Economic evaluation of alternative management strategies for the - - PowerPoint PPT Presentation

Economic evaluation of alternative management strategies for the disposal of tailings in Western Australia

Aida Carneiro

Young Persons’ Lecture Competition 2018

Mine Production Cycle

Run-of-mine (ROM) Mineral Processing Plant Tailings Tailings Storage Facilities (TSFs)

Slurry Thickened Filtered

Increased realised benefits & increased costs?

Concentrate

Tailings are the non-economic product

• f

the mineral processing operation (waste, chemicals, and process water).

What are Tailings?

• Sustainable development principles and leading practices
• TSFs under increasing scrutiny
• Current evaluation methodologies are limited
• CAPEX and OPEX only, and just of certain items
• Underestimation of closure costs, and overlook of non-technical

issues

Introduction

CAPEX OPEX ENVIRONMENTAL SOCIAL RISK

• Lack of economic data on tailings management

Review of increasing tailings management challenges

• Need to balance economic, environmental and social issues
• Water shortage and its increasing cost
• Desalination cost in Chile US$5/m3
• Social and environmental disputes
• Onerous obstacles to obtain SLO

Source: http://www.huffingtonpost.ca/2011/11/29/48-billion-peru-gold-mi_n_1119767.html http://www.yestolifenotomining.org/tia-maria-shouts-to-defend-their-land-peru/

Review of increasing tailings management challenges

• Catastrophic environmental and public health impacts from

TSF failures

Mishor Rotem Israel, June 2017 Luoyang, Henan Province China, August 2016

Review of increasing tailings management challenges

Samarco Brazil, November 2015 Mount Polley Canada, August 2014 Lithgow Australia, July 2015

Review of increasing tailings management challenges

• TSF failures drive public perception
• Increase regulatory burden and government oversight
• Brazil’s bill PL 3676-2016: ban upstream method
• Mining Rehabilitation Fund (MRF) – July 2013

Tailings physical characteristics,

• perating parameters, and design

considerations

• Non-acid generating gold tailings in WA
• 75-80% < 75 μm
• 266 mm rainfall, 2,500 mm evaporation
• Flat topography
• 2M dry tonnes per year
• 15 years operating LOM
• Conceptual TSF designs

– Conventional slurry tailings (55% w/w) rd = 1.4 t/m3 – Thickened tailings (65% w/w) rd = 1.5 t/m3 – Filtered tailings (80% w/w – MC 25%) rd = 1.85 t/m3

Typical Tailings Storage Facilities in WA

Source: Google Maps

Thickened tailings disposal using CTD method

2 km

Slurry tailings disposal in a paddock-type dam

Pond for surface water management Decant road

Typical Filtered Tailings Storage Facilities

Source: Google Maps

Filtered tailings disposal in a drystack-type facility in WA

Decant road

TSF design for slurry tailings

Thickener Thickener UF Pump Tailings Deposition Pipeline TSF

25 m Φ x 3m sidewall 10 x Centrifuge pumps 272 m3/h

55% Solids

200 mm Φ HDPE 4,640 m long

Source of Make-up Water Make-up Water Pipeline Make-up Water Pump Water Return Pump Water Return Pipeline

200 mm Φ HDPE 1,940 m long 180 mm Φ HDPE 5,000 m long 1,000 m away 5,000 m away 2 x Centrifuge pumps 104 m3/h 2 x Centrifuge pumps 85 m3/h

Supply and Installation

• High-rate thickener (HRT)
• Pumps and pipeline (tailings, return and make-up

water)

• Pipe for spigot dropper
• Spigot offtakes
• Earthworks (site preparation, embankment

construction, underdrainage and decant systems)

Spigot Dropper

Thickener Thickener UF Pump Tailings Deposition Pipeline TSF

25 m Φ x 4.5m sidewall 1 x Piston-diaphragm PD pump, 208 m3/h

65% Solids

200 mm Φ HDPE 2,121 m long

Source of Make-up Water Make-up Water Pipeline Make-up Water Pump Water Return Pump Water Return Pipeline

225 mm Φ HDPE 1,038 m long 225 mm Φ HDPE 5,000 m long 1,000 m away 5,000 m away 125 m3/h – 6 months

• High-compression thickener
• Pumps and pipeline (tailings, return and make-up

water)

• Spigot offtakes
• Earthworks (site preparation, embankment

construction, tailings deposition system, pond for water management)

Pond for Water Management

TSF design for thickened tailings

Supply and Installation

125 m3/h – 6 months

Filter Cake Tailings Transport by Truck TSF

289 t/h

80% Solids MC 25%

Source of Make-up Water Make-up Water Pipeline Make-up Water Pump Water Return Pump Water Return Pipeline

160 mm Φ HDPE 1,000 m long 160 mm Φ HDPE 5,000 m long 1,000 m away 5,000 m away 58 m3/h – 6 months

• Filtration plant (filters, pumps, compressors, cake

conveyors, and slurry tank agitator)

• Pumps and pipeline (return and make-up water)
• Earthworks (site preparation, and pond for water

management)

Pond for Water Management

TSF design for filtered tailings

Supply and Installation

58 m3/h – 6 months

Fast-opening Filter Press Tailings Placement by Dozer

3 filters 60 chambers each

Comparative evaluation summary

Item Conventional Slurry Thickened Tailings Filtered Tailings Solids content of discharged tailings 55% (w/w) 65% (w/w) 80% (w/w) Dewatering unit type High-rate thickener High-compression thickener Fast-opening filter press Tailings discharge method Spigotting from a ring dyke in a paddock dam Central Thickened Discharge (2% beach angle) Drystack Deposited tailings dry density 1.4 t/m3 1.5 t/m3 1.85 t/m3 TSF footprint area 94 ha 324 ha 48 ha Tailings transport system 5 centrifugal + 5 standby pumps and pipeline 1 piston-diaphragm PD pump + 2 charge pumps and pipeline Truck, dozer and compactor Flow of water discharged with tailings 189 m3/h 125 m3/h 58 m3/h

Results and Discussion

1% 56% 78% 50%

20 40 60 80 100 120 140 160

Slurry Tailings Thickened Tailings Filtered Tailings

Estimated Cost (AUD)

Millions

Net Present Cost @ 10%

CLOSURE OPEX CAPEX

AUD 1.11 / t AUD 3.26 / t AUD 0.98 / t

CAPEX comparison

• Technology for high-density tailings = High CAPEX

50%

Filtering technology High-density thickening technology Low-density thickening technology

• Filtered tailings = technology
• Slurry and thickened tailings =

earthworks (site preparation, water management, and embankment construction)

• PD vs centrifugal pump 18%

5 10 15 20 25 30 35

Slurry Tailings Thickened Tailings Filtered Tailings Estimated Cost (AUD)

Millions

Dewatering Technology Thickener Underflow Pump Water Return Pump Make-up Water Pump Pipeline Earthworks

OPEX comparison

• High cost of transporting, spreading and

compacting filter cake

• Increase TSF capacity, pump slurry and make-

up water

• If water costs $3/m3 = costs of make-up water

78%

Distribution of operating costs for filtered tailings 70% 1% 28%

Slurry

47%

Thickened

54%

Filtered

8%

5 10 15 20 25 30 35 40 45 50 Increase TSF Capacity Tailings Thickening Filtration Tailings Transport and Placement Water Return Pumping Make-up Water Pumping MRF

Estimated Cost (AUD)

Millions

Slurry Tailings Thickened Tailings Filtered Tailings

OPEX comparison

• MRF Regulation = $50,000/ha
• Rehabilitation cost + project management + 20 years monitoring
• $185,000/ha (slurry), $46,000/ha (thickened), $38,000/ha (filtered)
• MRF = $100,000/ha and FCR = 1.5%

MRF thickened tailings = 1/3 of total OPEX

• Land under rehabilitation = $2,000/ha

Closure and rehabilitation cost comparison

• Rehabilitation cost higher for CTD option

Thickened tailings 324 ha

• Complex rehabilitation works for wet tailings
• Different life-cycle considered for discounting rehabilitation costs

– LOM 34 years for slurry option – LOM 29 years for CTD and drystack options

$76k / ha

84%

$15k / ha $12k / ha Slurry tailings 94 ha Filtered tailings 48 ha $ 2.5M $ 1.3M $ 0.5M

• Technology to improve water efficiency and lower the risks of

catastrophic TSF failures

• Key elements driving the cost of disposal

– Transport and placement of filter cake (information on costs???) – Large footprint for tailings storage – Volume of retaining embankment – Water loss – Rehabilitation work

Conclusion

Land use Risk of failure Water scarcity Tightening regulations

Ongoing research

Can the real costs of disposing tailings be estimated?

Direct and Indirect Financial Costs – Capital, Operational, and Closure Costs “Recognised” Contingent Costs A Broader Range of Direct, Indirect, Contingent and Less Quantifiable Costs - Environmental Costs External Social Costs Borne by Society - Social Costs

Conventional Cost Accounting Total Cost Assessment

Estimate not only private but also environmental, social, and risk costs to internalise them in the decision making process

Source: after International Institute for Sustainable Development, 2013

Full Cost Assessment

Life Cycle Sustainability Assessment LCSA

Ongoing research

• Due account of environmental, social and risk costs for the

selection of the most cost-effective option

• Disposal method should be selected based on the assessment
• f the accumulated costs using an integrated approach

Can the real costs of disposing tailings be estimated?

Thank you!