Cation exchange properties of soils derived from lignite ashes

Abstract

In Saxony‐Anhalt, Germany, an area of about 6000 ha is covered by lignite‐ash‐derived substrates. In some cases, pollutants like heavy metals or toxic organic compounds had been disposed of together with the lignite ashes. For this reason, we assessed factors influencing the cation exchange capacity (CEC) of lignite‐ash substrates exposed to natural weathering.We chose four research sites reflecting the different methods of disposal: two dumped landfills and two lagooned ashes of different ages. After determining the CEC at pH 8.1 (CECpot), we evaluated the influence of the content of silt and clay and the content of total organic C. As lignite‐ash‐derived substrates are rich in oxalate‐extractable Si, Al, and Fe, we performed an oxalate extraction and determined afterwards the CECpot to assess the contribution of oxalate‐soluble compounds to the CECpot. Moreover, we determined the variable charge of selected samples at pH values ranging from 4 to 7.The lignite‐ash‐derived soils had a high CECpot with means ranging from 25.1 cmolc kg–1 to 88.8 cmolc kg–1. The influence of the parent material was more important than the degree of weathering. The content of total organic C consisting of pedogenic organic matter and coked lignite particles together with the content of silt and clay played a statistically significant role in determining the CEC.Another property that influenced the amount of CEC in medium textured lignite ashes was the content of oxalate‐soluble silica and aluminum. After oxalate extraction, they lost about 30% of their CEC due to the dissolution of oxalate‐soluble compounds. In coarse textured lignite ashes, oxalate extraction led to higher amounts of CEC, probably due to an increase of surface area resulting either from the disintegration of particles or from etching caused by insufficient dissolution of magnetite and maghemite. Moreover, lignite‐ash‐derived substrates exhibit a high amount of pH‐dependent charge. The CEC decreased by 40% in a topsoil sample and by 51% in a subsoil sample as the pH declined from 7 to 4.

Classification of Urban and Industrial Soils in the World Reference Base for Soil Resources (5 pp)

“…Contaminant loads are often much higher, parent materials are diverse and often of extreme chemical composition. Soils from technical materials such as industrial wastes often experience rapid weathering unlike that in natural soils [3,4].…”

Water repellency of fly ash‐enriched forest soils from eastern Germany

“…Fly ash accumulation led to substantial changes of the properties of forest soils. Chemical properties of the enriched soils such as pH, base saturation, organic C, cation exchange capacity and the content of heavy metals were distinctly influenced by the fly ash (Neumeister et al, 1991;Rumpel et al, 1998;Koch et al, 2002;Zikeli et al, 2004). The enrichment of fly ash also changes soil physical characteristics of FFHs.…”

Changes in soil physical properties of forest floor horizons due to long-term deposition of lignite fly ash

“…determined that persistent deposits consisted of ironcontaining stable glasses, aluminum-iron-silicates, slag fragments, and lignite-derived fossil carbon, and they had a total ash content of up to 77%. Hence, atmospheric fly ash deposits modify soil chemical properties like pH levels, base saturation, organic C, and cation exchange capacity (Fritz and Makeschin 2007;Klose and Makeschin 2004;Koch et al 2002;Neumeister et al 1991;Rumpel et al 1998;Schaaf et al 2001;Weisdorfer 1999;Zikeli et al 2004). Fly ashes are characterized by a strongly sorted texture dominated by fine sand or silt fractions.…”