Use of ochre products for remediation of metal-contaminated soils and waters Kate Heal School of GeoSciences University of Edinburgh

Need for remediation of metal- contaminated waters and soils in UK Industrial and mining legacy 27% assessed sites contaminated by metals and metalloids EU WFD: England and Wales 2472 km rivers at risk; 2428 probably at risk Costs of contamination: remediation, loss of fisheries, ecosystems

Why ochre for remediation of metal- contaminated waters and soils? Expected to have fewer environmental side-effects than other treatment methods Sustainability advantage; avoidance of landfill Readily available from MWTPs close to sites of metal contamination

Metal removal in shaking experiments MetalConcentration (mg l -1 ) StartAfter 1 minAfter 24 hrs PolkMintoPolkMinto Fe <LOD Mn Zn Cu4.44.0<LOD 0.01 Ni <LOD Cd <LOD Cr5.03.8<LOD0.03<LOD

Zinc removal in columns of ochre pellets (Kaiyang Zhang, University of Newcastle, 2004)

3 potential modes of ochre application Mixed tank reactor and clarifier to remove metals from surface runoff Contaminated soil Soil amendment to reduce metal leaching at source Permeable reactive barrier to treat leachates and groundwater

New project proposal (1) Identification of processes and rates of metal removal by ochre Assess different forms of ochre Batch and column experiments Effect of pH Column leaching experiments with ochre-soil mixtures Surface of ochre pellet after reaction with P solution X 65 SEM analysis

(2) Long-term stability of metals removed by ochre Standard landfill leaching tests of metal-rich ochre Field microcosm experiments with metal- rich ochre Forms of metals identified by sequential extraction Preparation of metal-rich ochre

(3) Field demonstrations Plant experiments –Soil metal availability –Plant health –Leachate quality Treatment of contaminated surface waters at former metal mining site

(4) Permeable reactive barrier Monitor performance –Water level –pH, Eh, DO, TDS –TOC –Potentially toxic metals –Fe 2+ /Fe 3+, Mn 2+ /Mn 4+, SO 4 2- /S - Construct PRB Choose ochre type

(5) Issues for industrial implementation Market research of end-user community Decision tree: effectiveness of different forms of ochre for site type and conditions Ochre production costs Maintenance costs (including ochre removal and disposal) Cost-benefit analysis framework for remediation methods Regulatory framework