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Conductivity is a typical physico-chemical property that has a substantial effect on electrical energy consumption in the electrorefining process. The objective of this study was to examine the validity of regression models predicting the conductivity of industrial copper electrorefining electrolytes. The models were based on data measured with synthetic solutions on a laboratory scale. The variables included in the models were temperature and the concentrations of copper, nickel, arsenic and sulfuric acid. Both first-order and combined effects of the variables were investigated. The measured data were analyzed using MODDE 8.0 modeling and design software. The validity of the models was investigated by comparing the predicted values with tankhouse conductivity measurements taken at the Boliden Harjavalta Copper Refinery in Pori in Finland. During the tankhouse tests, the conductivity and temperature of the industrial electrolyte were measured, and the composition of the electrolyte was analyzed. The measured conductivity values were compared with the predicted conductivities calculated using the developed models. The conductivity model developed in this paper was shown to be more accurate than previous models and suitable for industrial use.

This research details the spontaneous electroless and electrodeposition of copper onto carbon nanotube (CNT) film from a copper sulfate electrolyte. Inhomogeneous electrodeposition was found to occur on pristine CNT film due to differences in available active nucleation sites and the hydrophobic nature of the film. In order to improve the electrochemical response of CNT films, oxidative pre-treatments such as heat treatment and anodization were investigated. These treatments were shown to increase the amount of oxygen containing defects at the surface of CNT film material. Incorporation of functional groups were shown to enhance the wetting of the aqueous electrolyte and created a highly active surface suitable for homogenous electrodeposit. Cathodic polarization curves showed that the presence of functional groups decreased the required level of polarization for copper deposition. Nevertheless, after a certain level of functionalization the polarization starts to decrease due to increased resistivity of the CNT film. Oxygen grafted CNT films were also shown to exhibit enhanced adsorption and reduction of copper without applied voltage due to redox replacement reactions, which were observed to increase with enhanced levels of functionalization.

In the silver electrorefining process, the presence of gold as an impurity in anodes can affect process performance. In the present investigation, the effect of gold on anode passivation and the kinetics of dissolution at high current density were studied. Experiments were conducted using artificial silver anodes with gold contents of 2%, 5%, 10% and 20% (w/w) and acidic nitrate electrolytes containing 40 g/dm 3 and 60 g/dm 3 of Ag + . Results obtained from potentiodynamic measurements showed that in order to have higher current densities than 50 mA/cm 2 and higher energy efficient operation, the gold content in anode should be limited to ≤ 10% with 60 g/dm 3 of Ag + electrolyte. In contrast, the same current density operation for 40 g/dm 3 electrolyte will be applicable for anodes with ≤ 3.2% gold content with high energy inefficiency.

In production of stainless steel 10–70 kg of dusts per tonne of steel is produced. The final rolling and pickling stages produce significant amounts of metal-rich wastes and acid sludge. The dusts are usually treated by pyrometallurgical methods such as plasma processing or Waelz kiln. Hydrometallurgical methods have been developed especially for the recovery of zinc from electric arc furnace (EAF) dusts, focusing on unalloyed steel EAF dust. A new concept has been developed to selectively leach out zinc from stainless steel production dusts enabling recycling the remaining iron, nickel and chromium compounds back to melting. Zinc can be dissolved using either a strong alkaline solution or strong acid solution. Factors affecting the leaching efficiency have been determined. Mineralogical factors limiting the zinc dissolution have been determined and pre-treatment methods have been developed. Using the optimal conditions the zinc level in the treated dust has been low enough allowing recycling of the dust ...

A ferrochrome converter (CRC) is used for removal of silicon and carbon from ferrochrome in stainless steel production. The raw materials are molten ferrochrome and stainless steel scrap, and the process produces a raw material for argon-oxygen-decarburization (AOD). The zinc content prevents the utilization of CRC dust (CRCD). The objective of this work is characterization and sulfuric acid leaching of CRCD and evaluation of formation mechanisms and the effects of mineralogy and microstructure on the hydrometallurgical treatment. CRCD contains critical (Cr, fluorite) and economically important (Fe, Zn) materials. The mineralogy and microstructure of CRCD are complex. The dust has been formed by many mechanisms. Lime and ferrosilicon prove that take-off of solid particles during charging is important. Also, ejection of liquid droplets is considerable because ferrochrome and slag spheres are common. The highest Zn dissolution is 93–94% and at the same time 5–15% of Cr is leached. The existence of zincite explains the high dissolution of zinc. The encapsulation, e.g., magnesiochromite enclosed into glass, explains the low chromium dissolution. The best selectivity for Zn extraction over iron, chromium, and nickel is achieved with 0.5 M, at 30 and 60 °C with both L:S 10 and L:S 20.

Electrochemical deposition of copper on a carbon nanotube (CNT) fiber from a copper sulfate – sulfuric acid bath was studied in order to produce a carbon nanotube-copper composite wire. The high resistivity of the aerogel-spun fiber causes a non-uniform current distribution during deposition, which results in a drastic drop in the copper nuclei population density as sufficient overpotential is not available beyond a certain distance from the current feed point. Copper was found to fill the pores between CNT bundles from Focused Ion Beam (FIB) cut cross-sections confirming that aqueous based electrolytes can fill micropores between as-spun CNTs in a fiber network. The speed at which copper grows on the fiber surface was identified at ca. 0.08 mm/s with 1 mA applied current. The copper cladding showed columnar growth with a grain size an order of magnitude higher than the CNT-Cu region. The resulting composite was found to have specific conductivity similar to that of pure copper i.e. 98% of copper with 0.2 w-% of CNT, exhibiting a ninefold increase from the pure CNT fiber. Self-annealing was shown to decrease the resistance of the composite.

openaire: EC/H2020/609057/EU//ULTRAWIRE Copper-carbon nanotube (Cu-CNT) composite wires were produced by casting, rolling and drawing to produce composites with 0.05 wt% CNTs embedded at the grain boundaries of copper. The corrosion properties of wires were investigated in mild and highly corrosive media: solution I consisting of 0.05 wt% sodium chloride (NaCl) and 0.4 wt% ammonium sulfate (NH4)2SO4 and solution II consisting of 3.5 wt% NaCl. Composite samples showed similar behaviour and corrosion rates as oxygen free copper in solution I. In 3.5 wt% NaCl all composite samples showed slight improvement in corrosion resistance when compared with oxygen free copper. The corroded wire surfaces after five days in 3.5 wt% NaCl showed less dissolution for composite samples compared with pure copper. The observed decreased corrosion rate for composite wires with embedded CNTs is suggested to be due to reduced cathodic reaction. Galvanic current density between pure copper and carbon nanotubes was observed by mixed potential theory and zero resistance amperometry, neither of which showed tendency towards microgalvanic activity. The results indicate similar or slightly improved corrosion properties of copper containing small additions of CNTs in chloride containing media.

Pickling with hydrochloric acid is a standard method to clean steel surfaces before hot-dip galvanizing. When normal low strength steels are pickled, hydrogen formed in pickling reactions does not have any significant harmful effect on the mechanical properties of steel. However, in pickling of steels with higher strength, the penetration of hydrogen into the steel may cause severe damages. The effect of pickling of high-strength low-alloy (HSLA) steels was investigated using a cell construction based on the Devanathan-Stachurski method with modified anodic surface treatment and hydrogen production using acid. The penetration and the permeability of hydrogen were measured using an electrochemical cell with hydrochloric acid on the one side of the steel sample and a solution of NaOH on the other side. No protective coating, for example, palladium on the anodic side of the sample, is needed. The penetration rate of hydrogen into the steel and exit rate from the steel were lower for higher strength steel.

The primary production of sulfide concentrates includes smelting to copper matte or blister copper, conversion of matte to blister copper, and refining to copper. Smelting, converting, and fire-refining can use a limited amount of secondary materials. Molten copper can effectively dissolve many metals, from valuable noble metals to harmful impurities such as bismuth. However, some of the impurity metals in copper are valuable in other applications. In this paper, we outline the main material flows in copper smelting and electrorefining and describe how minor metals can be recovered from secondary raw materials using copper as a carrier material. We will use a system integrated approach to define the factors that affect the recovery of different metals and copper quality. Metals typical in copper production are used as examples, like noble metals, As, Bi, Se, and Te, including metals in the EU critical raw materials list like PGM and Sb

This paper presents a method for externalising and formalising knowledge involving the selection of hydrometallurgical process flowsheets for gold extraction from ores. A case-based reasoning (CBR) system was built using an open source software myCBR 3.0. The aim of the systems is to recommend flowsheet alternatives for processing a potential gold ore deposit. Nine attributes: Ore type, Gold ore grade, Gold distribution, Gold grain size, Sulfide present, Arsenic sulfide, Copper sulfide, Iron sulfide and Clay present were modelled and several literature sources of actual gold mines and processes were used for acquiring cases for the system. After preliminary testing, functional evaluation of the built CBR system was carried out by using five real mining projects as test cases. Additionally, human experts in the field of gold hydrometallurgy were interviewed to demonstrate the benefits of the CBR system as it holds no human biases towards any processing techniques. It was found that the suggestions of the CBR system provided useful information and direction for further process design and performed well compared to the interviewed human experts, thus confirming that the system is of practical relevance to the process engineer designing an industrial gold processing plant. The current model was found to be a functioning basis for further development through additional attributes, adjusted attribute weighting and increased number of cases.

The geometric properties of $\mathrm{Pb-MnO_2}$ composite electrodes are studied, and a general formula is presented for the length of the triple phase boundary (TPB) on two dimensional (2D) composite electrodes using sphere packing and cutting simulations. The difference in the geometrical properties of 2D (or compact) and 3D (or porous) electrodes is discussed. It is found that the length of the TPB is the only reasonable property of a 2D electrode that follows a 1/r particle radius relationship. Subsequently, sphere packing cuts are used to derive a statistical electrode surface that is the basis for the earlier proposed simulations of different electrochemical mechanisms. It is shown that two of the proposed mechanisms (conductivity and a two-step-two-material kinetic mechanism) can explain the current increase at $\mathrm{Pb-MnO_2}$ anodes compared to standard lead anodes. The results show that although $\mathrm{MnO_2}$ has low conductivity, when combined with Pb as the metal matrix, the behaviour of the composite is not purely ohmic but is also affected by activation overpotentials, increasing the current density close to the TPB. Current density is inversely proportional to the radius of the catalyst particles, matching with earlier experimental results. A hypothetical two-step-two-material mechanism with intermediate $\mathrm{H_2O_2}$ that reacts on both the Pb matrix and $\mathrm{MnO_2}$ catalyst is studied. It was found that assuming quasi-reversible generation of $\mathrm{H_2O_2}$ followed by its chemical decomposition on $\mathrm{MnO_2}$, results are obtained that agree with the experiments. It is further emphasised that both the Pb matrix and $\mathrm{MnO_2}$ catalyst are necessary and their optimum ratio depends on the used current density. Yet, additional experimental evidence is needed to support the postulated mechanism., Comment: 35 pages, 14 figures; Electrochimica acta, postprint as accepted; due to the limitation "The abstract field cannot be longer than 1,920 characters", the abstract appearing here is shortened, original is in the PDF file. doi is first valid when it is published electronically

Surface properties of stainless steel on nucleation and growth of copper under electrorefining conditions were studied using AISI 316L type stainless steel in rotating disc electrodes (RDE), stationary electrodes and Hull cell, and also worn industrial cathode blanks. The aim was to find correlations between surface topography and nucleation and growth using deposition tests, microscopy, and image analysis. Deposition tests were done galvanostatically using synthetic copper electrorefining electrolyte and current density 330 A/m2 typical in electrorefining. On the as-received stainless steel with 2B finish, nucleation happened at grain boundaries. Wet grinding resulted in deposition on the ridges and valleys of rough surface and ridges of smooth surface. The nucleation density was in the order of 106 nuclei/cm2 in RDE and Hull cell tests, and 105 nuclei/cm2 in stationary electrode tests. Used industrial blanks did not show the same deposition patterns on grain boundaries and scratch marks, and copper deposited on edges of larger damages. The nucleation density on industrial blanks was in the order of 103 nuclei/cm2.

Atomic force microscopy (AFM), conductive atomic force microscopy (CAFM) in air, and scanning electrochemcial microscopy (SECM) in 2 M H2SO4 have been used to investigate model composite electrodes obtained by pressing sieved MnO2 particles into a Pb matrix. These model electrodes shall resemble new composite electrodes produced by coldspraying and currently being tested for Zn electrowinning. CAFM showed a very uneven distribution of the current path through the matrix electrode with the highest currents measured at the MnO2/Pb domain boundary. SECM images in the substrate-generation/tip-collection mode in vertical and horizontal planes could show spatial concentration distribution of H+, O2 and H2O2 that could be evaluated qualitatively despite interfering turbulent convection due to raising gas bubbles. There is a concentration overvoltage due to deviations of the H+ and O2 concentration close to the surface from the bulk value. It amounts to about 40–50 mV for both compounds. H2O2 is formed as an intermediate and is consumed at the MnO2 catalyst particles.

Several modifications of manganese dioxide (MnO2) were investigated for use in composite electrode materials for oxygen evolution, the target application being anodes for the industrial electrowinning of metals. It is demonstrated that the performance of this material depends strongly on the modifications of MnO2. All modifications investigated were found to be more active than the usual anode of lead alloyed with silver (PbAg) used in zinc electrowinning. A composite sample containing chemical manganese dioxide (CMD) was found to give an oxygen evolution overpotential 0.25 V lower than the standard PbAg anode material. In the second part of the article, we investigate the effect of varying several parameters of the composite electrode assembly, including the size of the catalyst particles and percentage of the catalyst material used. A model is proposed where the performance of the material is proportional to the total length of the boundaries between the lead matrix material and the MnO2 catalyst particles. Physicochemical processes contributing to the observed data are discussed.

This study presents an investigation of chalcopyrite surfaces dissolving in concentrated cupric chloride solutions similar to those used in the HydroCopper® process, [NaCl] = 280 g/L, [Cu2+] = 30 g/L and T = 90 °C. The leaching of chalcopyrite and the parameters of the reaction product layer formed on the mineral surface were studied at the open circuit potential as a function of time (0.5 – 22 hours) and at pHs in the range 1 - 3. The electrochemical impedance spectroscopy (EIS) data indicated that there were two or three time constants present. These were suggested to be due to the double layer and to elemental sulphur and FeOOH. With pH 1 at OCP the reaction product layer was a single-phase layer of elemental sulphur (t = 0.5 – 9 h) or two-phase layer with elemental sulphur and FeOOH (t = 22 h). The apparent charge transfer resistance was higher (>25 Ωcm2) at the beginning of leaching (t ≤ 4 h), but decreased to about 4 Ωcm2 with increasing time to 22 hours. The reaction product layer resistanc...

The nature of the redox potential in concentrated cupric chloride solutions where [NaCl] = 280 g/L and [Cu2+] = 10–40 g/L was studied at temperatures 25–85 °C for 49 days. The redox potential of the solution was studied as a function of solution storage time, temperature and initial cupric chloride concentration. Measured redox potential values varied in the range 0.56–0.75 V vs. Ag/AgCl, increasing with increasing total copper concentration and temperature. The rate of reduction of cupric to cuprous species was highest in the most concentrated solution and occurred in 5 days, with the concentration of copper species 40 g/L. The solutions having initial copper concentrations of 30, 20 and 10 g/L reached steady state after 20, 26 and 26 days, respectively. The standard electrode potential, Eo, in concentrated cupric chloride solution was determined using the Nernst equation. The form of cuprous complex was proposed on the basis of the value of Eo, since the cupric/cuprous standard electrode potentials divide clearly in two groups. The Eo for redox couples, with cuprous present as a chloro-complex form, is a minimum of 0.3 V higher than the Eo for redox pairs with uncomplexed cuprous ions. Eo value for the redox pair existing in a HydroCopper® type environment was calculated to be − 0.039 (± 0.121) V vs. Ag/AgCl. This suggests that in a very concentrated cupric chloride solution without any additives, not all cuprous ions present are complexed with chlorides.

In this study we demonstrate the kinetics of Cu 2+ reduction in concentrated cupric chloride solutions. Experiments were carried out near the boiling point of the solution ([NaCl] = 280 g/l and [Cu 2+ ] = 1–40 g/l) at T = 90 °C, atmospheric pressure, pH = 2. Electrochemical methods such as cathodic polarization curves and cyclic voltammetry were used to investigate the cathodic reactions of copper complexes. To identify the nature and the rate-controlling steps of the reactions, rotating disk electrode (RDE) experiments were conducted. The chemical environment studied was similar to that of the Outokumpu HydroCopper TM process, which uses a cupric chloride solution to leach copper from the mineral chalcopyrite. The results suggest that the cathodic reactions are the reduction of [CuCl] + to the complex [CuCl 3 ] 2− , the reduction of [CuCl 3 ] 2− to solid copper and hydrogen evolution. The diffusion coefficient and the unit rate constants for the solution species were calculated. The exchange current density and rate constant for electron transfer were also estimated. A simulation was made of the cathodic polarization curve and it was in good agreement with the experimental data.

Most of the hydrometallurgical processes use sulphuric acid solutions. The main anodic reaction is oxygen evolution by decomposition of water. Traditional anode materials have been lead alloys that have high overpotential towards oxygen evolution. Oxide type anodes are more active but they are also more expensive. In this work, the activities of binary RuO2–TiO2 anodes were measured using different electrochemical techniques. The activity measurements were based on the measurement of the redox reaction between Ru(III) and Ru(IV) in cyclic voltammetry and on the oxygen evolution reaction in potentiostatic tests and galvanostatic electrochemical impedance spectroscopy. Factors related to intrinsic electrocatalytic properties and electrochemically active surface area could be separated. Above 30 mol% no significant increase in activity towards oxygen evolution is gained by increasing the concentration of active oxide. With low amount of active oxide most of the active sites are inside the pores and cracks. This will cause anode failure by bubble formation inside the anode.

The operation of ice-going vessels depends on the condition of the hull surface. Corrosion increases the roughness of ship hull, which increases drag and fuel consumption. The hull surface smoothness is maintained by using coatings and cathodic protection. The cold brackish water is different from ocean water as it has lower salt content, lower conductivity, and higher concentration of dissolved oxygen. These factors mean that the design of the cathodic protection system for ship hulls requires different design values, such as protection current density and protected length, than those given in cathodic protection standards. In this paper, we have estimated the protection current density with polarization curves and the protected length by using Wagner number and dimension and conductivity scaling. In brackish water the protection current density was two times that in ocean water. The protected length in brackish water varied between 10 and 15% of that in ocean water. In poorly conducting brackish water, the current capacity of a cathodic protection system is used mostly for overcoming the solution resistance, not for delivering protection current.

Polyaniline (PANI) has much been studied in the context of corrosion prevention, particularly on steel and aluminium. To prepare epoxy coatings consisting of PANI has turned to be nontrivial, due to its relatively rigid conformation and poor solubility. Therefore, as the aim has typically been first to dissolve PANI in the epoxy component before curing, auxiliary solvents have been required, and less attractive Lewis-type hardeners have been required if the conducting salt form has been used. In this work, we describe a particularly simple concept where emeraldine base (EB) form of PANI is first dissolved in specific aminic hardeners which are observed to be solvents for EB at low concentrations, and the mixtures are unconventionally cross-linked upon adding epoxy resin, diglycidyl ether of bisphenol-A (DGEBA). Suitable hardeners are N,N,N ′ ,N ′-tetrakis(3-aminopropyl)-1,4-butanediamine (DAB-AM-4) and trimethylhexanediamine (TMDA). Even if the subsequent cross-linking promotes phase separation, the forming cross-link sites may also control the phase separation. As a result, sufficiently homogeneous coatings are identified which contain only 1 wt% EB in the cured EB/DGEBA/TMDA composites where in aqueous 3.5% NaCl solution the corrosion front propagation is suppressed, and electrochemical impedance studies indicate the formation of a charged interface or reaction product layer between EB and steel. For reference, similar net EB/DGEBA/TMDA-compositions were prepared, where EB was first mixed in DGEBA without any solubility and which were cured by added TMDA, and they gave essentially no anticorrosion effect. We expect that the present concept opens new ways to prepare cured epoxy composites also with other conjugated or nonconjugated polymers for anticorrosion and other functional purposes.

Platinum, a DSA (dimensionally stable anode) mesh and gold electrodes were investigated for use as redox potential sensors for the Outokumpu HydroCopper™ process. The redox potential was measured in a standard HydroCopper™ solution with constant pH, temperature and sodium chloride concentration. The concentration of cupric ions was varied in the range 0–40 g/dm 3 . The redox potential was observed to increase logarithmically with increasing cupric ion concentration and to decrease linearly with time. Platinum and DSA-type electrodes were found to be electrochemically inert and allowed the measurement of the redox potential. With the gold the corrosion potential of the electrode was measured.

Outokumpu HydroCopper™ technology was developed by Outokumpu Research. It is a novel copper production method based on the efficient leaching properties of cupric chloride solutions. The leaching is operated at atmospheric pressure, near the boiling point of water in a stirred reactor and the pH is kept between 1.5 and 2.5. In the present work, an electrochemical study of the dissolution behaviour of chalcopyrite, the most common copper mineral, was made in a concentrated sodium chloride solution (250 g/L) with cupric ion concentrations varied in the range 0.09–26.6 g/L. The effects of pH (1–3) and temperature (70–90 °C) were also measured. The rotating disk electrode technique was used to determine the rate-controlling step in the leaching process. The increase in the dissolution rate was observed to be proportional to the increase in the temperature and to the cupric ion concentration with [Cu2+]>9 g/L. With [Cu2+]

A tightly adhering oxide scale is formed on stainless steels when they are annealed. The removal of the oxide scale and chromium-depleted subscale is one of the most important processes during the stainless steel production. Electrolytic pickling in neutral sodium sulphate is widely used for oxide scale removal. This study describes the different stages of the oxide scale removal on Polarit 725 (EN 1.4301) stainless steel in sodium sulphate solution. A mechanism of the scale dissolution is also proposed. The dissolution is proposed to proceed by the electrochemical reactions of the scale in three successive stages. At the beginning of the pickling process chromium and manganese of the outer oxide layer were preferentially dissolved. When the chromium content of the outer layer decreased, the scale was enriched of iron. The electrode potential was then increased and the scale thickness greatly reduced. Finally a steady state was obtained and a thin oxide layer, rich in iron and silicon, was left on the surface. Silicon could not be removed by the electrolytic pickling and post-treatment in nitric–hydrofluoric acid is required.

The corrosion behaviour of stainless steels in very oxidizing solution with redox-potential + 1200 mV vs. SCE was studied by corrosion potential and anodic polarization measurements. Some weight loss immersion tests were also carried out in order to verify the results of the electrochemical tests. Because the polarization curves and corrosion potentials for stainless steels give only a rough estimate of the corrosion behaviour, polarization curves and corrosion potentials were also measured for pure chromium, molybdenum, nickel and platinum as well as carbon steel in order to estimate the effect of alloying elements and the possibility of other chemical reactions in the transpassive region. It was found that this combination of measurements is a reliable method to evaluate the corrosion behaviour of stainless steels in dissolved ozone-containing solutions. .

We have characterized electrically conductive polymer, polypyrrole (Ppy), films on mild steel with atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). The Ppy films were polymerized electrochemically from sodium p-toluene sulphonate (ToS) water–ethanol solution. A very good corrosion protective effect of those films on mild steel has been observed previously. After drying in air, thin Ppy films (∽200 nm) were highly adhesive, whereas thicker films (∽7.5 μm) could easily be peeled off from the metal. All films had a nodular surface structure. Thin films were very smooth and their roughness increased with their thickness. The AFM study of the interface between the metal and the polymer showed areas of different morphology, which suggests that adhesive and cohesive failure of the polymer film occurs. A strong variation of the chemical composition at the interfacial layer was observed. A sulphur-rich layer was formed at the interface, indicating that the counter-anions (ToS) were accumulated on the surface of the metal. High-binding energy iron and imine-type nitrogen were detected in a thin Ppy film. Moreover, thin films were substantially overoxidized. The number of anions incorporated into the Ppy matrix varied as a function of film thickness: the ‘doping level’ was about 30% for thicker films and only 12% for thin ones. Nitrate counter-anion-containing Ppy films were also studied in some cases for comparison. © 1997 John Wiley & Sons, Ltd.

Many pyrometallurgical, hydrometallurgical and combined processes have been developed to allow better utilization of steelmaking dusts. The dusts contain metals and compounds that can harm the processes and one of these elements is zinc that is present in the flue dusts as zincite ZnO and franklinite ZnFe2O4. The effect of alkaline roasting on the dissolution of stainless steel flue dusts in acid and alkaline leaching was studied. The extraction of zinc from EAF dust was not significantly improved in alkaline leach (40 – 50 %) but there was indication of better extraction in acid leach (over 90 %). No improvement in extraction from AOD dust was seen either in alkaline (max. 58 %) or acid leach (max. 72 %). The acid leach of synthetic ferrite resulted in less than 32 % Zn recovery, and this must be studied further to find out the effect of franklinite in the dusts.

In this study Mode IV-corrosion fatigue (CF) characterized by additional superposition of pitting corrosion was investigated. Corrosion fatigue and polarization experiments were carried out on three austenitic (17Cr–13Ni–5Mo–0.15N, 25Ni–20Cr–5Mo–1.5Cu and 18Cr–10Ni–2Mo–0.5Ti) stainless steels in 0.05 M sulphuric acid to which 20000 ppm Cl− was added. The CF strength decreased drastically when Mode IV-conditions apply. The damaging effect of pitting corrosion in Mode IV was very pronounced. The relation between pitting, repassivation of the pits and Mode IV-CF was investigated and it was found that for rotaing beam CF the measured repassivation potential represents a conservative upper boundary value below which mode II-CF (i.e. CF under stable passivity) replaces Mode IV-CF, when operating below stress ranges of 75% of the fatigue strength measured in air. Bestimmung der oberen Grenze der Lochkorrosionswiderstandspotentiale fur austenitische nichtrostende Stahle unter Schwingungsriskorrosionsbedingungen In der vorliegenden Arbeit wurde die Schwingungsriskorrosion (Modus IV) untersucht, die durch uberlagerung von Lochkorrosion gekennzeichnet ist. Die SwRK- und Polarisationsversuche wurden mit drei austenitischen nichtrostenden Stahlen (17Cr–13Ni–5Mo–0,15N, 25Ni–20Cr–5Mo–1,5Cu und 18Cr–10Ni–2Mo–0,5Ti) in 0,05 M Schwefelsaure (mit 20000 ppm Cl−) durchgefuhrt. Die SwRK-Festigkeit nimmt unter den Modus-IV-Bedingungen drastisch ab, wobei die schadigende Wirkung der Lochkorrosion sehr ausgepragt ist. Die Beziehung zwischen Lochkorrosion, Repassivierung der Korrosionslocher und der Schwingungsriskorrosion nach Modus IV wurde untersucht. Es wurde dabei festgestellt, das im Falle der SwRK mit rotierender Probe das gemessene Repassivierungspotential einem konservativen oberen Grenzwert entspricht, unterhalb dessen die SwRK nach Modus IV durch SwRK nach Modus II (d.h. unter stabiler Passivitat) ersetzt wird, wenn die Belastungen unter 75% der an Luft gemessenen Dauerfestigkeit liegen.

Extraction of Cu, Ni, As and Te from copper electrorefining anode slimes was studied. Such parameters as sulfuric acid concentration, temperature and oxygen partial pressure had a positive effect on the oxidative pressurized acid leaching in the decreasing order in contrast to the solids concentration. For nickel extraction, temperature, sulfuric acid concentration, combined effect of temperature and sulfuric acid concentration as well as solids concentration and sulfuric acid concentration had a positive effect, in a decreasing order. In the case of arsenic extraction, combined effect of temperature and sulfuric acid concentration, temperature as well as sulfuric acid concentration had positive in the decreasing order. During tellurium extraction, none of the parameters investigated gave the statistically valid response. Basing on the regression analysis, appropriate models for the dissolution of copper and arsenic could be build.

The high temperature corrosion behaviour of some nickel aluminides alloyed with zirconium or hafnium is presented. The corrosion tests were carried out in the temperature range 920 to 1010°C, both in air and in atmospheres containing sulphur dioxide, using a thermobalance. The results obtained in air show that all the nickel aluminides display sufficient corrosion resistance up to 920°C. Nickel aluminide alloyed with hafnium is more resistant than the aluminide alloyed with zirconium. The oxide layer on the specimens tested in air is always very thin, exhibits low porosity and consists mainly of Al2O3. Without controlled preoxidation these materials are rather susceptible to corrosion in atmospheres containing sulphur dioxide. The preoxidation in gas mixture containing water vapor and hydrogen markedly improves the corrosion resistance of these alloys. The corrosion implies the selective oxidation of nickel aluminides. The protective layer consists mainly of aluminium oxide and protects the base material also in atmospheres containing sulphur dioxide. Korrosionsverhalten von Ni3Al-Legierungen in Schwefeldioxid enthaltenden Verbrennungsgasen Das Verhalten von einigen mit Zirkonium oder Hafnium legierten Nickelaluminiden unter den Bedingungen der Hochtemperaturkorrosion wird anhand der Ergebnisse behandelt, die bei Temperaturen zwischen 920 und 1010°C in Luft und in Schwefeldioxide enthaltenden Atmospharen mit Hilfe einer Thermowaage erhalten wurden. Die in Luft erhaltenen Ergebnisse zeigen, das alle Nickelaluminide bis 920°C gut korrosionsbestandig sind. Dabei ist mit Hafnium legiertes Nickelaluminid bestandiger als das mit Zirkonium legierte. Die in Luft entstandene Oxidschicht ist immer sehr dunn und sehr wenig poros und besteht vorwiegend aus Aluminiumoxid. In Schwefeldioxid enthaltenden Atmospharen werden diese Legierungen, wenn sie nicht voroxidiert wurden, stark angegriffen. Die Voroxidation in Wasserdampf und Wasserstoff enthaltenden Gasgemischen verbessert die Korrosionsbestandigkeit der Legierungen betrachtlich. Dabei wird das Nickelaluminid selektiv oxidiert, und es entsteht eine hauptsachlich aus Aluminiumoxid bestehende schutzende Schicht, welche den Grundwerkstoff auch in Schwefeldioxid enthaltenden Atmospharen schutzt.

A novel setup for the investigation of ion moving processes occurring in polymer films is proposed. The special crystal holder capsule was created to include EQCM (Electrochemical Quartz Crystal Microbalance) into CER (Contact Electric Resistance) equipment and provide its reliable operation. The dependence of the resistance and the mass change of the polypyrrole films on the polarisation potential in potassium iodide aqueous solutions were investigated combining the EQCM and CER techniques. The CER method reinforced with the EQCM technique gives us a helpful tool for the better understanding of the polymeric films preparation processes with well-defined physical and chemical properties.