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The removal and destruction of ceramic fibers wastes are presently an important problem for the society health. Among these, the asbestos, which are silicates, is the more dangerous. Usually their destruction is obtained by a melting way, but this needs high temperature (about 15001600•Ž) and presents an expensive treatment. In this paper we show that the sodium polyphosphate addition to different asbestos (chrysotile, amosite and crocidolite) permits to obtain the fiber's destruction at a temperature below than 900•‹C. This process may be applied to composite materials containing a few part of asbestos, like carpet tiles or building plaster. This process of waste's treatment can open a new and a large market for sodium polyphosphate. INTRODUCTION Phosphate compounds are extensively used in industry and human environment areas. Typical examples relate to fertilizers, animal and also human food, pharmacology and cosmetics. These applications consume a significant tonnage of the world phosphate production. In addition, the non-biological industrial applications also require large amounts of phosphates. For example, they are used in many areas like metal surface treatment, enameling, ceramics processing, flame retardant, washing powder, optical glasses, water treatment, paints, filler for plastics and papers, etc. Nevertheless, the use of phosphate processing for waste treatment particularly inorganic wastes -appears presently as a minor application for the phosphate productions. While some applications have been proposed in this area, especially for the treatment of nuclear wastes 1, 2, 3, these applications are rather a matter of basic researches without industrial counterparts. On the other hand, this kind of application does not require an important quantity of phosphates and derivatives. We propose here to use phosphate compounds, in particular polyphosphates, for the treatment of inorganic wastes, which could open a new and large market for these products. Because the polyphosphate solutions exhibit interesting properties like their colloid disperse power and their important wetting power on inorganic ceramic (or metal) particles. On heating, polyphosphates may react with these particles, in particular through oxoacidity reaction'. Finally, sodium polyphosphate which is commercially sold as Graham salts or as hexametaphosphate is an important and cheap industrial product. Proceedings of IMPHOS-IWPPC -Jena 2002 68 Phosphorus Research Bulletin Vol. 15 (2004) Among the inorganic wastes, an important world problem concerns the destroying (or the neutralization) of the inorganic fiber wastes. In this respect, asbestos presents a major concern which raises problems for the human health in many countries, because very large amounts were used during the last century, at once in industrial and domestic applications. Asbestos have been used directly as a protection against noise or heat propagation. Because of their mechanical properties, they have also been used as filler, in variable quantities, in "composites" materials based on organic or inorganic matrix. In these last cases, one may have to destroy these fibers inside the matrix, even if the relative amount of asbestos is limited. As a consequence, the waste tonnage to be treated is enormous. This outlines the economic importance of the treatment of asbestos which is often a mere filler in organic or inorganic matrix. The reasons of the asbestos hazards The asbestos are silicate compounds. About mineralogy they may classified in two categories 5. The serpentines with the chrysotile as the principal fiber (white asbestos) are the most used in human applications. The general formula is Mg3 Si2O5 (OH)4, with sometimes iron traces. They have a layered structure, but these silicates layers are coiled up in a principal direction, which results in a linear structure with an outside diameter about of 25 nm 6. The amphiboles make the second category. The main fibers are: ● The crocidolite ( Na2Fe5SiO22(OH)2)-(blue asbestos) ● The amosite (Mg2Fe5SiO22(OH)2) (brown asbestos) ● The tremolite (Ca2Mg5SiO22(OH)2) All amphibole structures are linear at the molecule size. So in natural site asbestos are not much toxic, but their mechanical treatments carry especially the breaks along the fiber direction and not across. For this reason during the elaboration of materials based on asbestos, the fibers become thinner and thinner. As they become more and more dangerous for the human respiratory system. In practice, it is acknowledged that the most dangerous fibers have approximately a length of 5 microns and a diameter of 3 microns. On the other hand, amphiboles dangerousness is not only due to the crystallographic structure, but also to the chemical toxicity induced by iron II presence. There is a major interest to cut by a chemical reaction the linear molecular structure of the asbestos because it is a way to destroy their hazards. But this reaction has to be obtained with an inexpensive process for economic reasons, and should not produce other hazardous wastes. The elimination of iron II is also a goal for the treatment of amphiboles. The use of sodium polyphosphate for the treatment of asbestos Commercial sodium polyphosphates are glasses. They have a chain structure with different chain length 7. Usually in the commercial product the value of the chain length lies between 10 and 25 units of PO3 8. It is the only polyphosphate which is soluble in water 7. In this case, it gives an acid solution. The wetting power of aqueous polyphosphate solution to the asbestos fibers is very interesting. For example the figure 1 shows the evolution versus time, of the wet part of a chrysotile tuft soaked partly above a 4M sodium polyphosphate solution9. This result Proceedings of IMPHOS-IWPPC-Jena 2002 69 Phosphorus Research Bulletin Vol. 15 (2004) exemplifies the interest of polyphosphate for the impregnation of asbestos items of important thickness such as the flock coating on building ceiling 16. This good wettability permits to impregnate to tuft core as shown in figure 2 which reports a TEM analysis. Another property may be used for the asbestos treatment9. Sodium polyphosphate aqueous solution gives a miscibility gap phenomenon by adding bivalent ions 8,9,10,11. In this way we obtain a segregation of the long chains of polyphosphate, which conducts to a new phase called coacervate 12. The pH of the mixture decreases during the coacervate formation down to 2 or 3 13. For this reason the coacervate formation is favored if asbestos are mixed with another salts containing bivalent ions. This behavior opens new possibilities because Figure 1: Wettability of chrysotile tuft by a sodium polyphosphate solution at room temperature Figure 2: TEM analysis of a fiber coming from a chrysotile tuft treated by sodium polyphosphate solution. In the areas 1 and 2 present respectively 4 and 5% of phosphorus element around the elementary fiber 70 Proceedings of IMPHOS-IWPPC Jena 2002 Phosphorus Research Bulletin Vol. 15 (2004) coacervates present interesting rheologic properties 14. They behave as a glue which prevents the departure of asbestos fibers during their mechanical removing 15,16. By curing we obtain in a first step a dehydration of coacervate in an oven drying conditions then up to 620•Ž their melting. The temperature of melting depends of the ratio of M++/Na 17. Molten polyphosphate are very reactive with respect to many ceramics 7. They also exhibit an important wetting power. Figure 3 shows as an example the thermal evolution of chrysotile fibers partly coated by a dried coacervate. This study implemented by SEM shows that fibers which were not completely coated in the first stage of the melting became wholly covered. STUDIES OF ASBESTOS DESTRUCTION BY THE SODIUM POLYPHOSPHATE In a first time, we have studied the destruction of three typical kinds of asbestos fibers. Our goal was to show the possibility of sodium polyphosphate to cut the linear structure of asbestos in a low temperature range, in order to decrease the dangerousness of this kind of fibers. Experimental The sodium polyphosphate is a Merck product sale as Graham salts. The chain length is 22 25 units of PO3 groups. The asbestos samples are supplied by Ward's natural science establishment Rochester, New York USA.

Treatment and Destruction of Inorganic Fibers Wastes Like Asbestos by Sodium Polyphosphate