Contaminated land solutions from mine water treatment by-products Brownfield Land in Wales Conference – 30 November 2017 Peter Thorn Principal Technical Innovation Manager

The Coal Authority manages the effects of past coal mining The Coal Authority was established in 1994 and responsible for: • licensing coal mining in Britain • managing the safety issues that have resulted from years of coal mining • communicating information to the public • making mining information available • dealing with water pollution caused by mining

Working to a flat line budget!

The role of the Coal Authority

• rebounding water within abandoned mines

• dissolved minerals to surface • coal mine pollutants • metal mines pollutants • 400km clean and protected rivers • aquifers protected for 0.5m people • value: £30.5m per annum

Why treat mine water?

The Coal Authority – innovation high level objectives

The Coal Authority – innovation high level objectives 1. to be self-sufficient of Government

Funding

2. to be a world expert in resolving the impact of mining legacy

3. to have a net beneficial impact upon the environment

4. to manage change safely

Innovation Programme

Build more mine water treatment schemes

• Income from water

• Income from heat

• Income/reduced cost from hydrous ferric oxide sludge

• Contractual efficiencies

• Reduce energy use

• Generate income from energy

• Create small footprint zero cost schemes

• Improve sustainability

• Income from expertise and IP

Innovation Programme 2016/17

Operate over 70 Coal mine water treatment schemes

Passive: gravity fed; aeration; cascades; lagoons; reed beds Semi passive: pumped water; chemical dosing; aeration cascades; lagoons; reed beds Active: Dawdon; Ynysarwed

Non-coal mine water treatment schemes Passive: Force Crag (Lead-Zinc Mine) Saltburn (Ironstone Mine) Active: Wheal Jane (Tin Mine)

Coal Authority schemes

Coal mine water treatment

Blenkinsopp Scheme, Northumberland. Google Maps

Conventional coal mine water treatment

Co-treatment with Northumbrian Water Ltd

• Built in 2005 • Treats 350 L/s • Total of 9 individual reed beds • Reed beds cover an area of 5.5 hectares • Phosphate removal enhanced by

presence of iron in mine water • Ochre precipitation removes suspended

solids in sewage water • Was the largest artificial wetland

constructed in the UK in 2005

Lamesley scheme

Lamesley Scheme, Northumberland. Microsoft, 2009

What does this have to do with brownfield regeneration?

HFO as a sorbent

• High Surface Area • High affinity sorption sites for both anionic and

cationic contaminants Anions: As (as AsO4

3-), Cr (as CrO42-), Se (as SeO4

2-), P (as PO4

3-), Sb (as Sb(OH)6-), V (as VO43-) & Cyanide

(CN- :note as sorption and reaction to ferricyanate). Cations: Cu, Cd, Ni, Hg, Pb, Zn,

• Literature Review • Modelling • Experimental work

Leaching profile of retarded and un-retarded ions The strong affinity of HFO sorption sites for Potentially Toxic Trace Elements (PTEs) leads to retarded subsurface transport phenomena, thus reducing the leaching of mobile ions to acceptable levels.

Ion Retardation

Conc

entr

atio

n

Time

Un-retarded

Retarded

Environmental Compliance Target

Sorption Characterisation

Modelled sorption isotherms Minteq v4 thermodynamic database

Lab work to determine for individual HFOs Mineralogy Measured sorption isotherms

Lab Work

pH dependencies

• Cations – in general (but not always) better sorption at higher pH

• Anions – in general better sorption at lower pH

Cation Critical pH range (literature values)

Cu, Pb, Hg 3-5 Zn, Co, Ni, Cd 5-6.5 Mn 6.5-7 Mg, Ca, Sr 6.5-9

Physical Characterisation

Lab Work

• Geotechnical Classification Moisture Content Particle size distribution Atterberg limits • Variable structure • Highly plastic initially – clay like in

behaviour • Once dried low plasticity – silt like

behaviour • Behaviours vary with mineralogy

Bench and Field Trials

Lab Work

• Bench and field trials will be needed on a case by case basis to establish mixes on a site specific basis

• Hydrock undertook bench-scale trials in order that a solution be found to address an arsenic leaching issue on one of their sites in the north of England

• HFO showed, in those trials, to reduce leaching to levels below that, that could be achieved by using quicklime

End of Waste & Waste Permits

Waste Licensing

• Currently end of waste for HFO for use in coagulant production

• In the absence of end of waste, the use of HFO within the land contamination sector for civil engineering projects would best be promoted through the adoption of CL:AiRE definition of waste code of practice utilising a hub and cluster style deployment system

• Future end of waste for defined bagged/bulk product to specification

• Remediation solution using recycled material

Next Steps

Drying Trials • Wet product available – c.30% ds • Granular bagged product aimed

for – >50% ds • Dry milled powder – high end

pigment, but possibly available for remediation.

Completion of Lab Trials • Better understanding of sorption

sites for range of materials • Understanding of chemistry for

cyanide remediation • Parameterisation for site specific

modelling • Product data sheets

Remediation Product