The main purpose of this research was to find a suitable, economical and simple way to recover mainly zinc from waste Zn-Mn batteries.The most feasible way can be leaching the soluble zinc content in diluted sulphuric acid after a proper physical separation of the raw material.The leachate however contains an equally high concentration of manganese, and the residual iron contentnot removed by magnetic separationgoes also into solution.Other significant impurities may be copper, nickel and cadmium, by experience.Electrolytic deposition of technically pure zinc is made possible by an efficient hydrolytic separation of iron at the end of the leaching step, followed by the oxidative precipitation of the manganese content.The practically neutral and pure zincsulphate solution can be utilized advantageously for electrowinning zinc.The procedure is still hardly economical, which shortcoming can be improved by the admixing of the easily available centrally stored electric arc furnace dust, containing comparable amounts of zinc, but very low concentration of other soluble metals.Experimental results have proved the viability of this combined processing, although complete recovery of the zinc content is not achieved from the added dust, which results in a basically zinc-ferrite type residue.It can be however recycled to ferrous metallurgy together with the manganese dioxide precipitate and the carbon-iron hydroxidemanganese dioxide containing residue from the battery waste leaching step.The other large scale source of secondary zinc is the electric arc furnace (EAF) dust, which is produced and stored at high quantities in a centralized manner.It is an interesting proposition to improve the availability of zinc by introducing the less soluble, but more accessible and less complex EAF dust into the processing scheme of the better leachable but more complex and less available Zn-Mn battery waste.The latter material represented a collected amount of 164 000 tons in 2003 in Europe consisting of ~30% Zn-carbon and ~60% Zn-Mn varieties [1].
The behavior of cuprous species at electrodes polarized in hydrochloric acid solutions has been investigated in order to obtain the fundamental knowledge o
In order to lay a foundation of a potentially efficient separation procedure for copper in hydrochloric acid solutions, we have investigated the adsorption of copper and several characteristic impurity elements on a strongly basic anion exchange resin in a wide range of HCl concentration. Further experiments were carried out to determine the HCl concentrations and activities in the resin phase. The initial increase of the obtained equilibrium distribution coefficients with increasing HCl concentration indicates the formation of negatively charged complex ions. This tendency of the adsorbability functions is generally reversed at higher HCl concentrations. Analysis of the ion exchange equilibrium based on the obtained adsorbability and activity functions in the higher HCl range provided an interpretation of anion exchange behavior and pointed out the probable average charges carried by the stable, exchangeable species. Possible associations of the examined ions have also been taken into consideration. Comparison of the adsorbability functions showed sufficiently large differences to allow effective purification of initially monovalent copper in chloride solutions, and the obtained average charge of the Cu(I) species can be applied to loading considerations.
Detailed potentiodynamic and galvanostatic methods have been used to investigate the electrodeposition of Zn and to develop a reliable recovery method from a purified and concentrated spent pickling liquor (SPL) of hot dip galvanization. Applying various combinations of Zn concentration, pH, agitation, apparent current density (c.d.) and additional NaCl concentration, a uniform initial deposit could be observed at the cathode, however the subsequent dendrite formation and the development of protrusion at the edges were targeted for a deeper investigation. The potentiodynamic experiments, showed the importance of H 2 evolution influenced by the electrolyte properties and the cathodic polarization. The cathodic current was dominated by Zn reduction in the pH > 2 range during the fast potentiodynamic runs of the 30 – 150 g/dm 3 Zn concentration range in the stationary electrolyte. Increasing the Zn concentration could considerably improve the deposit morphology. In the long-term galvanostatic experiments the current efficiency increased with the increase of pH in the examined wide Zn concentration range but the c.d. needs optimization. A current efficiency (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. At low (~10 g/dm 3 ) Zn concentrations the rate of hydrogen evolution increases dramatically. 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 as low Zn concentrations as e.g. 10 g/dm 3 . Higher NaCl additions or too high Cl - ion concentrations, however inhibit the cathodic reaction of the electroactive species by stronger chloro-complex formation. In this case the intensive H + reduction causes hydroxide precipitation.
The main characteristics of electrolytic reduction applied for indium recovery from aqueous chloride solutions were considered theoretically and examined experimentally. In comparison, also sulphuric and other media were examined. Potentiodynamic examinations pointed out that chloride electrolytes are superior to sulphuric, nitric and methanesulphonic acid ones for efficient In deposition. The optimum conditions allowing higher than 90% cathodic current efficiencies, were determined by galvanostatic experiments, confirming the findings of the potentiodynamic study. In contrast, similar sulphate electrolytes could only yield lower than 50% efficiencies, mainly because of stronger hydrogen evolution and the potentially slower transformations of the complex ions. The structure of the – relatively dense - cathodic deposit was examined. Various levelling agents were also tested, and gelatine was found efficient in preventing the formation of dendrites.
A better procedure for recovering high-purity Zn from the SPL solution has been devised. To provide a suitable electrolyte for the efficient cathodic deposition of high-purity Zn, complete anion-exchange purification had been done by chromatographic technique. The process was then continued by galvanostatic electrodeposition to determine the efficiencies. As the SPL needs to be neutralized before any attempts of Zn electrodeposition, NaCl may provide the required source of Cl- ions for complex formation. The equilibrium studies of the anion-exchange distribution in such solutions showed similar tendencies to those already known in HCl media. The anion-exchange chromatographic separation was devised – with the finer tuning of the parameters – according to the equilibrium result, but other physical parameters were also examined for improving the efficiency of separation and the recovery of Zn. The devised anion-exchange separation in chloride media can purify the SPL, containing Zn as the valuable component and higher concentrations of Fe as the main impurity. The most important impurities (Fe, Mn, Ni, Al and Co) can be efficiently separated in a dissolved state. At the same time, Zn is sorbed in the strongly basic anion[1]exchange resin at a moderate Cl- ion concentration (~ 2 M). Stirring with Fe chips provides a reduction of iron to the Fe(II) state. The remaining problem is minor copper contamination in the same effluent fraction as Zn, which however can be eliminated by a simple additional step of cementation or directly by pre-electrolysis.
A process consisting of anion exchange in a hydrochloric acid solution, electrowinning, plasma arc melting and electron beam melting of electrolytic cobalt has been developed for preparing high-purity cobalt. Glow discharge mass spectrometry (GDMS) and residual resistivity ratio (RRR) were applied for analysis and purity evaluation of the produced cobalt. Almost all the metallic impurities except for copper were removed efficiently and reduced to lower than 1 mass ppm by the anion exchange step. Electron beam melting at a final step was very useful for removal of copper by vaporization from the molten cobalt and the copper concentration could be lowered to below 1 mass ppm. As a result, high-purity cobalt with above 99.9995% in purity (RRR=210) was produced by this practical purification process.
Extraction of tin from tinned plates serves the double purpose of preparing steel scrap for re-melting and producing secondary tin. The best route to reach these goals is offered by hydrometallurgy. In order to compare the efficiency of chemical and electrochemical removal of tin coatings, the mechanisms of the principal processes were investigated. Laboratory analysis demonstrated that tin dissolution rates in oxygenated NaOH solutions are controlled by the oxygen transport to the reaction interface. Increased sodium hydroxide concentration (>0.1 M) has a negative effect on tin dissolution because of reduced oxygen diffusivity. The efficiency of electrolysis in alkaline stannate/stannite electrolytes strongly depends on the applied current density and temperature. Under the applied experimental conditions, cathodic extraction of tin (in an appropriate spongy form) could be stabilised at current efficiencies higher than 80%. Measurement of the anode potential was found to yield a proper end-point indication for de-tinning tinned steel plate scrap in anode baskets. The results demonstrate the practical advantages of electrochemical processing in alkaline media.
Different ways of investigation were applied to address the main difficulties of electrolytically refining the tin-based lead-free soldering waste materials in chloride solutions. The characteristics of electrorefining and the phenomena of electrocrystallisation have been targeted by examining the electrode processes with different copper and silver concentrations in the anodes. Galvanostatic experiments were carried out using a specially developed system detecting the changes in the electrode masses continually, complemented by the recording of the electrode potentials. In order to clarify the main cathode and anode processes, further investigations were carried out by the potentiodynamic technique. Galvanostatic results pointed out the causes of current losses and rough deposit structure. Potentiodynamic examinations have demonstrated the strong influence of material transport on the electrode processes. Nevertheless, with a quasi-optimised procedure, cathode tin of higher purity than technical standards could be achieved from the soldering waste material in a conventional cell.
No abstract is provided for this article.
Nagy mennyiségű és nagy sótartalmú végsalak származik az alumíniumötvözetek hulladék alapú gyártásánál keletkező primer olvasztási salakok meleg (termo-mechanikus) feldolgozásából. Az oxidos mátrix mellett ebben viszonylag kevés (5 ~ 10 %) fém és jelentős mennyiségű kloridos alkotók (30 ~ 40 % NaCl és KCl), valamint egyéb vegyületeket fordulnak elő. A vízben oldható, illetve azzal reagáló anyagok miatt, ez a Magyarországon is évi több ezer tonnás nagyságrendben keletkező ipari maradványanyag veszélyesnek minősül és valós környezetvédelmi terhet jelent. A gazdaságos technológiát célzó laboratóriumi kísérletek szerint, a kloridos alkotók kioldása néhány percen belül megtörténik legalább 1:1 cm3/g (víz térfogat:minta tömeg) folyadékarányt biztosítva a szedimentációt megakadályozó intenzitású vízszintes rázás mellett. Ugyanakkor, az edény telítettségi szintjének is van kimutatható hatása. A viszonylag kis költségű megvalósítás a só visszajáratását és a kezelt végmaradvány egyéb célú felhasználását is lehetővé tenné.
No abstract is provided for this article.
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.
Primarily, the mechanical removal of LCD panels from smartphones was examined, and a relatively easy and quick manual method was established. The LCD panels can be separated from the rest of the screen in a few seconds. In the cases of more tightly packed applications, the whole screen can be directly ground to a fine powder. The separated LCD screens were leached in different concentrations of HCl and H2SO4. The latter was found as practically more advantageous. Leaching with slightly acidic solutions (0.1 M H2SO4) results in longer leaching time, however solutions with higher purity can be obtained. If further purification is required, a relatively straightforward method of selective hydrolytic precipitation has also been examined. The practically recoverable amounts of indium may be close to the 400 mg/kg level in a dilute sulphuric acid solution containing less than 10 mg/dm3 of total impurities (Fe, Zn, Al, Cr, Ni and Cu).
The major goal of this potentiodynamic study was to explore the characteristics of zinc electrodeposition from chloride (ZnCl2 -HCl) media.The influence of various operating parameters such as zinc concentration in the 30 -150 g/dm 3 range, acidity level (pH in the 1.5 -5.5 range) and rotation speed (0 -950 r.p.m.) were investigated at room temperature.Deposit morphologies were recorded by a digital camera during cathodic polarization.The physical quality of the electrode surface seems to be one of the important parameters not only for the deposit structure but also for the side reaction of H2 evolution and also for the development of the polarization curves.There are three kinds of cathodic depositions occurring.It generally starts with a uniform and stable structure, followed by a sponge-like deposit and finally it turns into a dendritic growth due to concentration changes near the surface.However, electrolyte agitation can influence the deposition pattern.With increased rotation speeds (above ~ 500 r.p.m.), resulting in higher available concentrations of electroactive ions at the surface, there is not much sponge-like deposit, yet the dendrite formation at the edges could not be avoided.The strong increase in the actual specific surface area of the cathode, due to the sponge-like deposit and the dendrite formation, caused irregularities in the potential change executed by the computer controlled potentiostat.Although this instrument was designed and produced at the institute specifically for high speed measurements.By lowering the pH in the electrolytes of the lowest Zn concentrations, the side reaction of H2 evolution soon appeared, after the limiting current of Zn deposition was reached.At higher Zn concentrations though, instead of a clear limiting current, the slope of the polarization curve persisted all across the examined potential range, indicating a continual co-deposition of H2 together with that of Zn.
Pickling is one of the essential steps in galvanizing industries in which hydrochloric acid (HCl) is used as the main composition to clean up the steel surface. This HCl lost its pickling efficiency because of decreasing in its concentration as well as increasing metals content because of dissolution processes. Recovery processes could be done to this kind of waste, so circular economics and a nearly zero waste cycle industry can be established. Processing SPL by electrodeposition is possible to recover pure metal from the waste solution. However, the presence of iron in the zinc chloride solution changes the nature and the conditions. It was found that the effect of iron concentration on the polarization curves is complex. Initially it has a negative effect on the generated cathodic current because of the enhancement of hydrogen bubble formation. Further increased iron concentrations may make the composition of the Zn-Fe deposit dominantly in favour of iron, resulting in a hydrogen dominated cathodic mechanism. Controlling the parameters such as Zn and Fe concentration, and the electrolyte's agitation intensity could play essential impacts on the electrodeposition of zinc from chloride media. Nevertheless, separation is still essential; thus, introducing the anion exchange separation to prepare the electrolyte is needed to achieve an acceptable quality of zinc deposition. In the relatively low concentration of HCl, Zn tend to be retained in the resin as its more likely to produce chloro-complex. As in the higher concentration of HCl (>1), Fe(III) distribution fucntion in HCl will increase thus the Fe may retain in the resin. However oxidation state control can be the answer of this problem by reducing Fe(III) to Fe(II) or in order to optimalize the separation process partially precipitation of Fe might be an option.
Techniques of metal refining and purification rely on the differences in physicochemical properties of the base metal and the impurities. In order to reach the desired ultra-high purity, a sequence of complementary refining steps is required. These steps...
No abstract is provided for this article.
White light beads containing light emitting diodes (LED) were removed from the commercial light bulbs and treated with a complex, but easily implementable hydro-electrometallurgical method to recover pure Ga. Using concentrated H2SO4 as the digesting agent at 180 °C for 60 minutes resulted in >90% efficiencies of gallium and indium solubilization by the subsequent water leaching. All metals - except for Ag – could be fixed in a strongly acidic cation-exchange resin by loading the solution into a chromatographic column. Indium, Cd, Pb and Sn are selectively eluted with 1 M HCl, while Al can be transferred into the aqueous phase using a 0.25 M NaF solution. Gallium is recovered in a pure eluate from the resin with 3 M NaOH, and finally, Y is eluted with 0.5 M Na2CO3. The cathodic deposition of Ga from the alkaline eluate was studied by potentiodynamic and galvanostatic methods. As high current efficiencies as 99% could be reached in solutions of 50 g/dm3 Ga and 6 M free NaOH at 300 A/m2 cathodic current density. Decreasing the NaOH concentration to 1.5 M resulted in a 10 ~ 15% decrease in the current efficiency. Lower Ga concentrations also reduced the current efficiency significantly. The cell voltages were in the range of 2.1 – 2.4 V, yielding a relatively low (2 kWh/kg) specific energy consumption. The obtained cathodes were immersed into 2 M HCl at 55 °C, resulting in 99.999% Ga metal melted from Ti mother plates.
