The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
“ADDRESSING THE CHALLENGES OF SUSTAINABILITY IN THE
MINING INDUSTRY”
A Davis
Nalco Africa (PTY) Ltd
ABSTRACT
The UN in 1987 described sustainable development as “development that meets the needs
of the present without compromising the ability of future generations to meet their own
needs.”
Nalco sees sustainability as linking, or recognising, the three pillars of sustainable
development, social, economic and environmental drivers, into viable solutions for our
customers. Such that the impact of working with Nalco will improve our customers’ unit
costs of operations in a sustainable manner.
The purpose of this paper is to demonstrate through case studies how Nalco has been using
water mapping and process audit techniques coupled together with state of the art
technology, to identify areas on base metals mine sites where sustainable improvements in
water management result in reduced total cost of ownership.
The case studies will cover and show:
• How water mapping better identified and quantified water losses (over 50,000
m3/day via evaporation) from a mine site and what could be done to reduce this and
provide high quality water back to mining operations (9,000m3/day).
• How high quality water used for dust control could be reduced. 80% savings
(566m3/day) in water use and the ability to switch to lower quality tails water, with
minimal road preparation.
• How understanding what a client has on site via a process audit can help in
developing a solution which minimises capital outlays and provides a solution to
processing challenges. Using redundant site equipment and dams allowed for pretreatment operations to be carried out without the need to spend over US$1 million
for plant.
• Improved process management in RO processing can reduce maintenance costs
(such as membrane replacement) and increase RO plant availability from less than
30% to over 90%.
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Page 291
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
INTRODUCTION
The United Nations in 1987 described sustainable development as: “sustainable
development is development that meets the needs of the present without compromising the
ability of future generations to meet their own needs.”
By recognising the three pillars of sustainable development:
• Social
• Economic and
• Environmental drivers
And linking them into viable solutions for our clients and customers, Nalco has been able
to provide them with a return on the investment they make when working with Nalco.
The mining industry has particular issues with water and it’s management around mine
sites and as part of a “social license to operate”, many mines are looking to address the use
and management of the water they take onto their site, and how to extract the maximum
value from it, to reduce the amount of water they require.
In areas where water is scarce, mines which can use water more efficiently and reduce their
overall drawdown on resources are seen by the community in a more favourable
light.Likewise were there may be an abundance of water (such as acid mine water), it may
need some form of treatment to make it suitable for reuse or, alternatively, discharge.
This paper focuses on how water managementsolutions were arrived at for threemine
sites,to show the breadth of opportunities available to the mining industry.The particular
solutions were fitted with the requirements of each mine site to provide ongoing sustainable
outcomes.
HOW ARE SUSTAINABILITY ISSUES BEING ADDRESSED NOW?
Many mines will respond to problems or issues on a case by case basis. There is nothing
wrong in doing this, however, it does mean that potentially viable alternative solutions may
not even be thought about or considered, because they do not exactly appear to address the
issue being faced, or it could be that another area of the site has a need which could be
satisfied by a solution, but this need is unknown to the section of the plant facing the
problem. This is of particular concern on large integrated sites.
It may be that a potentially more cost effective solution (site or business wide) could be
arrived at, if a broader view is taken of the site in question. Depending on the situation, it
may be possible to utilise particular waste water in a different section of the plant, with
only minimal remediation efforts. Or with a more complete treatment, make the final
product one which would boost yield.
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Page 292
The So
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Paagee 29
93
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
Understanding processes and impacts upon these processes is critical to ensuring all the
potential options are investigated. For example, water quality has an impact on the flotation
process in base metals. Knowing what type of water chemistry is needed can help in the
scoping and design of the plant.Therefore, activities such as water mapping and water
audits can help in understanding the water circuit on a mine site.
Nalco uses processes such as water mapping and water audits, to initiate the process. By
having a complete understanding of the mechanical, operational, and chemical aspects of
the processes and site, it is then possible to drill down and better understand what is
occurring in particular areas of the plant.
This understanding of the whole circuit provides:
• What’s used in the circuit, such reagents, modifiers and pH correction
• Quality of inputs required at various points in the circuit
• Unit processes and any limitations
• Upstream and downstream impacts, an example might be, is dust control used on
feed stockpiles.Does this impact processing?
Once this is completed the process then moves onto addressing:
•
•
•
What is the current situation?
What is the desired outcome?
What is the gap that has to be bridged?
By then being able to place an economic value on the water used in, and across, the
processing circuit, the benefits from a particular solution are determined and compared to
other competingsolutions.Included in the sustainability assessment are considerations
whether there are any by-products which could be utilised elsewhere in the plant or sold to
add value to the project.
Examples of how Nalco used this methodology:
•
•
•
Base metals water mapping project
Iron ore water mapping project: 1) Dust and 2) Tailings
Coal mine, Acid Mine Drainage (AMD) process audit – Reverse Osmosis (RO)
process management and site water management
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Page 294
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
CASE STUDY 1
BASE METALS WATER MAPPING PROJECT
This project commenced because of a need to ensure the local community did not run out of
water. Forward thinking management could see that should the local water supplies deplete
to a level such that the town could run out of water, then the mine would have to reduce or
cease operations.
Nalco was asked if it could help and a project team was put together to map water use
around site.The result of this week long audit is shown in the water map (Figure 2).This
map was used to find potential sources of water to help meet the fresh water make up needs
to the plant.
Figure 3 then shows the water flows around the base metals concentrator.
The most obvious source of water was the tails, however, due to operational issues no
change could be made to the solids concentration in the tails.
The minequarries it’s old TSF (tails storage facilities) for use as underground fill in the
mine. The question was asked:“Would it be possible to remove solids from the tails
thickener feed, recover water and size the solids required to allow then to be used as
underground fill, for less than they paid to quarry the material now?”
After reviewing potential process options a plan was developed which would allow solids
recovery to occur(figure 4). It was believed that this plan could be carried out and would
make “fill” available for a similar figure to current quarrying costs and recovery water from
the tails which could then be recycled back into the plant and reduce the fresh make up
waterrequirement to the site. On figure 3, the location of the proposed solids and water
recovery plant in the process is also shown.
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Page 295
To Tails' thicks
Total:
Fresh water
Fresh Water
Water Source
Storage
249.9
235.5
171.5
922.4
117.4
250
1793.4
54
183.9
355.1
2734
Mining surface
X41
U'ground mining & Serv.
Other Process Water
Users
Lead smelter
Weak acid disposal
Acid plant
Smelter
Zinc filter plant
Reagent Mixing
Heavy Medium plant
#4 Concentrator
#2 Concentrator
Mineside
Admin, OH&S, Service
To Sister Mine
Users
2380.3
108.9
182.9
422.4
538.9
791.4
1063.7
1125.3
Losses
Others
General supply
Kennedy Quarry
Wheel wash
Paste Fill
Wet fill
Refrigeration
Oxygen plant
Compressed air
Mine power station
Tails Thickeners
Cooling Tower
828.8
Disposal
X Site STP
35563.7
Tails Dam
23328
8640
Un'ground water
Site rain water
NALCO Engineering Group
NALCO
Road dust control
Un'ground
Un'ground
Figure 2 – Base Metals Water Map
Underground
To reagent
11232
798.7
123.8
1267.3
Treatment
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Process
Water Tank
34560
58891.7
24066.04
Evaporated
Flow (KL/d)
Clean WW
6733.1
464.3
Wastewater
Sewage
544.94
453
Fresh Water
Flow Balance Chart
A Davis
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
dtL ytP ailartsuA OCLAN
8 87 42 4 0 00 1 4 NBA
31 03 6 13 9 2 1 6 :x aF 0 00 3 6 13 9 2 1 6 :hP
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,teertS nosrednA 2
A Davis
Nalco/OK Plant
9 ML/day
Page 297
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Figure 3 Water Flows around the Base Metals Concentrator
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Dav
D is
P e 2988
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Fiigurre 4 Pro
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Thee Southeern Afric
A can Insttitutee off Minningg andd Metall
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6th Sou
S therrn Affricaan Base
B e Meetals Connferrencee 20011
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
Next steps have been to validate the process. Nalco has put a RO plant on site to test
membrane performance and possible issues arising from the use of this process.
Figure 5 Reverse Osmosis Test Rig on site
As a separate possible process option, there has also been some investigation into tails
stacking. The pictures below show some of the initial testing.
Figure 6 Tails Management Testing
The audit and water mapping was able to identify and quantify water flows around the
whole site (which had not been done at whole of site level before) and quantify losses (over
50,000 m3/day via evaporation alone) from the mine site.
________________________________________________________________________________
Page 299
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
To address the requirement to reduce water requirements for site, an plan was presented
which allowed siterecover approximately 9000 m3/day from the tails system, and also
provide material which could be used as underground fill back to mining operations, upto
50,000 tonnes per month .
Subsequently, a second processing option was looked at to investigate tails stacking as a
means to recover even more water from the tails and reduce the requirement for additional
storage space in the TSF.
CASE STUDY 2
IRON ORE WATER AUDITING PROJECT
In a similar situation to the base metals processor, an iron ore processing site could see that
it had animperative to improve its operations from a sustainability point of view.
Significant amounts of water are used around its mill and mine sites, and Nalco was asked
if it could audit the water circuit and identify savings.
Again, an audit team was put together which then spent time on site understanding how
water was used around the mine site. Meetings were held with senior management to
understand the future desired situation and any current issues they had.
A water map was put together for the site, see Figure 7.
The water mappingshowedthat a significant portion of water used on site (approximately
43%) is used as road dust control, with the bulk of the remainder (31%) lost via evaporation
from the tails dam. Much of the water entering site comes in as high quality town water.
With a new plant being built the water flows around the site where changing. Figure 8
shows the proposed changes in flows. The crossover point for dust suppression water
between the new and old plants was now the Standpipe Buffer Tank. Again, dust control
and evaporation losses accounted for the bulk of the water usage.
Site then site has commenced investigations into options available for reducing the amount
of water sprayed onto its roads for dust control.A number of differing reagents had been
tried to reduce water consumption determined to provide sustainable solutions. Both as a
spray onto the road and incorporated into the surface.
Nalco proposed the use of Haul EZ® dust control reagent, based upon a renewable resource
which is mixed with water and sprayed onto the road surface. See Figure 9 for a photo of
the trial situation.
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Page 300
Iron Baron
Supply
Moisture in Ore
Water Sources
0
0
1557
65
68
3.4
Water Balance Chart
A Davis
705
35.3
OBP Plant
1335
66.8
300
15
Tailings Dam
Recovery
Figure 7. Iron Ore Mine Site Basic Water Map
705
35.3
787
39
Users
770
42.8
630.1
31.5
Water Cart for
Dust Control
Evaporation
Losses
Product &
Rejects
Final
Page 301
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Turkey's Nest
Hill Tank
Storage Tanks
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
Flow (KL/d)
Flow (KL/h)
Used Water
Clean Water
Process Water
SA Water Mains
Site Supply
Water Sources
96.23
15
577
127
89.1
54
59.6
577
214
32
39
10
127
1.83
Export Shed
Pellet Plant
F&F
PP Losses
Concentrator
Water in Slurry
Line
Conc Plant Tails
Loss
RMS Coarse Tails
Process Water
Pump
Plant Losses
Standpipe
Rail Car Capping
Pumps
298.1
155
30
9
10
82.2
0.2
2
Users
Crush & Screen
Stockpile Capping
Amenities Vehicle
washdown ect
OBP
Floc
Showers etc
Thickener
Turkey's Nest
Tailings Dam
20
Recovery
Figure 8 – Proposed Changes to Flows with a New Processing Plant
F&F Process Water
Tank (695KL)
Conc Process Water
Tank (1 ML)
Standpipe Buffer
Tank (>2000KL)
PS 6 Tank (200KL)
Storage Tanks
0
Underflow
Water Cart
127
Evaporation
Losses
Final
Page 302
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496.6
Flow (KL/h)
Used Water
Process Water
Clean Water
Water Balance Chart
A Davis
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
Figure 9. Treated Haul Road
Other areas which have been investigated involve determining if tailings can be dewatered
effectively and the water recovered before it enters the tails dam, as a method of reducing
water loss through evaporation.
On site testing and monitoring has shown reductions in water use of over 75%, through the
use of the Haul EZ®technology, and comments from site would indicate that the road
surface has become harder and more durable during usage. See Figure 9for a view of a
Haul EZ® treated road.
From the analysis of the site water usage, the customer was able to understand the
principle areas of water usage and loss. This understanding of the priority areas allowed
focus on methods to have significant impact in reducing water usage through dust control
and water loss, through tails water management. Results so far have seen a reduction in
water consumption of approximately 17,000 m3/month (566 m3 /day) compared to previous
use for road dust control. Investigations are still ongoing relating to the tails stacking.
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Page 303
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
CASE STUDY 3
HUNTER VALLEY COAL MINE
This underground coal mine had to dewater in order to maintain production. The mine is
essentially at the bottom of the seam, so water flows down through the seam from other
operations. Without mine dewatering the mine would flood.
The water from underground had high levels of iron(over 500 ppm) and manganese (over
20 ppm), plus other salts, and could not be discharged from site without treatment. The
water could be viewed as AMDtype of effluent.There was also an imperative to treat some
of the water to provide very clean water for mining equipment. The sitehad already
installed a SWRO (seawater reverse osmosis)plant to meet its requirements for treating the
discharge water and providing clean water for operations. This installation was completed
without consideration of the complete water circuit and therefore was not optimally
engineered. Consequently the mine was not satisfactorily meeting its water management
needs.
CHPP
At surface water
flows into Kalingo
Dam
2500-4000 m3/day
26000 TDS
(104000 kg solids)
Process Water Dam
P-7--
RO Plant
Austar Dam
Tailings
Pipeline
P-8--
Permate to Bellbird
Creek
<600 TDS
Pump to surface via
Kalingo Shaft
Underground workings
Figure 10, Basic Water Map of Coal Mine Site Flows
The system in place involved two SWRO trains in series with the brine from each going
through a third train. The brine was being sent underground for disposal.The output of the
SWRO plant varied sometimes good results, sometimes mediocre, and sometimes no result.
No apparent reasons could be seen for this, SWRO membranes life was poor and SWRO
plant output was falling.
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The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
Site knew one of the problems - the short life span of a set of membranes within the RO
trains was costing significant amounts of money in that a new set of membranes was
costing approximately US$80,000. They were changing out a set of membranes, on
average, every three months, which pointed to inadequate pre-treatment and insufficient
RO feed water scale inhibition treatments.
Feedwater to RO plants must be to a standard, and this required that site (once mining was
about to start again) develop a process to meet the RO plant feedwater requirements. This
meant the iron and manganese had to be removed to levels suitable for the RO (ideally
ferrous iron 4 mg/L max, ferric iron and manganese 0.05 mg/L max.))
Nalco was asked if we could investigate the water andhelp develop a plan to help treat the
mine water, such that reliable and economic water supply of consistent quality suitable for
the Coal Handling and Preparation Plant (CHPP)and underground operations.
The process involved:
1.
2.
3.
4.
Mapping the water circuit from mine to plant (Figure 10)
Analysing the mine water (Table 1)
Modellingtests to understand how the water reacted to pH correction
Predictive studies for scaling potential
The mine needs to pump approximately 2.5 ML per day to ensure the mine stays dry
enough for work to take place, and to provide the necessary amount of water for processing
to occur. This was to increase to 3.5 to 4 ML per day as the mine moves into lower areas of
the coal seamand mine.
Table 1. Typical Analysis of Acid Mine Water
Analyte
Iron (II)
Manganese
Sulphates
Calcium
Magnesium
Sodium
Chlorides
Total dissolved solids
pH
Level (ppm)
500
20
10 – 14,000
500
600
4,000
700
16 – 26,000
<4
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Page 305
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
The dissolved mineral species, and small particulates in the RO feed water could impact
RO, and due to the mechanics of RO there is the likelihood of scale and other types of
fouling occurring in the membranes.This meant consideration would have to be given to
negate or minimise these factors. Plus other issues to consider included where the brine will
go, and could it have any impacts on the process?
The initial thoughts to treat the water involved the following process steps:
•
•
•
•
pH correction of water when it comes to the surface
Solids/liquid separation of the flocs formed
Polishing of the pH corrected water to reduce any remaining iron or manganese
Filtration to remove any remaining suspended solids
Coagulant
Sodium Hypochlorite
Clarifier 50m3
Clarified Water Tank
Floc Column
Clarifier 50m3
Flocculant
Filtration
Lime or Caustic Soda
Process Water
Dam
Spray Vessel
or Kalingo Dam
Sludge Down
Kalingo Shaft
To Process
CHPP or
RO Plant
Pump from Underground
Figure 11. Proposed Process Flow to Treat Underground Water
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Page 306
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
The proposed solution involved aeration of the AMD water from the mine followed by pH
correction with lime or caustic soda, clarification of the treated water and filtration to
remove any remaining solids.
Site had some infrastructure in place which it was keen to utilise if possible. Calculated
capital costs for the above process was estimated at US$3 million, plus other construction
related costs. Other forms of clarification were investigated as we knew there would be
significant amounts of gypsum scale formed during the pH correction phase. These
involved recycle to help seed the scale. Cost became a major issue and it was decided to go
with a lower cost option.
There was a medium sized lime plant, which was believed to be somewhat undersized for
the calculated amount of pH correction and flows, and some other dams which could be
utilised for holding time to allow for settling purposes for any flocs form. Site decided that
they would try this first to save available capital for other projects.
The final process developed included aeration of the underground water once it arrived at
the surface. A number of dams had aeration devices installed to facilitate this process. The
major part of the pH correction utilises the existing lime plant on site, and settling of flocs
was carried out after flocculant addition in a “horseshoe” dam. As the treated water was
channelled out of the dam, it was polished with sodium hypochlorite to oxidise any
remaining iron and manganese. Levels of iron and manganese were reduced to lower than
1ppm and lower than 10ppm respectively.
The treated water was them stored in a large process water dam, which allowed gypsum to
deposit onto the bottom of the dam.
Figure 12. Gypsum Scale Growth over rocks and branches in the process water dam
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Page 307
The Southern African Institute of Mining and Metallurgy
6th Southern African Base Metals Conference 2011
A Davis
In Figure 12it can be seen the level of gypsum scale which formed onthe bottom of the
process water dam. Both Nalco and site were very concerned about the amount of scale and
how it could potentially impact the process water pipe work to the SWRO, and also the
final pre-treatment process (pre-filtration, green sand filters, and cartridge filters) for the
SWRO. An antiscalant wasused to help protect the pipework from the dam to the
SWRO.This immediately helped maintain flows to the SWRO plant and reduced downtime
for cleaning.
This all helped to ensure that the SWRO plant was supplied with feed water, and improved
availability of the plant. The final process involved:
•
•
•
•
•
Aeration of mine water once it arrived at the surface utilising existing site dams
pH correction to facilitate removal of iron and manganese
Solids/liquid separation of the iron and manganese hydroxides
Final polishing via oxidation after pH correction
Addition of an antiscalant to stop scale in pipework leading to the SWRO pretreatment stage
Finally, toimprove operation and importantly control of the SWRO units, a dosing and
controlsystem called RO TRASAR® was installed on one train as a trial. This system uses
“tagged” molecules to determine actual reagent dose rates required to respond to fluctuating
flows.Designed for real-time on-line monitoring of antiscalant concentration, the
technology actively controls antiscalant dosing down to a level of 0.5ppm of product. This
improves performance and helps reducing fouling of the membranes, thereby changing
cleaning cycles and increasing availability. This system also monitors pressure drops and
flows within the SWRO units and can send alarms when the unit reaches pre-set values.
The RO TRASAR®, helped get the SWRO plant back to design capacity and improved
overall plant efficiency and output. All three processing RO units are working closer to
design specs with Unit 3 recovering around 20% more permeate from the brine processing
cycle. Additionally, the plant has just achieved 14 months trouble-free operation from one
set of membranes, compared tothree months prior to the changes made to mine water
treatment and TRASAR® control.
CONCLUSION
Every situation on a mine site is different and it is rare that the same solution can be used
on more than one site. So it is important to understand what is going on at the mine site and
adapt a solution to fit the particular needs to the site. By working with a customer/client and
bringing know-how, expertise of MOC factors such as water chemistry, Nalco can then
bring innovation and technology to provide a solution to site needs.
Each of the case studies shows how auditing and mapping was able to identify areas where
water was used, and provided a place to start identifying those areas which could be
targeted to achieve the needs of the site.
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• Water mapping better identified and quantified water losses (over 50,000 m3/day via
evaporation) from the mine site and then allowed some focus on what could be done
to reduce this, and provide high quality water back to mining operations (9,000
m3/day).
• Identify other means of process water recovery from tails
Iron Ore
• How high quality water used for dust control could be reduced with 80% savings
(566m3/day) in water use and the ability to switch to lower quality tails water, with
minimal road preparation.
Hunter Valley Coal
• Process auditing developed a solution which minimises capital outlays and provides
a solution to processing challenges. Using redundant site equipment and dams
allowed for pre-treatment operations to be carried out without the need to spend
over US$3 million for a lime plant and other new water treatment plant components.
• Improved process management in SWRO processing reduced maintenance costs
(such as membrane replacement from 3 monthly to over 14 months) and increased
RO plant availability from less than 30% to over 90%.
TRASAR® and Haul EZ® are registered trademarks of Nalco Company
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