Surface Of Mineral Particles Research Articles

Modeling flocculation of colloidal mineral suspensions using population balances

Flocculation as well as dispersion of mineral suspensions has become increasingly important in mineral processing as we have to deal with fine and ultrafine particles. Population balance models for flocculation of such suspensions are discussed in this paper. Models ranging from those based on pure aggregation and fragmentation to those based on simultaneous aggregation–fragmentation are presented in detail. The two important parameters in the population balance model are the collision frequency factor and the collision efficiency factor. Differences among collision frequency models for impermeable and permeable aggregates are described. The main drawback of existing flocculation models is the disregard of forces between mineral particle surfaces. The collision efficiency is usually assumed to be unity or employed as a fitting parameter in a majority of the models. An approach for incorporating the influence of surface forces in the presence of salts and polymers is outlined. Another important lacuna of flocculation models is the assumption of homogeneous flow structure or uniform fluid velocity gradient in stirred flocculation tanks. Short-cut procedures adopted in the literature to address heterogeneous fluid flow structure are summarized. It is also stressed that an integrated approach be followed to tackle practically relevant issues such as selective flocculation of mineral mixtures, dual polymer flocculation, dynamics of polymer/surfactant adsorption, polymer–surfactant interactions, surface precipitation of dissolved species and presence of air bubbles in the suspension.

Enrichment adsorption of a labile substance to the surface of particular mineral particles in river water as investigated by SEM-EDX and dilute-acid extraction/ICP-MS.

The selective enrichment behavior of a labile substance, such as hydroxides, to the surface of particular mineral particles in river water was clarified by scanning electron microscopy/energy dispersive X-ray microanalysis (SEM-EDX). Individual particles other than diatom collected on a 0.45 microm filter from the Fuji and Sagami rivers, central Japan, were analyzed by SEM-EDX and classified into seventeen groups according to the chemical composition and shape. Phosphorus, sulfur, chlorine, manganese and copper detected in each particle collected on the 0.45 microm filter could be successfully used as effective indicators of labile substance secondarily formed and adsorbed afresh in river water, because the detection frequencies of such elements are quite low, or negligible, in fresh mineral particles derived from igneous rocks. The labile substance adsorbed on mineral particles collected on the 0.45 microm filter was also evaluated by dilute-acid leaching, followed by inductively coupled plasma mass spectrometry (ICP-MS). Almost all parts of the manganese detected in individual particles were those adsorbed afresh as hydroxides together with iron and aluminum. Also, anionic elements, such as phosphorus, sulfur and chlorine, formed complexes with the hydroxides and/or were incorporated in them. Mg and/or Ca-rich aluminosilicate groups were the most effective adsorbers of such labile species. However, Si-rich and Na-, K- and Na-Ca rich aluminosilicates did not significantly adsorb the labile substance. Consequently, the remarkable selectivity was clarified in the adsorption process of labile substance to individual mineral particles in river water.

Control of a flotation column using fuzzy logic inference

This paper describes a fuzzy controller that was developed for the control, in real time, of three main variables of the column flotation process. Column flotation is a solid–solid separation process based on the physical and chemical properties of mineral particle surfaces. It is applied to the concentration of low grade ores and to ores that require very fine grinding to achieve mineral liberation. The economic exploitation of the process, guaranteeing the desired final product characteristics from a feed of varying composition, requires a stable operation, which is accomplished through the automatic control of some key process variables. The difficulties encountered in the development of process controllers for this process are related to the lack of reliable measuring devices for the process variables involved, with the non-existence of mathematical dynamical models that can be used in a controller synthesis and with its non-linear and time-varying behaviour. The process and the problems related with its control are briefly explained and the main reasons for fuzzy logic control application are discussed. The real time control system and the fuzzy controller structure and parameters are presented. A general overview of the pilot plant where the experimental work was performed is presented. Finally, results of the experimental work, carried out with the two-phase system (air and water), are summarised and the conclusions are drawn.

Correlations between the shear strength of mineral filter cakes and particle size and surface tension

In this study the shear strength of filter cakes of various minerals such as dolomite, calcite, quartz and kaolin was investigated. Shear strength of the mineral filter cakes are influenced by the particle size and shape and surface tension as well as the applied pressure and saturation degree. As the particle size decreases the shear strength increases very sharply. The relation between the shear strength and the particle size has been found as: τ shear= K/ x 0.6. The decrease of the surface tension of the mineral suspension causes to decrease of the shear strength of the cake to a large extend.

Comparison of Radio-Frequency-Plasma- and Ion-Beam-Induced Surface Modification of Kaolinite

Modification of the surface of kaolinite mineral particles was carried out in nitrogen, argon, helium, and air environments using the radio frequency (RF) plasma technique. The modified surfaces of the kaolinite were investigated by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) to determine the surface speciation, the nature of the newly formed surface functional groups, and the interaction mechanism between the RF plasma and the kaolinite surface. Comparison with Ar+ ion beam modification of kaolinite has established that the surfaces of kaolinite undergo low-energy ion bombardment with very limited sputtering in the presence of the Ar plasma but with no observable ion implantation. Surface restructuring with modified bonding is implied by this evidence. The steady-state charge behavior and surface structure of the kaolinite processed in the RF plasma showed significantly different characteristics from those of both the untreated kaolinite and an ion-beam-treated kaolinite. New infrared (IR) absorption bands were observed on the surfaces of RF-plasma-treated kaolinite at 1407, 2805, 3010, and 3100 cm-1, along with some broad, partially resolved absorption bands which occurred near 1440 and 3280 cm-1. The intensities of the newly formed IR bands were a function of the period of plasma treatment and the energy applied but were generally independent of the nature of the gas used for the plasma treatment. They are attributed to plasma-induced surface species arising from hydrocarbon contamination in the gas phase. In contrast to ion beam modification, the skeletal vibrations of the kaolinite lattice are not measurably affected in plasma treatments implying that restructuring, giving rise to the new IR bands, is confined to the surface layers.

Effect of the clay minerals montmorillonite and kaolinite on the genetic transformation of competentBacillus subtilis cells

The effect of the clay minerals montmorillonite and kaolinite on the transformation of competentBacillus subtilis cells with chromosomal DNA was studied. Clay particles were found to substantially increase the transformation frequency of competent cells, as well as the rate of their spontaneous chromosomal and plasmid transformation. The effect was ascribed to the adsorption of bacterial cells on the surface of mineral particles.

INTRACELLULAR SURFACTANT REMOVAL FROM PHAGOCYTIZED MINERALS: Development of a Fluorescent Method Using a BODIPY-Labeled Phospholipid

Lung surfactant serves as a protective coating when adsorbed on particle surfaces, so its removal or rate of removal in vivo may affect expression of mineral cytotoxicity. Removal of phospholipid surfactant components from the surface of mineral particles ingested by alveolar macrophages (AM) was measured using fluorescence microscopy. Dipalmitoylphosphatidylcholine with a fluorescent label (BODIPY) substituted for C1-C4 on the second acyl chain (DPPC*), was mixed with dioleoylphosphatidylcholine (DOPC) to coat respirable quartz and kaolin particles. Fluorescence from quartz or kaolin particles of 3-4, 5-6 and 8-9 µm size decreased in intensity with increasing ratios of DOPC/DPPC* for the same DOPC concentration of 0.4 mg/ml. There was a direct correlation between fluorescence and residual phospholipid surfactant remaining on particles using phospholipase A2 (PLA2) digestion in a cell-free system, indicating that the presence of the fluorophore on DPPC did not hinder enzymatic recognition. Lavaged primary AM obtained from male Fischer rats were challenged in vitro with DOPC/DPPC* (10:1 mol:mol) coated particles at 50 µg particles/106 cells. In contrast to the biexponential response seen in cell-free experiments, the rate of fluorescence decay from ingested coated quartz or kaolin particles over 7 days was monoexponential, with the same t1/2 (41 h) for each dust. This study suggests that the rate of phagolysosomal digestion and removal of the adsorbed surfactant is not a determinant of the different mineral-specific pathogenicities or toxicities of quartz and kaolin, although residual fluorescence remained on particles even after 7-8 days.

Rheological Investigations of DLVO and Non-DLVO Particle Interactions in Concentrated Mineral Suspensions

The rheological behaviour of galena, sphalerite and gibbsite mineral particle suspensions has been studied using a concentric cylinder rheometer. The influence of pulp density, pH, salt concentration and processing reagents on the rheology and particle interaction behaviour is reported. The Bingham or extrapolated yield value is used to characterise particle interactions in both a qualitative and quantitative manner. For many mineral suspensions, over a wide range of conditions, the rheological behaviour can be described in terms of electrostatic and dispersive interactions, i.e., DLVO behaviour. In some circumstances however, non-DLVO interactions are observed, the sign and magnitude of these depend primarily on the mineral particle surface chemistry. For ultrafine galena (PbS) particle suspensions an attractive, non-DLVO interaction is observed which increases with decreasing pH. This finding correlated with flotation behaviour and a hydrophobic interaction was confirmed. For colloidal gibbsite (Al(OH)3) suspensions a repulsive non-DLVO interaction becomes apparent at pH values greater than 10. Hydration or steric interactions are thought to be responsible for this behaviour.

The effect of high intensity conditioning on the flotation of a nickel ore, part 2: Mechanisms

It has been found that High Intensity Conditioning (HIC) significantly increases the flotation rate of pentlandite from a nickel ore. A systematic investigation of slime surface coatings and the effect of HIC on surface cleaning of the nickel ore was carried out using Scanning Electron Microscopy (SEM), Image Analysis, X-ray Diffraction (XRD), and a sieving technique. The sieving technique was established to semi-quantitatively determine the state of slime (< 3 to 5 μm) surface coatings using a combination of sieving and laser diffraction particle size analysis. It was found that hydrophilic gangue slimes were present on both pentlandite and gangue mineral surfaces prior to HIC. The surface coating by the slime mineral particles was apparently non-selective towards any particular mineral. High intensity Conditioning removed slimes from the mineral particle surfaces, the amount removed depending upon both agitation intensity and time.

The ferric leaching kinetics of arsenopyrite

In this investigation batch, ferric leaching experiments were carried out in a 100 mℓ jacketed vessel maintained at 25°C. The parameters varied during the course of the experimental program included the initial redox potential, the total iron concentration, the solids concentration and the pH of the leaching solution. The initial redox potential used ranged from 625 to 470 mV, the overall iron concentration ranged from 8 to 32 g.ℓ −1, the mineral concentration ranged from 5 to 20 g.ℓ −1 and the initial pH used ranged from 1.10 to 1.45. The redox potential of the leach solution was monitored continuously using a redox probe connected to a computer. The leach rates were calculated from the measured change in the redox potential of the leaching solution. The variation in the ferric leaching rate of the arsenopyrite as a function of the solution redox potential displayed similar trends, irrespective of the conditions employed. The ferric leaching rate of the arsenopyrite decreased with decreasing redox potential of the leaching solution and could be accurately described using a modified Butler–Volmer equation; − r Fe 2+ = r 0(e αβ( E− E′) −e (1− α( β( E− E′) ). High concentrations of ferric iron and protons, and a reduction in the solids concentration were found to impede the leach rate. The `rest potential' ( i.e., the redox potential at which the dissolution of arsenopyrite stops) of the arsenopyrite was found to be higher under these conditions. However, no occluding sulphur layer could be detected on the surface of mineral particles, hence the results suggest that the reactivity of the mineral decreases with an increase in the effective concentration of the ferric iron species. Therefore, although the results suggest the likelihood of an electrochemical mechanism being operative, it is necessary to modify the Butler–Volmer-based model to account for the above observations in order to obtain a model capable of predicting the ferric leaching rate of arsenopyrite across a broad range of operating conditions.

Surface analysis of particles in mine tailings by time-of-flight laser-ionization mass spectrometry (TOF-LIMS)

Time-of-flight laser-ionization mass spectrometry was applied to study the chemical composition of mineral particle surfaces in a sulphide-rich mine-tailings impoundment. This surface-sensitive technique provides chemical information from surfaces of irregularly shaped mineral particles (both conductive and insulators) less than 100 μm in diameter, which are considered to be representative of particle surface coatings in the tailings pile (after drying). In addition, depth profiles in the mineral particles were obtained. The combination of speed of analysis (1 min), small beam-diameter (2–4 μm), surface sensitivity (2–10 nm), trace-element sensitivity, and capability to analyze rough surfaces makes this method useful as a complement to studies of pore-water geochemistry and tailings mineralogy. As an example, the behavior of Pb and As in the Kidd Creek tailings dam near Timmins, Ontario, Canada, was studied, using a combination of surface analyses, and pore-water geochemical data.

Mathematical modelling of the transient behaviour of cstrs with reactive particulates: Part 2 — Application to pyrite pressure oxidation

AbstractA population balance based transient reactor model is applied to a particulate process employed in the hydrometallurgical industry. The process is the pressure oxidation of pyritic concentrates, pertinent to the treatment of refractory gold materials. The chemical reaction system involves first an oxygen gas to aqueous mass transfer step, followed by a chemical reaction on the surface of mineral particles. The chemical reactor stimulated is a multi‐stage continuous autoclave with variable compartment size. The model accounts for recycling oxidized solids, as well as for venting the gas phase. A complex system of partial and non‐linear ordinary differential equations is rendered dimensionless and solved by a method developed previously using the Mathematica® software. The transient response of the reactor to different modes of reactor start‐up, as well as the response to a step change of a key variable, are examined. The validity of the steady‐state solution is assessed by comparing it to previous modelling attempts.

Surface and Electrokinetic Properties of Clays and Other Mineral Particles, Untreated and Treated with Organic or Inorganic Cations

Abstract The apolar (Lifshitz van der Waals)component (yLW) and the polar [electron-acceptor (y ) and electron-donor (y ) ] parameters of the surface tension of more than sixty different clay and other mineral particles or surfaces have been measured, as well as their -potentials. It is essentially the y parameter that determines the hydrophobic (target;⩾y28 mJ/m1)or hydrophilicy ( y target;⩾28 mJ/mJ) character of the mineral surface. The surface properties were measured for twelve ion exchanged smectites, as a funclion of substitution with various alkali and alkalin earth cations. The hydrophobizing influence of exchanged organic cations on the surface properties of a number of clay particles is also determined. Finally, the hydrophobizing influence of plurivalent cations is demonstrated with Ca2+and La 3+for three different negatively charged mineral particles.

Binding of adenine and adenine-related compounds to the clay montmorillonite and the mineral hydroxylapatite.

The first living things may have consisted of no more than RNA or RNA-like molecules bound to the surfaces of mineral particles. A key aspect of this theory is that these mineral particles have binding sites for RNA and its prebiotic precursors. The object of this study is to explore the binding properties of two of the best studied minerals, montmorillonite and hydroxylapatite, for possible precursors of RNA. The list of compounds investigated includes purines, pyrimidines, nucleosides, nucleotides, nucleotide coenzymes, diaminomaleonitrile and aminoimidazole carboxamide. Affinities for hydroxylapatite are dominated by ionic interactions between negatively charged small molecules and positively charged sites in the mineral. Binding to montmorillonite presents a more complex picture. These clay particles have a high affinity for organic ring structures which is augmented if they are positively charged. This binding probably takes place on the negatively charged faces of these sheet-like clay particles. Additional binding sites on the edges of these sheets have a moderate affinity for negatively charged molecules. Small molecules that bind to these minerals sometimes bind independently to sites on the minerals and sometimes bind cooperatively with favorable interactions between the bound molecules.

Study of the impedance of a galena electrode under conditions similar to those used in sulphide minerals flotation—II. Effect of oxygen bubbling

Abstract The influence of oxygen bubbling on the impedance of a natural galena electrode in alkaline solution without xanthate was studied. As in the absence of oxygen, the unusual potential dependence of the impedance may be explained by the growth of an oxidized film. This confirms that the anodic reaction contributing to the formation of a mixed potential at the surface of mineral particles during their flotation is the oxidation of galena forming a film. The distortion of the impedance behaviour in the presence of oxygen related to its reduction, the cathodic reaction forming the mixed potential, is qualitatively explained in the light of the new approach by changes in the film structure and perturbations in the transport vacancies in the film due to the presence of new reactions at both its interfaces. The appearance of a constant phase element (cpe) for only the most cathodic potentials also leads us to propose new insights for the origin of cpe at solid electrodes.

The Effect of Grinding Media and Environment on the Surface Properties and Flotation Behaviour of Sulfide Minerals

After the techniques for studying the alteration of surface and bulk properties of mineral particles caused by grinding have been presented, the influence of grinding media and environment on the surface properties, pulp chemistry and flotation behaviour of sulfide minerals is reviewed. It is shown that grinding media and environment affect the surface properties and floatability of sulfide minerals mainly through the following three aspects: electrochemical interaction, surface morphology and mechano-chemical reaction. When sulfides and grinding media are in contact with each other, galvanic cells are formed and redox reactions take place due to the differences in the open-circuit potentials of sulfide minerals and grinding media. The galvanic reactions are controlled by the mixed-potential principle. Materials with lower open-circuit potentials act as anodes and undergo surface oxidation. The floatability of sulfides and thereby the selectivity of separation can be either improved or deteriorated. Parti...

An approach to the essence of soil fertility

AbstractAfter a brief historical review of the study of soil fertility it is shown that in studying the essence of soil fertility, both the „physique”︁ and the „pedon structure”︁ of soil should be investigated. Under proper cultivation and fertilization, it is possible to maintain and enhance the level of fertility of black soils. Humic substances combined with the surface of mineral particles are the soil constituents restricting the fertility of black soils, and may be used as the main index to characterize the level of fertility of these soils. The humification and turnover of organic matter are regulated by the soil enzymes. The enzymatic activities in black soils form an important supplementary index of their fertility status. Soil particles aggregating more stable and forming a looser fabric play an important role in maintaining and harmonizing the status of soil moisture, nutrients, air and heat throughout the soil profile. The resistance power or self‐regulating capability of soil against unfavourable factors is an overall index reflecting the essence of soil fertility.

Populations of Spore-forming Bacteria in an Acid Forest Soil, with Special Reference to Bacillus subtilis

The distribution of Bacillus subtilis in a pine-forest soil has been investigated by using the fluorescent-antibody technique and dilution plating. In the acid, mineral horizon of the soil, the organism occurred mainly in the vegetative condition, while in the alkaline, mineral horizon it was mostly present as spores. Within these soil horizons, the bulk of the vegetative bacteria was found on organic matter particles, but of those found on mineral particle surfaces, almost all were on cryptocrystalline quartz particles with iron oxide inclusions.

The quantitative determination of flotation agents adsorbed on mineral powders, using differential thermal analysis

A quantitative method of estimating adsorbed flotation agents on the surface of mineral particles has been developed. The technique involves heating ca. 100-mg samples of the conditioned material under an oxygen atmosphere, using a DTA apparatus; heat liberated by combustion of the flotation agent gives a direct measure of the amount of adsorbate present. In this way, it is possible to estimate either dodecylamine or oleate adsorbed on titanium dioxide down to 0.1 mg g −1.

Reactivity of Ultrafine Powders Produced from Siliceous Rocks

Siliceous materials such as quartz and basic or devitrified volcanic rocks, which are not likely sources of active pozzolan, become highly reactive when ground to ultrafine powders. If grinding is sufficiently prolonged an upper limit of activity is attained, beyond which continued increase in surface area does not produce any further general increase in pozzolanic reactivity. With widely differing types of siliceous material the upper limit of pozzolanic reactivity attained at very high surface areas tends to be the same in all cases, regardless of whether the mineral powders would be classed as pozzolanic, weakly pozzolanic, or nonpozzolanic when ground to the usual fineness specified for pozzolans. These observations can be explained by the presence of a disturbed layer of highly reactive material which is formed on the surface of siliceous mineral particles as a result of prolonged grinding .