Nowadays, the uncontrolled dumping of used tires is an important environmental concern. From more than one billion used tire accumulated annually worldwide, only a small portion is reused. Considering high content of zinc in the tires, the possibility of using these residues as Zn fertilizer is of great importance. Zinc deficiency is a widespread constraint for crop productivity, particularly in arid and semiarid regions. In this study, the recovery of Zn from used tires using chemical solvents and a calcareous soil was investigated. Zinc, Fe, Pb, and Cd contents of car and truck tire powder sample obtained from Yazd and Tehran factories were measured. The tire sampeles from Yazd factory had the highest Zn content. Therefore, Yazd tire powder was selected for the rest experiment. The average particle size of the ground ash was estimated using SEM analysis as about 80 nm. Metals were extracted from tire using different extractants. HNO 3 4, 2 and 0.5 M, H 2 SO 4 1 M and dionized water no significant difference was found among different acids in extracting Zn. The mean Zn extracted with different acid was about 33 % of total Zn content of tire powder. Different tire: exractant ration of 1:5, 1:1 and 1:25 were investigated using to extract Zn, Fe, Pb and Cd from the sample. By increasing the ratio of extractant to the tire, extracted Zn increased. The highest amount of Zn (6700 mg kg -1 ) was extracted after 12 hours using HNO 3 4 N at a ratio of 1:5 tire: extractant. The kinetics of metal release from tire by HNO3 4 N at a ratio of 1:5 tire: extractant at 25, 50, and 70 C 0 were also studied. By increasing the temperature and time, Zn release from the tire increased. The retes of Zn release from the tire was faster than Fe and Pb. Activation energy calculated by Arhnius model for Zn release was higher than Fe and Pb. Isoterms of Zn, Fe, and Pb release from the tire were studied using HNO 3 4 N at a ratio of 1:5 tire: extractant during 30 times sequential extraction. The data were then modeled using Barewter, Barrow, and Raven and Hoer equations. All three models could well describe the release isotherm of Fe, Pb, and particularly Zn from tire. The kinetics of Zn release from the tire powder and ash nano-particles were best described by Parabolic and Elovich equation at low and high Zn concentrations, respectively. After metal removal from the tire, selected physicochemical properties of the acid-washed residues were determined and compared with some hydroponics beding substrates. The acid-washed tire
