The Release Characteristics Of Mineral Elements In The Slag-fertilizers

In order to reduce the environmental pollution of slag and enhance the comprehensive usage of slag, it could be made as an environmentally friendly resource, with the slag-fertilizers as the materials, the dissolution rate in water and release characteristics of mineral elements in soil were studied in this article. A simulated experiment with four different environmental factors (temperature, texture, rainfall and different soil) was carried out to study the effect of those factors on release characteristics of mineral elements in slag-fertilizer; and release mechanisms were researched by ESEM. Main results were as follows:1. The mineral elements dissolution regularity of slag-fertilizers was tested by the method of the dissolution rate in water. Results indicated that the dissolution rate of K was higher than that of other elements, and preliminary dissolution rate of K were more than 10%. Most elements'accumulated dissolution amount of No.5 slag-fertilizer were higher than that of other slag-fertilizers, especially K, it's accumulated amount was 82.46%; the accumulated amount of P in No.1 slag-fertilizer was at most, up to 33.19%, and that of Cr and Cu in No.2 slag-fertilizer and Mo in No.4 slag-fertilizer were at most, up to 13.19%,35.99%and 38.17%; and that of all elements in No.3 slag-fertilizer were lower than that of elements in other fertilizers.2. With the No.5 slag-fertilizer as the material, the effect of different environmental factors on mineral elements release characteristics was carried out by the method of soil column leaching. The results showed that Mg,Al,K,Zn,Cd,Cu,Pb,Mn,Fe,P,Cr,Ca,Mo and As showed different accumulated dissolution regularity of release under the different environmental factors. In the soil, as the soil temperature increased, the accumulated leaching amount of P and Cr decreased, however, the accumulated leaching amount of Pb increased; in soil plus fertilizer, only the element of P showed the same regularity as P in the soil. The most and least of the accumulated leaching amount were Ca,93.81‰and Fe,0.013‰。Under the different rainfall, the accumulated leaching amount of Al,P,K,Mn,Zn and Mo in the soil increased, as Al,P,K,Mn and Fe in the soil plus fertilizer, when the rainfall increased; the most and least of the accumulated leaching amount were Ca,93.81‰; Al and Cr,0.012‰.The media had a great impact on the accumulated leaching amount of mineral elements. In the different media, zeolite obviously raised the accumulated leaching amount of Mg,K,Cr,Fe,Zn,As,Cd,Pb,Al,P,Cu and Mo, but decreased the accumulated leaching amount of Ca and Mn; the most and least of the accumulated leaching amount were Ca,155.02‰and Al,0.021‰. In the case of different soil, the accumulated leaching amount of most mineral elements in the Hefei soil was higher than that of in other soils, the most of the accumulated leaching amount was Ca,137.27‰. However, the accumulated leaching amount of those mineral elements in the Beijing soil was the least, and the least of the accumulated leaching amount were Cd and Cr,which were below detection limit of instrument. 3.The release characteristics of mineral elements of four slag-fertilizers in soil were researched by the soil column leaching. The results showed that the release speed of Mg,Al,P,Ca,Mn,Zn and Cd was slower in soil plus fertilizer than that in soil ,but the release speed of K,As,Mo and Pb was faster in soil plus fertilizer than that in soil; the release speed of Fe was faster only in soil plus No.3 fertilizer and in soil plus No.4 fertilizer, however, the release speed of Cu was faster only in soil plus No.1 fertilizer and in soil plus No.2 fertilizer; Cr was just leached out in soil plus No.3 fertilizer and soil plus No.4 fertilizer. The accumulated amount of most mineral elements in soil plus No.3 fertilizer and soil plus No.4 fertilizer was smaller, but that of the other elements'was small in soil plus No.1 fertilizer and soil plus No.2 fertilizer, such as P,Fe,Cr,As,Mo. The most and least of the accumulated leaching amount were Ca,138.23‰,and Cr , which was below detection limit of instrument.4. The external surface and section structures of different slag-fertilizers were observed by ESEM. The results showed that the coated effect of No.5 and No.3 slag-fertilizers was better, then was No.1 and No.2 slag-fertilizer, the worst was No.4 slag-fertilizer. Two kinds of coated materials combined compact with No.3 slag-fertilizer, and they made external surface form waterproof layer and decrease the time which the fertilizer contacted with water. This made the mineral elements release speed decreased; the coated layer of No.1 and No.2 slag-fertilizers were stacked flocculently and had holes of uneven sides; the coated layer of No.4 slag-fertilizer was completely stacked by the coated materials and had many obviously holes of different sides. This may explain the different effect of mineral elements release of the fertilizers after the fertilizers were coated by different materials.