Structure and energetics of solvated ferrous and ferric ions: Car-Parrinello molecular dynamics in the DFT+U formalism

We implemented a rotationally-invariant Hubbard U extension to density-functional theory in the Car-Parrinello molecular dynamics framework, with the goal of bringing the accuracy of the DFT+U approach to finite-temperature simulations, especially for liquids or solids containing transition-metal ions. First, we studied the effects on the Hubbard U on the static equilibrium structure of the hexa-aqua ferrous and ferric ions, and the inner-sphere reorganization energy for the electron-transfer reaction between aqueous ferrous and ferric ions. It is found that the reorganization energy is increased, mostly as a result of the Fe-O distance elongation in the hexa-aqua ferrous ion. Second, we performed a first-principles molecular dynamics study of the solvation structure of the two aqueous ferrous and ferric ions. The Hubbard term is found to change the Fe-O radial distribution function for the ferrous ion, while having a negligible effect on the aqueous ferric ion. Moreover, the frequencies of vibrations between Fe and oxygen atoms in the first-solvation shell are shown to be unaffected by the Hubbard corrections for both ferrous and ferric ions.Comment: 13 pages, 2 figures, 1 table. Submitted to Journal of Electroanalytical Chemistr

Investigating ferric ion production and consumption trends in a simulated e-waste bioleaching environment for maximum metal dissolution efficiency

Electrical and electronic equipment has become an integral part of life in the modern world. When disposed of, it is termed Waste Electrical and Electronic Equipment (WEEE) and is one of the fastest growing waste streams in the world. Disposing the WEEE has associated risks as they contain a high amount of toxic metals (e.g. lead) which can leach into the soil, they place a high load on the land and they contain valuable metals making their recovery beneficial. Printed circuit boards (PCBs) are an essential part of WEEE. Although WEEE forms a small part of the waste stream (3 %), it contains a high concentration of metals. As such, PCBs form the focus of this study. Base metals, especially copper, hamper the recovery of gold and PGMs by cyanidation. Further the copper grades of WEEE exceed those of many low grade ores exploited. Hence copper recovery from PCBs has garnered considerable focus. Bioleaching using the ferric ion and ferrous ion regeneration cycle is applied to the recovery of metals from metal sulphides in virgin ores and there is growing interest in its application to WEEE. The two sub-processes in the ferric regeneration cycle are ferric ion production through microbial oxidation of ferrous ion for growth and metabolic activity; and ferric ion consumption through the reduction of metals leading to metal dissolution. The ferric ion consumption and production rates depend on each other and other factors. The metal dissolution through ferric iron reduction is a function of ferric iron concentration, affected by how fast ferric iron is produced through microbial oxidation. Ferric iron production is a function of both the ferrous iron and ferric iron concentrations and so depends on how fast the ferrous ion substrate is produced through the dissolution of metals which consumes ferric ion in the process. Ferric ion production is also affected by the microbial population and microbial specific rates of oxidation of ferrous ion. Ferric ion consumption is also dependent on the metal dissolution rate which is affected by mass transfer limitations and the type of metal for dissolution. These are two competing subprocesses where the dissolution efficiency of metals is limited by the slower process

A New Graphene Quantum Dot Sensor for Estimating an Antibiotic Concentration

The antibiotics have impacted the human ailments by curtailing the growth of microbes and by providing relief from microbial diseases. While there are a large number of analytical methods available for the determination of antibiotics concentration, they are time consuming and impractical for usage in the fields. This thesis is aimed at overcoming the deficiencies of those methods in developing a new sensor. It reports a study of graphene quantum dots (GQD) bound ferric ion for sensing an antibiotic, ciprofloxacin (CP). The interaction of ferric ion with CP was used as a probe for the analytical estimation of CP using differential pulse voltammetry (DPV). A solution containing ferric ion exhibits a well-defined cathodic peak at Epc=0.310 V vs saturated calomel electrode (SCE) with a peak width of 0.100V. When nanomolar to micromolar concentration of CP is present in the solution, along with ferric ion, three new peaks at EpcI=0.200V, EpcII=0.050 V and EpcIII=-0.085V are observed due to the binding of CP to ferric ion. The decrease in peak current of Epc at 0.310 V is proportional to the concentration of CP in the solution. The peak current at 0.200 V shows an increase corresponding to the CP concentration in solution. These results paved the way for examining the prospectus for developing a portable resistive sensor using interdigitated gold electrodes on alumina substrate. The principle of this sensor is based on that ferric ion bound to GQD will have a finite resistance and when it is bound to CP the resistance will increase as the charge transport faces a barrier due to bulky CP molecules. With a view to establish that ferric ion is binding to GQD, fluorescence of GQD has been recorded with ferric ion in solution. The approach adopted in developing resistive sensor is shown below. The numbers in the above picture denotes 1. Interdigitated gold electrodes 2. GQD bound interdigitated gold electrodes 3. Ferric ion bound to GQD 4. Attachment of CP to ferric ion. The sensor response is found to be dependent on the activity of the availability of ferric ion on GQD resulting in the usage of it as a disposable sensor. The interference of urea in the measurement of CP was examined for the practical usage of it in urine analysi

Oxygen application to chloride leaching of complex sulfide ores

The study investigates leaching of complex sulfide ores with simultaneous regeneration of the leaching solution and removal of dissolved iron to balance the iron concentration in the leaching process. To minimize environmental pollution and obtain high metal extraction from the ores, leaching with a ferric chloride solution is adapted to treat Delta sulfide ores. The experimental results indicate that under high oxygen pressure leaching, oxidation of ferrous ion to ferric ion and partial precipitation of iron from solution can occur simultaneously. However, the findings also indicate that leaching the ores with simultaneous iron precipitation in one operation is difficult. It is better to precipitate excess iron in one stage; then leach the ores in another stage using the regenerated leaching solution

Ferrichrome: Surprising stability of a cyclic peptide-FeIII complex revealed by mass spectrometry

Ferrichrome, a fungal siderophore that is also utilized by some bacterial species, was studied with liquid secondary ion mass spectrometry (LSIMS) and matrix-assisted laser desorption ionixation (MALDI) mass spectrometry. A strong ionic signal corresponding to a FeIII complex was observed with LSIMS in the positive ion mode. Switching the polarity of the mass spectrometer did not necessarily result in reduction of ferric ion, although certain conditions led to appearance of a FeII complex signal as well. The results of the structural studies of the metal ion-cyclic peptide complex with collisionally induced dissociation allowed unambiguous identification of the chelation sites. The action of the siderophore on FeIII was studied by in vitro chelation of ferric ion (from ferric citrate) by the iron-free ferrichrome. Effective chelation of ferric ion was compared to actions of the iron-free ferrichrome on other metal ions. Unlike LSIMS, desorption with MALDI did not form selectively molecular ions of intact ferrichrome: the spectra contained abundant peaks corresponding to the cyclic peptide itself and its nonspecific association with alkali metal ions

An Investigation into the Precipitation of Copper from Mine Water, using Sulfur Dioxide to Reduce the Ferric Ion Content

The experiments which were preformed showed that sulfur dioxide would reduce the ferric ion content of the mine waters to a very low figure. The reduction in the ferric ion content would improve the efficiency of the precipitation process, and also increase the recovery of copper

On the Formation of Complex Ions Applied in Analytical Chemistry. VIII : Studies on Complexbilities of Ferric Compounds by the Use of Radioisotope Element

Applying the ion exchange method reported by J. Schubert, the complexbilities of ferric tartrate, citrate and malonate were measured by the use of the radioisotope element of Fe^ and the ion exchange resin of Amberlite 1R-120. The hydrogen ion concentrations of the solution were measured by the use of the quinhydrone electrode. All the measurements were made at 25℃ and the following results were obtained : ferric tartrate, K=3.1×10^ citrate, K=2.2×10^ ; malonate, K=2.5×10^

Copper recovery from unground printed circuit board by biogenic ferric at high solid/liquid ratio

In this work, the recovery of Cu from large waste printed circuit board (PCB) pieces by biogenic ferric sulphate at high solid to liquid ratio was studied. PCB parts were packed in a column and biogenic ferric was constantly recirculated. A high oxidation reduction potential (ORP) decrease was observed in ferric leaching due to ferric ion consumption; this drop caused a slower copper dissolution kinetics. After 25 days, 62.2% of copper was leached from PCBs column. PCBs column was connected to a flooded packed-bed (FPB) bioreactor to study the biological regeneration of ferric ion consumed in chemical reaction. The bioreactor connection enabled working at a constant ORP (700 mV vs. Ag/AgCl) during the whole test time. The improvement of oxidising conditions hugely increased copper dissolution rate, reaching 90% of copper recovery after 25 days. The FPB bioreactor operated continuously without showing inhibition problems and generating a leaching liquor with a high and constant ORP. The novel proposed configuration consists of a chemical reactor, where large PCBs pieces are piled at a high solid load, connected to a FPB bioreactor that regenerates the spent ferric ion enabling the leaching without reagents consumption, is a simple, inexpensive, low energy consumption, eco-friendly and effective system to recover copper from PCBs

Ferric leaching of the sphalerite contained in a bulk concentrate: Kinetic study

A novel process for the integral treatment of polymetallic sulphide ores is proposed. The process consists of a global flotation, two stages of ferric leaching, the first stage dissolves the sphalerite and the rest of secondary sulphides, and the second dissolves the chalcopyrite with a silver catalyst, and finally a brine leaching to recover lead and silver (added as catalyst). The proposed process offers several advantages comparing to traditional pyrometallurgical techniques. This study is focused on the sphalerite dissolution with ferric sulphate, as the first stage of the treatment of Cu-Zn-Pb concentrates. The ferric ion concentration, the temperature and the particle size have an important role in the sphalerite oxidation. However, the initial sulphuric acid, ferrous ion and sulphate ion concentrations have no influence in the process rate. The formation of an elemental non-porous layer of sulphur along the reaction hinders the ferric ion transport to the sphalerite surface. Two kinetics regimes are proposed, in the beginning the chemical reaction is the rate controlling step, and, at 30% Zn extraction, the rate controlling step changes to diffusion through a non-porous film of elemental sulphur. The activation energy obtained for the chemical reaction has a value of 51.3 kJ/mol, and the apparent activation energy in the diffusional stage is the 47.7 kJ/mol. The reaction order with respect ferric ion is 0.26 and the reaction rate is proportional to the zinc sulphide amount in the first stage. The behaviour of sphalerite, contained in a bulk concentrate, is similar to the pure sphalerite or the sphalerite contained in a differential concentrate.CLC Company - PRJ201602665/012

Kinetic studies of the dissolution of copper in ferric chloride solutions

M.S.Walter H. Burrow