Mine iron success as Landia’s mixers help keep local water supply safe

The iron content, especially in the sludge holding tank is particularly abrasive due to the physical nature of the sludge – and is further complicated as chloride levels can be as high as 30,000mg/litre, approximately twice as salty as sea water.

The 316 stainless steel Landia mixers are mounted on a stainless steel post within the tank and are adjusted to optimum height operation position by stainless steel wire.

The Coal Authority’s Environment Manager, Andy Morritt said: “Without the Landia mixers keeping the sludge in suspension, the solids would soon separate, resulting in a highly dense mass in the holding tank that is far too thick to be pumped to the dewatering plant”.

A key part of the Coal Authority’s infrastructure that prevents pollution of the aquifer that overlays a mine’s workings, Horden demonstrates how water enters the former mine’s workings and becomes contaminated with dissolved iron from the surrounding strata. If allowed to continue, the polluted minewater would come into contact with the aquifer, which at 8million gallons a day, provides approximately 20% of the local water supply.

Capable of treating a flow of 150L/sec, a solution of 47% Sodium Hydroxide is added to the minewater to raise the pH to around 7.8, which allows the iron to be precipitated out. The sludge formed by the precipitation process is then separated from the minewater as it passes through a lamella clarifier, with the treated water discharged into the North Sea.

Prior to being dewatered and disposed of, the sludge is transferred to a holding tank where the Landia mixers are installed. The incoming mine-water contains around 100mg/litre of iron, and by the time the sludge has entered the holding tank the iron content has been increased to around 150grams /litre.