69 publications from this institution
Indium recycling by a hydrometallurgical method must include the reduction of the dissolved ionic In compound to its metallic state. We have examined the easily implemented cementation of In with Fe, Zn, Mn, Al and Mg. It was found that the cementation with Zn turns slow as the produced layer lacks sufficient porosity to allow the solution to reach the metal surface, and the strongly adhering deposit is hard to be removed. On the other hand, Al may perform efficiently if the pH is set correctly. The indium layer is fast growing, can be easily removed. After mechanical compacting, it is easily melted. The Al consumption is close to the stoichiometric value at pH 1 and the produced indium sponge can be of 99.99% purity.
A large amount of currently useless basically oxide residue is produced by the treatment of dross obtained from the melting of alloyed aluminium scrap.Its negligible residual metallic component does not make it feasible for any further metallurgical processing.On the other hand, it may have a high content of chloride salts.Its removal may not only serve the purpose of recycling but it may be mandatory to make this residue suitable for applications in preparing construction and road paving materials, or as a slag forming additive in the steel industry.A hydrometallurgical treatment with pure waterafter fine grindingmay be efficient in this respect and it may even reduce the residual metallic content if acidic or alkaline media are also used.In order to develop a suitable method of purification, the composition of the raw residue has been examined by SEM and XRD techniques and carried out experiments to determine the efficiencies of the treatments with water, sulphuric acid and sodium hydroxide.The results show that leaching with water can remove the main salt components of NaCl and KCl in a short time.However, the evolution of some NH3 gas from the side reaction of the AlN compound formed during the preliminary thermos-mechanical treatment cannot be avoided.The application of sulphuric acid can be efficient not only in removing the residual metal content but also in suppressing the evolution of NH3.Although the sodium-hydroxide reagent is capable of aggressively dissolve aluminium not only in the metallic but also in the oxidised states, but it may also enhance the evolution of NH3.According to the phase composition and structure of the treated materials, water leaching -perhaps combined with an extra step of sulphuric acid leachingcan be satisfactory for assuring the state of the residual dross to be accepted in non-metallurgical applications.1.
Recent advances in modem technology have created an increasing demand for ultrahigh purity metals. For example, ultra-high purity copper could be used as a bonding wire and interconnector in integrated circuits or as a superconductor stabilizing material, highfield...
White LED bulbs contain significant quantities of Cu, Sn, Pb, Al and appreciable amounts of Ga and traces of In. A feasible recovery of the valuable components – either in metallic or compound forms - has been devised and examined. Leaching the assemblies with 4 M HNO3 at 80 °C could leach Cu, Fe, Pb and Ag, while Al is passivated and Sn precipitates. In this step, the LED beads are detached from the aluminium base plates. The solid residue comprises of practically pure Al plates and Sn(OH)4. Pure Cu hydroxide was recovered by precipitation. The physically liberated solid bodies of the detached LED beads were roasted to convert Ga and In into soluble compounds. While a simple oxidative roasting could assure ∼80% recovery, alkaline fusion with NaOH or roasting with Na2CO3 yielded >90% recoveries. Leaching the roasted material with 1–6 M NaOH could efficiently dissolve Ga, while In was only slightly attacked. However, the major portion of In could be leached by applying as high as 10–11 M NaOH with similar efficiencies. Finally, the extractions of Ga and In were studied by electrowinning from the alkaline solutions yielding 99.99% pure Ga and 99.9% pure In deposits, respectively.
Potentiodynamic and galvanostatic experiments have been used to investigate the electrodeposition of Zn and to develop a reliable recovery method from a purified spent pickling liquor (SPL) of hot dip galvanization. The main bjective was to find the suitable conditions to deposit high-grade Zn from the purified ZnCl 2 –HCl–NaCl solution in a conventional electrowinning cell holding the stationary electrolyte. The effects of pH (1.5–4.5) in and Zn concentration (30–150 g/dm 3 ) in the stationary electrolytes were studied first by the potentiodynamic method to reveal the major characteristics of the cathodic process and to give reference for further practical examinations by the galvanostatic technique. The electrowinning experiments pointed out the effects of these major parameters, beside other practical factors, like apparent current density (c.d.) and additional NaCl concentration. The long-term galvanostatic experiments proved that the current efficiency (c.e.) increases significantly as the pH and the Zn concentration are increased. A c.e. of ~ 99% can be reached with an electrolyte of pH ~ 5, Zn concentration ~ 50 g/dm 3 applying a c.d. in the 300–600 A/m 2 range. Increasing the Zn concentration could considerably improve also the deposit morphology. The addition of NaCl can practically improve the c.e. if the Zn concentration is at least around 50 g/dm 3 . In contrast, this improvement is largely off-set by the negative effects of strong H 2 evolution at low (e.g. < 10 g/dm 3 ) Zn concentrations. Extremely high Cl − ion concentrations, however, inhibit the cathodic reaction by stronger chloro-complex formation. In this case the intensive H + reduction causes hydroxide precipitation.
A residual dross of high quantity and high salt content arises from the hot (thermo-mechanical) treatment of the primary dross generated by the production of aluminium alloys from scrap. It contains a relatively low concentration of metal (5 – 10 %) but a high amount (30 - %) of chloride salts and some other components beside the oxide matrix. Due to the components dissolved in or reacted with water, this industrial residue - arising in thousands of tons also in Hungary – qualifies as hazardous and causes a real burden to the environment. According to the laboratory experiments aimed at an economical technology, the chlorides are dissolved within a few minutes when a liquid/solid ratio of 1:1 cm3/g (water volume:sample mass) is assured with an intensity of the horizontal shaking to prevent sedimentation. However, the filling ratio of the vessel also appears to have an effect. An implementation of relatively low cost would allow the recycling of the salt and the application of the final residue for alternative purposes.
Recent application in advanced electronics have increased the practical importance of ultrahighpurity cobalt. Anion exchange in HCl media is considered an
Solvent extraction with Kelex 100 has been recognised as a possible method for recovering gallium from Bayer liquors, but the practical process has not been so attractive as to cause a general technological break-through. The purpose of this research was to enhance the Ga/Al selectivity and efficiency of the extraction and re-extraction processes, while making the method as simple as possible. Instead of applying various additives and modifiers, the approach was based on the fundamental extraction kinetics with the pure kerosene/Kelex 100 system and a method of selective re-extraction boosted by possible chloro-complex formation in HCl media. The main factors examined during the extraction tests were solution pH, concentration of Al, amount of the reagent and the intensity of agitation, whereas HCl concentration was varied to improve the performance of the re-extraction step. The extraction results were interpreted in terms of the heterogeneous transfer mechanism. A Ga/Al selectivity index of almost 100 could be achieved at a Ga yield of ∼70% with 10–20% Kelex 100 in kerosene and the pH set to ∼14.3 from a NaOH solution containing 100 ppm Ga and 1100 ppm Al. As a practical source, the zeolite mother liquor has also proved suitable for the procedure. Aluminium carried over to the extractant can be separated from gallium during the combined re-extraction procedure, removing aluminium with 5–6 M HCl from the organic phase, then eluting gallium with ∼2 M hydrochloric acid solution.
Zn recovery from spent pickling liquors (SPL) from hot dip galvanization was examined with modelled solutions by combining anion exchange separation and electrodeposition processes. The solution was purified to be suitable for the electrodeposition of Zn with the main goal of eliminating the iron content. The anion-exchange resin bed in a chromatographic column primarily retained Zn, while divalent Fe was removed in the loading and rinsing steps. At the end of the process, the elution of Zn was carried out by a significantly reduced Cl– ion background. In parallel with the purification process, the potentiodynamic study (1 min runs at 40 mV/s polarization speed) of Zn electrodeposition in the series of Fe concentrations was examined. During the separation process, the preliminary reduction of the iron to its divalent state was found to be of utmost importance. The separation of iron could be improved by controlling the preliminary reduction. It was found that the effect of iron concentration on the polarization curves is complex. Initially, hydrogen bubble formation causes inhibition, but at higher iron concentrations a Zn-Fe deposit is soon formed, promoting hydrogen evolution, thereby depressing polarization but also the current efficiency. The loss of the dendritic structure obtained from pure zinc solutions also characterizes the effect of mixed Fe-Zn deposition. In order to recover pure zinc at the cathode, the pre-purification of the Zn electrolyte is essential.
No abstract is provided for this article.
Recycling of the impure tin generated by the hot dip tinning and wave soldering technologies widely applied in modern electronic industry can be carried in a flexible and economical way even at relatively low production rates by electrorefining. In order to avoid the economical disadvantages of the alkali stannate or the sulphuric acid – cresylic phenylic sulphonic acid baths, the hydrochloric acid tin chloride electrolyte solutions can be applied. The major difficulties of solution stability, cathode corrosion and rough electro-crystallization can be overcome by optimizing the solution composition and the current parameters. Strong chloro – complex formation in the hydrochloric acid solution enhance stability of the Sn(II) species and the consequent natural inhibition promotes a cathodic deposition of acceptable quality. The virtual current efficiency and the morphology of electro-crystallization were improved by applying periodically reversed (PCR) current. Although cathode corrosion could be depressed to a negligible level, dendritic crystal growth remains to be dominant, therefore special cell arrangement and cathode handling should be applied. The cathode deposit is easily removed and melted, allowing to obtain a recycled tin of high purity.
A flexible and efficient process of tin electrorefining has been devised, using aqueous solutions of relatively low HCl and tin chloride concentrations. Any additives have been avoided, which enhances purity but also incurs the difficulty of obtaining compact cathode deposits. This feature is however assisted by the natural inhibition in complexing chloride solutions and the modulation of the current. Due to the rough dendritic crystal growth, special provisions are required to avoid short circuiting. Using short pulses in the 50-250 μs range of periodically reversed or interrupted currents, the lengths of the usually large dendrites can be moderated. The periodic current with extremely short cycle times and special electrode arrangement can be utilized for averting short circuits and for achieving better coverage of the cathode surface. This technique can be applied efficiently to obtain pure tin from soldering waste materials.
The waste material produced in lead-free wave soldering is melted, skimmed and cast into anodes.Anode slime, the by-product of electrorefining in hydrochloric solutions is collected and the basically undissolved silver and copper constituents are removed by selective leaching.The first step is the elimination of metallic tin using HCl of high concentration and temperature, followed by the leaching of the nobler metallic components in HNO 3 under similar conditions.Kinetic study on the leaching behavior of the raw anode slime in both media has shown the optimum conditions.The metallic tin content of the anode slime can be dissolved virtually completely in 10 M HCl at the highest possible temperature of 85 o C, however it takes about 3 hours.On the other hand, silver can be o quickly dissolved in about 15 minutes by applying approx.50% HNO 3 at 90 C. Combination of the two steps in this order can result in an efficient recycling of the slime by producing relatively pure SnCl 2 and AgNO 3 solutions, respectively.The tin content can be recycled conveniently to the tin electrolysis and the silver containing solution can be used for recovering silver by electrowinning or precipitation.
The production of ferro-alloys from waste Li-ion batteries has been examined thermosdynamically and experimentally. It was found that Co and Ni can be reduced even with relatively low pCO/pCO2 ratios in the gas phase, while the reduction of Mn or Fe requires strongly reducing conditions and higher temperatures. Even the reduction and selective recovery of Li are thermodynamically possible due to the possible evaporation. The optimum slag compositions were evaluated theoretically, followed by an experimental investigation. Ferrocobalt, ferrocobalt-nickel and ferrocobalt-nickelmanganese were produced using calcium-magnesium-ferrite type slags. Furthermore, secondary Al dross – containing Al – was also tested both as a reducing and a slag-forming agent for the production of ferrocobalt and ferromanganese affiné.
The rotary converter melting of Al-containing drosses with and without NaCl addition was examined. It was found that simple NaCl can enhance the recovery by 9% while decreasing the mass of the secondary dross. It implied a significant decrease in the metallic Al concentration, which indicates a superior coalescence of the molten metal drops when NaCl is present. However, the thermodynamic analysis showed that it might also imply the possibility of a certain degree of aluminothermic and magnesiothermic reduction of NaCl. On the other hand, neither the analysis of the flue dust nor that of the tapped metal showed the presence of the reaction products; thus, no melt contamination occurred.
Promising applications in advanced electronics have created a demand for ultra-high purity iron. Anion exchange in chloride solutions may offer an efficient and practical way of purification. Examination of anion-exchange distribution functions revealed a variety of behavior patterns to be exploited. Elution tests in laboratory-scale columns suggested that virtually all the impurities can be separated from the iron chloride solution by anion exchange. The hydrochloric acid concentration and volume of the rinsing and eluent solutions determine the efficiency of the procedure. Separation of certain elements (e.g. copper and molybdenum) requires strict control of redox conditions. The designed procedure consists of two anion-exchange steps. In the first step and during solution preparation, those impurities are separated which can be precipitated by iron, or sorbed in the resin at low HCl solutions under reducing conditions determined by the addition of Fe powder. The remaining impurities are separated from iron, applying a second ion exchange step under oxidizing conditions. Performance characteristics (yield, purification ratio and volume efficiency) of the separation indicate the optimum parameters of the rinsing and eluent solutions and the suitable way of defining the collected volume fraction of the effluent.
