Kinetics of leaching of zinc ferrite in aqueous hydrochloric acid solutions
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I.
INTRODUCTION
IBERIAN pyritic minerals are complex sulfide ores containing predominantly pyrite. The reserves amount to some 364 • 106 tonnes. Ores can be divided into sulfur ores of >44 pct of S and 1000/xm 3 300 to 1000/zm 3 76 to 300/zm 36
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120
160
2}I> TIME
(rain)
Fig. 6--Dissolution of ZnFe204 as a function of time for several concentrations of HC1 (95 ~ 300 rpm).
relationship is observed. The initial stage of the attack involves a morphological change in the sinter surface. This effect may be the reason for the deviations observed at low fraction reacted. Values of kCi were calculated between 0.05 -< x --< 0.8, and are summarized in Table V. The aHcl was calculated by Meissner's method. 16 This method corrects the variation of activity with temperature. 224--VOLUME 15B, JUNE 1984
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90
TIME ( m i n )
Fig. 8--Dissolution of ZnFe204 at several temperatures for a solution 5.59 molal HC1 (300 rpm). METALLURGICAL TRANSACTIONS B
HCL
Table V. Kinetic Data for the Dissolution of Zinc Ferrite in Aqueous Hydrochloric Acid
HC1 (Molality) 2.08 3.19 4.34 4.94 5.59 5.59 5.59 5.59 6.74 6.74 6.74 6.74
Temperature (~ 95 95 95 95 100 95 90 85 100 95 90 85
2.1
(mole cm 2 min- ]) 0.478 x 10 5 0.813 X 10 5 1.38 X 10 5 1.74 x 10-5 2.87 x 10 5 2.25 x 10 5 1.51 x 10-5 1.03 X 10 5 3.37 x 10-s 2.77 • 10-5 1.70 • 10-5 1.18 • 10-5
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67
0.5
C. Concentration Effect Figure 9 shows the effect of activity of HC1, between 0 to 12, on the kCi values, which is linear. Certain deviation of its linear nature was observed only when the activities were above 18, which corresponds to HC1 concentrations near the azeotrope. However, an analogous value of E~ (Figure 10) was determined under these conditions.
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For HC1 the term qO of Meissner's equation is 6.69 at 25 ~ However, to obtain better agreement with the results usually accepted by many authors, ~7 the q~5 value decreased at concentrations above 4 M, and was 6.45 at 5 M and 6.24 at 6 M.
4.3
3.2
2.5
kC~ aHc~ 1.94 3.82 6.85 8.91 11.4 11.7 12.0 12.3 17.6 18.1 18.6 19.2
(molality)
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aHCt
D. Temperature Effect
Fig. 9 - - E f f e c t of activity of HCI on the rate of the reaction (95 ~
Arrhenius plots of rate constants obtained from data of Figures 7 and 8 are presented in Figure 10. The activation energy, Ea, equal to 83 kJ mole -] (20 kcal mole 1) was calculated between 85 and 100 ~
~ 100
95
90
85
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- 4.3
E. Leaching of Zinc from Pyrite Ashes The material was examined by X-ray powder diffractometry. Hematite was found to be the major phase and spinels, such as ZnFezO4 and Fe304, were also present as secondary phases. Mineralogical investigations by conventional reflected-light microscopy, as well as Scanning Electron Microscopy in conjunction with Energy Dispersive X-ray Analysis (EDAX), show that the
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