Properties of electrolyte solutions relevant to high concentration chloride leaching I. Mixed aqueous solutions of hydrochloric acid and magnesium chloride

A computer code based on a Pitzer model has been developed for the comprehensive prediction of the thermodynamic properties of MgCl₂–HCl aqueous solutions over a wide range of conditions from 25 to 120 °C and from 0–350 g L^− 1 chloride. This code was applied to the calculation of (i) water activities and mean ionic activity coefficients for mixed aqueous solutions of hydrochloric acid and magnesium chloride over a wide range of concentrations and to 100 °C, (ii) solubilities of MgCl₂·6H₂O in MgCl₂–HCl solutions to 80 °C, (iii) partial pressures of HCl(g) and H₂O(g) over MgCl₂–HCl aqueous solutions at various temperatures and (iv) partial pressures of HCl(g) at the normal boiling point of these mixed electrolyte solutions. The model predictions are in excellent agreement with available experimental data and confirm evidence from the literature that MgCl₂(aq) and HCl(aq) mix almost ideally at constant water activity.     

Cadmium extraction from chloride solutions with model N-alkyl- and N,N-dialkyl-pyridine-carboxamides

N-alkyl- and N,N-dialkyl-pyridine-carboxamides with the amide group at the 2nd, 3rd or 4th position were used to recover cadmium(II) from acid chloride solutions. It was found that N,N-dialkyl-pyridine-carboxamides in toluene diluent are effective extractants for the recovery of cadmium from chloride solutions at pH < 2. Cadmium extraction ability rises as the distance of the amide group from the pyridine nitrogen increases. In strongly acid chloride media, extractants (L) with N,N-dialkyl-amide group at position 3 or 4 in the pyridine ring form cadmium ion pairs: (LH⁺)₂(CdCl₄²⁻) but the dialkyl derivative of picolinamide probably forms the complex (LH⁺)₂(CdCl₄²⁻)(LHCl). Monoalkyl-pyridine-carboxamides are not suitable for cadmium extraction from chloride solutions because in weak-acid systems (pH > 3, [Cl⁻] = 0.02–4 M) the N-alkyl-pyridine-3-carboxamides form very slightly soluble cadmium complexes and the N-alkyl-pyridine-2-carboxamides do not extract cadmium(II) from chloride solutions under these conditions. In strongly acid systems ([HCl] = 0.01–4 M) N-alkyl-pyridine-2-carboxamide with a branched carbon chain is ineffective, but the hydrochlorides and cadmium complexes of the rest of the N-alkyl-amides are slightly soluble in hydrocarbon diluents. In ethanol solutions hydrophobic pyridine-3-carboxamides form (CdCl₂)_nL₂ complexes (n = 2 or 3) with cadmium chloride.     

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.     

Cathodic deposition of copper in the presence of aqueous sulfurous acid,bivalent aquacobalt ion,or both using a stainless steel cathode and a graphite anode

A study on cathodic deposition of copper in acidic aqueous sulfate solution has been carried out using a stainless steel cathode and a graphite anode. The individual and the combined effects of added [H₂SO₃·aq] and [Co²⁺·aq] on cathode potential, current efficiency, crystal orientations, and deposit morphology have been investigated and are compared. The maximum decrease of ≿50 pct in cathode potential is more pronounced in the presence of ≿10.25 g/L of H₂SO₃ alone in the electrolyte than that (≿30 pct) in the presence of ≿100 ppm of added Co²⁺ (aq) alone; however, the presence of added Co²⁺ (aq) along with H₂SO₃ (aq) does not cause further decrease in cathode potential in comparison to that observed in the presence of only H₂SO₃ (aq) in the electrolyte. The current efficiency is found to decrease in the presence of [H₂SO₃·aq] in the range of 1.32 to 30.75 g/L or in the presence of added [Co²⁺·aq] in the range of ≿10 ppm to 600 ppm, while the decrease of about 4 pct in current efficiency is more pronounced in the presence of only H₂SO₃ (aq) in the electrolyte, it is about 2 pct in the presence of only added Co²⁺ (aq) in the same electrolyte. The addition of Co²⁺ (aq) to the electrolyte containing H₂SO₃ (aq) does not alter the current efficiency (94 pct) of copper at the cathode. The linear sweep voltammetry (LSV) method was used to study the effect of added [H₂SO₃·aq], [Co²⁺·aq], or both, on the copper deposition at the cathode. The presence of each of these two additives or both causes a depolarization effect; the extent of the depolarization depends on the concentration of H₂SO₃ (aq), Co²⁺ (aq), and the current density. X-ray diffraction (XRD) data suggest that there is a change in the order of the preferred crystal orientations (viz., from the (220) plane in the absence of added H₂SO₃ (aq) and Co²⁺ (aq) to the (111) plane in the presence of added H₂SO₃ (aq) and Co²⁺ (aq) in the electrolyte solution) due to a change in the preferred plane of relative crystal growth. Results of scanning electron microscopy (SEM) indicate that cathode deposits of better surface morphology due to small-sized crystallites are found in the presence of added H₂SO₃ (aq)+Co²⁺ (aq) in the electrolyte solution. 1000 ppm=1.0 g/L=1.0 × 10⁻³ kg dm⁻³     

Transgranular stress-corrosion cracking of disordered Cu-25Au in aqueous chloride and sulfate media

Transgranular stress-corrosion cracking (T-SCC) in disordered copper-25 at. pct gold single crystals was studied in two chloride media: 2 pct (0.13 M) FeCl₃ and oxygen-free 0.6 M NaCl. A limited number of tests were also performed on polycrystals in the chloride media and also in acidified 1 M Na₂SO₄. Potentiostatic polarization, constant deflection tests, and high-resolution SEM examination were used to relate the electrochemical and fractographic features of T-SCC in these systems. Exclusive selective electro-dissolution of copper occurs over the potential domain investigated, and the polarization behavior is characterized at low potentials by a “passive≓ domain in which the current is very low (2 to 4 microamps/cm²), increasing only very slowly with increasing potential up to a “transpassive” potential,E _c. AboveE _c the current increases by a factor of 10₃ in a very narrow domain of rising potential ( ≈ 50 mv). In both chloride media E_c was found to be +430 mv (sce). At and above E_c a porous gold-rich “sponge” is readily formed on the surface, and in aq. FeCl₃ metallographic evidence for sponge formation was also found in the low-current region of potential, well below E_c. In all three media, fracture surfaces display the characteristic cleavage-like features scen in other T-SCC systems. For the constant deflection loading employed in the present investigation, the lower limit of potential for susceptibility to cracking in aq. NaCl occurs at +400 mv (sce), which is slightly below E_c; whereas, for aq. FeCl₃ the limiting potential is 0 mv (sce), considerably belowE _c. For both chloride media, the upper limit, if it exists, is greater than +600 mv (sce). These results are analyzed in order to distinguish between proposed mechanisms for T-SCC. T.B. CASSAGNE, formerly with the Department of Mechanical and Materials Engineering, Vanderbilt University     

The solvent extraction of zinc chloride with di-n-pentyl pentaphosphonate

The extraction of divalent zinc from aqueous solutions containing sodium chloride using di-n-pentyl pentaphosphonate [C₅H₁₁PO(OC₅H₁₁)₂] in kerosene has been investigated.Equilibrium data were in good agreement with equations of the form x/y = a + bx, where coefficients a and b have been mathematically demonstrated to have a physicochemical meaning: a is the reciprocal of the distribution coefficient at infinite dilution and b is the reciprocal of the maximum loading capacity of the organic solution.By adjusting the extraction isotherms to such a type of equation by the least-squares method, the effects of chloride concentration in the aqueous phase and di-n-pentyl pentaphosphonate (DPPP) concentration in the organic phase were determined, showing that the extraction of divalent zinc from chloride solutions by DPPP proceeds according to the solvating reaction:

$\text{Zn}{}^{\mathrm{2+}}\text{(a) + 2Cl}{}^{\mathrm{?}}\text{(a) + 2 DPPP(o) ? ZnCl}{}_2\text{· 2DPPP(o)}$

where (a) and (o) represent aqueous and organic phases respectively.The extraction equilibrium constant of such a reaction was also determined, resulting in K_EX = (30°C). Moreover, a mathematical model for the extraction reaction was established, allowing the calculation of equilibrium data as a function of the initial aqueous chloride concentration and organic DPPP concentration. Values of such data are given in comparison with experimental data and their perfect agreement demonstrates the validity of the theoretical model which will be used in a computer program for process flow-sheet simulation.     

Thermal expansion in the Ni−Cr−Al and Co−Cr−Al systems to 1200°C determined by high-temperature X-ray diffraction

The effect of temperature on the lattice parameters of phases in twelve nickel-chromium-aluminum (Ni?Cr?Al) alloys and nine cobalt-chromium-aluminum (Co?Cr?Al) alloys was determined using high temperature diffraction (HTXRD). The temperature range was from 25 to 1200°C. The data for each phase of each alloy were computer fit to an empirical thermal expansion equation developed in this study: \(LP_T = LP_{25^\circ C} (1 + R)^{(1 + T/273)^{1.5} } \) and a value forR was derived for each. Excellent fits were obtained for nearly all cases. A comparison ofR values revealed that for a given phase (ψ/ψ′, β and α in Ni?Cr?Al and αCo and β in Co?Cr?Al),R was independent of alloy composition. In the Ni?Cr?Al systemR for γ/γ′ was 19.2×10^?4,R for β was 19.9×10^?4 andR for αCr was 13.4×10^?4. In the Co?Cr?Al system theR value for αCo was 20.9×10^?4 and theR for β was 17.8×10^?4. Of all of the phases only the αCr in the Ni?Cr?Al system had anR sufficiently low to reduce to an unimportant level the stress generated from thermal expansion mismatch between Al₂O₃ and substrate or coating and substrate with either Ni?Al or Co?Al coatings on a γ/γ′-δ substrate.     

A ferric chloride hydrometallurgical process for recovery of silver from electronic scrap materials

A hydrometallurgical method for the recovery of silver from electronic scrap materials is suggested. Electronic scrap materials, containing silver with the accompanying brass and beryllium bronze, are leached at 80°C with ferric chloride. The leaching should be carried out with the concentration of ferric chloride and phase ratio chosen so that in the final phase of leaching the concentration ratio of Fe(III) to Fe(II) is not lower than 1. Under such conditions silver is found to be only slightly solubilized. This was confirmed by electrochemical studies.Potentiodynamic studies of the behaviour of silver in hydrochloric acid demonstrated that at the electrode potential value of 0.77 V, corresponding to the redox potential at 25°C of the solution where the concentration ratio [Fe(III)]/[Fe(II)] = 1, the silver surface is passivated not only by silver chloride but also by silver oxide. This prevents solubilization of silver in chloride solutions owing to the formation of AgCl₂^? and AgCl₃^2? complexes. The lowering of the solution oxidation potential resulting from consumption of Fe³⁺ ions during the leaching process causes a sudden increase in silver concentration in solution.     

Solvent extraction of metals by carboxylic acids

The solvent extraction behaviour of solutions of Versatic 10, naphthenic, 2-bromodecanoic and 3,5-diisopropylsalicylic acids in xylene towards a large number of metal cations is described. The effect of the structure of the carboxylic acids upon their extraction behaviour is discussed, and relationships between the experimental pH_0.5 values and characteristic properties of the metal cations, such as the stability constants of carboxylate complexes and ionic radii, are examined.For some metals (Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pd²⁺, Fe³⁺, AI³⁺, Ga₃₊, In³⁺, and Tl³⁺), a comparison of their extraction from nitrate and, chloride media has been made, and the observed differences have been quantitatively related to the formation constants of the chloro-complexes of the respective metals.     

Extraction of chromium(III) from sodium chloride solutions by means of carboxylic acids

Studies of Cr(III) extraction with carboxylic acids showed that the extraction process takes place at a pH of the aqueous phase ranging from 4 to 5. It was shown that sodium chloride is active with respect to chromium(III) as a salting-out agent. For extraction of Cr(III) with hexanoic acid it was shown that in the organic phase trinuclear complexes of the [Cr(OH)R₂·HR]₃ formula are formed.     

Aliphatic Non-Chelating Aldoximes as the Effective Extractants for Recovery and Separation of Nickel and Cobalt from Halide and Thiocyanate Solutions

Nickel recovery from solutions containing nickel and cobalt is a problem because the cobalt oxidation in the organic phase and the slow rate of nickel extraction, or small value of separation coefficient (β_Ni/Co) are characteristic of many extraction systems suggested for this purpose. The extraction systems with aliphatic non-chelating aldoximes do not have the above-mentioned shortcomings.

The extraction of metal halides from acid solutions by aliphatic aldoximes occurs by coordination. Cobalt in extracts does not oxidize during a day or more. The extraction and stripping equilibriums are reached in 2-5 min. During extraction, Ni and Co do not form mixed extraction complexes. β_Ni/Co increases with halide-ions concentration rising in aquoeus phase and is approximately equal to 100 at their concentration > 3 M/l. From chloride to bromide solutions the distribution coefficients of Ni and Co (D_Ni, D_Co) decrease, but β_Ni/Co does not decrease. In extraction from thiocyanate solutions D_Ni, D_Co and β _Ni/Co reach the values comparable with the same in extraction from chloride solutions, but the process of metal extraction is accompanied by co-extraction of HSCN. The dependence of Ni recovery on out-salting cation has been investigated. Ni recovery has been shown to increase in the order: Na⁺ < Ca²⁺ < Al³⁺, which could have resulted from increasing of hydration energy of out-salting cation.

Rising of the chain length of alkyl radical in the order: heptaloxime, nonaloxime, decaloxime, 2-methyldecaloxime brings some decrease of D_Ni and D_Co, however does not influence the β_Ni/Co value.

The optimum conditions for extraction separation of Ni and Co by aldoximes from halide and thiocyanate solutions have been determined.     

The dissolution of chalcopyrite in ferric sulfate and ferric chloride media

The literature on the ferric ion leaching of chalcopyrite has been surveyed to identify those leaching parameters which are well established and to outline areas requiring additional study. New experimental work was undertaken to resolve points still in dispute. It seems well established that chalcopyrite dissolution in either ferric chloride or ferric sulfate media is independent of stirring speeds above those necessary to suspend the particles and of acid concentrations above those required to keep iron in solution. The rates are faster in the chloride system and the activation energy in that medium is about 42 kJ/mol; the activation energy is about 75 kJ/mol in ferric sulfate solutions. It has been confirmed that the rate is directly proportional to the surface area of the chalcopyrite in both chloride and sulfate media. Sulfate concentrations, especially FeSO₄ concentrations, decrease the leaching rate substantially; furthermore, CuSO₄ does not promote leaching in the sulfate system. Chloride additions to sulfate solutions accelerate slightly the dissolution rates at elevated temperatures. It has been confirmed that leaching in the ferric sulfate system is nearly independent of the concentration of Fe³⁺, ka[Fe³⁺]^0.12. In ferric chloride solutions, the ferric concentration dependence is greater and appears to be independent of temperature over the interval 45 to 100 °C.     

Extraction of cadmium from phosphoric acid solutions with amines Part I. Extractant selection,stripping, scrubbing and effects of other components

Cadmium can be effectively removed from wet-process phosphoric acid (WPA) by solvent extraction using long-chain amines, preferably tertiary amines, as extractants. Stripping can be performed either with water or with acids such as phosphoric or sulphuric acid depending on the final conversion of the cadmium waste. Scrubbing could be necessary in some cases and can be performed with alkali.A factorial design experiment was performed to determine the effects of four different components (H₂SO₄, HCl, HF, H₂SiF₆) in WPA on cadmium extraction with Alamine 336. The largest influence on cadmium extraction is seen for the hydrochloric acid, drastically increasing the distribution coefficient. Variations of the concentrations of H₃PO₄, HCl, HF, Fe and Al were also studied. The extraction of cadmium was seen to be strongly dependent on phosphoric acid concentration.A simple extraction model is proposed indicating that CdCl₄^2? ions are extracted.     

Removal of iron and formation of copper(i) from solutions containing iron(ii) and copper(ii) by addition of chloride ion or acetonitrile

Solutions of Cu(II) and Fe(II) establish the redox equilibrium

$\text{Cu(II) + Fe(II)}\text{?}\text{K}\text{Cu(I) + Fe(III)}$

which is displaced to the right by addition of either Cl^? or acetonitrile (AN). Log K varies from ?10.5 in water to about ?2.5 in 4 M NaCl or AN, allowing iron to be removed selectively from copper (II) solutions either by solvent extraction with Versatic acid or by precipitation as goethite or j jarosite. To establish the required conditions Eh-pH diagrams have been developed for the CuH₂OCl and CuH₂OANSO₄²-systems at 25°C and 90°C. It is demonstrated that the catalytic effect of Cu(II) on the oxidation of Fe(II) to Fe(III) by O₂ is dependent on the concentration of Cl^? or AN and on the position of this redox equilibrium. Applications to removing iron from hydrometallurgical solutions are discussed and tested.     

Some physicochemical properties of aluminum and iron chloride solutions

Some physicochemical properties of aluminum and iron chloride solutions are considered. The density and viscosity of aluminum and iron chlorides are plotted as functions of the FeCl₃/(FeCl₃ + AlCl₃) ratio and temperature, and pH of aluminum hydroxochlorides is plotted as a function of the Al₂O₃ content in a solution and its basicity (ratio of contents Al/Cl). The joint solubility of aluminum hydroxochloride and sodium chloride in water has been analyzed.     

Extraction equilibria in the system GaCl3-AlCl3-HCl-H2O-tributyl phosphate

Partition equilibria and solution chemistry of the system GaCl₃-AlCl₃-HCl-H₂O-tributyl phosphate is characterized by a simultaneous extraction of gallium chloride, hydrochloric acid, and water by a solvating mechanism. The salting-out power of the aqueous phase was explained by taking into account the stability of aluminum chloride and gallium chloride complex species and the calculated concentration of free chloride ions actually available for the extraction of gallium. Three gallium extraction mechanisms in the range of compositions studied are the extraction of GaCl₃ at low H⁺ and salt concentrations, the extraction of GaCl^- ₄ at moderate H⁺ and salt concentrations, and the competition between the extraction of GaCL^-4 and an HC1-TBP complex at high H+ and salt concentrations. The extraction of gallium over a wide range of distribution ratios (D = 1 to 1 x 10⁴) could be represented by a chemically based model taking into account the free chloride concentration and the activity coefficient of the total chloride ions. Formerly Visiting Scientist, Ames Laboratory, USDOE     

Etude spectrophotometrique de solutions aqueuses chlorurees de chlorure cuivreux,a concentrations elevees

The behaviour of CuCl was investigated from 10^?3M up to quasi saturation by absorption spectrophotometry between 200 and 1000 nm, in aqueous solutions of (NaCl + HCl), 1 to 5 M, at pH 0 and 25°C. The spectra show a shoulder at 230–235 nm and two bands, respectively at 195–215 nm and at 273–290 nm (273 to 275 nm for solutions of up to 4 M Cl^? and 5 M Cl^? solutions with (CuCl) < 0.6 M, and 275 to 290 nm for 5 M Cl^? solutions with (CuCl) < 0.6 M. The shoulder corresponds to the complex ion CuCl₂^?; the band at 273–275 nm to the complex ion CuCl₃^2? and the one at 275–290 nm to the stepwise formation of the dinuclear complex ion Cu₂Cl₄^2?. The equilibrium constant for the reaction CuCl₂^? + Cl^? ?CuCl₃^2? was determined to be 0.45. At 273–275 nm, the Lambert-Beer law is satisfied for all concentrations of dissolved copper up to quasi saturation when the Cl^? (Na⁺ + H⁺) concentration does not exceed 4 M. A diagram showing the concentrations of the complex copper species in terms of CuCl and (NaCl + Hcl) concentrations has been established.     

An investigation of the thermodynamics and kinetics of the ferric chloride brine leaching of galena concentrate

The solution thermodynamics of acidified ferric chloride brine lixiviants and the dissolution kinetics of a galena concentrate in such solutions have been investigated. The distribution of the various metal chloro complexes calculated from available thermodynamic data shows that the distribution is shifted to the higher complexes, predominantly FeCl ₃ ^o , FeCl ₂ ^o , and PbCl ₄ ⁼ , as the total Cl^? concentration increases, and that the distribution is unaffected by the extent of reaction. The dissolution of PbS concentrate is presented as a competition between a nonoxidative reaction with H⁺ and the oxidative reaction with ferric ion. Acid dissolution of PbS predominates when the activity ratio of hydrogen ion to ferric ion is high. Under these conditions H₂S is produced. When the activity ratio of hydrogen ion to ferric ion is low, and especially when the concentration of Fe³⁺ is greater than 0.15 M, oxidative dissolution of PbS becomes the controlling reaction. The dissolution can be represented by a shrinking core model with a surface chemical reaction as the rate controlling step. This is supported by the activation energy of 72.1 kJ/mole and the dependence of the rate on the inverse of the particle radius. The following rate equation was found to be in excellent agreement with the experimentally observed leaching behavior for 0.15 to 0.6 M [Fe⁺³] _T up to approximately 90 to 95 pet extraction: $$1 - \left( {1 - \alpha } \right)^{1/3} = \left[ {\frac{{2.3 x 10^{12} }}{{r_0 }}\left[ {{\text{Fe}}^{{\text{ + 3}}} } \right]_T^{0.21} \exp \left( {\frac{{ - 72100}}{{{\text{R}}T}}} \right)} \right]t$$ The rate deviates from the 0.21 order for Fe⁺³ concentrations greater than 0.6 M. The deviation from the surface model at higher values of PbS conversion is due to the presence of solid PbCl₂ in the pores of the reacting particles.     

The extraction of Zinc(II) from sulphate and chloride solutions with kelex 100 and versatic 911 in kerosene

Zinc(II) is extracted from sulphate or chloride solutions by Kelex 100 (HX) in kerosene, comparable extraction taking place under more acid conditions from chloride media. The addition of Versatic 911 (HA) leads to synergistic enhancement of extraction; equilibrium studies with the mixed extractants indicate that a mixed complex of the form ZnX₂ · (HA)₂ is extracted, and infra-red spectra suggest that Versatic is present as a solvating agent. The effect of chloride ion concentration on extraction was examined, and tracer studies showed that chloride takes no part in the constitution of the extracted zinc complex.     

Effective Dissolution of Platinum by Using Chloride Salts in Recovery Process

Platinum (Pt) is typically recovered by employing dissolution processes in aqueous solutions; however, these processes require a long processing time and considerable quantities of acids with strong oxidants owing to the high chemical stability of Pt. In order to develop an efficient dissolution process, we studied chlorination treatments for Pt prior to dissolution. Chlorination was carried out at 673?K to 873?K (400?°C to 600?°C) using copper(II) chloride (CuCl₂) as a chlorine source. While pure Pt was insoluble in hydrochloric acid (HCl(aq)), the entire Pt component of the treated sample dissolved in HCl(aq) under certain conditions. Therefore, the proposed method can be used as a new, environmental friendly Pt recovery process.