Aneek Krishna Karmakar

Recovery of manganese and zinc from waste Zn-C cell powder: Mutual separation of Mn(II) and Zn(II) from leach liquor by solvent extraction technique.

Acidic organophosphorous extractants were screened for the mutual separation of Mn(II) and Zn(II), in a leach solution of waste Zn-C cell powder. This was done using a 2mol/L H2SO4 solution containing 2g/L glucose. Extraction characteristics of both metal ions in this mixture have been examined as functions of equilibrium pH. Although tech. and anal. grade D2EHPA are not so effective for the separation, PC88A, Cyanex 272, Cyanex 302 and Cyanex 301 are all promising for this purpose. Strippings of Mn(II) and Zn(II) from the extracted organic phases have been examined, using 0.25, 0.50 and 1mol/L H2SO4; and 1mol/L HCl, HNO3 and HClO4 at different phase ratios. H2SO4 appears to be the best stripping agent. A 1mol/L H2SO4 solution strips almost 100% of target metal ions in 10min, regardless of the extractant used. As ΔpH1/2=2.75 and as the max. separation factor (β)=1793 for Cyanex 302 at pH(eq)=4.0, a flow sheet has been developed for their mutual separations. Finally, classical precipitation methods have been adopted to obtain MnS and ZnS, which can be easily oxidized to MnO2 and ZnO, respectively.

Kinetics of Solvent Extraction of Iron(III) from Sulfate Medium by Purified Cyanex 272 using a Lewis Cell

Abstract The kinetics of the forward and backward extraction of the title process have been investigated using a Lewis cell operated at 3 Hz and flux or (F) – method of data treatment. The dependences of (F) in the forward extraction on [Fe3+], [H2A2](o), pH, and [HSO4 −] are 1, 0.5, 1, and −1, respectively. The value of the forward extraction rate constant (k f ) has been estimated to be 10−7.37 kmol3/2 m−7/2 s−1. The analysis of the experimentally found flux equation gives the following simple equation: F f =100.13 [FeHSO4 2+] [A−], on considering the monomeric model of BTMPPA and the stability constants of Fe(III)‐HSO4 − complexes. This indicates the following elementary reaction occurring in the aqueous film of the interface as rate determining: [FeHSO4]2++A−→[FeHSO4.A]+. The very high activation energy of 91 kJ mol−1 supports this chemical reaction step as rate-determining. The negative value of the entropy change of activation (−94 J mol−1 K−1) indicates that the slow chemical reaction step occurs via the SN2 mechanism. The backward extraction rate can be expressed by the equation: F b =10−5.13 [[FeHSO4A2]](o) [H+] [H2A2](o) −0.5. An analysis of this equation leads to the following chemical reaction step as rate-determining: [FeHSO4A2](int)→[FeHSO4A]+A(i) −. However, the activation energy of 24 kJ mol−1 suggests that the backward extraction process is intermediate controlled with greater contribution of the diffusion of one or the other species as a slow process. The equilibrium constant obtained from the rate study matches well with that obtained from the equilibrium study.

Recovery of manganese and zinc from waste Zn–C cell powder: Characterization and leaching

A large number of waste Zn-C cells (Haquebrand) were broken down and collected as agglomerated powder. This powder was sun-dried, dry-ground and sieved down to 300 mesh size and stored. The sample was analysed and found to contain (35.4 ± 0.2)% Mn, (11.0 ± 0.1)% Zn and ∼ 2.5% Fe as major metallic constituents. The phases, ZnMn2O4 and Zn(ClO4)2 · 2H2O or MnO(OH) were identified in the hot water washed sample. The material was found to be leached effectively by a 2 mol/L sulfuric acid solution containing glucose (2g/L). However, the dissolution was dependent on (S/L) ratio; and the stage-wise leaching was not fruitful for Mn-dissolution. On leaching 5 g of powder (<53 μm) with a 250 mL of 0.5 g glucose containing 2 mol/L sulfuric acid solution (S/L=20 g/L), at 100°C and 300 rpm for 1h, a solution containing (7.08 ± 0.10)g/L Mn(2+), (2.20 ± 0.06) Zn(2+) and ∼ 0.40 g/L Fe(3+) was recovered corresponding to cent percent dissolutions of Zn and Mn and 80% dissolution of Fe.

Recovery of manganese and zinc from spent Zn-C cell powder: Experimental design of leaching by sulfuric acid solution containing glucose.

The spent Zn-C cell powder, containing ZnMn2O4, ZnO, MnO(OH) and possibly Mn2O3 and Mn3O4, can be leached by a sulfuric acid solution mixed with some glucose. The leaching is found to be dependent on solid to liquid (S/L) ratio, amount of glucose, concentration of sulfuric acid solution, time and pulp agitation speed. For 5g powder (S), 1h leaching time and 300rpm pulp agitation speed, two-level four-factor (2(4)) experimental designs have been carried out to derive models for extraction of both Mn(II) and Zn(II). Amount of glucose (G, g), concentration of H2SO4 solution (C, mol/L), volume of H2SO4 solution as leachant (L, mL) and leaching temperature (T, °C) are considered as factors (variables). The model in both cases consists of mean, factor effects and interaction effects. The four-factor interaction effect is observed in neither of the cases. Some two-factor and three-factor effects are found to have produced positive or negative contributions to dissolution percentage in both cases. The models are examined for comparison with experimental results with good fits and also used for optimization of factors. At optimized condition (G=0.50g, C=2mol/L, L=250mL and T=100°C), an aliquot of 5g powder in 1h and at 300rpm produces a solution containing (7.08±0.10)g/L Mn(II) and (2.20±0.06)g/L Zn(II) corresponding to almost 100% extraction of both metal ions.

Solvent Extraction of Ti(IV) from Acidic Sulphate Medium by Cyanex 301 Dissolved in Kerosene

The solvent extraction of Ti(IV) from sulfate medium by the commercial extractant Cyanex 301 (HA) has been studied in order to examine this novel system. Heptan-1-ol (5% (v/v) in the organic phase) is used as a de-emulsifier. The equilibration time is 45 min. The experimental results suggest that the extracted species is always TiOA2 (o), though the composition of the reacting aqueous Ti(IV) species may vary depending on the concentration levels of Ti(IV), pH, HA and . The equilibrium constant (Kex) at 303 K is measured to be 101.117 and 10−1.243 for the reaction of monomeric, non-sulfated, mono, and non-hydrolyzed TiO2+, respectively. The effects of heptan-1-ol, temperature, loading, and diluent type have been reported. Stripping can be done effectively by a solution of 1 mol/dm3 H2SO4 containing 5%(v/v) of “100 volume” H2O2. The possibilities of separation of Ti(IV) from Cu(II), Zn(II), Fe(III), Co(II), and Ni(II) have been predicted. It is proved to be an effective extractant for Ti(IV)/Fe(III) separation from sulphate medium at pH ∼ 1.

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

ABSTRACT 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[SO42–])–1. The activation energy, Ea, 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 SN2 mechanism as suggested by high negative ΔS± values. However, in certain cases, the extraction process appears as intermediate controlled as supported by Ea value of less than ~48 kJ/mol.

KINETICS AND MECHANISM OF FORWARD EXTRACTION OF MN(II) FROM SULFATE-ACETATO MEDIUM BY CYANEX 272 DISSOLVED IN KEROSENE USING THE SINGLE-DROP TECHNIQUE

The flux of Mn(II) transfer in -Cyanex 272-kerosene system was investigated using the single-drop technique and the flux method of data treatment. The empirical flux equation at 303 K is: F f = 10−3.6 [Mn(II)] (1 + 104.5 [H+])−1 (1 + 1.58 [ ])−1. The activation energy (E a ) varies within 15–59 kJ/mol depending on experimental conditions. On analyzing the flux equation and with the help of E a values, it is concluded that either the extraction reaction step Mn2+ + A− → MnA+ or the diffusion of reactants (or products) to (or from) the reaction site is rate controlling depending on the reaction parameters. At high pH and at intermediate pH-higher temperature regions, low E a (≤20 kJ/mol) suggests that the process is under diffusion control. But at low pH and at intermediate pH-lower temperature regions, high E a (≥50 kJ/mol) suggests that the process is under chemical control. High negative ΔS ± value indicates that the slow extraction reaction step occurs by means of an SN2 mechanism.

Kinetics and Mechanism of Backward Extraction of Mn2+ from Mn2+-Cyanex 272 Complex Dissolved in Kerosene by Acidic Sulfate-Acetato Solution Using the Technique of Single Drop

The rate of acidic sulfate-acetato solution stripping of Mn2+ from kerosene solution of Mn2+-Cyanex 272 complex (MnA2) is investigated using the falling single drop technique. To study the kinetics of this process, the reaction orders and the value of backward extraction rate constant (kb) have been determined to get the Mn2+-transfer flux equation in backward extraction as: Fb = 10−4.88 [MnA2](o) (1 + 0.002 [H+]−1)−1 (1 + 5.13 ). The energy of activation (Ea), entropy variation on activation (ΔS‡), and the enthalpy variation on activation (ΔH‡) have also been determined. It is noticed that the reaction orders with respect to [H+] and , and the values of Ea, ΔS‡, and ΔH‡ depend on the concentration regions of H+ and used in stripping. The analysis of flux equation at low-concentration region of H+ and points out that the dissociation of A− from MnA+ is a rate-controlling chemical reaction step. On the other hand, at high-concentration regions of H+ and , the rate determining chemical reaction step is the replacement of A− in MnA+ by . In other conditions, the process is either diffusion or intermediate control. High negative ΔS‡ values indicate that the rate controlling chemical reaction steps occur via SN2 mechanisms. Rate data have been compared with the equilibrium data for the Mn2+-Cyanex 272 extraction system.

Kinetics of Forward Extraction of V(IV) in V(IV)-SO2- 4(H+, NA+)-Cyanex 302-Kerosene System Using Lewis Cell Technique

Kinetics of V(IV) extraction from acidic sulfate medium by Cyanex 302 (2,4,4-trimethylpentylmonothio phosphinic acid, [H2A2](o)) dissolved in kerosene were investigated using a Lewis cell operated at 3 Hz and flux (F) method of data treatment. The F (kmol/m2s) is inversely proportional to (1 + 0.01 [V(IV)]−1), (1 + 2000 [H+]), and (1 + 0.089 ) and directly proportional to (1 + 0.2 [ ]). The activation energy (E a ) depends on the temperature region and is a function of reactants (f(R)). When log f(R) <−1.0, E a > 48 kJ/mol and when log f(R)>−0.3, E a < 20 kJ/mol. Within log f(R) values of −1.0 to −0.3, E a varies within 20–50 kJ/mol. The rate constant (k) at 293 K is 10−7.335 kmol/m2 s. The entropy changes in activation (ΔS ‡) were measured as negative value always. The complicated empirical rate equation was analyzed to provide extraction mechanisms in different parametric conditions, being supported by E a values. In most cases, the extraction process is either diffusion controlled or mixed controlled; a mixed-controlled process can be converted to a diffusion-controlled process at a lower temperature region and to a chemical-controlled process at a higher temperature region. For systems with log f(R) <−1.0, the process is completely chemical controlled. The rate-determining chemical reaction steps in order are: → ; and → at lower and higher concentration regions of . The negative ΔS ‡ values suggest that the rate-determining chemical reaction steps occur by SN2 mechanisms.