Transport of toxic metals in clay mineral barriers:Influences of mobile sorbent nanoparticles

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

Landfill leachates and contaminated land pore waters contain a wide range of pollutants, such as xenobiotic organic compounds (e.g. aromatic halogenated hydrocarbons) and potentially toxic metals (e.g. Cr, As, and Cd). The most widely used strategy for containing these toxic substances is through the use of low hydraulic conductivity clay liners. Initial models of such systems were largely predicated on solute transport models based on batch sorption data, in which species were defined as partitioned between liquid and solid phases. It is apparent, however, that colloidal materials, also termed as mobile sorbent nanoparticles (MSNs), play an important role in transport of dissolved organic matter and metals.In evaluating the impact of MSNs on toxic metal transport in landfills and contaminated land, there is a need for more quantitative data that can be used to develop generic models to describe and predict the transport of potentially toxic species in these environments. This will require study of MSNs derived from landfill leachates of different ages and management practices, together with experimental study of commercially manufactured MSNs of defined size, charge and concentration under simulated landfill conditions. Size, charge and concentration are the key attributes influencing straining and filtering of MSNs by clay liner materials and are parameters that can be manipulated through the use of manufactured microspheres. Quantification of interactions between manufactured nanoparticles and clay liners thus permits elucidation of the effects of these parameters on the potential for MSNs to facilitate or prevent cross-barrier transport of contaminants, therefore providing a means through which containment failure can be more accurately predicted. The data derived from these studies are an absolute pre-requisite for developing the models required to make accurate and precise predictions of toxic metal behaviour in contaminated sites, and thus develop robust and cost-effective strategies for ensuring compliance of landfill practice with legislative requirements, in particular those set out in EU Groundwater Directive 80/68/EEC and the new Groundwater Daughter Directive (2006/118/EC).

Planned Impact

The research will benefit the research community, government agencies and regulators, waste management companies and consultants, and society as a whole. It will also benefit the research community by enhancing the science base through the development of new levels of understanding of the role of geochemistry in the sorption/desorption and transport of contaminants in low hydraulic conductivity sub-strata, particularly when associated to natural or engineered mobile sorbent nanoparticles. It will benefit regulators, consultants and waste management companies through the development of more robust environmental risk assessment tools. It will also benefit society as a whole by ultimately reducing the likelihood of ground and groundwater contamination from in-ground and on-ground waste repositories. All of these will benefit from the production of highly qualified personnel, who will go out to work and improve the UK's technical performance in this field. The key to realizing the potential benefits of the research will be by wide dissemination to and engagement with government agencies and the waste industry to ensure that the research results are implemented.

Publications

10 25 50
 
Description Landfill leachates contain a wide range of pollutants including potentially toxic metal(loids) e.g. arsenic. Current landfill risk assessment models predict the fate and transport of these pollutants in the environment, however they consider all species below 0.45 µm to be dissolved, thus the presence of these pollutants in colloidal form is not considered. To investigate the presence and distribution of metal(loids) within the nanocolloidal fraction (<100 nm), a method using assymetric field flow fractionation (AF4) was developed. AF4, coupled with HR-ICP-MS, UV and Fluorescence spectroscopy, was optimised for use with landfill leachates. A key part of this study was the successful development and validation of the coupled analysis system for use with a complex matrix like landfill leachate.

The method was validated by fractionation of a MSW leachate, an aged MSW leachate and a MBT leachate. All three leachates were found to show the same nanocolloidal distribution with two distinct nanocolloid populations present: a low MW organic rich fraction; and a larger, less organic rich fraction consisting of a mixture of organic and inorganic particles. Metals predominated in the lower MW fraction associated with humic or fulvic-like particles. The similarities between the leachate metal distributions showed that treatment of leachate prior to landfill did not alter the colloidal characteristics. Preliminary results examining the effects of pH and ionic strength of metal distribution showed that pH had no effect; however the lowering of ionic strength appeared to cause aggregation of colloidal Fe particles, presumably due to the lower organic content, which appears to control the distribution of metals in this size fraction.

This research highlights the importance for landfill risk assessments to be updated to include the presence of colloidal facilitated transport and the necessity for further particle transport studies to be conducted.
Exploitation Route The advances in the analytical method can be used for examination of nanomaterials especially with complex matrices by the research community.
Sectors Agriculture, Food and Drink,Chemicals,Environment

 
Description Collaboration on engineered nanomaterials in solid waste management 
Organisation University of Natural Resources and Applied Life Sciences
Country Austria 
Sector Academic/University 
PI Contribution Contributed towards a review of the fate of engineered nanomaterials in municipal solid waste streams
Collaborator Contribution Contributed towards a review of the fate of engineered nanomaterials in municipal solid waste streams
Impact Journal paper A review of the fate of engineered nanomaterials in municipal solid waste streams" accepted by Waste Management
Start Year 2016
 
Description Collaboration on engineered nanomaterials in solid waste management 
Organisation University of South Carolina
Department Department of Civil and Environmental Engineering
PI Contribution Contributed towards a review of the fate of engineered nanomaterials in municipal solid waste streams
Collaborator Contribution Contributed towards a review of the fate of engineered nanomaterials in municipal solid waste streams
Impact Journal paper A review of the fate of engineered nanomaterials in municipal solid waste streams" accepted by Waste Management
Start Year 2016