DIRECT OBSERVATION OF THE ALTERATION OF T HOMAS SLAGS AFTER INCORPORATION IN A CULTIVATED ACID SOIL

The forms of phosphorus present in Thomas' slags and their fate in a c ultivated acidic soil were studied with physico-chemical analysis, X-r ay diffraction and scanning electron microscopy coupled to an X-ray en ergy dispersive spectrometer. The phosphorus content of the slag reach ed 59 g kg-1, 80% of it being present in particle size fractions coars er than 20 mum. The slag particles had a ''beehive'' like structure. T he cells had a high P, Si and Ca content while the walls presented a h igh Fe, Ca and Mn content. A silicato-calcium phosphate was the prevai ling form of P in the cells. The slags were quickly weathered in the s tudied acidic soil. This weathering was then discussed as a function o f the nature of the phosphate mineral, and more precisely of the subst itution of the PO4 ions within the mineral by other ions, and of the s oil type.