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Optimal Concentration Of TailingsFor Transportation

By Dr. George Shou

Pipeline System, Inc., USA

September 2003

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Collahuasi Tailings Pond

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Conventional disposal

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Thickened Tailings Disposal (TTD)

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Conventional Disposal Vs. TTD

Courtesy of Eli I. Robinsky

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Advantages of TTD

§More tailings can be stored in a given storage

area, as the average beach angle of tailings

deposition increases with solids concentration.

§More water can be recovered in the thickening

process. This is more significant in areas like

Northern Chile where fresh water is scarce.

§Less contaminated water available in thetailings voids for seepage.

§Lower risk of liquefaction under earthquake.

§

Less dust from the surface of the deposition.

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Thicker is better?

 No necessarily!

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TTD System

Thickening 

Placement

Pipeline

Transportation

Transportation system can be thedetermining factor in the feasibilityof TTD system

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0

50

100

150

200

250

300

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Solids Weight Concentration

   Y   i  e   l   d   S   t  r  e  s  s ,

   P  a

Tailings from mill

Tailings thickened by thickeners

Conventional thickeners

Deep thickeners

Vacuum filters

Pressure filters

Mixture of thickener underflow and filter cakes

Target disposal concentration range

Thickening Concept

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Case Study

§ Throughput = 4 million tons copper tailings per year 

§ Thickener underflow = 60% solids

§ Thickening cost = US$0.12/t

§ Filter cake = 80% solids

§ Filtering cost US$0.14/t

§ Transportation distance = 6 km

§ Elevation drop = 30 m

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Case Study

§ Power cost = US$0.04/kwh

§ Value of saved water = US$0.80/m³

§ Design life = 20 years

§ Discount rate = 10%

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Centrifugal Pump

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Concrete Pump

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High pressure PD pump

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Conveyor 

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Trucking

Courtesy of AMEC

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Thickening Process

12

34

5

6

Hydro-cyclone

Mixer 

Mixer 

Thickener 

Belt Filter 

 pumps

7

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Capitalized cost= Capital Cost

+ Operating Cost in NPV

Costs

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Pump cost comparison for 

transport 100 t/h tailings

$20,000

$200,000

$1,200,000

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Operating Costs

Power cost

Material cost

Labor cost

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Operating Costs

Power cost

Material cost

Labor cost

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Relation Between Solids

Concentration and Yield Stress

0

100

200

300

400

500

600

700

800

900

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

Solids Weight Concentration

   Y   i  e   l   d   S   t  r  e  s  s   (     τ  y   ) ,   d  y  n   /  c  m   ²

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Relation Between Solids

Concentration and Viscosity

0

500

1000

1500

2000

2500

3000

3500

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

Solids Weight Concentration

   P   l  a  s   t   i  c   V   i  s  c  o  s   i   t  y   (     η   ) ,  c   P

Wrong concept

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0

500

1000

1500

2000

2500

55% 60% 65% 70% 75% 80% 85%

Solids weight concentration

   H

  y   d  r  a  u   l   i  c  p  o  w  e  r   (   k   W   )

Hydraulically

optimal

concentration

Hydraulically optimal concentration

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Capitalized Cost

0

2

4

6

8

10

12

14

16

64% 66% 68% 70% 72% 74% 76% 78% 80%

Solids weight concentration

   C  a  p   i   t  a   l   i  z  e   d  c  o  s   t ,  m   i   l   l   i  o  n   U

   S

1 centrifugal pump station1 PD pump station 2 PD pump stations

Optimal

Transportation

concentration

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Conclusions

It is not necessary to pursue an over high solids

concentration for applying TTD technology. The optimal

disposal concentration is determined based on thebalance between the incremental costs of thickening

and transportation and the incremental environmental

benefits.

 A detailed feasibility study is essential for financialsuccess of a tailings project. Hydraulics modeling is thekey to estimate the transportation cost curve