The Influence of Impurity Monovalent Cations Adsorption on Reconstructed Chalcopyrite (001)-S Surface in Leaching Process

Hydrometallurgical processing of chalcopyrite is hindered predominantly due to the passivation layers formed on the chalcopyrite surface. However, the effects of impurity cations released from the gangue are not yet well understood. Density functional theory (DFT) calculations were carried out to investigate monovalent cations of Na+ and K+ on chalcopyrite (001)-S surface using Materials Studio. The results show that the 3d orbital of Fe and 3p orbital of S predominantly contribute to their activities during chalcopyrite oxidation and dissolution processes. In addition, SO42− is more likely to be adsorbed on one Fe site in the presence of Na+, while it is preferentially adsorbed on two Fe sites in the presence of K+. However, the adsorption of both Na2SO4 and K2SO4 on the chalcopyrite (001)-S surface contributes to the breakage of S–S bonds, indicating that the impurity cations of Na+ and K+ are beneficial to chalcopyrite leaching in a sulfuric environment. The adsorption energy and partial density of states (PDOS) analyses further indicate that the adsorption of Na2SO4 on chalcopyrite (001)-S surface is favored in both -BB (bidentate binuclear ) and -BM (bidentate mononuclear) modes, compared to the adsorption of K2SO4

Preparation of CoP films by ultrasonic electroless deposition at low initial temperature

Electroless deposition technology has been considered as a kind of common ways to obtain cobalt alloy films. However, in order to get cobalt alloy films, high temperature (353 K) is necessary during the electroless deposition process which will increase costs and energy consumption. Ultrasonic was introduced during electroless plating process to obtain cobalt alloy films at lower initial temperature. It was found that the cobalt thin films could be prepared at lower initial temperature (323 K) with the introduction of ultrasonic. Therefore, different powers of ultrasonic were applied during the electroless deposition process to prepare CoP thin films on copper substrates from an alkaline bath in this investigation. The effects of different powers of ultrasonic on deposition rate, surface morphology, anticorrosion performance and magnetic property of films were studied. It was found that the deposition rate increased gradually with the rise in ultrasonic powers due to cavitation phenomenon. All the CoP lilms presented the typical spherical nodular structures with the impact of ultrasonic. Smaller and regular shaped structures could be observed when the films were deposited with higher power of ultrasonic which contributed directly to enhancement of anticorrosion performance. Saturation tnagnetization and coercivity of thin films increased gradually with the rise in ultrasonic powers during the electroless deposition process due to the higher amounts of cobalt. (c) 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved

The Influencing Mechanisms of Sodium Hexametaphosphate on Chalcopyrite Flotation in the Presence of MgCl2 and CaCl2

Sea water has been used in flotation plants, showing a promising way to save fresh water usage. Previous studies indicated that divalent salts in sea water played negative roles in chalcopyrite flotation, but not much work have been conducted to understand the eliminating mechanisms. This study systematically investigated the effects of divalent cations of Ca2+ and Mg2+ on natural flotability of chalcopyrite in the absence of collectors and frothers. The reduced recovery was mainly due to the adsorption of Mg and Ca hydroxyl complexes and precipitation on chalcopyrite surfaces, giving rise to a less hydrophobic surface. The addition of sodium hexametaphosphate (SHMP), however, significantly improved chalcopyrite recovery. Species calculation, contact angle, zeta potential, FTIR and XPS analyses were conducted to understand the influencing mechanisms of divalent ions and the beneficial effects of SHMP on chalcopyrite recovery. The primary mechanism was that SHMP prevented the adsorption of positively charged Mg and Ca compounds or precipitation with hydrophilic properties such as Mg(OH)2 on chalcopyrite surfaces, confirmed by the Derjguin-Landau-Verwey-Overbeek (DLVO) theory. Secondly, SHMP reacted with Mg2+ and Ca2+ to form dissolvable complexes, thereby declining the formation of insoluble Mg2+ and Ca2+ compounds or precipitation

Fundamental Studies of SHMP in Reducing Negative Effects of Divalent Ions on Molybdenite Flotation

Seawater has been considered as an alternative to freshwater for flotation. However, many ions in seawater were reported to depress molybdenite (MoS2), with the depressing mechanisms being insufficiently understood. In this study, the influence of divalent ions (e.g., Ca2+ and Mg2+) and dispersant on MoS2 flotation was systematically investigated. It was found that the detrimental effects of Ca2+ and Mg2+ on the natural flotability of MoS2 were mainly due to the attachment of formed CaMoO4 precipitates and Mg(OH)2 colloids onto MoS2 surface. However, the addition of sodium hexametaphosphate (SHMP) reduced the negative effects. Various measurements, including contact angle, zeta potential, fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), were conducted to understand the influencing mechanisms of divalent ions and the beneficial effects of SHMP on MoS2 flotation. In addition, the Extended Derjguin–Landau–Verwey–Overbeek (EDLVO) theory was applied to investigate the total interaction energy between MoS2 particles and formed colloids, revealing that the reduced attraction force between MoS2 and Mg(OH)2 colloids in the presence of SHMP primarily resulted in the increased MoS2 recovery. In addition, SHMP combined with Mg2+ and Ca2+ to form dissolvable complexes, thereby reducing insoluble Mg2+ and Ca2+ compounds or precipitation. Thus, this study demonstrated for the first time two influencing mechanisms of SHMP in improving MoS2 recovery in the presence of Ca2+ and Mg2+

Effects of Magnetic Fields on the Electrodeposition Process of Cobalt

Magnetic fields parallel to electric fields were applied in the experiment to prepare cobalt thin films from the electrolyte without chemical additives. Influences of various magnetic intensities on the electrochemistry process, deposition mass and surface morphology were studied. According to the experiment, steady state current and deposition mass decreased gradually with the increase of magnetic intensities. The result of electrochemical impedance showed that transfer resistance increased with the magnetic intensity ranged from 0 to 1 T. During the electrodeposition process, cobalt near cathode is lower than other places in the solution. A gradient in the concentration of paramagnetic cobalt ions leads to a gradient in the magnetic susceptibility which would induce to a magnetic driving force when the magnetic field was applied. This magnetic driving force would push the cobalt ions away from cathode to hinder cobalt deposition resulting in decrease of steady state current and transfer resistance. The cobalt films are composed of typical nodular structures. However, hill-like structures could be observed with the increase of magnetic intensity. Cobalt grains tend to grow perpendicularly to the substrate with the condition of higher magnetic intensity due to the ferromagnetic property of cobalt atoms

Kinetics and Mechanisms of Chalcopyrite Dissolution at Controlled Redox Potential of 750 mV in Sulfuric Acid Solution

To better understand chalcopyrite leach mechanisms and kinetics, for improved Cu extraction during hydrometallurgical processing, chalcopyrite leaching has been conducted at solution redox potential 750 mV, 35–75 °C, and pH 1.0 with and without aqueous iron addition, and pH 1.5 and 2.0 without aqueous iron addition. The activation energy (Ea) values derived indicate chalcopyrite dissolution is initially surface chemical reaction controlled, which is associated with the activities of Fe3+ and H+ with reaction orders of 0.12 and −0.28, respectively. A surface diffusion controlled mechanism is proposed for the later leaching stage with correspondingly low Ea values. Surface analyses indicate surface products (predominantly Sn2− and S0) did not inhibit chalcopyrite dissolution, consistent with the increased surface area normalised leach rate during the later stage. The addition of aqueous iron plays an important role in accelerating Cu leaching rates, especially at lower temperature, primarily by reducing the length of time of the initial surface chemical reaction controlled stage

An Improved Understanding of Chalcopyrite Leaching Mechanisms: The Influence of Anisotropic Crystal Planes

Chalcopyrite (CuFeS2) particles, exposing anisotropic crystal planes during the grinding process, possess comprehensive surface properties that affect their leaching behaviors. In order to investigate the influence of anisotropic crystal planes on the leaching mechanisms, CuFeS2 particles with anisotropic crystal planes were produced by employing three-head laboratory grinder mill (TM), rod mill (RM), and ball mill (BM) and were then leached in a sulfuric acid solution at pH = 1. Based on the XRD, SEM, XPS, and simulation results, (112), (102), (312), (110), (116), (100), and (001) planes were mainly exposed on the CuFeS2 surface during the crushing and grinding process. In addition, fewer (112), (102), (312), and (110) planes but more (116), (100), and (001) planes were exposed on the CuFeS2 samples in the TM method than in the RM and BM methods. Since the leaching rates were in the order of (001) > (100) > (116) > (110) > (312) > (102) > (112) planes, the Cu extractions followed an order of TM > RM > BM. This study, therefore, provides an excellent theoretical basis for the effect of anisotropic crystal planes on CuFeS2 leaching, further improving the understanding of CuFeS2 leaching mechanisms

Effect of cerium on the corrosion behaviour of sintered (Nd,Ce)FeB magnet

For the balanced consumption of rare-earth elements, cerium (Ce) was partially used for NdFeB magnets instead of Nd. The corrosion behaviour of the (Nd,Ce)FeB magnet with different Ce contents in 3.5% NaCl solution was investigated by SEM, XRD, EDS and electrochemical tests. After immersion, the weight loss was calculated and the magnetic properties of the samples were measured. Results showed that Ce affected the corrosion of the (Nd,Ce)FeB magnet. Compared with the NdFeB magnet without Ce but of the same grade as the magnetic energy product, (Nd,Ce)FeB magnet showed better corrosion resistance. With increased Ce content, the corrosion resistances and magnetic properties of (Nd,Ce)FeB magnets were investigated. (C) 2017 Elsevier B.V. All rights reserved

Improved corrosion resistance of novel Fe-based amorphous alloys

Developing amorphous alloys with good corrosion resistance have attracted wide interests recently. In this work, a series of Fe-71 - xCrxMo3.5Ni5P10C4B4Si2.5 (x = 0, 4, 8, 10, 12, 14 at.%) amorphous alloys are fabricated. Thermal stability of this alloy system increases slightly with appropriate Cr content. The corrosion resistance in 3.5 wt.% NaCl solution is sensitive to the minor addition of Cr (<= 4 at.%) whereas higher Cr does not significantly improve the corrosion resistance according to the results of electrochemical measurements, SEM and XPS. These Fe-based amorphous alloys show comparable corrosion resistance with the well-known amorphous steel (Fe48Mo14Cr15Y2C15B6) despite the low Cr and Mo content, making them good candidates as corrosion-resistant coating materials. (C) 2016 Elsevier Ltd. All rights reserved