Attenuation of landfill leachate by clay liner materials in laboratory columns: 2. Behaviour of inorganic contaminants

Abstract

The chemical attenuation of inorganic contaminants in methanogenic landfill leachate, spiked with heavy metals (Cd, Cd, Ni and Zn), by two UK clay liner materials was compared in laboratory columns over 15 months. Ammonium was attenuated by ion-exchange but this attenuation was finite and when exhausted, NH4 passed through the liners at concentrations found in the leachate. The breakthrough behaviour of NH4 could be described by a simple distribution coefficient. Heavy metals were attenuated by sorption and precipitation of metal sulphide and carbonate compounds near the top of the liner. Adequate SO4 and CaCO3 in the liner is necessary to ensure the long term retention of heavy metals, and pH buffering agents added to stabilise reactive metal fractions should be admixed with the liner. Some metals may not be chemically attenuated by clay liners due to the formation of stable complexes with organic and/or colloidal fractions in leachate. Flushing of the liners with oxygenated water after leachate caused mobilisation of attenuated contaminants. Sorbed NH4 was released by the liners but groundwater loadings were manageable. Re-oxidation of metal sulphides under these conditions resulted in the release of heavy metals from the liners when the pH buffering capacity was poor. Contaminant attenuation by the clay liners was similar and the attenuation of NH4 and heavy metals could be predicted from the geochemical properties of the liner using simple tests. A conceptual model of clay liner performance is presented. Chemical attenuation of inorganic pollutants can be included in containment liner design to produce a dual reactive-passive barrier for landfills.

Cu(II) and Zn(II) adsorption capacity of three different clay liner materials

“…The ability of the bottom liner to adsorb heavy metals becomes a significant design issue. The sorption properties of natural clays are thus of fundamental importance in evaluating their potential use as landfill barrier material (Thornton et al, 2001;Sezer et al, 2003;Kaoser et al, 2005;Du and Hayashi, 2006;Bezzar et al, 2010;Koutsopoulou et al, 2010;Ghorbel-Abid and Trabelsi-Ayadi, 2011;S anchez-Gim enez et al, 2012).…”

Application of the buffer theory for evaluating attenuation and natural remediation of ionic pollutants in aquatic ecosystems

“…Having only this information, it is impossible to predict the future development of the metal amounts and its species in contaminated ecosystems under the change of environmental conditions (e.g., pH, Eh 1 , cations, organic matter and other metalcomplexing ligands) (Stumm andMorgan 1996, Povar andSpinu 2014a).…”

“…The oldest buffers described in the literature are mono-phase acid-base buffer systems (Fernbach and Hubert 1900;Povar and Luca 2003;Povar 2000b) in respect to pH. These pH buffers are described in detail (Butler 1991;Perrin and Dempsey 1974;Stumm and Morgan 1996).…”

Hazardous Waste Pollution Prevention Using Clay with Admixtures

“…One major concern about clay liners is that they may be directly or indirectly attacked by the chemical wastes or leachate they are meant to contain. This interaction of metals with soil may cause the transport of heavy metals through the soil liner and result in the groundwater being contaminated [4,5]. Many organic and inorganic chemicals have the ability to shrink the diffuse double layer that surrounds clay particles, causing the cracking of liners, increasing the permeability of soil, with the result that the groundwater is contaminated.…”