Processes and impacts of acid discharges on a natural substratum under a landfill

Abstract

Analyses of substratum samples under a landfill were performed to assess the pollution impact of waste over a clay-sand material after nine years of exposure. These samples presented different illite/kaolinite ratios and an acid pH, especially low near the waste/soil contact in a 1-1.5 m soil thickness with low density and despite the basic pH of the collected actual methanogenic leachate. This study has raised the effects of a presumably acid stage in the waste leachate on the substratum final quality of clay and its physical-chemical properties as an attenuation buffer. These effects were the dissolution of carbonate minerals, decrease of dry density, increase of hydraulic conductivity, release of metals and formation of clays with low cationic exchange capacity (CEC) as kaolinite. The large presence of H(+) and Al(OH)(3-x)(x+) depleted the neutralizing capacity of the substratum and occupied exchangeable sites, decreasing therefore the available sites for retaining leachate pollutants, which traveled further than the first-meter depth of the substratum. In order to combat and prevent pollution as well as to preserve the good barrier properties under new landfills it is proposed to select illitic materials better than kaolinitic substratum, to avoid acid landfilling and if not possible to add lime.

The Role of Natural Clays in the Sustainability of Landfill Liners

“…This is good for Coal Measures Clays which have no pH buffering capacity to attenuate acidic episodes caused for example by oxidation of sulphides (pyrite) by infiltrating rainwater (Thornton et al, 2001). This oxygenated water can re-oxidized sulphide phases, resulting in the release of previously attenuated metals that precipitated earlier in such immobile phases (Regadío et al, 2013). Bicarbonates in the leachate itself would provide acid neutralization capacity to Coal Measure Clays which lack calcite.…”

Physicochemical indicators of the influence of a lined municipal landfill on groundwater quality: a case study from Poland

“…The chemical composition of leachate water is determined by the composition of the waste, the way it is used, the age of the landfill, the availability of oxygen, the hydrogeological conditions and the ambient temperature and precipitation (Ilies and Mavinic 2001;Chen 2006;Longe and Balogun 2009;Regadío et al 2013;Przydatek 2019c). Sari et al (2013) divided leachates into young, middle-aged and mature, which is considered important in the choice of technology to neutralise them because, due to its toxic content, leachates pose a threat to surface water, groundwater and the soil (Barbieri et al 2014;Naveen et al 2017).…”

Containment and attenuating layers: An affordable strategy that preserves soil and water from landfill pollution

“…( 3)). This confirms the importance of calcite and its pH-buffering to keep a less-aggressive leachate and backgroundpollutants concentrations (Brun et al, 2002;Regadío et al, 2013) and to offer appropriate conditions for heavy metals to suffer natural attenuation processes such as redox, coprecipitation, sorption reactions and incorporation in the crystal structure (Hua et al, 2007;Mostbauer, 2003;Sanchez-Pastor et al, 2011;Tang et al, 2007;Yanful et al, 1988).…”

“…The alkaline pH is in concordance with the low metals contents in the leachate (Table S3). Basic pH promotes metals/cations immobilization by mineral-formation and sorption because it favours: (1) redox states of metals that precipitate as oxy-hydroxides, carbonates or sulphides minerals and (2) H + depletion with a consequent decrease in the cations competition for being sorbed in negatively charged surfaces such as those of clays (Regadío et al, 2013). Though MW are not toxic by themselves, their organic matter releases H + during the biodegradation in the acetogenic stage, making the leachate acidic.…”