Studies on the Oxidation of Pyrite : (Part 1) Thermal Decomposition of Pyrite

The kinetics of the thermal decomposition of pyrite and the properties of the thermal decomposition products were studied and the following results were obtained. 1. Thermal decomposition of pyrite is not followed by the first order reaction. In the (-log x)-t diagram (where x is mol fraction of pyrite), a knick point was observed at x≒0.3. From the linear parts before and after this knick point, an activation energy of 50.9kcal is obtained for the initial period of the reaction and that of 40.3kcal. for the final period of the reaction. 2. The composition of the thermal decomposition products can be represented by FeS₁₊ₓ, and this coefficient of the formula becomes smaller with an increase in the temperature of decomposition. Of these decomposition products, FeS₁.₁₃ and FeS₁.₁₁ are ferromagnetics whose Curie point is 295°C, and FeS₁.₀₉ and FeS₁.₀₈ are antiferromagnetics whose Curie point is about 220°C. And, FeS₁.₀₆, Fes₁.₀₅ and FeS₁.₀₀ are paramagnetics. 3. The thermomagnetic properties of antiferromagnetic or paramagnetic FeS₁₊ₓ remain unchanged when they are heated to 300°C in vacuum sealed capsules or in high vacuum ; on the other hand, they change into the ferromagnetic ones when they are heated in low vacuum or in the air. By this change, their lattice parameter and axial ratio also change to those of the ferromagnetic ones. From these results, it may be said that this change is due to the initial stage of oxidation of FeS₁₊ₓ and that, by this change, ferromagnetic FeS₁₊ₓ, whose composition is near the upper limit of solubility of sulphur in FeS₁₊ₓ, is formed

Studies on the Nickel Matte : I. Nickel-Iron-Sulphur System

Main raw material for metallic nickel in Japan is garniellite, and the matte-smelting process is usually adopted here. The nickel matte produced in this process is, therefore, a ternary mixture of nickel, iron and sulphur, and it is usually ferromagnetic. The relationship of the magnetic properties of the nickel matte to its composition is considered to be important both from fundamental and practical points of view. The authors conducted measurements of the intensity of magnetization, thermomagnetic analyses and X-ray studies on prepared specimens of the binary system Ni-S and of the ternary system Ni-Fe-S. In the system Ni-S and Ni-Fe-S, ferromagnetism was found in a limited region, and it is due to the metallic nickel phase in Ni-S and the nickel-iron alloy phase in Ni-Fe-S. The hexagonal phase NiS and the cubic ternary compound (Ni, Fe)₉S₈ were investigated with X-ray, and their lattice parameters were determined. Furthermore, the range in which (Ni, Fe)₉S₈ exists was also fixed. They are as follows : a=3.436 kX, c=5.351 kX and c/a=1.557 in NiS, and the range of the existence of (Ni, Fe)₉S₈ ; 22.2 atom.% Ni and 30.7 atom.% Ni in the section of 47.1 atom.% S, and a=10.129 kX in (Ni, Fe)₉S₈ saturated with FeS a=10.095 kX in (Ni, Fe)₉S₈ saturated with Ni₃S₂. The continuous solid solution of NiS and FeS₁₊ₓ, the hexagonal phase η, was also investigated with X-ray. The Curie temperature of the specimens in the ternary system showed rather peculiar behaviors in relation to their compositions. This peculiarity of the Curie temperature seems to be due to the deviation in the content of nickel in the alloy phase of matte. Other two magnetic transformations were also observed ; one was found with the specimens in the region γ+δ+π (see Figs. 1 and 9) at about 480°C in heating and at about 420°C in cooling. The authors considered this transformation to be related to the order-disorder transformation in the Ni₃Fe lattice. The other was found in the region γ+ε and in the iron side of the region γ+ε+π. This transformation was found to be due to the α⇄γ transformation in the nickel-iron alloy phase. The properties of the nickel matte taken from the converter of a nickel smelter were also examined, and the results were in good agreement with those of the prepared specimens

Studies on the Oxidation of Pyrite III : The Intermediate Products in the Oxidation of Pyrite

The intermediate products in the oxidation of pyrite were investigated by measurement of the intensity of magnetization, thermomagnetic analysis and X-ray diffraction. In the course of the oxidation, the intensity of magnetization of the sample increases, reaches a maximum, and then decreases. The maximum value of the sample oxidized at low partial pressures of oxygen was found to be much higher than that oxidized at high partial pressures of oxygen. FeS₁₊ₓ and Fe₃O₄ were the main products of oxidation at low partial pressures of oxygen, and Fe₃O₄ changed into Fe₂O₃ immediately before the end of the oxidation. On the other hand, Fe₂O₃ was formed in addition to Fe₃O₄ from the early stages of the oxidation at high partial pressures of oxygen. The FeS₁₊ₓ formed in the intermediate stage was ferromagnetic, and its composition was near the upper limit of the solubility of sulphur in FeS₁₊ₓ. Samples taken from the roasting hearths of the Herreshoff furnace were investigated by measurement of the intensity of magnetization and thermomagnetic analysis. Pyrite decomposes into FeS₁₊ₓ in the upper hearths and, in the middle hearths, FeS₁₊ₓ is oxidized mainly to Fe₃O₄, and finally, Fe₃O₄ changes into Fe₂O₃ in the lower hearths. The intensity of magnetization reaches the maximum in the middle hearths of the furnace. The formation of a large amount of Fe₃O₄ in the middle hearths indicates that the partial pressure of oxygen in the layer of the charge in the furnace was remarkably low

Studies on the Oxidation of Pyrite : (Part 2) Kinetics of the Oxidation of Pyrite

The kinetics of the oxidation of pyrite in the atmosphere of the mixed gas of O₂, SO₂ and N₂ was studied. The results obtained were summarized as follows : 1. At 700°〜900°C where the thermal decomposition of pyrite proceeds quickly, the reaction occurs in two stages, the initial one is of the thermal decomposition of pyrite and the final one is of the oxidation of the thermal decomposition product, FeS₁₊ₓ. This phenomenon is more obvious at lower partial pressure of oxygen. The rate constant of the oxidation of FeS₁₊ₓ was found to be proportional to the partial pressure of oxygen, and the activation energy of this reaction was determined to be about 8.3 kcal. 2. At 550°〜650°C, the thermal decomposition of pyrite proceeds slowly and, as a result, the following three reactions occur simultaneously, FeS₂ = FeS₁₊ₓ+(1-x)/2S₂(g), FeS₁₊ₓ+(7/2)+2x)O₂ = 1/2 Fe₂O₃+(1+x)S₂, FeS₂+11/4 O₂ = 1/2 Fe₂O₃+2SO₂. For the mol fraction of x, y and z respectively for FeS₂, FeS₁₊ₓ and Fe₂O₃, the simultaneous differential equations were brought out and they were solved approximately. We defined also the ratio of weight decrease w and it was shown as a function of time t by applying the solutions of the above equations. From the expression of this w, the rate constant of the direct oxidation of pyrite, k₃, was obtained. This rate constant, k₃, was also found to be proportional to the partial pressure of oxygen and its activation energy to be about 11.9 kcal. 3. The change of mol fraction x, y and z along the oxidation was computed. From this computation, the amount of FeS₁₊ₓ formed as an intermediate product of the reaction was found to be dependent on the temperature of oxidation and the partial pressure of oxygen. 4. The calculated ratio of weight decrease w coincides considerably with the observed values at lower temperatures of the oxidation, but the coincidence is not good at higher temperatures. Since the thermal decomposition proceeds very quickly at higher temperatures, the following assumptions on the reactions fit better than the simultaneous progress of the three reactions mentioned above ; a) at the initial stage, the thermal decomposition proceeds preferentially and FeS₁₊ₓ is formed, and b) toward the end of the thermal decomposition, the oxidation of FeS₁₊ₓ commences, followed by the decomposition

OUR ENVIRONMENTAL ANALYSIS TOOLS PREPARED AND THE APPLICABILITY TO JOINT RESEARCH WITH VIETNAM

Joint Research on Environmental Science and Technology for the Eart

Studies on the System Nitric Acid―Water―Tri-n-butyl Phosphate

It is intended in this study to determine the composition of species formed in the equilibrated organic phase and to clarify the extraction mechanism in the system of HNO₃-H₂O-TBP. Similarly as the previous papers on the systems of mineral acid-H₂O-TBP, physico-chemical measurements of volume swelling, density, viscosity and electrical conductivity were carried out on the equilibrated organic phase, in addition to the conventional distribution measurement of HNO₃ and water between organic and aqueous phases. It was found that the major extracted species are (TBP)₂·HNO₃·H₂O and (TBP)₂·H₂O·H₃0⁺···NO₃－ in the medium acidity region and TBP·HNO₃ and TBP·HNO₃·H₃O⁺··· NO₃－ in the higher acidity region. Apparent degree of dissociation in the organic phase is below 0.05 over the whole range of nitric acid concentration studied, and the extracted species are almost undissociated or ion-paired

Studies on the System Sulphuric Acid-Water-Tri-n-Butyl Phosphate

It is intended in this study on the system H₂SO₄-H₂O-TBP to determine the species formed in the equilibrated organic phase and to clarify the extracting mechanism of aqueous sulphuric acid into organic phase. As in the previous report published in this Memoir, physico-chemical measurements of volumeswelling, density, viscosity and electrical conductivity were carried out with the equlibrated organic phase in addition to the conventional distribution measurement of sulphuric acid and water. It was found that the extracting species is [TBP·Hᴏ] at the equilibrated acid concentration in aqueos phase below 2.0M and that three other species were found to exist above 2.0M ; the one formed at lower acid concentration has the general formula [(TBP)₃·H₃O⁺(x+2)H₂O···HSO₄⁻], (x was determined as 2.5), the one formed at medium acid concentration is [TBP·H₃O+(x+2y/3)H₂O···HSO₄-] (y was determined as 0.25), and the one formed at higher acid concentration is [TBP·2{H₃O+(x+5y-3/6)H₂O···HSO₄}] They dissociate partly. The activities and activity coefficients of the two species [TBP·H₂O] and [(TBP)₃·H₃O⁺4.5H₂O···HSO₄⁻] stable at lower acid concentration and the equilibrium constant between them were determined with Redlich-Kister equations

Studies on the System Perchloric Acid-Water-Tri-n-Butyl Phosphate

It is intended in this study on the system HClO₄-H₂O-TBP to determine the species formed in the equilibrated organic phase and to clarify the extraction equilibrium in a part of the system. On the same line as the previous papers published in this Memoir, physico-chemical measurements of volume swelling, density, viscosity and electrical conductivity were carried out on the organic phase in addition to the distribution measurements of perchloric acid and water between organic and aqueous phases. The extracting species determined are summarized in Table 1. The species at lower acidity regions are supposed to be almost completely ionized. Dehydration of the organic phase occurs at higher acidity regions. The activities and activity coefficients of the two species [TBP·H₂O] and [(TBP)₂₀H₃O+(H₂O)₂₃]+[ClO₄⁻] stable at the lowest acidity region were determined with Redlich-Kister equations

On the Nonuniformity in Fluidized Bed

Mean (μc) and variance (σ) of local particle concentration in fluidized bed were measured by capacitance probe method using integrator and vacuum tube thermocouple. Particle concentration in bubble and dense phases (cb and cd), rise velocity of bubble (ub), bubble thickness (y) and its frequency (f) were also measured from the signal current recorded on oscillograms. The effects of fluidizing conditions on μc and σ were studied. In the bulk of bed, μc remains at a value fixed by the fluidizing conditions. It decreases with air velocity. σ, on the other hand, increases with probe level up to considerably higher portion of bed and there arrives at a constant value which increases with bed height and air velocity. The following equation was introduced to represent μc by the fluidizing characteristics. μc=yf/ubcb+(1-yf/ub)cd μc calculated by this equation coincides well with the measured μc. A regression equation of σ upon fluidizing characteristics, σ=0.72{yf/ub(1-yf/ub)}⁰.⁴⁶(cd-cb)².⁸⁹ was obtained, and the statistical analyses on this equation revealed that σ changes chiefly with (cd-cb), and accordingly, σ represents the nonuniformity in fluidized bed mainly in the form of particle concentration difference between bubble and dense phases