New paper on Geoforum

A new paper from our team at the University of Hull has just been published on the journal  Geoforum. The paper entitled “Resource recovery and remediation of highly alkaline residues: a political industrial ecology approach to building a circular economy” is now online, on open access.

 

We focused on the valorisation of highly alkaline industrial residues, such as steel slag, bauxite processing residue (red mud) and ash from coal combustion, which have been  identified as stocks of potentially valuable metals. Currently, there is demand for metals, such as vanadium and certain rare earth elements, in electronics associated with renewable energy generation and storage.

Current raw material and circular economy policy initiatives in the EU and industrial ecology research all promote valorisation, primarily from an environmental science perspective. This paper begins to address the research gap into the governance of resource recovery from a novel situation, where reuse involves extraction of a component from a bulk residue that itself represents an environmental risk.

Past and current arrangements produced a complex blend of ownership and liabilities

Taking a political industrial ecology approach, we present emerging techniques for recovery and consider their regulatory implications in the light of potential environmental impacts. The paper draws on EU and UK regulatory framework for these residues along with semi-structured interviews with industry and regulatory bodies. A complex picture emerges of entwined ownerships and responsibilities for residues, with past practice and policy having a lasting impact on current possibilities for resource recovery.

 

Removal and recovery of vanadium from steel slag leachates with exchange resins

Our team has another publication  entitled: “Removal and recovery of vanadium from alkaline steel slag leachates with anion exchange resins” by Helena I. Gomes, Ashley Jones, Mike Rogerson, Gillian M. Greenway, Diego Fernandez-Lisbona, Ian T. Burke, and William M. Mayes,  now published on the Journal of Environmental Management.

This work tested the efficiency of anion exchange resins for vanadium removal and recovery from steel slag leachates at pH 11.5.  The results show, for the first time, that the resins can be used successfully to both remove and recover vanadium from steel slag leachate.

As an environmental contaminant, removal of vanadium from leachates may be an obligation for long-term management requirements of steel slag landfills. Vanadium removal coupled with the recovery can potentially be used to offset long-term legacy treatment costs.

The maximum adsorption capacity  was 27 mg of vanadium per gram of resin. In the column tests, the concentration in the effluent was only 14% of the initial concentration after passing 90 L of steel slag leachate. We could recover 57–72% of vanadium from the resin. Trials on the reuse of the anion exchange resin showed that it could be reused 20 times without loss of efficacy, and on average 69% of vanadium was recovered during regeneration.

New open access paper on V recovery

Out team just published a new paper on vanadium recovery from red mud leachates using ion exchange resins. The paper is available on open access here.

Bauxite residue or red mud is an important by-product of the alumina industry, and current management practices do not allow their full valorisation, especially with regard to the recovery of critical metals, like vanadium.

This paper focus on vanadium removal and recovery from the leachates, with emphasis on the environmental remediation of bauxite residue disposal areas or closed legacy sites where vanadium is both a contaminant and a metal with economic interest present in the effluent.

As an environmental pollutant, removal of vanadium from leachates may be an obligation of bauxite residue disposal areas (BRDA) long-term management requirements. Vanadium removal from the leachate can be coupled with the recovery, and potentially can be used to offset long-term legacy treatment costs in legacy sites.

This study has shown that anion exchange resins can be used for metal removal and recovery from bauxite residue leachates in a highly alkaline pH range (up to 13).

The results showed that using simulated undiluted bauxite residue leachate as feed solution limited the resin efficacy, due to the presence of competing ions. However, the resins are very effective at V removal for simulated post-closure bauxite residue disposal areas (BRDA) effluent.

In the column experiments, V was readily eluted from the resins in concentrations similar to some industrial process liquors, which holds promise for recovery and recycling of V into downstream industrial processes.

Further research is required to scale-up laboratory findings. This should include assessment pretreatments and optimisation of operating parameters, such as flow rate and bed height. This will help facilitate life cycle assessments of anion exchange resins as a potentially efficient and cost-effective option for both the treatment of bauxite residue leachates and the recovery of metals of critical importance such as vanadium.

 

New paper published

The paper “Advances in understanding environmental risks of red mud after the Ajka spill, Hungary” was just published in the Journal of Sustainable Metallurgy.

This paper reviews the over 45 scientific studies published in the last 5 years assessing the key risks and impacts associated with the largest single release of bauxite residue to the environment  – the 2010 Ajka red mud spill.

 

Categories of scientific papers and conference proceedings after the Ajka spill.

 

The main environmental concerns were covered in these studies, which also evaluated the  effectiveness of the remedial actions taken. The key immediate risks after the spill were associated with the highly caustic nature of the red mud slurry and fine particle size, which once dry, could generate fugitive dust. Studies on affected populations showed no major hazards identified beyond caustic exposure. The dust risks were considered equal or lesser to those provided by urban dusts.

The longer term environmental risks were related with the potential salinization of inundated soils and release and potential cycling of metals and metalloids (e.g. Al, As, Cr, Mo, V) in the soil-water environment. Of these, those that are soluble at high pH, inefficiently removed from solution by dilution and likely to be exchangeable at ambient pH are of chief concern (e.g. Mo and V).

However, extensive management efforts in the aftermath of the spill greatly limited these exposure risks through neutralisation and red mud recovery from affected land. Monitoring of affected soils, stream sediments, waters and aquatic biota (fungi, invertebrates and fish) have all shown a very rapid recovery towards pre-spill conditions.

The accident also prompted research that has also highlighted potential benefits of red mud use for critical raw material recovery (e.g. Ga, Co, V, rare earths), carbon sequestration, biofuel crop production and use as a soil ameliorant.

 

New review paper published in Journal of Cleaner Production

A 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)