Thermal decomposition of potassium persulfate in aqueous solution at 50°C in an inert atmosphere of nitrogen in the presence of acrylonitrile monomer

The rate of thermal decomposition of persulfate in aqueous solution in the presence of acrylonitrile (AN) monomer (M) and of nitrogen, may be written as: in the concentration range of persulfate (1.8 to 18.0) ×10^-3, and of monomer (M), 0.30 to 1.20, mol dm^-3. It was observed that the pH of the solution containing persulfate and monomer did not alter during polymerization if the monomer concentrations were close to its solubility under the experimental conditions. Conductance of the aqueous solutions of persulfate and monomer was found to decrease during the reactions. In an unbuffered aqueous solution containing only persulfate, however, the pH was found to decrease continuously at 50°C with time, while the conductance of the solution was found to increase. The monomer (AN) had no effect on the glass electrodes of the pH meter in aqueous solutions, and also on the electrodes of the conductivity cell. It has been suggested that the secondary or induced decompositions of persulfate were due to the following elementary reactions: where (M_j^· radicals (j = 1 to 10) are water-soluble oligomeric or polymeric free radicals. k_x and k_y at 50°C have been estimated as 1.70 X 10^-5 and 5.08 × 10³ dm³ mol^-1 s^-1, respectively. By measuring pH of freshly prepared persulfate solutions at 25°C, it is suggested that 0.05–0.30% of persulfate reacts molecularly with water (i.e., hydrolysis), as soon as it (10^-3 to 10^-2 mol dm^-3) is added to distilled water (pH 7.0). This hydrolysis was found to be stopped in dilute sulfuric acid solution (pH 3–4).     

Kinetics and mechanism of the thermal decomposition of potassium persulphate ions in aqueous solutions at 50°C in the presence of nitrogen gas and methacrylonitrile monomer

The initial rate of persulphate (I) decomposition at 50°C in the presence of nitrogen and methacrylonitrile (MAN) in an unbuffered aqueous solution (pH 4–7) may be written as: in the concentration ranges of persulphate (I) (0.25–2.50) × 10^?2 (m/dm³) and of (MAN) 0.18–0.36 (m/dm³). During the reaction, a white substance (polymethacrylonitrile) separates out in the colloidal state or in the precipitate form from the medium depending on the ionic strength of the medium. The pH of the medium was found to decrease rapidly and continuously with time in the absence of methacrylonitrile, but it decreased slowly and continuously with time in the presence of the monomer, MAN. If an additional quantity of MAN is injected late in a run, the rate of persulphate decomposition is further accelerated in a given run. However, the rate of persulphate decomposition is found to decrease continuously in the presence of MAN with time, i.e., as the monomer is converted to polymer. It is suggested that MAN accelerates the decomposition of persulphate ions, due to the following reactions in the aqueous phase: and where (M_j^˙)w is a-water soluble oligomeric or polymeric (j = 1–10) free radical. The estimated values of k₅ and k₁₀ are 1.05 × 10^?5 and 1.14 × 10³ (in dm³/m/s), respectively.     

Thermal decomposition of potassium persulfate in aqueous solution at 50°C in the presence of ethyl acrylate

Potassium persulfate modes of thermal decomposition and reactions with ethyl acrylate in aqueous solution at 50°C in nitrogen atmosphere have been investigated. It has been found that the rate of persulfate decomposition may be expressed as ?d(S₂O)/dt ∝ (S₂O)^{1.00 ± 0.06} × (M)^0.92±0.05 while the steady state rate of polymerization (R_p) is given by R_p ∝ (S₂O)^{0.50 ± 0.50} × (M)^{1.00 ± 0.06} in the concentration ranges of the persulfate, 10^?3?10^?2 (m/L), and monomer (M), 4.62?23.10 × 10^?2 (m/L), i.e., within its solubility range. In the absence of monomer, the rate of persulfate decomposition was slow and first order in persulfate at the early stages of the reaction when the pH of the solution was above 3.0. The separating polymer phase was a stable colloid at low electrolyte concentrations even in the absence of micelle generators. It has been shown that the oxidation of water soluble monomeric and oligomeric radicals by the S₂O ions in the aqueous phase, viz., \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm M}_j^ \cdot + {\rm S}_2 {\rm O}_8^{2 - } \to {\rm M}_j - {\rm O} - {\rm SO}_3^ - + {\rm SO}_4^{ \cdot - } $\end{document} is not kinetically significant in this system. It has been found that the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm M} + {\rm S}_2 {\rm O}_8^{2 - } \rightarrow{k}{\rm M} - {\rm O} - {\rm SO}_3^ - + {\rm SO}_4^{ \cdot - } $\end{document} would also lead to chain initiation at the outset of the polymerization reaction. k has been estimated as 5.41 × 10^?5 (L/m/s) at 50°C. Taking k_p as 10³ (L/m/s), k_t has been estimated as 0.168 × 10⁶ (L/m/s). The partition confficient (β) of the monomer between the polymer phase and the aqueous phase was found to be 16 ± 2, at 50°C. The rate constant for persulfate ion dissociation has been found as 1.40 × 10^?6 s^?1 at 50°C.     

Reactive extraction of succinic acid using supercritical carbon dioxide

Reactive extraction using supercritical carbon dioxide (scCO₂) and tri-n-octylamine (TOA) was evaluated as a separation method of succinic acid from an aqueous solution. The reactive extraction of succinic acid was performed at varying initial acid concentrations in aqueous solution (0.07–0.45 mol?dm^?3), temperature (35–65°C) and pressure (8–16 MPa). The succinic acid separation was conducted in both batch mode and semi-continuous mode. The highest reactive extraction efficiency of approx. 62% was obtained for the process conducted in semi-continuous mode at 35°C and 16 MPa for the initial acid concentrations in aqueous phase of 0.39 mol?dm^?3.     

One pot synthesis of xanthan gum‐g‐N‐vinyl‐2‐pyrrolidone and study of their metal ion sorption behavior and water swelling property

In this article, graft copolymerization of N‐vinyl‐2‐pyrrolidone onto xanthan gum initiated by potassium peroxydiphosphate/Ag⁺ system in an aqueous medium has been studied under oxygen free nitrogen atmosphere. Grafting ratio, grafting efficiency, and add on increase on increasing the concentration of potassium peroxydiphosphate (2.0 × 10^?3 to 12 × 10^?3 mol dm^?3), Ag⁺(0.4 × 10^?3 to 2.8 × 10^?3 mol dm^?3), and hydrogen ion concentration from 2 × 10^?3 to 14.0 × 10^?3 mol dm^?3. Maximum grafting has been obtained when xanthan gum and monomer concentration were 0.4 g dm^?3 and 16 × 10^?2 mol dm^?3, respectively, at 35°C and 120 min. Water swelling capacity, swelling ratio, metal ion uptake, and metal retention capacity have also been studied, and it has been found that graft copolymer shows enhancement in these properties than pure xanthan gum. The graft copolymer has been characterized by FTIR and thermal analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Free radical polymerization kinetics of monomers functionalized with ?AsO(OH)2 in aqueous media

The free radical polymerization kinetics of the isomer sodium salts of o‐ and p‐methacryloylaminophenylarsonate in aqueous solution have been studied using a dilatometric method. The polymerizations, initiated with potassium persulfate, were carried out at a constant monomer initial concentration of 0.50 mol/L and the initiator initial concentration was fixed at one of the following: 1.00, 2.00, 5.00, 8.00, or 10.00 (× 10^?3 mol/L). Another set of polymerizations were carried out at a constant initiator initial concentration of 2 × 10^?3 mol/L and the monomer initial concentration was fixed at one of the following: 0.20, 0.30, 0.50, 0.70, or 1.00 (mol/L). The polymerization reactions were conducted isothermally at 70°C. The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to monomer was greater that unity. The effects of temperature on the polymerization rate were also investigated and the activation energy gave values of 20.66, 22.68, and 23.22 kcal mol^?1 K^?1 over a temperature range of 50–70°C. For the case of o‐methacryloylaminophenylarsonic acid monomer, its kinetic study was carried out in DMF as solvent and AIBN initiator. p‐Methacryloylaminophenylarsonic acid was too insoluble in DMF to be studied. The polymers obtained were characterized by H‐NMR, IR, and viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1662–1669, 2004     

Sodium metabisulphite initiated aqueous polymerisation of methyl methacrylate

Sodium metabisulphite (Na₂S₂O₅) has been found to initiate the aqueous polymerisation of methyl methacrylate (MMA) at 35°C in phosphate buffer solutions of pH 6.85 and a constant ionic strength (μ) of the media in an inert atmosphere of pure nitrogen. The reaction has a well defined induction period which is a function of the concentrations of the initiator, of the monomer and also of temperature. The polymerisation is signalled by the sudden appearance of a haze at the end of the induction period in a given run, and the polymer separates out as a coarse precipitate during the progress of the polymerisation reactions. When the conversion is over 50 per cent complete, the polymerisation media looks like a thick curd if the monomer concentration is relatively high. The rate of polymerisation is found to decrease with conversion or time in a given run, and the initial rate (v_p), obtained by extrapolating the linear yield/time versus time curves to zero time, keeping the conversion below 10 percent, is found as where (I) = initiator concentration in the range, (0.26 to 3.94) × 10^?3 (mol dm^?3), and (M) = monomer concentration in the range 0.019 to 0.141 (mol dm^?3). At high initiator concentrations, the rate of polymerisation is found to decrease. In a given run, the viscosity average molecular weights (M _v) of the polymers is found to increase quickly with a conversion of up to 25 to 30 percent, and then slowly with the further increase in conversion. (M_v) however is found to decrease with the increase of the initiator concentrations at a given conversion but increases with the increase of the monomer concentrations. Hydroquinone inhibits the polymerisation reactions, whereas air is found to increase the induction period, but later enhances the polymerisation rate in the same run. It has been shown that the bisulphite addition reaction of MMA is not important under the experimental conditions, and the polymerisation occurs by the free radical mechanism. The rate constant (k₂) of the reaction, has been estimated from the analytical data as, k₂ = 14.62 × 10^?2 (dm³ mol^?1 s^?1) at 35°C.     

Kinetics of vinyl polymerization initiated by potassium permanganate/β-hydroxybutyric acid redox system

The aqueous polymerization of acrylamide initiated by potassium permanganate/β-hydroxybutyric acid has been studied volumetrically at 35 ± 0.01°C in an inert medium. The rate of polymerization shows nearly square root dependence on β-hydroxybutyric acid at low concentration (3.12 – 12.5 · 10^?3 mol dm^?3). The order with respect to potassium permanganate has been found to be 0.6 indicating thereby a bimolecular mode of termination. The polymerization rate has been varied linearly at low monomer concentrations i.e. from 2.5 –7.0 · 10^?2 mol dm^?3. The dependence of number average degree of polymerization on the initial rate of polymerization and temperature has been determined. The over-all activation energy has been found to be 51.66 kJ mol^?1. A kinetic reaction scheme is proposed on the basis of experimental results.     

Reactivity ratios and monomer partitioning in the microemulsion copolymerization of vinyl acetate and butyl acrylate

The true monomer reactivity ratios for the vinyl acetate/butyl acrylate system were determined with experimental data from the cumulative copolymer composition at low, intermediate, and high conversions and with the monomer partitioning among the aqueous, microemulsion droplet, and polymer particle phases taken into account. A mixture of sodium dodecyl sulfate and poly(ethylene oxide) (23) dodecyl ether (Brij‐35; 3 : 1 w/w) was used as a stabilizer. Potassium persulfate was used as an initiator. The true values of the monomer reactivity ratios were 0.028 ± 3.2 × 10^?3 for vinyl acetate and 6.219 ± 3.1 × 10^?1 for butyl acrylate, and these were in agreement with those reported in the literature for bulk copolymerizations but differed from values reported for other compartmentalized copolymerizations. Thus, these results indicate that the monomer partitioning and cumulative copolymer composition throughout the reaction have to be duly accounted for in the determination of monomer reactivity ratios in heterogeneous polymerizations. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Protein hydrolysis under anaerobic,saline conditions in presence of acetic acid

The hydrolysis of soluble proteins in an anaerobic, saline (24 g dm^?3 NaCl) and mesophilic (37 °C) environment was studied. The inhibitory effect of a volatile fatty acid, acetic acid (HAc), on the hydrolysis rate and hydrolytic biomass activity for a model saline wastewater with a high protein load (total organic carbon, 1153 mg dm^?3 and 1572 mg dm^?3 proteins) was studied. Initial inhibitor concentrations were tested in the range of 0–2000 mg dm^?3 HAc. The microbiological characterization was performed using a total microorganism count by epifluorescence, and hydrolytic bacterial activity was determined by plate count. The protein hydrolysis was modeled according to first order kinetics. The effect of biomass on hydrolysis was analyzed by varying its concentration in the range of 42–210 mg dm^?3 volatile suspended solids. The following apparent hydrolysis kinetic constants (K_h) for proteins at 37 °C were obtained: 1.3, 0.8, 0.6, 0.2 and 0.1 d^?1 for initial concentrations of 250, 500, 750, 880, and 1000 mg dm^?3 HAc, respectively. At concentrations of HAc greater than 1000 mg dm^?3, total inhibition of hydrolysis was observed. The intrinsic hydrolysis constant ( ) at 37 °C, without inhibition, was 2.3 d^?1. The hydrolysis kinetic constant was not affected by the biomass concentration. The hydrolysis kinetics constant was filted to three models: Luong, Levenspiel and non‐competitive inhibition. The model that best represented the experimental data was Luong, obtaining an inhibition constant (K_I) of 1087 mg dm^?3 of HAc and the exponent γ = 0.54. The hydrolysis was inhibited by the presence of HAc, which corresponds to an intermediate compound of the anaerobic process. Copyright © 2004 Society of Chemical Industry     

Denitrification in aqueous FeEDTA solutions

The biological reduction of nitric oxide (NO) in aqueous solutions of FeEDTA is an important key reaction within the BioDeNOx process, a combined physico‐chemical and biological technique for the removal of NO_x from industrial flue gasses. To explore the reduction of nitrogen oxide analogues, this study investigated the full denitrification pathway in aqueous FeEDTA solutions, ie the reduction of NO₃^?, NO₂^?, NO via N₂O to N₂ in this unusual medium. This was done in batch experiments at 30 °C with 25 mmol dm^?3 FeEDTA solutions (pH 7.2 ± 0.2). Also Ca²⁺ (2 and 10 mmol dm^?3) and Mg²⁺ (2 mmol dm^?3) were added in excess to prevent free, uncomplexed EDTA. Nitrate reduction in aqueous solutions of Fe(III)EDTA is accompanied by the biological reduction of Fe(III) to Fe(II), for which ethanol, methanol and also acetate are suitable electron donors. Fe(II)EDTA can serve as electron donor for the biological reduction of nitrate to nitrite, with the concomitant oxidation of Fe(II)EDTA to Fe(III)EDTA. Moreover, Fe(II)EDTA can also serve as electron donor for the chemical reduction of nitrite to NO, with the concomitant formation of the nitrosyl‐complex Fe(II)EDTA–NO. The reduction of NO in Fe(II)EDTA was found to be catalysed biologically and occurred about three times faster at 55 °C than NO reduction at 30 °C. This study showed that the nitrogen and iron cycles are strongly coupled and that FeEDTA has an electron‐mediating role during the subsequent reduction of nitrate, nitrite, nitric oxide and nitrous oxide to dinitrogen gas. Copyright © 2004 Society of Chemical Industry     

Synthesis and characterization of polysaccharide based graft copolymer by using potassium peroxymonosulphate/ascorbic acid as an efficient redox initiator in inert atmosphere

Polysaccharide based graft copolymer (xanthan gum‐g‐4‐vinyl pyridine) was synthesized using potassium peroxymonosulphate/ascorbic acid redox initiator in inert atmosphere at 40°C. By studying the effect of the concentration of monomer, peroxymonosulphate (PMS), ascorbic acid (AA), xanthan gum (XOH), hydrogen ion along with effect of time and temperature on grafting characteristics: grafting ratio (%G), add on (%A), conversion (%C), efficiency (%E), homopolymer (%H), and rate of grafting (Rg), the reaction conditions for optimum grafting were determined. The optimum concentration of AA, H⁺ ion, 4‐VP for maximum grafting were found to be 10.0 × 10^?3 mol dm^?3, 2.5 × 10^?2 mol dm^?3, 10.0 × 10^?3 mol dm^?3, respectively. Maximum %G was obtained at minimum concentration of xanthan gum i.e., at 40.0 × 10^?2 g dm^?3 and at maximum concentration of PMS i.e., at 10.0 × 10^?3 mol dm^?3. The optimum temperature and time duration of reaction for maximum % of grafting were found to be 45°C and 120 min respectively. The synthesized graft copolymer was characterized by FTIR analysis. Thermogravimetric analysis showed that the xanthan gum‐g‐4‐vinyl pyridine is thermally more stable than pure gum. A probable mechanism was suggested for the graft copolymerization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

One‐pot synthesis of a polysaccharide‐based graft copolymer with an efficient redox pair (Fe2+/BrO3−)

A graft copolymer based on a polysaccharide (sodium salt of carboxymethylcellulose) and a vinyl monomer (acrylamide) has been synthesized in a nitrogen atmosphere, and its reaction conditions have been optimized for a better yield with ferrous sulfate and potassium bromate as a redox initiator. The effects of ferrous ion, bromate ion, hydrogen ion, sodium carboxymethylcellulose, and acrylamide along with the reaction time and temperature have been studied through the determination of the grafting parameters: the grafting ratio, add‐on, conversion, efficiency, homopolymer, and rate of grafting. The maximum yield has been found to occur when the acrylamide concentration is 8.0 × 10^?2 mol/dm³, whereas the maximum conversion occurs at a minimum concentration of acrylamide, that is, at 3.0 × 10^?2 mol/dm³. The grafting parameters have been found to increase with an increasing concentration of the redox initiator (Fe²⁺, from 2.0 × 10^?3 to 10.0 × 10^?3 mol/dm³; BrO, from 2.2 × 10^?3 to 4.0 × 10^?3 mol/dm³). The maximum efficiency occurs with a reaction time of 210 min. The rate of grafting has been found to be maximum up to 60 min; after that, it decreases rapidly. In this article, it is shown that the hydrogen ion leads to a very clear decrease in the grafting parameters as its concentration increases from 2.1 × 10^?3 to 11.3 × 10^?3 mol/dm³. Grafted gum and ungrafted gum have been characterized with Fourier transform infrared spectroscopy and thermogravimetric analysis. A probable mechanism has been suggested for graft copolymerization. It has been observed that the graft copolymer is thermally more stable than the parent backbone. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Equilibrium and kinetic studies on the extraction of gadolinium(III) from nitrate medium by di‐2‐ethylhexylphosphoric acid in kerosene using a single drop technique

The liquid–liquid extraction of Gd(III) from aqueous nitrate medium was studied using di‐2‐ethylhexylphosphoric acid (HDEHP) in kerosene. On the basis of the slope analysis data, the composition of the extracted species was found to be [Gd A₃(HA)] with the extraction equilibrium constant (K_ex) = (1.48 ± 0.042) × 10^?12 mol dm^?3. The results of the effect of temperature on the value of the equilibrium extraction constant indicated the endothermic character of the extraction system. The kinetics of the forward extraction of Gd³⁺ from nitrate medium by HDEHP in kerosene was investigated using the single drop column technique. The rate of flux (mass transfer per unit area) was found to be proportional to [Gd(III)], [H₂A₂]_(o), [NO₃^?], and [H⁺]^?1 in the liquid drop organic phase. The forward extraction rate constant, k_f, was 2.24 × 10^?3 m s^?1 using the equation: Copyright © 2005 Society of Chemical Industry     

Synthesis and characterization of PET fibers grafted with binary mixture of 2-methylpropenoic acid and acrylonitrile by free radical: its application in removal of cationic dye

Grafting of binary vinyl monomer mixtures such as 2-methylpropenoic acid (MPA) and acrylonitrile (AN) onto poly (ethylene terephthalate) fibers (PET) was achieved in an aqueous medium with using benzoyl peroxide like free radical initiator. A new reactively fibrous adsorbent was used for removal of dye such as methylene blue (MB) from aqueous media through batch sorption method. Fibers adsorbent was swelled in solution to support the graft and the subsequent polymerization of MPA/AN onto polyester fibers. Optimum conditions for grafting were discovered and reactive fiber were characterized. Variations of graft yield with time, temperature, initiator concentration and monomer mixture ratio were investigated. The optimum initiator concentration was found to be 8 × 10^?3 mol/L. The percentage of grafting rose steadily with the vinyl monomer mixture monomer concentration (50 %). The optimum temperature and polymerization time were found to be 80 °C and 120 min, respectively. The use of AN and MPA monomers together in grafting produce a significant increased in the graft yield. Experimental studies showed that the percentage removal of MB was a great higher on the MPA/AN grafted PET (MPA/AN-g-PET) fibers than on the original PET fibers. The adsorbed quantity of MB improved with pH and basic pH was appropriate for the elimination of MB. MPA/AN-g-PET fibers removed 98 % of cationic dye when initial concentration diverse from 10 to 80 mg L^?1 at pH 9.0. Almost all of the adsorbed cationic dye was eluted by ethanoic acid in methanol. Ten removal–desorption cycles indicated that the reactive fibers were favorable for repetitive use without notable change in removal capacity. Consequently, the MPA/AN-g-PET fibers have demonstrated potential as an effective adsorbent for the extremely effective removal of cationic dyes from aqueous media.     

Synthesis and properties of fluorinated hydrophobic association polyacrylamide as thickener for hydraulic fracturing fluid

A novel, anionic fluorinated hydrophobic association polyacrylamide (FAPAM) was successfully synthesized from acrylamide (AM), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), acrylic acid (AA), and 1H,1H,2H,2H-heptadecafluorodecyl acrylate (HFA) by radical micellar polymerization using sodium dodecyl sulfonate and potassium persulfate as a surfactant and an initiator, respectively. This synthesis was confirmed by Fourier transform infrared and nuclear magnetic resonance spectroscopy techniques. The results showed that the optimal content of the added HFA monomer was 0.3–0.5% in weight to the as-prepared FAPAM, which possessed 300–400 mg L^?1 of critical association concentration. The results also showed that the properties of FAPAM3-0.4 were best for the appropriate mass ratio of AM:AA:AMPS = 7:1:2. The apparent viscosity of FAPAM3-0.4 was 1350 mPa s in the aqueous solution, and the apparent viscosities of other samples were 161.5 and 148.3 mPa s when the Na⁺ and Ca²⁺ concentrations were 5000 and 2000 mg L^?1, respectively. Moreover, the FAPAM3-0.4 showed excellent temperature resistance and shearing resistance, in which the apparent viscosity was approximately 478.8 mPa s at 100 °C for 120 min. The viscosity could be completely restored or even it could be slightly higher than its original value when the shearing rate decreased. The results indicated that the excellent performance of FAPAM3-0.4 may make it a potential candidate as thickener for hydraulic fracturing fluid in oil and gas fields.     

Corrosion of the zinc negative electrode of zinc–cerium hybrid redox flow batteries in methanesulfonic acid

Corrosion of zinc in aqueous methanesulfonic acid has been evaluated over a wide range of concentrations of acid (0.5–5 mol dm^?3), dissolved zinc (0.5–2 mol dm^?3), and electrolyte temperature (22–50 °C). The corrosion rate of zinc, in terms of weight loss and the volume of hydrogen evolved, varied with time and it was found to be highly dependent on the surface state and electrolyte conditions. With an initial active layer of zinc present, the corrosion rate rapidly increased following a decline when the proton concentration in the solution decreased to ca. 0.56 mol dm^?3. Organic and inorganic inhibitors were added to the electrolyte to suppress the zinc corrosion in 1 mol dm^?3 methanesulfonic acid. The strong adsorption and blocking effects of cationic organic adsorption inhibitors, such as cetyltrimethyl ammonium bromide and butyltriphenyl phosphonium chloride, led to a significant decrease in zinc corrosion over a 10 h immersion period. With the addition of indium and lead ions inhibitors, the zinc surface showed less activity. Zinc corrosion continued to a smaller extent in the presence of these metallic inhibitors during the first few hours, but the metallic layer of the inhibitors did not cover the surface completely resulting in continued hydrogen evolution and making the inhibitors less effective at longer times.     

Removal of trivalent chromium(III) from solution by biosorption in cork powder

The removal of trivalent chromium from solutions using biosorption in cork powder is described. The adsorption isotherm was determined, along with the effect of different variables, such as biomass particle size, solid–liquid ratio, reaction time, metal concentration and pH, on the efficiency of chromium removal. It was concluded that the adsorption is slow and favoured by an increase in pH. Therefore, using a solid–liquid ratio of 4 g dm^?3 it is possible to reduce the chromium concentration in the solution from 10 mg dm^?3 to less than 1.5 mg dm^?3 in 2 h at 22 °C. The kinetic studies verified that the sorption of chromium by cork was described by a second‐order model. The elution results showed that 50% of the chromium bound to the cork was eluted using 0.5 mol dm^?3 H₂SO₄ and that cork maintains its binding capacity over four cycles of biosorption/elution. © 2002 Society of Chemical Industry