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.
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No abstract is provided for this article.
The redox equilibria – also taking chloro–complexation into account – and the thermodynamics of the HCl – Co – Ni – Mn system have been examined. The leaching efficiencies of the LiCoO2 (LCO), LiNiMnCoO2 (NMC111), and LiFePO4 (LFP) black masses were studied in the 1 – 10 M HCl concentration and the 25 – 95 °C temperature ranges. A minimum of 2 M HCl concentration with an 80-minute contact time at 95 °C was sufficient to achieve > 98 % leaching yields from the LCO material. By increasing the HCl concentration to 6 M, the leaching time could be halved. The NMC cathode material could even be leached completely at 80 °C with 2, 4, 8, and 10 M HCl in 50, 40, 10, and 8 min, respectively. The same yield could be achieved even at only 25 °C using 6, 8, and 10 M HCl for ∼ 310, 125, and 50 min, respectively. A relation was found between the chloride ion activity and the leaching yields, while the evolution of Cl2 was also examined to help explain leaching kinetics. The purity of the graphite residue reached 99.9 % (referring to Co, Ni, Mn, Li) after two cross-current leaching steps. The oxidative precipitation – using hypochlorite solutions - partially generated by utilizing the Cl2 from leaching - was examined in the 1–6 pH range showing that selectivity significantly increases with decreasing pH, but the degree of reagent utilization also decreases. Kinetic factors were also pointed out to markedly affect selectivity. The combined hydrolytic–oxidative precipitation process could recover 96–98 % pure raw oxides, which were further refined to 98–99.8 % purity by scrubbing in acidic MnSO4 and CoSO4 solutions.
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.
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...
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The Liquid Crystal Display (LCD) panels were removed and crushed to be leached. Sulphuric acid of 0.25 M H2SO4 was found best for relatively fast reactions and selectivity, recovering >99% of the indium from the indium‑tin oxide (ITO) layers, while >95% of the tin content was left in the solid residue. As potential impurities, Sn, Fe, Mn, Ni, Zn, Bi, Pb, Al and Cu were analysed in the solutions and in the final product. Synthetic solutions of larger volumes corresponding to the obtained leachate were used for developing the purification and metal recovery steps. Metallic indium was extracted selectively from the solution by cementation on Al plates. The purity of the primary indium deposit was controlled by increasing the temperature to 50–60 °C and keeping the pH in the 0.25–0.5 range, while the aluminium consumption was close to the stoichiometric value. The cemented sponge was vacuum-melted to produce an indium anode block of >99.9% purity for electrorefining. According to the galvanostatic and potentiodynamic results, the optimal electrolyte conditions were found as 50 g/dm3 In, 1 M free Cl− ions, pH 1. The cathodic deposition of Zn, Mn, and Fe was negligible; however, the prior removal of Cu and Sn from the solution is required for producing high-purity indium. Generally, increasing the cathodic current density in the range of 150–600 A/m2 enhanced the purity of the cathodes, while a maximum pH 2 value should be assured. Chloride ion concentration strongly influences the deposit morphology.
In the aluminium industry, the large amount of dross – a by-product of scrap melting – is usually further processed at high temperature re-melting to reclaim the high metallic content entrapped in material. The residue of the hot dross treatment is mainly composed of oxides, and chloride salts from the flux added during the thermo-mechanical process. The major NaCl and KCl components of the added salt are removed by a technically simple leaching process, however, the brine must be treated to remove the dissolved chlorides. We have investigated the energy requirement and efficiency of the evaporation procedure with a simple vessel of insulated walls and submerged heater. The specific heat capacity of the examined NaCl/KCl saturated solution of 2 : 1 mass ratio was determined as ~3155 J/kgK and the latent heat as 1538 J/kgK. The heat efficiency obtained with the system at room temperature initially was found to approach a 97% level as stable conditions were reached. The crystallized NaCl/KCl salt mixture – with possible modifications of it composition – can be recycled to the furnace.
Tin refining in solutions containing just the necessary concentration of HCl for stability (1 mol/dm 3 ), has been investigated in different types of electrolysis cells.A rotating cathode with a centrally placed vertical axis was used to demonstrate the importance of the cathode crystal structure.A computer controlled special potentiostat and current supply was developed for the purpose of potentiostatic and galvanostatic experiments.The virtually even surface of the rotating cathode could offer a uniform conditions over also the anode surface.Cathodic and anodic current densities vs. overpotential were plotted and analysed, as well as cathode potential vs. time at different current densities, applying different tin concentrations.At low tin concentrations, the diffusion limiting current sets in early at the, followed by a shift of the dominant cathodic process for hydrogen evolution, whereas at higher tin concentrations tin deposition was undisturbed.Anodic processes were found virtually unaffected by any of the applied conditions.The optimum energy requirement was found at 30-90 g/dm 3 Sn in the 1M HCl solution at ~ 300 A/m 2 anodic current density.1.
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.
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...
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. The potentiodynamic experiments of the nickel effects on the zinc electrodeposition have been done to understand the impact of Ni impurities on the electrowinning of Zn from spent pickling liquor. The nickel chloride solutions of Ni concentrations 90 and 1 g/dm3 were used as the electrolytes. The latter was also mixed with 90 g/dm3 Zn in the experiments. All the runs were carried out at room temperature with 40 mV/s continuous polarization speed and with 1/s sampling rate. It was observed that nickel electrodeposition from chloride media containing 90 g/dm3 Ni started with the generation of hydrogen bubbles, entirely blocking the cathode surface. Only a slight current development was observed until the polarization potential ~ -0,8 V. The visual observation showed bubbles also formed at the anode, which may represent chlorine and/or oxygen evolution. While, in the electrodeposition of nickel with only 1 g/dm3 Ni concentration in the electrolyte, metal deposition was hardly observed, but visible hydrogen bubbles constantly blocked the cathode surface. A similar tendency was observed in the mixed-solution electrolysis cell; the initial tiny bubbles accumulated at the cathode surface more than in the pure Zn solution. The enhancement of H2 evolution indicates how nickel deposition may contribute to the loss of useful current in the process of Zn electrodeposition. The mass of nickel deposited from the mixed solutions significantly decreases as the Ni concentration decreases in the electrolyte, while the mass of deposited zinc is relatively constant. It means that the purity of the produced Zn is appreciably higher – with respect to Ni – if nickel is efficiently eliminated from the solution before electrowinning.
