Technical Market Support

Management of Trace Elements in Ash Dams

Technical Market Support » Thermal Coal

Published: October 02Project Number: C10056

Get ReportAuthor: Ken Riley, O Farrell, R Jung | CSIRO Energy Technology, CCSD

This project was undertaken to make an assessment of the practicality of "alternative" strategies to manage trace elements, in particular, arsenic, boron, molybdenum, selenium and vanadium in ash dams. These elements form oxyanions in flyash leachates and are soluble at the pH ranges occurring in the dams. Their release can have a detrimental effect on the environment.

Although some conventional water treatment processes should be able to remove the targeted trace elements from water, there are significant capital and operational costs involved in treating the large volumes of water discharged from ash handling systems. For example, it is possible to treat ash dam water with ferric salts to induce the formation of ferric oxyhydroxide at an optimum pH. This would remove arsenate, molybdate, selenite and vanadate from the ash dam water. Borate and selenate will not be removed.

It has been reported in a study by Tarong Energy that the cost of treating ash dam water in a reverse osmosis plant was estimated to be $1023/ML. There is currently some 10 Mt of ash produced yearly in Australian bituminous coal-fired power stations. Although not all of this ash is stored in ash dams (some is utilised and much is stored as "dry" landfill), the magnitude of the expense required to treat the volumes of ash dam water or leachate that may be discharged is evident.

Preliminary work had indicated that the following two processes :

  • direct addition of ferric chloride to ash
  • use of zero-valent iron to treat ash dam water

have the potential to minimise the release of the trace elements, arsenic, molybdenum, selenium and vanadium.

This project continued the study commenced by CSIRO and the CRC for Coal in Sustainable Development. Further experimental work including field work was completed into the use of iron as a reductant. As well, an assessment of the use of biological treatment in bioreactors and wetlands has been included. Thermodynamic calculations using MINTEQ have also been completed both on the process of reduction with iron and by anaerobic bacteria (used in bioreactors and naturally present in wetlands).

The results of the experimental work and assessment of the data indicate that:

  • the "inpond" process in which ferric chloride is added directly to flyash to prevent the release of the targeted trace elements would be limited to ashes with a circum neutral pH (the pH range is critical and at greater than approximately pH 8, there is a release or poor adsorption of the elements). Further study would be required to assess the long term leach behaviour of the treated ash
  • a strategy based on the use of iron metal (zero-valent iron) as a reducing agent has obvious potential. The oxidation (corrosion) of the iron acts to chemically reduce some species including selenate and also results in the formation of ferrous and ferric oxides/hydroxides on the metal's surface. Arsenate, molybdate, selenite, selenate and vanadate can be removed from ash dam water. The process requires that the water contact a large surface area of iron/iron oxide to be effective. Further work is required to design efficient operational plants that could utilise materials such as scrap iron, steel wool waste or commercially available iron powder. A disadvantage in the use of the iron metal is the release of ferrous ions and possibly trace amounts of other elements.
  • constructed wetlands could be used to remove some of the targeted trace elements. The data is limited but the biological activity will remove the arsenic and selenium (certainly the selenite). Further work is required to assess the behaviour of molybdenum and vanadium
  • none of the above processes were able to remove boron. It appears that even costly commercial processes such reverse osmosis have limitations in removing this trace element.

The two most promising strategies to manage the trace elements, arsenic, molybdenum, selenium and vanadium in ash dam water are the use of iron metal (zero-valent iron) as a reducing agent and constructed wetlands. The results indicate that there may be alternatives to use of conventional water treatment processes to treat ash dam waters. There is an obvious need for further pilot scale studies and careful assessment prior to the installation of any large scale processes.

Further work is required to identify processes that can effectively treat ash dam water to remove boron. Initially a full literature survey including the patent literature is required.


Health and safety, productivity and environment initiatives.


Open Cut

Safety, productivity and the right to operate are priorities for open cut mine research.

Recently Completed Projects

C19024Establishing Ecologically Sustainable Mine Water Release Criteria In Seasonally Flowing Streams

Extreme rainfall conditions in the Fitzroy Catchment over an approxi...

C25030Coal Mine Open Pit Final Void Closure And Relinquishment - Addressing Uncertainty In Coal Mine Environmental Planning

This report addresses uncertainties faced by coal mine operators whe...

C27046Estimation Of True Deformation Vector From Slope Radar Monitoring

Slope deformation radar monitors are now widely used in open cut coa...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C27004Improving Coal Flotation With Oscillatory Air Supply

This report provides detailed information on coal flotation with os...

C25018Improving Solids Recovery And Moisture Reduction In Ultrafine Coal Dewatering

This report provides detailed information on fine coal dewatering in...

C27028Lab Froth Flotation Testing Guide With Coal Quality

Correct outcomes from laboratory froth flotation testing in coal bor...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C26039Nanoporosity In Cokes: Their Origin, Control And Influence On CO2 Reactivity

This project using the outcomes of previous project C24060, examine...

C28063A Comprehensive Technical Review Of High-Efficiency Low-Emission (HELE) Pulverised Coal Combustion Technologies For Power Generation

Research and development has been undertaken worldwide to realise co...

C28064Carbon Structure Transformation During Coking Of Australian Coking Coals: Better Understanding The Coke Formation

Carbon structures of coke that are formed during the plastic layer a...

Technical Market Support

Mine Site Greenhouse Gas Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C28076Selective Absorption Of Methane By Ionic Liquids (SAMIL) - Phase 2 Demonstration In A Packed Bed Reactor

An alternative approach to high temperature oxidation of ventilation...

C26004CFD Modelling Of Reverse Thermal Oxidisers For VAM Abatement - CFD Modelling Of Fixed-Bed RTO Devices

The project is part of a larger multi‐phase program of study a...

C27058Technological Assessment Of A Recycle Reactor For VAM Abatement

Underground coal mining emits high volumes of methane, diluted in ve...

Mine Site Greenhouse Gas Mitigation

Low Emission Coal Use

Step-change technologies aimed at reducing greenhouse gas emissions.

Recently Completed Projects

C17060BGasification Of Australian Coals

Four Australian coals were trialled in the Siemens 5 MWth pilot scale ga...

C17060AOxyfuel Technology For Carbon Capture And Storage Critical Clean Coal Technology - Interim Support

The status of oxy-fuel technology for first-generation plant is indicate...

C18007Review Of Underground Coal Gasification

This report consists of a broad review of underground coal gasification,...

Low Emission Coal Use

Mining And The Community

The relationship between mines and the local community.

Recently Completed Projects

C16027Assessing Housing And Labour Market Impacts Of Mining Developments In Bowen Basin Communities

The focus of this ACARP-funded project has been to identify a number...

C22029Understanding And Managing Cumulative Impacts Of Coal Mining And Other Land Uses In Regions With Diversified Economies

The coal industry operates in the context of competing land-uses that sh...

C23016Approval And Planning Assessment Of Black Coal Mines In NSW And Qld: A Review Of Economic Assessment Techniques

This reports on issues surrounding economic assessment and analysis ...

Mining And The Community


National Energy Research,Development & Demonstration Council (NERDDC) reports - pre 1992.

Recently Completed Projects

1609-C1609Self Heating of Spoil Piles from Open Cut Coal Mines

Self Heating of Spoil Piles from Open Cut Coal Mines

1301-C1301Stress Control Methods for Optimised Development...

Stress Control Methods for Optimised Development and Extraction Operations

0033-C1356Commissioned Report: Australian Thermal Coals...

Commissioned Report: Australian Thermal Coals - An Industry Handbook