STUDY ON PHYSICAL AND CHEMICAL PROPERTIES OF FLY ASHES AND THEIR AGROCHEMICAL BEHAVIOURS

This paper deals with physical and chemical properties of fly ashes and their agrochemical behaviours. Results are summarized as follows:(1) The physical sand accountes for 85% in fly ash. The major matter phase is amorphous substance. The contents of Si, Fe, Al, P, K, Ca, Mg in fly ashes are coordinated with those in soils. The contents of heavy metal elements: Pb, Cr, Cd, Hg,As don't exceed the national standards, and they exist in the aggregate that their activities are lower.(2) The contents of available Si (SiO2) in fly ashes are between 5. 56g/kg and 11. 57g/ kg, and their rates of releasing are 2. 0~11. 0 times as high as those in soils, so that the fly ashes can supply growth of rice with Si when their rate of application exceed 75t/ hm2. The releasing proccesses of Si in fly ashes could be goodly described with Elovich equation, in which parameter b value can express the releasing capacity of Si in fly ash.(3) The availability of P in fly ashes is low, and the stronger fixatiori of P is found when P fertilizer is added in fly ashes, and fixation is increased with higher content of water in fly ashes. The fixation of P in fly ashes must be considered when fly ash is used as soil conditioner or filling substances of compound fertilizers.