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By Robert De Saro, Willis Bateman, Ramesh Jain

A Vertical Floatation Melter (VFM) has been developed (sponsored by DOE) which simultaneously decoats and melts organic laden scrap in a single unit. Scrap aluminum is fed into the top of the VFM where it falls through a cone. Hot gases flow upwards through the cone, imposing a variable drag force on the scrap. Equilibrium is reached in which the scrap weight equals the drag force and the scrap becomes suspended. The gases strip off and vaporize the organics. Next, the scrap reaches a liquid state, taking on a more aerodynamic teardrop shape, allowing it to fall into a holding furnace. Heat transfer coefficients are 10 times higher than that of a conventional furnace, allowing rapid melting at a low gas temperature. Typical energy use is well under 2,324 joules/g (1,000 Btu/lbm) with a metal yield from 92 to 98%. This paper reports on the operation and data of a 453 kg/hr (1,000 pph) pilot-scale VFM.

Jan 1, 2000

By V. Bredykhin

The efficiency of scrap processing depends firstly on reliability of information about its chemical composition. The paper presents the results of the investigation and development regarding solid copper alloy scrap in the range of lump size 40÷300 mm. Nowadays the sorting of lump scrap is done by two methods: 1. Sorting according to metals and alloys is done at places of scrap generation, and further till metallurgical processing each lot has its "certificate"; 2. Hand sorting of scrap is done according to the marks on solid items in special shops using proximate analyzers or manually by experienced workers. This sorting process is labor - consuming low efficient and involves mistakes. The informational method is a promising trend in the copper scrap sorting. The method is direct, i.e. as a result of sorting the chemical composition of each scrap lump or main elements is determined, and assured data of qualitative and quantitative composition are received.

Jan 1, 2006

By Neal Schwartz, Robert De Saro, Richard Rosenthal, Ed Kear

"A Stack Melter has been installed and is currently operating at Lexington Die Casting. The Stack Melter consists of a 1 meter (3 foot) diameter refractory tube, 2 meters (7 feet) high. Specification ingots are continuously fed to the top of the melter and piled to nearly the top. A burner fires through the scrap which melts the lower portion and preheats the upper portion. As the lower portion is melted, it is drawn out and the upper preheated scrap falls to a lower level where it in tum melts. The molten metal is fed to one of two holding furnaces for eventual delivery to a casting machine.The Stack Melter's energy use is approximately 2900 joules/g (1,250 Btu/lbm), resulting in an overall energy savings of about 58%. This energy savings is brought about primarily because the flue gases preheat the scrap and the flue gas temperature is dropped to well under 528°C (1000°F)."

Jan 1, 2000

By Sunil Jayasekera

This paper describes the results of a study carried out to examine the feasibility of electrolytic recovery of silver from cyanide leach liquor generated from a Western Australian silver mine tailings using a novel high mass transfer electrowinning cell. The proposed circuit involves heap leaching and electrowinning in a closed loop. The filter-press-like closed electrode arrangement of the cell allowed much improved mass transfer of metal ions to the cathode surface, making direct electrowinning of metals from dilute solutions feasible. The tests were conducted both in the laboratory and at large scale using a prototype with ~1.0 m2 cathode area. The results showed that the recovery of silver from as low as 250 mg L-1tenor was feasible. The silver deposit produced with the prototype cell was non-adherent and powdery and could be readily removed from the closed cell. A system was developed so that silver powder was discharged continuously during the run.

Jan 1, 2003

By Ralph P. Hackl

Bacterial leaching of the Doe Run Company?s cobalt/nickel-containing copper concentrate at low pH (pH 1.0-1.2) and high redox potential (>750 mV vs. SHE) enabled the cobalt and nickel to be preferentially dissolved over copper and iron due to the rapid passivation of the chalcopyrite component. Selective leaching of the cobalt and nickel was achieved with a mesophilic culture comprised mainly of Leptospirillum-like bacteria and Acidithiobacillus thiooxidans. This finding led to the conception of a novel hydrometallurgical process for passivating chalcopyrite and recovering the cobalt and nickel. The bacterial leaching process was tested extensively at the bench and pilot plant scales during 1997-1998. A pilot plant containing four leaching stages processed 30-40 kg/day of chalcopyrite concentrate continuously for 87 days. The cobalt extraction ranged from 75% to 86% during 6- and 8-day retention times respectively, whereas the copper extraction was limited to about 9%

Jan 1, 2003

By Kandipati Sreenivasarao

A promising method for removing heavy metal ions from dilute effluents is ion- or precipitate- flotation, in which a suitable collector is added to form hydrophobic metal-collector complexes or compounds that can be collected as foams. We have successfully removed Cu(II), Cd(II), and Pb(ll) from dilute solutions using sodium dodecylsulfate and ethanol as collector and frother respectively. However the process would not be economically viable unless the collector could be recycled, and the heavy metals recovered in a concentrated, preferably marketable, form from the foams. We investigated four different methods to decompose heavy metal-dodecylsulfate complexes, namely precipitation of hydroxides, precipitation of sulfides, chemical stripping, and electrolysis. We compare the performance of these methods. In each case the observed behavior is related to known thermodynamic data, and potential applications are discussed.

Jan 1, 1995

By Armin D. Ebner

A hetero-f1occulation model is developed to calculate the net force exerted on a paramagnetic nanoparticle that is moving in the proximity of a magnetite particle that is fixed or supported within an open flow and magnetically energized packed bed. Important variables investigated include the size and surface charge of the particles, the magnetic field, the ,flow velocity, the electrolyte concentration and the magnetic susceptibility of ,the nanoparticle. The ?influence: of other naturally occurring forces, such as hydrodynamic and DLVO(Le., van der Waals and electrostatic) forces on the magnetic attractive forces between the magnetite particle and the nanoparticle are also examined. This model reveals the feasibility of using magnetite particles instead, of stainless steel as the energizable element for high gradient magnetic separation.

Jan 1, 1999

By G. Upadhya

Considerable success has been achieved recently in modeling microstructural evolution during solidification of castings bthrough the coupling of macroscopic heat transfer with microscopic solidification kinetics models. However, a complete model for simulation of solidification in complex shaped castings involves: (i) the description of fluid flow, during and after mold filling, coupled with (ii) heat transfer to the mold and surroundings by use of a macro model, followed by (iii) a description of subsequent solidification of liquid metal by use of a micro model for solidification of the alloy under consideration. This paper describes the coupling of solidification kinetics model to a 3D, transient, fully coupled fluid flow and heat transfer model. Coupling between the macremicro models is achieved by using the latent heat method. Micro models for the eutectics of gray, white and ductile iron are discussed. This coupled code has been used for predicting the thermal history and microstructural data for shaped castings. Various applications of the model, including prediction of shrinkage defects, grain density contours, and graylwhite transition region in the casting, are presented for a relatively complex casting geometry.

Jan 1, 1992

By Michael D. Odekirk

The U.S. Bureau of Mines investigated solvent extraction methods for recovering scandium from water leach filtrates of sulfated tantalum tailings. These complex solutions typically contained 20 or more metals in significant quantities. Two commercially available organics, DEHPA and PC-88A, were identified as effective scandium extractants. The two organics were tested in continuous solvent extraction circuits to compare loading and stripping kinetics, recyclability, and general processibility. Results showed that 95 pct of the scandium, greater than 80 pct of the zirconium, and only small amounts of other solubilized metals were extracted. Scandium was stripped directly as a 3.6 pct Sc precipitate when a 3n NaOH liquor was used as the stripping agent. This precipitate was subsequently upgraded to 94 pct ScE3 via a selective HE leach.

Jan 1, 1993

By D. W. Collins

The uptake of gold from halide solutions by activated carbon has been investigated using various techniques. Halide systems typically exhibit combined adsorption-reduction type behavior. In an attempt to gain more information about the nature of these processes, samples of synthetic highly-oriented pyrolytic graphite (HOPG) were contacted with aqueous solutions of gold-iodide. HOPG represents a model structure for activated carbon comprising of basal- plane sites, edge sites, and various defect sites. Two basic instrumental methods were used to examine the uptake of gold by HOPG. The first was standard X-ray photoelectron spectroscopy (XPS). The other involved several scanning probe techniques. XPS clearly indicated a preferred uptake of gold at edge sites. However, iodine appeared to be distributed on both basal-plane and edge sites. At low iodine additions, tapping mode AFM showed that clusters were concentrated along steps and surface defects. At high iodine concentrations, the HOPG surface was uniformly covered by iodine.

Jan 1, 1998

By Ehsan Vahidi, Fereshteh Rashchi, Amirhossein Shahnazi

"The pig iron from steel manufacturing plants contains a high concentration of vanadium-bearing materials smelted with iron ore. During the oxidation process of the molten pig iron with oxygen lances, vanadium transfers to the slag. In this research, recovery of vanadium from LD (Linz-Donawitz) converter slag of steelmaking plant was investigated. The leaching residue was characterized by XRD and XRF techniques. The maximum vanadium recovery was achieved at optimum leaching conditions of 70 °C, S/L: 1/15, sodium hydroxide concentration: 3 M and leaching time: 150 minutes. The dissolution rate increased with rising sodium hydroxide concentration and temperature and decreasing particle size. The experimental data are treated graphically to explain the kinetics of the vanadium recovery process using shrinking core model (SCM). As a result, the controlling regimes in the SCM were analyzed separately using liquid film diffusion control, solid product diffusion control, and reaction control mechanisms.IntroductionVanadium is commercially important as a constituent of several alloys and catalysts. Nowadays, vanadium is mostly recovered as a by-product from secondary sources or from industrial waste streams such as titaniferrous magnetite, fly ash, spent catalysts, and petroleum coke. Steelmaking operations are specifically concerned by this problem due to the production of a huge quantity of by-products [1]. These by-products, including LD converter slag, sludge, fly ash, spent catalyst, ash, and alloyed scrap, contain a notable amount of heavy metals which may cause environmental problems. Solvent extraction is one of the techniques being increasingly used for the recovery of vanadium [2]. Apart from vanadium ore, secondary resources such as titanmagnetite, ilmenite and slag from the ferrous industry are a major source of supply. The pig iron from steel manufacturing contains a majority of vanadium-bearing materials smelted with iron ore. In a heat resistant shaking ladle the molten pig iron is oxidized with oxygen lances, causing the vanadium to be transferred to the slag. Normally, the vanadium in LD converter steel slag (coming from Linz-Donawitz steelmaking process) is ca. 5% as vanadium pentoxide (V2O5). This slag is the world's principal raw material for vanadium production [3, 4]. Moskalyk and Alfantazi [4] reported that a roast-leach process is used in South Africa for the production of vanadium oxides from magnetite ores while some of the slag was converted to ferrovanadium. A portion of the slag was exported to Europe for the production of vanadium oxide. The researchers mentioned that alkaline roasting was the main process at that time employed to extract vanadium pentoxide from vanadium slags."

Jan 1, 2012

By B. Nebreda, I. Vegas, R. Vigil, O. Rodríguez, M. I. Sánchez de Rojas, M. Frías, R. García, J. Urreta

"This paper shows the possibility of reutilize paper sludge waste as supplementary cementing material for the cement manufacture. This industrial waste consists essentially of a mixture of organic matter (30%) and inorganic compound, such as calcite and clay minerals. The raw paper sludge does not present pozzolanic properties, but once calcined at 650ºC during 2 hours, exhibits high pozzolanic activity, similar to silica fume at 28 days, as a consequence of the transformation of kaolinite into metakaolinite. Calcined paper sludge was used as partial Portland cement replacements of 0, 5, 10 and 20%. Enhancement in compressive strength was appreciably obtained for 10 and 20% substitution levels from 7 days on. Furthermore, calcined paper sludge slightly reduces the initial and final setting times of cement paste. Introduction Natural pozzolanic materials have been ordinary used in different aspects of construction, mainly for their influence on the microstructure and durability of blended cement matrixes [1, 2]. Due to the regulations of environmental protection, many researches are focusing on the possibility of obtaining pozzolanic materials from industrial wastes and not from natural materials (ceramic wastes, silica fume (SF), activated clays) [3–5]. One of the most used pozzolanic products is the metakaolin (MK) obtained from the activation of natural clay (kaolinite). The positive effect that MK has on blended cement performances [6,7] and also the influence that curing temperature and matrix nature have on the reaction kinetics and stability of hydrated phases produced during the pozzolanic reaction, according to the studies carried out by Frías et al. [8,9] are well known. However, there is a worldwide trend towards the use of recycled products in cement industry. In this line, some authors have reported an alternative way of obtaining MK from waste paper sludge [10-14]. The raw paper sludge (PS), once calcined under controlled conditions (700-800ºC), produces a MK with pozzolanic properties [15-20]. The present research is part of an experimental study about alternative source for MK from the Spanish paper recycling industry and its use as supplementary cementing material. This contribution pays special attention to the option of reducing activation temperature below 700ºC. This fact has a positive effect in reducing the energy consumption, as well as in reducing environmental impacts associated with decarbonation of calcite. The chemical and mineralogical characteristics of raw paper sludge and derived calcined product are described. In addition, the influence and behavior on blended cement properties (setting times and mechanical properties) are also discussed."

Jan 1, 2008

By Carla Lupi, Mauro Pasquali

"Photographic technology is based on light sensitivity of silver halides that, because of silver properties, are capable of forming photographic images. Photographic laboratories and hospital departments because of digital photographic systems less use this technology today. Nevertheless recovery of silver is still advantageous because environmental problems related to Ag ions danger to biological system. Many processes have been studied to treat silver containing photographic bath: cementation, chemical precipitation and electrowinning. In this work, after preliminary voltammetric tests, a batch electrometallurgical process has been studied to completely deplete the silver containing photographic fixing baths. The effect, of silver concentration in the electrolyte, varying over the range 0,2-1 g/L, bath stirring and current density ranging from 10 to 500 A/m2 on process yield and deposit quality, has been investigated. Introduction Photographic wastes, electronic scrap and spent catalysts constitute the main sources of materials for silver recycling. Among those silver secondary sources, the photographic discharged material could be still important and useful, even if photographic laboratories and hospital departments, because of digital photographic systems, less use photographic technology. Several processes have been developped in order to recover silver used in the field of photography from both photographic solutions and scrap film paper[1-5]. Fixing solutions are very complex baths but, because of silver position in the electromotive series, electrolysis could represent an advantageous method for silver recovery. Electrolysis produces high purity silver without generating new pollutants, while the fixer can be reused: obviously it is necessary to purge off a portion of this solution in order to avoid the excessive build up of other deleterious compounds into solution. A tested recovery method was constituted by the dissolution of silver from X-ray films with concentrated nitric acid. Internal electrolysis and external electrolysis methods were carried out using a steel electrode as cathode and a copper electrode as anode [6]. Silver recovery from photographic chemical solutions has been also performed in a special cell [7]: the solution is supplied to the bottom of a non-agitated cell having a vertically elongated form and including a central anode enclosed by a cathode. An other study discloses the use of an electrolytic cell comprising at least one anodic compartment and one cathodic compartment: the solution is treated in the cathodic compartment and then recycled in the anodic one [8]. A more recent work proposes the use of zirconium cathode for the recovery of silver from photographic fixing solution [9]: studies carried out by cyclic voltammetry showed that about 98% of total Ag can be recovered with an electrical efficiency close to 92%."

Jan 1, 2008

By Laila A. Guirguis

Impurities are removed from crude phosphoric acid (57.75% P2O5) with a mixture of low and high molecular weight alcohols, one of which is hydrophilic and the other is hydrophobic i.e. methanol and hexanol. In a single stage, the phosphate values segregate to the high molecular weight alcohol fraction and the impurities segregate to the low molecular weight alcohol fraction. The optimum ratio for the extraction is found to be 0.5 part methanol, one part impure acid and four parts hexanol where an extraction percent of more than 95% is achieved. Re-extraction of the phosphate value from the solvent is obtained by 6% phosphoric acid and the different factors affecting the re-extraction process have been studied. Finally, the purified acid is concentrated under reduced pressure and passed through activated carbon column, whereas the alcohols are re-circulated. The produced phosphoric acid was found to be in good match with the international specifications of food grade quality acid. A technological flow sheet is elucidated.

Jan 1, 2006

By R. A. Sharma

Neodymium metal was successfully produced by the reduction of Nd203 with Na in the presence of CaC12-NaCl melts by the overall reduction reaction Nd203 + 3 CaC12 + 6 Na ? 2 Nd + 3 CaO + 6 NaCl at -750°C. The metal produced was extracted from the salt media by dissolving it in a Nd-Fe alloy pool. The yield (percentage of theoretical neodymium produced) was found to depend on the salt composition and the mass ratio of salt to neodymium in the reactor. A yield of 95% was obtained with salt ratios as low as 3.5. Further decrease in the salt ratio below 3.25 decreased the yield. Stirrer position had little effect on yield; while increasing the temperature and placing fins in the reactor increased the yield. The Nd-Fe alloy produced was of as good quality as that produced using Ca reductant, and was suitable for direct use in producing General Motors MAGNEQUENCH? alloy for permanent magnets.

Jan 1, 1989

By V. L. Stolyarova

As part of an effort to develop the fluoride electrolysis route for the production of rare earth metals and alloys, a study of the thermodynamic properties of DyF3 has been carried out by Knudsen cell mass spectrometry. A quadrupole mass spectrometer QMS 420 was used in conjunction with the Knudsen cell arrangement. The experiments were carried out in the temperature range 1280-1440 K. Vaporization was carried out from platinum, molybdenum and tantalum cells. The Dy*, DyF+, DyF2+ fragment ions and the DyF3 parent ion were identified in the mass spectrum of the DyF3 vapour. The DyF, vapour pressure was obtained by the complete isothermal vaporizadon method as well as the ion current comparison method, and the enthalpy of sublimation of DyF3 was evaluated. From the DyF3 vapour pressure data obtained at different temperatures, the enthalpies of formation of DyF3 in the gaseous as well as condensed phases have been evaluated. The experimental data are compared with the thermodynamic information available in literature.

Jan 1, 1995

By V. Jiricny

The novel spouted-bed electrode (SBE) is a cathode system where copper is deposited at a high current density in a moving bed of copper particles. Preliminary results on the deposition of copper from acidic sulfate electrolytes using this novel cathode system were described during Copper '95 conference. Despite a high current density, the electrical energy consumption was equal to or lower than that in the conventional electrowinning. The present paper describes more investigations on SBE. The SBE consists of copper particles with approximately 1 mm diameter onto which copper is deposited from acidic sulfate electrolyte whose composition is similar to conventional electrowinning. Three types of anodes were used in conjunction with the spouted-bed cathode, namely, DSA anode for oxygen evolution, and two novel anodes. One anode is less expensive than DSA; however it showed much promise in energy consumption. At a superficial current density of 2200 A/m2, the energy consumption was around 1.0 kWh/kg copper. The research activities described in this paper were supported by BHP Copper.

Jan 1, 1999

By Dirk Verhulst

The Altair process employs digestion of ilmenite ore in concentrated hydrochloric acid, solvent extraction to concentrate Ti in a purified stream and spray hydrolysis to produce a TiO2 hydrate, followed by final calcining and milling. HCl gas is regenerated by pressure-swing distillation and reinjected in the leaching solution. All chloride streams are recycled. Chromium compounds generally remain in the residue. Solvent extraction provides flexibility for the removal of naturally occurring radioactive elements (NORMs) present in some ilmenites. The process was previously tested at a 5 t/day feed scale. Recent work at pilot scale (40 liter reactor) led to further improvements. Recovery of Ti in solution is now at least 90% with ilmenite ores, while crystallization at lower temperature lowers the amount of Fe in solution to about 5 g/l and improves solvent extraction, which is now conducted in columns. Higher Ti and lower Fe concentrations in the SX eluate improve the economics. A new formula for pigment production via spray hydrolysis produces a pigmentary base with a narrow particle size distribution.

Jan 1, 2003

By Daniel Gauthier, Patrick Sharrock, Cedric Verwilghen, Gilles Flamant, Ange Nzihou, Jocelyn Ramaroson

Clean processes are needed to dispose of many wastes. The incineration of 1 ton of municipal solid waste generates 6000 Nm3 of combustion gases contaminated with heavy metals and other pollutants. Gas scrubbing processes are required to clean incineration fumes in order not to transfer pollution to the atmosphere. We are investigating the use of Hydroxylapatite (Ca-HA) particles for use as sorbent for the removal of volatile heavy metals. We have carried out the synthesis of Ca-HA by two precipitation methods from solution and obtained solids with specific surface areas reaching more than 100 m2/g. Preliminary adsorption experiments were conducted in a horizontal furnace by mixing Ca-HA with 5% by weight of cadmium chloride in solid state. The mixture was heated to 600°C under air atmosphere during 6 hours. Chemical analysis of the solids confirmed that 85 % of the cadmium was retained in the solid phase. Such laboratory results showed that Ca-HA is capable of adsorbing cadmium chloride vapors, and pilot scale studies confirmed cadmium abatement in an industrial context.

Jan 1, 2008

By Eustathios S. Kikkinides

This work presents an integrated approach for the optimal design and control of hydrogen storage beds. A detailed 2-D mathematical model is developed for metal hydride beds and validated against experimental and theoretical literature results. Based on recent advances in dynamic optimization, the model is used to find the optimal process design and operating strategy in order to minimize the storing time, while satisfying, a number of operating constraints (such as pressure drop limitations, cooling fluid availability and maximum tank temperature). Trade-offs between various objectives, alternative design options and optimal cooling control policies are revealed illustrating the potential of the approach. In a further step the model is used to exploit the benefits between material and process design. Systematic simulation and optimization studies are performed at two different length scales (tank and adsorbent pore level) for carbon based materials. The macroscopic approach determines the optimal values of the sorption parameters while, based on these results molecular simulation techniques are employed to determine the pore size distribution of the adsorbents.

Jan 1, 2006