New paper in ES&T on vanadium leaching from steel slag published!

Our latest paper on the leaching of vanadium from steel slag is published open access in Environmental Science and Technology this month.

Vanadium is a potential aquatic pollutant that can be released when steel slags are weathered, either during disposal or in conditioning of the material so it can be re-used as aggregate.  Our study aimed to improve our understanding of how vanadium is released from slags into the surrounding environment using a range of geochemical techniques.

We found that vanadium is more readily released under aerobic conditions and that its release to water is controlled by calcium vanadate mineral phases.  We also observed significant accumulation of newly-formed calcium silicate hydrate (C-S-H) phases in a rind around the surface of slag that is weathered.  These surface minerals are also important in taking up some vanadium from solution.

An understanding of these weathering processes helps give us greater insight into the potential environmental risks of slag processing and re-use.  The observed leaching and precipitation processes on the surface of the slag have positive implications for slag after-uses (e.g. as an aggregate).  The presence of a surface rind may limit (or significantly slow) further dissolution, preventing significant alkalinity generation or the release of metals to the environment.

V

Written by Dr William Mayes (R3AW) University of Hull

New publication available online

A new paper entitled “Hydraulic and biotic impacts on neutralisation of high-pH waters has just been published online and in open access on the journal Science of the Total Environment. This paper is available here.

Our research showed that cascades lower pH and alkalinity more successfully than ponds, and that configuration should be adopted, if possible, in the passive treatment of high-pH waters.

 

TOC-artwork_Flumes

 

We could also observe that biofilms promote neutralisation due to CO2 from respiration. In fact, photosynthesis and respiration in biofilms induce a diurnal effect at high pH. The pH variation in biofilm colonized systems shows a diurnal cycle of 1 to 1.5 pH units due to CO2 uptake and release associated with respiration and photosynthesis. However, the hydraulic configuration has more influence on neutralisation of alkaline waters than biofilm.

The management of alkaline (pH 11-12.5) leachate is an important issue associated with the conditioning, afteruse or disposal of steel slags (an important by-product of the steel industry). Passive in-gassing of atmospheric CO2 is a low cost option for reducing  alkalinity,  producing calcium carbonate.

IMG_7313

View of the biofilm colonized systems used in the experiments

 

Can slag heaps help save the planet?

A new research project with Dr Phil Renforth (Cardiff University) has been highlighted in The Guardian. You can read the full article here.

This new three-year project, which has just been awarded a £300,000 grant by the Natural Environment Research Council (NERC), aims to to test the feasibility of using iron and steel slag deposits to remove carbon dioxide from the atmosphere and it is set to begin in Consett, County Durham, and Port Talbot, south Wales.

During the process of steel-making, iron ore is mixed with limestone or dolomite and heated to extremely high temperatures. The end results are steel and slag, a waste mixture of calcium and magnesium silicates and oxides. Piles of this ore-processing leftover have been dumped around the countryside over several centuries.

“Often these heaps have been landscaped very nicely,” said Renforth, who has worked on the project with Will Mayes of Hull University. “There is one in Consett that has been turned into lovely parkland where people can walk their dogs. They are all round the country. Wherever we have made iron, we have left a pile of slag.”

Earlier research by Renforth has shown that carbon dioxide from the atmosphere is absorbed by material inside slag heaps. “We now want to see if we can improve the rate of this absorption so that can we make significant reductions in atmospheric levels of carbon dioxide in the future,” added Renforth.

To do this, Renforth’s project will proceed in two stages. “First, we will drill into one of these old, historic slag heaps and see what has been happening there over the years and understand what chemical processes have been going on as rainwater has brought carbon dioxide into the heap.

“And then we will start the second stage. We will create our own mini-heap – about the size of a skip – and play with its chemistry to try to optimise its ability to sequester carbon from the atmosphere.” These slag-based carbon sequestrators could then be used as models of larger devices that could reduce carbon levels in the atmosphere, Renforth added.

The UK produces 3-4m tonnes of slag a year while the total global production is estimated as being about 500m tonnes a year at present. However, this rate could increase as developing nations catch up, added Renforth. “Our calculations suggest that we might produce between 100bn and 200bn tonnes of slag cumulatively by the end of this century,” added Renforth. “That has the potential to remove 50-100bn tonnes of carbon from the atmosphere, we believe.”

Pilot plant at Scunthorpe

The field trial at the Scunthorpe British Steel plant started this month. We are currently monitoring the existing wetland for passive treatment of the steel slag leachate. We are aiming to understand better what happens to vanadium (plant uptake / partitioning) and also to determine the treatment buffering rates. We hope to be able to publish some exciting results soon!

Coffee and a Chat at Tees Valley Wildlife Trust

As part of the R3AW research we are interviewing a wide range of stakeholders to understand how they view the prospects for deployment of the remediation and resource recovery technology that we are developing here at the University of Hull.

 P1080962Dr Pauline Deutz at Coatham Marsh

So with that in mind Dr Pauline Deutz and I set off up to Tees Valley Wildlife Trust to find out about their experiences of managing a site which was formed by the legacy of Redcar’s industrial past, but is affected by leachate from historic steel slag. After having driven over the spectacular North York Moors we pulled up outside the Trust’s offices and were warmly welcome with an offer of a much-needed cup of coffee. Our interviewee, who heads up the team at the Tees Valley Wildlife Trust, spoke to us for over an hour about the issues pertaining to managing such a complex site, which is bordered by Redcar town on one side and Redcar Steelworks on the other. Coatham Marsh is home to a myriad of wildflowers and over 200 species of birds as well as providing a haven for small mammals and invertebrates . Protecting sites such as this from the effects of legacy steel slag while recovering valuable resources is fundamental to the approach being taken by the R3AW research team. The experiences and thoughts of stakeholders like Tees Valley Wildlife Trust are helping us to understand how the current policy and regulatory environment is working and what other factors influence the way in which areas impacted by historic and legacy steel slag off being managed.

P1080958Looking out from Coatham March to the steel works

After we had to finished the interview we were given directions on how to get to Coatham Marsh so we could see for ourselves the work being done by Tees Valley Wildlife Trust and understand the interesting geography of the site which is bisected by a railway line! Once we found our way to the site, we were greeted by steel sculptures including, reeds and even a pair of walking boots and a rucksack. Despite dullness of the day and the ever threatening prospect of a downpour the site itself provided us with ample colour with displays of wildflowers, ponds and reed beds. Looking east out over the sea provided us with a dramatic view of offshore wind turbines and the view to the north the Redcar Steelworks. We explored the site for over an hour seeing the variety of flora and fauna that Coatham Marsh is home to. The impact that the legacy from the steel slag that surrounds site is something that the research of the R3AW project will hopefully be able to resolve so that sites like this can continue to provide a home for wildlife and a resource for local people into the future. Coatham provides a dramatic illustration of the way in which industry has shaped the environment and is continuing to do so, juxtaposing the rich and biodiverse Marsh with the Redcar Steelworks and Teesside Offshore wind farm.

P1080924

Example of the art work found at Coatham

We would like to thank Tees Valley wildlife trust for sparing the time to talk to us, the contribution of stakeholders and their willingness to talk to us as part of this research project is much appreciated by everyone on the R3AW team.

Written by Dr Helen Baxter, University of Hull.

 

 

Renewable chemicals from waste – securing the molecular value from waste streams

We presented a poster at the Symposium “Renewable chemicals from waste – securing the molecular value from waste streams” in the Royal Society of Chemistry, London, the 20th November. We displayed some preliminary results from the experiments on vanadium recovery from steel slag leachate with a commercial ion exchange resin.

Challenging pollutants such as vanadium  are released during leaching of alkaline wastes . While it is contaminant of concern, vanadium (V) is also highlighted in recent strategic reviews of mineral security as being of critical importance to green technologies (with other elements such as La, Li, Co, V, Te, Ga, Se).

Our results demonstrate for the first time the extended alkaline pH range over which anion exchange resins can be used for metal removal and recovery from waste leachates. These results are promising for both the treatment of hazardous alkaline leachates and the recovery of metals of critical importance. Ongoing experiments are scaling-up the resin columns for pilot scale.

banner

New review paper published in Journal of Cleaner Production

jcleproA new review paper on alkaline wastes is now online, after been accepted by the Journal of Cleaner Production. This paper focuses on the environmental impacts associated with alkaline residues, such as coal fly ash, bauxite residues or red mud, steelworks slags, concrete crusher fines, flue gas desulphurisation waste, Air Pollution Control (APC) residues, Solvay process waste, and chromite ore processing residue (COPR).

While there are significant differences in bulk mineralogical composition among these residues, all are characterised by the presence of Na, Ca or Mg oxides that rapidly hydrate to produce soluble hydroxides. A large range of Ca and Na silicate, aluminate and aluminosilicate phases are also present, hydrating and dissolving to generate alkalinity. Finally, any Ca and Mg carbonates present provide a stable (low solubility) alkaline phase. Initially, dissolution of soluble Na or Ca hydroxides tends to dominate (pH > 12). The  leachates of these residues have pH above typical regulatory thresholds for discharge to water bodies (usually 9), and a major influence on the mobility of contaminants potentially soluble at high pH, because they form oxyanions (e.g. As, Cr, Mo, Se and V).

The paper discusses the environmental impacts of the residues, highlighting the acute episodes, such as the dam failure in Ajka, Hungary,  as well as the widespread chronic impact of the leachate on receiving waters, especially in old and abandoned disposal sites. Pollutant pressure and biological impacts are also reviewed.

The management options for the residues and their leachates are also discussed, distinguishing active and passive treatment options. Potential reuses of these materials, in construction materials, as agricultural amendments, and in environmental applications are identified. The mechanisms of carbon sequestration by alkaline residues are assessed, and the potential for enhancing its rate as a climate change off-setting measure for the industry is evaluated. The potential for recovery of metals critical to e-technologies, such as vanadium, cobalt, lithium and rare earths, from alkaline residues is considered. Finally, research needs are identified, including the need to better understand the biogeochemistry of highly alkaline systems in order to develop predictable passive remediation and metal recovery technologies.

Reference: Gomes, H.I., Mayes, W.M., Rogerson, M., Stewart, D.I., Burke, I.T., (2015) Alkaline residues and the environment: A review of impacts, management practices and opportunities. Journal of Cleaner Production. (In Press)

Picture1

Consett, Co. Durham

The University of Hull team made a field trip to collect samples and data in a historical legacy site (Consett, Co. Durham). We made simultaneous water quality monitoring and flow measurements at various locations in Howden Burn and Dene Burn. These watercourses drain areas with steel slag from the former Consett Iron and Steelworks, which has occupied the site from the middle of the 19th century up to 1980, when it was closed. The Dene Burn receives a subterranean drainage network beneath the Grove Heaps area of the site, where blast furnace bottom and steel slag were deposited. The Howden Burn drains an area north of the Dene Burn previously occupied by the workings blast furnaces, power station, and steel plant. The data collect will allow us to quantify rates of calcite precipitation and transport/attenuation of trace elements downstream of the leachate sources.