Treatment for Water Re-use
ACID ROCK DRAINAGE – COAL LOADING FACILITY – INDONESIA
- pH raised to near neutral conditions
- Aqueous metal concentrations lowered
- Enabled reuse of water for dust suppression
- Treatment precipitates contained within base of the water storage pond
East coast of Kalimantan, Indonesia.
SETTING AND CLIMATE
This large coal loading facility is situated close to the equator. The port is surrounded by undulating coastal lowlands dominated by dense tropical rainforest and localised mangrove swamps. The mean annual rainfall is approximately 2,500mm, with a potential evaporation of 1,750mm.
The terminal is owned and operated by an international coal mining company.
The coal terminal services several coal mining operations in east Kalimantan. At each of these operations, coal is extracted from opencuts by a range of methods, and is sometimes washed on site. It is transported to the coast and stockpiled at a number of locations prior to being directed to the coal terminal by barge for centralised dispatch to world markets.
The terminal handles approximately 250,000 tonnes of coal per month, and all of this material is stored in uncovered stockpiles. During storage and handling, dust suppression is a significant issue. For every tonne of coal stored, 20 litres of water are required to manage this issue.
The coal contains approximately 1-3 weight % pyrite, which begins to oxidise on extraction, and continues to generate acid forming material throughout the handling process.
Rainfall percolates through the stockpiles and combines with acid forming material to produce acid drainage. At the coal terminal, this drainage is diverted into channels and collected in a large pond (refer to plates) for use in dust suppression. Dust control measures require recycling of site water and irrigation over an extensive conveyor system and stockpile. Equipment corrosion would be extensive and rapid if highly acid water were used for this purpose.
During periods of excessive rainfall, the stormwater storage capacity is exceeded, and discharge to the ocean is necessary. This water is required to comply with Indonesian Government water quality standards.
- Conduct an assessment of acid drainage management issues.
- Assess the existing water treatment practices.
- Evaluate available water chemistry.
- Examine rainfall, evaporation and catchment data with a view to reviewing the existing stormwater storage capacity.
- Provide recommendations for minimising acid drainage.
- Evaluate and scope water treatment requirements.
- Provide recommendations for cost-effective treatment of acid drainage.
- A report evaluating acid drainage issues and providing recommendations for avoiding, minimising, quantifying and treating acid drainage.
- Acid drainage acidity measurements indicated a likely maximum treatment rate of 1.0 tonne of hydrated lime per megalitre, and an average rate of 250 kg of hydrated lime per megalitre. Variable treatment requirements were a function of coal type, size of stockpile and seasonal rainfall.
- A single portable Multi Purpose Neutra-Mill was supplied to the coal terminal to ensure compliance with Government discharge requirements, and to facilitate re-use of stormwater for dust suppression and washdown purposes.