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.
Written by Dr William Mayes (R3AW) University of Hull
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!
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.
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.
Dr Helena I. Gomes and Dr Helen Baxter, both postdoctoral research associates of the project, were interviewed by Anthony Daniele and Matthew Grantham for the Beyond Zero radio program. This program focuses on Climate Change Science and Solutions, airs bi-weekly in Melbourne, Australia on 3CR Radio, and is broadcasted via the Community Radio Satellite.
Previous guests on the program include:
Dr David Suzuki
Dr James Hansen – NASA
Prof Martin Green – UNSW
Mr Arnold Goldman – Luz II
Dr David Mills – Ausra
Dr Keith Lovegrove – ANU BigDish
The interview was about the article on vanadium published recently on The Conversation. Vanadium is the key element used in redox flow batteries which can store large amounts of energy almost indefinitely, perfect for remote wind or solar farms.
Listen the podcast here.
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.
Some preliminary results of the experiments conducted with the ion exchange resins were presented in the 24-26 June 2015 NICOLE Network meeting and Workshop: Unconventional Contaminants, University of Manchester, UK. Here is our poster: