Kinetics of chloridization of nickel oxide with gaseous hydrogen chloride

Abstract

The kinetics of chloridization of finely divided as well as granulated nickel oxide by gaseous HCl were studied in the temperature range 150 ЊC to 400 ЊC. The rate of chloridization depended upon temperature, partial pressure of HCl, and granule size. The conversion of NiO to NiCl 2 follows the logarithmic rate law or a pore-blocking model, which is attributed to the large increase in molar volume of the product phase. The blocked pores decreased the diffusion of gaseous reactant through the product layer. This observation has been supported by the low value of activation energy, the high order of reaction with respect to the partial pressure of HCl (g), and a slope value of Ϫ2 for the log-log plot of rate constant vs grain size. The morphological characteristics of both unreacted and chloridized nickel oxide have been studied with the help of a scanning electron microscope.

Kinetics of chloridization of nickel-bearing lateritic iron ore by hydrogen chloride gas

“…The physical characteristics of the samples were determined according to the methods described in the previous article. [11] III. RESULTS…”

“…[11] The chloridized mass was leached in a slightly acidified (pH 2.0 to 2.5) water and filtered. The filtrate was made of up to 100 mL.…”

“…Nevertheless, a possible occurrence of the 3-D diffusion process can be easily derived from the simple model presented by earlier investigators [18] and also used in a modified form in our previous article. [11] However, this is valid when the reaction interface proceeds uniformly within the spherical laterite granules. The mass balance equation within the solid phase can be expressed as follows.…”

“…The melting may explain an increase in the product volume leading to the reduction in porosity of the oxide during the chloridizing reaction, as demonstrated in the previous article. [11] The thermal decomposition behavior of ferric chloride hydrate is more complex than that of nickel chloride hydrate. Curve III in Figure 1 shows that the salt undergoes complete melting at temperatures around 40 ЊC followed by two broad endothermic effects.…”

“…Although from the process development point of view the presence of H 2 O (g) may have certain advantages, it is difficult to study the kinetics of such a gas-solid system, as HCl (g) and H 2 O (g) form a highly polar reactant mixture for which the evaluation of basic physical parameters is very complicated. [10] It has been shown in a preceding article [11] that the rate of chloridization of NiO is considerably reduced when pure HCl (g) is replaced by a mixture of HCl (g) and N 2 , even at an increased flow rate. This suggests that apart from the concentration effect, interdiffusion of the reactant through the product layer of low porosity is an important factor in such a reaction.…”