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By W. L. Dalmijn, J. M. Krowinkel

A recycling concept of end-of-life televisions starting with shredding will produce a complex material mixture, very heterogeneous in size, shape and degree of liberation. Basically all materials in television scrap are valuable, which means that recovery is important for either economic, environmental or sustainability reasons. However glass, plastics and metals are the materials with the highest potential for recovery. Non-magnetic materials from shredded television sets can be separated into three characteristic size fractions that need further separation for a high value-added recycling of the materials. This study investigated the potential of physical separation of these size fractions into valuable material streams using polyseparator, tlrldy current separator, dry and wet shaking tables and electrostatic separator. An overall mass balance of the mechanically processed televisions was calculated. Evaluation of the produced material fractions showed that heterogeneity in particle shape and size together with the presence of unliberated materials caused sever difficulties in separation when exclusively based on mechanical techniques. The results indicate that a certain degree of dismantling is necessary to achieve products of appropriate quality in physical separation. In order to improve recycling of electronic scrap through design for recycling cooperation between the electronics industry, the manufacturers and the recyclers of electronic goods is necessary.

Jan 1, 2000

By N. M. Komkov

The main operation of obtaining zinc from sulfide raw materials by hydrometallurgical technologies is the oxidation roasting of zinc concentrates in fluidized bed furnaces. The technical-economic parameters are determined by the parameters of the roasting process, which depend on the composition of the initial raw materials, the temperature of the bed and on other factors. The predetermined roasting temperature is maintained due to the change of specific efficiency as well as to the quantity of the heat removed from the bed. The efficiency of caissons depends at a high degree on the composition and the thickness of the accretion formed on the surface of the caissons. Forecasting the roasting results is impossible unless we know the mechanism of the accretion formation. The aim of the present paper is the thermodynamic analyses of the behavior of the charge compositions under roasting and the determination of the potential mechanism of the accretion formation. The thermodynamic analyses show that under conditions of the oxidation roasting the thermodynamic probability of the formation of zinc sulfate is higher than the probability of the oxide formation until a temperature of873 OK is reached. The thermodynamic probability of the formation of the lead sulfate is higher than the probability of oxide formation in the entire temperature range of roasting. The probability of formation of ferrites and silicates of zinc decreases only insignificantly the sulfate stability. The results of the investigation of the accretions composItion formed under roasting of concentrates with particle sizes less than 0.02 J..lm (60%), containing 65% of sphalerite (ZnS), 12% of pyrite and chalcopyrite (FeS2 and CufeSz) each, 3% of galenite (PbS), 7% of silica and other non-ore minerals, have shown that the composition of accretion varies depending on the depth of the accretion layer. The accretions on the caissons and the thermo-siphons consist mostly of zinc sulfate (more than 50%). The accretions of forehamber consist mostly of zinc oxide. They also contain ferrites and silicates. The formation of the sulfate zinc accretion in the cold parts of the fluidized bed furnace (the caissons and thermo-siphons) may be explained by a lower temperature on the surface and probably by a catalytic influence of the present oxides in the formation of S02 and sulfates. The nature of the structure of the accretion in the hotter parts of the furnace may supposedly be explained by the formation of elemental vaporous zinc during roasting.

Jan 1, 2003

By Jing Zhang, Qing Xiao, Xulong Liu, Qiuju Li

"Pickling sludge generated from stainless steel production process contains large quantity of Cr, Ni, and Fe. The disposal of and fill sludge directly not only leads to the heavy metal dissolves in the soil and underwater, but also loss value metals. However, the major mineral phases of value metal are hydroxides and there are lots of calcium fluoride and water in the sludge. So the pickling sludge has to be pretreated before reduction-magnetic separation. The TG analysis, reduction reaction and magnetic separation were all used to study the pickling sludge. The result indicated that up to 900°C the total weight loss of pickling sludge was 22.32%. The mass contents of Fe, Cr and Ni in the tailings (non-magnetic) were 4.27%, 0.067% and 0.041% respectively.IntroductionSince 21st century, the stainless steel production in the world has been continuously increasing because of its excellent performance [1]. However, high stainless steel production means a high pickling sludge production. For example, in a stainless steel plant with waste water quantity of 100m3 /h, the production of pickling sludge will exceed 15 Kt/a. Pickling is essential for generating of a homogeneous and corrosion-resistant surface during stainless steel production subsequent process. Pickling of stainless steels is predominantly carried out with an aggressive solution, sulfuric acid H2S04 or composed of nitric acid HN03 and hydrofluoric acid HF [2]. During the pickling process, the pickling acids are recovered through ion exchange and metal ions such as Fe3+, Cr3+ and Ni2+ get into the acids forming the pickling waste water [3]. Then, the pickling waste water is precipitated with lime, forming pickling hydroxide sludge. It is not feasible to recycle or treat the pickling sludge using conventional methods, because the sludge has high contents of calcium fluoride and water but low contents of iron, chromium and nickel. However, it would also pose a potential environmental problem if deposited outdoors over a long term because it contains heavy metals such as Cr and Ni. At present, solidification/stabilization (S/"

Jan 1, 2014

By Samson Adeosun, Sanmbo Balogun, David Esezobor

"Iron and steel making processes give rise to large amounts of usable and unusable materials, the latter generally being termed wastes. It is sometimes difficult to distinguish between re-usable by-products and wastes which cannot be sold or land-filled. Much depends on circumstances such as the local market for the material. This can itself vary from time to time with by-products which cannot be used or sold becoming wastes and vice versa. This paper defines the concept of “waste-free technology”, discusses its development in the steel industry and highlights the benefits of the technology to the manufacturing sector and the environment. The paper also articulates how the “waste-free” technology could be applied in the proposed Ajaokuta integrated steel plant in Nigeria.IntroductionIn the past, nature was considered an inexhaustible store. Its resources were consequently exploited and waste products therefrom were discarded. Today, attitudes have not changed appreciably even as raw materials cost rise by the year to pose a series of socio-economic problems, which, among others, may include the rational and optimum utilization of resources, environmental protection and reduction of waste formation. Consequently, industrialists now face unexpected regulatory pressure in areas of pollution prevention, waste minimization and hazardous waste disposal.Iron and steel making processes give rise to significant amounts of usable and un-usable materials, the latter generally being termed waste. It is sometimes difficult to distinguish between re-usable by-products and wastes which cannot be sold or land-filled. Much depends on circumstances such as the local market for the material. This can itself vary from time to time with by-products which cannot be used or sold becoming wastes and vice versa. In this paper, the term waste refers to those materials that are either irrationally utilized or, land-filled and part of the byproducts that are not utilized. It includes that part of used materials which is not incorporated into the products manufactured during a process stage and which in contrast to reuseable materials, is considered not suitable for any further use, owing to technical or economic factors. In general, these materials are inorganic and parts of them are either utilized or passed to the other processes; the other part should be disposed of using well-established waste disposal practices to avoid any environmental threat.Thus, creative methods must be developed to modify the manufacturing processes to reduce emissions and process wastes by fully utilizing all resources. One method of eliminating the negative effect of waste formation is the use of purification and cleaning structures (pollution control system, PCS). These are, however, quite expensive."

Jan 1, 2008

By H. Y. Sohn, S. PalDey

"A new chemical synthesis process for the preparation of intermetallic compounds has been developed. It involves the vapor-phase reduction of mixtures of constituent metal chlorides by magnesium vapor to produce intermetallic compounds in the form of fine powder. The advantages of the process include (a) the use of inexpensive raw materials, (b) low reaction temperatures, and (c) products in the form of fine particles. Titanium and nickel aluminides were prepared by this method. The effect of AlCl/TiCl3 partial pressure ratio on the formation of different titanium aluminides was studied. A two-phase mixture containing 80 mol % of TiAl and 20 mol % of TiA13 formed at an AlC13/TiC13 ratio of 10. The amount of TiA13 was maximized to 72 mol% at an AlC13/TiC13 ratio of 16. The maximum conversion of the limiting chloride TiCl3 was 94 % . In the case of nickel aluminides, NiAI, NiAl3, and Ni2Al3 were formed by reducing mixtures of NiC12 and A1Cl3 vapors. The effect of the partial pressure ratios AlCl3/NiC12 and Mg/NiC12 on the formation of nickel aluminides was studied. The maximum content of NiAl obtained was 98 mol % . At the AlC13/NiC12 ratio of 19, a two-phase mixture of 17 mol% of NiAl and 83 mol% of NiA13 was produced. The product particles were very fine in the size range of 0.05 to 0.2 µm.A. IntroductionIntermetallic compounds are attracting much attention [1]. Titanium and nickel aluminides have attracted a great deal of attention from the aerospace as well as automobile industries because of their potential for high-temperature application (e.g., low density, good oxidation resistance, and high-temperature strength retention [2, 3]). Gamma TiAl and two-phase (TiAl and Ti3Al) alloys [4] are used for gas turbine engine rotational components as well as automobile exhaust valves. TiAl3 is one of the most extensively investigated aluminum-rich intermetallics. Nickel aluminides are attractive because of their low densities, relatively high melting point and good high-temperature strength properties. For example, Ni3Al shows increasing rather than decreasing yield strength with increasing temperature [5]."

Jan 1, 1998

By H. Bai, B. G. Thomas

"A three-dimensional finite difference model has been developed to study the liquid steel-argon bubble two-phase turbulent flow in continuous casting tundish nozzles. Experiments have been performed on a 0.4-scale water model to verify the computational model by comparing its prediction with velocity measurements using PIV (Particle Image Velocimetry) technology. The computational model was developed using CFX and then employed to investigate the effects of various casting process variables. A fast, simple inverse model to quantify relationships between those process variables was developed, based on interpolation of the numerical model results, using Bernoulli's Equation and advanced multivariable curve fitting methods. Predictions using this model compare well with plant measurements. The model has been applied to present trends and observations on the relationship between casting speed, tundish depth, slide gate opening, and argon gas injection rate. The results can also be used to predict .the theoretical steel flow rate through the nozzle, so that clogging conditions can be identified in the plant.IntroductionTundish nozzle geometry is one of the few variables that are both very influential on the casting process and relatively inexpensive to change. Designing an effective nozzle requires quantitative knowledge of the relationship between nozzle geometry and other process variables on the influential characteristics of the flow exiting the nozzle. This relationship depends on the flow pattern within the nozzle components. Most previous modeling studies of flow in the nozzle have focused on single-phase flow [1-4]. Argon injection into nozzle is an efficient and widely employed method to reduce nozzle clogging, even though the real working mechanism(s) are still not fully understood [5]. Argon injection may greatly affect the flow pattern in the nozzle, and subsequently in the mold. Therefore, two-phase flow modeling is needed to improve understanding of fluid flow in the nozzle."

Jan 1, 2000

By Duan Xin-hui, Wang Xin, Peng Jin-hui, C. Srinivasakannan, Zhang Li-bo

The work attempts to optimize the process of preparation of modified semi-coke from semi-coke using phosphoric acid (H3P04) as the activating agent using the response surface methodology (RSM). The influences of three major dependent variables, the impregnation ratio, activation time, and activation temperature were assessed on the independent variables yield and the iodine number. The empirical relationship between the dependent and the independent variables were established using the quadratic response surface models, which were utilized to optimize the process parameters. The significance of each of the parameters and interaction among the parameters on the independent variable was assessed based on analysis of variance (ANOVA). The process variables were varied within the range of impregnation ratio (IR) from 1.5 to 4, activation time from 30 to 90 min and activation temperature from 550 'C to 650 'C. The optimized process conditions were estimated to be an IR of 2.29, activation time of 32 min, and an activation temperature of 605°C respectively using the process optimization tool. The BET surface area of modified semi-coke of the optimized sample was estimated to be 915m2/g, with the pore volume of0.71cm3/g, with an average pore diameter of 3.09 nm, with micropore volume fraction being 52.36%. The scanning electron microscope (SEM) images were utilized to visualize the surface pore structure.

Jan 1, 2013

By R. P. Tavares, M. Isac, R. I. L. Guthrie

"The configuration of the metal delivery system used in twin-roll casting can play a significant role in determining both internal and surface quality of the strips produced by this process.In the present work, a mathematical model for coupled turbulent fluid flow, heat transfer and solidification was developed and used in the study of metal delivery systems for twin-roll casting of low-carbon steels. This study was applied to a pilot twin-roll caster being investigated in Canada, with a roll radius of 0.3 m, producing strips of thicknesses from 4 to 7 mm, at roll speeds ranging between 4 and 12 m/min. Various configurations of metal delivery systems were simulated and their effects on the advance of the interdendritic solidification front and levels of turbulence and temperature within the caster investigated. According to the predictions of the model, an extended nozzle with inlet flow towards the surface of the rolls seems to be the best alternative for feeding liquid steel into twin-roll casters.A full scale water model of a pilot twin-roll caster was also built and used to qualitatively validate the predictions of the mathematical model.Various techniques for fluid flowvisualization were applied. In general, the predictions of the mathematical model were in reasonable agreement with the experiments with the water model."

Jan 1, 1999

By J. B. Winter

The present Inspiration Consolidated Copper Company Smelter/Acid Plant complex located near Miami, Arizona, was designed and built specifically to conform to the ambient air quality standards imposed by the Federal Clean Air Act of 1971. The present plant replaced a facility which had been in operation since 1915. The electric furnace, siphon converters and acid plant complex were commissioned in May, 1974 (1). At that time, the Plant was considered to be one of the most extensively monitored and instrumented facilities of its kind in the world. Several control areas were located in close proximity to the controlled process, in addition to so-called central control rooms in the Smelter and Acid Plant. The control rooms were staffed with officials below the foreman level. Instrumentation consisted of conventional analog devices, except for a computer used in monitoring ambient air environmental conditions and limited use of programmable logic controllers. The harsh service conditions prevalent in the plant rendered a significant portion of the instrumentation unreliable and, in many cases, inoperable. Failure of the facility to obtain the total sulfur collection for which it was designed was, in part, due to serious inadequacies in control system logic and sulfur recovery averaged 79% in the early years. After careful study of the smelting process, engineering hardware and high labor cost inherent in the organizational structure, management made a judgement decision to convert to centralized control of the process with high level supervision 24 hours per day. A distributed digital control system with supervisory arid data acquisition/information reporting computers was selected to satisfy the requirement of central control. Operations are now controlled and coordinated from a primary control room in the Smelter and a satellite control area in the Acid Plant.

Jan 1, 1983

By N. M. Komkov

The main operation of obtaining zinc from sulfide raw materials by hydrometallurgical technologies is the oxidation roasting of zinc concentrates in fluidized bed furnaces. The technical-economic parameters are determined by the parameters of the roasting process, which depend on the composition of the initial raw materials, the temperature of the bed and on other factors. The predetermined roasting temperature is maintained due to the change of specific efficiency as well as to the quantity of the heat removed from the bed. The efficiency of caissons depends at a high degree on the composition and the thickness of the accretion formed on the surface of the caissons. Forecasting the roasting results is impossible unless we know the mechanism of the accretion formation. The aim of the present paper is the thermodynamic analyses of the behavior of the charge compositions under roasting and the determination of the potential mechanism of the accretion formation. The thermodynamic analyses show that under conditions of the oxidation roasting the thermodynamic probability of the formation of zinc sulfate is higher than the probability of the oxide formation until a temperature of 873°K is reached. The thermodynamic probability of the formation of the lead sulfate is higher than the probability of oxide formation in the entire temperature range of roasting. The probability of formation of ferrites and silicates of zinc decreases only insignificantly the sulfate stability. The results of the investigation of the accretions composition formed under roasting of concentrates with particle sizes less than 0.02 um (60%), containing 65% of sphalerite (ZnS), 12% of pyrite and chalcopyrite (FeS2 and CuFeSz2 each, 3% of galenite (PbS), 7% of silica and other non-ore minerals, have shown that the composition of accretion varies depending on the depth of the accretion layer. The accretions on the caissons and the thermo-siphons consist mostly of zinc sulfate (more than 50%). The accretions of forchamber consist mostly of zinc oxide. They also contain ferrites and silicates. The formation of the sulfate zinc accretion in the cold parts of the fluidized bed furnace (the caissons and thermo-siphons) may be explained by a lower temperature on the surface and probably by a catalytic influence of the present oxides in the formation of S02 and sulfates. The nature of the structure of the accretion in the hotter parts of the furnace may supposedly be explained by the formation of elemental vaporous zinc during roasting.

Jan 1, 2003

By Brad Wahlquist

An ex-situ biological treatment system was implemented at a gold mine site in South Dakota. The system removes selenium and nitrate from a mixture of groundwater and surface water runoff at ambient water temperatures. The Applied Biosciences? system replaced a denitrification system that did not perform consistently, did not treat for selenium and required heating of the influent water. Installation was completed in phases starting with the selenium circuit being brought into operation in February, 2002 and the nitrate circuit in March, 2002. System design can accommodate average flows of 380 L/min (100 gallons/minute) and a maximum flow of 1,136 L/min (300 gallons/min). Four cells were designed to remove nitrate from approximately 30 mg/L to below 10 mg/L and two cells were designed to remove selenium from 0.01 mg/L and higher, to below 0.005 mg/L. No pretreatment is required to operate the system at ambient temperatures, which can fall as low as -12C in the winter, and treat water at temperatures ranging between 8C to 16C. Nutrient requirements are met using a sugar based nutrient mixture that includes a balanced C:N:P:S ratio, trace elements and vitamins. Since start up, the system has consistently been in compliance for nitrate and selenium, treating water to below detection limits for both contaminants. This paper discusses laboratory biotreatability testing of a system designed to remove selenium, arsenic, and nitrate and full-scale implementation and optimization of a system to remove nitrate and selenium.

Jan 1, 2003

By Evan Jamieson

The conditions under which various iron(III) oxy-hydroxides phases precipitate from iron(III) chloride and sulfate solutions at ambient temperatures (<60°C) are reviewed. Many of these precipitates are slow settling and gelatinous but ultimately transform into other more stable or crystalline phases. The phase that forms depends upon the rate of precipitation and pH. A comparison has been made of the iron(III) oxides formed upon the neutralisation of various iron(III) solutions with caustic, slaked lime or slaked magnesia which provide different rates of neutralisation and slowly dissolving solids with localised high pH. Mössbauer spectra of ferrihydrites precipitated under these different conditions are compared and interpreted. Particular attention is paid to the settling rate and settled volume which is likely to relate to industrial thickener and filter performance. It is shown that in pure chloride solutions, poorly settling ferrihydrite is usually produced at 20oC regardless of the choice of base. However in sulfate solutions fast settling precipitates are produced using lime and magnesia but not with caustic. In mixed chloride/sulfate solutions, optimum settling rates occur when the molar ratio of [SO4]2to Fe3+ is about 1:1 and when the sulfate concentration is <0.20 M. It is proposed that ?dense amorphous basic iron sulfate? or well-ordered ferrihydrite is formed on slowly dissolving lime or magnesia surfaces. Implications for industrial liquors are considered.

Jan 1, 2003

By C. A. Nogueira, F. Pedrosa, F. Margarido, R. N. G. Guerra

"A hydrometallurgical process for recycling spent Zn-MnO2 batteries was developed, involving leaching with sulfuric acid, purification by precipitation and metals separation for further recovery. Leaching of zinc oxide was easily attained while for manganese oxide was rather difficult depending on temperature and acid concentration. At 90°C and with the liquid/solid ratio of 20 L/kg, more than 95% of zinc is recovered in 30 minutes with 0.5M H2SO4. To attain similar recovery for manganese, higher levels of acid concentration and time are needed (e.g 0.7 M and 2 hours). After leaching a purification step is necessary to remove iron co-dissolved through Fe(III) precipitation. Separation of zinc from manganese by solvent extraction with 1M DEHPA follows in the process route. The countercurrent multistage separation diagram developed allows the production of a zinc electrolyte with 120 g/L Zn and 0.005 g/L Mn, and a raffinate with 16 g/L Mn and 0.013 g/L Zn.IntroductionThe recycling of spent Zn-MnO2 batteries is carried out by dedicated recyclers using several process alternatives [1]. Most of the running processes use pyrometallurgical technologies [2] based on zinc distillation. Alternative treatments by hydrometallurgy have been reported [3-5] but its application is scarce.In order to contribute to the development of alternative solutions, a process for recycling batteries based on Zn-MnO2 systems has been studied. The process is based on the hydrometallurgical treatment of spent batteries in sulfuric acid media (Figure 1). The process starts with the physical processing by shredding using cutting grinders, where the batteries are opened and size reduced, allowing the liberation of the interior electrode particles or pastes. The fines can be then separated and the coarse material containing the steel scrap can be treated to remove the remaining aggregate electrode. The final scrap also contains some plastics and other non-metal materials and can be further valorized."

Jan 1, 2008

By William Petruk, J. H. Gilles Laflamme, Jean Robitaille, Louis J. Cabri

"A quantitative mineralogical study using ore microscopy, electron microscopy, proton-microprobe, image analysis, and material balances was done on samples from the circuit of a concentrator in Quebec, with particular emphasis on the Cu concentrate. The ore contains many different minerals, of which the principal ones, in decreasing order of abundance, are pyrite, sphalerite, chalcopyrite, bornite, galena, tennantite, and pyrrhotite. Minor to trace amounts of covellite, chalcocite, stannoidite, mawsonite, colusite, wittichenite, miharaite, hessite, petzite, electrum, and an unidentified Cu-Pb-Bi-sulfide also occur.Liberation of pyrite is very high in all size fractions for all samples (ranging from 80-91 %). Liberation of chalcopyrite, bomite, sphalerite, and tennantite is relatively high, on average, in the head .sample and Cu concentrate (55-78% and 66-88%, respectively). Most of the chalcopyrite in the flotation tails is not liberated, whereas about one half of the tennantite and sphalerite are liberated in both the flotation and :final tails. Recoveries calculated for the Cu concentrate (on the basis of assays, mineralogy, and image analysis) are chalcopyrite 72. 5%, bornite 73. 7%, sphalerite 41.0%, tennantite 70.9 %, and galena (together with some trace minerals) 34.2%. It was also calculated that the Cu concentrate contains 10.0 % of the pyrrhotite and i.4 % of the pyrite.Materials balance calculations were done on the five major sulfide minerals to determine the mineralogical distribution of 13 major, minor, and trace elements (as determined by protonmicroprobe analyses). It was determined that tennantite is the principal carrier of Bi (67%), As (90%), and Te (86%) in the Cu concentrate. Therefore, removal oftennantite, which is mostly liberated in the Cu concentrate would significantly reduce these three contaminant elements, but at a loss of9% of the Cu, 2.0% of the Zn, and 0.7% of the Ag. The precious metals (Au, Ag) occur as discrete minerals (electrum, petzite, hessite). Some of the Ag also occurs in solid solution in bornite (23.1% of Ag in Cu concentrate), tennantite, and sphalerite. Four of the major sulfides (chalcopyrite, bomite, sphalerite, tennantite) in the ore also contain measurable concentrations of the following trace elements: Se, Cd, In, Sn, and Sb, occurring mostly as solid solutions. Some of these elements are also concentrated (up to about 18%) in minor and trace minerals such as colusite, stannoidite, and mawsonite."

Jan 1, 1999

By T. T. Chen

Gold in the Twin Creeks ore is primarily associated with arsenian pyrite. During pressure oxidation, the sulphides are solubilized, but part of the dissolved iron reprecipitates as jarosite and as an iron sulphate-arsenate-phosphate phase. The pressure oxidation products are subjected to cyanide leaching. The cyanide leach residues consist of quartz, gypsum, bassanite, anhydrite, small amounts of jarosite, an iron-sulphate-arsenate-phosphate phase, as well as trace amounts of orthoclase, rutile, pyrite, hematite and monazite; all these particles are dispersed in a fine grained matrix of illite-muscovite. The autoclave leach residues contain a small amount of carbonaceous matter. Many gold grains are detected on the surfaces of the carbon particles, and these gold particles are not leached during cyanidation. The gold particles are typically 0.1-0.2/Lm in size and commonly are embedded in the carbon surface or are coated with a K-AI-Si-S-O phase on the surface of the carbon. The gold grains are consistently associated with elevated CI contents (50-300 ppm Cl). The poor gold cyanide leach recoveries, which initially occurred in the Twin Creek developmental circuit under certain operating conditions, are attributed to the presence of chloride in the feed. This results in the formation of soluble gold chlorocomplexes in the autolcave and the subsequent sequestering of the gold on the surfaces of the carbon particles.

Jan 1, 2000

By Michael L. Sorokin

The behaviour of cobalt during processing of nickel raw material is analysed within the Ni-Co-Fe-S-O-SiO2 system using the computer model. For this purpose the thermodynamic parameters for "three-suffix" Margules&apos;s equations in Co-Fe-S and Co-Fe¬Ni-O-S1O2 systems were computed! Phase and iso-activity diagrams for Co-Fe-S system, and phase diagrams for the systems Co-O, Co-Fe-O, Co-Ni-O, C-oO=SiO2 and Co-Fe-O¬SiO2 are calculated using the developed computer programs and identified parameters. The diagrams are used to analyze cobalt behaviour at smelting and converting.

Jan 1, 1995

By T. Wang, R. G. Reddy, D. Mantha

"A new eutectic LiN03-NaN03-KN03-KN02 quaternary molten salt system was calculated using thermodynamic modeling. The eutectic temperature was predicted to be 100°C. The melting point and heat capacity of the salt eutectic composition were determined using DSC. The experimentally determined melting point is in excellent agreement with the predicted value. The melting point is more than 124°C lower than that of the KN03-NaN03 solar salt. The density of the molten salt was experimentally determined as function of temperature. Using the density, heat capacity and the melting point, thermal energy storage density and gravimetric storage density of the quaternary molten salt were calculated and compared with that of solar salt. The larger storage density value of this molten salt indicates that this salt has a better energy storage capacity for solar power generation systems.IntroductionMolten salts have been used as thermal energy storage media for solar energy applications. Nitrates are being used in the solar energy applications for their low melting point, low unit cost, high heat capacity, high thermal stability, negligible vapor pressure and high energy storage density [l]. Solar salt (NaN03/KN03: 60/40) is the most popular thermal energy storage medium which is currently being used with the freezing point of 221 ·c [2]; another ternary system HITEC® which contains NaN03, KN03 and NaN02 has freezing point of 141°C [3]. Newer nitrate salt mixtures are being studied and projected as potential candidates for thermal energy storage (TES) and heat transfer (HT) applications. Based on these favorable features, molten salt can work directly as the energy storage medium below 500°C [l]. Development and synthesis of newer molten salt mixtures with freezing point lower than those currently used for thermal energy storage applications is necessary for sustained utilization of solar energy. The approach to develop lower freezing point molten salt mixtures is by the prediction of new eutectic mixtures and also by the development of new nitrate compounds."

Jan 1, 2012

By Takeshi Yoshikawa

For the development of low-cost silicon refining process for solar cells, the present authors have been studying the low temperature refining technique, ?solidification refining of Si with Si-Al melts at 1173 ? 1273K?. In the present work, we have investigated the B removal in that refining, utilizing the segregation effect and also the effect of Ti addition to the melt. Segregation ratio of B between solid Si and Si-Al melt was measured by the temperature gradient zone melting technique and it indicated the B removal fraction would be as much as 90%. Titanium addition to the melt was found to produce the TiB2 precipitation with soluble B in that melt and bring the effective B removal of refined Si to its content of 1ppma.

Jan 1, 2006

By H. J. Garcia

Biodegradation of cyanide by microorganisms isolated from solids previously exposed to cyanide has been investigated. Initial sodium cyanide concentration was 300 ppm at pH 10.5. The kinetics of biodegradation were found to be first order with respect to cyanide concentration, and the overall reaction rate constant is k = 0.102 day-1. The activation energy and the frequency factor were determined to be { A }Ea = 5.45 Kcal/mol and A = 1.28 x 10-2 sec-1, respectively. Based on these values, thermodynamic properties of an intermediate activated complex were assessed. All tests resulted in cyanide concentrations less than 0.1 ppm in about 35 days at 250C, whereas at 350C the time of biodegradation to reach this cyanide level was 30 days. Kinetic data were also established to relate biodegradation to amount of inoculum. The maximum theoretically-attainable rate, Vm , and the optimum amount of inoculum, K , were determined to be 4.8 x 10-4 M NaCN/day and 7.5 % of amount of inoculum. With respect to the mechanism of biodegradation, cyanide was shown to decompose to carbonate, bicarbonate and ammonia. Titrimetric analyses revealed concentrations of 5.6 x 10-3, 4.8 x 10-3 M, and 70.2 ppm for carbonate, bicarbonate and ammonia, respectively. The average cell population was determined to be 3.75 x 108 cells/mL.

Jan 1, 1994

By Steven E. Follin

In-situ leaching is commonly used to recover uranium from low-grade deposits in sandstone formations. Acceptable recovery rates can only be obtained if the formation retains its permeability during leaching. Field experiences indicate that microbial growth, stimulated by the leaching pro- cess, can cause plugging problems. To investigate this hypothesis, leach solution and solid samples from well casings and submersible pumps were obtained from four in-situ mining sites. Chemical and microbiological analyses were performed. Bacillus species, Micrococcus species, pseudomonads, and xanthomonads were isolated from these samples. A mixed culture of these organisms was inoculated into a uranium core that was being leached in the laboratory. The permeability of this ore sample decreased to one-third its original value after 16 days. The addition of hydrogen peroxide (0.2 g L-1) to the leach solution killed the microbes and restored the permeability to its original value. This suggests that periodic injection of hydrogen peroxide into production wells may reduce microbial plugging in these wells and the immediate surrounding formation.

Jan 1, 1985