 |
PNM710S - Pyrometallurgy of Non-Ferrous Metals - 2nd Opp - June 2022 |
|
|
1 Pages 1-10 |
▲back to top |
|
|
1.1 Page 1 |
▲back to top |
nAmlBIA UnlVERSITY
OF SCIEnCE Ano TECHn OLOGY
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)
SUPPLEMENTARY QUESTION 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 6 PAGES {Including this front page)
|
|
1.2 Page 2 |
▲back to top |
|
|
1.3 Page 3 |
▲back to top |
Question 1
(a) Discussthe factors that you would consider in order to set up an Aluminium smelter in a
given location. What measures could be taken for Namibia to be a favourable destination
for such an investment (S marks).
(b) From first principles and applying Stoke's law, derive an expression for the settling
velocity V of a matte droplet of density pd in a molten slag of density psi in terms of the
radius r and density of the matte droplet, and the viscosity µ and density of the slag.
Assume that the rate of settling obeys Stoke's law, and that the frictional force between
matte droplets and slag= 6Vµnr (5 marks)
(c) Given that matte density is 5200kg/m 3, slag density is 3500kg/m 3 and slag viscosity is 0.1
kg/m.s, calculate the settling velocities of matte droplets of radii in mm; 1O; 8; 3 settling
through 1.5m of slag? (5 marks)
(d) How do matte droplets get entrained in slag during converting and what practical measures
are applied in industry in order to increase the rate at which matte droplets settle out of the
slag (5 marks)
(e) What are the environmental and economic impacts of not treating off-gases from a
smelter? How would you rehabilitate land that has been contaminated by acid rain
caused by such off-gases? (S marks).
Question 2
(a) Explain the properties required for an effective furnace refractory (5 marks)
(b) An oil-fired furnace is used to reheat metal 'x' stock from ambient to the working
temperature before further treatment. Given the data below,
0
• Operating temperature: 1300 C
0
• Exit flue gas temperature after preheater: 750 C
0
• Ambient temperature: 40 C
• Specific gravity of fuel oil: 0.90
• Average fuel oil consumption: 0.5 m3 / hr
• Calorific value of oil 14.2 Megajoules/kg
• Weight of stock: 5.5 t/hr
0
• Specific heat of metal 'x': 0.5 MJ/kg/ C
|
|
1.4 Page 4 |
▲back to top |
|
|
1.5 Page 5 |
▲back to top |
Calculate
(i) the heat content of metal 'x' as it comes out of the furnace (5 marks)
(ii) the heat input into the furnace (5 marks)
(iii) the efficiency of the furnace (5 marks)
(b) Ideally, all heat added to the furnaces for smelting or other heating purposes should be
used to heat the load or stock. In practice, however, a lot of heat is lost in several ways,
resulting in typical thermal efficiencies below 50%. Discuss some of the ways by which
heat losses occur in the furnace (5 marks).
Question 3
(a) With the aid of a flowsheet, explain the unit processes that are involved in the
pyrometallurgical treatment of a copper sulphide concentrate from a filter cake through
to blister copper with concentration of 99.5% copper (5 marks).
(b) In one roasting unit, 1500 kg of an ore concentrate of the composition given
below is roasted using excess air.
Ni3S2
FeS2
SiO2
H2O
21%
40%
31%
8%
The roasting unit is heated by oil of composition 85% C and 15% H, the amount of oil is
6.2% of the weight of the ore.
The gases from combustion and roasting mix together and are carried through as flue
gases. Sis converted to SO2. The roasted product consists of NiO, Fe2O3and SiO2and
the roasting reactions are given as;
Ni3S2+ 7/202 = 3NiO + 2SO2
2FeS2+ 11/202 = Fe2O3+ 4502
(i) Explain the mechanism by which roasting is achieved. How would you increase the kinetics
of roasting and hence the production rate" (5 marks)
(ii) Calculate:
|
|
1.6 Page 6 |
▲back to top |
|
|
1.7 Page 7 |
▲back to top |
a)
Weight of roasted product (5 marks)
b)
Volume of the fuel oil used given that its density is 0.89 g/cm 3 (5 marks)
c)
Volume of S02 in m3 (5 marks)
{Note: Atomic weights are Ni= 59, Fe= 56, S = 32, 0 = 16, H = 1}
Question 4
(a) Explain three of the potential benefits of a Green hydrogen industry in Namibia. What is
the significance of green hydrogen globally (5 marks).
(b) The partial phase diagram below shows the Fe-O-S-Si02system slag-matte immiscibility
which develops due to addition of Si02.
(i) Explain the behaviour of the slag as a result of Si02 addition to the bath at a
temperature of 1200°C and give the composition of the saturation points A and B in
terms of FeSand Si02 (5 marks)
1200°c
,
Solid SiO2
', + single liquid
''
Si02 Addition
Mass% FeS
d
Solid SiO2
+ two liquids
Solid SiO2
+ single liquid
10
20
30
40
Mass% SiO2
(c) Discuss the construction of a Flash Smelting Furnace (FSF)and explain how the shell of
the FSFis protected from being burnt through by hot metal (5 marks)
|
|
1.8 Page 8 |
▲back to top |
|
|
1.9 Page 9 |
▲back to top |
(d) What operational factors contribute to the accumulation of 'reverts' during smelting and
converting? Explain why such accumulation of 'reverts' during operations is considered
to be poor metallurgical practice (5 marks).
(e) Explain in terms of composition and temperature why the region shown in the ternary
phase diagram below is the common region for slags (5 marks).
SiO:,
1723,
Trydimite
Wollaslcnito
C~i0-1
Lime-
Criotobolile
Common Slag Region
CoO
2570
FcO
13G~
Question 4
(a) Explain the reason why the blast furnace has generally been replaced by other types of
furnaces such as reverberatory and electric furnaces in the smelting of lead rich ores.
(b) A furnace is charged with 15000 kg/min of copper concentrate which is composed of
the following constituents;
Chalcopyrite (CuFeS2):
65%
Pyrite (FeS2):
20%
Silica (Silica):
15%
The Copper Matte produced contains
60% Cu;
15% Fe;
25%S
and the Slag contains
35% Fe
Assume that the reactions involved are;
2CuFeS2
=
Cu2S+ 2FeS+ 1/zS2
FeS2
=
1/zS2 + 02 =
|
|
1.10 Page 10 |
▲back to top |
|
|
2 Pages 11-20 |
▲back to top |
|
|
2.1 Page 11 |
▲back to top |
FeS+ 3h02 =
Fe0 + 5i02 =
Fe0 + 502
Fe0.5i02
Determine the amount of;
(i) air blown into the furnace (5 marks),
(ii) matte formed (5 marks),
(iii) slag formed (5 marks), and
(iv) 502 in flue gases leaving the furnace (5 marks)
{Note: Relevant Atomic weights are Cu= 64; Fe= 56; S = 32; Si= 28; O = 16)
--------------------------------------End--------------------------------------
|
|
2.2 Page 12 |
▲back to top |
