Technology for the Cost Effective Treatment of Acid Mine Drainage (AMD)

Presentation to the Parliamentary Committee on Water and Environmental Affairs

07 & 08 September 2011

Dr Roger Paul

Needs Analysis

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South Africa is a water stressed country, and access to adequate quantities of clean potable water by all the peoples of South Africa is a major challenge.

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Water pollution and the generation of Acid Mine Drainage (AMD) is today one of the biggest issues associated with the production of South Africa’s biggest foreign exchange earners; i.e. gold, platinum group metals (PGMs), and coal.

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Decanting of underground AMD is becoming a serious threat for South Africa.

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Access to water problem in South Africa may surpass the energy issues and shortages that have been experienced over the past few years.

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A need to resolve and control the pollution of rivers (eg. Vaal River) and dams, and the poisoning of waters in reservoirs and dams is also of importance.

Challenges

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Acid mine drainage (AMD) is a legacy that is being generated when the sulphide minerals in mining dumps are oxidised naturally.

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Technology to treat AMD is available from overseas, but the costs are typically 2-3 times the cost of potable river water, and hence not economically viable.

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Heavy metals and acid in the AMD are contaminating ground waters, and volumes in the Witwatersrand basins are increasing a rate of 100 million litres per day.

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The water level in the basins are expected to reach ground level within the next 2 years, and overflow into the natural rivers and eco-systems.

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Locally developed technology that is much cheaper to build and operate is required if there is any hope of treating the AMD before it overflows into the eco-system.

Project Background

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The main stream Savmin process consists of three sequential treatment steps involving:

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Neutralisation, metals removal and gypsum crystallisation–

Selective sulphate removal by ettringite precipitation–

Softening and pH adjustment by re-carbonation.

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The SAVMIN process has been tested at laboratory scale as well as on pilot plant scale

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Stilfontein Gold Mine for Anglogold, at a throughput of 24 m3/day – 2000–

Navigation Plant, Witbank for Anglocoal, at a throughput of 5 m3/day – 2001–

Mogale Gold Mine for Western Utilities Corporation, at a throughput of 100m3/day - 2008

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Preliminary economic evaluations indicate that Savmin has the potential to reduce the cost of treating AMD.

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Opex / Capex calculations performed independently by a Coaltech 2020 study:

Outcome of CoalTech 2020 Study (2002)The estimated capital expenditure is summarised for the different treatment technologies:

Treatment ProcessCapital expenditure

(R million per Mλ

/ day capacity)Biological sulphate removal, CSIRosure process R4.8

Electrochemical sulphate removal, Ecodose process R2.8

Chemical sulphate removal, SAVMIN process R3.9

Treatment ProcessOperating and maintenance cost

R/m3 treated R/kg SO4 removed

Biological sulphate removal, CSIRosure process R5.30 R2.28

Electrochemical sulphate removal, Ecodose process R4.48 R5.09

Chemical sulphate removal, SAVMIN process R3.98 R1.71

The operating and maintenance cost estimates for the different treatment technologies are summarised below:

Study completed in 2002 –

Costs quoted in Rands of 2002

SAVMIN Pilot Plant at Mogale Gold Mine

Project Outputs

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Years 1 and 2 of the requested funding will be used as follows:

Technical improvement to the Savmin process;

A small demonstration plant will be constructed.

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MSc degree students will taken in and plant design engineers and operators will gain valuable industrial experience during the operation of the plant

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The data generated will be utilised to generate a techno-economic model for Savmin which can be used to estimate the capex and opex for various size plants in different locations.

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Each waste water treatment plant built would create new jobs as it would require operators, engineers and maintenance staff to keep the plant running all the time.

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MTEF Funds awarded - 2012/13 R10 million- 2013/14 R20 million

Economic and Social Benefits

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This research is directly aligned with the Department of Water Affairs report on “water for growth and development framework 2009”, in their “drive to develop flexible regulatory mechanisms to enhance regional water treatment approaches”.

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Treatment of AMD is the Gauteng Province will assist in making water available to all.

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Treatment of AMD will reduce the extent of the environmental impact associated with AMD discharge into local river courses.

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University undergraduates and graduates will use the laboratory research and pilot plant facilities as their career development training / university industrial training. Thus creating human capacity and knowledge.

Thank you

www.mintek.co.za