The potential of an Fe waste by-product as an Fe fertilizer in alkaline soil

Abstract

An Fe dust waste accumulates as a by-product from the steel industry and poses a disposal problem. Since the waste contains approximately 43% Fe, 5.4% Zn, and 1.9% Mn, it shows potential for recycling as a plant food. Therefore, laboratory and greenhouse experiments were conducted to evaluate this Fe waste material as a possible source of agricultural Fe fertilizer. In a laboratory experiment, selective dissolution and fractionation were used to determine Fe dust solubility and to partition total Fe into solubility classes. The release of Fe was in the following order: water < DTPA < 0.25 M HCl < 0.25 M H(,2)SO(,4) < dithionite-citrate-bicarbonate < < acid NH(,4)-oxalate. The x-ray diffraction patterns and transmission electron micrographs of Fe dust and residue remaining after each extraction revealed the presence of magnetite as a major component of the material. This water insoluble material was treated with H(,2)SO(,4) to increase Fe solubility and enhance its value as a fertilizer. Water soluble and DTPA extractable Fe were directly proportional to the amount of acid used. The effect of particle size on Fe solubility indicated that the smaller particles within the Fe dust size range did not increase Fe solubility. An incubation study of Fe waste (with and without H(,2)SO(,4)) in a calcareous Fe deficient soil indicated that available soil Fe decreased sharply with soil reaction time. In a greenhouse experiment, Fe waste material was evaluated to alleviate Fe chlorosis of sorghum (Fe efficient and inefficient cultivars) grown in Fe deficient calcareous soil. The Fe waste (dust and pellet) with and without acid at a ratio of 1:2 (Fe/H(,2)SO(,4)), was mixed with the soil at 3 rates before planting. Vegetative growth and dry matter yields clearly showed superior performance of acidified Fe materials over nonacidified Fe dust or pellet. Extractable soil Fe increased linearly with rate of acidified Fe materials. Likewise, Fe concentration in plants increased proportionally to available soil Fe.A comparison of a Fe waste material with other Fe sources (FeSO(,4) and Fe EDDHA) at various rates to prevent Fe chlorosis was studied. Similar alleviation resulted from Fe dust 1000 ppm, FeSO(,4) 100 ppm, and Fe EDDHA 10 ppm. Iron pellet failed to correct Fe chlorosis. Soil incorporation of plant residue (chopped sorghum stover) as a carrier for Fe sources produced greater dry matter yield in all treatments. Available soil Fe increased with added plant residue and also with rate of Fe applied.