Chrysotile Particles Research Articles

Effect of pulp rheology on flotation of nickel sulphide ore with fibrous gangue particles

Tests are carried out with suspensions of fibrous chrysotile particles and nickel sulphide ore containing chrysotile as a gangue. They corroborate published results, and indicate a very strong effect of particle shape on slurry rheology. Such suspensions exhibit time dependent properties. The flotation tests revealed that the viscosity of this system strongly affects flotation performance. At a solids concentration of 15–20% (w/w), the concentrate yield increases and the concentrate grade dramatically declines. This deterioration is observed when the Casson yield stress exceeds 1·5–2 Pa. The tests imply that the rheological properties of the investigated system are mainly determined by fibrous components. However, because of the presence of anisotropic mineral particles, the effect of particle–particle interactions cannot be separated from the effect of particle shape in this system.On effectue des essais avec des suspensions de particules fibreuses de serpentine et de minerai de sulfure de nickel contenant de la serpentine comme gangue. Ces essais confirment les résultats publiés et indiquent un effet très prononcé de la forme des particules sur la rhéologie de la boue. De telles suspensions exhibent des propriétés dépendantes du temps. Les essais de flottation ont révélé que la viscosité de ce système affecte grandement le rendement de la flottation. À une concentration en solides de 15 à 20% (poids/poids), la production de concentré augmente et la qualité du concentré décline dramatiquement. Cette détérioration est observée lorsque la contrainte de Casson excède 1·5 à 2 Pa. Les essais impliquent que les propriétés rhéologiques du système étudié sont déterminées principalement par les composantes fibreuses. Cependant, à cause de la présence de particules minérales anisotropes, on ne peut pas séparer l’effet des interactions particule-particule de l’effet de la forme des particules dans ce système.

Effects of in Vitro Exposure to Chrysotile Particles or Sodium Nitrite on the Production of Eosinophil Chemotactic Substance by Guinea Pig Peritoneal Macrophages

Effects of in Vitro Exposure to Chrysotile Particles or Sodium Nitrite on the Production of Eosinophil Chemotactic Substance by Guinea Pig Peritoneal Macrophages

The effects of chrysotile mineralogical properties on the rheology of chrysotile suspensions

Chrysotile (serpentine) is a phyllosilicate mineral that occurs as a major gangue mineral in many ores (e.g. Mt. Keith nickel sulphide ore, Western Australia). It is believed that the distinctive morphology and electrical surface charge of chrysotile particles are central to the problematic rheological behaviour and low solids throughput typically experienced in the processing of such ores. This study investigates the effects of both these factors on the rheology of chrysotile suspensions. Chrysotile particles were found to carry a net positive charge over the range pH 2–11, with an apparent point of zero charge at pH 8.23. This is a direct result of the convoluted mineral structure of chrysotile fibres, which comprise a positively charged brucite outer layer. The disparity in the point of zero charge and range of maximum yield stress for chrysotile is consistent with the anisotropic nature of chrysotile particles. The long, thin fibres are easily entangled to form suspensions with much higher plastic viscosities and Bingham yield stresses than non-fibrous particles. Although chrysotile shape and surface charge are fundamental to the rheology of chrysotile suspensions, it was found that shape plays a more significant role.

Structure and characteristics of chitosan-based fibers containing chrysotile and halloysite

With the use of the methods of X-ray diffraction and electron microscopy, chitosan fibers prepared by coagulation into an alcohol-alkali mixture are shown to possess a two-phase structure containing C- and O-type crystallites. These fibers and composite fibers containing halloysite and Mg chrysotile nanotubes are characterized by anisotropic structure, i.e., by the orientation of both chitosan crystallites and Mg chrysotile particles along the fiber axis. A comparison of the rates of shear induced by passing of a polymer solution through a die and the data of rheological studies allows the conclusion that the structuring of chitosan solution under the applied field of shear stresses and the orientation of polymer macromolecules and filler nanotubes occur. An increase in the draw ratio during fiber spinning does not assist orientation of polymer crystallites but, in contrast, increases surface defectiveness and leads to the nucleation of longitudinal cracks; as a result, the strength of fibers decreases. The introduction of 5 wt % Mg chrysotile into the chitosan matrix markedly increases the mechanical characteristics of the composite fibers owing to the reinforcing action of oriented filler nanotubes.

Thermal decomposition of chrysotile-containing wastes in a water vapor atmosphere

A simple thermal decomposition technique to convert asbestos-containing wastes (ACWs) into non-asbestos products has been developed by heating ACWs in a water vapor atmosphere. It was confirmed that cement slates containing 18 mass % chrysotile were converted into non-asbestos products by the thermal treatment in a water vapor atmosphere at 800°C for 2 h. In contrast, the thermal treatments in air required temperatures as high as 900°C to convert the cement slates into non-asbestos products. It should be noted that any chrysotile particles were not detected by the phase-contrast microscopic observation in the products after the thermal treatments in a water vapor atmosphere at temperatures beyond 800°C but three or less chrysotile particles remained after the thermal treatments in air at high temperatures beyond 900°C. In a water vapor atmosphere, ACWs were successfully converted into non-asbestos products at low temperatures below 800°C for 2 h by accelerated solid-state reactions between decomposed products of chrysotile and cement components to form calcium magnesium silicates. This technique may contribute to large-scale decomposition of ACWs with low energy consumption in comparison with the traditional melting method.

Formation of Ultra-Thin Nanotubular Chrysotile Particles and Their Thermal Properties

A simple method of forming ultra-thin chrysotile nanotubes was developed. A solution of MgCl2 and NaOH was treated hydrothermally in the presence of silica or silicate glasses. The thinnest tubular particles, containing pores with an inner diameter of 8–10 nm, an outer diameter of ca. 15 nm and length ca. 150 nm, were formed in the Mg-rich systems. As the NaOH content in the system was increased, the wall thickness increased while the outer diameter was unchanged, i.e. the inner pore size decreased. Newly formed chrysotile decomposed at ca. 500°C, i.e.between the corresponding temperatures for Mg(OH)2 (350°C) and natural chrysotile (600° C). The mesoporosity of the nanotubes was confirmed by the appearance of hysteresis loops in both nitrogen adsorption and water vapour adsorption measurements. Heat treatment led to a narrowing of the pore edges and brought about the sealing of the tube ends. Nitrogen and water adsorption measurements were also performed to analyze the effect of heat treatment on the poro...

Evaluation of Heated Chrysotile Using Phase-Contrast Microscope

According to XED analysis, the chrysotile changed to an amorphous phase after heating at 600°C for 3 h. With heating at temperatures exceeding 700°C, chrysotile changed to forsterite. After heating at 1000°C for 3 h, observation by phase-contrast microscopy revealed that only a very small number of chrysotile particles remained in the sample. In contrast, treating of the JIS A 1481: 2006 sample under the same conditions (1000°C, 3 h) resulted in the complete disappearance of chrysotile particles.

Chestnut bur-shaped aggregates of chrysotile particles enable inoculation of Escherichia coli cells with plasmid DNA.

In the present study, Escherichia coli cells exhibited antibiotic resistance after transformation with exogenous plasmid DNA adsorbed onto chrysotile particles during agar-exposure. We previously demonstrated penetration of E. coli by chrysotile particles during agar-exposure. To further investigate the mechanism by which transformation of E. coli is achieved through the use of chrysotile fibers, the interaction between E. coli cells and chrysotile was examined during agar-exposure. Dispersion of chrysotile particles within the chrysotile solution was analyzed by flow cytometry. A suspension containing E. coli cells expressing blue fluorescence protein and chrysotile particles was exposed to agar using stirring apparatus, which allowed a constant vertical reaction force to be applied to the surface of the gel. Fluorescence microscopy was then used to illustrate the adsorption of fluorescein isothiocyanate-conjugated DNA oligomers to chrysotile. Larger aggregates were observed when increasing concentrations of chrysotile were added to the solution. With prolonged exposure, during which surface moisture diffused into the agar gel, greater concentrations of chrysotile were observed on the agar surface. In addition, chrysotile aggregates exceeding 50 microm developed on the agar surface. They were shaped like a chestnut bur. The chrysotile aggregates penetrated the cell membranes of adherent E. coli cells during agar-exposure due to sliding friction forces generated at the interface of the agar and the stirring stick. E. coli cells thus acquired plasmid DNA and antibiotic resistance, since the plasmid DNA had been adsorbed onto the chrysotile particles. The inoculation of plasmid DNA into E. coli cells demonstrates the usefulness of chrysotile for E. coli transformation.

Asbestos Particle Characteristics Important for the Filter Cake Formation

AbstractTwo types of asbestos fiber, chrysotile and amosite, form filter cakes of different permeabilities while having a similar degree of dispersion.The filter cake resistance depends on the disperse phase characteristics and the conditions of cake formation. The main reason for the effects mentioned is different particle flexibility influenced by the specific structure of each type of asbestos particle.The flexible chrysotile fibers in the cake form dense and rigid, amosite, porous deposits. An increase in the velocity of the suspended chrysotile particles, caused by pressure difference and agitation, results in significant differences in filter cake resistance.

Commentary: Asbestos Fibers in the Colonic Wall

As part of a long-term study, rats were fed a standard diet consisting of 65% cellulose, some casein, and a salt mix together with 6% of fairly pure chrysotile. After 3 months on this diet some of the rats were sacrificed and their colonic mucosa examined with the electron microscope. Two types of fixation were used: potassium permanganate and osmium. The permanganate gives very little cellular detail, but this is ideal in scanning large numbers of fields for asbestos fibers. The small chrysotile particles were easily distinguished by the typical concentric double tubule structure. These particles were found in the mucus of the goblet cells, within the cytoplasm of the epithelial cells, and down into the smooth muscle layers. We tried to eliminate the possibility of these findings being artifacts. Many of the fibers appeared in seciton, indicating that they had been embedded in the tissue at an angle to the knife and were genuine cell enclosures. To eliminate the possibility that fibers from the lumen of the gastrointestinal tract had been pushed into the section, we eliminated asbestos from the diet of other rats for 3 days, at which time no fibers could be found in the feces. Particles were still present in the tissues, although in smaller numbers, probably due to clearance processes. It was interesting to note that we could find no membrane surrounding the fibers in the cells; the fibers did not appear to be situated in lysosomes or phagosomes. This is in line with another study that we performed, looking at phagocytes with asbestos, in which some of the fibers appeared to be in the cytoplasm and not bounded by a membrane. Continued observation of the surviving rats did not reveal the development of any tumors. In another experiment we placed pellets of chrysotile in the pleural space of rats. After some months the pellets were organized by fibroblasts and invaded by histiocytes. Within the histiocytes we found phagocytic vacuoles containing asbestos. We also found that the characteristic structure of the chrysotile changed gradually, becoming amorphous. We postulated that some of the magnesium or silicate had been removed. We checked this by putting some chrysotile in an acid medium and found that there was leaching when the fibers were examined by the electron microscope. With appropriate staining methods we concluded that chrysotile can be broken down in lysosomes with the formation of polysilicic acids.