PRECIPITATION CONDITIONS OF CHEVREUL'S SALT FROM SYNTHETIC AQUEOUS CuSO4 SOLUTIONS

In this study, synthetic aqueous CuSO₄ solution was prepared at various concentrations. Chevreul's salt was precipitated by passing SO₂ through these solutions. Chevreul's salt, a mixed valence copper sulfite, Cu₂SO₃·CuSO₃·2H₂O, was characterized by XRD and SEM. The effects of parameters such as initial solution concentration, SO₂ feeding rate, reaction time, and initial solution pH on precipitation of Chevreul's salt were investigated. 2ⁿ factorial experimental design and orthogonal central composite design methods in the precipitation experiments were used. It was observed that the effective parameters on the precipitation of Chevreul's salt were initial solution concentration, SO₂ feeding rate, and initial solution pH. The optimum conditions obtained for maximum copper precipitation were: initial solution concentration 1.14 M, SO₂ feeding rate 329.35 L.h.^?1, reaction time 25 min, and initial solution pH 8.5. Constant parameters chosen at the initial stage of the reaction were: temperature 62°C, stirring speed 600 rpm, and reaction pH 3 (Çalban et al., 2006). Under these optimum conditions, the percentage of precipitated copper from synthetic aqueous CuSO₄ solutions was 99.95.     

Determination of the efficiency and removal mechanism of cobalt by crab shell particles

The effects of contact time, solution pH and ionic strength on interactions between cobalt (⁵⁹Co) ions in synthetic liquid waste and particles of raw crab shell, Portunus trituberculatus, in batch reactions were studied. Approximately 19.5 mg dm^?3 Co was removed within 6 h after contact with 1.0 g dm^?3 crab shell at an initial concentration of 20 mg dm^?3 Co. Due to the dissolution of calcium carbonate in the crab shell, the solution pH changed spontaneously to 10, leading to precipitation of cobalt ions. The efficiency of cobalt removal depended on solution pH, but was less pH sensitive than for controls without crab shell. The maximum uptake of Co at an initial pH value of 5.0 was 510 mg g^?1 crab shell. The removal efficiency was affected slightly by ionic strength up to 2.0 mol dm^?3 of NaCl. Scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) indicated that the removal mechanism of Co by crab shell resulted primarily from the dissolution of calcium carbonate followed by precipitation of cobalt on the surface of the shell. Compared with commonly used ion‐exchange resins such as natural zeolite, Durasil 70, and Durasil 230, the efficiency of Co removal by a column of mixture of crab shell and activated carbon was at least three‐fold greater, indicating that crab shell is a suitable biosorbent for the removal of cobalt from liquid waste. Copyright © 2004 Society of Chemical Industry     

Kinetics of Uranium Adsorption from Seawater with Imidedioxime Adsorbent

Abstract

Complexation between glutar-imidedioxime and uranyl ion in artificial seawater containing 600 ppm uranium at pH 10.3 was investigated by a spectroscopic method. The complexation rate and the complex concentration at equilibrium increased with decreasing concentration of total carbonate ions. In the range of the total carbonate concentration of 4 x 10^?3 to 5 x 10^?2 mol·L^?1, the complexation proceeded by ligand exchange between a carbonate ion and a deprotonated imidedioxime. At lower total carbonate concentrations, the elimination of more than two carbonate ions from one uranyl ion was suggested.     

EXTRACTION OF ALUMINUM FROM A PICKLING BATH WITH SUPPORTED LIQUID MEMBRANE EXTRACTION

ABSTRACT

Large amounts of waste are produced yearly in the galvanic and chemical surface treatment industry. Bath liquids used in the various processes lose their function due to contamination. The spent bath liquids have to be replaced and treated prior to disposal, leading to high costs and a high environmental burden. In this paper, a proposed solution to the problem is investigated: the selective removal of the contaminant with supported liquid membrane extraction. The extraction of aluminum, a contaminant at high concentrations, from a pickling bath liquid with hydrofluoric acid and phosphoric acid as its main components has been carried out with the basic extractants Alamine 308 and Alamine 336 in a flat sheet-supported liquid membrane setup. Aluminum transport rates were obtained in the order of 10^?6?10^?5mol/(M²·s), which are normal values for this technique. The extraction was not completely selective as dissolved phosphorus was coextracted. In all experiments, precipitation took place on the surface of the liquid membrane and in the bulk of the strip phase. Increasing the stripping alkalinity from pH = 8 to pH = 13 reduced the amount of precipitation in the bulk of the strip phase but caused a substantial decrease in the aluminum flux. The precipitation prevents industrial application of the systems investigated.     

Enantiomeric Separation of Tryptophan by Ultrafiltration Using the BSA Solution System

Abstract

The optical resolution of racemic tryptophan was performed by ultrafiltration using the BSA solution system. The pH of the feed solution had a strong influence on the complexation constants between BSA and tryptophan, especially for L-tryptophan. The complexation constant for L-tryptophan reached a maximum value at pH 9 (K _L = 110,000), varying by 2 orders of magnitude in the range from pH 6 (K _L = 1000) to pH 11 (K _L = 21,000). Smaller variations of the complexation constant of D-tryptophan were observed. Based on these data, the recovery and the purity of the permeate were optimized by a proper control of the physicochemical parameters of the feed solution (essentially pH and initial concentrations). In one stage, 91% purity with a 89% recovery of D-tryptophan has been easily obtained with a high permeation rate (6.3 × 10^?4 mol·m^?2s^?1 at 1.5 bar).     

Studies on two‐dimensional coordination polymer cadmium phosphate and its high efficient adsorption of Pb(II) ions from aqueous solutions

The two‐dimensional coordination polymer cadmium phosphate with the morphology of rectangle layers was prepared by solid‐state template reaction at room temperature, and was characterized by XRD, FTIR, and TEM techniques. The as‐synthesized sample is a layered cadmium phosphate material, in which the structure is poly (CdPO₄^?) anion framework with ammonium ions and water species residing in the space between the layers, and cadmium ions are coordinated by the phosphate oxygen atoms. This article also presents the adsorption of Pb(II) ions from aqueous solution on the as‐synthesized coordination polymer cadmium phosphate, and the results showed that this inorganic polymer adsorbent had good adsorption capacity. It could reach to the saturation adsorption capacity within an hour, and its excellent adsorption capacity for Pb(II) was 5.50 mmol/g when the initial solution concentration was 1.68 × 10³ μg/mL at T = 278K. Moreover, the adsorption kinetics and adsorption isotherms were studied, it revealed that the adsorption kinetics can be modeled by pseudo second‐order rate equation wonderfully. The apparent activation energy (E_a), ΔG, ΔH, and ΔS were 3.16 kJ mol^?1, ?13.97 kJ mol^?1, ?11.84 kJ mol^?1, and 7.66 J mol^?1 K^?1, respectively. And it was found that Langmuir equation could well interpret the adsorption of the as‐synthesized coordination polymer cadmium phosphate for Pb(II) ions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Development of a Precipitation Based Separation Scheme for Selective Removal and Recovery of Heavy Metals from Cadmium Rich Electroplating Industry Effluents

Abstract

The treatment of electroplating wastes is a serious worldwide problem, because of their high content of many different heavy metals. Chemical precipitation based treatment methods could be an important alternative for fractional selective separation of heavy metals if they are systematically developed by sequencing of pH, adjusting the added portions of precipitating agents, and selecting the optimum time period before removing the precipitate from the solution. In this study, for selective removal and recovery of Cd from real electroplating bath wastewater (containing high amounts of Cd, medium amounts of Zn, Cu, Fe and small amounts of Ni, Co, Mn), a precipitation based separation scheme was developed. The scheme comprised of three consecutive steps: 1) Acid treatment with nitric acid (HNO₃). Cyano‐metal complexes were decomposed in acidification step and complete removal of iron was achieved. 2) Alkali precipitation by sodium hydroxide (NaOH). Large portion of Cd was recovered as pure Cd(OH)₂. 3) As a polishing step sulfide precipitation by sodium sulfide (Na₂S) was applied. pH was the critical parameter in sulfide precipitation. Addition of sodium sulfide in alkali pH range led to cadmium precipitation whereas copper was totally precipitated in acidic pH range. The sulfide precipitation step may be replaced by more environmentally friendly steps (e.g. polymer enhanced ultrafiltration) until the heavy metal concentrations were reduced down to suitable discharge limits.     

Dynamics and Thermodynamics Studies on the Lead and Cadmium Removal from Aqueous Solutions by Padina sp. Algae: Studies in Single and Binary Metal Systems

Raw and modified biomasses prepared from Padina sp. algae have been used as sorbent for the removal of lead and cadmium from single and binary aqueous solutions. The effects of chemical pretreatment, exposure time, initial solution pH, initial metal concentration, and temperature on the metal uptake by the algae were investigated. It was observed that initial solution pH considerably influenced Pb and Cd uptake. The maximum removal occurred at initial pH of 5.0 for lead and 6.0 for cadmium. Also, alkali modified biomass has been shown to have a high uptake capacity for both lead and cadmium. The kinetic and equilibrium experimental data fitting tested with various models. The pseudo-first-order kinetic model and Langmuir isotherm provided the best correlation of the kinetic and equilibrium experimental data, respectively. The maximum uptake estimated from the Langmuir isotherm was 264 mg g^?1 for lead and 164 mg g^?1 for cadmium ions. Experimental biosorption data in binary system were well described by the extended Langmuir model. Various thermodynamic parameters, such as ΔG°, ΔH°, and ΔS° were calculated.     

Separation of Copper and Nickel from Ammoniacal/Ammonium Carbonate Solutions Using ACORGA PT5050

ABSTRACT

ACORGA PT5050 diluted with iberfluid (kerosene-type diluent, mostly aliphatic) was used to coextract copper and nickel from ammoniacal carbonate solutions. The influence of kinetics, temperature, equilibrium pH, and extractant concentration on the extraction of both metals has been studied. It was observed that nickel extraction is very sensitive to aqueous pH and that the extraction falls beyond an equilibrium pH of 9. For a typical solution containing near 3 g/L each of copper and nickel and 60 g/L ammonium carbonate, conditions were established for the coextraction and selective stripping of nickel and copper.     

Polymerization of pyrrole by isopolymetallates of vanadium/molybdenum and preparation of a polypyrrole–molybdenum blues nanocomposite

Oxidative polymerization of pyrrole (PY) was achieved in high yield (>90 %) by adding the monomer directly to isopolyvanadate (IPV) and isopolymolybdate (IPMo) solutions at selected pH. In the case of the IPV solution instantaneous precipitation of a black mass was obtained while in the IPMo solution in situ precipitation of polypyrrole (PPY) onto molybdenum blues (MB) formed through reduction of IPMo by PY resulting in a PPY‐encapsulated MB nanocomposite (PPY–MB). Formation of PPY was confirmed from Fourier‐transform infrared (FTIR) and thermogravimetric (TG) analyses. Transmission electron microscope (TEM) photographs for the composite revealed the formation of spherical particles of average size ≈75 nm. Scanning electron microscope (SEM) analyses showed the distinctive morphological patterns for PPY and PPY–MB composite. The direct current conductivity values for PPY prepared by IPV, IPMo and PPY–MB were of the order of 10^?2, 10^?4 and 10^?6 S cm^?1, respectively. Copyright © 2004 Society of Chemical Industry     

Extraction and Adsorption Behavior of Co(II) on HTTA-Impregnated Polyurethane Foam

Abstract

The batch extraction of Co(II) from aqueous solutions with open cell polyethertype HTTA-loaded polyurethane (PU) foam has been studied using a radiotracer technique. The effect of pH, shaking time, and loading capacity has been investigated. The membrane properties of loaded PU foam sorbent offer unique advantage of adsorption. The fundamental studies of adsorption show that the classical Freundlich and Langmuir isotherms are followed in the entire concentration range of a 10^?5 to 10^?2 M solution of cobalt. The sorption mean free energy from the Dubinin-Radushkevich isotherm is found to be 13.8 kJ·mol^?1 and the loading capacity 4.44 mg·g^?1, suggesting that the ion-exchange or chemisorption mechanism operates. The kinetic parameters of adsorption also support a chemisorption mechanism and the first-order rate law. The rate constants and activation energies of sorption and desorption have been evaluated. The thermodynamic function of adsorption of ΔH, ΔS, ΔG, and equilibrium constant K _c have been calculated. The process of adsorption is established to be endothermic and chemisorption, stabilized through thermodynamic functions.     

Effect of pH on microbial hydrogen fermentation

The influence of initial pH of the culture medium on hydrogen production was studied using sucrose solution and a mixed microbial flora from a soybean‐meal silo. Hydrogen production was not observed at pH values of 3.0, 11.0 and 12.0 but low production was observed at pH values 5.0 and 5.5. The pH of the experimental mixture decreased rapidly and produced hydrogen gas within 30 h. Methane was not detected at initial pH values between 6.0 and 10.0. The sucrose degradation efficiency increased as the initial pH value increased from 3.0 to 9.0. The maximum sucrose degradation efficiency of 95% was observed at pH 9.0. The maximum specific production yields of hydrogen, VFAs and alcohols were 126.9 cm³ g^?1 sucrose (pH of 9.0), 0.7 gCOD g^?1 sucrose (pH of 8.0) and 128.7 mgCOD g^?1 sucrose (pH of 9.0), respectively. The relationship between the hydrogen ion concentration and the specific hydrogen production rate has been mathematically described. The best kinetic parameters on the specific hydrogen production rate were K_OH = 1.0 × 10^?7 mol dm^?3 and K_H = 1.1 × 10^?4 mol dm^?3 (r² = 0.86). The maximum specific hydrogen production rate was 37.0 cm³ g^?1 VSS h^?1. © 2002 Society of Chemical Industry     

Removal of phosphate by adsorption onto oyster shell powder—kinetic studies

Kinetic studies on the removal of phosphate by adsorption onto oyster shell powder have been investigated at 24 °C. The results showed that the equilibrium occurred in 10 min and the equilibrium data followed the Freundlich isotherm. Freundlich constants were found to be k_f, 1.4 × 10^?2, and n, 0.71. The phosphate removal was not influenced by pH over the range 5.0–10.5. Continuous agitation studies at 24 °C and 530 rpm reached equilibrium after 7.7 days, when 24 g dm^?3 of oyster shell powder reduced the phosphate concentration from 50 to 7.0 mg dm^?3. The Lagergren rate constant for the slow adsorption process was observed to be 3.81 × 10^?4 dm³ min^?1. Comparison with calcium carbonate, GR grade, showed that oyster shell powder and CaCO₃ behave more or less in the same way. Copyright © 2004 Society of Chemical Industry     

Variations in the Composition of Bromine Water During Oxidation Reactions

A cubic equation has been derived that permits calculation of the composition of aqueous bromine solutions in terms of HOBr, BrO^?, Br₂, Br^?₃ and Br^? as a continuous function of the pH, the initial oxidant concentration and the mole fraction of oxidant consumed. The calculations were performed by computer for the pH range 0–14 at bromine concentrations (c₀) of 10^?1 to 10^?7 M. Throughout the course of an oxidation at pH 0 and c₀= 10^?4, bromine water is pure Br₂. No Br^?₃ exists at c₀ < 10^?3. In the pH range 4–6, dilute bromine solutions are pure HOBr (+ equimolar Br^?). For pH > 10, bromine water is pure BrO^?, while at pH < 7, no BrO^? is present. These conditions are unchanged during oxidant consumption.     

Biosorptive uranium uptake by a Pseudomonas strain: characterization and equilibrium studies

The biosorptive uranium(VI) uptake capacity of live and lyophilized Pseudomonas cells was characterized in terms of equilibrium metal loading, effect of solution pH and possible interference by selected co‐ions. Uranium binding by the test biomass was rapid, achieving >90% sorption efficiency within 10 min of contact and the equilibrium was attained after 1 h. pH‐dependent uranium sorption was observed for both biomass types with the maximum being at pH 5.0. Metal uptake by live cells was not affected by culture age and the presence of an energy source or metabolic inhibitor. Sorption isotherm studies at a solution pH of either 3.5 or 5.0 indicated efficient and exceptionally high uranium loading by the test biomass, particularly at the higher pH level. At equilibrium, the lyophilized Pseudomonas exhibited a metal loading of 541 ± 34.21 mg g^?1 compared with a lower value by the live organisms (410 ± 25.93 mg g^?1). Experimental sorption data showing conformity to both Freundlich and Langmuir isotherm models indicate monolayered uranium binding by the test biomass. In bimetallic combinations a significant interference in uranium loading was offered by cations such as thorium(IV), iron(II and III), aluminium(III) and copper(II), while the anions tested, except carbonate, were ineffective. Uranium sorption studies in the presence of a range of Fe³⁺ and SO₄^2? concentrations indicate a strong inhibition (80%) by the former at an equimolar ratio while more than 70% adsorption efficiency was retained even at a high sulfate level (30 000 mg dm^?3). Overall data indicate the suitability of the Pseudomonas sp biomass in developing a biosorbent for uranium removal from aqueous waste streams. © 2001 Society of Chemical Industry     

Mixing and Crystallization Kinetics in Gas‐liquid Reactive Crystallization

A study of gas‐liquid reactive crystallization for CO₂‐BaCl₂‐H₂O system was performed in a continuous flow crystallizer. The influences of mixing on the crystallization kinetics of barium carbonate crystals were investigated. The mixing parameters are stirrer speed, feed concentration, gas‐flow rate, pH of solution, addition rate of NaOH solution, and mean residence time. Under pH‐stat operation, the crystallization mechanism can be assessed by the addition rate of NaOH solution, which acts as an indicator for the absorption rate of carbon dioxide. Assuming a size‐independent agglomeration mechanism, the nucleation rate, growth rate and agglomeration kernel can be obtained, simultaneously, at steady state, by the method of moments. Evidence shows that feed concentration, feed rate, gas‐flow rate, and stirrer speed have a significant influence on the nucleation rates and mean particle sizes. This shows the effect of micromixing. The crystallization mechanism tends to be reaction limited when the feed concentration of barium chloride solution is higher than 5 mM, while at lower stirrer speeds and feed concentrations, the mechanism tends to be both mixing and reaction controlled. The growth rate depends on the mean supersaturation value and the pH of the solution and the mass‐transfer resistance cannot be completely eliminated in this work. For a monodispersal collision model, in the viscous sub‐range of turbulence, the agglomeration kernel can be expressed as β ∝ d^{3 –1/4}, showing a low efficiency of collision. The result is also demonstrated by the agglomeration kernel expression. Comparison with a liquid‐liquid‐mixing reactive crystallization system is also discussed.     

Ethylene carbonate—propylene carbonate mixed electrolytes for lithium batteries

Electrolytic characteristics of propylene carbonate (PC)ethylene carbonate (EC) mixed electrolytes were studied, compared with those in PC electrolytes. Conductivity and Li charge—discharge efficiency values increased with EC contents increasing. For example, 1 M LiClO₄ECPC (EC mixing molar ratio; [EC]/[PC] = 4) showed the conductivity of 8.5 ohm^?1 cm^?1, which value was 40% higher than that in PC. Also, 1 M LiClO₄ECPC([EC]/[PC] = 5) showed the Li charge—discharge efficiency of 90.5% at 0.5 mA cm^?2, 0.6 C cm^?2, which value was ca. 25% higher than that in PC. ECPC mixed electrolytes were considered to be practically available for ambient lithium batteries in regard to the high Li⁺ ion conductivity and also high Li charge—discharge efficiency.     

Impact of pH on Binding Metal Ions by Datura innoxia Biomass

Abstract

Metal ion binding to biomaterials derived from cultured antheral cells of Datura innoxia has been investigated as a function of solution pH. Specifically, the binding of Ba²⁺, Cd²⁺, Cu²⁺, Ni²⁺, and Sr²⁺ was studied at pH 1–6, inclusive, in 0.1 M MES solutions. For 10 mg·L^?1 metal ion solutions, maximum binding was observed for solutions at pH 5. The dependence of metal ion binding on solution pH was studied for the biomass both free in solution and immobilized in a polysilicate matrix. A significant change in the pH-dependent binding of each of these metals was observed when the cell material was immobilized. These variations in the impact of metal solution pH could not be explained by the Lewis acidity of the metal ions. The involvement of conformational changes of the macromolecular components of the material for the formation of metal-selective coordination sites is postulated.     

Adsorption of diclofenac sodium from aqueous solution using polyaniline as a potential sorbent. I. Kinetic studies

This study describes dynamic uptake of antibiotic drug diclofenac sodium from aqueous solution using polyaniline as sorbent. The sorbent polyaniline was prepared by oxidative polymerization of aniline and characterized by FTIR spectrum analysis and TGA. The optimum sorbent/sorbate mg/mL ratio and pH range for maximum drug uptake have been found to be 2.0 and 5.5 to 10.5, respectively. Out of various kinetic models applied, the pseudo second‐order kinetic equation has been found to fit well on the kinetic uptake data. The pseudo second‐order rate constants for adsorption have been found to be 0.982 × 10^?2, 7.24 × 10^?2, and 18.09 × 10^?2 min^?1 mg^?1 g for drug solutions with initial concentrations of 10, 20, and 30 mg L^?1, respectively. The overall sorption process has been found to be governed by intraparticle diffusion.The sorptive removal of drug from aqueous solution has also resulted in enhancement in bacterial growth of Escherichia coli. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010