacity for lead ions than cadmium ions. To investigate the kinetic models of...
Nordic Pulp and Paper Research Journal, 2007
Metal ions have generally negative effects in closed cycle pulp mill operations and totally chlorine free bleaching. To study the binding of different metal ions to oxygen bleached hardwood pulp in more detail an ion exchange model was applied. By using a column chromatographic method even rather small differences in metal ion affinities could be detected. A method of competition was used in the experiments with an excess of respective metal ions in comparison to the total binding capacity of the pulp samples. The following series with decreasing affinities to the pulp studied was obtained:
Extraction of magnesium and copper using a surfactant and water in supercritical carbon dioxide
The Journal of Supercritical Fluids, 2008
Magnesium and copper were extracted in supercritical carbon dioxide with the addition of a surfactant, ammonium carboxylate perfluoropolyether, and water. For Mg 2+ the percent extracted reached a maximum of 65% at a temperature of 393 K, a pressure of 220 bar and a mole ratio of water to surfactant, w 0 of 185. For Cu 2+ the maximum percent extracted was 73% at a temperature of 333 K, a pressure of 250 bar and a w 0 of 333. The influence of parameters including molar ratio of surfactant to metal and molar ratio of water to surfactant was examined for Mg 2+ extraction at a temperature of 333 K and pressure of 150 bar. The percent Mg 2+ extracted increased from approximately 19-31% as the mole ratio of surfactant to Mg 2+ increased from 0.4 to 4. The percent extracted does not change appreciably with further increases in surfactant/metal ratio. The percent Mg 2+ extracted increased from 5% up to 31% as the molar ratio of water to surfactant increased from 0 to 5.6. Further increases of molar ratio of water to surfactant showed no significant increase in metal extracted. The system was operated as a closed-system until equilibrium was achieved.
Interaction of manganese and copper with wood pulp fibres
2003
The metal ions of Mn and Cu interact with the lignocellulosic matrix of pulp fibres and their presence is detrimental in pulp processing. The design of suitable strategies for effective management of metals requires understanding the behaviour of these NPEs in kraft pulp suspensions. The present study is focused on the characterization of kraft pulps and provides experimental data for chemical interactions of metals with wood fibres. Kraft pulps from two different geographic locations were studied. Also, the pulps were collected from different processing stages (chemical environment). Metal profile of pulps was obtained and their removal efficiency using an acid assisted chelation process was studied. Fibre properties like Fibre Saturation Point (FSP) and fibre charge essential for understanding metal partitioning behavior were determined. Metal partitioning between fibre and bulk solution (pH ) was carried out by introducing various concentrations of Mn and Cu and the effect of pH ...