The effect of chloride ion on the ferric chloride leaching of galena concentrate
- PDF / 2,109,949 Bytes
- 11 Pages / 583.28 x 777.28 pts Page_size
- 39 Downloads / 198 Views
a) '/'
5.01
• 10"[Fe3+]~176
/-72100'~ ] exp~------~---/jt/
F0
The model is in excellent agreement with experimental results up to about 95 pct reaction as long as the solubility of PbC12 is greater than about 0.051 M. Where these conditions are not met, deviation from the surface reaction model occurs due to the extremely slow dissolution rate of PbCI2. Therefore the effect of C1- on the brine leaching of PbS is attributed to two factors, the direct reaction of C1with the PbS surface and the effect of C1- on the dissolution rate of PbCI2. The overall dissolution process is viewed as occurring in three stages; in the first stage the reaction is controlled by the surface reaction and described by the model above, then as solid PbC12 is produced the diffusion of CI- would be equal in importance with the surface reaction, i.e., the second stage. As the reaction proceeds further, a shift in the rate-limiting step from surface reaction to product layer or pore diffusion occurs, the third stage. Thus the rate-determining step would no longer be just the surface reaction as observed experimentally at longer reaction times. The practical implications of these results for the processing of a complex sulfide concentrate using sequential, selective, or total leach approaches are also discussed.
I.
INTRODUCTION
The form of the rate equation in this case was given by
IN a previous publication the leaching reaction of PbS concentrate in acidified ferric chloride-brine solutions was shown to be controlled by a surface reaction involving ferric ion up to about 90 to 95 pct lead extraction for the various conditions investigated. 1The kinetics of the reaction of PbS with Fe 3+ was explained in terms of a shrinking core model based on a rate limiting surface reaction. Under these conditions the following relationship between fraction reacted, a, and time, t, is well established: 2 1 -- (1 -- (It) 1'3 =
k,
=
ko
--
k,t
[1] [2]
r0
G.W. WARREN is Associate Professor, Department of Metallurgical Engineering, University of Alabama, Tuscaloosa, AL 35487. SEON-HYO KIM, Graduate Student, and H. HENEIN, Associate Professor, are with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted March 24, 1986.
METALLURGICALTRANSACTIONS B
Zq. [3].' 1 - (1 - a) ~'3
/-72100\] [2.3 • 10~Z[Fe3+]o.z, = 1_ to exp,,. ~ lit [3]
This equation was found to be valid for four size fractions of galena particles ranging from 58 to 98 /xm in diameter, ferric ion concentrations of 0.15 to 0.6 M, and a temperature range of 27 to 57 ~ Deviation from the model was observed for values of a greater than approximately 0.9, and the deviation was observed to occur at higher values of fraction reacted for higher reaction temperatures and smaller concentrate particle sizes. The activity ratio of H § to Fe 3§ was also found to be significant in that the nonoxidative reaction of galena with H § became more important as the aH+/aFe3+ratio increased. In addition, this study point
Data Loading...
