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.
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.
View of the biofilm colonized systems used in the experiments
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.
Our team has now available a Ph.D. opportunity at the University of Leeds on “Long-term management of leachates produced from highly alkaline bauxite residues” with Dr Ian Burke (SEE), Prof Doug Stewart (Civil Eng), Dr Will Mayes (Hull) and Amiel Boullemant (Rio Tinto Legacy Management).
- Investigate the fate and mobility of soluble metals (Al, As, Mo. V) in relevant leachate management systems (e.g. neutralisation, re-circulation) using a combination of on-site measurement and laboratory experimentation (with synchrotron and electron microscopy based characterisation of metal(loid) speciation in the solid phases produced).
- Determine the effectiveness of residue treatments (e.g. in situ neutralisation, carbonation reactions) for controlling trace metal(loid) leaching and their long-term role in promoting residue stability and rehabilitation/ revegetation prospects.
- Investigate the fate of released oxyanions (chiefly V) in natural environments receiving treated leachates in order to understand the role of interactions with soil minerals and organic matter in controlling metal(loid) mobility and risk.
Project partner(s): Rio Tinto Legacy Management
Contact email: email@example.com
You can find detailed information here.
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.
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:
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.
Calcite precipitates in Howden Burn
Measuring water quality parameters
Overflow from the slag mound drainage network
Water, sediments and invertebrates sampling in Coatham Marsh, Redcar