Experimental Assessment of Using Soluble Humic Substances for Remediation of Heavy Metal Polluted Soils

Comparison of Natural Humic Substances and Synthetic Ethylenediaminetetraacetic Acid and Nitrilotriacetic Acid as Washing Agents of a Heavy Metal–Polluted Soil

“…The results of the sequential extraction of the residues after multistep extraction of Cu by 25, 50, and 100 mmol L −1 DOC of the three extractants are shown in Table 4, and the partitioning of the three metals after the single‐step extraction with 50 mmol L −1 DOC as EDTA, NTA, and HS is shown in Table 3 From a soil washing point of view, the results in Tables 3 and 4 are not very informative (i.e., encouraging) except for Cu (Table 4), where the exchangeable fraction remains very low and both the carbonate‐bound and oxide‐bound fractions are strongly reduced by the three extractants compared with the control, in agreement with previous results (Borggaard et al, 2009). In contrast, exchangeable Cd and Pb remain high after extraction with EDTA, NTA, and HS, and, although the other Cd and Pb fractions are lower after extraction, substantial carbonate‐bound and oxide‐bound fractions persist.…”

“…By the sequential extraction, the Cd, Cu, and Pb contents of the soil were partitioned into specific but operationally defined pools with increasing bonding strength: exchangeable < carbonate‐bonded < oxide‐bonded < residual metal (Tessier et al, 1979; Barona et al, 2001; Sun et al, 2001; Rao et al, 2008; Borggaard et al, 2009). In relation to soil washing, sequential extraction can be used to assess the fraction(s) removed by the extraction; ideally the weakest bonded metal fraction(s), which are the most available/mobile pools, should be removed by the extraction (Barona et al, 2001; Tandy et al, 2004; Borggaard et al, 2009).…”

“…Therefore, HS cannot be recommended for cleaning Pb‐polluted soil, at least not if it is a calcareous soil that has been polluted over a long time because removal of the pollutant from such soils is especially difficult (Heil et al, 1999; Kim et al, 2003; Meers et al, 2007). On the other hand, because substantial amounts of Cd and Cu can be removed by HS (Tables 1, 3, 4) (Bianchi et al, 2008; Steponkaite et al, 2008; Borggaard et al, 2009), HS may replace EDTA and NTA as a cleaning agent for Cd‐ and Cu‐polluted soils. Replacement of the synthetic EDTA and NTA by the natural HS is environmentally very attractive.…”

“…Despite these limitations, the data in Table 2 indicate that HS is a less efficient extractant than EDTA and NTA, in accordance with the results in Table 1 The constants cannot explain the discrepancy between the substantial amounts of Cu (∼54%) extracted by HS compared with the very limited extractability of Pb (<4% of total content) in as much as the Cu‐HS and Pb‐HS constants are similar. Despite this, the present investigation has, in accordance with previous studies (Conte et al, 2005; Bianchi et al, 2008; Steponkaite et al, 2008; Borggaard et al, 2009), demonstrated that HS is an environmentally friendly and fairly effective washing agent for soils polluted with Cd, Cu, and other pollutants.…”

Solubility of Heavy Metals/Metalloid on Multi-Metal Contaminated Soil Samples from a Gold Ore Processing Area: Effects of Humic Substances

“…However, although humic substances have been investigated as a washing agent for soils contaminated by polyaromatic hydrocarbons and other organic pollutants (Borggaard et al, 2009;Soleimani et al, 2010) and testing on heavy metal polluted soils is limited, in recent years some studies have been performed (Fonseca et al, 2013;Tang et al, 2014;An et al, 2015;Hwang et al, 2015).…”