Studies on kinetics of reduction of NiO by hydrogen

Studies on the kinetics of reduction of nickel oxide briquette to metallic Ni in a low temperature range (573-723 K) by using very low partial pressur e of H-2, (0.10 - 0.25 atm) diluted with argon, have been carried our. The nickel oxide is obtained by the decomposition of pure nickel carbonate at a desired temperature. The effect of time (t minutes), temperature (T K), pa rtial pressure of hydrogen (PH2 arm) and the decomposition temperature (T* K) of NiCO3, has been investigated. The reduction reaction kinetics has bee n found to follow the following relationship; after 15-16% of reduction; ln(1-alpha/alpha) = kt + c where alpha is the fraction of NiO reduced in time, t, k is the rate consta nt and c is the integration constant. The k has been found to be directly p roportional to PH2 in the range 0.10 to 0.25 arm, studied. The activation e nergy of the process has been calculated from the kinetics results in the t emperature range of 573-723 K, by using PH2 of 0.10 arm and is found to be 44.6 kJ/mole. The fraction of NiO reduced during the initial stage of reduc tion (up to 15 to 16%) has been found to follow approximately the following topochemical model equation: 1 - (1 - alpha)(1/3) =k(1)t where alpha is the fraction of NiO reduced in time t and k(1) is the rate c onstant for the topochemical reaction model equation. In this case, the app roximate activation energy has been found to be 67 KJ/mol. The NiCO3, decom position temperature (848 to 1148 K) has been found to have an inverse effe ct on the rate of NiO reduction with H-2. Based on these kinetics results, a mechanism for the NiO reduction with H-2 has been proposed. The Ni metal briquettes obtained under two different experimental conditions, have been characterized by XRD technique.