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     

Mass transfer kinetics of neodymium(III) extraction by calix[4]arene carboxylic acid using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamics and kinetics data are both important to explain the extraction property. In order to develop a novel separation technology superior to current extraction systems, many promising extractants have been developed including calixarene carboxylic acids. The extraction thermodynamics behavior of calix[4]arene carboxylic acids has been reported extensively. In this study, the mass transfer kinetics of neodymium(III) and the interfacial behavior of calix[4]arene carboxylic acid were investigated. RESULTS: The rate constant (K_ao) becomes constant when the stirring speed was controlled between 250 rpm and 400 rpm. The activation energy (E_a) was calculated to be 21·41 kJ mol^?1 or 88·17 kJ mol^?1 (dependent on temperature) from the slope of log K_ao against 1000/T. The linear relationship between the specific area and the extraction rate is the characteristic of an interfacial reaction control. The minimum bulk concentration of the extractant necessary to saturate the interface (C_min) is lower than 4·19 × 10^?4 mol L^?1. CONCLUSION: The effect of stirring speed, temperature, and species concentration on the extraction rate demonstrates that the extraction regime depends on the extraction conditions. The chemical reaction control governs the extraction regime at temperatures below 303 K and a mixed control regime occurs when the temperature is between 303 K and 318 K. The probable locale for the chemical reaction is at the liquid–liquid interface and the rate equation is deduced to be: ? d[Nd³⁺]_(a)/dt = k_f[Nd³⁺]_(a)[H₄A]_(o)^0·727[H⁺]_(a)^?0·978. The rate‐controlling step was suggested by the analysis of the experimental results. Copyright © 2008 Society of Chemical Industry     

A bipolar electrospray source of singly charged salt clusters of precisely controlled composition

The few clusters [B^?_nA⁺_n+1]⁺ (n = 0,1) with resolvable mobilities formed in electrosprays of large salts have been used for nanoparticle instrument testing and calibration at sizes smaller than 2 nm. Extensions of this modest size range by charge reduction with uncontrolled gas phase ions has resulted in impure singly charged clusters. Here, we combine two oppositely charged electrosprays of solutions of the same salt B^?A⁺, including: (C_nH_2n+1)₄N⁺Br^? (n = 4,7,12,16), the large phosphonium cation (C₆H₁₃)₃(C₁₆H₃₃)P⁺ paired with the anions Im^? [(CF₃SO₂)₂N^?] or FAP^? [(C₂F₅)₃PF₃^?], and the asymmetric pair [1-methyl-3-pentylimidazolium⁺FAP^?]. Both polarities are simultaneously produced by this source in comparable abundances, primarily as singly charged A⁺_nB^?_n±1, with tiny contributions from higher charge states. Some but not all of these clusters produce narrow mobility peaks typical of pure ions, even beyond n = 43. Excellent independent stable control of the positive and the negative sprays brought very close to each other is achieved by isolating them electrostatically with a symmetrically interposed metallic screen. Two nanoDMAs covering the size range up to 30 nm (Halfmini and Herrmann DMAs, with classification lengths of 2 and 10 cm) are characterized with these standards, revealing resolving powers considerably higher than previously seen with unipolar electrospray sources. The bipolar source of pure and chemically homogeneous clusters described permits studying size and charge effects in a variety of aerosol instruments in the 1–4 nm size range.

Copyright © 2017 American Association for Aerosol Research     

Solvent extraction and separation of rare earths from chloride media using α-aminophosphonic acid extractant HEHAMP

Solvent extraction and separation of rare earths (REs: La ~ Lu, plus Y and Sc) by a novel synthesized extractant, (2-ethylhexylamino)methyl phosphonic acid mono-2-ethylhexyl ester (HEHAMP, abbreviated as H₂A₂), were investigated in chloride medium. The favorable separation factors (SFs) between adjacent heavy REs suggested that HEHAMP has a better separation performance than P507. The extracted complex of trivalent REs was determined to be REClH₂A₄ by the slope analysis method. Thermodynamic parameters (ΔH, ΔG, and ΔS) of Lu were calculated as 7.47 kJ mol^?1, ?6.05 kJ mol^?1, and 45.4 J mol^?1 K^?1 at 298.15 K, respectively, which indicate that the extraction reaction of Lu is an endothermic process. The loading capacity of 30% (v/v) HEHAMP toward Lu(III), Yb(III), and Y(III) was about 15.17 g Lu₂O₃/L, 14.46 g Yb₂O₃/L, and 12.64 g Y₂O₃/L, respectively. HCl is the most efficient stripping acid, and 92% of the loaded Yb(III) can be stripped by one-stage stripping with 2 mol/L HCl.     

Ionic liquid-based extraction and separation trends of bioactive compounds from plant biomass

Ionic liquids have been projected as the best solvent for extraction and separation of bioactive compounds from various origins. This review offers a collection of the published results, using ionic liquids for the extraction and purification of biomolecules. Ionic liquids have been studied as solvents, co-solvents and supported materials for separation of bioactive compounds. The ionic liquids-based extraction procedures were previously reported, such as ionic liquids-based solid-liquid extraction, liquid-liquid extraction and ionic liquids-modified materials are reviewed and compared to their performance. In this review, the main activities and future challenges are discussed, with major gaps identified using ionic liquids in extraction procedures and by advancing few steps to overcome these drawbacks.

Abbreviation: [(HSO₃)C₄MIM]⁺: 1-(4-sulfonylbutyl)-3-methylimidazolium; [(C₆H₃OCH₂)₂im]⁺: 1,3-dihexyloxymethylimidazolium; [C_nC₁MIM]⁺: 1-alkyl-2,3-dimethylimidazolium; [C_nMIM]^{+; [Cn, 2, 3, 4, 6, 8, 10, 12]}: 1-alkyl-3-methylimidazolium; [C_nC₁pyr]⁺: 1-alkyl-3-methylpyridinium; [C_nim]⁺: 1-alkylimidazolium; [C_npyr]⁺: 1-alkylpyridinium; [aC_nim]⁺: 1-allyl-3-alkylimidazolium; [C₇H₇MIM]⁺: 1-benzyl-3-methylimidazolium; [C₄(C₁C₁C₁Si)im]⁺: 1-butyl-3-trimethylsilylimidazolium; [(HOOC)C₂MIM]⁺: 1-carboxyethyl-3-methylimidazolium; [(OH)C_nMIM]⁺: 1-hydroxyalkyl-3-methylimidazolium; [(C₂H₅O)₃SiC₃MIM]⁺: 1-methyl-3-(triethoxy)silypropyl imidazolium; [(NH₂)C₃MIM]⁺: 1-propylamine-3-methylimidazolium; [C_wH_xN_yO_z]⁺: Chirally functionalized methylimidazolium; [P_{10(3OH)(3OH)(3OH)}]⁺: Decyltris(3-hydrox- ypropyl) phosphonium; [N_111(2OH)]⁺: N,N,N-trimethyl-N-(2-hydroxyethyl) ammonium (cholinium); [N_00nn]⁺: N,N-dialkylammonium; [N_0nn(2OH)]⁺: N,N-dialkyl-N-(2-hydroxyethyl) ammonium; [C₁₀C₁₀C₁gluc]⁺: N,N-didecyl-N-methyl-d-glucaminium; [N_11(2(O)1)0]⁺: N,N-dimethyl(2-methoxyethyl) ammonium; [N_{11(2OH)(C7H7)}]⁺: N-benzyl-N,N-dimethyl-N-(2-hydroxyethyl) ammonium; [P₆₆₆₁₄]⁺: Trihexyltetradecylph- osphonium; [P_i(444)1]⁺: Triisobutyl (methyl) phosphonium; P.minus: Polygonum minus; NPs: Nanoparticle; ZnO : Zinc oxide nanoparticles ; Ni NPs: Nickel nanoparticles; MO: Methyl orange; UAE: Ultrasonic-assisted extraction; LLE: Liquid-liquid extraction; ABS: Aqueous biphasic system ; [Ace]^?: Acesulfamate; [Ala]^?: alalinate; [TMPP]^?: bis(2,4,4-trimethylpentyl)phosphinate; : ; [NTf₂]^?: bis(trifluoromethylsulfonyl)imide; [[Br]^–]: [Br]omide; [Calc]: calkanoate; [Cl]^–: chloride; [Bz]^?: benzoate; [PF₆]^?: hexafluorophosphate; [HSO₄]^?: hydrogenosulfate; [OH]^?: hydroxide; I^–: iodide; [Lac]^?: lactate; [NO₃]^?: nitrate; [[Cl]O₄]^?: perchlorate; [Phe]^?: phenilalaninate; [BF₄]^?: tetrafluoroborate; [SCN]^?: thiocyanate; [C(CN)₃]^?: tricyanomethanide; [CF₃CO₂]^?: trifluoroacetate; [CF₃SO₃]^?: trifluoromethanesulfonate; [FAP]^?: tris(pentafluoroethyl)trifluorophosphate; ILs: Ionic liquids; Ag NPs: Silver nanoparticle; Cu NPs: Copper nanoparticle; MB: Methylene blue; MR: Methyl red ; MAE: Microwave-assisted extraction; SLE: solid-liquid extraction.     

Investigation of the Thermal Decomposition Kinetics of Chalcopyrite Ore Concentrate usıng Thermogravimetric Data

The kinetics of the thermal decomposition of chalcopyrite concentrate was investigated by means of thermal analysis techniques, Thermogravimetry/Derivative thermogravimetry (TG/DTG) under ambient air conditions in the temperature range of 0–900°C with heating rates of 2, 5, 10, 15, and 20°C min^?1. TG and DTG measurements showed that the thermal behavior of chalcopyrite concentrate shows a two-step decomposition. The decomposition mechanism was confirmed using X-ray diffraction (XRD), Scanning Electron Microscope (SEM)/energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) analyses. Kinetic parameters were determined from the TG and DTG curves for steps I and II by using two model-free (isoconversional) methods—Flyn–Wall–Ozowa (FWO) and Kissinger–Akahira–Sunose (KAS). The kinetic parameters consisting of E_a, A, and g(α) models of the materials were determined. The average activation energies (E_a) obtained from both models for the decomposition of chalcopyrite concentrate were 72.55 and 300.77 kJ mol^?1 and the pre-exponential factors (A) were 15.07 and 29.39 for steps I and II, respectively. The most probable kinetic model for the decomposition of chalcopyrite concentrate is an first-order mechanism, i.e., chemical reaction [g(α) = (?ln(1?α))], and an Avrami–Eroeyev equation mechanism, i.e., nucleation and growth for n = 2 [g(α) = (?ln(1?α)^1/2)], for steps I and II, respectively.     

Conductivity and ion transport in silver—tin pyrophosphate baths

Mass transfer of metal ions and a pyrophosphate ion in silver—tin pyrophosphate baths was studied. The complex ion, [Sn₂(P₂O₇)₂]^6?, is formed in a solution of pH greater than 9.7 with a pyrophosphate to Sn²⁺ ratio of 2:1. The pyrophosphate ion simultaneously functions for enhancing conductivity as a complexing agent to promote the codeposition of silver. The diffusion coefficients of [Ag(CN)₂]^? and [Sn₂(P₂O₇)₂]^? were 1.39 × 10^?5 and 7.87 × 10^?6 cm² s^?1, respectively, but that of [Sn₂(P₂O₇)₂]^6? become larger as the pyrophosphate concentration was increased. The apparent activation energy of diffusion of [Ag(CN)₂]^? was 3.1 kcal mol^?1 and that of [Sn₂(P₂O₇)₂]^6? was 2.7 kcal mol^?1.     

Study on adsorption performance of 2-amino-4-methylbenzothiazole onto chemical modification adsorption resins

A series of functional hyper-cross-linked resins were successfully synthesized by incorporating anhydride, sulfoacid and menthanone groups into post-cross-linked polymer. They were evaluated for adsorption of 2-amino-4-methylbenzothiazole (2A4MBT) from aqueous solution. The five resins were efficient for adsorption of 2A4MBT from aqueous solution. The adsorption process includes both physical adsorption and irreversible chemical adsorption. The absolute value of adsorption enthalpy had an order of PRLMR (3.24 kJ mol^?1) < IDLMR (7.96 kJ mol^?1) < TMAMR (9.72 kJ mol^?1) < PAMR (?13.1 kJ mol^?1) < SAMR (21.8 kJ mol^?1). Phthalic anhydride-modified resin could be regenerated by 10% HCl/methanol solution after adsorption equilibrium.     

Kinetics of ylide-initiated radical copolymerization of 4-vinylpyridine and methyl methacrylate

The ylide-initiated radical copolymerization of 4-vinylpyridine (4-VP) with methyl methacrylate (MMA) at 60°C using carbon tetrachloride as inert solvent yields non-alternating copolymers. The kinetic parameters, average rate of polymerization (R_p) and orders of reaction with respect to monomers and initiator, have been evaluated and the kinetic equation is found to be R_pα[ylide]^0.94 [MMA]^1.0 [4-VP]^1.5. The values of the energy of activation and k_p²/k_t are 48 kJ mol^?1 and 6.6 × 10^?5 litre mol^?1s^?1, respectively. The copolymers have been characterized by IR and NMR spectroscopy.     

Graft copolymerization of methacrylic acid onto xanthan gum by Fe2+/H2O2 redox initiator

The graft copolymer of xanthan gum with methacrylic acid was synthesized in inert atmosphere by using Fentos reagent as a redox initiator. The effect of reaction conditions on grafting parameters [G(%), E(%), C(%), A(%), H(%), and R_g] was investigated. Similar trend was observed on increasing the concentration of ferrous ion and hydrogen peroxide from 4.0 to 20.0 × 10^?3 mol dm^?3 and 2.5 to 10 × 10^?3 mol dm^?3 respectively, i.e., initially grafting parameters increased and after a certain range of concentration grafting parameters showed decreasing trend. Hydrogen ion shows influenced result i.e., small increment of concentration in hydrogen ion presents much increment in percent of grafting. It was observed that the [G(%), E(%), C(%), A(%), and R_g] increased upto 6.67 × 10^?2 mol dm^?3 concentration of methacylic acid after that it decreased. Maximum G(%) was obtained at minimum concentration of xanthan gum i.e., at 40 × 10^?2 g dm^?3. The optimum temperature and time duration of reaction for maximum percentage of grafting were found to be 45°C and 150 min respectively. Thermogravimetric analysis showed that the xanthan gum‐g‐methacrylic acid is thermally more stable than pure gum. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Interaction of polystyryl radical with Cu(DMF)2Br2

The kinetics of 2,2′-azobisisobutyronitrile (AIBN) initiated polymerization of styrene in N,N-dimethylformamide (DMF) at 60°C were investigated in the presence of dibromo(N,N-dimethylformamide)copper(II) complex. The complex was prepared in situ by mixing tetrakis (N,N-dimethylformamide)copper(II) perchlorate with LiBr in the molar ratio of 1 : 2. The equilibrium constant for [Cu(DMF)₄]²⁺ + 2Br^? ? Cu(DMF)₂Br₂ + 2DMF was calculated by the limiting logarithmic method as 1.80 × 10³ L² mol^?2. The velocity constant at 60°C for the interaction of polystyryl radical with Cu(DMF)₂Br₂ is 7.46 × 10⁴ L mol^?1 s^?1.     

Kinetics of extraction of Ti(IV) from SO42– medium by Cyanex 301 dissolved in kerosene containing 5% heptan-1-ol

The kinetics of Ti(IV) extraction by Cyanex 301 (HA) were investigated by measuring initial flux of Ti(IV) transfer (F, kmol/m²s), using a Lewis cell, operated at 3 Hz. The empirical flux equation at 298 K is found to be as follows: F (kmol/m²s) = 10^–4.288 [Ti(IV)] (1 + 447 [H⁺])^–1 [HA]_(o) (1 + 1.18[SO₄^2–])^–1. The activation energy, E_a, has been measured to be within 37–60 kJ/mol, depending on experimental parameters and temperature region. The ΔS^± value is always highly negative. Analysis of the flux equation has been done, given various parametric conditions, to elucidate the mechanism of extraction. The rate-determining chemical reaction step, in most parametric conditions, appears to be as follows: TiO²⁺ + A^– → TiOA⁺; and this step occurs via an S_N2 mechanism as suggested by high negative ΔS^± values. However, in certain cases, the extraction process appears as intermediate controlled as supported by E_a value of less than ~48 kJ/mol.     

Study on Isothermal Formation Dynamics of Calcium Barium Sulphoaluminate Mineral

The formation dynamics of calcium barium sulphoaluminate mineral with the composition of 2.75CaO·1.25BaO·3Al₂O₃·SO₃ (C_2.75B_1.25A₃ $\overline{\text{S}}$ S ¯ ) was studied. The results suggest that, under the preparative conditions, the formation of C_2.75B_1.25A₃ $\overline{\text{S}}$ S ¯ mineral is controlled by a diffusion mechanism from 1,100 to 1,380 °C; and, the formation dynamics fits nicely with D ₄ = 1 ? 2α/3 ? (1 ? α)^2/3 = Kt. From 1,100 to 1,300 °C, the apparent activation energy is 227.45 kJ mol^?1. From 1,300 to 1,380 °C, the apparent activation energy decreases to 175.94 kJ mol^?1, making the formation of C_2.75B_1.25A₃ $\overline{\text{S}}$ S ¯ mineral faster and easier.     

First‐Principle Calculation and Assignment for Vibrational Spectra of Ba(Mg1/2W1/2)O3 Microwave Dielectric Ceramic

Ba(Mg_1/2W_1/2)O₃ ceramic was synthesized using a conventional solid‐state reaction method at 1500°C for 4 h. The face‐centered cubic crystal structure of the material was confirmed by Rietveld refinement of X‐ray diffraction (XRD) data, and vibrational modes were obtained by Raman and Fourier transform far‐infrared (FTIR) reflection spectroscopies. First‐principle calculations based on density functional theory with local density approximation were used to calculate Gamma‐point modes and dielectric properties of Ba(Mg_1/2W_1/2)O₃. The Raman spectrum with nine active modes can be fitted with Lorentzian function, and the modes were assigned as F_2g⁽¹⁾ (126 cm^?1), F_2g⁽²⁾ (441 cm^?1), E_g(O) (538 cm^?1), and A_1g(O) (812 cm^?1). Far‐infrared spectrum with 12 infrared active modes was fitted using both the Lorenz three‐parameter classical and four‐parameter semiquantum models. Consequently, the modes were assigned as F_1u⁽¹⁾ (144 cm^?1), F_1u⁽²⁾ (284 cm^?1), F_1u⁽³⁾ (330–468 cm^?1), and F_1u⁽⁴⁾ (593–678 cm^?1). The active modes were represented by linear combinations of symmetry coordinates that were obtained by group theory analyses. The Raman mode A_1g, which has the highest wave number (812 cm^?1) is dominated by the breath vibration of the MgO₆ octahedron. The infrared modes F_1u⁽²⁾, that can be described as the inverted vibrations of Mg atoms in the MgO₆ octahedron along the x_i, y_i, and z_i axes have the most contributions to the microwave permittivity and dielectric loss.     

Development of a Green Process for the Preparation of Antioxidant and Pigment-Enriched Extracts from Winery Solid Wastes Using Response Surface Methodology and Kinetics

Red grape pomace (RGP), an abundant wine industry solid waste, was used for the recovery of polyphenols and anthocyanin pigments, using ultrasound-assisted extraction and water/glycerol mixtures as the solvent. Glycerol concentration (C_gl) and liquid-to-solid ratio (R_L/S) were first optimized by implementing Box?Behnken experimental design and the process was further studied through kinetics. The optimal conditions were found to be C_gl = 90% (w/v) and R_L/S = 90 mL g^?1, and under these conditions the extraction of total polyphenols (TP) and total pigments (TPm) obeyed first-order kinetics. Maximum diffusivity (D_e) values were 4.22 × 10^?12 and 12.59 × 10^?12 m² s^?1, for TP and TPm, respectively, and the corresponding activation energies were (E_a) 13.94 and 8.22 kJ mol^?1.     

Tracking the Transformation Process of a Pair of Zn(II) Coordination Clusters: Crystallography and Mass Spectrometry

Two zinc clusters Zn₄(H₃L)₄(NO₃)₄?5H₂O ( Zn₄ , H₄L=(1,2‐bis(1H‐benzo[d]imidazol‐2‐yl)ethane‐1,2‐diol) and [Zn₅(H₂L′)₆](NO₃)₄]?8H₂O?2CH₃OH ( Zn₅ , H₃L′=(1,2‐bis(benzo[d] imidazol‐2‐yl)‐ethenol) have been obtained by the reaction of Zn(NO₃)₂?6H₂O with H₄L at 80 °C or 140 °C under solvothermal condition. Powder X‐ray Diffraction (PXRD) of precipitate and Electrospray Ionization Mass Spectrometry (ESI‐MS) of reaction solution revealed the existence of transformation behavior from Zn₄ to Zn₅ by increasing the temperature from 80 °C to 140 °C, or directly heating Zn₄ at 140 °C via solvothermal reaction. Here we proposed a possible mechanism involves split process of Zn₄ and reassembly to form Zn_{5 .} ESI‐MS for single crystals revealed [Zn₄(H₃L)₄?3H]⁺ splits to [Zn(H₃L)]⁺ via [Zn₂(H₃L)₂?H]⁺. Time dependent ESI‐MS of reaction solution revealed the [Zn(H₂L′)]⁺→[Zn₂(H₂L′)₂?H]⁺→[Zn₅(H₂L′)₆?H]³⁺ stepwise assembly. It also has been captured the in situ reaction mainly occurs in the step of [Zn(H₃L)]⁺ to [Zn(H₂L′)]⁺.     

The Reaction of Ozone with Bisulfide (HS−) in Aqueous Solution – Mechanistic Aspects

The ozone demand to oxidize HS^?/H₂S [pK_a(H₂S) = 6.9, k(HS^? + O₃) = 3 × 10⁹ M^?1 s^?1, k(H₂S + O₃) = 3 × 10⁴ M^?1 s^?1] to SO₄ ^2? is only 2.4 mol ozone per mol SO₄ ^2? formed, much lower than stoichiometric 4.0 mol/mol if a series of O-transfer reactions would occur. As primary step, the formation of an ozone adduct to HS^?, HSOOO^–, is suggested that decomposes into HSO^– and singlet oxygen (16%) or rearranges into peroxysulfinate ion, HS(O)OO^– (84%). Potential reactions of the above intermediates are discussed. Some of these can account for the low ozone demand.     

New nanohybrids from poly(propylene imine) dendrimer stabilized silver nanoparticles on multiwalled carbon nanotubes for effective catalytic and antimicrobial applications

Five types of multiwalled carbon nanotubes noncovalently functionalized with poly (propylene imine) dendrimer (PPI (G2))-silver nanoparticle hybrids were prepared by varying the [Ag⁺] load from 2 to 6 mM. These nanohybrids were characterized with FTIR, UV-Vis, FESEM, EDS, HRTEM and Raman analyses. The catalytic potential was studied through the reduction of 4-nitrophenol as a model reaction under pseudo first-order reaction conditions. The calculated k_obs value (16.94 × 10^?2 min^?1) reveals that the 4 mM [Ag⁺] loaded catalyst showed higher efficiency than with rest of the catalysts. Further, the in vitro antimicrobial activities of all nanohybrids were inspected against Pseudomonas aeruginosa and Staphylococcus aureus.     

Leaching Kinetics of Fe2Al5 and Skeletal Iron Formation

Caustic leaching of fine particles of Fe₂Al₅ alloy to produce skeletal Fe catalysts was studied using a 2⁴ factorial experimental design, in which alloy particle size, aqueous NaOH concentration, temperature and stirrer speed were varied. Analysis of the results from the design showed that the BET surface area of the skeletal iron increased with decreases in temperature, caustic concentration and particle size according to S_BET = 222.7 ? 0.461 · T ? 2.35 · c_NaOH ? 0.0245 · D _p. An Avrami–Erofeev model ?ln(1 ? α) = kt with an activation energy of 55 ± 5 kJ mol^?1 and a shrinking core model for volume contraction 1 ? (1 ? α)^1/3 = kt and an activation energy of 56 ± 5 kJ mol^?1 provided the best fit to the kinetic data for leaching.