Dissolution kinetics of malachite in ammonia/ammonium carbonate leaching

The leaching of oxide copper ore containing malachite, which is the unique copper mineral in the ore, by aqueous ammonia solution has been studied. The effect of leaching time, ammonium hydroxide, and ammonium carbonate concentration, pH, [NH₃]/[NH₄⁺] ratio, stirring speed, solid/liquid ratio, particle size, and temperature were investigated. The main important parameters in ammonia leaching of malachite ore are determined as leaching time, ammonia/ammonium concentration ratio, pH, solid/liquid ratio, leaching temperature, and particle size. Optimum leaching conditions from malachite ore by ammonia/ammonium carbonate solution are found as ammonia/ammonium carbonate concentrations: 5 M NH₄OH+0.3 M (NH₄)₂CO₃; solid/liquid ratio: 1:10 g/mL; leaching times: 120 min; stirring speed: 300 rpm; leaching temperature: 25 °C; particle size finer than 450 μm. More than 98% of copper was effectively recovered. During the leaching, copper dissolves as in the form of Cu(NH₃)₄⁺² complex ion, whereas gangue minerals do not react with ammonia. It was determined that interface transfer and diffusion across the product layer control the leaching process. The activation energy for dissolution was found to be 15 kJ mol⁻¹.     

The extraction of nickel from ammoniacal media and its separation from copper,cobalt and zinc using hydroxyoxime extractants I. SME-529

Nickel extraction from ammoniacal media, containing, initially, 0.03 mol dm^?3 of nickel, by 10% v/v Shell metal extractant 529 in MSB 210 or Shellsol A, has been studied as a function of pH, counter anions (nitrate or sulphate), ammonium salt concentration, temperature (10 to 50°C), and the presence of copper, cobalt and zinc. The extraction of copper as a function of pH was studied in the presence of nickel. The pH for maximum nickel extraction decreased from 8.2 to 7.4 as the ammonium sulphate concentration increased from 0.1 to 3.4 mol dm^?3. Nickel extraction was lower from sulphate than from nitrate media and with Shellsol A, and at higher temperature. The enthalpy and entropy of extraction were negative. The presence of copper, cobalt and zinc decreased nickel extraction. Separation factors between copper and nickel are reported as a function of pH and indicate that initial removal of copper is desirable.From a consideration of the equilibrium, the extraction of nickel (with MSB 210 diluent) at 25°C could be expressed by the equation:

$\text{log}\text{D}{}_{\mathrm{<mtext>Ni</mtext>}}\text{= ?9.25 +}\text{log}\text{α}{}_0\text{+ 2}\text{log}\text{(C}{}_{\mathrm{HR}}\text{?2[}\text{Ni}\text{]}{}_{\mathrm{<mtext>org</mtext>}}\text{) + 2}\text{pH}$

where D_Ni represents nickel distribution coefficient, C_HR the total extractant concentration, [Ni]_org the organic nickel concentration (both in mol dm^?3) and α₀, the fraction of uncomplexed nickel in the aqueous phase calculated from the overall stability constants of Ni(NH₃)_i²⁺ complexes and the formation constant of NiSO₄ ion pairs.The limiting slope of ?1 for long D_Ni versus log [NH₃]_free plots indicated an average co-ordination number of 3 for nickel by ammonia in the aqueous phase.The uptake of SO₄^2?, NO₃^? and water by the organic phase was negligible. The uptake of ammonia was dependent upon pH and the ammonia content of the aqueous phase, and was negligible in the absence of metal.     

Extraction of nickel,cobalt and other metals [Cu,Zn, Fe(III)] with a commercial β-diketone extractant

The extraction of nickel, cobalt, copper and zinc from ammoniacal solutions of ammonium carbonate or ammonium sulphate by solutions of Hostarex DK-16 in kerosene has been investigated as a function of phase contact time, aqueous-phase pH and organicphase reagent concentration. Besides copper, Hostarex DK-16 also partially extracts iron (III) from moderately acidic solutions whereas nickel, cobalt(II), copper and zinc are extracted from neutral or ammoniacal ammonium sulphate and ammonium carbonate solutions. Extraction decreases in the following order of metals: Cu > Co > Ni > Zn. Cobalt(III) is not extracted, but the complex of cobalt(II) with Hostarex DK-16 is slowly oxidized to a cobalt(III) complex which cannot be stripped even when 10 N sulphuric acid is used. Absorption spectra for cobalt complexes with Hostarex DK-16 (purified by preparative thin-layer chromatography) in benzene also suggest oxidation of cobalt(II) to cobalt(III) in the organic phase. Nickel, cobalt(II), zinc and copper can be stripped easily from organic solution with dilute solutions of sulphuric acid. Hostarex DK-16 extracts iron very slowly, nickel moderately rapidly and copper, cobalt(II) and zinc rapidly. Slope analysis and extraction isotherms suggest that the complexes CuR₂, NiR₂ ·HR and CoR₂·HR are present in the organic phase. Nickel can easily be separated from cobalt by extraction with Hosterex DK-16 after oxidation of cobalt in aqueous ammoniacal solution by hydrogen peroxide; however, LIX 64N seems to be a more promising extractant owing to the higher extraction of nickel under analogous conditions and the poorer extraction of zinc in comparison with Hostarex DK-16.     

Stoichiometry of liquid-liquid extraction of nickel and cobalt by LIX63

Distribution and spectrophotometric studies were conducted in order to characterize and identify the nickel and cobalt complexes extracted by LIX63 (H₂Ox). The extraction of these metals was found to proceed by a varied and complicated process. Nickel is initially extracted as Ni(HOx)₂ which subsequently converts to Ni(HOx) (H₂Ox) ₂ ⁺ . The equilibrium position between these two complexes depends upon the pH of the adjacent aqueous phase. Formation of Ni(HOx)₂ is favored at pH > 4.5 and conversion to Ni(HOx) (H₂Ox) ₂ ⁺ is favored at lower pH. These two extractable species may fit into a reaction scheme that also involves the complexes Ni(HOx)₂(H₂Ox) and Ni(H₂Ox) ₃ ²⁺ . The extraction of cobalt by LIX63 first forms Co(HOx)₂ which apparently slowly oxidizes to Co(HOx)₂(H₂Ox)⁺. Formerly Graduate Assistant, The Pennsylvania State University     

Preparation of Nd(III) carbonate by precipitation stripping of Nd(III)-loaded VA10

The preparation of fine particles of Nd(III) carbonate from kerosene solution, from which Nd(III) was extracted with versatic acid 10 (VA10) by a precipitation stripping technique using an aqueous NH₃-(NH₄)₂CO₃ solution as stripping medium, was studied. In preliminary experiments, we were unable to recover simple Nd(III) carbonate from Nd(III)-loaded VA10 by CO₂ gas bubbling, when water, (NH₄)₂CO₃, NH₄HCO₃, NaHCO₃, or NA₂CO₃ solution saturated with CO₂ was used as the stripping solution. To obtain simple Nd(III) carbonate, it is necessary to use more than the stoichiometric amount of NH₃ compared to VA10 and about 10 times as much (NH₄)₂CO₃ as Nd(III). The solution mixture of NH₃-(NH₄)₂)CO₃ acts as a pH buffer, an adductor for VA10, and a CO ₃ ²⁻ ion source. Although it was concluded that the precipitates are Nd₂(CO₃)₃·xH₂O (x⊧4), their X-ray pattern does not coincide with that quoted by JCPDS. By heating these precipitates, cubic Nd₂O₃ was obtained at 823 K, while, at 973 K, hexagonal Nd₂O₃ was formed. Since the stripping solution consisting of NH₃-(NH₄)₂CO₃ was highly alkaline, VA10 was also stripped in the aqueous phase. To use a closed-circuit system for the precipitation stripping of Nd(III) carbonate from Nd(III)-loaded VA10, it is important to regenerate VA10 in the organic phase. For this purpose, evaporation of NH₃ by air bubbling was studied. By bubbling air into a stripping solution warmed at 333 K, almost all the VA10 can be transferred to the organic phase.     

Chemical conversions of osmium (VI) sulfite complexes in ammonia–sulfate solutions

It has been found that osmium (VI) sulfite complexes having composition [OsO₂(SO₃)₂(H₂O)₂]²⁻ in ammonia and sulfuric acid solutions enter into reaction of intrasphere substitution resulting in the formation of new complexes of osmium (VI). The rate of their formation depends on the concentration of constituents in the system and the temperature of solutions. Water-soluble ammonia–sulfite complexes of osmium (VI) (final form is [OsO₂(SO₃)₂(NH₃)₂]²⁻) are formed in ammonia-sulfate solutions. These complexes are converted into sulfate derivatives—water-soluble ([OsO₂(SO₃)(SO₄)(NH₃)₂]²⁻) and insoluble ([OsO₂(SO₄)₂(NH₃)₂]²⁻) in solutions containing (NH₄)₂SO₄ and H₂SO₄.     

Leaching of chrysocolla with Ammonia-Ammonium carbonate solutions

Chrysocolla was leached in solutions of ammonium hydroxide and ammonium carbonate as a function of the variables: temperature (25 to 55 ‡C), ammonia-ammonium ratio (0.0:1.0 to 1.0:0.0), total ammonia concentration (0.25 to 6.0 M), and particle size (100 to 400 mesh). A model of the leaching behavior was deduced based on: (1) the activation energy of 60.75 kJ/mole (14.51 kcal/mole) for 3 M total NH₃ which was dependent on both total ammonia concentration and temperature; (2) first-order dependence of rate on [(NH₄)₂CO₃]; (3) dependence of initial reaction rate on reciprocal of particle diameter; and (4) morphological evidence from SEM and ED AX measurements of diffusion and leaching occurring primarily in surface microcracks and not in the submicroscopic pores. In addition to the importance of diffusion through microcracks in rate control chemical reaction at active surface sites to produce the species, CuNH ₃ ^{2 +}, is also important. Only a fraction of the Cu atoms react that are exposed to lixiviant. Higher ammonia-ammonium ion concentrations, higher temperatures, or much longer times are required for more refractory Cu atoms to dissolve. Formerly Graduate Student, Department of Metallurgy and Metallurgical Engineering, University of Utah     

Characterization and alkaline decomposition–cyanidation kinetics of industrial ammonium jarosite in NaOH media

A complete characterization was carried out on a jarositic residue from the zinc industry. This residue consists of ammonium jarosite, with some contents of H₃O⁺, Ag⁺, Pb²⁺, Na⁺ and K⁺ in the alkaline “sites” and, Cu²⁺ and Zn²⁺ as a partial substitution of iron. The formula is: [Ag_0.001Na_0.07K_0.02Pb_0.007(NH₄)_0.59(H₃O)_0.31]Fe₃(SO₄)₂(OH)₆. Some contents of franklinite (ZnO^·Fe₂O₃), gunninguite (ZnSO₄·H₂O) and quartz were also detected. The jarosite is interconnected rhombohedral crystals of 1–2 μm, with a size distribution of particles of 2–100 μm, which could be described by the Rosin–Rammler model.The alkaline decomposition curves exhibit an induction period followed by a progressive conversion period; the experimental data are consistent with the spherical particle with shrinking core model for chemical control. The alkaline decomposition of the ammonium jarosite can be shown by the following stoichiometric formula:NH₄Fe₃(SO₄)₂(OH)_6(s)+3OH_(aq)⁻→(NH)_4(aq)⁺+3Fe(OH)_3(s)+2SO_4(aq)²⁻.The decomposition (NaOH) presents an order of reaction of 1.1 with respect to the [OH⁻] and an activation energy of 77 kJ mol⁻¹. In NaOH/CN⁻ media, the process is of 0.8 order with respect to the OH⁻ and 0.15 with respect to the CN⁻. The activation energy was 46 kJ mol⁻¹. Products obtained are amorphous. Franklinite was not affected during the decomposition process. The presence of this phase is indicative that the franklinite acted like a nucleus during the ammonium jarosite precipitation.     

Molecular modeling of the octacoordinated tetracarbonato-Nd(III), [Nd(CO3)4], complex and its nonacoordinated fluoro- and aquo-adducts

Theoretical investigation on the structures of the octacoordinated [Nd(CO₃)₄]^5- and the nonacoordinated [Nd(CO₃)₄.OH₂]^5- complexes, using the SPARKLE parameters of the lanthanides within MOPAC, revealed that they possessed dodecahedral and square antiprismatic structures respectively with an average Nd-O distance of 0.249 nm. These structures and the Nd-O distances agreed well with those experimentally found in the crystal structures. Replacing the water molecule with a fluoride ion or a mondentatecarbonato ligand resulted in a nonacoordinated distorted square antiprismatic structures where the trans-carbonato groups were twisted. The corresponding decacoordinated structures with two fluoride ions or a bidentatecarbonato group, [Nd(CO3)₄·F₂]^7- and [Nd(CO₃)₅]^7-, were also investigated. In both cases considerable twisting of the transcarbonato groups was observed.     

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.     

Solvent extraction of cobalt and nickel by organophosphorus acids I. Comparison of phosphoric,phosphonic and phosphonic acid systems

The solvent extraction of cobalt(II) and nickel(II) by xylene solutions of commercial dialkyl-phosphoric (D2EHPA), phosphonic (Shell RD 577) and phosphinic acids (Cyanex CNX) has been investigated. In each case, cobalt is extracted at lower pH values than nickel; under comparable conditions, the cobalt-nickel separation increases in the order phosphoric < phosphonic < phosphinic acids. Application of the slope analysis technique indicates stoichiometries of Co(HA₂)₂ and NiHA₂)₂(H₂A₂)_x(H₂O)2?x for the cobalt and nickel complexes, respectively, where H₂A₂ represents the dimerized extractant molecule and x = 0, 1, or2. The effect of a range of organic phase additives has been examined. Typical emulsion inhibiting reagents such as isodecanol and tributyl phosphate cause the cobalt—nickel separations to decrease significantly. A novel synergistic effect has been found with mixtures of D2EHPA and 2-ethylhexanal oxime (EHO); the synergism is so marked in the case of nickel as to reverse the selectivity for cobalt over nickel shown by D2EHPA alone. The electronic spectra of the organic extracts show that the organophosphorus acids examined from complexes of tetrahedral structure with cobalt and octahedral structure with nickel. In the D2EHPA—EHO system, however, the deep blue tetrahedral cobalt-D2EHPA complex is transformed into a pink octahedral complex, presumably of the type Co(HA₂)₂(EHO)₂, whilst the green octahedral nicke—D2EHPA complex is converted to a bright blue species of similar geometry, in which the neutral oxygen-donor ligands (H₂A₂ and/or H₂O) have been displaced by the nitrogen-donor oxime ligands.     

Preparation of palladium-based alloy powders by the thermal decomposition of binary complex ammonium oxalate salts

The possibility of obtaining powder alloys (solid solutions) by thermal decomposition of salts of the types [Pd(NH₃)₄[M(C₂O₄)₂] and (M(NH₃)_n[Pd(C₂O₄)₂] was investigated. Salts of the desired compositions were synthesized by double decomposition of the ammonium and oxalate complexes of the metals in aqueous solution. The production of new compounds was confirmed by x-ray diffraction analysis. It was shown that pyrolysis of the salts (Pd(NH₃)₄][M(C₂O₄)₂] occurs in stages: initially one of the oxalate groups migrates to the cationic part, and later the products obtained, (Pd(NH₃)₂](C₂O₄)] and MC₂O₄, decompose. The decomposition temperatures of the salts obtained correlated with those of MC₂O₄. Pyrolysis of [Pd(NH₃)₄] [M(C₂O₄)₂] produced highly dispersed solid solution powders of palladium with copper, nickel, and copper, respectively, with the atom ratio Pd:M = 1:1, and the intermetallic compound PdZn. The powder particle sizes did not exceed 1 m. Initial salts, intermediate products, and oxides were not detected in the powders.Krasnoyarsk State Academy of Nonferrous Metals and Gold. Institute of Chemical and Chemical-Metallurgical Processes. Siberian Division of the Russian Academy of Sciences. Translated from Poroshkovaya Metallurgiya. Nos. 3/4(384), pp. 6–10, March–April. 1996. Original article submitted December 12. 1994.     

Simulation ofin situ uraninite leaching-part III: The effects of solution concentration

The effects of variations in the concentrations of leaching reagents have been simulated forin situ leaching of UO₂ by H₂O-(NH₄)₂CO₃-NH₄HCO₃. The model used in the simulations incorporates rate laws for the mineral reactions, equilibrium reactions among the solution species, and a mixing cell representation of solution flow. Of the component concentrations, the major factor affecting the rate of uraninite dissolution is the oxidant concentration. High peroxide concentrations lead to more rapid reaction with an early maximum in the U(VI) concentration. If lower oxidant concentrations are used, the reaction is under mixed kinetic and mass transfer control and the U(VI) concentration is lower but approximately constant for an extended period. Because they increase the concentration of the HCO _3/- anion, high ammonium carbonate and ammonium bicarbonate concentrations also result in some enhancement in the rate of U leaching; the reaction is known to be half-order in both HCO₃ ^- and H₂O₂. A 10:1 ratio of (NH₄)₂CO₃ to NH₄HCO₃ concentrations was found to result in a nearly constant pH during most of the leaching process. Calcite-containing gangue causes an immediate pH increase from about 8.9 to 9.4. The rate of the calcite reaction, calcite saturation index, and porosity are all independent of the lixiviant concentrations. Detailed calculations of solution speciation are necessary to predict the concentrations of individual species from those of components.     

Leaching kinetics of malachite in ammonium carbonate solutions

Leaching of malachite was conducted with ammonium carbonate as lixiviant and with temperature, lixiviant concentration, and particle size as variables. Two stages of reaction were found. In Stage I, the initial dissolution of malachite proceeds rapidly, but after about 10 pct reaction the rate is reduced by surface blockage due to the presence of a needle-structured intermediate, presumably Cu(OH)₂. Subsequently, malachite and the intermediate dissolve concurrently. In Stage II, after 90 pct reaction, essentially all of the malachite has dissolved and only the intermediate remains. It dissolves in Stage II. The activation energy is 64 kJ/mole (15.3 kcal/mole) for Stage I and 75 kJ/mole (18 kcal/mole) for Stage II. The rate of reaction in Stage I is proportional to the reciprocal of particle size and is 0.8 order with respect to the concentration of ammonium carbonate. The structures of leaching residues were studied using a scanning electron microscope. The kinetic data (activation energy and entropy), particle size and concentration dependence, residue morphology, and general leaching behavior evident from microscopic monitoring during leaching were used to develop the geometric equation for leaching in Stage I. The equation, based on a heterogeneous reaction with geometric rate control, is: 1 − (1 − α^1/3 = K₀₁/r₀/[(NH₄)₂C0₃]^0.8 exp(-64,000/RT)t. It was deduced that initial steps in reaction were: (1) release of Cu²⁺ from malachite; (2) initial complexing with ammonia to form Cu(NH₃)²⁺; and (3) subsequent complexing to produce Cu(NH₃) ₄ ²⁺ which is stable in solution at pH 8.8, the buffered pH of reaction. Stage II appears to be a similar reaction except that the reaction obeys cylindrical geometry instead of spherical geometry as in Stage I.     

The leaching kinetics of chalcopyrite (CuFeS2) in ammonium lodide solutions with iodine

The leaching kinetics of chalcopyrite (CuFeS₂) in ammonium iodide solutions with iodine has been studied using the rotating disc method. The variables studied include the concentrations of lixiviants, rotation speed, pH of the solution, reaction temperature, and reaction product layer. The leaching rate was found to be independent of the disc rotating speed. The apparent activation energy was measured to be about 50 kJ/mole from 16 °C to 35 °C, and 30.3 kJ/mole from 35 °C to 60 °C. The experimental findings were described by an electrochemical reaction-controlled kinetic model: rate =k [NH₃]^0.69[OH⁻]^0.42[I ₃ ⁻ ]^0.5.     

Catalytic ozonation of NH4+-N in wastewater over composite metal oxide catalyst

Large amounts of water containing-ammonium nitrogen(NH₄⁺-N)have attracted increasing attention.Catalytic ozonation technology,involving the generation of hydroxyl radical(OH)with strong oxidation ability,was originally utilized to degrade organic-containing wastewater.In this paper,Ce/MnOx composite metal oxide catalysts prepared with different preparation conditions were used to degrade wastewater containing inorganic pollutant(NH₄⁺-N).The as-prepared catalyst features were characterized using X-ray diffraction(XRD),Brunauer-Emmett-Teller method(BET),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and H₂-temperature programmed reduction(H₂-TPR)techniques.The results show that the catalyst,prepared by conditions with precipitant Na₂CO₃ and Ce/Mn molar ratio 1:2 calcined at 400℃for 3 h in pH 11.0,displays the optimal performance,with the removal rate of NH₄⁺-N and selectivity to gaseous nitrogen,88.14 wt%and 53.67 wt%,respectively.The effects of several operating factors including solution pH,initial NH₄⁺-N concentrations and scavengers were evaluated.In addition,XRD patterns of catalyst with the best performance and the comparative study on decontamination of NH₄⁺-N by various processes(O₃,catalyst and catalyst/O₃)show that the primary metal oxides are CeO₂ and MnO₂ in Ce/MnOx composite metal oxide catalysts,which have a synergistic effect on the catalytic ozonation of NH₄⁺-N,and the new phase MnO₂ plays a great role.After 5 consecutive use cycles,the degradation efficiency is declined slightly,and can still achieve better than 70 wt%over 1 h reaction.Additionally,the application of catalytic ozonation for actual wastewater on the removal rate of NH₄⁺-N was investigated.Possible mechanism and degradation pathway of NH₄⁺-N were also proposed.In a word,the application of CeO₂-MnO₂ composite metal oxide catalysts in catalytic ozonation can be regarded as an effective,feasible and promising method for the treatment of NH₄⁺-N.     

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.     

Degradation of ammonium carbonate based uranium leach solutions by sulphide minerals and possible methods of control

One problem in the use of ammonium carbonate solutions in conventional metallurgy is reagent loss following the oxidation of sulphide minerals in the ore. This problem could be of importance in solution mining. Degradation of a stock feed solution of 1 g/l (NH₄)₂CO₃ and H₂O₂ as an oxidant by a variety of sulphide minerals was studied. The minerals including pyrite, sphalerite, chalcopyrite and bornite were each loaded into a column of sand and the degradation was studied by analysing the effluent obtained when a leach solution was allowed to percolate through the column. Pyrite was the only mineral studied that showed degradation of carbonate above 10%. This however, was reduced c considerably by treatment with lead nitrate or sodium silicate. The indications are that losses in the order of 0.1 gram (NH₄)₂CO₃ per gram of pyrite might be expected in solution mining.     

Solvent extraction of base metals by mixtures of organophosphoric acids and non-chelating oximes

The effect of non-chelating oximes on the extraction of several transition and nontransition metals by solutions of organophosphoric acids (H₂A₂) in xylene has been investigated. Synergistic enhancements of extraction of divalent transition metal ions were found with the oximes of aliphatic aldehydes, the enhancements of extraction increasing in the order VO²⁺ < Mn²⁺ < Mn²⁺ < Co²⁺ < Cu²⁺ < V²⁺ < Ni²⁺. Large synergistic effects were also found for copper(I) and silver(I). Among the divalent non-transition metals studied (Mg, Ca, Zn, Cd, Sn, and Pb), only cadmium showed a synergistic effect. No significant synergism was found for any of the trivalent metal ions studied (Fe, Cr, V, Al, Bi, La, Ce, and Nd). The extracted complexes of copper, cobalt, and nickel were shown to be octahedral in structure, with the compositions Cu(HA₂)₂(oxime)₂, Co(HA₂)₂(oxime)₂, and NiA(HA₂)(oxime)₃, respectively, in which HA₂^? acts as a bidentate ligand. Extraction rates were found to be rapid, even for nickel, and complete stripping of metal-loaded organic phases was effected by contact with 0.5 M mineral acid. Some practical applications, such as the recovery of nickel from acidic leach liquors, are envisaged.     

The precipitation of ammonium uranyl carbonate (AUC): Thermodynamic and kinetic investigations

The aim of this study is to determine the predominant chemical reaction during precipitation of ammonium uranyl carbonate (AUC) based on thermodynamic analysis and to investigate its kinetics. Four chemical reactions were considered. The Gibbs free energies, Δ_rG°(T) derived from the Ulich calculations as a function of temperature have been determined between 293.15 K and 353.15 K. The predominant chemical reaction of AUC precipitation was UO₂(NO₃)₂·6H₂O_(aq) + 6NH_3(g) + 3CO_2(g) → (NH₄)₄UO₂(CO₃)_3(s) + 2NH₄NO_3(aq) + 3H₂O_(l). According to the AUC precipitation kinetics results, the reaction best fits a second order rate equation. The rate constants k₂ were calculated at 313.15 K and 330.15 K and the activation energy E_a determined using the Arrehenius equation was found as 17.4 kJ/mol.