EXTRACTION OF CADMIUM FBOM PHOSPHORIC ACID WITH DIORGANYLDITHIOPHOSPHINIC ACIDS. Part II: Rate of Extraction and Decomposition.

Liquid-liquid extraction of cadmium ions from 55-65 w% “black” phosphoric acid from a Nissan H process with diphenyldithio-phosphinic acid (DPP) or dicyclohexyldithiophosphinic acid (DCP)dissolved in an alkane(c₁₂or c₁₆) at 90°C was investigated.The rate of extraction of Cd from chemically pure phosphoric acid (55 w% H₃Po₄,90°C) is mainly determined by film diffusion of cadmium ions in the phosphoric acid phase to the interface. In the extraction from “black” acid, mass transfer in the organic phase or chemical reaction (ligand exchange) is probably the rate limiting step. An apparent mass-transfer coefficient (based on -5 [Cd] in the phosphoric acid phase) of about 1.6?10^?5 m/s was obtained for the extraction from “black” acid.

A fast decompositon of DPP was observed and in a batch experiment the Cd concentration was already more than 50% of the initial value after 6 hours. This phenomenon is probably caused by the formation of solid complexes with Cu, Cd and Zn, which are dispersed in the phosphoric acid phase and then oxidized. The decomposition of DCP proceeded much slower and after 30 hours the Cd concentration was still below 50% of the initial value. Cu formed a solid complex with DCP, whereas t.he Cd and Zn complexes were soluble in the organic phase. A surface decomposition rate constant of the free ligand in the organic phase of 4?10^?8m/s was obtained.     

REMOVAL OF CADMIUM BY ANION EXCHANGE IN A WET PHOSPHORIC ACID PROCESS. PART 2: EQUILIBRIA,KINETICS AND REGENERATION

The removal of cadmium by anion exchange from 55 w% H₃PO₄ (black acid from a Nissan H process) at 90^°C in the presence of small amounts of halides (Cl^-, Br^-, I^-) was investigated. Cadmium distribution coefficients, [CD]^resin/[CD]_acid (concentrations in mol/1), larger than 250 were obtained with HBr equilibrium concentrations of more than 0.10 w% in the phosphoric acid solution or with HI concentrations of more than 150 ppm. The regeneration of the Cd loaded resin was performed with a very dilute phosphoric acid solution (< 1 w% H₃PO₄).

The excess of iodide in the phosphoric acid solution could also be- removed by anion exchange. A value of about 90 was obtained for the iodide distribution coefficient of a weakly basic resin. This resin could be regenerated with an 1 M NH₃ solution at 50^°C.

The rate of adsorption and desorption of both cadmium and iodide were mainly determined by the diffusion in the resin|particle. Effective diffusivities of about 3*10^-13 m^Z/s and 1.3*10^-11m^Z/s were obtained for the adsorption of cadmium in the presence of HI and for the adsorption of iodide respectively.     

SOLVENT IMPREGNATED RESINS CONTAINING DI(2-ETHYL-HEXYL)PHOSPHORIC ACID.II. STUDY OF THE DISTRIBUTION EQUILIBRIA OF Zn(II), Cu(II) AND Cd(II).

ABSTRACT

The extraction of Zn(II), Cu(II) and Cd(II) from nitrate solutions at 0.1 M ionic strength by impregnated resins containing di(2-ethylhexyl)phosphoric acid has been studied at 25 °C.

The distribution coefficient was determined as a function of both pH and extractant concentration in the resin phase. The data were analyzed graphically using the slope analysis method, and numerically using the program LETAGROP-DISTR. The composition of the extracted species in the resin phase has been determined.

Analysis of the results showed that the extraction of these metal ions can be explained assuming the formation of metal complexes in the resin phase with a general composition ML₂(HL) _q where q takes different values depending on the metal. An extraction reaction is proposed and the extraction constants of these species are given.

Finally, a comparison between the extraction of Zn(II), Cu(II) and Cd(II) by di(2-ethylhexyl)phosphoric acid into Amberlite XAD2 and the extraction using organic solvents has been made.     

EXTRACTION OF COPPER,CADMIUM AND RELATED METALS WITH POLY(SODIUM ACRYLATE - ACRYLIC ACID)HYDROGELS.

ABSTRACT

The extraction of copper, cadmium and related metals (M²⁺) with poly(sodium acrylate - acrylic acid) PAA hydrogels has been studied. pH variations are consistent with a cation exchange process. Saturation of the gel is achieved for a metal/carboxylate ratio R ≈ 1/2 and a gel swelling of ≈ 40 which is that of the uncharged gel : (-COO)₂M complexes are expected to be formed, but also complexes of higher stoichiometry (R = 1/3 for Cu and Cd, R = 1/4 for Pb) at low metal concentrations. The selectivity is that observed in liquid-liquid extraction of metal cations with fatty carboxylic acids (Pb > Cu > Cd > Zn > Ni ≈ Co). Metal stripping from the gel is readily achieved by washing with 0.1 M HNO₃. PAA hydrogel extraction allows to remove cadmium from a diluted aqueous solution down to a final concentration of 5 ppb.     

Potentiometric Studies on Ternary Complex Formation between Cu(II), Ni(II), Zn(II), Cd(II), nitrilotriacetic acid and amino acid

The formation of ternary complexes of the type MAB (where M = Cu(II), Ni(II), Zn(II) or Cd(II); A = nitrilotriacetic acid and B = glycine, α-alanine or dl-aspartic acid) has been shown by potentiometric studies. The nature of titration curves indicates that the secondary ligand B is added stepwise to the initially formed metal nitrilotriacetates. The formation constants (log K_MAB) and the free energies of formation (ΔF°) of the mixed complexes have been calculated at 25 ± 1 °C and m̈ = 0.10 (KNO₃) at different pH values. The formation constants of the resulting 1:1:1 ternary complexes follow the order Cu(II) > Ni(II) > Zn(II) > Cd(II).     

Preparation and characterization of urchine-like cadmium zinc sulfide nanostructured powder

The cadmium zinc sulfide (CdZnS) nanostructured powders with different morphologies such as nanorods, urchin like, microsphere were synthesized by co-precipitation method. In this approach, zinc nitrate (Zn(NO₃)₂), cadmium nitrate dihydrate (Cd(NO₃)₂·2H₂O) and mercaptoacetic acid (MAA) were used as a Zn, Cd, and S source, respectively. The products were characterized by XRD, SEM, TEM, EDS and TG/DTG analysis. The result show that urchin like CdZnS spheres self-assembled from sword-like nanorods with diameter of 40–50 nm. Then, the optimized sample was calcined at 300 °C and morphology stability and FTIR of cadmium zinc sulfide nanostructured powder was evaluated.     

Recovery of zinc,cadmium and mercury (ii) from chloride and sulphate media by solvent extraction

The extraction of zinc, cadmium and mercury from chloride and sulphate media by solvating extractants, liquid anion and liquid cation exchangers has been reviewed both from the literature and by experiment. The results have been discussed in terms of both practical process possibilities and the use of slope analysis to identify the extracted species. These show that slope analysis cannot give positive unambiguous identification of extraction stoichiometry in systems in which the extracted metal species contains coordinating ligands from the aqueous phase. However, in the extraction of Zn and Cd from sulphate media by di(2-ethylhexyl)phosphoric acid (DEHPA) the extracted species is shown to be an MR₂(HR)₂ monomer by slope analysis demonstrating its use in simple systems. In the case of amines and solvating reagents such as TBP^c and TOPO zinc appears to be extracted from Cl^– media as either ZnCl₂ or sometimes HZnCl₃ whereas Cd and Hg(II) appear to be always extracted as HCdCl₃ and HHgCl₃ species. The use of aqueous phase complexing by Cl^– to improve the separation of Zn and Cd by extraction is clear. Some results are presented for the recovery of zinc from sulphate media by oximes and mercury from sulphuric acid media by amines and DEHPA.     

Synthesis and characterization of functional copolymer of Linalool and vinyl acetate: A kinetic study

Linalool (LIN) and vinyl acetate (VA) were copolymerized by benzoyl peroxide (BPO) in p‐xylene at 60°C for 90 min. The system follows nonideal kinetics: R_pα[I]^0.6[LIN]^1.2[VA]^1.1. It results in the formation of alternating copolymer as evidenced from reactivity ratios as r₁ (VA) = 0.01, r₂ (LIN) = 0.0015, which have been calculated by Kelen–Tudos method. The overall activation energy is 82 kJ/mol. The FTIR spectrum of the copolymer shows the presence of the band at 3425 cm^?1 due to alcoholic group of LIN and at 1641 cm^?1 due to >C?O group of VA. The ¹H‐NMR spectrum shows peaks at 7.0–7.7 δ due to hydroxy proton of LIN and at 1.0–1.4 δ due to acetoxy protons of VA. ¹³C‐NMR spectrum of copolymer shows peaks at 167 ppm due to acetoxy group and at 75–77 ppm due to C? OH group. The Alfrey–Price Q–e parameters for LIN has been calculated as Q₂ = 1.24 and e₂ = 3.11. The copolymer is highly thermally stable and has a glass transition temperature (T_g) of 85°C, evaluated from DSC studies. The mechanism of copolymerization has been elucidated. This article also reports measurement of Mark–Houwink constants in THF at 25°C by means of GPC as α = 0.8 and K = 3.0 × 10^?4 dl/g. The thermal decompositions of copolymer are established with the help of TGA technique. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1134–1143, 2004     

Kinetics of the metal exchange reaction of a Cu(II)-poly(vinyl alcohol) complex with Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid in aqueous solution

The kinetics of the metal exchange reaction between Cu(II)-poly(vinyl alcohol) [Cu(II)-PVA] and Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid [Zn(II)-EDTA] has been studied by mixing both solutions in a spectrophotometer at pH 10.0 to 11.0, ionic strength μ=0.10(KNO₃), and 15 to 35°C. The reaction is initiated by the formation of unstable Cu(II)-H-PVA through attack of H⁺ ion on the Cu(II)-PVA complex, and both reactions, ligand exchange and metal exchange, proceed simultaneously. The metal exchange step may be rate determining. The rate equation and rate constants of this reaction were determined as follows: ?d[Cu(II)-PVA]/dt=k _0(H)[PVA^?][Cu(II)-PVA] [Zn(II)-EDTA], wherek _0(H)=k ₁+(k′₂+k′₃)[H⁺],k ₁=5.98±1.64M ^?1 s^?1, andk ₂+k ₃=k′₂ K _Cu(II)-H-PVA ^?H +k′₃ K _Zn(II)-EDTA ^H =(5.91±0.89)×10⁷ M ^?2 s^?1.     

Conductometric studies of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) tetrafluoroborates in N,N—dimethylacetamide solutions

Results are reported for the molar conductivities at 25°C of N,N—dimethylacetamide (DMA) solutions of Bu₄NBF₄ and Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) tetrafluoroborates. The limiting molar conductivities of [M(DMA)₆]²⁺ (M  MN, Co, Ni, Cu, Zn) and BF^?₄, as well as association constants for Co(BF₄)₂ in DMA solutions have been calculated. The slight differences between conductometric curves of different metal ions are discussed.     

Adsorption of cadmium and zinc from aqueous solution on natural and activated bentonite

The adsorption of cadmium and zinc ions on natural bentonite heat-treated at 110°C or at 200°C and on bentonite acid-treated with H₂SO₄ (concentrations: 0·5 mol dm^?3 and 2·5 mol dm^?3), from aqueous solution at 30°C has been studied. The adsorption isotherms corresponding to cadmium and zinc may be classified respectively as H and L types of the Giles classification which suggests the samples have respectively a high and a medium affinity for cadmium and zinc ions. The experimental data points have been fitted to the Langmuir equation in order to calcualte the adsorption capacities (X_m) and the apparent equilibrium constants (K_a) of the samples; X_m and K_a values range respectively for 4·11 mg g^?1 and 1·90 dm³ g^?1 for the sample acid-treated with 2·5 mol dm^?3 H₂SO₄ [(B)-A(2·5)] up to 16·50 mg g^?1 and 30·67 dm³ g^?1 for the natural sample heat-treated at 200°C [B-N-200], for the adsorption process of cadmium, and from 2·39 mg g^?1 and 0·07 dm³ g^?1, also for B-A(2·5), up to 4·54 mg g^?1 and 0·45 dm³ g^?1 [B-N-200], for the adsorption process of zinc. X_m and K_a values for the heat-treated natural samples were higher than those corresponding to the acid-treated ones. The removal efficiency (R) has also been calculated for every sample; R values ranging respectively from 65·9% and 8·2% [B-A(2·5)] up to 100% and 19·9% [B-N-200], for adsorption of cadmium and zinc.     

Synergistic effects in the solvent extraction of some divalent metals by mixtures of versatic 10 acid and pyridinecarboxylate esters

Pyridinecarboxylate esters were found to cause appreciable synergistic shifts in the pH₅₀ values for the extraction of some divalent base metals by solutions of Versatic 10 acid in xylene. For n-octyl 3-pyridinecarboxylate, the synergistic shifts decreased in the order Ni > Co > Cd > Cu ≈ Fe > Mn > Zn, and for the commercial extractant Acorga DS5443A in the order Ni > Cu > Co > Fe > Cd > Mn > Zn. No synergistic effects were observed for divalent lead, calcium and magnesium. On the basis of the pH₅₀ values obtained, several possible practical metal separations are suggested. No loss of metal-loading capacity was found when the organic phases were contacted with 1 M sulphuric acid for prolonged periods at 30°C. The effect of changes in the structure of a series of isomeric octyl pyridinecarboxylates is reported for one of the smaller cations studied (copper), as well as for one of the larger cations (cadmium).     

Application of a carbon sorbent for the removal of cadmium and other heavy metal ions from aqueous solution

Treatment of flax shive with sulfuric acid produces a carbonaceous material that has been used to remove metal ions from aqueous solution. Metal ions including Cd(II), Cu(II), Cr(III), Co(II), Ni(II), Zn(II) and Pb(II) have been investigated for kinetic behaviour and sorption capacities. These metal ions show fast sorption kinetics following a first order rate equation. Cadmium was chosen as representative of these metal ions and a detailed study was carried out. The effect of pH on sorption was studied and it was found that maximum uptake occurred above pH 3–7, sorption was accompanied by release of protons into the solution and a ratio of [H⁺] released to [Cd²⁺] sorbed of approximately 2 was found. The sorption capacity showed no significant increase with increase of temperature. The presence of other metal ions such as K⁺, Na⁺, Mg²⁺ and Ca²⁺ decreases the Cd(II) capacity, indicating competition for the ion exchange sites. Successive sorption of Cd(II) shows that the capacity exceeds the monolayer capacity calculated from the Langmuir equation. Column studies showed good performance over a total of seven cycles of loading/stripping. These studies indicate that the sorption mechanism for these metal ions is related to a reversible ion exchange process on the carbon surface. © 2002 Society of Chemical Industry     

EXTRACTION OF DIVALENT METALS WITH BIS(2,4,4 TRIMETHYLPENTY) PHOSPHINIC ACID

The extraction of Cd(II), Cu(II) and Zn(II) from 0.1 mol dm^minus3 aqueous nitrate solutions with bis(2,4,4-trimethylpentyl)phosphinic acid (HBTMPP) dissolved in Isopar-H has been studied with relation to the total extractant concentration, the equilibrium pH and the total metal concentration in the aqueous phase.

The stoichiometry of the extracted species and their equilibrium constants have been determined by graphical and numerical methods and appear to be CdA₂ (HA)₂ and CdA₂ (HA)₃ for Cd(II), CuA₂(HA)₂ for Cu(II) and ZnAzHA and ZnAz(HA)₂ for Zn(II). The extraction efficiency follows the order Zn(II)<Cu(II)<Cd(II)     

Synthesis and Characterization of Pure Phase Zn(II) and Cd(II) Oxide Nanoparticles via Thermal Decomposition of Four New Zn(II) and Cd(II) Coordination Polymers

Four new Zn(II) and Cd(II) coordination polymers, [Zn(2-AMP)₂(N₃)₂]_n (1), [Zn(2-AMP)₂(SCN)₂]_n (2), [Cd(2-AMP)(N₃)₂]_n (3) and [Cd(2-AMP)₂(SCN)₂]_n (4) {2-AMP: 2-Aminomethylpyridine}, have been synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy and elemental analyses. The Zinc(II) oxide and Cadmium(II) oxide nano-particles have been synthesized from thermolysis of 1–4 at 600 °C under air atmosphere for 4 h. The ZnO and CdO nanoparticles were characterized by X-ray diffraction and scanning electron microscopy (SEM). SEM images show the average size of produced ZnO and CdO nanoparticles are 60–70 nm in all compounds.     

Potentiometric and polarographic studies of cadmium(II) complexes with tetraethylenepentamineheptaacetic acid

Stability constants for cadmium(II) complexes with tetraethylenepentamineheptaacetic acid (TPHA, H₇L) were determined by the pH titration method. In an aqueous solution (μ = 0.1), three complex species, CdH₂L, CdHL and CdL are confirmed. The structure of uninuclear complexes are discussed. The formation constants of the complexes stated above have been calculated as follows (at 25 ± 0.1°C): log K_CdL = 15.35, log K_CdHL = 13.33 and log K_CdH2L = 7.89. The polarographic behaviour of the cadmium(II) in the presence of TPHA was studied over the pH range 3–5. Mechanisms of the electrode processes were elucidated and electrochemical kinetic parameters were evaluated from dependence of the half-wave potentials on the hydrogen ion and TPHA concentration. In the presence of an excess of TPHA, the wave B is assigned to the irreversible reductions of the complex, CdH₂L^3? (pH range 3–4) or CdHL^4? (pH range 4–5). The electrode reaction can be written:

and

Where k_e (the rate constant) = 2.3 × 10^?2 cm s^?1 and k′_e = 1.59 × 10^?4 cm s^?1. The other polarographic methods were also used in the elucidation of the electrode process.     

Microstructure and mechanical properties of Al2O3/Cu joints brazed with Ag–Cu–Ti+Zn composite fillers

In this study, Al₂O₃ ceramic and Cu bars were brazed with newly designed Ag–Cu–Ti(ABA)+Zn composite fillers. Systematic analysis of the microstructure of the brazed joints indicated that the volatilization of Zn atoms during the brazing process could promote the spreading of liquid brazing fillers on the surface of the Al₂O₃ ceramic, resulting in a uniform dendritic interfacial structure. The typical interfacial structure was an Al₂O₃/TiO/(Cu, Al)₃Ti₃O+Ag(s, s)/Cu interface. Notably, the tensile strength was improved to 20.89 MPa for Al₂O₃/Cu joint brazed with ABA+Zn composite fillers at 900 °C for 20 min, approximately 67.6% higher than the sample brazed without Zn foil. In this case, the fracture model was straight and sharp-angled inside the Al₂O₃ ceramic. In addition, the joint strength decreased with increased brazing temperatures from 900 to 940 °C.     

Utilization of peanut shells as adsorbents for selected metals

Peanut shells of mesh size 10–20 were modified by combinations of treatments following a 3² factorial design. Treatments consisted of either no wash, water wash or base wash followed by no modification or modification with 0.6 M citric acid or 0.6 M phosphoric acid. The nine samples were evaluated for their uptake of five metal ions (Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II)) from solution. The results were compared with metal ion adsorption by three commercial cation exchange resins, namely, Amberlite® 200, Amberlite® IRC 718 and Duolite® GT‐73. The percent of metal ions adsorbed per gram of adsorbent was significantly increased by each of the acid treatments, average values ranged from 19 to 34% compared with non‐acid treated samples at 5.7%. The percent of metal ions adsorbed for base‐washed samples were higher than water‐washed or unwashed shells. Interaction between wash and acid treatment was not significant for most of the experimental conditions used. Acid‐treated samples were as effective as Duolite® GT‐73 in the adsorption of Cd(II) and almost twice as effective in the adsorption of Zn(II) from solutions containing a single metal ion. In solutions containing multiple metal ions, citric acid samples were found to be most effective and selective for Cu(II) compared with Cd(II), Ni(II), and Zn(II). In general, phosphoric acid‐modified shells removed the most metals from solution for the experimental samples and were more effective in removing Cd(II) and Zn(II) than two of the three commercial resins. Acid‐modified peanut shells are promising as metal ion adsorbents. © 1999 Society of Chemical Industry     

Recovery of 2,4‐dichlorophenol from acidic aqueous streams by Membrane Aromatic Recovery System (MARS)

This study describes the successful recovery of 2,4‐dichlorophenol (DCP) from wastewater using the Membrane Aromatic Recovery System (MARS). In the MARS process a non‐porous membrane separates a wastewater stream and a stripping solution. DCP is extracted from the wastewater and concentrated in its ionic form in the stripping solution, with pH ? pK_a DCP. The MARS extraction stage was operated in batch mode with the stripping solution placed inside, and the wastewater stream outside, the membrane tubes. Advantages of this configuration are avoidance of membrane blockage, reduction of stripping solution volume and operational flexibility. The stability and mass‐transfer characteristics of two different membrane materials, poly(dimethylsiloxane) (PDMS) and ethylene–propylene diene terpolymer (EPDM), were tested in DCP solutions with different acidities in order to simulate real industrial waste streams. EPDM exhibits one order of magnitude lower mass‐transfer rates than PDMS (1.4 × 10^?7 m s^?1 vs 20 × 10^?7 m s^?1 at 30 °C and 2.4 × 10^?7 m s^?1 vs 39 × 10^?7 m s^?1 at 60 °C), however its higher resistance to acid attack provides higher membrane lifetimes. This can be crucial for MARS processes treating real acidic industrial wastewater. A 97% recovery of DCP with a water content of 15 wt% was obtained upon neutralisation of the stripping solution. Copyright © 2004 Society of Chemical Industry     

Dehydration,Water Vapor Adsorption and Desorption Behavior of Zn[B3O3(OH)5] · H2O and Zn[B3O4(OH)3]

The dehydration behaviors of two different hydrated zinc borate species, Zn[B₃O₃(OH)₅] · H₂O and Zn[B₃O₄(OH)₃], which are industrially important flame retardants, were studied by thermal gravimetric(TG) analysis and in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Dehydration onset temperatures of Zn[B₃O₃(OH)₅] · H₂O and Zn[B₃O₄(OH)₃] were 129 and 320°C, respectively, at a 10°C/min ramp rate. A very small amount of boric acid was volatilized in addition to water vapor when both samples were heated at 250°C. A significant amount of water vapor was adsorbed by Zn[B₃O₃(OH)₅] · H₂O from air at 25°C. However, Zn[B₃O₄(OH)₃] adsorbed a very small amount of water under the same conditions. Both zinc borates did not have a tendency to cake during storage.