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PNM710S - Pyrometallurgy of Non-Ferrous Metals - 1st Opp - June 2022 |
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nAmlBIA unlVERSITY
OF SCIEnCE Ano TECHnOLOGY
FACULTY OF ENGINEERING AND SPATIAL SCIENCES
DEPARTMENT OF MECHANICAL, MINING AND PROCESSENGINEERING
QUALIFICATION: BACHELOR OF ENGINEERING IN METALLURGY
QUALIFICATION CODE: 08BMET
LEVEL: 8
COURSE CODE: PNM710S
COURSE NAME: PYROMETALLURGY OF NON-
FERROUS METALS
SESSION: JUNE 2022
DURATION: 3 HOURS
PAPER: THEORY
MARKS: 100
EXAMINER(S)
FIRST OPPORTUNITY QUESTJON PAPER
Prof. Godfrey Dzinomwa
MODERATOR:
Prof. Sofya Mitropolskaya
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.
PERMISSIBLE MATERIALS
1. Examination paper.
THIS QUESTION PAPER CONSISTS OF 5 PAGES (Including this front page)
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Question 1
(a) A copper sulphide ore concentrate assaying 30% Cu, 25% Sand 10% H2O is to be treated to
produce metallic copper assaying 99.5% Cu. The process incorporates recovery of Sulphur in
the form of Sulphuric acid. Assuming 150 tph of ore concentrate;
(i) Outline the flowsheet, indicating the main stages in the process of Cu and S recovery (5
marks)
(ii) Determine the amount of H2SO4(dry) produced in tph if 65% of the S in the feed is
recovered in the H2SO4acid plant (5 marks)
(iii) The process flowsheet shows that Cu is upgraded at four main stages, and 1.5% of the Cu
is lost at each of the stages. How much of the final product is produced in tph? (5 marks)
(iv) In what form is the Copper likely to be lost at each of the stages and what steps would you
take to minimize the losses (5 marks)
{Note: Atomic weights are Cu= 64, S = 32, 0 = 16, H = 1)
(b) For the reaction of lkg-mol of methane {CH4)gas at 101.32 kPa and 298K,
CH4{g) +
H2 0(1)
=
CO(g) +
3H2{g)
Calculate the standard heat of reaction H0 at 298K and comment on whether the reaction
can be expected to proceed spontaneously without heat addition, given the following
standard heats of formation at the same temperature (5 marks);
CH4(g)
b.H0 =
-74.848 x 103 kJ/kg mol
H2O{I)
co (g)
-285.840 x 103 kJ/kg mol
-110.523 x 103 kJ/kg mol
H2 (g)
0
Question 2
(a) A copper ore mixture amounting to 2500kg is roasted in a furnace to produce a calcine ready
for smelting in an electric furnace. The percentage analysis of the ore mixture is provided
as
Feed Constituents
Cu
8.5
SiO2
24.5
Fe
30.5
s
25.7
H2O
5.0
Calcine
Cu 9.5
s
12.0
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• The Copper is present in Calcine in the form of Cu2S,and Fe is in the form of FeSand
Fe2O3_Air is supplied and Sulphur burns to produce SO2.The overall roasting reaction is
simplified as: 2Cu + 3Fe + 3S + 5/202 = Cu2S+ FeS+ Fe2O3+ SO2
Calculate the following;
(a) Weight of calcine produced (5 marks)
(b) Volume of Air used in m3 per to roast the ore (10 marks)
(c) The weight of Fe2O3formed in the calcine (5 marks)
(d) Percentage sulphur removal (5 marks)
Question 3
(a) You are the Metallurgical Manager of an integrated Copper Smelter comprising Drying,
Smelting and Converting Plants. The Dryer develops a fault and has to undergo repairs for a
week. The feedstock for the smelter, and hence the Converter will run out in three days'
time at the normal plant throughput (rate). What options will you implement to avoid
cooling down the furnace and converter thus damaging refractories? (5 marks)
(b) According to Stokes' law, the rate at which matte droplets settle through a layer of slag is
given by;
V
_l Pctrop - Pslag (d. )2
g
Y"'drop
18
Pslag
In this expression V is the settling rate of the matte droplets (m/s), g the
gravitational constant (9.8 mis\\
Pdrop matte density (3900-5200
kg/m
3
),
PslJ& slag
density (3300-3 700 kg/m3), Psbg slag viscosity (~0.1 kg/m·s) and ¢10,11 the
diameter (m) of the settling matte droplet.
(i) Given that matte density is 5100kg/m 3, slag density is 4000kg/m 3and slag viscosity is 0.1
kg/m.s, calculate the settling velocities and residence times of matte droplets of radii in mm;
8; 5; 2; 1; 0.5 settling through l.0m of slag (10 marks)
(ii) Explain the practical steps the Plant Metallurgist should take to increase the settling rate of
the matte drops in slag and therefore increase the rate at which matte and slag separate in
the furnace/converter (5 marks)
(c) With the aid of a sketch, discuss the key features of the Imperial Smelting Process for Zinc
sulphide concentrates. Explain why it has become universally favoured as well as its
disadvantages (5 marks)
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Question 4.
(a) As Chief Metallurgist of a Group of companies, you find that the electrostatic precipitator
and the rest of the off-gas treatment plant of Smelter X (Ni-S) has not been operating for
some weeks and the Smelter X Manager seems to be accepting the position, mainly
motivated by the reduced electricity bill due to the offline units. Outline to the Manager the
disadvantages posed to the Company by this situation (S marks).
(b) With the aid of the Cu-S equilibrium phase diagram given below, explain the changes in the
composition of the matte bath during the Copper Converting process along the
temperature line abed (S marks)
1400
molten
- blister
copper
1300
molten 'blister copper' + molten 'white metal'
mol ten
'whi le metal'
- u
D
(l)
120Od
~----4E--
L..
converting temperature ______
ba
Cll
L..
(l)
0.
E
(l)
1100
I-
0.9% S
'0.8% S
1105 ·c
molten blister copper+ solid Cu2S
1067 ·c
113 1 ·c
19.7%S
1000
solid copper+ solid Cu2S
900
0
I
5
10
15
20
Mass% S
Fig. ..... , Cu-S equilibrium phase diagram showing coppcrmaking reaction path (a, b, c,
d, l 200°C) (Shonna und Chong. 1980).
(b) If the operator mistakenly allows the bath temperature to drop from 1200°C to 1100°c when
the Sulphur level in the 'white metal' has been reduced to 10%, what products do you expect
in the Converter (5 marks).
(c) Below is a ternary phase diagram showing the CaO-MgO-SiO2 system. Explain, in terms of
composition, acidity and viscosity, the differences experienced with the two slags in the
regions marked A and Bon the diagram (S marks)
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Si02
0.8
0.7
0.7
Cao ~------------------------MgQ
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Cao (mass fraction)
(e) The concentrate charge in an electric furnace separates into matte whose density is 5.0
g/cm 3 and slag with a density of 3.2 g/cm 3 . If the residence time in the furnace settler is 7.5
minutes for both matte and slag, what is the volume of matte and slag in the furnace if they
are both tapped at the steady rate of 10 tph without build-up.
{5 marks)
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