1) Mining projects require steel infrastructure that must withstand challenging environments including water, humidity, temperature fluctuations, and abrasion. Proper corrosion protection is critical given the difficulty of maintenance access. 2) Hot dip galvanizing provides effective corrosion protection in mining environments. It has proven successful in withstanding decades of use in applications involving full water immersion, high humidity, varying pH and water chemistries. 3) Case studies of mining facilities around the world demonstrate that hot dip galvanizing can provide 50+ years of protection with minimal maintenance, resulting in lower total lifetime costs compared to painted coatings requiring frequent reapplication. Understanding the environmental conditions and proper design and application are keys to success.

1. The use of Galvanizing in the
Mining sector in the World
by
Frank Goodwin
William Marques
Rob White
International Zinc
Association

2. Underground facilities
• Mining projects require much steel-based
infrastructure
• The environments can be severe (water and air)
• Maintenance of structural components can be
difficult (limited and difficult access)
• A robust corrosion protection system is required

3. The mine environment can
include:
•
•
•
•
•
Full water immersion
Long-term surface wetness, high humidity
Elevated temperatures
Acidity and alkalinity
Impact and abrasion

4. Corrosion in South African
mine shaft, uncoated, 20 years
service

5. Blasting effect of sharp stones on
galvanized structure

6. Effect of pH on the
rate of corrosion
of zinc:
(a)rapid corrosion
(b) stable film –
low corrosion rate
(c) rapid
corrosion
Otherwise pure H2O !

7. Corrosion in Mine Waters
Mine water can vary in pH from 2.8 to 9.0, depending on
origin and possible pretreatment
Mine water can be very hard, then it can contain salts
that help create a stable protective film on Zn
In: normal waters:
ZnO +H2O
Zn(OH)2 (both slightly insoluble)
5Zn(OH)2 + 2CO2
Zn5(OH)6(CO3)2 + 2H2O (highly insoluble)
5Zn2+ + 2HCO3- + 8(OH) Zn5(OH)6(CO3)2 + 2H2O (highly stable)
Fe + water = rust
Fe + Zn + water
Fe + Zn(OH)2
(cathodic protection and precipitation))

8. With Cl- contamination
With SO4-2 contamination

9. Other reactions are present
A galvanized coating will be attacked fairly rapidly at
1000 ppm Cl- levels in soft water
But, similar levels of Cl- may be tolerated on galvanized
surfaces in hard water (>100mg CaCO3).
Hard water, including water high in SO4-2, can precipitate
a deposit of protective Ca salt, such as carbonate or
sulphate, on to the galvanized surface.
Such deposits retard the dissolution of underlying Zn as
soluble ZnCl2 or ZnSO4

10. The mine environment
Rate of
corrosion
observed on a
galvanized
coating fully
immersed for
100 days
in South African
mine water
having a pH of
5.7 (chloride
986 p.p.m.,
sulphate 270
p.p.m., total
dissolved solids
2689 p.p.m.).

11. The mine environment
In high humidity, pH of condensed moisture on Zn is
influenced by contamination from acidic gases (e.g.
CO2 and NO2), also deposited dust contamination.

12. Example from Black Mt., S. Africa
Pb/Zn mine, HDGASA inspection

13. Flowing water can cause
erosion/corrosion
(Black Mt. HDGASA inspection)
Use of cover to prevent flow
contact is effective

14. In many cases very satisfactory
performance is seen
238 µm of Zn remaining
165 µm of Zn remaining

15. Hot dip galvanized shaft guides
before installation

16. Surface Facilities
In many cases mine surface facilities are viewed
as “chemical” environments (SO2, Cl-) where
galvanized steel would not be applied, but many
are benign as, apart from some acidic and
alkaline reagents, generally in small quantities,
their processing streams are at near to neutral pH
values

17. Atmospheric Corrosion
Corrosivity Categories

18. Life of galvanized coatings

19. Life of galvanized coatings
to first maintenance

20. 6500 tons of superstructure hot
dip galvanized steel at BafokengRasimone Platinium Concentrator
Plant, S. Africa

21. Galvanized steel, Marula
Platinum Smelter, S. Africa

22. Douglas Middelburg Opimisation
(BHP Billiton)
Primary Crusher
26 km of Conveyors

23. Sishen Iron Ore Beneficiation
Plant, S. Africa

24. Anglo Platinum’s Spud shaft
193µm of galvanized coating being indicated
on horizontal hand railing.
101µm of galvanized coating being indicated
on the “ball” of the stanchion.

25. Alcoa Pinjarra Alumina Refinery,
Western Australia

26. Teck Red Dog, Alaska
54 tons of galvanized
structurals

27. Actual costings
ESTIMATE OF TOTAL COSTS FOR STRUCTURAL STEEL PROJECT
(ACTUAL PROJECT – 30 YEAR LIFE EXPECTANCY)
South African Rand (R)
Amount of Steel to be protected = 6300 tonnes
Hot Dip Galvanizing 1
Heavy Duty Coating 2
Initial Cost of Application
R9 072 000
R11 340 000 3
Total Initial Cost
R9 072 000
R11 340 000
Future Maintenance Costs 4
Years 5 - 30
Nil
R250 000 pa
Total Maintenance Costs
Nil
R8 250 000
Total Lifetime Cost
R9 072 000
R19 590 000
Notes:
1.
Actual Cost
2.
Based upon – vinyl primer, vinyl intermediate, vinyl enamel finishing coat
to total DFT 200µm
3.
Includes scaffolding, abrasive blast cleaning and all inspection
4.
Based on experience at similar sites by consultant mining engineer and all
estimates at current prices including scaffolding and inspection

28. Typical duplex coating
specifications for SA mining
industry
Environment
Underground
corrosive
conditions
Primer coat
(um)
Epoxy (40)
Intermediate
coat (um)
Epoxy tar
(90)
Top coat (um)
Epoxy tar
(90)
ISO 12944-5
Surface plant corrosive conditions
Epoxy
(100)
Surface plant moderate
conditions
Epoxy
(75)
Epoxy
(40)
Epoxy
(75)
Vinyl (15)
Vinyl (80)
Epoxy
(75)
PU
(50)
Epoxy
(125)
HB vinyl
(100)
S9.11
S9.09
S9.01
Phenolic
(100)
PU
acrylic
(30)
S9.10
Vinyl (40)

29. Remarks
• Mining industry applications can be severe, but
many successful applications are realized
• Success depends upon:
-Understanding the environment of application: use
test samples when situation uncertain
-Understanding of how to design steelwork for
galvanizing
-Work with fabricators on correct practices for
galvanizing
-Good coordination between galvanizer and
contractors