Metal Dissolution Rate Research Articles

Analysis of heavy metal content in edible honeysuckle (Lonicera japonica Thunb.) from China and health risk assessment

Honeysuckle is a commonly used medicine for health care and treatment. To detect heavy metal pollution in honeysuckle from China and quantify the health risk of heavy metal via dietary intake, the Pb, Cd, Cr, As, Hg, Ni, Mn, Cu, and Zn contents in honeysuckle samples were determined by ICP-MS. The dissolution rate of heavy metals in honeysuckle was measured by decoction and soaking. The hazard quotient (HQ) and total hazard index (HI) were used to evaluate the noncarcinogenic risk of nine heavy metals in honeysuckle, and the carcinogenic risks of Cd and As were evaluated using the carcinogen risk. Cd exhibited the maximum permissive limit standard-exceeding rate (40.2%) in honeysuckle, followed by Cu (37.6%) and Pb (8.5%). As and Hg did not exceed the standard values, and Cr, Ni, Mn, and Zn had no limits. In a decoction fluid after 30 min of boiling, the transfer rates of Pb, Cd, As, Ni, Mn, Cu, and Zn ranged from 11.9% to 19.9%, whereas that of Cr was low (1.0%). In a soaking fluid, the transfer rates ranged from 17.0% to 56.9%; no transfer rate was detected for Hg in neither the decoction fluid nor the soaking fluid. In addition, the 95th percentile Rs of As and Cd in honeysuckle were 5.93 × 10−6 and 8.12 × 10−5, respectively. The carcinogenic risk of Cd at 56.99th percentile reached the threshold set by the World Health Organization (1.0 × 10−5). The results showed that intake of Pb, Cd, Cr, As, Hg, Ni, Mn, Cu, and Zn by the human body through honeysuckle could not cause noncarcinogenic damage. The element As had no carcinogenic risk, but Cd had a carcinogenic risk to a certain extent.

Electrochemical impedance spectroscopy analysis of corrosion product layer formation on pipeline steel

Pipeline steels exhibit intergranular corrosion (IGC) and stress corrosion cracking at active dissolution potentials in carbonate-bicarbonate solutions. The evolution of electrochemical behavior of API X70 pipeline steel during active dissolution in 1 M NaHCO3 was investigated by electrochemical impedance spectroscopy (EIS). Electrochemical modeling of EIS revealed that the metal dissolution rate is limited by slow inward diffusion of CO3−2 ions through a porous precipitated corrosion product layer to the steel surface. The porosity of the carbonate layer decreases over time as its thickness increases, both factors contributing to a strongly suppressed corrosion rate due to impeded CO3−2 diffusion. Decreasing steel corrosion rates with time in carbonate-bicarbonate solutions can be understood on this basis. Growth of the carbonate layer at the steel-carbonate interface intensifies tensile wedging stress in corroded grain boundaries, thereby facilitating intergranular crack initiation.

Study of Anodic Dissolution of Stainless Steel in HCl by the Method of Measuring Ohmic Resistance

The aim of the work is to show the potentialities of the method of measuring ohmic resistance for investigating the anodic dissolution of metals. It is shown that simultaneous measurement of metal dissolution rate by using this method (by a change in the specimen weight, which is calculated by a change of its resistance) and by the charge consumed for the metal polarization enables us to determine the electrochemical equivalent of stainless steel. The dependence of cathodic component of the current on the anodic potential is obtained and the potential range adjacent to the open-circuit potential, where both anodic and cathodic reactions should be taken into account, is determined.

Natural diatomite mediated spherically monodispersed CoFe2O4 nanoparticles for efficient catalytic oxidation of bisphenol A through activating peroxymonosulfate

Porous magnetic CoFe2O4/diatomite catalyst (CFD) was rationally synthesized via a facile citrate combustion process. The relationship between catalytic performance and material properties of the prepared catalysts was comprehensively investigated by various characterizations, especially for the interface interaction between CoFe2O4 and diatomite as well as crystallization regulation of CoFe2O4. Overall, higher specific surface area, overspreading surface hydroxyl groups, better crystal dispersion and abundant surface-active sites make CFD have better degradation performance of bisphenol A (BPA) than pure CoFe2O4 in the presence of peroxymonosulfate (PMS), and the pseudo-first-order reaction rate constant of 40-CFD (40% CoFe2O4/diatomite) is almost 5.32 times higher than that of pure CoFe2O4. Besides, CFD has excellent magnetic properties, lower metal dissolution rate and good reusability. In addition, electron paramagnetic resonance (EPR) and radical quenching experiments show that sulfate radicals (SO4−) and singlet oxygen radicals (1O2) generated from the electron transfer of BPA molecule and valence state change of transition metals should be the predominant oxidation species. Moreover, possible degradation pathways of BPA are determined by the detection of intermediates derived from the results of liquid chromatograph–mass spectrometer (LC–MS). In brief, it is indicated that the CoFe2O4/diatomite composite material is an efficient and environmentally friendly catalyst, which has a great potential application in wastewater treatment by activating PMS.

Simultaneous Leaching of Seafloor Massive Sulfides and Polymetallic Nodules

Simultaneous leaching of seafloor massive sulfides (SMS) from Loki’s Castle on the Arctic Mid-Ocean Ridge (AMOR) and polymetallic nodules (PN) from Clarion Clipperton Zone (CCZ) of the Central Pacific Ocean was studied. Leaching tests were conducted using sulfuric acid and sodium chloride, at a temperature of 80 °C for 48 h under reflux. The effect of PN-to-SMS ratio was examined. It was shown that simultaneous leaching of two different types of marine resources was possible resulting in high dissolution rates of metals. The proposed process has many advantages as it does not require pyrometallurgical pretreatment, and yields solid products (i.e., silica, barite, elemental sulfur, albite, microcline, muscovite), which might be utilized for various industrial applications.

Silica nanoparticles as copper corrosion inhibitors

Nanoparticle suspensions (or ‘nanofluids’) employed as heat transfer fluids (HTF) enhanced the thermal conductivity and the effectiveness of the heat exchangers as well as efficacy of thermal energy storage (TES) platforms by augmenting the effective specific heat capacity of various solvents. In prior studies, molten salt nanofluids also reduced corrosion by 50% (compared to that of neat molten salts and pure molten salt eutectics). Here, we demonstrate that silica nanoparticle suspension could be beneficial not only from the point of higher rates of heat transfer and thermal energy storage but also as corrosion inhibitors of copper substrates, that are typically used for thermal systems (e.g., HTF and TES). Combined use of Quartz Crystal Microbalance (QCM) technique and atomic force microscopy indicate a significant lowering of the corrosion rates (up to 4 times) when only 10% of the surface is covered by silica nanoparticles with a nominal diameter of 10 nm. These results are attributed to the negative surface potential of silica nanoparticles. As a result when the nanoparticles precipitate on the copper surface and form surface ‘nano-fins’—they preferentially prevent negatively charged ions (such as chlorine ions) from approaching the metal surface and thereby serve as an impediment from increasing the metal dissolution rate. This counter-intuitive behavior occurs even when the nanofins are formed randomly (i.e., without forming a uniform coating) and are sparsely dispersed on the copper substrate. This phenomenon of reduced corrosion is attributed to be another manifestation of the ‘nano-Fin Effect (nFE)’.

One-dimensional HKUST-1 nanobelts from Cu nanowires

The controllable synthesis of one-dimensional (1D) structural morphology of metal-organic frameworks (MOFs) is significant for its application in catalysis, sense and gas separation. In this communication, we report a simple and moderate synthetic strategy to obtain uniform HKUST-1 nanobelts (NBs) by using copper nanowires (Cu NWs) as a metal source as well as a template. The control experiments showed that synergy between metal dissolution rate and crystal formation plays a key role in the formation of nanobelts. Our study represents an attractive synthetic strategy of 1D MOFs-based material for applications.

Boosting Stability and Activity of Oxygen Evolution Catalyst in Acidic Medium: Bimetallic Ir−Fe Oxides on Reduced Graphene Oxide Prepared through Ultrasonic Spray Pyrolysis

AbstractElectrolysis of water in acidic media generally requires noble metals (oxides) to enhance the catalyst activity and durability in the oxygen evolution reaction (OER). Bimetallic Ir−Fe supported on reduced graphene oxide (IFG) is prepared by ultrasonic spray pyrolysis, followed by acid and/or heat treatment. Physical and electrochemical methods are used to elucidate the effect of the physical and chemical properties of the IFG catalysts modified by spray pyrolysis and post treatment on the OER activity and stability under harshly oxidizing conditions in 0.1 M HClO4. The IFG‐AHT catalyst synthesized via ultrasonic pyrolysis followed by acid and heat treatment exhibits superior OER activity among the IFG catalysts. The mass activity was two‐fold higher and the stability is superior to that of the commercially available Ir catalyst, indicating that the metal (oxide) dissolution rate and the interaction between Ir and the hybrid support affect the cost and lifetime of OER catalysts.

Localized Corrosion: Passive Film Breakdown vs. Pit Growth Stability: Part IV. The Role of Salt Film in Pit Growth: A Mathematical Framework

In Part II of this series, a framework for pit stability established, and it was expanded in Part III to describe salt film formation in pits. It was shown that a salt film was not required for pit stabilization; it is just a consequence of a pit achieving diffusion-controlled growth. A salt film can form on the surface of both metastable and stable pits when the maximum pit dissolution current density, idiss,max, exceeds the diffusion-limited current density, ilim. Based on this clarifying framework, this paper shows mathematically that the main function of a salt film is to adjust the actual potential at pit surface by regulating its thickness, thus to restrict the anodic dissolution rate of pit surface metal at the value of diffusion-limited current density. As a result, the film thickness will respond to any changes in the applied potential, temperature, pit depth, ohmic potential drop in the solution and perforation radius of the pit cover. Additionally, the pit stability criteria that have been discussed previously in the literature are reinterpreted using the new framework, and they are unified by the critical temperatures, potentials and pit depths for pit stabilization and salt film formation proposed in Part III.

A Study of the Initial Stages of Local Dissolution of Carbon Steel in Chloride Solution

The simultaneous application of optical and electrochemical methods has allowed us to investigate in detail the initial stages of the local dissolution of steel in a chloride-containing solution. The incubation period, the rate of defect formation on the surface, and the rate of individual defects development have been evaluated with high precision. It has been demonstrated that the emergence and development of local defects is possible under potentials more negative than the pitting potential determined from the polarization curve. The metal dissolution rates that occur at the initial stages of pitting formation from an individual defect have been calculated. It has been established that the initial process of defect formation under anode polarization consisted of two stages. The first stage corresponds to the emergence and intense formation of the freshly formed defect and is primarily determined by electrode potential. The second stage is shown by the development of a defect that did not depend on potential.

Estimation of bioaccessibility and risk assessment of heavy metals in decoction pieces of Bupleuri Radix

This project was launched to study on the overall residual status of heavy metals of comprehensive understanding in decoction pieces of Bupleuri Radix (DPBR) from different habitats and risk assessment. In this study, inductively coupled plasma mass spectrometry was used to determine the heavy metals of 30 batches of Bupleuri Radix in different producing areas. Simulated gastrointestinal fluid method was used to determine the dissolution rate of heavy metals in the simulated gastrointestinal fluid and the average daily intake Average Daily Dose (ADD) and Hazard Quotient (HQ) index were used to assess the risk of heavy metals in DPBR. The results showed that the contents of copper (Cu), lead (Pb), arsenic (As), cadmium (Cd), and mercury (Hg) in the 30 batches of DPBR didn't exceed the limit of Chinese Pharmacopeia, however, the chromium (Cr) in DPBR exeeded the limit set by NSF in USA and the limit for herbal ingredients in Canada. The mean bioaccessible heavy metal concentrations decreased from Cu (5.27 mg·kg⁻¹)>Cr (4.67 mg·kg⁻¹)>As (0.18 mg·kg⁻¹)>Pb (0.12 mg·kg⁻¹)>Cd (0.06 mg·kg⁻¹), and Hg was not detected in this test. In addition, cumulative non-carcinogenic health risks (HI) for adults and children were 0.799 and 0.714, respectively. Both HI values in adults and children for combined trace element and heavy metal element exposures were below the value of 1 (HI<1), indicating very low carcinogenic health risk. Heavy metals toxicity in herbal medicines and its health risk to humans would be overestimated when assessed only by the total concentrations without considering the bioaccessibility. Therefore, bioaccessibility has great significance for evaluating the human health risks induced by heavy metals.

INFLUENCE OF FORMATION OF THE COMPLEXES WITH DIFFERENT KIND OF LIGANDS ON KINETICS OF OXIDATIVE DISSOLUTION OF METALS

Rotating disk method has been used to study the dissolution of gold in the presence of an oxidizer and a mixture of dissimilar ligandforming reagents. Kinetic regularities of gold dissolution were investigated in aqueous systems thiourea-thiocyanate with Fe (III) and Cu (II) ions as the oxidizer; thiosulfate-thiocyanatewithFe(III)EDTA oxidizing complex and thiosulfate-thiocyanate with ammonia complex [Cu(NH3)4]2+ asoxidizing agent. Peculiarities of these mixed systems is a possibility to form the monoligandas as well as geteroligand complexes of gold. The influence of gold complexes formation with different sorts of ligands on the metal dissolution rate have been considered. The dependence of the dissolution rate on the ratio of ligands concentrations and on the oxidizing agent nature was investigated. Interrelation was established: the use of dissimilar ligandforming reagents - the higher thermodynamic stability of the geteroligand complexes of gold (relative to the homoligand ones) - synergistic increase of the gold dissolution rate. It was found that the heterophase reaction makromechanism for the thiourea-thiocyanate-Fe(III) system is determined by the proximity of the rates of chemical and diffusion stages (experimental activation energy - 21.6 kJ/mol; the reaction order in respect to the disk rotation frequency – 0.23). Diffusive limitation is due to the slow withdrawal of the reaction products -Au (I) compounds - from the solid phase surface. The formation of stronger heteroligand complexes and the corresponding increase in the reaction products concentration at the surface increases a rate of the metal diffusion into the solution. For the thiourea-thiosulfate-Fe(III)EDTA system a film formation of the reaction solid products on the gold surface was observed. To identify it the infrared reflection spectra of the polished gold surface after the etching were obtained. There is a strong absorption band on the spectra at 804 cm-1. Absorption in this area has been associated with the stretching vibrations of C=S bond of the thiourea molecules joined to the surface and the products of their oxidation.

Synthesis of magnesium chloride complex electrolyte: Galvanic couple assisted catalytic dissolution of magnesium in ethereal solution

Herein, we reveal the critical role of CrCl3 and the mechanism for the synthesis of magnesium chloride complex (MaCC), an advanced conditioning-free electrolyte for rechargeable magnesium batteries. This involves a catalytic dissolution of Mg metal by nanoscale bimetallic galvanic couples in an ethereal solution: At the initial stage, nanoscale amorphous Cr-rich ‘islands’ form on Mg surface, creating numerous Cr-Mg galvanic couples. These Cr-rich islands act as local cathodic sites due to partial electron transfer from Mg metal substrate. Furthermore, the first-principles calculation shows that Al prefers to bind at Cr-rich regions rather than Mg. These trigger a heterogeneous catalysis for the selective deposition of Al on Cr-rich islands and a dramatic increase in the dissolution rate of Mg metal on the neighboring region. This leads to an ultrahigh Mg2+-to-Al3+ concentration ratio in the resultant solution, a key property of the conditioning-free electrolyte. This study is potentially applicable to many other fields like metal-air batteries and corrosion protection of metals, where a subtle manipulation of passive layer is required.

Effect of hydrostatic pressure on the corrosion behavior of HVOF-sprayed Fe-based amorphous coating

Understanding corrosion behavior under hydrostatic pressure is crucial for the design of materials for deep-sea industrial applications. In this work, the corrosion behavior of a Fe48Mo14Cr15Y2C15B6 amorphous coating was examined under high hydrostatic pressure (80 atm), and compared to that at atmospheric pressure (1 atm). The results from immersion and potentiodynamic polarization tests indicate that the general corrosion rate of the coating increased at 80 atm with respect to that at 1 atm, yet the localized corrosion resistance did not change much. However, the stability of passive films at 80-atm is declined compared to that at 1-atm, which is attributed to the lower compactness and higher density of point defects in the passive film at high hydrostatic pressure. Finally, TEM observations reveal that the passive film formed at 80 atm is much thicker (nearly 3 times) than that formed at 1 atm due to a faster dissolution rate of metals and diffusion rate of ions under high hydrostatic pressure, which have a compensation for the decrease of stability and compactness of the passive film, such that the good localized corrosion resistance of the amorphous coating is reserved at high hydrostatic pressure. This study sheds light on the dynamics of passive film formed on amorphous metals and will also be helpful for designing corrosion-resistant materials for deep-sea applications.

Interface layer formed in a low-temperature plasma of hydrocarbons on iron

The method of uncovering the interphase layer in the systems “iron-nanosized polymer film” obtained in a low-temperature plasma on iron from hydrocarbons was used. A method of interface layer uncovering based on electrochemical dissolution of the iron substrate was proposed, which allowed one to achieve a high rate of metal. Ammonium sulfate solution was used as an electrolyte. A method of interface layer uncovering based on electrochemical dissolution of the iron substrate was proposed in the work. This allowed one to achieve a high rate of metal dissolution and make it possible to control the composition of the dissolution product. Salt solution was used as an electrolyte. Interface layer studies were carried out using the AFM and XPS methods, which allowed establishing the relief and chemical composition of the interphase boundary, as well as the location on the interphase surface of the metal-containing phase. The application of a double-layer iron substrate consisting of a plate of 56Fe nonresonance isotope with a 57Fe ultrafine layer deposited on its surface allowed one to use the Mössbauer spectroscopy for investigation of the chemical state of iron atoms in the interfacial region of “iron-nanoscale polymer film” systems.

Influence of Citrate on Metal Dissolution and Respiration Rate of Microbial Leaching Cultures

The application of acidophilic iron oxidizing bacteria is an established technique in tank and heap leaching of mainly sulfidic minerals. Even though bioleaching is broadly studied, there are still several issues to solve. Especially, the formation of iron precipitates, leading to co-precipitation of valuable metals, as well as the inhibition due to coating, considerably decrease the leaching efficiency. Consequently, the addition of chelating agents should result in an increased dissolution rate.However, organic acids, which have chelating characteristics, are generally regarded as highly toxic for leaching bacteria. Nonetheless, we found that both the addition of sodium citrate and citric acid leads to an increased iron oxidation rate of 42% and 84%, respectively, compared to standard culture medium without citrate. Chemical leaching tests with ZnS and ferric iron showed similar concentrations of dissolved zinc with and without citrate. However, the actual leaching efficiency is yet to be evaluated.

Low temperature dissolution flowsheet for Pu metal

ABSTRACTThe Savannah River National Laboratory was requested to develop a Pu metal dissolution flowsheet at two reduced temperature ranges for implementation in the Savannah River Site H-Canyon facility. The dissolution and H2 generation rates during Pu metal dissolution were investigated using a dissolving solution at ambient temperature (20–30°C) and for an intermediate temperature of 50–60°C. The Pu metal dissolution rate measured at 57°C was approximately 20 times slower than at boiling (112–116°C). The dissolution rate at ambient temperature (24°C) was approximately 80 times slower than the dissolution rate at boiling. Hydrogen concentrations were less than detectable (<0.1 vol%).

Strain-induced reactivation of corrosion pits in austenitic stainless steel

The reactivation of a corrosion pit under the synergetic effect of strain and electro-chemical polarisation has been observed in a type 304L stainless steel using X-ray computed tomography. The pit reactivation process was associated with the formation of a new pit, directly adjacent to a pre-existing pit. Pit growth kinetics were estimated, revealing an increase of the diffusivity parameter (Deff ΔC) from 3.0×10−8molcm−1s−1 to 4.5×10−8molcm−1s−1 with the application of strain, indicating higher metal dissolution rates. Applied strain resulted in fractured lacy metal covers, and its effect on pit growth kinetics is discussed.

Computational and Experimental Study of the Inhibition Effects of Purple Sweet Potato Leaves Extract on Mild Steel Corrosion in 1M H2SO4

The alkaloid and non-alkaloid fractions of purple sweet potato (Ipomoea batatas) written as AEIB and NEIB respectively were used as inhibitors in the corrosion reaction of mild steel in 1.0 M H2SO4 solutions. The corrosion rate decreased with increase in the concentration of the AEIB and NEIB as evidenced in the experimental results obtained from the gravimetric and gasometric techniques. This proved that the AEIB and NEIB are effective inhibitors of mild steel corrosion. Also, the experimentally obtained data fitted well into the Temkin isotherm while the computed thermodynamic parameter values showed that the inhibitors effectively reduced the rate of metal dissolution by becoming physically adsorbed on the mild steel surface.

The Synergistic Effect of Iodide and Sodium Nitrite on the Corrosion Inhibition of Mild Steel in Bicarbonate-Chloride Solution.

The effect of potassium iodide (KI) and sodium nitrite (NaNO2 inhibitor on the corrosion inhibition of mild steel in chloride bicarbonate solution has been studied using electrochemical techniques. Potentiodynamic polarisation data suggest that, when used in combination, KI and NaNO2 function together to inhibit reactions at both the anode and the cathode, but predominantly anodic. KI/NO2− concentration ratios varied from 2:1 to 2:5; inhibition efficiency was optimized for a ratio of 1:1. The surface morphology and corrosion products were analysed using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The latter shows that the addition of I− to NO2 facilitates the formation of a passivating oxide (γ-Fe2O3) as compared to NO2− alone, decreasing the rate of metal dissolution observed in electrochemical testing. The synergistic effect of KI/NO2− inhibition was enhanced under the dynamic conditions associated with testing in a rotating disc electrode.