- Iron exists in the ferrous form within the country's mine workings.
- Upon exposure to the surface, the Ferrous Iron oxidises to become ferric iron - a hydrolysis reaction which causes the precipitation of ferric hydroxide - these particles fall from the solution and join together to form a thick substance that coats the river bed. It is this substance that causes effected watercourses to appear a red / orange colour.
Over time the iron ochre builds up in the treatment lagoons and periodic desludging is required to maintain the efficient operation of the process. The ochre sludge is pumped out as a liquid sludge before undergoing a process of dewatering and/or drying (e.g. centrifuge, plate filter press or drying bed). These processes result in the production of a solid ochre material which can be either safely landfilled as an inert waste, or put to beneficial reuse.
The beneficial re-use of ochre is being actively pursued by the Authority. Ochre has a number of vaulable properties: from use as a pigment in building materials; to adsorption of phosphate in waste-water and agriculture; to treatment of metals/arsenic contaminated soils.