Abstract:This paper reviews the fruitful results and main shortcomings in the study of the environmental safety of fibrous mineral dusts, and proposes that attention should be paid not only to the requirements of characteristic divergences in fiber dose, length and fineness but also to the impacts of the method of sample preparation, sample locality, origin, composition etc. Emphasis is put on the effects of the broken bonds of fiber, active free radicals, activity center, fiber charge, catalysis, oxidization_reduction,“surface media”etc. The authors explain the importance of revealing the disease_causing mechanism of fiber dusts from the surface activity and mineral-bio-chemical processes, i.e. discuss the surface chemical activity-biological activity_biological toxicity-bio-resistibility environmental safety of natural fiber material from the surface groups and total features of minerals, and seek to assess an attribute of mineral application from a combination of industrial minerals, environmental medicine and material value. Finally, the authors suggest that consensus should be reached on the definition of fibers, sample surface and test method, and that the types of asbestos minerals should be strictly distinguished.

Abstract:The dissolving characters and bio_resistance of 6 pairs of mineral dusts in a simulated human body environment for 96 days were studied by using Gamble solution and three acid series. The results show that the iron dissolving rates in most mineral dusts have two peaks, and that magnesium is dissolved simultaneously with iron in dusts with tri_octahedral structure. Most of the dissolving rates of high_magnesium mineral dusts display peaks in the first dissolving stage. The calcium dissolution rates of zoelite and wollastonite are relatively stable, and wollastonite show the feature of being high in the front and low in the rear in the low_pH area. The dissolution peak of Si appeared in the first 48 days in Ph5 Gamble solution, but after 48 days in the pH7 series. Al dissolution is easy in the pH3 and pH5 series and difficult in pH7. The cumulate dissolution amount of all elements in Gamble solution of fibrous mineral dusts increases with time, and the total dissolution amount of fibrous samples is mostly larger than that of the clayey ones. There are phenomena of cracking, etching and peeling on the surface of fibrous minerals and fibers tend to be scattered or break during dissolution. The dissolving rate of flaky dusts is positively correlated to the step densities and oxidizing rate of iron_bearing samples. The total dissolution amount is basically positively proportional to the system acidity and total organic ions. The dissolving rate of Ca-, Mg- or Al-rich mineral dusts is higher than that of K- or Si_rich dusts. The low pH, high solubility of O2 or oxidizing reaction and high salinity solution of the environment may accelerate the dissolution of dusts.

Abstract:The process of dissolution of fibrous wollastonite dust in amino acid aqueous solution at body's temperature 37℃was studied and the variations of pH and conductivity in 72 hours in the dissolution process were measured. Results suggest that the dissolution of wollastonite fibers in amino acids is related to the nature of acid: the capacity of mineral's dissolution is strongest in acid amino acids, less strong in neutral amino acids and weak in alkali amino acids. The sat- uration point appears in about 8 hours when the mineral is in acid and alkali amino acids, while in neutral amino acids no saturation point appears within 72 hours. The solubility has a trend of increasing linearly with time. The dissolution characters of wollastonite show that wollastonite's resistibility is not strong in nearly neutral body liquid. Metal ions can be remobilized by amino acids, and in the process of dissolution the organic reaction between metal ions and amino acids may damage the structure of amino acids to some extent, which may be one of the causes for the damage of normal protein.

Abstract:Fibrous brucite (FB) may release free radicals in water, display chemical activity in acid solution and has cytotoxicity in body liquid. In solution, FB can react with all substances that release ammonia ions and give off protons because of FB can ionize out hydroxyl in water. The existence of ferrous iron in FB usually results in concomitant occurrence of oxidation and reduction, finally forming compound ferric iron ammonia salts. So, the brucite dusts may react with and be dissolved partly in soluble ammonia salts of the human body and ammonia ions of body liquid. The increase in grain size and temperature is beneficial to the increase of dissolved magnesium in the balance system. High-concentration ammonia salts have a large dissolving capacity at high temperature. The total amount of Mg and Fe ions in the equilibrium solution depends on the solubility of resulting double salts. The reaction speed is decided by the speeds of ionization of ammonia salts and brucite together. NH4Cl (1.25 mol/L), (NH4)2SO4(0.5 mol/L) and NH4HSO4(1.25 mol/L) are the ammonia salts that can not only prevent Fe2+from being oxidized or precipitated but also cause brucite to be dissolved better at 40~80℃.

Abstract:The dissolubilities of fibrous clinoptilolite, sepiolite, palygorskite and chrysotile dusts in amino acid liquor at the simulated human body temperature (37℃) were investigated, and the changes of pH values and electric conductivity in the dissolving process in 72 hours were studied. The dissolution of fibrous minerals in amino acid is related to the acid types: the dissolution of fibrous minerals in acid amino acid (glutamic) is greater than that in neutral amino acid (valine), and the dissolution is weakest in alkaline amino acid (lysine). The dissolubility increased in the first 8 hours and then tended to be stable. The relative dissolution rates of fiber minerals in the same acid are: clinoptilolite < sepiolite and palygorskite < chrysotile, which shows that clinoptilolite has stronger corrosion_resisting ability and higher bio-resistibility, while chrysotile displays lower corrosion resistance.

Abstract:In this paper the conductivities and pH values of 6 pairs of mineral dusts were measured and a comparative analysis was performed of the influences of the shape, granularity, temperature and time on their electric chemistry. The research results show that there is a positive correlation between the pH values/conductivities and finenesses of the minerals in water medium and that the conductivity is sensitive to temperature change with its maximum located at ca.60℃and a turning point showing a large_amplitude decrease appearing after 80℃in all samples. The pH values of most samples show a trend of rising progressively with time and all the samples approach stable values during balance after 8 hours. A new type of model has been proposed for the dissolution, ionization and conductivity of mineral dusts with cation exchange property. The dissolution rates of minerals are influenced by the granularity, surface activity,temperature, differential concentration, time etc. The pHand conductivity of mineral dusts are their surface characteristic values and can all_sidedly reflect the behavior tendencies of their sol- ubility, chemical activity, surface electricity, decomposition and remaining, preservation, compatibility etc.

Abstract:Minerals dusts are harmful to human health when a great amount of dusts, especially fibrous dusts, are taken into a human body. Through the digestive system, these dusts will come into the stomach and then are dissolved by acid and no influence will be exerted on health, but when dusts come into the breathing system, their reaction with the human body is very complex. They can move, be deposited, penetrate or be dissolved, and may cause cancer or silicosis. The dissolving process is simulated in this study.SEM analysis was made of the residues of mineral dusts dissolved in the simulated human body fluid———Gamble solution, organic acid and inorganic strong acid. The results have revealed the following: the fibers of the fibrous mineral dusts become shorter, the length diameter ratio is reduced, the flexibility weakens, the ends become rounded and a part of fibers are dissolved and become strings of beads; the coarse grains are loose and collapsed and their surface roughness increases; planar dusts become granulated and fine; silicate mineral dusts have a tendency to be dissolved into subspherical nanometer_sized grains composed dominantly of SiO2.The authors further propose that it is of great value to study of the nosogenesis by dusts on the nanometer size.

Abstract:According to the tests for the stability of some mineral fiber dusts in inorganic acid and chemical activity of acid-etched residue, the authors discuss the acid etching process of mineral fiber dusts, especially the changes in surface active groups in the acid etching process, and the factors that affect acid-resistance and chemical activity of mineral fiber dusts. Besides, on the basis of the results of the tests combined with the previous research results of the authors and predecessors, the authors discuss the relationships between the acid-resistance of mineral fiber dusts and the changes of surface active groups in the acid etching process with the bioactivity. The tests indicate that the acid resistance of mineral fiber dusts is related to the crystal structure, crystallinity and quantity of lattice defects, as well as the types and position and exposure degree of the groups. Besides, it is in positive correlation with the specific surface area, properties and number of microholes, and quantity of Lewis acid sites. After acid attack or surface modification, the latent biological toxicity of mineral fiber dusts may be reduced or even disappears totolly.

Abstract:In order to study the damaging mechanism of pulmonary alveolar macrophages, the changes of their death ratio,malandialdthyde (MDA) content and activities of dehydrogenate (LDH) and superoxide dismitase (SOD) were determined, and the technique of VITRO cell culture was used to investigate the cytotoxicity of dusts of six minerals (twelve cryst habits) from twelve mineral deposits. The results show that wollastonite and zeolite have no cytotoxicity while dusts of other fibrous and grainy minerals may damage pulmonary alveolar macrophages in various degrees. The cytotoxicity of fibrous mineral dust exceeds that of the grainy one; the cytotoxicity of dust is positively correlated with the active OH- content in dust, but not necessarily so with its SiO2 content; the high pH values produced by dust is unfavorable for the survival of cells; the dust with a low bio-resistance is safe for cells; the content of variable_valency elements may influence cytotoxicity. It is suggested that the shape of mineral dusts is one of the factors affecting cytotoxicity, and that the cytotoxicity of mineral dusts mainly depends on its properties.

Abstract:Fibrous sepiolite has cytotoxicity to human erythrocyte. In order to evaluate the hemolysis of fibrous sepiolite from Guangji of Hubei Province, the fibrous sepiolite was treated by cation exchange, Gamble solution, organic acid and nicotine, and then the changes of the percentage of hemolysis and malandialdehyde (MDA)———the main product of superoxidation of lipids———before and after the treatment were observed. The results indicate the following: the RBC toxicity of fibrous sepiolite treated by cation exchange and Gamble solution decreases significantly and its possible mechanism is to decrease the intensity of lipid superoxidation and prolong the time of surface/membrane formation; the RBC toxicity of fibrous sepiolite increases significantly in the presence of nicotine; while fibrous sepiolite treated by organic acid has insignificant effect on human erythrocyte.

Abstract:Adsorption of organic vapors by palygorskite and sepiolite was studied with IR spectrometry, XRD analysis and electrophoresis in this article. It was proved that the adsorption is produced by the static electric force .The adsorbed water on the surface of the minerals which can weaken the static electric force will hinder palygorskite and sepiolite from adsorbing organic vapors, and after drying at 110℃, the absorbed vapors increase obviously.The absorptive capacity is related to the temperature and pressure of vapors, dipole moments of vapor molecules, purity of the samples and crystallinily of the minerals. The adsorbed vapors will be reduced if the temperature rises because the strengthened molecular movement of vapors makes it more difficult for palygorskite and sepiolite to adsorb vapor molecules. If the dipole moment of vapors is enhanced the amount of adsorbed vapors will increase accordingly.Increasing vapor pressure can increase the frequency of collision between vapor molecules and minerals and then increase the adsorptive capacity. The increase of the rate of substitution of the ion Si4+by other ions will intensify the static force and will also increase the adsorptive ca- pacity of organic vapors. The purity of samples can affect the adsorbed amount too, i.e. the purer the samples, the larger the adsorbed amount. The organic molecules were proved to be physically absorbed on the surface of palygorskite and sepiolite through experiments. It is very easy to desorb.

Abstract:By use of vacuum organic adsorption and infrared spectrometry, the authors studied the characters of vacuum organic adsorption of hexane, ether and pyridine (their dipole moments are very different: hexane is 0, ether is 1.16 and pyridine is 2.19) by several kinds of fibrous mineral dust and changes of surface groups. The study found that the adsorbability of fibrous mineral dusts to organic reagents are not completely directly proportional to the dipole moments of organic reagents. Clay mineral dust has stronger adsorbability to organic reagents (such as hexane) with a smaller dipole monent, and fibrous mineral dusts have stronger adsorbability to organic reagents (such as pyridine) with a bigger dipole moment. Most of fibrous mineral dusts do not possess the ability of detaining the adsorbed molecules. But the adsorption of some fibrous mineral dusts to hexane is chemical adsorption, and there appear 1262~1267 cm-1and 1311 cm-1new IR bands after desorption. These bands should be IR bands of -SiCH3bonds which were formed after chemical adsorption took place between several kinds of mineral dust and hexane. This paper discusses the changes of surface groups of fibrous mineral dusts after adsorbing organic reagents, especially those of surface OH and surface Si-O-Si.

Abstract:The adsorption of substances in human serum on mineral dusts was studied by measuring the composition of the serum after the adsorption and using infrared spectra. The results suggest that the adsorption of substances in human serum on mineral dusts is selective and that the adsorpted substances are mostly biological macromolecules in the serum, such as protein and lipids. Infrared spectra have shown that the adsorption mechanism is mainly physical adsorption and that there is possibly chemical adsorption. The adsorption selectivity of biological macromolecules on varying minerals in the serum is mainly related to the structure and surface activity of the minerals. On the other hand, the cationic exchange and dissolution of mineral dusts occur in the human serum to some extent.

Abstract:This paper for the first time discusses the relations of the configuration, surface structure and surface properties of chrysotile asbestos with bio_activity based on nanometer-sized material and nanostructure effect. Chrysotile asbestos is a kind of special mineral occurring naturally as one-dimensional nanometer-sized silk. It has the general properties of nanometer-sized material in configuration, structure and surface properties, which are chiefly marked by the configuration of one-dimensional nanometer-sized silk, tubular structure and high activity behavior of the surface (interface). And its bioactivity is formed by the very small size and very high surface activity of fibers. The injuries done by chrysotile asbestos fibers to creatures include not only those of general fibers but also those of the amorphous SiO2 phase. The bioactivity of asbestos fibers increases greatly due to the nanometer-sized effect and the high surface activity of asbestos fibers.