Kinetics of chloridization of nickel-bearing lateritic iron ore by hydrogen chloride gas
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I.
INTRODUCTION
VARIOUS methods[1,2] have been developed for the recovery of nickel and cobalt from lateritic iron ores. Although only a few of them have been put into industrial production,[3,4,5] research and development activities in this field are still being continued to use the vast deposits of nickel-bearing laterites by adopting a method suited to the local conditions.[5] Heertjis and co-workers[6,7] have carried out chloridization roasting to extract nickel from lateritic ores by using a mixture of gaseous HCl and steam. This particular reaction system was chosen to accelerate the decomposition of hydrated chlorides of iron, aluminum, and chromium to their insoluble oxides at temperature below 300 7C.[8] On the other hand, anhydrous nickel and cobalt chlorides are thermally stable up to 400 7C.[9] Steam is also used to maintain the product layer in sufficiently moist condition to facilitate the diffusion of HCl (g) in a dissolved state. Although from the process development point of view the presence of H2O (g) may have certain advantages, it is difficult to study the kinetics of such a gas-solid system, as HCl (g) and H2O (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 N2, 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. Further, the decomposition of ferric chloride hydrate at lower temperatures greatly affects the chloridization of nickel oxide. Keeping all these constraints in view, an attempt has been made in this article to study the rate of chloridization of nickel in S.B. KANUNGO, Scientist-F, and S.K. MISHRA, Research Associate, are with the Regional Research Laboratory, Bhubaneswar 751013, India. Manuscript submitted September 19, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS B
lateritic ores of Sukinda valley (Orissa, India). The total reserve of nickel-bearing laterite, including the chromite ore overburden in this region, is more than 120 million tons,[12] and despite extensive research and development work, this vast resource of nickel has remained unexploited. II.
EXPERIMENTAL
A. Material The limonitic laterite was collected from the Kansa area of the Sukinda valley, Cuttack district of Orissa, and analyzed as follows (in wt pct): 74.2Fe2O3, 2.38Cr2O3, 4.5Al2O3, 3.1SiO2, 1.1NiO, and 12.5LOI. X-ray diffraction data indicate that iron occurs only as goethite. No definite nickel-bearing mineral has been identified by either ore microscopic or petrographic method. The fine powdery ore was slightly moistened by spraying water from an atomizer and was granulated on a flat disc by swirling it manually until a sufficient quantity of granules of assorted sizes was formed. These were heated for 2 to 3 hours at
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