Slime Particles Research Articles

Experimental Studies of the Effects of Anode Composition and Process Parameters on Anode Slime Adhesion and Cathode Copper Purity by Performing Copper Electrorefining in a Pilot-Scale Cell

Copper electrorefining tests were conducted in a pilot-scale cell under commercial tankhouse environment to study the effects of anode compositions, current density, cathode blank width, and flow rate on anode slime behavior and cathode copper purity. Three different types of anodes (high, mid, and low impurity levels) were used in the tests and were analyzed under SEM/EDS. The harvested copper cathodes were weighed and analyzed for impurities concentrations using DC Arc. The adhered slimes and released slimes were collected, weighed, and analyzed for compositions using ICP. It was shown that the lead-to-arsenic ratio in the anodes affects the sintering and coalescence of slime particles. High current density condition can improve anode slime adhesion and cathode purity by intensifying slime particles’ coalescence and dissolving part of the particles. Wide cathode blanks can raise the anodic current densities significantly and result in massive release of large slime particle aggregates, which are not likely to contaminate the cathode copper. Low flow rate can cause anode passivation and increase local temperatures in front of the anode, which leads to very intense sintering and coalescence of slime particles. The results and analyses of the tests present potential solutions for industrial copper electrorefining process.

Thiosulfate leaching of Au, Ag and Pd from a high Sn, Pb and Sb bearing decopperized anode slime

Compared with Au+ and Ag+, Pd2+ is easier to be complexed by S2O32− in ideal situation, based on DFT (density functional theory) calculation. Thermodynamics analysis shows that palladium can also be effectively leached by ammoniacal thiosulfate solution besides gold and silver. The Sn and Sb in a high Au, Ag, Pd, Sn, Pb and Sb bearing decopperized anode slime had no obvious detrimental effect on thiosulfate leaching of the precious metals, but the Pb could cause seriously detrimental impact. Only 37.3% of Au, 69.2% of Ag and 43.8% of Pd in the decopperized anode slime could be extracted by direct thiosulfate leaching. After sodium hydroxide pretreatment where 56.9% of Pb and 13.6% of Sb in the slime were removed, thiosulfate leaching under optimal operating conditions only extracted 68.1% of Au, 81.7% of Ag and 67.6% of Pd in the pretreatment residue. The low extraction is probably because there was a PbO passivation layer on slime particle surfaces. After the carbonate transformation and subsequent acetic acid pretreatment in which 93.8% of Pb in the transforming residue was removed, thiosulfate leaching could extract as much as 88.0% of Au, 93.4% of Ag and 80.7% of Pd in the pretreatment residue. There was no such passivation layer on the surfaces of slime particles during the leaching, attributing to comparatively thorough removal of Pb by the pretreatment.

Simulation Study of Electrolyte Flow and Slime Particle Transport in a Newly Designed Copper Electrorefining Cell

A model based in COMSOL Multiphysics (a finite element analysis software) consisting of a specially designed electrorefining cell was developed to simulate copper electrorefining. This cell has its inlet on the side wall near the cell top and its outlet on the opposite side wall near the cell bottom. The electrolyte enters from the inlet, flows directly into the gap between electrodes, and exits the cell from the bottom outlet. Unlike the flow field in conventional electrorefining cells that have inlets near the cell bottom and outlets near the cell top, the natural convection between electrodes in this cell can be suppressed by the inlet flow, which leads to concurrent downward flows along both the anode and the cathode. Copper concentration profile and fluid density profile were acquired as electrochemical simulation results. Electrolyte flow velocity field, slime particle trajectory, and slime particle distribution were obtained as fluid flow and particle transport simulation results. Features of the copper concentration profile, the electrolyte flow field, and the slime particle transport are discussed. The simulation results of this cell were compared with those of a conventional cell, and some advantages of this cell can be found: copper ions in the cell are more uniformly distributed between electrodes by the strong forced convection; electrode reactions can reach steady state at higher current densities and lower electrolyte copper concentrations; slime particles are more likely to settle to the cell bottom without affecting the cathode purity.

The ignition characteristics and combustion processes of the single coal slime particle under different hot-coflow conditions in N2/O2 atmosphere

The ignition characteristics and combustion processes of single coal slime particle in a vertical heating tube furnace in N2/O2 oxidant atmosphere were investigated under different hot-coflow conditions, including variations in coflow temperature (Tc = 923, 1073, and 1173 K), gas flow rate (V = 0–30 L/min), and oxygen concentration (O2% = 5%–100%). All investigated hot-coflow conditions exhibited three ignition behaviors, homogeneous ignition of volatiles, heterogeneous ignition of char, and heterogeneous ignition of coal. Additionally, three corresponding ignition regimes were observed in the oxygen concentration-coflow temperature plane. Critical conditions for the transitions of the three ignition mechanisms varied as flow was increased from 0 to 30 L/min. Various ignition mechanisms resulted in various combustion processes. Under medium-to-low oxygen concentration and low coflow temperature, the heterogeneous ignition of char resulted in flameless combustion. The ignition temperature and ignition delay decreased as coflow temperature and oxygen concentration were increased. The trends became more obvious when test conditions progressed in medium-to-low oxygen concentrations. As the flow rate increased, ignition temperature and delay became increasingly sensitive to oxygen concentration. Experimental results are then discussed in conjunction with the various observed trends influencing mechanisms of different hot-coflow conditions.

Experimental and Simulation Studies of Electrolyte Flow and Slime Particle Transport in a Pilot Scale Copper Electrorefining Cell

Copper electrorefining tests were conducted in a pilot scale cell made of transparent cell walls, allowing direct observation and microscopic video recording of the electrolyte flow. Fluid flow velocities in the gaps between adjacent anodes and cathodes were measured by analyzing the recorded video using a video analysis and modeling software. Modeling and simulation of copper electrorefining in this cell were performed using COMSOL Multiphysics, a finite element method simulation software. The flow velocity field results from modeling agree reasonably well with the measured electrolyte velocities. The transport of slime particle in electrolyte flow was also simulated and the appearance frequencies of slime particles in the domain within 200 microns from cathode surface at different positions of cathodes were compared with impurity levels in the copper cathodes harvested from experimental tests. The results show good correlation especially with the total concentration of major impurities. Thus the cathodic contamination can be predicted by the slime particle appearance frequency in front of the cathode.

Studies of Anode Slime Sintering/Coalescence and Its Effects on Anode Slime Adhesion and Cathode Purity in Copper Electrorefining

Four series of copper electrorefining tests were performed using four different types of anodes, which have different inclusion types. Test results show that the high impurity anodes and the scrap cycle anodes have more inclusions associated with the Pb-Bi-S compounds that show evidence of sintering at 50°C, whereas the low impurity anodes and the strip cycle anodes have more inclusions related with the Pb-Bi-S-As compounds that demonstrate evidence of sintering above 65°C. Inclusion (slime) particles sinter and adhere to the anode surface, which happens at lower temperatures for the high impurity anodes and the scrap cycle anodes. Correspondingly, there are different slime distributions for each type of anode. The anode slimes layers in front of anode surfaces for different types of anodes were observed and analyzed by SEM/EDS. Results show significant effects of particle sintering near anode surfaces, which was also demonstrated by slime size distributions at different cell temperatures. Experimental results demonstrate that slime particle sintering and coalescence can improve anode slime adhesion and reduce the amount of suspended slimes, which are a major source of copper cathode contamination. Arsenic content in copper anode and cell temperature are major factors affecting slime sintering and coalescence.

The effect of polyether on the separation of pentlandite and serpentine

The effect of polyether on the separation of pentlandite from serpentine has been studied. In addition to flotation and sedimentation tests, electrophoresis and adsorption tests have been conducted. The flotation and sedimentation results show that serpentine impairs flotation performance of pentlandite, by adhering to the pentlandite particles. Addition of the polyether could promote the dispersion of the mixed sample of pentlandite and serpentine in alkaline conditions and significantly reduce adverse effects of serpentine on the pentlandite flotation. The electrophoresis and adsorption tests show that polyether can selectively adsorb onto pentlandite surface through hydrophobic reaction and remove serpentine slime particles from pentlandite surfaces by steric hindrance effect.

Influence of the active mass particle suspension in electrolyte upon corrosion of negative electrode of a lead-acid battery

The influence of the suspension of positive active mass particles in the electrolyte on the performance of the negative electrode in a lead-acid battery is studied. A significant increase in the rate of corrosion of the lead electrode is shown when slime particles get in contact with its surface, which may result in the rise of macro-defects on the lugs of the negative electrodes.

Recovery Improvement of Fine Magnetic Particles by Floc Magnetic Separation

The performance of floc magnetic separation (FMS) has been compared with wet high-intensity magnetic separator (WHIMS). This study was performed on low-grade iron ore slime contained 59.58% Fe with 4.57% silica and 3.78% alumina. Detailed characterization data indicated that a substantial amount of the slime was below 20 µm in size. Beneficiation studies indicated that the FMS process is effective to recover fine hematite and goethite particles, compared with the conventional magnetic separation. In conventional magnetic separation, the extent of the fluid drag force exceeds the magnetic force exerted on ultrafine particles. Thus, ultrafine magnetic particles were usually not recovered effectively by magnetic separators, resulting in the loss of valuable ultrafine slime particles. The FMS process significantly increases the magnetic force on the ultrafine iron ore in the form of hydrophobic flocs in a magnetic field, thus the ultrafine particles can be picked up effectively as magnetic concentrates. The FMS process improved the Fe recovery from 37.35% to 79.60%.

Bound-abrasive grinding and polishing of surfaces of optical materials

Problems of efficiency and quality improvement of diamond-abrasive finishing of optical materials by tools with bounded polishing powders, including diamond powder, are considered. The dependences of the particle number on the diffusion angle and coordinate of the contact have been derived in the studies of the dynamics of collision and diffusion of slime particles. The coordinate dependence of the flat surface roughness of glass K8 optics in fine diamond grinding has been described. Interaction and dispersion of deterioration particles in a contact zone of the tool and the processed sample in the course of polishing is described and the dispersion structure of deterioration particles of the tool on slime particles and on deterioration particles is explained oscillatory. It is shown a that differential dispersion section of deterioration particles on slime particles is not less than on deterioration particles and is maximum at corners of dispersion close to 0° and 180° on the central sites of a contact zone. Coordinate dependence of the full dispersion section of deterioration particles of the tool and dependence of microprofile height of the processed surface on circular zones radius are calculated.

Efeito da dispersão em polpas de minérios itabiríticos

A flotação reversa do minério de ferro é antecedida de uma operação de deslamagem, cuja eficiência aumenta com o uso de um reagente que promova a dispersão da polpa. O trabalho avaliou a influência do tipo e da concentração do dispersante na eficiência da dispersão e nos resultados da flotação. Os resultados foram avaliados em termos de tamanho das partículas da lama, grau de dispersão e Índice de Seletividade de Gaudin, obtido na flotação. Os resultados mostram a importância da dispersão antes da deslamagem e sugerem que o reagente escolhido, como dispersante, não pode ser depressor para o quartzo. O hidróxido de sódio parece ser a melhor alternativa entre os reagentes testados.

Selective Classification of Mineral Sand Slimes in an Air Fluidized Bed

Studies were carried out for selective classification of mineral sands to remove unwanted slimes (particles of <0.63 µm in size). Vertical and arched fluidized bed setups were tested to retain the coarser heavy mineral particles from fluidized mineral sand beds. Theoretically calculated process parameters were used to develop the experimental setups. The mathematical model given by Nguyentranlam and Galvin (“Particle classification in the reflux classifier.” Minerals Engineering, 14(9), 2001, pp. 1081–1091) was used to develop an arched fluidized bed setup. Experiments were carried out at six different superficial air velocities (0.21, 0.25, 0.34, 0.41, 0.64, and 0.82 m/s) in the vertical and arched fluidized bed setups. An acceptable agreement was found in the experimental and theoretical results. The overall process capability of the vertical fluidized bed to selectively remove the slimes was 44.8% with the loss of 3.93% of heavy minerals. The overall process capability was improved up to 52% with the loss of 4.08% of heavy minerals by the proposed arched fluidized bed setup. The developed arched fluidized bed setup showed improved performance for selective elutriation of mineral sand slime particles with compromising heavy mineral losses.

The effect of iron contaminants on thiosulphate leaching of gold

Metallic iron and ferric ions were subjected to wet grinding with a sulphide ore in a ceramic ball mill to simulate the fine grinding process using mild steel, in an attempt to investigate the effect of iron species on the ammoniacal thiosulphate leaching of gold. Metallic iron and ferric ions decreased gold leaching in both kinetics and overall extraction when they were added in the wet grinding of a sulphide ore. This detrimental effect became more pronounced with the addition of metallic iron and ferric ions at higher concentrations. Metallic iron retarded the gold leaching more than ferric ions at the same dosage. The decomposition of thiosulphate in the leaching of the sulphide ore increased with the addition of metallic iron and ferric ions in the wet grinding. Thermodynamic analysis indicated that the predominant species for iron was ferric hydroxide under the leaching conditions. Wet grinding at a higher pH of 9 and use of ethylenediaminetetraacetic acid (EDTA) were ineffective in improving the gold leaching with the addition of metallic ions and ferric ions in the wet grinding. Iron oxide and hydroxide slime coatings at the surfaces of pyrite and pyrrhotite were reduced using carboxymethyl cellulose (CMC) to render the sulphide and slime particle surfaces highly negatively charged. Precipitation of iron oxide species at the surfaces of pyrite and pyrrhotite was observed in the morphological study of the leach residues with the addition of metallic iron in the wet grinding. The addition of CMC effectively reduced iron oxide slime coating at the sulphide surfaces and the aggregation of fine particles.

Colloidal iron oxide slime coatings and galena particle flotation

Microflotation was used to investigate the influence of colloidal iron oxide “slimes” on galena (PbS) particle flotation. Complementary particle adsorption (heteroaggregation) studies were undertaken to investigate the formation of iron oxide slime coatings and to develop methods for their removal. Trace quantities of hematite (Fe 2O 3) colloids have a significant depressant action on both the collector-induced and collectorless flotation of galena particles. For example, slime particle surface coverage as low as 10% of an equivalent close-packed particle monolayer decreased the flotation rate constant of galena by an order of magnitude. In the pH range 4 to 7, high affinity Fe 2O 3 particle adsorption was observed on PbS and the surface coverage approached that of an equivalent particle monolayer. In contrast, in mildly alkaline solutions, particle adsorption isotherms were of low affinity, with plateau surface coverages significantly less than an equivalent particle monolayer. These observations are discussed in terms of the surface chemistry of galena and slime coating mechanisms. The use of shear, sonication, pH control and chemical reagent addition to quantitatively remove iron oxide slime coatings is also reported. A combination of physical and chemical methods is most effective at iron oxide particle removal and synergistic effects have been observed.

Recovery mechanisms for pentlandite and MgO-bearing gangue minerals in nickel ores from Western Australia

The flotation behaviour of a Western Australian nickel ore was characterised by size-by-size flotation rate tests to extract rate constant information. The aim was to identify the effect of surface interactions on the flotation of the nickel sulphide mineral, pentlandite, with magnesium-silicate bearing minerals (predominantly serpentines). Flotation tests were carried out using collector (amyl xanthate), both with and without the other standard reagents for this ore. In this study the latter were carboxy-methyl cellulose (CMC) and soda ash. The addition of soda ash and CMC was shown to improve pentlandite flotation rate and recovery. Soda ash addition was found to be essential for improving flotation performance, as without it nickel recovery was unacceptably low. It is proposed that carbonate ions, derived from soda ash addition, enhance dispersion in the pulp and that CMC may assist removal of adhering slime particles from pentlandite surfaces. Drawing on the literature in this area, a number of mechanisms are proposed to explain the observed flotation behaviour of gangue magnesium-silicate bearing minerals.

Rheological investigations of sulphide mineral slurries

The flotation separation of ultrafine (−5 μm) sulphide mineral particles is inherently problematic, since even strongly hydrophobic fines have relatively low flotation rate constants. Selective aggregation of fines provides a route for enhanced flotation selectivity, but requires detailed knowledge and ultimately control of the electrostatic and hydrophobic inter-particle forces acting in concentrated sulphide mineral slurries. Rheological investigations offer insight into these inter-particle interactions. Rheological studies of ultrafine sphalerite particle slurries at pulp densities akin to those experienced in flotation practice were undertaken; the influence of pH, electrolyte concentration, activating copper (II) ions and ethyl xanthate ions on the level of pulp aggregation, as defined by the yield values and viscosities, are reported. The rheological behaviour of oxidised, and effectively hydrophillic, sphalerite particles (in the pH range 4 to 10) are controlled by electrostatic repulsive forces and yield values scale inversely with electrophoretic mobilities. Copper (II) activation, ethyl xanthate treatment and addition of slime particles dramatically affect pulp rheology and, depending on the particular concentrations and conditions employed, cause either aggregation or dispersion of the pulp. We show that an understanding of the theological behaviour of sulphide mineral pulps enhance our knowledge of particle-particle (and bubble-particle interactions) and may enable fine particle flotation performance to be optimised.

Carrier Coagulation of Chromite Fines in Wet Magnetic Separation

A "carrier" or "piggy–back" coagulation process was applied to improve the separation efficiency of chromite slimes in wet high–gradient magnetic separation. This was achieved by the addition of a coarse chromite fraction to the slime fraction (&lt; 10 mm). Three coarse chromite fractions were investigated in the present study with size ranges &lt;106&gt;75, &lt;75&gt;53 and &lt;53&gt;38 μm. The results suggested that the &lt;53&gt;38 μm coarse fraction was the most effective in improving the process efficiency. Superior performance was also found to occur between pH 5 and 6. The results were discussed by computing the various components for potential energy of interaction between the slime particles and the "carrier" or "piggy‐back" particles at a range of surface potentials in the absence or presence of the magnetic field.

Mineralogical Characterization of Anode Slimes: Part 7—Copper Anodes and Anode Slimes From the Chuquicamata Division of Codelco–Chile

Copper anodes and anode slimes from the Chuquicamata Division of Codelco-Chile were examined mineralogically. The copper matrix of the anodes contains most of the Ag and much of the As and Sb in solid solution. Numerous inclusions are present at the copper grain boundaries, and these consist mostly of Cu2O although grains of Cu2O–Cu2Se and Cu2O–Cu2 Se–(Cu–Sb–As oxide) also are present. The Cu2Se has a significant solid solution Te and S content. The anode slimes consist principally of an oxidate matrix phase which agglomerates or cements the finer slimes particles. The oxidate matrix phase is a complex Cu–Ag arsenate-antimonate-selenite (or selenate)-sulphate--ehloride although many of the particles approximate copper arsenate in composition. Silver is present in the oxidate matrix phase, and seems to substitute for Cu in some grains of CuSO4·5H2O. Metallic silver is present as sponge-like masses and as <0.5 μm spheroidal grains which are commonly embedded in CuSO4·5H2O. Silver chloride occurs on masses of the oxidate matrix phase and as tiny isolated particles. Much of the silver, however, occurs as Ag2Se or (Ag, Cu) 2Se. Gold is readily detected as a <1 μm film of Au or Au-rich Au–Ag selenide on fragments of Ag2Se or as <1 μm inclusions in some of the selenide particles. Surprising is the presence of trace amounts of Cu sulphides, Cu–Ag sulphides and porous masses of Ag–Cu telluride–sulphide. Résumé Une analyse minéralogique des boues anodiques et des anodes de cuivre provenant de la Division Chuquicamata de Codelco–Chile a été effectuée. L'anode de cuivre contient la majeure partie de l'argent et beaucoup d'arsenic et d'étain en solution solide. Plusieurs inclusions sont situées le long des joints de grains du cuivre. Elles sont principalement composees de CuO, bien que Cu2O–Cu2Se et Cu2O–Cu2Se–(Cu–Sb–As oxyde) soient aussi presents. Le Cu2Se a une teneur importante en Te et S en solution solide. Les boues anodiques sont principalement composées d'une matrice d'oxydate liant les particules les plus fines. La matrice d'oxydate est un complexe Cu–Ag.

Review of methods of improving mineral liberation

Most of the important developments in comminution have been aimed at reducing its high operating costs. However, the most important role of comminution in the minerals industry is not merely to reduce particle size, but to liberate minerals from each other. Conventional methods liberate relatively inefficiently, due to the indiscriminate nature of the breakage process. Inadequate mineral liberation in itself leads to higher operating costs, as finer grinding has to be performed to achieve an adequate degree of liberation, and this can lead to the generation of ultra-fine slimes particles, which may be lost in the downstream process. This paper reviews the methods that have been researched in order to enhance mineral liberation by directing comminution energy to grain boundaries in order to promote intergranular rather than transgranular fracture.

Mineralogical Characterization of Anode Slimes: Part 6—Pressure Leached Slimes From the CCR Division of Noranda Minerals Inc.

AbstractThe raw anode slimes from the copper refinery of the CCR Division of Noranda Minerals Inc. consist principally of AgCuSe, (Ag,Cu)2Se, PbSO4, BaSO4, CuSO4·5H2O and an oxidate matrix phase which agglomerates the slimes particles. The principal silver carriers are the selenides; minor amounts of Ag occur in the copper sulphate, in the oxidate matrix phase and as tiny inclusions of Ag-Sb chloride in CuSO4. Only traces of silver powder are present. The dominant tellurium carrier is the selenide phase in which Te replaces Se; minor amounts of Te also are present in the oxidate matrix phase. During O2-H2SO4 pressure leaching at 180°C, significant amounts of Cu, Ni, Ag, Se and Te are solubilized with the subsequent formation of Ag2SO4, Ag2Se and a silver-rich oxidate matrix phase different in composition from that in the raw anode slimes. Most of the Te reports as tellurate or tellurite in the oxidate matrix phase although minor amounts remain in solid solution in the Ag2Se. Oxygen pressure leaching of th...