A surface reaction kinetic model to compare the reductive leaching of iron from goethite, magnetite, and limonitic nickel laterite ores by acidic sulfur dioxide

Abstract

The kinetic modeling of iron dissolution at low pH in the presence of SO 2 or Na 2 SO 3 is of particular interest due to the fact that iron oxides are major components in limonitic nickel laterite ores, [1] deep sea nodules, [2] weathered rare earth (RE) mud, [3] and manganiferrous ores, [4] and are common to many soils. [5] Table I lists the conditions under which the leaching experiments have been carried out by previous researchers and the pct Fe extracted from different types of iron oxide materials. The reactivity of hematite is 1/10th that of goethite, magnetite, and laterite, as shown by the pct Fe leached in 1 hour. Despite the different iron contents and the leaching conditions in the case of laterite and RE mud, the pct Fe extracted in 2 hours is similar. The relatively high reactivity of the mud at low temperature is most likely attributed to finely divided iron oxide in the particle. Nevertheless, the low rates of iron dissolution from hematite in RE mud, particularly at low pH and low SO 2 concentrations, show the selective leaching of manganese. [3] Figure 1 compares the fraction of iron leached from variously sized particles of goethite and magnetite as a function of time; the slope represents the rate of leaching. Despite the lower temperature of 20°C, the leaching of the ultra fine (0.1 m) goethite is much faster than the leaching of coarse (150 m) goethite at 110°C, which is nearly the same as that of 75-m magnetite at 50°C.Previous attempts to rationalize the kinetics of reductive leaching of iron oxides were based on the adsorption theory [5,6,7] and electrochemical studies [8,9] with limited success in some investigations. [10] Little or no attempt has been made to compare the available kinetic data for the reduction of goethite, [6] magnetite, [7] and laterite [1] by SO 2 under a range of leaching conditions, which gave the results shown in Table I and Figure 1. The effect of some of these parameters has been successfully incorporated into the well-known shrinking sphere model, which is useful for kinetic modeling and reactor design: [11] [1]where X ϭ fraction of Fe reacted at time t (s), k ϭ intrinsic rate constant of the surface reaction (cm s Ϫ1 ), r ϭ initial particle radius of solid (cm), ϭ molar density of Fe in the solid (mol cm Ϫ3 ), k ss ϭ apparent rate constant (s Ϫ1 ), andϪ ] n r Ϫ1 r Ϫ1 t ϭ k ss t m, n ϭ reaction order with respect to [H ϩ ] and [HSO 3 Ϫ ] in equilibrium with SO 2 :The shrinking sphere model takes into account the decrease in particle size and thus the surface area with time. In general, the value of k ss is obtained from the slope of a plot of 1 Ϫ (1 Ϫ X) 1/3 against t. This is used in the Arrhenius equation, k ss ϭ A exp (ϪE/RT), to examine the effect of temperature for leaching under a given set of conditions (r, , [SO 2 ], pulp density, and sufficient agitation to avoid masstransfer limitations to the surface), and to determine the activation energy E and the Arrhenius constant A. The use of the intrinsic rate constant k, instead of k ss , in the Arrhenius...

Sulfur dioxide leaching of spent zinc–carbon-battery scrap

“…The iron dissolution during the same time period was only 10%, indicating selective dissolution. This is in accordance with the faster leaching kinetics of manganese dioxide compared to iron oxide by sulfur dioxide [4][5][6][7][8].…”

“…(17) [4,6,8]. However, the reductive leaching of iron from limonitic nickel laterite and the reductive leaching of manganese from manganiferous ore followed a shrinking core kinetic model described by Eq.…”

Reductive acid leaching of laterite and metal oxides — A review with new data for Fe(Ni,Co)OOH and a limonitic ore

“…Table 12, irrespective of the different iron oxides considered in Fig. 6b (Senanayake, 2003a). However, the value of k ap for FeOOH dissolution in 3 mol dm -3 H 2 SO 4 (2.05 h -1 ) in Table 10 is relatively unaffected by the presence of Na 2 SO 3 (2.02 h -1 ).…”

“…However, the reaction mechanism in scheme 6 does not consider the electrontransfer step for the oxidation of SO 2 or HSO 3 -to S 2 O 6 2-(dithionate) or HSO 3 radical, which are further oxidised to HSO 4 -/SO 4 2- (Kumar et al, 1993;Das et al, 1997;Zhang et al, 2000;Senanayake, 2003a;Das and de Lange, 2011). This warrants further discussion of the rates of iron dissolution from different oxide systems on the basis of surface active sulphur species in the adsorption/reaction mechanisms listed in Table 12 to rationalise the leaching behaviour of iron.…”

SO2removal with coal slurry in a double-stirred vessel

“…There have been many reports about the aqueous oxidation of pyrite in the absence of sulphur dioxide [2][3][4][5][6], and about the leaching of minerals containing metal oxides or metal sulphides in the presence of sulphur dioxide [7][8][9][10][11][12][13]. However, papers concerning SO 2 removal by leaching coal pyrite are relatively fewer.…”