Extraction equilibrium and extraction kinetics of nickel from aqueous ammonium nitrate solution with versatic 10 in n-hexane

The mechanism of extraction of nickel from an aqueous ammonia-ammonium nitrate mixture by an n-hexane solution of Versatic 10 was investigated from the viewpoint of extraction equilibrium and extraction kinetics. From the equilibrium study, it was found that nickel is extracted according to the following two extraction reactions which are in accordance with the loading ratio of nickel to Versatic 10:

$\text{Ni}{}^{\mathrm{2+}}\text{+ 3 H}{}_2\text{R}{}_{\mathrm{2org}}\text{?NiR}{}_2\text{·4 HR}{}_{\mathrm{org}}\text{+2 H}{}^{\mathrm{+}}{}_{\mathrm{aq}}$

in the range of lower loading ratio, and

$\text{2 Ni}{}^{\mathrm{2+}}{}_{\mathrm{aq}}\text{+ 4 H}{}_2\text{R}{}_{\mathrm{2org}}\text{?(NiR}{}_2\text{·2 HR)}{}_{\mathrm{2org}}\text{+4 H}{}^{\mathrm{+}}{}_{\mathrm{aq}}$

in the range of higher loading ratio. The equilibrium constants for each reaction were also determined. From the study of extraction kinetics, the extraction rate was found to be proportional to the total concentrations of nickel and Versatic 10 and inversely proportional to that of hydrogen ion. A reaction mechanism is proposed in order to give a reasonable explanation for the observed concentration dependence of each of the reactant species.     

The effect of pH on cadmium extraction by Lix 34

The pH dependence of the extraction of cadmium from nitrate solution using LIX 34 diluted with Kermac 470B has been studied. The optimum pH for cadmium extraction in the system studied is in the neighborhood of 8.3. Below pH 7, the reagent forms a two-to-one ligand to cadmium ion chelate, whereas, at pH greater than 7, the extraction mechanism is extremely complicated due to the presence of NH₃, NH₄⁺ and some other unknown buffers. Moreover, the difference between the initial and equilibrated aqueous pH values, ΔpH, can be estimated by the following equation

$\text{Delta;}\text{pH}\text{=}\text{log}\text{1}\text{1 +(i?2)}\text{[}\text{cd}\text{]}{}_0\text{[}\text{NH}{}_3\text{]}{}^{\mathrm{<mtext>I</mtext>}}$

where i is the average co-ordination number of cadmium by ammonia in the aqueous phase. [Cd]₀ represents the equilibrium cadmium concentration in the organic phase and [NH₃]^I denotes the initial aqueous ammonia concentration.     

The extraction of mercury(II) from concentrated HBr solutions by benzene. A comparison of various representations of single-ion activity coefficients in concentrated aqueous solutions

The extraction of tracer Hg(II) from aqueous HBr solutions can be described by the reaction

$\text{HgBr}{}_2\text{(aq)}\text{?}\text{HgBr}{}_2\text{(org)}$

This reaction has been used to test various conventions for the single-ion activity of bromide ion as well as chloride ion using data already published. It is found that {X^?} = y_x?C (y_x? given by a simple semiempirical equation cf. below) and {X^?} = C give a good fit, but the popular function {X^?} = y_±C does not work at all. It thus seems that it is better to use the stoichiometric concentration than its product with the mean ionic activity coefficient, and this simple convention for ligand activity might be a useful starting point when evaluating complex formation in concentrated electrolytes.The extraction of HgBr₂ by TLAHBr (TLA = trilaurylamine) dissolved in benzene can be fairly well described by the reaction

$\text{TLAHBr(org) + HgBr}{}_2\text{(aq)}\text{?}\text{TLAHBr·HgBr}{}_2\text{(org)}$

and the stoichiometric distribution coefficient D can be given by D = KD° (α_1,0 + α_1,0) where K is a constant and α_1,0 + α_1,1 the fraction of TLAHBr not containing acid in excess of the 1:1 composition.     

A study of equilibria in the extraction of uranium (VI) from aqueous sulphate solution by tri-n-octylamine in benzene or petroleum spirit

An account of a fundamental equilibrium study on the distribution of uranium(VI) between an acidic sulphate solution of ionic strength 1.0 and non-aqueous tri-n-octylammonium sulphate solutions of practical significance in the processing of uranium ores is given. Most previous work has concerned only the stoichiometry of U (VI) species. Experimental conditions were chosen to avoid aggregation effects. The study required aqueous phase pH between 2.6 and 3.6. A detailed model developed to describe the system and the quantitative data derived from its study are presented. For the reactions:

$\text{L}{}_2\text{SO}{}_4\text{+ UO}{}_2\text{SO}{}_4\text{?}\text{L}{}_2\text{UO}{}_2\text{(SO}{}_4\text{)}{}_2\text{and}\text{2}\text{L}{}_2\text{SO}{}_4\text{+ UO}{}_2\text{SO}{}_4\text{?}\text{L}{}_4\text{UO}{}_2\text{(SO}{}_4\text{)}{}_3$

equilibrium constants in the ranges 10³–10⁴ and 10⁶–10⁸ are obtained respectively, depending on the composition of the non-aqueous phase. (L₂SO₄ is amine sulphate and a bar indicates a non-aqueous species.) The effect of the composition of the non-aqueous phase (benzene or petroleum spirit, with or without 2-octanol) on the actual constants is discussed. The dissociative reaction

$\text{L}{}_4\text{(SO}{}_4\text{)}\text{? UO}{}_2\text{SO}{}_4\text{+}\text{L}{}_2\text{SO}{}_4$

with an equilibrium constant in the region of 10^?3 is obviously of little consequence.     

A study of chalcopyrite dissolution in acidic ferric nitrate by potentiometric titration

A pure chalcopyrite sample was studied using a potentiometric titration technique, which measures the oxidant consumption in the dissolution of sulphide mineral slurries in acidic ferric ion solutions. Rate measurements were made over a period of days at constant solution pH and oxidation potential at 25 and 40°C. Long term leaching followed the parabolic kinetics and dissolution stoichiometry previously described in the literature, but there was an initial reaction in which more iron than copper dissolved from the lattice and a metal-deficient “chalcopyrite-like” surface phase was rapidly formed. The subsequent dissolution reaction (observed specific reaction rate, $\text{s}{}_0\text{= 1.4 × 10}{}^{\mathrm{?11}}\text{mol cm}{}^{\mathrm{?2}}\text{s}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ at 25°C; activation energy, E_a = 14 kcal mol^?1) was far more sensitive to temperature change and much slower than the rate of pore diffusion of oxidant ($\text{s}{}_0\text{≈ 10}{}^{\mathrm{?7}}\text{mol cm}{}^{\mathrm{?2}}\text{s}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$, E_a ≈ 2 kcal mol^?1) and was interpreted in terms of a solid state diffusion step within the crystal lattice.     

The kinetics of the sulphuric acid leaching of nickel and magnesium from reduction roasted serpentine

Nickel may be extracted with partial selectivity over magnesium from laterites containing serpentine by reduction roasting followed by sulphuric acid leaching. This paper describes the results of a kinetic study of the sulphuric acid leaching of nickel and magnesium from the reduction roasted serpentine component of a typical laterite. The serpentine used in this work analyzed 1.65% nickel, 20.2% magnesium and 6.10% iron.Initially, leaches were carried out at temperatures of 30, 50 and 70° C to determine the acid requirement for complete nickel extraction using practical leaching conditions (25% solids) under which the acidity drops to a low level. A minimum acid addition of 60 g/l was needed, which gave 80% to 83% nickel extraction from material in which 85% of the nickel was reduced using hydrogen at 700° C. Under these conditions, about 17% of the magnesium was leached at each of the temperatures studied.To facilitate an understanding of leaching kinetics, leaches were then performed using constant acidities (0.1% solids) of 60, 30 and 15 g/l acid at temperatures of 30, 50 and 70° C. Closely sized particles (?65 + 100 mesh) were leached so that magnesium dissolution rates could be tested against established “shrinking core” models.The main conclusions are that, under the experimental conditions, nickel dissolution rates were chemically controlled by either $\text{2}\text{H}{}^{\mathrm{+}}\text{+}\text{1}\text{2}\text{O}{}_2\text{+ 2e →}\text{H}{}_2\text{O}$ or 2 H⁺ + 2e → H₂ occurring at the surfaces of the 40% nickel/iron alloy platelets formed during reduction. The rate controlling process had an activation energy of 11kcal/mole.During extraction of metallic nickel, the dissolution of magnesium follows a “shrinking core” kinetic model, which assumes the reaction is unimpeded by a surface layer of silica - a reaction product. Rates of magnesium dissolution during this stage of the reaction (up to 25% dissolved) were chemically controlled with an activation energy of 12 kcal/mole.At magnesium extractions above 25%, at which point all the metallic nickel had been extracted, the rate of silicate attack was limited by diffusion through a silica coating attached to particle surfaces.The results indicate that selectivity for nickel dissolution over that of magnesium does not depend strongly on acidity and temperature at the levels investigated.     

Selective extraction and separation of metals especially silver (and copper) using poly(2-S-vinyl-1,3,4-thiadiazole-5-thiol)

There have been many attempts to prepare polymeric reagents which are capable of selectively extracting metal ions such as those of silver. The title polymer (PVTT) was used to extract ions of Ag(I) and Cu from separate and mixed solutions. The polymer has a capacity of 1.86 mol kg^?1 of Ag(I) with respect to the dry polymer from silver nitrate solution and 0.88 mol kg^?1 of Cu from copper(II) chloride solution. In a mixed Ag(I) and Cu(II) nitrate solution only the Ag(I) is extracted. The polymer does have low capacities for many other ions including Fe(II), Fe(III), Co(II), Ni(II) and Zn(II). The time ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) for the silver uptake on half the sites of the polymer is well under five minutes at pH 5. The polymer is cheap and stable and, for example, is not subject to hydrolysis under the conditions used for metal extraction and can be made from readily available chemicals. The silver can be eluted from the polymer-silver complex using KCN (0.1 M). The time ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) for half of the silver to be eluted is under five minutes. The regenerated polymer can be used for repeated separations without loss of capacity. When copper ions are complexed by the polymer there is evidence that some, at least, of the ions are reduced to Cu(I). The time ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) for copper extraction is approximately five minutes and the copper is probably eluted as a Cu(I) species.In the copper complex of 2-S-methyl-1,3,4-thiadiazole-5-thiol (MTT) the copper is present entirely as Cu(I). The bonding in this and the corresponding Ag complex is thought to involve the 2-S-methyl and 5-thiol sulphur atoms which gives rise to polymeric species with linear SMS stereochemistry. The bonding in the polymer-metal compounds is thought to be similar. The selectivity of the polymer for Ag(I) ions arises from the ability of the thiol group to bond to this ion which causes it to separate out of solution. The polymer is able to satisfy the stereochemical requirement of the silver ion. The thiadiazole ring is resistant to oxidation or reduction under the conditions required for metal extraction purposes. The presence of NH groups on the ring increases the hydrophilicity of the polymer and enables rapid diffusion of the aquated ions to the site of co-ordination. The regenerated polymer can be used for extracting Ag(I) ions from very dilute (5 mg/l solutions.     

Solvent extraction of Ti(IV), Fe(III) and Fe(II) from acidic sulfate medium with di-o-tolyl phosphoric acid-benzene — hexan-1-ol system: A separation and mechanism study

The extraction of Ti(IV), Fe(III) and Fe(II) with di-o-tolyl phosphoric acid (HDTP, HA)-benzene-20% hexan-1-ol system was studied as function of contact time, concentrations of extractant in the organic phase and of H₂SO₄ in the aqueous phase, and temperature. The order of extractability under identical conditions is: Ti(IV) > Fe(III) ? Fe(II). The relative separations of these metal ions are also dependent on the above four factors. The maximum values of the separation factors, $\text{β}{}_1\text{=}\text{E}{}_{\mathrm{<mtext>Ti(IV)</mtext>}}{}^0\text{E}{}_{\mathrm{<mtext>Fe(IlI)</mtext>}}{}^0\text{= 175}$ at 0.10 M HDTP and 3.50 M H₂SO₄ concentrations, and $\text{β}{}_2\text{=}\text{E}{}_{\mathrm{<mtext>Ti(IV)</mtext>}}\text{E}{}_{\mathrm{<mtext>Fe(II)</mtext>}}{}^0\text{= 7800}$ at 0.10 M HDTP and 0.50 M H₂SO₄ concentrations, indicate that the separation of Ti(IV) from iron seems to be promising if iron is present in the divalent state. The mechanisms of extraction are discussed.     

Kinetic and mechanistic study of FeS dissolution in aqueous sulfur dioxide solution

FeS leaching was carried out in aqueous sulfur dioxide solution at low temperature and pressure (T = 60°CC;P_SO2 = 51.7 kPa) using both a constant-pressure gas-uptake apparatus and conventional glass-leaching equipment. In the initial stages of the leaching reaction the ratio [SO₂]/[Fe²⁺] was found equal to 1.3. This suggests a stoichiometry given by the following sequence of equations

$\text{FeS + SO}{}_2\text{·H}{}_2\text{O ? FeS + H}{}^{\mathrm{+}}$

$\text{FeS · HSO}{}_3{}^{\mathrm{?}}\text{+ H}{}^{\mathrm{+}}\text{→ Fe}{}^{\mathrm{2+}}\text{+ H}{}_2\text{S + SO}{}_3{}^{\mathrm{2?}}$

As the reactions progressed a build up of various oxy-sulfur species was observed.The leaching process appears to proceed by two concurrent dissolution paths, namely acid dissolution and aquated sulfur dioxide dissolution. In both cases the rate determining step (r.d.s.) involves a surface desorption reaction. In the constant leaching region, the kinetics can be represented by the following rate expression:

At low [H+] relative to [SO₂-H₂O], path I predominates. This can be represented by:

$\text{|}{}_{\mathrm{s}}\text{FeS +SO}{}_2\text{· H}{}_2\text{O ? |}{}_2\text{FeS SO}{}_2\text{· H}{}_2\text{O}$

$\text{|}{}_{\mathrm{s}}\text{FeS SO}{}_2\text{· H}{}_2\text{O ? |}{}_{\mathrm{s}}\text{FeS HSO}{}_3{}^{\mathrm{?}}\text{+ H}{}^{\mathrm{+}}$

$\text{|}{}_{\mathrm{s}}\text{FeS HSO}{}_3{}^{\mathrm{?}}\text{→ Fe}{}^{\mathrm{2+}}{}_{\mathrm{(aq)}}\text{r.d.s.}$

At high [H⁺] relative to [SO₂·H₂O], path II predominates. This can be represented by:

$\text{|}{}_{\mathrm{s}}\text{FeS + H}{}^{\mathrm{+}}\text{? |}{}_{\mathrm{s}}\text{FeS H}{}^{\mathrm{+}}$

$\text{|}{}_{\mathrm{s}}\text{FeS H}{}^{\mathrm{+}}\text{→ Fe}{}^{\mathrm{2+}}{}_{\mathrm{(aq)}}\text{r.d.s.}$

The apparent activation energy was found to be 41.6 kJ per mole.     

Reaction kinetics for the leaching of MnO2 by sulfur dioxide

The reaction kinetics for the leaching of MnO₂ by sulfur dioxide have been studied using studied using monosize particles at dilute solid phase concentrations in a stirred reactor to determine the important chemical factors which govern the kinetic response of the system. The conclusion that the reaction rate is limited by a chemical reaction at the MnO₂ surface is supported by: (1) an apparent activation energy of 35.9 kJ/mol (8.6 kcal/mol), (2) the inverse first-order relationship between the rate constant k and the initial particle diameter, (3) the independence of the reaction rate on stirring speed and, more importantly, the magnitude of the calculated reaction velocity constant (～10^?3 cm/s compared to predicted mass-transfer coefficients of 10^?2 cm/s), and (4) the one-half order dependence of the reaction rate with respect to the SO₂ concentration.The rate-limiting step is considered to be an electrochemical surface reaction, a conclusion which is substantiated by electrode half cell potential measurements. Using the Butler-Volmer equation, a theoretical analysis of the electrochemical reaction resulted in the following rate equation:

which was consistent with the experimental results.     

Extraction of metals using poly[N-(dithiocarboxylato)-iminoethenehydrogenoiminioethene]

The polymer poly [N- (dithiocarboxylato)iminoethenehydrogenoiminioethene] (PIED) reacts with metal ions such as iron, cobalt, nickel, copper, zinc and silver to produce stable compounds in which the metal is co-ordinated to the sulphur atoms in the dithiocarboxylate groups. The capacity of the polymer PIED for a particular metal is a function of the sulphur content, pH, complexing agents, and other metals which are present in solution. The polymer rapidly takes up the metals (e.g. Co²⁺ at pH 6.5 has a $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of one and a half minutes). The polymer is stable between pH values of 6.5 and 9.0 but rapidly decomposes at low pH due to the protonation of the amino group adjacent to the dithiocarboxylate groups and the loss of carbon disulphide. The pK_a values of these amino groups is over the range 3.5 to 6.5. Above a pH of 10 the polymer dissolves but is reprecipitated on the addition of acid. The stable metal—polymer complexes can be used for metal extractions over a wide pH range e.g. cobalt(II)—PIED can be used to extract silver from a solution containing cobalt and silver. Consequently the metal salts are recommended for metal extraction. It is not possible to elute the metals using standard reagents such as cyanide but the cobalt—PIED is reduced by hydrogen at 1400 K to give cobalt metal although the polymer backbone is destroyed. The nickel(II)—PIED compound can be quantitatively oxidised to nickel(IV)—PIED which is stable in air and in which all of the nickel ions are oxidised to nickel(IV).     

The oxidation of Fe(II) in aqueous sulphuric acid under oxygen pressure

An experimental investigation is presented on the oxidation of Fe(II) in aqueous sulphuric acid under oxygen pressure. The effects of partial oxygen pressure, p_O2, temperature and initial concentrations of H₂SO₄ and Cu(II) on the oxidation process rate have been determined within the ranges applied in a new hydrometallurgical process for copper recovery from its sulphide concentrates [13–16]. The Fe(II) oxidation reaction rate was found to be described by a second-order kinetic equation at a ferrous iron concentration exceeding 3–8 g/l:

     

A numerical method for computing hydrometallurgical activity-activity diagrams

A modification of the DIAGRAM computer program has been developed to facilitate graphical representation of hydrometallurgical equilibria. The method is based on dissociation equations with corresponding log equilibrium constants, K_i, and log reaction quotients, Q_i; K_i equals Q_i at equilibrium. The ith dissociation equation is written in terms of Q_i, the log activity of the ith metallic species (P_i), and a certain set of variables (V_j), representing the log activities of species whose stability fields are not to be plotted (e.g., log{Me²⁺}, log{e}, log{H⁺}):

$\text{Q}{}_{\mathrm{i}}\text{= B}{}_{\mathrm{i}}\text{P}{}_{\mathrm{i}}\text{+}\text{∑}\text{j=i}\text{n}\text{C}{}_{\mathrm{ij}}\text{V}{}_{\mathrm{j}}$

where B_i is the reaction coefficient of the ith metallic species in the ith dissociation equation, and C_ij is the reaction coefficient of the jth variable in the ith dissociation equation. One of the variables is designated the balancing variable and allows comparison of the relative stability of any two metallic species to be made in terms of a single equation. By means of the balancing variable, the program generates internally the m(m?1)/2 relative stability equations linking pairs of the m metal-containing species. The stability region of each metallic species is then determined by a systematic scanning of the plotting area using the criterion (K_L>Q_L?). DIAGRAM can calculate and plot stability diagrams using any two of the system variables. Thus not only Eh-pH diagrams, but additional plots of log {Metal}-pH, log{Metal}-Eh, log{NH₂ + NH₄⁺}-pH, etc. can be generated readily. The numerical and thermodynamic bases of the program are described and the capability of DIAGRAM is illustrated with some selected hydrometallurgical examples.     

Single cell extraction of zinc and manganese dioxide from zinc sulphide concentrate and manganese ores

The hydrometallurgical processing of zinc sulphide concentrates with sulphuric acid in the presence of manganese dioxide (manganese ore has been employed) and subsequent electrolytic co-deposition of cathodic zinc metal and anodic manganese dioxide is described.The influence of various parameters on the reaction

$\text{ZnS + MnO}{}_2\text{+ 2H}{}_2\text{SO}{}_4\text{= ZnSO}{}_4\text{+ MnSO}{}_4\text{+ S}{}^0\text{+ 2H}{}_2\text{O}$

has been studied. Optimum conditions for rapid and efficient reaction have been determined.The simultaneous electrowinning of zinc at the cathode and γ-MnO₂ at the anode from the leach liquor was studied. The effects of variation of current density, temperature, electrolyte composition etc. have been described in detail. During leaching 99% extraction of zinc, 98% of manganese, and 96% liberation of elemental sulphur was achieved. 80–90% anodic and cathodic current efficiencies can be obtained under optimum conditions with impurity levels of only a trace of manganese in the zinc deposit and vice-versa.The anodically deposited manganese dioxide was the γ-battery active variety and was found to be satisfactory.The results indicate the potential for the development of a technique for zinc and manganese dioxide production in a single cell.