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.     

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.     

Separation of cobalt from nickel in ammonia-ammonium carbonate solutions using pressurized ion exchange

High resolution pressurized ion exchange has been used successfully to study and separate the various cobalt and nickel complexes present in commercial ammonia-ammonium carbonate solutions produced by the Caron process. Using chromatographic elution from Dowex 50W-X8 (15–25 micron) resin with ammonium carbonate solutions, three cobalt species, identified as the purple carbonato tetrammine complex, [Co(NH₃)₄CO₃]⁺, the red carbonato pentammine complex, [Co(NH₃)₅CO₃]⁺, and the yellow hexammine complex [Co(NH₃)₆]³⁺, were separated from a single nickel species. Nickel sorption was found to be a strong function of pH, whereas sorption of the cobalt complexes was essentially independent of pH over a rather wide range, extending from ～pH 7.8 to 10. Distribution ratios for all species increased significantly with decreasing ammonium carbonate concentration. With ammonium carbonate solution at pH 9.5, the complexes were eluted in the following order: [Co(NH₃)₄CO₃]⁺, [Co(NH₃)₅CO₃]⁺, [Ni(NH₃)_6-x(H₂O)_x]²⁺, and [Co(NH₃)₆]³⁺. From 4 M (NH₄)₂CO₃, distribution ratios were 5.0, 7.5, 18, and 75 for the respective complexes identified in the order above. This study points out some of the difficulties and opportunities in developing a viable ion exchange process for the recovery and separation of these metal ions.     

How oxidation affects selective flotation of complex sulphide ores

Abstract

Selective flotation of complex sulphide ores containing Cu-Pb-Zn-Fe sulphide minerals is very difficult. Oxidation is one of the most important factors.

The oxidation of complex sulphide ore is found to be enhanced by the presence of pyrite. Pyritic complex sulphide ore sometimes behaves like elemental sulphur in flotation. Such troublesome behaviour is often experienced for flotation systems in which the natural pH of the. pulp is low.

Elemental sulphur formation can be predicted thermodynamically. The potential-pH diagrams of the Me-S-H₂O systems were constructed to show the stable domain of elemental sulphur. An explanation of enhanced oxidation of sulphide minerals in the presence of pyrite involves an electrochemical mechanism. Pyrite has the highest rest potential among all the sulphide minerals in an acidic solution. Since the condition of pyrite in its natural state may be regarded as electrochemically passive, we may anticipate that when pyrite is in galvanic contact with other sulphide minerals, the oxidation of the other sulphide minerals will.be enhanced under flotation conditions. The enhanced elemental sulphur formation on sulphide minerals in the presence of pyrite was confirmed experimentally.

Résumé

Le triage par flottation des complexes minéralogiques constitués de sulfures de Cu-Pb-Zn-Fe est trés difficile. L'oxidation est un paramétre important.

La pyrite de fer accélère l'oxydation de ces complexes. Un complexe de pyrite parfois se comporte comme du soufre élémentaire lorsque le pH du milieu de flottation est bas.

La formation de soufre élémentaire se prévoit par calcul d' énergétique. Les diagrammes potentiel-pH des systèmes Me-S-H₂O furent établis en vue d'indiquer les domaines de stabilité du soufre élémentaire. L'accélération de l'oxydation des minéraux sulfurés par la pyrite s'explique en se servant d'un mécanisme électrochimique. De tous les minéraux sulfurés, la pyrite possède dans les milieux acides, Ie plus haut potentiel d' équilibre. Puisque la pyrite è l' état naturel semble électrolytiquement passive, l'oxydation des autres sulfures, en conditions de flottation, serait alors accélérée. En présence de pyrite, l'experience conflIme la formation de soufre élémentaire sur les minéraux sulfurés.     

Effect of the composition of some sulphide minerals on cyanidation and use of lead nitrate and oxygen to alleviate their impact

An investigation was carried out on synthetic ores containing high purity pyrite, pyrrhotite and chalcopyrite and on two gold ores currently processed to evaluate the impact of cyanicides on cyanidation and to improve the leaching performance by using a pre-leaching, injecting oxygen and adding lead nitrate. With regard to the synthetic ores, it was found that pyrrhotite did not generate a high cyanide consumption while pyrite and chalcopyrite were detrimental. Pre-leaching was deleterious for the ore containing chalcopyrite while pre-leaching with lead nitrate was very efficient to decrease the reactivity of the ore containing pyrite. The two gold ores studied had very different compositions. The low sulphide ore had a low sulphide content (1.36% S), present as pyrrhotite while the second had a very high sulphide content (20.2% S), in the form of pyrite, pyrrhotite and chalcopyrite. The efficiency of the process conditions was peculiar to the ores. The high sulphide ore required a stronger, longer pre-leaching period (12 h) with greater amounts of lime (7.0 kg/t) and lead nitrate (600 g/t) than the low-sulphide ore. The ore with a low sulphide content required a pre-leaching of only 1 h with a small quantity of Pb(NO₃)₂ (50 g/t) and leaching can be performed at 360 ppm NaCN to allow a recovery of 96.4% Au and a low cyanide consumption at 0.18 kg/t. As for the high sulphide ore, cyanidation had to be conducted at 560 ppm NaCN to recover 88.4% Au with a cyanide consumption of 0.80 kg/t. An increase in the amount of lime enhanced oxidation of soluble sulphides. Lead nitrate stabilized copper and iron dissolution by forming a passivation layer at the surface of sulphide minerals. Lead nitrate also prevented the formation of a passive layer at the surface of gold.     

Galvanic Interaction Studies on Sulphide Minerals

Abstract

Galvanic interactions occurring when two sulphide minerals are in contact with each other have been investigated by electrochemical techniques for pairs of the following: pyrite, chalcopyrite, galena and sphalerite. Combination potentials of pyrite electrodes in galvanic contact with a second sulphide were significantly lower than the rest potential of pyrite alone. This suggested electron transfer to pyrite which makes it more reducing. Similar results were obtained with the chalcopyrite galena couple, chalcopyrite becomes more reducing by galvanic interaction with galena.

Galvanic interactions are weakened in nitrogenated water due to the lower activity of dissolved oxygen. This is shown by: (a) much smaller drop in potential when pyrite is in galvanic contact with another sulphide in nitrogenated water; (b) Zn²⁺ ions released into solution: dissolution of Zn²⁺ ions in sphalerite pyrite mixtures is decreased in nitrogenated water; and (c) xanthate uptake at pyrite-sphalerite mixtures is increased by appropriate use of nitrogen.

In aerated water the flotation behaviour of a mineral in a mineral mixture differs significantly from that of the single mineral. The use of nitrogen promotes pyrite flotation from the mixture.

A model of galvanic coupling and the role of N₂ are discussed.     

Reduction of CO2 Emissions from Steel Plants by Using Steelmaking Slags for Production of Marketable Calcium Carbonate

By carbon dioxide mineralization, CO₂ can be stored safely and leakage‐free for very long times. Owing to their high calcium content, steelmaking slags are suitable for mineral carbonation. In a country like Finland, where no suitable geological formations for CO₂ storage seem to exist, steelmaking slag carbonation offers an important CO₂ emissions reduction option for steel plants. If calcium could be extracted selectively from the slags prior to carbonation, a pure, and possibly marketable, calcium carbonate may be produced. This could replace some of the natural and synthetic CaCO₃ used in industry, combining savings in natural resources with CO₂ emissions reduction. Development work on the production of pure calcium carbonate from steelmaking slags by carbonation is presented in this study. Selective extraction of calcium from steelmaking slags was investigated using various solvents. Precipitation of CaCO₃ from dissolved calcium at atmospheric pressure was also investigated. Amongst the various tested solvents ammonium salt solutions (NH₄Cl, CH₃COONH₄, NH₄NO₃) were found to be the most promising for selectively extracting calcium from steel converter slag. These solvents dissolved calcium efficiently also from desulphurization slag, while extraction of calcium from two other types of slag was poor. CaCO₃ was successfully precipitated from the solution containing ammonium salt and dissolved steel converter slag.     

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.     

Optimization of the Wet Mechanochemical Process Conditions of SrSO4 to SrCO3 and (NH4)2SO4 by Using Response Surface Methodology

The wet mechanochemical process was optimized for insoluble SrCO₃ and soluble (NH₄)₂SO₄ formation from celestite (SrSO₄)-(NH₄)₂CO₃-H₂O mixtures in a planetary ball mill by Box-Behnken design (BBD). The products formed during wet milling were analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. For converting to SrCO₃ of celestite (SrSO₄) and to (NH₄)₂SO₄ of (NH₄)₂CO₃, a hydrometallurgical process optimization via the wet mechanochemical conversion using (NH₄)₂CO₃ was developed the first time in this work using response surface methodology. The wet mechanochemical conversion was carried out by varying ball to grinding material mass ratio, (NH₄)₂CO₃ to SrSO₄ mole ratio and the rotational speed of mill in a planetary mill. Under the optimum experimental conditions (9.24 of ball to grinding material mass ratio, 1.86 of (NH₄)₂CO₃ to SrSO₄ mole ratio and 400 rpm of the rotational speed of mill), the conversion of SrCO₃ was 99.08 pct. The (NH₄)₂SO₄ obtained as byproduct was crystallized.     

The Oxidation of Sulphur Dioxide and the Formation of Sulphuric Acid in Situ at Atmospheric Pressure in the Leaching of a Uranium Ore

Abstract

The oxidation of SO₂ to form H₂SO₄ in situ, at atmospheric pressure and temperatures from 25 to 80°C, was examined by passing a mixture of SO₂ dioxide and air for 7 hrs through a reaction vessel containing quartz- or uranium-bearing solids moistened with H₂O to 85% solids. At the end of the contact period the solution was analyzed for free acid and other constituents of SO₂ and extraction of Uranium.

In tests with quartz at 80°C, the addition of Fe₂(SO₄)₃ or Fe₂O₃ increased the amount of SO₂ converted to H₂SO₄. E.g. without Fe₂(SO₄)₃ added the conversion obtained was 2% with 0.7 and 2.3 1b/ton quartz of Fe₂(SO₄)₃ the conversions were 18 and 24% respectively.

Tests were conducted on a mixture of flotation tailings, and a residue, which contained 24.3 per cent Fe⁺⁺⁺ as oxide, derived from the roasting of a sulphide concentrate at 500°C. The tailings and sulphide concentrate were obtained from the flotation of a uranium ore containing brannerite and about 9 per cent pyrite Roasting of the sulphide concentrate yielded "160 to 180 lb per ton of ore of sulphur dioxide of which 80,to, 100 lb was introduced into the conversion system over a 7-hour period. At 80°C, 40 per cent of the sulphuric dioxide introduced was converted to sulphuric acid which dissolved 93 per cent of the uranium in the mixturet of solids.     

Simulation of in situ uraninite leaching. part I: A partial equilibrium model of the NH4HCO3-(NH4)2CO3-H2O2 leaching system

In situ leaching of uraninite and calcite by H₂O2-NH₄HCO₂-(NH₄)₂CO₃ solutions has been simulated using a partial equilibrium model which incorporates a one-parameter mixing cell model of solution flow. Rate laws for UO₂ dissolution and for CaCO₂ dissolution/precipitation were taken from the literature, as were equilibrium constants for solution phase reactions. Parameters of the model include the UO₂ and CaCO₃ ore grades, the concentrations of the H₂O₂, NH₄HCO₃, and (NH₄)₂CO₃ components, porosity, exit solution flow rate, ore and mineral densities, and mineral rate constants and surface areas. Mineral conversions, component and species concentrations, and porosity are among the time-dependent quantities calculated using the model. For the conditions simulated, calcite dissolved somewhat faster than uraninite. The results emphasize the importance of the coupling between the mineral reactions and solution flow. Changes in the concentrations of the CO ₃ ^2- and HCO ₃ ^- species are particularly complicated and not predictable from the calcite kinetics alone or from a purely equilibrium model; although the simulations did not reveal any conditions under which the solution would become saturated with CaCO₃, the pH continued to change throughout the calcite dissolution and is buffered only after calcite has been consumed.     

Preparation of ammonium chloroplatinate by a precipitation stripping of Pt(IV)-loaded alamine 336 or TBP

The possibility of preparing ammonium chloroplatinate powders by precipitation stripping from Pt-loaded Alamine 336 or TBP was investigated experimentally. A similar examination was done for the precipitation stripping of Pd(II). Furthermore, the possible separation of Pt(IV) from Alamine 336, loaded with both Pt(IV) and Pd(II), was studied. Precipitation stripping of (NH₄)₂PtCl₆ from Pt(IV)-loaded Alamine 336 was possible using an aqueous NH₃ solution and aqueous mixed solutions of NH₃-NH₄Cl or NH₄Cl-HClO₄. It was found that the use of 0.2 kmol m⁻³ HClO₄-2 kmol m⁻³ NH₄Cl as a stripping solution was most effective. The precipitation of (NH₄)₂PtCl₆ from Pt(IV)-loaded TBP was almost completely achieved using an aqueous NH₃ solution concentrated above 2 kmol m⁻³. Pt(IV) can be efficiently separated as (NH₄)₂PtCl₆ precipitates from both Pt(IV) and Pd(II)-loaded Alamine 336, using 0.2 kmol m⁻³ HClO₄-4 k mol m⁻³ NH₄Cl, with soluble Pd(II) remaining in both the aqueous and organic phases.     

Sm-MnOx catalysts for low-temperature selective catalytic reduction of NOx with NH3: Effect of precipitation agent

A series of Sm-Mn mixed oxide catalysts were prepared via precipitation using various precipitants,namely Na₂CO₃(NH₄)₂CO₃,and NH₃·H₂O,and evaluated for the selective catalytic reduction(SCR) of NO_x with NH₃ at low temperatures.Various characterisation techniques were used to determine the physicochemical properties of the catalysts,and it is found that their catalytic performance is greatly influen...     

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.     

Production of Metallic Oxide and Metal Powders by Crystallization Stripping Applying Solvent Extraction

Abstract

The fundamental studies on production of metallic oxide and metal powders with crystallization-stripping using NH₄HF₄, (NH₄) ₂S04 and pressurized C0₂ gas as crystallization-stripping agent in solvent extraction were carried out in order to develop a new production method of fine powders.

The reaction significantly relates to the stripability of the extracted metal tons and the solubility of the metal compounds formed in crystallization process. Furthermore, the reaction depends on the various factors, such as extractant concentration, metal concentration in the organic phase, the sort of stripping solution and still more CO₂ pressure in the pressurized CO₂ process.

The resultant crystallized products can be converted to fine powders of high-purity metallic oxide and metal in micron order by thermal decomposition in air or hydrogen atmosphere, respectively.     

提高某铅矿金铅回收率的选矿试验研究

针对某铅矿矿石特点,试验通过提高矿石磨矿细度,使部分细粒金矿物有效单体解离,加强对黄铁矿的活化及对矿泥的分散,采用碳酸钠替代石灰,丁基黄药与sk9011合理配比使用,延长粗选浮选时间,控制氧化铅矿物浮选时硫化钠的用量等措施,使金铅回收率有大幅度提高。     

The effect of combinations of iron-bearing minerals and quartz on coke reactivity

The effect of combinations of iron-bearing minerals and quartz on the reactivity of coke analogues with CO₂ was examined in a TGA. Troilite–quartz, pyrite–quartz and magnetite–troilite binary combinations and the troilite–magnetite–quartz ternary combination were examined. For the troilite–quartz and pyrite–quartz binary combinations the reactivity in general decreased non linearly with increasing Si:Fe ratio. The magnetite–troilite combination had a non-linear effect on the reactivity in that mixes of these two minerals show a higher reactivity than would be expected from a simple proportional mixing approach. Some evidence of sulphur transfer from the troilite to the magnetite was observed. The reactivity of the ternary magnetite–troilite–quartz combination can largely be understood from the trends in the axes. These were largely followed across all compositions, allowing better understanding and prediction of the effect of these minerals on the reactivity of industrial cokes.     

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.     

Ammoniacal Percolation Leaching of Copper Ores

Abstract

The general feasibility of ammoniacal percolation leaching of copper sulphide ores has been demonstrated. The rates are comparable to those of conventional ferric sulphate-sulphuric acid systems, but without the attendant problems of carbonate or iron dissolution, For the ore column heights studied, the copper leaching rate increased approximately as the square root of the total NH₃ concentration, but was independent both of the ratio of ammonium carbonate to ammonium hydroxide and of solution pH's above 9,5, There was no dependence on the solution flow rate over a broad flow regime, and the rate increased only very slightly with increasing temperatures. Initially, increasing the ore column height or finer comminution of the ore were beneficial, but the percolation leaching rate soon became essentially independent of both variables. The percolation leaching rate under the test conditions employed was controlled by both chemical kinetics and oxygen transport; it was concluded that the oxygen transport mechanism would become more significant as the scale of operations was increased. Ammonia gas losses appear to be the most significant technical barrier to commercial adoption of ammoniacal percolation leaching.

Résumé

La possibilité de lixiviation par percolation ammoniacale de minerais sulfureux a été démontreé. Ses performances sont comparables aux systèmes sulfate ferrique-acide sulfurique, sans les inconvénients des dissolutions de fer ou de carbonate. Selon la hauteur de la colonne de minerais qui a servi de modéle dans cette étude, le taux de lixiviation du cuivre augmentait proportionnellement selon la racine carré de la concentration totale de NH₃, mais était indépendante de la proportion carbonate d'ammonium-hydroxide d'ammonium et du pH de la solution au dessus de 9.5. La variation dans le volume du flot de la solution n'affectait pas le rendement, et la performance était un peu sensible à l'augmentation de la température. Une augmentation de la hauteur de la colonne de minerais ou la réduction de la grosseur du minerai était bénéfique ou début, mais bientôt le rendement de la lixiviation par percolation s'avèrait indépendant de ces deux variables. Le rendement de la lixiviation par percolation suivant les conditions choisies pour les présents essais était dépendant de la cinétique-chimique et de l'approvisionnement d'oxygène. Avec un accroissement dans l'échelle des opérations on conclu que cet approvisionnement d'oxygène prendre une importance majeure. La perte de l'ammoniaque gazeux semble être le problème technique le plus sérieux à résoudre dans l'adaptation de la lixiviation par percolation ammoniacale.     

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.