Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1985"

Mathematical Modeling of Porosity Formation in Solidification

Abstract: Shrinkage porosity and gas porosity occur simultaneously and at the same location when conditions are such that both may exist in a solidifying casting. Porosity formation in a solidifying alloy is described numerically, including the possible evolution of dissolved gases. The calculated amount and size of the porosity formed in Al-4.5 pct Cu plate castings compares favorably with measured values. The calculated distribution of porosity in sand cast Al-4.5 pct Cu plates of 1.5 cm thickness matches experimental measurements. The decrease of the hydrogen content by strong degassing and the increase of mold chilling power are recommended to produce sound aluminum alloy castings. The calculated results for steel plate castings are in agreement with the experimental work of Pellini. The present modeling has clarified the basis of empirical rules for soundness and suggests that the simultaneous occurrence of shrinkage and gas evolution is an essential mechanism in the formation of porosity defects.

Metal-Mold interfacial heat transfer

Abstract: During the solidification of metal castings, an interfacial heat transfer resistance exists at the boundary between the metal and the mold. This heat transfer resistance usually varies with time even if the cast metal remains in contact with the mold, due to the time dependence of plasticity of the freezing metal and oxide growth on the surface. The present work has studied interfacial heat transfer on two related types of castings. In the first type, a copper chill was placed on the top of a cylindrical, bottom gated casting. Using the techniques of transducer displacements and electrical continuity, a clearance gap was detected between the solidified metal and the chill. The second type of casting had a similar design except that the chill was placed at the bottom. Owing to the effect of gravity, solid to solid contact was maintained at the metal-chill interface, but the high degree of interface nonconformity resulted in a relatively low thermal conductance as indicated by solution of the inverse heat conduction problem. Finally, the influence of interfacial heat transfer on solidification time with three mold ma-terials is compared by a numerical example, and criteria for utilizing Chvorinov's rule are discussed.

Distribution of the heat and current fluxes in gas tungsten arcs

Abstract: The distribution of heat flux on a water-cooled copper anode as a function of welding process parameters has been determined experimentally following an experimental technique developed previously. The results indicate that arc length is the primary variable governing heat distribution and that the distribution is closely approximated by a gaussian function. The half width of the heat flux is defined by a distribution parameter, σ, which was determined from the experimental data and is expressed as a function of arc length, current, and electrode tip angle. The distribution parameter, σ, increases from 1.5 mm to 3.6 mm as the arc length increases from 2 mm to 9 mm for a 100 A arc. The experimental data also show that arc energy transfer efficiency is greater than 80 pct on the water-cooled anode which is much higher than has been measured in the presence of a molten metal pool. For this reason, it is believed that the distribution of the heat flux and not the magnitude is the most useful information obtained in this study. The effect of helium additions to the argon on the heat distribution is also reported.

Effect of suspension potential on the oxidation rate of copper concentrate in a sulfuric acid solution

Abstract: A chalcopyrite concentrate containing 17 pct pyrite was oxidized in 1 mol/dm3 sulfuric acid solution at 90 °C (363.2 K). The suspension potential (Ptvs SCE, in the presence of Fe3+/Fe2+) was maintained constant in the range 0.30 to 0.65 V by controlled additions of KMnO4 solution. The oxidation appeared to be under surface reaction control. The rate constant was nearly independent of total Fe concentration (0.01 to 0.5 mol/dm3), but increased rapidly with a rise in suspension potential until it reached a maximum at 0.40 to 0.43 V, after which there was marked decrease at around 0.45 V. Chalcopyrite in the concentrate was oxidized to form elemental sulfur over the whole of the suspension potential range, whereas the oxidation of pyrite took place only above 0.45 V and yielded sulfate ion. At 0.40 V the apparent activation energy was 47 kJ/mol. An analogy between the potential dependence of the rate and the Tafel correlation for an electrode process is discussed.

Experimental study of continuous electromagnetic casting of aluminum alloys

Abstract: This work begins with a summary of the characteristics of electromagnetic casting and the present knowledge of the subject. Also described is the use of new local measurement techniques for velocity, magnetic field, current density, and phase difference, which allow experimental investigation of the flow of molten metal in industrial equipment (up to 700 °C) in the presence or absence of an induction magnetic field. Next, these methods are applied to the study of electromagnetic and hydrodynamic phenomena, inside the sumps of both rectangular and circular cross-section ingots of aluminum alloys cast in electromagnetic molds. The important shield effect as a function of the screen location is studied by means of a mercury pool simulating electromagnetic casting.

The kinetics of dissolution of sphalerite in ferric chloride solution

Abstract: The dissolution of sphalerite in acidic ferric chloride solution was investigated in the temperature range 320 to 360 K. Both sized particles from three sources and polished flat surfaces were used as samples. The effect of stirring rate, temperature, ferric and ferrous ion concentration, purity, and particle size on the dissolution rate were determined. During the initial stages of the process chemical reaction at the mineral surface is rate controlling while during the later stages diffusion through the product sulfur layer is rate controlling. Overall the process follows the mixed-control model embodying both chemical reaction and diffusion. The activation energy for the dissolution of sphalerite particles was found to be 46.9 kJ/mol.

Hydrodynamic Modeling of Some Gas Injection Procedures in Ladle Metallurgy Operations

Abstract: Experimental studies of flows generated in a 0.30 scale water model of a 150 ton steelmaking ladle are reported. These were used to test the adequacy of a generalized two-dimensional computational scheme for predicting flows generated by fully submerged and partially submerged gas injection lances. The roles of turbulence models and grid configuration were assessed. Predictions for flow fields generated in a 150 ton steelworks ladle with and without tapered side walls, and with and without surface baffles around the rising plume were considered.

Interfacial phenomena between molten metals and sapphire substrate

Abstract: Interfacial energies and contact angles for liquid Cu-sapphire and liquid Ag-sapphire systems as a function of O2 partial pressure were experimentally determined using the sessile drop technique. For very low values of Po2the variation of γlg is small, but at Po2, values high enough to establish a monolayer on the liquid metal, γlg decreases linearly with increasing logP o2. The slope of this line is related to the surface concentration of oxygen through Gibb's absorption equation. For various metal-sapphire systems, γlg is found to be a cosine function of the contact angle (θ) whereas γsl seems to be a linear function of (θ). A theoretical model has been developed to predict this behavior. One empirical constant relating to the free energy of formation of an interfacial compound was employed. The validity of the model has been tested for the Cu, Ag, Fe, and Ni-sapphire systems. The model has also been used to predict the effect ofP o2on the interfacial energies and contact angle for the Co-sapphire system.

Characteristics of round vertical gas bubble jets

Abstract: Radial and axial profiles of gas concentration and bubble frequency have been measured for vertical gas bubble jets in the systems air/water, helium/water, and nitrogen/mercury using an electroresistivity probe. Gas velocities have been determined in the air/water system. All radial profiles were close to Gaussian. An integral model was applied to calculate axial distributions theoretically. Entrainment coefficients were determined for the experimental conditions. Axial profiles were correlated also in nondimensional representations. The bubble frequencies were used to compute local and average values of bubble size. Jet expansion and bubble size were found to depend considerably on the physical properties of the system.

Effect of oscillation-mark formation on the surface quality of continuously cast steel slabs

Abstract: In a study of early solidification during the continuous casting of steel slabs, the effect of the formation of oscillation marks on the surface quality of the slabs has been examined by metallographic in-vestigation of slab samples and by performing a set of mathematical analyses. Positive segregation of solute elements, especially phosphorus and manganese, has been observed at the bottom of the oscillation marks and has been classified into two categories. One type is observed at the end of the overflow region on subsurface hooks which originate from partial solidification of the meniscus. A heat-flow model which takes into account the shape of the oscillation marks has revealed that this type of positive segregation is caused by local delay of solidification at the bottom of the oscillation marks. The other type of positive segregation has been found in a layer on the bottom of the oscillation marks without subsurface hooks. This form of segregation cannot be explained by the heat-flow model, but is likely due to a penetration mechanism in which the negative pressure in the flux channel generated during the upward motion of the mold draws out interdendritic liquid from the semi-solidified shell. Transverse cracks are found along the bottom of oscillation marks. The surface of the transverse cracks exhibits an interdendritic appearance in the vicinity of the slab surface, which implies that the cracks are initiated as hot tears in the mold region. A heat-flow analysis predicts that deep oscillation marks cause nonuniformity of the shell in the mold, which also was observed in the metallographic in-vestigation. According to the heat-flow analysis, not only the depth but also the pitch of the oscillation marks affects the shell profile. Therefore increasing the frequency of mold oscillation effectively reduces transverse cracks, by decreasing both the depth and the pitch of oscillation marks.

Chemical reactions during submerged arc welding with FeO-MnO-SiO2 fluxes

Abstract: Measurements have been made of the compositional changes of fluxes and weld metal during submerged arc flux welding with a series of synthetic MnO-FeO-SiO2 model fluxes containing 40 wt pct SiO2 and different ratios of MnO to FeO. Mechanisms for the transfer of Mn, O, Si, C, S, and P are discussed in terms of the thermodynamic driving forces and kinetic factors such as diffusion, nucleation, and segregation. One unique deduction is that interfacial, not bulk activities of components (such as FeO) govern transfer into (or out of) the metal phase. The concentrations of C, P, S, and possibly Si tend to be larger in the molten weld metal than in the base plate.

Microstructure of rapidly solidified laser molten AI-4.5 Wt Pct cu surfaces

Abstract: The microstructure of rapidly solidified laser molten or electron beam molten Al-4.5 wt pct Cu alloyed surfaces has been investigated. A variety of electron microscopy techniques was employed. The epitaxially resolidifying melt undergoes three different solidification modes: about 3 μm to 5 μm of material near the fusion line resolidify in a plane front mode. The next bulk resolidifies in a cellular dendritic mode, which then turns dendritic. The major impact of resolidification is refinement of the surface microstructure, which by itself shows various characteristics for the different resolidification modes. Particularly, the validity of the relationship of secondary interdendritic arm spacing, as inversely dependent on the one-third power of the average local cooling rate, was verified for cooling rates up to 106 K per second.

Nitrogen solubility and nitride formation in austenitic Fe-Ti alloys

Abstract: The equilibrium nitrogen solubility and nitride formation in austenitic Fe and Fe-Ti alloys were measured in the temperature range from 1273 to 1563 K. Specimens 0.5 mm thick were equilibrated with four different nitrogen-argon gas mixtures containing 1 pct hydrogen. The nitrogen solubility in austenitic iron obeys Sieverts' law. The equilibrium nitrogen content was determined to be log (wt pct N)γ-Fe, PN2=1 atm = (539 ± 17)/T − (2.00 ± 0.01). The precipitated titanium nitride was identified as cubic TiN, and the solubility product was determined to be log(wt pct Ti) (wt pct N) = −14,400/T + 4.94.

Thermodynamics and Phase Relationships of Transition Metal-Sulfur Systems: Part V. A Reevaluation of the Fe-S System Using an Associated Solution Model for the Liquid Phase

Abstract: The relevant thermodynamic and phase equilibrium data for the Fe-S binary system have been reevaluated in light of more recent data. An associated solution model is used to describe the thermodynamic properties of the liquid phase as a function of composition and temperature. For the pyrrhotite phase, a statistical thermodynamic model based on the formation of Frenkel defects in the lattice is used. For the austenite and ferrite phases, the solute is assumed to follow Henry’s law, and pyrite is taken to be a stoichiometric compound. The model parameters for the various phases are obtained by evaluating all relevant experimental data reported in the literature. The calculated phase diagram is in good agreement with the experimental data. The calculated sulfur activity values for the liquid phase agree well with experimental values including those at higher sulfur concentrations. This is an improvement of an earlier evaluation by Sharma and Chang using the same model with the same number of parameters.

Centerline porosity in plate castings

Abstract: Centerline porosity in horizontally cast steel plates has been examined analytically. The presence and extent of porosity has been calculated on the basis of heat flow in the system and interdendritic fluid flow. The calculated distribution of porosity was found to agree closely with measured values reported in the literature. Several solidification parameters have been proposed to indicate the onset of porosity. The present investigation shows that the parameter G/R1/2 is the best of the parameters suggested, where G andR are the centerline temperature gradient and growth velocity, respectively.

Kinetics of the zinc slag-Fuming process: Part i. industrial measurements

Abstract: A study involving industrial measurements and mathematical modeling has been conducted to eluci-date kinetic phenomena in the zinc slag fuming process. In the first part of this three-part paper, the results of industrial measurements and observations are presented. In Part II a mathematical model of the process is developed, and finally in Part III the implications of a kinetic conception of the process for process improvement are explored. The industrial work consisted primarily of slag sampling through the fuming cycles of five different fuming operations. In addition, tuyere back-pressure mea-surements, tuyere photography using a tuyerescope, and sampling of the fume product were under-taken at one operation. Analysis of the slag samples has shown that, in general, the zinc elimination curve is linear with time and that a portion of the injected coal entrains in the slag. Analysis of tuyere back-pressure fluctuations and movie photographs of the tuyere tip indicate that the coal-air mixture enters the slag in the form of discrete bubbles. From these results it can be deduced that the fuming furnace consists of two reaction zones which are created by the division of coal between the slag and the tuyere gas stream. The coal entrained in the slag reduces ZnO and Fe3O4 in a “reduction zone” which is responsible for fuming. The coal remaining in the tuyere gas stream combusts in an “oxidation zone” although a fraction passes through the bath unconsumed and reports to the solid products. The oxidation zone supplies heat to the endothermic reduction reactions and heat losses.

An Experimental Study of Segregation in Rotary Kilns

Abstract: An experimental study has been conducted to elucidate the mechanism of radial segregation in the bed of a rotary kiln and to determine the size and composition of the segregated core Bed-behavior diagrams were obtained, and slumping and rolling characteristics were measured, for two sand mixtures and one limestone mixture containing fines The fines resulted in significant changes in bed behavior, but no effects were observed on either static or dynamic angle of repose, shear angle, slumping frequency, or active-layer thickness Therefore it was concluded that the fines do not segregate according to the differential flow of particles down the surface of the bed Instead percolation, in which the fines pass through the voids in the coarser solids, appears to be the operative mechanism The size of the segregated core was measured by sampling the bed of solids Predictions of core width based on geometric considerations and a core composition having the minimum void fraction agreed reasonably well with measurements A second region of segregation was found adjacent to the wall The two zones of segregation can influence deleteriously kiln performance Solids in the central core are not exposed to the hot freeboard gases and therefore may only partially react The zone of fines at the kiln wall can reduce wall/bed friction to the extent that the bed slips against the wall

A unified approach to bubbling-jetting phenomena in powder injection into iron and steel

Abstract: The injection of powder into liquids has been investigated by physical modeling and by multi-phase fluid dynamic modeling. The transition from gas-particle jets which penetrate deeply into the liquid and a gas bubbling regime was found to depend on the coupling between gas and particle phases in the conveying line; fine particles at high loading couple well and form jets, whereas coarse particles separate from the gas during bubble formation. The measured penetration depths of submerged jets in water and lead and top jets in water were very well described by equations balancing the momentum of the jet and its buoyancy. A regime of particle-liquid jets that forms in conjunction with bubbling also appears to depend on coupling, between the particle and liquid phases. The effect of surface tension on the particle penetration through a bubble interface was modeled for the single particle and multi-phase cases and compared with the work of others. On the basis of this modeling, the expected regime of flow for many powder injection conditions can be predicted. The flow regimes of existing processes are discussed, and guidelines for the design of processes employing various types of reactions are presented.

Interfacial tension of aluminum in cryolite melts

Abstract: The interfacial tension between aluminum and cryolite melts containing different salt additions has been measured based on a combination of the sessile drop and X-ray radiographie technique. A computer program was used to calculate the interfacial tension from approximately twenty randomly measured coordinate points of the drop profile. Aluminum and salt mixtures containing different amounts of Na3AlF6, A1F3, NaF, A12O3, CaF2, KF, LiF, and NaCl were melted in a graphite or alumina crucible in a graphite resistor furnace under an argon atmosphere. The interfacial tension was found to be strongly dependent on the NaF/AlF3 ratio. At the cryolite composition the interfacial tension was 481 mN/m at 1304 K, while it was 650 mN/m when the NaF/AlF3 ratio was equal to 1.5. The change in interfacial tension with composition is explained by sodium enrichment of the Al/melt interface. Additions of A12O3 increased the interfacial tension for a given NaF/AlF3 ratio. KF was found to be surface active, while CaF2, LiF, and NaCl slightly increased the interfacial tension by decreasing the sodium activity.

The Leaching of Hematite in Acid Solutions

Abstract: The reactions of hematite in aqueous hydrochloric acid, perchloric acid, and sulfuric acid solutions with or without the addition of common or uncommon salts were studied using monosized particulates in a well-stirred reactor and dilute solid concentration to obtain fundamental details of the reaction kinetics. The experimental rate data suggest that the entire leaching reaction is controlled by a chemical process. The leaching rate of hematite was seen to be first order with respect to hydrogen ion activity, a(H+), in hydrochloric acid or perchloric acid solutions, with or without the addition of common salts, while the rate was of a half order in sulfuric acid solutions with or without the addition of sodium sulfate. A theoretical analysis showed that the anions next to the surface in the double layer were chloride ion and perchlorate ion in hydrochloric acid and perchloric acid solutions, respectively, and sulfate ion in sulfuric acid solutions, with or without the addition of sodium sulfate. The fact that the leaching rates of hematite were quite different in various acids having identical α(H+ values indicates the importance of anion adsorption. The dependency of the leaching rate upon α(H+) appeared to be controlled by adsorbed anions next to the surface in the double layer.

The utilization of galvanic cells using Caβ″-Alumina solid electrolytes in a thermodynamic investigation of the CaO- AI2O3 system

Abstract: Caβ″-alumina solid electrolytes have been used in calcium concentration electrochemical cells to determine the standard free energies of formation of the calcium aluminates, from their constituent oxides, in the temperature ranges specified: (1) CaO(s) + 6Al2O3(s) → CaO6Al203(s) ΔG° =-42709 - 94r(K)(±200)cal = -178694 - 393T (±840)J; 1100 to 1500 K (2) CaO(s) + 2Al2O3(s) → CaO2Al2O3(s) ΔG° = -30871 - 639HK) (±300)cal = -129164 -2674T (±1260)J; 1100 to 1500 K (3) CaO(s) + Al2O3(s)→ CaO-Al2O3(s) ΔG° = -36121 -435T(K) (±200)cal = -151130 - 182r(±840)J; 1050 to 1500 K (4) 3CaO(s) + Al2O3(s) → 3CaO-Al2O3(s) ΔG° = -18687 - 705T(K)(±200)cal = -78186 - 2957(±840)J; 1050 to 1320 K

Physical refining of steel melts by filtration

Abstract: The removal of nonmetallic inclusions from steel melts prior to casting has significant merit. Laboratory prepared steel melts containing carefully prepared alumina inclusions have been successfully filtered at 1600 °C. Two distinct types of filters were used: (i) tabular alumina packed bed (0.2 to 0.5 cm nominal diameter) and (ii) extruded monolithic alumina (400 cells per square inch). The kinetics of the filtration process have been modeled, and inclusion removal efficiency of up to 96 pct has been achieved in laboratory melts. The results show that inclusion removal efficiency is a strong function of melt velocity in the range of 0.08 to 0.68 cm per second and is weakly dependent on filter length. The type of filter utilized affects inclusion removal efficiency significantly. The inclusion capture kinetics and the filtration characteristics of the filter media tested are discussed.

Activities of As, Sb, Bi, and Pb in copper mattes

Abstract: The transportation method was used to determine the activity coefficients of the minor impurity components As, Sb, Bi, and Pb in homogeneous copper mattes (Cu-Fe-S) as functions of the Cu/Fe mole fraction ratio and of the sulfur content of the matte at 1200 °C. All matte samples contained about 0.2 wt pct As, Sb, Bi, and Pb. The activity coefficients were calculated on the basis of primary experimental data and available thermodynamic values of the gas components, which exist over the mattes. The sulfur-to-metal ratio, which controls the activities of the main matte constituents, was found to be the most important factor influencing the activities. When the sulfur-to-metal ratio of the matte changed from sulfur deficit to sulfur excess, the activity coefficient of As varied from 0.52 to 38, Sb from 3.3 to 82, Bi from 75 to 3.4, and Pb from 25 to 0.079 in the matte. The activities of AsS1.5, AsS, SbS1.5, BiS1.5, and PbS had negative deviations from the ideal behavior.

Thermodynamic study of Na2O-SiO2 melts at 1300° and 1400 °C

Abstract: The vapor pressures of Na above stirred Na2O-SiO2 melts in equilibrium with graphite and CO were determined at 1300° and 1400 °C using the transpiration technique. Compositions studied ranged from about 60 mole pct SiO2 to close to SiO2 saturation. Activities of components Na2O and SiO2 were calculated from the data. Log aNa2O (pure liquid as standard state) varies from about −8.7 and −8.5 at silica saturation to −6.3 and −6.1 at 40 mole pct Na2O at 1300° and 1400 °C, and the molar Gibbs energy of mixing, ΔG m, at the disilicate composition (XNa2O = 0.33) at each of these temperatures is −83.0 and −85.4 kJ, respectively. The Toop and Samis, Yokokawa and Niwa, and Lin and Pelton solution models for binary silicates were applied to the ΔG m data at 1350 °C and parameters for the models were estimated to give best fits. All three models show good correspondence with the measured ΔG m curve. The capabilities of the models in predicting activity data in this system have been compared.

The kinetics of the nitrogen reaction with liquid iron-chromium alloys

Abstract: An experimental apparatus was designed and constructed which permits utilization of both the modified Sieverts' technique and the isotope exchange technique for study of the kinetics of ni-trogen reaction with liquid iron alloys. Experimental results from the two techniques are used in con-junction with the current knowledge in the field to readdress several persisting questions dealing with the nitrogen reaction. Results from this study have confirmed that N2 dissociation is the rate lim-iting step in the intrinsic chemical reaction mechanism of nitrogen absorption. In addition, the ex-istence of a residual nitrogen absorption rate at high sulfur concentrations has been reaffirmed and possible reasons for the phenomenon are discussed. Lastly, results of an investigation into the in-fluence of carbon on the nitrogen reaction rate in liquid Fe-C-S alloys indicate that carbon has a negligible effect on the rate.

Effect of inclusions on LCF life of HIP plus heat treated powder metal rené 95

Abstract: Effects of inclusions on 538 °C (1000 °F) strain control low cycle fatigue life of hot isostatically pressed and heat treated powder metal Rene* 95 compacts were evaluated. Size and location (surface or internal for the test bar) effects along with inclusion types and sources are categorized. Five types of inclusions were identified based on fracture initiation site appearance, although only two major types commonly contribute to significant life low cycle fatigue life degradation. Prior particle boundary decoration reactive type inclusions typically cause the most severe low cycle fatigue life degradation, and those are followed by the discrete ceramic type inclusions. Known potential contaminant seeding study evaluations were used to confirm sources for specific inclusion types. Attempts to minimize the sources for introduction of these contaminants in the argon gas atomization process facilities were only partially successful. An advanced processing approach for the manufacture of Rene 95 to achieve superior low cycle fatigue life has been proposed based on the improved understanding of the inclusion problem.

Mixing in ladles by vertical injection of gas and gas-particle jets—A water model study

Abstract: Simulation effectuee en vue d'optimiser le temps de melange d'une addition dans une poche de metal liquide avant la coulee. Etude sur un modele a eau en vue de determiner l'effet de changements des parametres d'injection sur le temps necessaire pour le melange

Sintering kinetics and alumina yield in lime-soda sinter process for alumina from coal wastes

Abstract: An investigation of the application of the lime-soda sinter process to alumina extraction from coal wastes has been carried out. In the sintering stage, the optimal operating conditions have been obtained for the highest yield of alumina. The kinetics of sodium aluminate formation have also been studied in the sintering stage. The sinter mixes have been fired isothermally in air in the temperature range 1100 to 1350 °C. Alumina recovery of about 80 pct has been obtained by sintering coal-waste mixes having molar ratios of Na2O/Al2O3 = 1.3 and CaO/SiO2 = 1.8 at 1200 to 1250 °C for 20 to 30 minutes. Insoluble alumina compounds are responsible for the incomplete recovery. The major sinter components are identified as sodium aluminate and β-dicalcium silicate. The nucleation and growth kinetics equation is used to correlate the experimental data of sodium aluminate formation obtained under atmospheric pressure in the temperature range 1000 to 1200 °C. An activation energy of 286 kJ/mol has been calculated for fine coal-waste powder mixtures.

Sodium aluminate leaching and desilication in lime-soda sinter process for alumina from coal wastes

Abstract: Sodium aluminate in the sinter produced from coal wastes using the lime-soda sinter process can be leached with dilute alkaline solutions. The extraction of alumina by leaching with water and sodium hydroxide solutions was comparable to extraction by leaching with Na2CO3 solutions. However, leaching with water dissolved the least amount of silica. The optimal conditions for water leaching were determined to be temperatures of 60 to 70 °C and times of 30 to 40 minutes. The sodium aluminate solution obtained under these conditions readily responded to desilication with Ca(OH)2 suspensions at atmospheric pressure, reducing the silica-to-alumina ratio to less than 10-3, which is lower than the specification for reduction-grade alumina.

Water and solute activities of H 2 SO 4- Fe 2 (SO 4 ) 3- H 2 O and HCl-FeCl 3- H 2 O solution systems: Part II. Activities of solutes

Abstract: The mean activity coefficients of solutes such as H2SO4 and Fe2(SO4)3 in the solution system H2SO4-Fe2(SO4)3-H2O, and HCl and FeCl3 in the solution system of HCl-FeCl3-H2O at 298 K were calculated by the McKay-Perring method using the water activities of these solution systems. The mean activity coefficients calculated by the McKay-Perring method were sufficiently accurate for use on concentrated mixed solutions. A Gibbs-Duhem equation, which is applicable for calculating mean activity coefficients of one component using the activity data of the other components, was also used to calculate the mean activity coefficient of Fe2(SO4)3 in aqueous solutions of H2SO4-Fe2(SO4)3 by using both the activity of water measured by an isopiestic method and that of H2SO4 determined by the McKay-Perring method. The Gibbs-Duhem method was more tedious for calculation than the McKay-Perring method, and it required thermodynamic data other than water activities.