IRRIGATION OF LAND WITH NEUTRALISED ACID MINE WATER IN THE WESTERN BASIN.

Mr BP Mohasoa

Department of Environmental, Water and Earth Sciences

ARC Head Office, Hatfield, Pretoria 28 May 2014

It is feasible to treat and reuse neutralised AMD for irrigation as a cost-effective AMD treatment alternative and thereby protect large volumes of public streams from acidity, salinity and metals.

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1. Introduction to AMD

2. Situation in the Witwatersrand

3. General concern on AMD

4. Governance context and recommendations

5. Neutralisation/Irrigation study

6. Conclusion

OVERVIEW

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• Mining a key economic sector

– South Africa is well endowed with vast mineral resources and the wealth created through mining, particularly gold mining, which has promoted the development of the country.

• Environmental footprint by mining activities

– Among mining most pressing environmental issues is AMD.

– AMD is generated when sulphide bearing minerals, often in the form of pyrite (such gold and coal), are exposed to oxygenated water (derived from rainfall)

1.INTRODUCTION TO AMD

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• Mining’s water legacy

– AMD dates back to Gold Mining Era, in Witwatersrand area, Gauteng

– About 120 mines were operating

– Today, operations have ceased and pumping has stopped, as a result flooding occurs and subsequently AMD decant to environment

– Gold tailing dumps are also a major contributor to AMD as they contain pyrite

• AMD at a national level

– The Witwatersrand is not the only region affected by AMD, but it is currently the area of greatest concern.

– Other regions are Mpumalanga, Limpopo, KZN coalfields, KOSH, Free-State and O’kiep Copper district

INTRODUCTION TO AMD (CONTINUES)

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INTRODUCTION TO AMD (CONTINUES)

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INTRODUCTION TO AMD (CONTINUES)

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• AMD is decanting at a volume of 20 ML/d into the Tweelopies Spruit near Randfontein (Western Basin)

• It is estimated that a further 60ML/day will decant near Boksburg (Central Basin) by 2013; and

• An additional 120ML/day near Springs (Eastern Basin) by 2014

2. SITUATION IN THE WITWATERSRAND

SITUATION IN WITWATERSRAND (CONTINUES)

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• Extensively contaminates surface water

• Contaminates ground water

• Water unfit for agriculture

• Soil pollution

• Detrimental ecological impacts

• Health risk to downstream users ( humans and animals)

• Threat to heritage sites

• Corrosive to infrastructure and equipment

NOTE: South Africa is a water-scarce country.

3. GENERAL CONCERNS ON AMD

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• Government has taken lead in addressing this situation particularly since it relates to Derelict and Ownerless mines (Abounded mines)

• Inter-Ministerial Committee on AMD

– In August 2010, Cabinet convened an Inter-Ministerial Committee (IMC) on Acid Mine Drainage, consisting of the Ministers of Water & Environmental Affairs, Mineral Resources, Finance, Science & Technology and the Minister in the Presidency for National Planning

– The IMC appointed a Team of Experts made up of prominent scientists and government representatives to respond to the AMD issue and ultimately produce a report outlining the short-term, medium-term and long-term response to AMD in Gauteng

4. GOVERNANCE CONTEXT AND RECOMMENDATIONS

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• Short-term recommendations include (among others):

– Pumping and treating water from the mine voids

– Stopping water flowing into the old mine voids, with the aim of reducing the amount of water that has to be treated and pumped over the long term

– Monitoring and remediation of other sources of acid mine drainage, such as tailings dams

• Long-term consideration

– Various technologies are available for treatment

– Lime/Limestone and Reverse-Osmosis (Desalination) used at a large-scale

GOVERNANCE CONTEXT AND RECOMMENDATION

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• Neutralisation (Advantages and Disadvantages)

– Lime/Limestone neutralisation cost-effective

– Mining companies can afford this technology

– Salinity challenges discharge affects downstream users

• Desalination (Advantages and Disadvantages)

– Removes salts almost completely, can be used for domestic purposes

– Neutralisation required as pre-treatment

– Produces highly concentrated brine which required treatment prior disposal

– Highly expensive, only blue-chip mining companies can afford this technologies

GOVERNANCE CONTEXT AND RECOMMENDATION

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• AMD contamination of surface and groundwater resources renders these water resources unfit for use in most economic sectors including the agricultural sector.

• Costs of many treatment options such as RO are too high for most mining companies. As a result, most mining companies prefer the neutralisation method as it is more affordable although it does not completely address the salinity challenge.

• The current AMD challenge requires an alternative treatment approach, neutralisation/irrigation that will result in reduced treatment costs and achieve environmental protection.

5.NEUTRALISATION/IRRIGATION STUDY

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• The risks of this alternative treatment approach have to be understood and it needs to be assessed what these risks mean for neutralisation/irrigation being implemented by mining companies and government in practice, and how the challenges posed by these risks can be overcome.

NEUTRALISATION IRRIGATION STUDY (CONTINUES)

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• Aims and Objectives

– To determine environmental risk and financial costs and benefits associated with neutralisation of AMD for use in irrigation. The study will focus on the following environmental parameters – groundwater and soil.

– To address the concern of leaching of contaminants into groundwater.

– To explain the governance context of the AMD issue, including the different actors, roles and responsibilities and dynamics that are at play.

– To determine which legislation and policy is relevant to the neutralisation/irrigation treatment option and how this legislation may promote or hinder the implementation of this option.

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NEUTRALISATION/IRRIGATION STUDY (CONTINUES)

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• Aim and Objectives

– To understand how the risks identified may impact implementation of the neutralisation/irrigation option and to understand how the challenges these risks pose for the implementation of this option could be overcome.

– To make recommendations about how the neutralisation/irrigation option could be implemented in the context of current government and mining industry AMD treatment initiatives.

NEUTRALISATION/IRRIGATION STUDY (CONTINUES)

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• Design of the study

– An existing AMD neutralisation plant in the Western Basin will be used;

– 20ML/d of AMD will be treated (AMD contains free acid, Fe (II), heavy metals and salts) ;

– The neutralisation process requires limestone (CaCO3) for neutralisation of 90% [free acid, Fe (II), Fe (III) and Al (III)] of the acid content and lime (Cao) for the final 10% Manganese removal;

– Neutralised water will be taken to an irrigation site for the irrigation;

– A 20m x 20m x 1m deep irrigation area will be used (site already contaminated);

– Bottom 10cm will be a layer of stones to allow leachate to run to the outlet for collection;

– Drainage systems will be installed underground the irrigation area in order to trap contaminants.

NEUTRALISATION/IRRIGATION STUDY (CONTINUES)

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• Progress to date

– Site identified and discussions on-going with the farm owner

– Neutralisation plant is on-site

– Bamboo plantation will be used

– Bamboo expert has joined this project

– Discussions on-going with relevant authorities

NEUTRALISATION/IRRIGATION STUDY (CONTINUES)

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• The mining industry, particularly gold mining has promoted the development of the country. However, today we are beginning to grasp the environmental legacies of mining Abounded mines and AMD

• AMD renders water resources unfit for use for most economic sectors including the agricultural sector.

• Most effective treatment technologies such as RO are expensive, as result small mining companies neutralise and discharge water into the river systems. Neutralisation does not completely address the salinity.

• There is a need for a long-term technology that is both cost-effective and environmental-friendly. Neutralisation/Irrigation is proposed.

6. CONCLUSION

THANK YOU FOR YOUR ATTENTION

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