Current Methods (Wheal Jane)

**Figure 1:** Veolia Wheal Jane Treatment Plant

The current method of mine water treatment at the Wheal Jane site is provided by Veolia Ltd. The company, who operates under the Coal Authority, delivers the services and facilities to treat the water. The safe long term storage of the resultant hazardous residue from the treatment process is ensured by pumping the waste into a dam controlled by the Wheal Jane LTD.

**Figure 2**: The diagram above is schematic of the treatment process at Wheal Jane

Water extraction from the mine

10 stainless steel pumps costing £13,000 each are used to pump water from a mine shaft at rates of 50-60 l/s. The plant is separated into two distinct stream of treatment, so that if one fails the plant may continue treatment.

Pre-reaction Chamber

Mine water is mixed with recirculated sludge to encourage the formation of dense particles.

Reaction Chamber

A Lime Slurry is created from hydrated lime powder and is then added to the mine water for two purposes: 1) to increase the pH of the acidic water to a target value of approximately 9.2 pH, 2) to cause the precipitation of metal ions. Air is circulated into the reaction chambers.

Lamella Clarifiers

A polymer is added to the mine water, binding to the metal it causes them to coagulate. Under the force of gravity the mixture separates out into distinct layers, the higher density sludge particles sink to the bottom and the water rises forming the top layer. The sludge is recirculated in the system until it reaches a specific density.

Clemows Valley Tailing Dam

When the Sludge reaches the required density it enters a holding tank and is later pumped to the Clemows Valley Tailing Dam. This is a 69m high Dam designed to contain hazardous waste. Over 17 years Veolia Treatment plant has deposited 7,002,000 tonnes of sludge.

Evaluation

Although the company does offer safe long term storage of the sludge by transferring it to a tailing dam it means that as result the waste containing toxic and hazardous chemicals is exposed to the environment.
The process relies on the addition of a significant amount of lime in order to increase the pH so that elements such as Manganese can precipitate out, which occurs at pH 9.1. Quarried in Derbyshire, the lime must be transported 325 miles to Cornwall. This is a significant contribution to the plants carbon footprint and demonstrates how unsustainable methods like these are.

References

All information displayed on this page was taken from an interview with Technical Process Electrician at the Wheal Jane Veolia Treatment Plant Chris Nappin on 10 August 2017

Team:Exeter/Current Methods