Behaviour of cesium and lithium during the precipitation of jarosite-type compounds

End-member cesium jarosite [CsFe₃(SO₄)₂(OH)₆] and end-member lithium jarosite [LiFe₃(SO₄)₂(OH)₆] do not exist. Cesium-bearing potassium, sodium and rubidium jarosites were synthesized, however, with cesium contents > 2 wt% being noted in potassium jarosite. The cesium content of the jarosites increases with increasing cesium concentration in solution, and the order of cesiumincorporation is potassium jarosite > sodium jarosite > rubidium jarosite. Only trace amounts of lithium are incorporated in jarosite; the maximum obtained was ∼ 0.2 wt% lithium in potassium jarosite. The lithium content increases with increasing lithium concentration in the synthesis solution, but is nearly independent of the potassium concentration or the solution pH. Although some of the lithium may be structurally incorporated in the jarosite, most seems to be physically entrained.     

Rubidium jarosite and thallium jarosite — new synthetic jarosite-type compounds and their structures

Rubidium jarosite (RbFe₃(SO₄)₂(OH)₆) and thallium jarosite (TlFe₃(SO₄)₂(OH)₆) were synthesized as single phase products by precipitation from aqueous solution. Hydronium ion (H₃O⁺) substitutes for part of the “alkali” metal in these compounds. Both jarosites are hexagonal (R3m) and have similar unit cell dimensions. During heating rubidium jarosite undergoes two major decompositions; initially water is evolved and subsequently sulphur oxides are emitted. Thallium jarosite decomposes in three principal stages during programmed heating. The first two stages are similar to the decomposition of rubidium jarosite; the third decomposition involves the breakdown of thallium sulphate and the subsequent sublimation of thallous oxide.     

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.     

The behavior of thallium during jarosite precipitation

Jarosite precipitation provides an effective means of eliminating thallium from zinc processing circuits, and a systematic study of the extent and mechanism of thallium removal during the precipitation of ammonium, sodium, and potassium jarosites was carried out. Thallium (as Tl⁺) substitutes for the “alkali” ion in the jarosite structure. Nearly ideal jarosite solid solutions are formed with potassium, but thallium is preferentially precipitated relative to either ammonium or sodium. Approximately 80 pct of the dissolved thallium precipitates during the formation of ammonium jarosite; the extent of thallium removal is virtually independent of thallium concentrations in the 0 to 3000 mg/L Tl range and of the presence of 75 g/L of dissolved Zn. Although the deportment of thallium is nearly independent of (NH₄)₂SO₄ or Na₂SO₄ concentrations >0.1 M, the precipitates made from more dilute media are relatively enriched in thallium. Likewise, the precipitates made from dilute ferric ion media are also Tl-rich. Low solution pH values or low temperatures both significantly reduce the amount of jarosite formed, but the precipitates made under these conditions are enriched in thallium. Furthermore, because thallium jarosite is more stable than the ammonium or sodium analogues, the initially formed precipitates are consistently Tl rich. The presence of jarosite seed accelerates the precipitation reaction, but dilutes the thallium content of the product. The results suggest that most of the thallium in a hydrometallurgical zinc circuit could be selectively precipitated in a small amount of jarosite, by carrying out the precipitation reaction for a short time in the absence of seed and from solutions having low alkali concentrations.     

Synthesis, Thermodynamic, and Kinetics of Rubidium Jarosite Decomposition in Calcium Hydroxide Solutions

Rubidium jarosite was synthesized as a single phase by precipitation from aqueous solution. X-ray diffraction and scanning electron microscopy energy-dispersive spectrometry analysis showed that the synthetic product is a solid rubidium jarosite phase formed in spherical particles with an average particle size of about 35???m. The chemical analysis showed an approximate formula of Rb_0.9432Fe₃(SO₄)_2.1245(OH)₆. The decomposition of jarosite in terms of solution pH was thermodynamically modeled using FACTSage by constructing the potential pH diagram at 298?K (25?°C). The E-pH diagram showed that the decomposition of jarosite leads to a goethite compound (FeO·OH) together with Rb⁺ and $ {\text{SO}}_{4}^{2 - } $ ions. The experimental Rb-jarosite decomposition was carried out in alkaline solutions with five different Ca(OH)₂ concentrations. The decomposition process showed a so-called ??induction period?? followed by a progressive conversion period where Rb⁺ and $ {\text{SO}}_{4}^{2 - } $ ions formed in the aqueous solutions, whereas calcium was incorporated in the solid residue and iron gave way to goethite. The kinetic analysis showed that this process can be represented by the shrinking core chemically controlled model with a reaction order with respect to Ca(OH)₂ equals 0.4342 and the calculated activation energy is 98.70?kJ mol^?C1.     

Hematite formation from jarosite type compounds by hydrothermal conversion

Abstract

The hydrothermal conversion of K jarosite, Pb jarosite, Na jarosite, Na–Ag jarosite, AsO₄ containing Na jarosite and in situ formed K jarosite and Na jarosite to hematite was investigated. Potassium jarosite is the most stable jarosite species. Its conversion to hematite in the absence of Fe₂O₃ seed occurred only partially after 5 h reaction at >240°C. In the presence of Fe₂O₃ seed, the conversion to hematite was nearly complete within 2 h at 225°C and was complete at 240°C. The rate of K jarosite precipitation, in situ at 225°C in the presence of 50 g L^?1 Fe₂O₃ seed, is faster than its rate of hydrothermal conversion to hematite. In contrast, complete conversion of either Pb jarosite or Na–Pb jarosite to hematite and insoluble PbSO₄ occurs within 0·75 h at 225°C in the presence of 20 g L^?1 Fe₂O₃ seed. Dissolved Fe(SO₄)_1·5 either inhibits the conversion of Pb jarosite or forms Pb jarosite from any PbSO₄ generated. The hydrothermal conversion of Na–Ag jarosite to hematite was complete within 0·75 h at 225°C in the presence of 20 g L^?1 Fe₂O₃ seed. The Ag dissolved during hydrothermal conversion and reported to the final solution. However, the presence of sulphur or sulphide minerals caused the reprecipitation of the dissolved Ag. The conversion of AsO₄ containing Na jarosite at 225°C in the presence of 20 g L^?1 Fe₂O₃ seed was complete within 2 h, for H₂SO₄ concentrations <0·4M. Increasing AsO₄ contents in the Na jarosite resulted in a linear increase in the AsO₄ content of the hematite, and ～95% of the AsO₄ remained in the conversion product. Increasing temperatures and Fe₂O₃ seed additions significantly promote the hydrothermal conversion of in situ formed Na jarosite at 200–240°C. However, the conversion of previously synthesised Na jarosite seems to proceed to a greater degree than that of in situ formed Na jarosite.

On a examiné la conversion hydrothermale en hématite de la jarosite de K, de la jarosite de Pb, de la jarosite de Na, de la jarosite de Na-Ag, de la jarosite de Na contenant de l’AsO₄, et de la jarosite de K et de la jarosite de Na qui sont formées in situ. La jarosite de potassium est la plus stable des espèces de jarosite. Sa conversion en hématite ne se produisait que partiellement après 5 h de réaction à >240°C en l’absence d’amorce de Fe₂O₃. En présence d’amorce de Fe₂O₃, la conversion en hématite était presque complète à moins de 2 h à 225°C et était complète à 240°C. La vitesse de précipitation de la jarosite de K, in situ à 225°C en présence de 50 g L^?1 d’amorce de Fe₂O₃, est plus rapide que sa vitesse de conversion hydrothermale en hématite. Par contraste, la conversion complète soit de la jarosite de Pb ou de la jarosite de Na-Pb en hématite et en PbSO₄ insoluble se produit à moins de 0·75 h à 225°C en présence de 20 g L^?1 d’amorce de Fe₂O₃. Le Fe(SO₄)_1·5 dissous soit inhibe la conversion de la jarosite de Pb ou forme de la jarosite de Pb à partir de tout PbSO₄ produit. La conversion hydrothermale de la jarosite de Na-Ag en hématite était complète à moins de 0·75 h à 225°C en présence de 20 g L^?1 d’amorce de Fe₂O₃. L’Ag se dissolvait lors de la conversion hydrothermale et se rapportait dans la solution finale. Cependant, la présence de soufre ou de minéraux sulfurés avait pour résultat la re-précipitation de l’Ag dissous. La conversion de la jarosite de Na contenant de l’AsO₄ à 225°C en présence de 20 g L^?1 d’amorce de Fe₂O₃ était complète à moins de 2 h, avec des concentrations d’H₂SO₄ <0·4 M. L’augmentation de la teneur en AsO₄ de la jarosite de Na avait pour résultat une augmentation linéaire de la teneur en AsO₄ de l’hématite et ～95% de l’AsO₄ demeurait dans le produit de conversion. L’augmentation de la température et d’additions d’amorce de Fe₂O₃ favorisait significativement la conversion hydrothermale de la jarosite de Na qui est formée in situ à 220–240°C. Cependant, la conversion de la jarosite de Na synthétisée antérieurement semblait se produire à un plus grand degré que celle de la jarosite de Na qui est formée in situ.     

The mineralogical deportment of germanium in the Clarksville Electrolytic Zinc Plant of Savage Zinc Inc.

A mineralogical study was carried out on the neutral leach residue and weak acid leach residue generated from Gordonsville zinc concentrate at the Clarksville Electrolytic Zinc Plant of Savage Zinc Inc. The intent was to characterize the mineral forms and associations of germanium. The Gordonsville zinc concentrate consists mostly of sphalerite which has a solid solution Ge content of ~400 ppm; the sphalerite is the dominant, if not only, Ge carrier in the concentrate. The neutral leach residue consists principally of iron gel-silica gel, ZnO, and basic zinc sulfate, (Zn,Cu)₄(SO₄)(OH)₆·4H₂O, together with minor amounts of ZnFe₂O₄, sphalerite, Zn₂SiO₄, Zn-Fe-Pb silicate, and PbSO₄, as well as traces of quartz, silicates, Pb-K jarosite solid solution, Fe₂O₃, and FeO·OH. The major Ge carrier is the iron gel-silica gel phase, but modest amounts of Ge are present in the ZnO, ZnFe₂O₄, sphalerite, and Zn-Fe-Pb silicate phases. The weak acid leach residue consists mostly of iron gel-silica gel, ZnFe₂O₄, PbSO₄, Pb-K jarosite, Zn-Fe-Pb silicate, and quartz. The major Ge carrier is the iron gel-silica gel phase which contains up to 1.7 pct Ge and accounts for ~70 pct of the total Ge content of this residue. The remaining Ge is carried by the Zn-Fe-Pb silicate, ZnFe₂O₄, and some of the rare Mn-Pb-Fe oxide phases.     

Factors affecting the precipitation of chromium(III) in jarosite-type compounds

Jarosite precipitation is a useful means of stabilizing toxic species, and accordingly, the factors affecting the precipitation of chromium(III) in jarosite-type compounds was systematically investigated in a series of laboratory experiments. Although end-member Cr(III) analogues of jarosite-type compounds could not be precipitated at temperatures <100 °C, several percent Cr(III) substitution for Fe(III) in potassium jarosite and sodium jarosite was observed. However, at temperatures >200 °C, the Cr(III) analogue of potassium jarosite (KCr₃(SO₄)₂(OH)₆) is readily precipitated. The Cr(III) analogue has the R $\bar 3$ m structure characteristic of jarosite-type compounds, with a=7.23±0.02Å and c=17.02±0.02 Å. The well-crystallized material typically contains (wt pct): ～7K, ～25Cr, and ～41SO₄. The composition suggests the partial substitution of hydronium ion for potassium and some chromium vacancies in the structure. The formation of the Cr(III) analogue is promoted by increasing temperatures, retention times, and Cr(III) concentrations. Increasing acid concentrations reduce the amount of product formed but suppress the undesirable precipitation of amorphous phases. Although increasing K₂SO₄ concentrations result in a greater mass of precipitate, the products formed from concentrated K₂SO₄ solutions are contaminated with an amorphous phase. In fact, the overall results suggest that an amorphous phase precipitates initially and that the Cr(III) analogue of potassium jarosite forms by the recrystallization, or the dissolution-reprecipitation, of the amorphous phase.     

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.     

The effect of electrolyte composition on the cathodic reduction of CuFeS2

The electrochemical reduction of CuFeS₂ mineral electrodes has been investigated by performing cathodic polarization curves, constant potential experiments, and cyclic polarization curves in various electrolytes. The effects of H₂SO₄, Fe²⁺ and Cu²⁺ concentrations have been examined as well as the effects of various dissolved gases, air, O₂, H₂S and N₂. Decreasing H₂SO₄ only shifts the curve to more negative potentials but initial concentrations of 0.36 M Fe²⁺ cause up to a ten-fold enhancement in the observed current. The presence of oxygen or Cu²⁺ also leads to an increase in the reduction current but in either case further increases in current are observed when Fe²⁺ is added to the electrolyte. Chalcocite (Cu₂S) or djurleite (Cu_1.96S) have been identified as products of reaction, although it is possible that a thin layer of a different copper-iron sulfide may form as an intermediate based on the color changes which appear after cathodic excursions. In addition, scanning Auger microprobe analyses of these surfaces show an increasing Cu:Fe ratio as the time at potential is increased. The results also indicate that the solid product layer is porous. A mechanism which accounts for the observed current increase in the presence of Fe²⁺ is proposed which involves a redox reaction between dissolved Fe²⁺ and cupric ion in the copper sulfide product layer.     

Kinetic model for the cyanidation of silver ammonium jarosite in NaOH medium

A synthesis of silver ammonium jarosite has been carried out obtaining a single-phase product with the formula: [(NH₄)_0.71(H₃O)_0.25Ag_0.040]Fe_2.85(SO₄)₂(OH)_5.50. The product consists on compact spherical aggregates of rhombohedral crystals. The nature and kinetics of alkaline decomposition and also of cyanidation have been determined. In both processes an induction period followed by a conversion period have been observed. During decomposition, the inverse of the induction period is proportional to [OH⁻]^0.75 and an apparent activation energy of 80 kJ mol^− 1 was obtained; during the conversion period, the process is of 0.6 order (OH⁻ concentration) and an activation energy of 60 kJ mol^− 1 was obtained. During cyanidation, the inverse of the induction period is proportional to [CN⁻]^0.5 and an apparent activation energy of 54 kJ mol^− 1 was obtained; during the conversion period the process is of 0 order (CN⁻ concentration) and an activation energy of 52 kJ mol^− 1 was obtained. Results obtained are consistent with the spherical particle model with decreasing core and chemical control, in the experimental conditions employed. For both processes and in the basis of the behaviour described, two mathematical models, including the induction and conversion periods, were established, that fits well with the experimental results obtained. Cyanidation rate of different jarosite materials in NaOH media have also been established: this reaction rate at 50 °C is very high for potassium jarosite, high and similar for argentojarosite and ammonium jarosite, lower for industrial ammonium jarosite and negligible for natural arsenical potassium jarosite and beudantite. These results confirm that the reaction rate of cyanidation decreases when the substitution level in the jarosite lattice increases.     

Factors affecting lead jarosite formation

The importance of lead jarosite in hydrometallurgical processing and the factors affecting its formation in both the slow addition and autoclave synthesis techniques are discussed. In the slow addition method the principal factors are the amount and rate of delivery of soluble lead to the hot ferric sulphate solution; high temperatures and good agitation are also essential to avoid the formation of PbSO₄. The key step in the autoclave synthesis process is the selective removal of residual PbSO⁴ from the reaction product and methods of accomplishing this are described. The major factors affecting the autoclave synthesis of lead jarosite are the ratio of $\text{PbSO}{}_4\text{Fe}{}^{\mathrm{3+}}$, acid concentration and the ionic strength of the solution. Time, temperature, degree of agitation and seeding all affect the reaction but to a lesser degree. The principal techniques identified to suppress lead jarosite formation were high acidity (> 0.3 M H₂SO₄ or the presence of substantial quantities (> 0.3 M) of other jarosite formers such as K₂SO₄. Lead jarosites containing more than 16% Pb were produced and X-ray diffraction data for such material are presented.     

The action of sulfur trioxide on chalcopyrite

Chalcopyrite reacts readily with SO₃ at about 100°C to form water-soluble sulfates; the reaction is approximately: 3CuFeS₂+26SO₃→3CuSO₄+FeSO₄+Fe₂(SO₄)₃+25SO₂ The presence of about 4 pct O₂ in the gas phase greatly accelerates the reaction presumably due to the complete transformation of ferrous into ferric sulfate in an extremely porous form: 2CuFeS₂+17SO₃+1/2O₂→2CuSO₄+Fe₂(SO₄)₃+16SO₂ A stoichiometric mixture of SO₂+1/2O₂ behaves towards chalcopyrite in nearly the same way as SO₃ although only in the temperature range 350° to 700°C.     

Effects of additives on zinc electrowinning from industrial waste products

An investigation of the effects of some additives on zinc electrowinning from a weak acidic sulphate electrolyte prepared from an industrial waste product has been carried out. Experiments were done in the presence of additives such as aluminium sulphate, animal glue and an extract of horse-chestnut nuts (HCE), used alone or in different mixtures.Using a rotating disc electrode (RDE) and cyclic voltammetry, the influence of the additives on the polarization curves and on the voltammograms was studied. SEM was used to determine the structure and the morphology of deposits.The results indicated that the additives tested exert a beneficial effect on the quality of the zinc deposits. They increase the cathodic polarization and promote levelling. Al₂(SO₄)₃ influences the reduction of zinc ions, increasing the nucleation overpotential and the deposition rate of zinc on the cathode. The conjoint use of Al₂(SO₄)₃, animal glue and HCE results in smooth, slightly bright deposits, showing a beneficial effect of the mixture on zinc electrodeposition. The analysis of deposit purity suggested that the additives inhibit the discharge rate of impurity metal ions, such as copper and lead, whose deposition is diffusion controlled.     

Preparation of an As(V) solution for scorodite synthesis and a proposal for an integrated As fixation process in a Zn refinery

A method for producing an As(V) solution from an As-bearing material obtained from a nonferrous hydrometallurgical process was investigated. Preparation of the As(V) solution included oxidative leaching of As with a NaOH solution, elimination of As as a calcium arsenate precipitate (johnbaumite: Ca₅(AsO₄)₃(OH)) with a Ca(OH)₂ secondary salt, washing the Ca–As compounds, and reaction of the Ca–As precipitate with H₂SO₄. This process was shown to be industrially applicable. The As ions and Cu ions were effectively separated by oxidative leaching with O₂ gas injection under strongly basic conditions. In this system, As dissolved in the NaOH solution and Cu precipitated with the residue. The dissolved As in this highly concentrated NaOH solution was then effectively precipitated from the solution by addition of a surplus amount of CaO, which allowed recycling of the NaOH solution. The addition of surplus Ca precipitated Ca₅(AsO₄)₃(OH) and Ca(OH)₂, which inhibited the leaching of As but did leach Ca and Na. When the Ca–As compounds were dissolved with H₂SO₄, Ca ions precipitated in the form of gypsum from the As-bearing solution. The gypsum produced by this process is likely to give rise to a number of As-related issues and the As level, therefore, needs to be reduced. This process is advantageous for the treatment of As since it is stabilized as scorodite. The production of an As(V) solution could be applied to hydrometallurgical operations as it necessary for the removal of As. This process is shown to be practically useful to As removal in Zn refining and a closed flow circuit is proposed for integration of this process into a Zn hydrometallurgical operation.     

The production of very fine copper powder

Conclusions A study was made of the possibility of preparing copper powder by the method of reduction by titanium compounds in aqueous solutions, and it was established that, as a result of the reaction of titanium sulfate Ti₂(SO₄)₃ with copper sulfate CuSO₄ in a solution with an addition of 200–250 g/dm³ I₂SO₄, a very fine, pure copper powder with rounded particles is produced.Two methods of preparing copper powder were developed: one employing the gradual addition (drop by drop) of a saturated CuSO₄ solution to a Ti₂(SO₄)₃ solution (periodic method) and another employing the anodic dissolution of metallic copper in a Ti₂(SO₄)₃ solution (continuous method). In both cases, the process is carried out with the simultaneous electrochemical reduction Ti⁴⁺+eTi³⁺ on a lead or copper cathode.The periodic method is more suitable for the preparation of powders of extra-high purity, because it is easier to remove impurities from salts than from metals. The advantages of the continuous method comprise the possibility of utilizing various forms of copper scrap as anodes, absence of losses of titanium and copper salts, and possibility of performing the process automatically.The following have been developed: a procedure for the treatment and drying of powder, and methods of determining powder size and the degree of purity of the product. It is shown that, for determining the degree of oxidation of copper powder, it is possible to use a visual method of comparing the color of the product with that of specially prepared reference specimens.     

Quantum-Chemical Substantiation of Properties of a Bioreagent Oxidizing Nonferrous Metal Sulfides

A structural formula and quantum-chemical characteristics of the most energetically probable stable conformation of a bioreagent molecule, which is formed upon oxidizing iron(II) ions by Acidithiobacillus ferrooxidans autotrophic mesophilic iron-oxidizing bacteria in a sulfuric acid solution consisting of iron(III) ions and three acidic residues of glucuronic acid, are determined. The bioreagent oxidant is widely applied in industry for leaching metals from sulfide ores of nonferrous metals and concentrates of concentration. Quantum- chemical characteristics of the bioreagent molecule are analyzed in comparison with anhydrous iron(III) sulfate, which is also used in hydrometallurgy as an oxidant. To investigate the structure and quantum- chemical characteristics, the molecular computer simulation method, the theory of boundary molecular orbitals, and the Pearson principle are used. It is established that the most energetically probable stable conformation of the bioreagent molecule contains acidic residue of glucuronic acid with a noncyclic structure. According to the results of investigations, the bioreagent is referred to more rigid Lewis acid (the electron acceptor) than Fe₂(SO₄)₃. The bioreagent molecule is less polarized and has lower absolute electronegativity and a twofold larger volume. The theoretical substantiation of the larger persistence of primary sulfides (pyrite, pentlandite, and chalcopyrite) relative to secondary minerals (pyrrhotine, chalcosine, and covellite) is proposed based on calculated values of boundary molecular orbitals; absolute rigidity; and the electronegativity of iron, copper, and nickel sulfides. Characteristics determining the interaction efficiency (volume, heat of formation, steric energy and its components, total energy, etc.) of the bioreagent are multiply larger than for Fe₂(SO₄)₃. The larger oxidative activity of the bioreagent relative to Fe₂(SO₄)₃ can be substantiated by a higher partial charge of the iron atom and a longer bond length between the atoms, the lower energy of the lowest free molecular orbital, and increased degree of the charge transfer during the bioreagent interaction with sulfide minerals.     

Physico-chemical properties of copper electrolytes

A systematic study was undertaken to determine the diffusion coefficient(D) for Cu⁺² in the CuSO₄-H₂SO₄ system at different Cu and H₂SO₄ concentrations and temperatures. An empirical equation for predicting theD value was developed and checked for its validity. Conductivities, densities, and viscosities of copper electrolytes were measured in a wide range of Cu and H₂SO₄ concentrations and temperatures and the results are reported. Such information also was gen-erated for complex solutions containing the impurities Ni, Co, Fe⁺², Fe⁺³, and Mn. These prop-erties were calculated further using empirical equations and compared with the measured values.     

Investigations into complex processing of zinc cakes

Investigations are carried out into the processing of zinc cakes with the purpose of transferring zinc, copper, and iron from ferrites into a solution and of concentrating noble metals in the lead-containing silicate product. Zinc cakes are subjected to sulfatization by oleum followed by leaching with a concentrated H₂SO₄ solution. With the use of a planned multifactor experiment according to the Box plan, the effect of the H₂SO₄ content in the leaching solution on the cake leaching process, its duration, and temperature has been studied. Due to this, the models of the dependence of the listed factors on the extraction of Zn, Fe, and Cu into the solution have been obtained. The possibility of an almost complete extraction of these metals into the solution is demonstrated. The following leaching conditions are suggested as optimal: H₂SO₄ concentration of 8.33 g/l in the leaching and washing solutions, leaching time of 2 h, and leaching temperature of 75°C.