Phosphorus removal from waters by ochre -- Using one pollutant material to catch another Keith Smith School of GeoSciences University of Edinburgh

Background Ochre: a polymeric hydrated iron oxide/hydroxide material, Fe(OH) 3 and FeO.OH –Released from iron-rich waters emerging from anaerobic environments –Damaging to aquatic life, visually intrusive –Major problem associated with old coal workings Coal Authority has responsibility to prevent pollution from this source, so treatment plants at many old mines and open-cast workings Increasing quantities of ochre being accumulated –If no large-scale use identified, likely to end up in landfill –However, chemical properties offers promise as a means of adsorbing phosphate from solution:  chemically very similar to soil materials responsible for inducing phosphate deficiency in soils in many regions

Impact of elevated phosphorus concentrations in rivers and lakes Ochre accumulation in mine water treatment plants

Phosphorus removal Shaking dried sludge with phosphorus solution showed that removal rates of the dried sludge were an order of magnitude higher than for other materials. Dried sludges from two different mines with different processes for ochre precipitation removed almost all phosphorus from solution, with particularly rapid uptake by Minto sludge.

Adsorption capacity of ochre and other materials

Phosphorus solution flowing continuously into trough Dried sludge Flow measured and sampled Long-term P removal by ochre

Long-term P removal P concentration in applied solution P concentration in effluent

Maximum phosphorus adsorption capacities of different materials (after Drizo (1998) and Mann (1997))

Properties of ochre material from two sources

Project evolution Support for Edinburgh Univ from Coal Authority for pilot studies –Removal of both phosphate and heavy metals from solution Parallel developments at Newcastle Univ. Collaboration with Newcastle on phosphate removal from waters –Ochre pelletisation, application to P removal from both sewage effluent and agricultural runoff Experimenting with ochre when saturated with P as a slow-release p fertiliser Now: developing additional research on removal of metals