Studies on the chlorination of zircon: Part I. Static bed investigations

Carbochlorination is an important unit operation in the processing of zirco nium resources. In the article, the use of different reducing agents in zir con chlorination, to produce zirconium tetrachloride, has been examined on thermodynamic and other considerations. While numerous workers have investi gated zircon chlorination, a literature survey shows that there is a wide v ariation in the reported effect of various process parameters on the chlori nation rate and a wide scatter in the values for kinetic parameters such as order of reaction, activation energy, rate constant as also the rate law e xpression. This work is an extensive study on zircon chlorination and the a rticle discusses the effect of process parameters such as charge particle s ize, gas and solid composition, gas flow rate, temperature, reaction durati on, etc, on the chlorination rate, over a much wider range of the parameter values. During investigations in the static bed chlorinator, it was notice d that the initial rate and the total extent of chlorination are proportion al to the exposed surface of the solid zircon-coke charge but independent o f the depth or amount of the charge. Further, the stalled chlorination coul d be reactivated by remixing the solid charge. Also, while the reaction rat e in general increased as the charge became finer, the effect of zircon par ticle size was much more predominant. The activation energy value for the c hlorination showed a wide variation with other operating conditions. Likewi se, the order of reaction with respect to chlorine decreased from two to ze ro as the chlorine concentration in the gaseous atmosphere increased. Inter estingly, the chlorination rate initially increased with gas flow rate, the n decreased, before finally becoming independent of the gas flow rate. Resu lts also indicated that there is an optimum charge composition that yields the maximum chlorination rate and the article discusses the effect of the z ircon to coke particle number ratio in the initial charge on the chlorinati on kinetics. With the help of these observations, it is possible to explain the wide variation in the reported effect of the various process parameter s on zircon chlorination.