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HMY720S - Hydrometallurgy 324 - 1st Opp - Nov 2022 |
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1 Pages 1-10 |
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1.1 Page 1 |
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n Am I BI A u n IVER s I TY
OF SCIEn CE Ano TECHn OLOGY
FACULTYOF ENGINEERINGAND THE BUILTENVIRONMENT
DEPARTMENT OF CIVIL, MINING AND PROCESSENGINEERING
QUALIFICATION: BACHELOR OF ENGINEERING IN METALLURGY
QUALIFICATION CODE: 08BMET
LEVEL: 8
COURSE CODE: HMY720S
COURSE NAME: HYDROMETALLURGY 324
SESSION: NOVEMBER 2022
DURATION: 3 HOURS
PAPER:1
MARKS: 100
EXAMINER(S)
FIRSTOPPORTUNITYQUESTIONPAPER
Prof D Groot
MODERATOR:
Dr T Coetsee, University of Pretoria
INSTRUCTIONS
1. Answer all questions.
2. Read all the questions carefully before answering.
3. Marks for each questions are indicated at the end of each question.
4. Please ensure that your writing is legible, neat and presentable.
PERMISSIBLEMATERIALS
1. Examination paper.
2. Scientific calculator, non-programmable
THIS QUESTION PAPER CONSISTS OF 6 PAGES (Including this front page)
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1.2 Page 2 |
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1.3 Page 3 |
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Question 1
Consider the Outokumpu nickel refinery flowsheet.
Ground NJ-C11 Matte
cower
Sponl
a.arol),'\\"
1-------
loDd
SuJphotct/
&mm
Sulphotct
COPPER
El.£CTROWINNING
Cu Powder
Nici.el Anolyt"
Cobalt Hydn>te
(to Co Rc,finlOl)I)
CuS R"3idue (to Smelter)
NI Co\\hod•
F;gure 4. OutokumpuHarjavalta Mickel Refinery F,~~sh~t
(a) Comment on the suitability of the Outokumpu nickel refinery flowsheet for processing the
feed composition shown in the table below. This feed composition is close to the standard
base metal matte feed.
[6]
(b) What changes would you make to the standard Outokumpu flowsheet to produce better
quality copper? Be specific about the proposed changes and state reasons for your changes.
[3]
(c) Write a balanced chemical reaction for the Cobalt Removal stage.
[2]
(d) Focussing on the main issues, write brief notes on the Safety, Health and Environmental
aspects of your modified flowsheet.
[5]
(e) Electrowinning is done using a specific current density at the cathodes. Briefly discuss the
advantages and disadvantages of using a lower than normal current density, and a higher
than normal current density.
[4]
(f) If you wished to model the leaching kinetics, would you use a shrinking particle or a
shrinking core model? Explain your answer.
[4]
PGM
Ni
Cu
Co
Fe
s
5%
55-70%
25-30%
0.6%
0.3%
6%
2
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1.5 Page 5 |
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Question 2
The 4f elements play an important role in modern electrical motors and generators, while some Sf
elements are important in power generation.
(a) Give an outline of how the individual 4f elements are produced from a mineral concentrate
such as monazite.
(8)
(b) What Safety, Health and Environmental precautions would have to be taken in the process
outlined in (b)? See a typical elemental analysis in the table:
[SJ
Monazite concentrate, %
P20s
24-29
Ln203
55-65
Th02
5-10
LJ30a
0.2-0.4
Si02
1-3
Cao
0.2-0.8
Fe203
1-2
Ab03
0.1-0.8
Zr02
0.7
(c) Discussthe roles that iron and acid play in the acid leaching process of uraninite. Write
suitable, balanced chemical reactions to supplement your discussion.
[5]
Question 3
The typical pyrometallurgical production of copper results in impure (blister) copper. Anodes are
cast from the blister copper, and these are electrorefined to produce marketable copper.
(a) Discussthe effects of masstransfer at the electrodes.
(8)
(b) Discussthe role of electrolyte additives.
(7)
(c) Discussthe typical methods used in the tankhouse to prevent the build-up of nickel in the
copper electrolyte.
(4)
Question 4
The chemistries of nickel and cobalt are very similar, yet their electrowinning processes generally
differ.
(a) Discusswhy nickel is generally electrowon in divided electrochemical cells, yet cobalt is
normally electrowon in undivided cells.
(2)
(b) Describe the operation of a nickel divided cell.
(6)
(c) What are the disadvantages of using divided cells?
(2)
3
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1.7 Page 7 |
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Question 5
Various types of reactors are used in the metallurgical industry: leach and CIPreactors, flotation
cells, autoclaves, etc.
(a) Explain how laboratory testwork can be used to estimate the retention time for a series of
equally sized CSTR'son a plant.
[SJ
(b) A leaching plant needs to be designed to process a cobalt ore. In a laboratory test a sample
of the milled ore was stirred in a beaker with the required reagents. It was found that after
an hour, 91% of the ore had been leached. However, at least 97% leach efficiency is desired.
What retention time would be needed for a series of three stirred tank reactors? State your
assumptions.
(6)
(c) Explain how a stirred tank reactor on a plant differs from a CSTR.
(3)
(d) Discusshow the difference in performance between a real reactor and a CSTRcan be dealt
with during plant design.
[6)
Question 6
A sample of xenotime ore was reacted with a hot, concentrated solution of NaOH. The leach resulted
in a solution containing sodium phosphate and a slurry containing the lanthanide values.
(a) For the same leaching efficiency, how much longer would you expect the leaching time to be
if the particle size was doubled? State your assumptions.
[S]
(b) Could the leaching time be shortened by using a higher temperature or increasing the
stirring rate? Explain your answer and state your assumptions.
[4)
Given information
See following pages (2).
kT
=
N[{
1
1-XA
Jl/N
-1]
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1.9 Page 9 |
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--·--.-..·~-•·-·-1-·--r'l·.-·L -----------__,_-----,-----....-------
I.--··.. ·•·.·.... ·-•··•- ··---·-
.
;l
I
l
, 4.,__•-••l ........ ..,,.t....-,-·.--•••.,•--•
..-•--•~ ......, --~•h•t ! •,..
••-..-- ---•-•--•
..-.,,.._••• .,..,,,_., . .._,.,., _
....
C. ·--·
~----··"·•-
'
?
..........
i! ; ... -- ·-·· --· ----···,··.\\....._. .~ ------
•--·••!-•·-•
!
I
·-1:---1"--,,----
...---l +----·'.
I
,....
__,,f-1
\\
,___...._ _____
0
('r')
....._.._. ______
_..._..__ __,.___. _____
0
.-f
- Snfd(O'rl.:I/A0.\\/;;)
SJ-OP~cU N (O'r.l:1/;\\ O'v:J)
N1, ".)"j:!:!J
.J.
dJ,
.L
' II
\\. -·8-·
n
\\<:
\\
\\ 0....
ci ..-i
5
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2 Pages 11-20 |
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2.1 Page 11 |
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Table25.l Conversion-TimEexpressionfsorVariousShapesof ParticlesS, hrinking-CoMreodel
FilmDiffusionControls
AshDiffusionControls
ReactionControls
Flatplate
Xi,=1-L 1
-t =X
TB
]
L = halfthickness -r=-- r>nL
\\,.)
'E
bkgCAg
-t=Ln
'T
r>nL2
T = 2hgpC
t Ag
-Tt=X II
f>BL
r= bk"CAg
.N...
...
i::
l:!
Cylinder
-I =Xn
-(~Y X8 = 1
T
r= r>nR
2hkgCAg
-I =
T
X8
+ (1-
X8)
ln(l -
X8)
fJBR2
T=4b~ t CAg
-t = 1 -
T
(l
-
X8)12'
fJBR
-r= bk''C
Ilg
0
(r' Sphere
X8 = 1-
-f =Xa
T
-r= PaR
3bkRCAg
(11)
!.=1 -
T
3(1-
X8) + 213 2(1-
X8)
PaRi
(10)
r=
6bq)tCAg
(18)
(
- = 1-
(1 -
X0)131
(23)
T
r>nR
(17) T=bk"C
(22)
Ag
Smallparticle
Stokesregime
-t = l - (1 - Xn)213(30)
'T
-t:
r= fJBR5
(29)
2b~Ag
()/)
-..i.::s:...:.
Largeparticle !.= 1- (1- Xn)112(31)
I..
(u = constant) T
r= (const)R-l0-/2
CAs
Nor applicable
Not applicable
!.= 1-
1
(1 -
X8)'13
PoRo
r= bknC,y,
!.= 1- (1- Xa)113
T
f>BR
r= bk"C
Ag
°'
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2.2 Page 12 |
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