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Surface deposit effects in the kinetics of copper cementation by iron
Abstract
The nature of the cement copper deposit was shown to control the kinetic response of the cementation reaction under certain
circumstances. In essence, the nature of the surface deposit determines the effective cathodic area and is controlled by a
number of variables. What appeared to be a temperature region (0 to 35°C) where a surface reaction mechanism was rate controlling,
ΔE
a
≊10 kcal per mole, was, in fact, a consequence of the variation of the area of the surface deposit with temperature. Further
evidence of this phenomenon was demonstrated by the results of cementation experiments in an ultrasonic field, and by the
results obtained from initial “strike” experiments. Also considered in this study was the effect of the initial cupric ion
concentration and the back reaction kinetics. The basic conclusion reached from this investigation was that the cementation
reaction rate is controlled by boundary layer diffusion processes at all temperatures and concentrations with an activation
energy of approximately 5 kcal per mole. When surface deposit effects are neglected, interpretation of cementation rate data,
as well as rate data of any heterogeneous reaction involving a solid phase, can often be misleading.
... The Cu cementation mechanism can be described using the first-order reaction kinetic as follows [23,24]: ...
... It indicates that the reaction of Cu cementation by Fe is mainly controlled by the boundary layer diffusion. Therefore, the high temperature is favoured for the Cu cementation; hence, 60°C is efficient among the four tested temperatures and avoids too much dissolution of Fe [24,25]. ...
In this paper, an efficient and product-oriented hydrometallurgical recycling process including pre-treatment is developed to handle the spent automotive Li–ion batteries. The possibility to recover the high-grade graphite, cathode metal salts and lithium carbonate is investigated. In the designed process, leaching, solution refining, cathode metals precipitation and lithium carbonate crystallisation are implemented. The leaching efficiencies of valuable metals (Co, Ni, Cu and Li) are in the range of 98.6–99.9 % under the optimum conditions: 80 °C, 50 g/L of hydrogen peroxide, 2 mol/L of sulphuric acid or 4 mol/L of hydrochloric acid in 2 h. Meanwhile, the filtered graphite with purity of 99.8 % is obtained. In the following Cu cementation, an optimum temperature of 60 °C is found and the calculated activation energy of the cementation reaction is 12.9 kJ/mol. In the hydroxide precipitation, pH 3.5–4 is suggested for Al and Fe removal and pH 10 is high enough for cathode metal (Co, Ni and Mn) salts precipitation. The carbonate and sulphide precipitation methods are also demonstrated to be successful. In all, several marketable products are obtained, such as graphite, Cu powder, cathode metal salts and lithium carbonate.
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... where [Ag z ] is silver concentrations in solution at t; [Ag z ] 0 is initial silver concentration; t is time (s); A is initial exposed magnesium disc area (cm 2 ) and V is solution volume (cm 3 ). Such dependence of k 0 on the initial concentration of [Ag(SCN) 3 ] 22 ions is caused by the structure of reduced silver deposit. In the absence of the induction period the silver deposit covers the magnesium surface very quickly (Fig. 5). ...
... The formation of only dispersed porous deposits takes place in the process of the cementation. The increase of the initial concentration of [Ag(SCN) 3 ] 22 leads to increase of specific rate of silver reduction reaction: k 0 is equal to 0?029, 0?041 and 6 Images (SEM) of cemented silver precipitates, obtained by cementation on magnesium disc from solutions nM 22 . It is caused by the formation of dendritic deposits of reduced metal with larger pore sizes. ...
The cementation of silver on rotating magnesium disc from 0·005–0·02M thiocyanate solution was studied. It was established that the process proceeded with a high rate in the absence of the induction period. Metal recovery was >99%. The formation of dispersed porous deposits and the dependence of their structures on the initial concentration of silver ions were shown using SEM. The cementation product is silver powders with purity ≥99·9 mass-%. Consumption of magnesium is 0·15–0·2 g magnesium in account of 1 g of obtained silver. On a étudié la cémentation de l’argent sur disque rotatif en magnésium à partir d’une solution de thiocyanate de 0·005–0·02M. On a établi que le procédé se produisait à grande vitesse sans période d’induction. La récupération du métal était >99%. On a démontré la formation de dépôts poreux dispersés et la dépendance de leurs structures sur la concentration initiale d’ions d’argent en utilisant le SEM. Les produits de cémentation sont des poudres d’argent ayant une pureté de ≥99·9% (en masse). La consommation de magnésium était de 0·15 à 0·2 g par g d’argent obtenu.
... The morphology of Cu deposits on iron or other sacricial metals has been reported to be related to reaction kinetics. [27][28][29] Fast kinetics cause numerous crystalline Cu nuclei to precipitate on the surface at the onset of the reaction. Since copper is a more efficient cathode surface than iron, these nuclei accelerate the reaction and promote the formation of ne, loose dendrites. ...
... Thus, the ne-textured copper deposits observed in this work show a rapid reaction between nZVI and Cu(II). 28,29 XRD analysis of nZVI. To determine the composition of the reaction products, XRD analyses were performed with fresh nZVI and reacted nZVI from both the batch and pilot reactors. ...
A field demonstration was conducted to assess the feasibility of nanoscale zero-valent iron (nZVI) for the treatment of wastewater containing high levels of Cu(ii). Pilot tests were performed at a printed-circuit-board manufacturing plant, treating 250 000 L of wastewater containing 70 mg L(-1) Cu(ii) with a total of 55 kg of nZVI. A completely mixed reactor of 1,600 L was operated continuously with flow rates ranging from 1000 to 2500 L h(-1). The average Cu(ii) removal efficiency was greater than 96% with 0.20 g L(-1) nZVI and a hydraulic retention time of 100 min. The nZVI reactor achieved a remarkably high volumetric loading rate of 1876 g Cu per m(3) per day for Cu(ii) removal, surpassing the loading rates of conventional technologies by more than one order of magnitude. The average removal capacity of nZVI for Cu(ii) was 0.343 g Cu per gram of Fe. The Cu(ii) removal efficiency can be reliably regulated by the solution Eh, which in turn is a function of nZVI input and hydraulic retention time. The ease of separation and recycling of nZVI contribute to process up-scalability and cost effectiveness. Cu(ii) was reduced to metallic copper and cuprite (Cu2O). The end product is a valuable composite of iron and copper (∼20-25%), which can partially offset the treatment costs.
... The additional mass loss is defined by the term of a synergistic effect, which has a substantial contribution to the total metal loss of the components suffering The precipitation reaction of a noble metal from its salt solution by a less noble metal is called cementation in hydrometallurgy, and is widely used in industry for the recovery of metals and purification of electrolyte solutions. For example, recovery of dissolved copper with iron as the precipitant metal from leach solutions by the cementation process has been successfully used for several centuries [41,42]. Due to different standard reduction potentials (Cu II /Cu 0 : +0.34 V; Fe II /Fe 0 : -0.44 V), Cu 2+ ion becomes readily reduced on Fe 0 surface, while the corresponding amount of iron is dissolved (Eq. ...
... When surface deposit effects are neglected, interpretation of cementation rate data, as well as rate data of any heterogeneous reaction involving a solid phase, can often be misleading [41]. ...
A review of the approach used by environmental remediation researchers to evaluate the reactivity of Fe0-based alloys reveals the lack of consideration of the results available from other branches of science. This paper discusses the limitations of the current approach. The discussion provided here suggests that the current assumption that redox-sensitive species serve as corrosive agents for Fe0 maybe incorrect because water as the solvent is also corrosive. A new approach is proposed in which water is considered as the primary Fe0 oxidizing agent and the impact of individual relevant solutes (including contaminants) should be assessed in long-term laboratory experiments. It is expected that the application of the proposed approach will help to reliably characterize the reactivity of Fe0 materials within a few years.
... The precipitation reaction of a noble metal from its salt solution by a less noble metal is called cementation in hydrometallurgy, and is widely used in industry for the recovery of metals and purification of electrolyte solutions. For example, recovery of dissolved copper with iron as the precipitant metal from leach solutions by the cementation process has been successfully used for several centuries [41,42]. Due to different standard reduction potentials (Cu II /Cu 0 : +0.34 V; Fe II /Fe 0 : −0.44 V), Cu 2+ ion becomes readily reduced on Fe 0 surface, while the corresponding amount of iron is dissolved (Eq. ...
... Another important result from hydrometallurgy that has not been properly considered is the importance of surface deposits. When surface deposit effects are neglected, interpretation of cementation rate data, as well as rate data of any heterogeneous reaction involving a solid phase, can often be misleading [41]. Accordingly, the significant of oxide film on Fe 0 surface should have been closer investigated. ...
A review of the approach used by environmental remediation researchers to evaluate the reactivity of Fe0-based alloys reveals the lack of consideration of the results available from other branches of science. This paper discusses the limitations of the current approach. The discussion provided here suggests that the current assumption that redox-sensitive species serve as corrosive agents for Fe0 maybe incorrect because water as the solvent is also corrosive. A new approach is proposed in which water is considered as the primary Fe0 oxidizing agent and the impact of individual relevant solutes (including contaminants) should be assessed in long-term laboratory experiments. It is expected that the application of the proposed approach will help to reliably characterize the reactivity of Fe0 materials within a few years.
... The evolution of hydrogen gas causes increasing in pH of the solution and due to that, activation energy also gets increased (Krause, 2014). The formation of cement sludge due to the complex morphology also affects the rise in activation energy (Miller and Beckstead, 1973). ...
Cementation is a prominent purification technique used for removal of copper, cadmium, cobalt, and nickel from impure zinc sulphate solution obtained after leaching of zinc ore. Zinc dust is primarily used for this purpose still the extent of purification is limited. The present study represents the encouraging result in context to utilization of zinc dust for better purification by altering its dosage, size and morphology. The investigations showed that 300% excess zinc dust dosage than stoichiometric results in enhanced cement formation. The study also revealed that fine size and ball milling of zinc dust favors cementation. Zinc dust of −300 mesh (BSS) after 2 h ball milling highly purifies the impure solution within 2 h contact time. The yield of the impurities removal after the optimized cementation is 100, 99.99, 100 and 15% for Cu, Cd, Ni and Co respectively. The kinetics of cementation has been also studied and revealed that the reaction is in mixed controlled mechanism for copper and cadmium cementation. At the same time, for nickel, it is considered to be chemically controlled. The activation energy for the cementation of copper, cadmium and nickel were 38.19, 30.87 and 68.15 kJ /mol, respectively. The estimated activation energies were found within the range which corroborates with the mixed and reaction model and ensures industrial feasibility of the proposed process.
... The increase in structure size, mainly in the case of porous deposits results in improving the effective cathodic area which is indirectly responsible for providing mass transfer. Therefore, higher cementation rates obtained by increasing temperature was the consequence of higher mass transfer due either to shorter diffusion paths or increased ionic diffusivities (Annamalai and Murr, 1979;Miller et al., 1973). ...
A green approach was introduced to regenerate Sn-Pb solder from waste printed circuit boards (PCBs). For this purpose, waste Al-based heat sinks were used as cementing agent to precipitate Sn and Pb from pregnant leach solution (PLS) obtained from the dissolution of waste PCBs in HCl. 97% and 94.9% of Sn and Pb were recovered, respectively, under optimum conditions at Al powder size of 300 μm, Al dosage of 1.516 g/L and reaction time of 15.41 min. Thermodynamic analysis was performed to predict the effect of temperature on the main reactions relevant to the cementation process. The structure of the Sn-Pb cement changed as function of temperature, leading to enhancement of the cementation rate via improving cathodic area. Kinetic modeling indicates that product layer diffusion is the rate limiting step for Sn and Pb cementation. However, the reaction mechanism shifted to chemical reaction control at high temperatures. The results of solder characterization indicated that the melting point of solder was 184.76 °C. The electrical resistivity and conductivity of the recovered pure alloy were measured to be 34.73 μΩ-cm and 2.88×106 Sm-1, respectively. The characterization revealed that the regenerated product is adequate as an alternative solder alloy.
Keywords: Regeneration, Sn-Pb solder, Waste PCBs, Recycling, Cementation
... Lopez et al. (5) studied the removal of copper ions from aqueous solutions in rolling mill scale and found that the removal capacity of up to 40 mg Cu(II) per gram of mill scale was possible at a temperature above 60 • C. Ku and Chen (6) had found first-order kinetics with respect to both copper concentration and surface area of iron powder and it was shown that the cementation reaction was best operated at pH 4-5. Miller and Beckstead (7) reported that the reaction rate was controlled by boundary layer diffusion at all temperatures (0-35 • C) with activation energy of approximately 5 kcal per mol (20 kJ per mol). ...
The cementation of copper ions from copper sulfate solution was studied using iron wire and iron powder. The influence of initial copper concentration has considerable effect on cumulative copper deposition. The copper deposition rate data could be interpreted by using shrinking core model. The effects of temperature and pH were substantial and have been studied and interpreted. The activation energy of the system within the temperature range of 23-54 degrees C was found to be 14.23 (iron wire) and 30.20 kJ per mol (iron powder), respectively. The morphology of copper deposits studied showed that the reactions have the potential to produce particle sizes within nano range.
The term chemical deposition of metals and/or alloys from aqueous solutions is usually used to refer to the production of metallic coatings or powders of various surface morphology and properties without an application of the external current source. As explained in previous chapters in the electrochemical deposition, electrons used for the reduction of metal ions are provided by an external current source. For the chemical deposition, electrons used for the reduction of metal ions are released under specific conditions from an appropriate reducing agent. These appropriate reducing agent may include compounds such as hypophosphite (NaH2PO2), borohydride (NaBH4), formaldehyde (HCOH), ascorbic acid (C6H8O6), etc., or metals which are less noble than the metal aimed to be deposited. These concepts of chemical deposition will be examined in details in the following text.
This work investigates the effect of operating conditions on the rate of Cu2+ removal from synthetic waste of copper sulphate solution by cementation on a fixed bed of zinc cylinders under different conditions of solution flow rate, initial copper sulphate concentration, bed height, cylinder diameter and solution temperature. The values of the mass transfer coefficient was found to increase with increasing solution flow rate and temperature, while it decreased with increasing bed height, cylinders diameter and initial copper sulphate concentration. The value of the activation energy of the reaction ranged from 2.5 to 4.60 kCal/mol with lower and higher solution flow rates, respectively, which show that the reaction is diffusion controlled. The mass transfer correlation was deduced by dimensional analysis and was found to be in the form that: Sh = 2.1 Re0.867 Sc0.33 (d/h)−1.02. In addition, another correlation was deduced for the effect of entrance region by removing the calming section which was found to be in the form that: Sh = 2.30 Re0.870 Sc0.33 (d/h)−0.96. The obtained results can help in the design of a continuous flow reactor that may be used for the removal of heavy metals from wastewater.
A large demand of electric vehicle (EV) Li-ion batteries is seen in the near future. The reutilization and recycling of EV Li-ion batteries are decisive for their widely applications in the automobile industry. This paper presents and compares three recycling concepts for EV Li-ion bat-tery recycling: "IME-Accurec H&P", "Gas Control" and "Direct". They vary in the application of pre-treatment (including pyrolysis and mechanical treatment) as well as hydrometallurgical and pyrometallurgical modules. Validation experiments in lab-scale have been conducted and the industrial approval is foreseeable. This paper has focused on the hydrometallurgical route which is combined in the above mentioned recycling concepts. The metal values from the batteries are leached, purified and recovered. The whole process is composed of leaching, Cu cementation, Fe and Al precipitation, Mn oxidation, Co (and Ni) precipitation and lithium carbonate crystallization. The reusing of recycled products has been evaluated. The influences of operating parameters have been investigated to obtain the optimum working conditions.
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A novel technique was developed where vapor-deposited thin films of aluminum and iron approximately 0.2 /jm thick were utilized as substrates in the Cu/AI and Cu/Fe cementation systems. The nucleation of the incipient copper deposit upon the film surfaces was examined by transmission and scanning electron microscopy. Cement copper nuclei were observed to be crystal polyhedra which enlarged and coalesced in the Cu/Fe system to form a continuous, botryoidal deposit while in the Cu/AI system isolated nuclei and clusters developed dendritic structures which grew to massive form with extended solution contact times. There was more apparent initial replacement of individual iron grains with copper in the Cu/Fe system than aluminum replacement in the Cu/AI system but the overall cementation mechanism, while exhibiting differences on comparing these systems, was fundamentally consistent with earlier concepts involving galvanic corrosion.
The kinetics of cementation of copper from copper sulphate solutions in a stirred tank reactor fitted with a rotating perforated basket of novel geometry packed with zinc Raschig rings were studied. The effect of different parameters such as initial copper sulphate concentration, basket rotational speed, temperature and the effect of presence of some alcohols, such as methanol, ethanol and butanol were studied. The rate of cementation was found to increase with increasing initial copper sulphate concentration, basket rotational speed, and temperature, while a decrease in the rate of copper cementation was observed in the presence of alcohols according to the following order: butanol > ethanol > methanol. The thermodynamic activation parameters ∆H≠, ∆G≠ and ∆S≠ were calculated within the range of temperature studied. The activation energy was found to be 6 J/mol K which confirms the diffusion controlled nature of the reaction. Mass transfer study of the process has revealed that the present data can be correlated by the equation:Sh=0.0013Sc0.33Re0.943for the conditions: 2056 < Sc < 2202 and 6700 < Re < 28,300. A comparison between the present modified stirred tank reactor with the rotating cylinder reactor and the rotating disc reactor has shown that a higher rate of cementation was obtained in the present reactor.
The kinetics of the cementation of copper ions from copper sulfate solution onto a horizontal single screen and an array of closely packed iron screens were investigated in a bubble column. Variables studied were physical properties of the solution, superficial gas velocity and number of screens per array. The rate of cementation was found to increase with increasing superficial gas velocity to a certain limit and then remains constant and increases with increasing the number of screens per array. The rate of cementation was expressed in terms of the liquid–solid mass transfer coefficient (k). The data were correlated by the equation:j=3.99Re.Fr−0.078.The high rates of mass transfer obtained in this work and the high area per unit volume of gas sparged fixed bed of horizontal screens to qualify them for building high space time reactors suitable for purification of hydrometallurgical leach liquors and removal of heavy metal from waste water by cementation.
Reaction rates have been found experimentally to increase, without any change in the mechanism of the rate-determining step, during kinetic studies of cementation in the CuFe system and in batch-type electrolytic reduction of U(VI). Generally, the cementation reaction of Cu2+ by Fe consists of two distinct steps, both of which appear to be first order with respect to the concentration of cupric ions. In the initial step, the rate constant for cementation was found to be independent of the concentration of cupric ions, while, surprisingly, a concentration dependency of the rate constant was detected in the final step. The calculated flux of cupric ion toward the iron surface increases following the initial step of cementation, passes through a maximum, and then decreases in the final step. It was observed that the cemented copper began to peel off from the iron surface at the maximum flux of cupric ion. The thickness of the concentration boundary layer at the iron surface is decreased dramatically to a thickness less than that observed under vigorous agitation. A similar phenomenon has been observed in batch-type electrolytic reduction of U(VI) in acidic solutions. Although evolution of hydrogen gas occurring in the final stage of batch-type electrolysis, causes a decrease in current efficiency, the reduction of U(VI) proceeds considerably faster than that expected theoretically. Experimentation has shown that this phenomenon is a result of thinning of the concentration boundary layer by the liberation of hydrogen gas from the cathode surface.
Electrolytic removal of Se (VI) in waste water (15 ppm) is studied at pH 1 and 3 and at room temperature. Prior to electrolysis, there was a drop in concentration due to adsorption of Se onto activated carbon. In the initial half of electrolysis, the decrease in residual concentration followed the nucleation growth reaction without an increase in Se (IV). In the later half, plots were scattered, due to desorption of Se. The reaction has a maximum of removal rate; this was in accordance with those of data. Current efficiency was about 3 % at the maximum, owing to generation of hydrogen. The current density for particles suspended is compared with those for suspension electrolyses of the S-Cu system.
The effect of nonylphenylpolyethylene glycol (D1) and cementing agents zinc, iron, copper and aluminum on silver cementation kinetics and deposit morphology was investigated. It was found that D1 inhibits both silver cementation and cementing agent dissolution with greater effect on cementing agent dissolution. The silver deposition rate and metal consumption per mole silver decreased in the order Zn, Fe, Cu, Al. The addition of D1 resulted in the rate of cementation decreasing to 77–90% of that when D1 was absent. The slower deposition resulted in more efficient consumption of cementing agent with 15–34% less dissolved when D1 was present. The deposit morphology strongly depends on the cementing agent: a coarse layer with high porosity was obtained on zinc, a fish-gill deposit morphology on iron, a compact fine deposit on copper and a patchy dendritic deposit on aluminum. D1 strikingly decreased the porosity of the deposits on zinc and iron.
Copper recovery by cementation using iron nails surrounded by a fluidized bed of spherical copper particles was studied in a laboratory scale drum reactor. The rate of cementation was found to be directly proportional to cupric ion concentration and the surface areas of the nails and fluidized copper particles. The fluidized copper particles served as a cathode for copper cementation and enhanced the cementation rate. The activation energy for the process was found to be 22.0 kJ/mol. The rate controlling process is thought to be diffusion of cupric ion through a solution boundary layer surrounding the copper particles. Granular activated carbon was shown to be effective as a fluidized cathode material, but did not enhance the cementation rate.
An analysis of the physics of cementation processes (metal displacement) is presented. Hydrogen, H+, and hydride, H-, ions are shown to be the key intermediate species in cementation processes. The possibility of either diffusional transport of noble species or migrational transport of hydrogen species is suggested, and a kinetic model of the cementation migration regime is developed and partially verified by experimental data.
The effects of various chelating agents and deposit morphology on the rates of copper cementation on pure aluminum disks have been studied. The change in the structure and morphology of the resultant copper deposits agrees with the change in the kinetic results calculated from the rate data. The decrease in pH would have accelerated the rate of deposition, by increasing the rate of nucleation and further growth of the deposit into fine dendrites. The copper dendrites protrude into the diffusion boundary layer and increase the mass transfer rates. Experimental data suggest that at fixed pH the specific rate constants increase with the order of EDTA, NTA, no chelating agent, and citrate. The bulbous deposit corresponds to lower rate, the crude dendrites correspond to moderate rate, the dendrites with coarse-textured secondary arms correspond to higher rate, and the featherlike dendrites correspond to the highest rate. No correlation could be drawn between the specific rate constant and deposit grain size. The deposit morphology and the reduction of the diffusivity due to chelating agents should have equal influence on the cementation rate for Cu-EDTA and Cu-NTA systems. In the Cu-citrate system, the deposit morphology should be the dominant factor for cementation.
By introducing the concept of ''surface activation'', the kinetic model of cementation on the metallic rotating disk limited by either mass transfer or surface reaction was formulated. This work is an extension of the two-step model and detailed discussion is presented. Furthermore the model was verified with the experimental data of the cementation of copper ions on aluminum disks made from pure aluminum foils. Before and after cementations, aluminum disks were also characterized thoroughly by SEM and X-ray diffraction. The results show that high-purity copper is extracted from the solution. The change in the morphology of the resultant copper deposits agrees with the change in the kinetic results. The copper dendrites protrude into the diffusion boundary layer and increase the mass transfer rates. The finer dendrites may have a better agitating effect which increases the rate of mass transfer. Since the induction time decreases with the increase of the specific rate constant, the induction time is dominated by the time needed for the ''critical deposit mass'' to be completely grown.
The effect of Polyox WSR-301 drag-reducing polymer on the rate of cementation of copper from copper sulfate solution over packed beds of zinc pellets was investigated. The mass transfer coefficient was found to increase with increasing superficial liquid velocity for solution free of polymer. The mass transfer data were correlated in the absence of drag-reducing polymer, using the following equation Jd = 12.55 Re–0.5 for the conditions 10 < Re < 1970 and 1265 < Sc < 1393. In the presence of polymer, starting from a Reynolds number (Re) 550, the rate of mass transfer was found to decrease by an amount ranging from 7.5 to 51 % depending on Re and polymer concentrations. The percentage decrease in the rate of mass transfer increased with increasing Re, passed through a maximum at Re = 1400 and then decreased rapidly with further increase in Re.
The kinetics of copper cementation on pure iron substrates were studied using a rotating disc geometry. The effect of rotational speed of the iron disc, copper ion concentration, hydrogen ion concentration, and temperature on the kinetic response was investigated. The range of each parameter studied was selected with some consideration for commercial operations for copper recovery using iron as the precipitant metal. The optimum values of each parameter for maximum cementation rate were determined. At low temperatures (10–30°C), an experimental activation energy of 22.89 kcal mol−1 was calculated indicating that the system is strongly controlled by a surface reaction mechanism or pore diffusion process. At high temperatures (30–60°C), an experimental activation energy of 7.94 kcal mol−1 was obtained which shows that the system may be controlled by both diffusion and surface reaction mechanisms. The deposits obtained were pure copper and not a copper-iron alloy. The total iron consumption, presented as can factor, was around 1.0.The structural characteristics of the resultant deposits were studied with the help of a scanning electron microscope. The structure and morphology of the deposits were analyzed in conjunction with their respective specific rate constants. A change in the surface roughness of the rotating disc and hence in the effective deposition surface area as a result of modification to the deposit morphology obtained for different experimental conditions was found to be the major reason for variations in the reaction rate. For the experimental conditions employed in this study, most of the deposits seen were bulbous or botryoidal crystal masses of different degrees of texture and size.
The present study is concerned with the removal of Cd (II) ions from wastewater by cementation on zinc Raschig rings placed in a rotating basket reactor. The influence of several parameters on the rate of cementation such as initial concentration of cadmium ions, temperature, basket rotation speeds and diameter of zinc rashing rings have been investigated. The rate of cementation was found to increase with increasing bed rotational speed and temperature. On the other hand the rate decreases with increasing the initial cadmium ions concentration in solution and the diameter of zinc Raschig rings. The activation energy was found to be 3.99 kCal/mol. The present reactor proved to be an efficient reactor for cementation reactions in view of its high area per unit volume and its high rate of mass transfer. Rates of cementation which can be expressed in terms of the rate mass transfer were correlated to the controlling parameters by the dimensionless equationSh=0.046Re0.45Sc0.33The present mass transfer data was found to agree with the surface renewal theory.
Cementation and corrosion were investigated in a batch cell to highlight the improvement of the kinetics observed after a certain lapse of time. Experiments on cementation with the Cd(II)/Zn and Ag(I)/Cu systems, and on corrosion with the Ce(IV)/Zn and Cr(VI)/Zn couples, were carried out on a rotating disc electrode immersed in relatively concentrated solutions. Time variations of the concentration of the reacting species and SEM observations showed that the change in reaction kinetics was due to the roughness of the changing surface of the electrode, depending on the chemical system considered. For corrosion, the average roughness was shown to exceed the thickness of the Nernst diffusion layer, and the rougher surface created allows local flow disruption and mass transfer enhancement. Besides, corrosion by Cr(VI) species results in greater roughness of the metal surface with more significant flow disruption than with Ce(IV) at the same concentration.
Conducting polypyrrole electrodes obtained under galvanostatic electropolymerization on iron from aqueous solutions of pyrrole and oxalic acid were modified with copper particles using the electrochemical cementation process. The electrochemical response of these modified electrodes was compared to that of the unmodified polymer electrode and also to that of bare metallic copper. The modified polypyrrole electrode showed noticeable enhancement for the rate of proton reduction.
This paper describes the impact of low frequency (20kHz) ultrasound (US) on Cd(II)/Zn cementation implemented on a RDE geometry. With and without US the reaction is mass-transfer controlled with two-step first-order kinetics mainly connected to deposit evolution. US improves the kinetics but to a lower extent than expected from electrochemical Cd(II) reduction. The favourable turbulence enhancement due to the deposit without US is not present when applying US because the deposit is continually removed from the surface. The influence of parameters such as temperature, initial concentration of reactants and US power is also analysed.
The nature of the reaction between Ag+ and pyrite in 0.25 M H2SO4 solutions has been investigated in order to determine whether Ag+ can enhance the ferric sulfate leaching of this mineral. Analysis of reacted pyrite particles using scanning electron microscopy,
X-ray photoelectron spectroscopy (XPS), and low-angle X-ray diffraction (XRD) indicates that elemental silver and elemental
sulfur are the primary surface species formed by this interaction. Rest potential measurements of a pyrite electrode immersed
in a solution containing 10−2 M Ag+ are also consistent with what is expected for the deposition of metallic silver. Furthermore, the XRD data reveal that, at
the most, only minor amounts of Ag2S are being produced. The presence of Ag2O has also been detected, but this is due to oxidation of silver after the experiment is complete and while the particles
are being transferred for surface analysis. When 1 M ferric sulfate is contacted with pyrite which has been pretreated in
a AgNO3 solution, most of the silver immediately redissolves and does not redeposit while ferric ions are present. This indicates
that the kinetics of the transfer reaction between Ag+ and pyrite is slower than the reaction between Fe3+ and pyrite and suggests that Ag+ does not likely enhance the ferric sulfate leaching.
Zerovalent iron (nZVI) nanoparticles have long been used in the electronic and chemical industries due to their magnetic and catalytic properties. Increasingly, applications of nZVI have also been reported in environmental engineering because of their ability to degrade a wide variety of toxic pollutants in soil and water. It is generally assumed that nZVI has a core-shell morphology with zerovalent iron as the core and iron oxide/hydroxide in the shell. This study presents a detailed characterization of the nZVI shell thickness using three independent methods. High-resolution transmission electron microscopy analysis provides direct evidence of the core-shell structure and indicates that the shell thickness of fresh nZVI was predominantly in the range of 2-4 nm. The shell thickness was also determined from high-resolution X-ray photoelectron spectroscopy (HR-XPS) analysis through comparison of the relative integrated intensities of metallic and oxidized iron with a geometric correction applied to account for the curved overlayer. The XPS analysis yielded an average shell thickness in the range of 2.3-2.8 nm. Finally, complete oxidation reaction of the nZVI particles by Cu(II) was used as an indication of the zerovalent iron content of the particles, and these observations further correlate the chemical reactivity of the particles and their shell thicknesses. The three methods yielded remarkably similar results, providing a reliable determination of the shell thickness, which fills an essential gap in our knowledge about the nZVI structure. The methods presented in this work can also be applied to the study of the aging process of nZVI and may also prove useful for the measurement and characterization of other metallic nanoparticles.
The cementation of copper on various types of nickel discs has been studied in dilute cupric sulphate solutions. Activation of the cathode nickel discs with Te+4 was necessary to achieve reproducible rates, whereas satisfactory results were obtained with mint nickel discs using only a chemical polishing treatmen t Attempts to cement copper on discs of nickel-copper alloys were unsuccessful. The cementation process on pure nickel takes place by two different rate-controlling mechanisms. At low temperatures the process is probably controlled by a surface reaction, whereas at higher temperatures the process is probably controlled by diffusion through surface layers. When the acidify of the solution is increased, the cementation rate increases. The rate decreases with increasing thickness of the cemented deposit.
The work described here was undertaken to study, under conditions of high fluid velocity, the effect of temperature on the specific rate up to 200 degree C and, subsequently, at temperatures of 100 and 150 degree C the effect of solution concentration, stirring speed, pH and atmosphere on the specific rate. These batch tests were undertaken with a view to the development of an efficient commercial copper recovery process at a later stage. Tests were carried out a 1-l stainless-steel autoclave fitted with a magnedrive impeller. Results obtained show that the cementation rate increases up to about 100 degree C at high solution flow rate, ant that above this temperature the increase is only marginal - indicating a predominant diffusion control. The copper powder formed acquires reducing properties which are not present at ambient temperatures. This reducing characteristic was indicated by an iron consumption less than the theoretical value for the cenemtation reaction, and further investigation showed that at high temperatures it is possible for copper powder to react with cupric sulphate to form cuprous oxide.
An examination of the rate data from many cementation reactions reveals some characteristic kinetic results that appear to deviate from the widely accepted model that cementation is a diffusion-controlled, first-order rate process. One particularly striking example is that the rate constant depends on the initial concentration of the noble metal ion. Another example, in some systems, is that as the temperature is lowered, the reaction mechanism appears to change from boundary-layer diffusion-control to surface-reaction control. Recent work has shown that these reactions may be diffusion controlled even at low temperatures where the apparent activation energies, which vary from 10 to 45 kcal/mol, seem to be a consequence of the nature of the surface deposit. Generally speaking, however, the behavior of most systems follows predictable trends and in most cases a diffusion-controlled, first-order rate law can be reconciled by considering the nature of the surface deposit and the concentration dependence of self-diffusion coefficients.
The cementation of copper on various types of nickel discs has been studied in dilute cupric sulphate solutions. Activation of the cathode nickel discs with Te+4 was necessary to achieve reproducible rates, whereas satisfactory results were obtained with mint nickel discs using only a chemical polishing treatment Attempts to cement copper on discs of nickel-copper alloys were unsuccessful.The cementation process on pure nickel takes place by two different rate-controlling mechanisms. At low temperatures the process is probably controlled by a surface reaction, whereas at higher temperatures the process is probably controlled by diffusion through surface layers. When the acidify of the solution is increased, the cementation rate increases. The rate decreases with increasing thickness of the cemented deposit.
Résumé
Le dépôt de cuivre sur divers types de disques de nickel a été étudié en solution diluée de sulfate cuivrique. Afin d'obtenir des taux reproductibles il a été nécessaire d'activer les disques de nickel cathodique avec du Te+4 alors que pour du nickel à monnaie des résultats satisfaisants étaient atteints apnès un polissage chimique. Les essais de dépôt de cuivre sur des alliages de nickel-cuivre se sont avénés infructueux.Le processus du dépot sur du nickel pur se fait par deux mécanismes différents. A basses températures le processus est probablement contrôlé par une réaction de surface tandis qu'a plus haute température il serait contrôle par diffusion au travers de la surface. Quand l'acidité de la solution est augmentée, le taux de dépôt augmente également. Ce taux diminue au fur et à mesure que l'épaisseur du dépôt augmente.
Die direkte Bestimmung von Ionendiffusionskoeffizienten auch bei hohen Konzentrationen gelingt mit Hilfe einer modifizierten Diaphragmenzelle nach McBain. Die gegenseitige Beeinflussung der Wanderung von Kationen und Anionen in der Zelle üblicher Bauart läßt sich dadurch aufheben, daß die Lösung des zu untersuchenden Ions gegen eine gleich konzentrierte Lösung eines Salzes mit einem dem untersuchten Ion möglichst ähnlichen Ion und dem gleichen Gegenion diffundiert. Die notwendige gründliche Durchmischung der Lösungen in den Diffusionsräumen wird bei der modifizierten Zellenausführung durch Thermokonvektion erzwungen. Die Methode erlaubt, wie durch Messungen an Cu-, Cd-, Cu-ammin- und Cd-amminionen gezeigt, genaue Messung der Ionendiffusionskoeffizienten auch in konzentrierten Lösungen.The direct estimation of ion diffusion coefficients at high concentrations is achieved by means of an improved McBain diaphragm cell. The mutual influence between the migration of cations and anions is cancelled by diffusion of the solution of the ion being investigated into a solution which contains, at the same concentration, a very similar ion and the same counterion as the test solution.The cell was checked by precise determinations of the diffusion coefficients of Cu++, Cd++, [Cu(NH3)4]++, and [Cd(NH3)4]++ ions.
Kinetics of Copper Cementation on a Rotating Iron Disc
- J V Calara
- J. V. Calara
J. V. Calara: "Kinetics of Copper Cementation on a Rotating Iron Disc," Master's Thesis, University of the Philippines, Department of Metallurgy, Manila, Philippines, 1970.
An Analysis of Concentration and Temperature Effects in Ce-mentation Reactions," to be published in Mineral Science and Engineering
- L D Miller
L D. Miller: "An Analysis of Concentration and Temperature Effects in Ce-mentation Reactions," to be published in Mineral Science and Engineering, in press.
A Kinetic Study of the Cementation of CoppeT and Nickd
- Ill Miller
ILL. Miller: "A Kinetic Study of the Cementation of CoppeT and Nickd," Ph.D. Thesis, University of Utah, Department of Mining, Metallurgical and Fuels Engineering, Salt Lake City, Utah, 1968.
A Kinetic Study of the Cementation of Copper with Iron Advances in Extractive Metallurgy, Institute of Mining and Metallurgy
- R M Nadkami
- M E Wadsworth
R. M. Nadkami and M. E. Wadsworth: "A Kinetic Study of the Cementation of Copper with Iron," Advances in Extractive Metallurgy, Institute of Mining and Metallurgy, London, 1968, pp. 918-41.
A Kinetic Study of the Cementation of Copper with Iron
- R M Nadkami
- M E Wadsworth
- R. M. Nadkami
A Kinetic Study of the Cementation of Copper and Nickel
- R L Miller
- R. L. Miller
Surface Deposit Effects in the Kinetics of Copper Cementation by Iron
- L W Beckstead
- L. W. Beckstead