DEVELOPMENT OF AN IRON REMOVAL PROCESS FROM KAOLIN BY THIOUREA LEACHING: KINETIC AND RELATED STATISTICAL ANALYSIS

摘要

In the present paper an iron removal process by leaching of kaolin using thiourea as a leachant agent in the presence of H_2SO_4 was studied. The leaching process can improve its economic value and its utilisation in the ceramic and paper industry becomes possible. The effect of thiourea was investigated together with other factors such as sulphuric acid concentration, temperature and different treatment times. The largest iron extraction yield (94.1%) was obtained after 150 min of treatment at 90°C, H_2SO_4 0.25 M and with 10 g/l of thiourea. At the same temperature the iron extraction yield was of 68.4% after 120 min of treatment with H_2SO_4 0.1 M and thiourea 1 g/l. A kinetic analysis indicates that the chemical reaction is the limiting step in the leaching process (Activation energy 74+-9 kJ/mole). The overall kinetic model that describes the iron extraction yield vs. time has been pointed taking into consideration iron extraction yield, acid concentration, thiourea concentration and leaching time. From the analysis of the literature the use of thiourea in the iron removal from industrial minerals was found to be original and technically feasible.