Sorption of Pb, Cu, Cd, and Zn by Municipal Solid Waste Composts: Metal Retention and Desorption Mechanisms

Abstract

In this study, the ability of two municipal solid waste composts to adsorb Pb, Cu, Cd, and Zn ions (Me(II)) from aqueous solutions was investigated. Sorption experiments, carried out at pH 4.5 to simulate acidic Me(II)‐polluted environments, showed for both composts higher affinity for Pb (∼0.45 mmol g−1) and Cu (∼0.31 mmol g−1) compared to Cd (∼0.25 mmol g−1) and Zn (∼0.10 mmol g−1). The sorption isotherms data fitted the Freundlich model better than the Langmuir in both composts, suggesting the presence of heterogeneous Me(II) adsorption sites. The humic acids (HA) extracted from composts contributed to 16, 23, 17, and 20% in the sorption of Pb, Cu, Cd, and Zn, respectively, while the compost water‐soluble‐fractions hardly affected the sorption/precipitation of the Me(II) (<5%). The Fourier transform infrared (FT‐IR) spectra of the different Me(II)–HA systems also indicated that the carboxylate groups of HA mainly interacted with Pb(II) and Cu(II) by forming monodentate and bidentate complexes, respectively. The sequential extraction data showed that a significant amount of Cd and Zn was retained by composts through electrostatic interactions (>65% of the respective total amounts sorbed) while most of Cu and Pb (40 and 54%) was strongly complexed and/or precipitated. The treatment of the Me(II)‐composts with citric and malic acids favored the release of >78 and 48% of Zn, 65 and 30% of Cu, and 40 and 30% of Cd, sorbed by both composts, respectively. This release was lower for Pb (<20%) as the cation more strongly retained by the organic or inorganic components of composts.

Evaluation of Cynara cardunculus L. and municipal solid waste compost for aided phytoremediation of multi potentially toxic element–contaminated soils

“…The reduction of Zn concentration in roots after MSWC addition was also observed (~ 18.4-fold in the amended soils). Likewise As and Sb, the reduced metal uptake by cardoon in amended soils was explained with a substantial fixation of labile metal cations by compost as previously found (Manzano et al 2016 ; Silvetti et al 2017 ; Garau et al 2019a ).…”

“…Plants can modify the rizhospheric soil by the uptake of macro- and micro-nutrients and the release of organic or inorganic compounds which can alter the solubility and bioavailability of PTE (Ali et al 2013 ; Gomes et al 2016 ). In particular, the release of low molecular weight organic compounds such as oxalic, malic and citric acids can increase the solubility of metals (Castaldi et al 2013 ; Bothe and Słomka 2017 ), while the release of polygalacturonic acid can be an effective strategy for the immobilization of metal cations and the reduction of their bioavailability (Castaldi et al 2010 ; Kelly-Vargas et al 2012 ; Silvetti et al 2017 ). Moreover, also rhizospheric microorganisms can influence PTE mobility in soil, e.g., through the release of siderophores (Gomes et al 2016 ).…”

Evaluation of Commercial Humic Substances and Other Organic Amendments for the Immobilization of Copper Through 13C CPMAS NMR, FT-IR, and DSC Analyses

“…It was also possible to observe a peak at 1400-1470 cm −1 , attributable to the -COOantisymmetric stretching of carboxylic acids and the C-O stretching and O-H deformation of phenolic groups [2,11,20,32,33], that was reduced at pH 5.0 compared to pH 2.5. The intensity of its band also decreased with increasing Cu concentration, even disappearing in HS100 at pH 5.0, and a shift to higher wavenumbers of the peak 1433 cm −1 in HS0 (1429 cm −1 in HS 100 spectrum) at pH 5 was observed, similar to the results obtained by Silvetti et al [48] who studied the Cu adsorption capacity of humic acids, suggesting a bidentate chelating mode for Cu with the carboxylic groups. These results were consistent with those of previous studies [8,20,46], in which this band changed its intensity with the addition of metals (Cu, Cr, and Zn), providing evidence of interactions between metal ions and carboxylic and phenolic groups.…”

Innovative amendments derived from industrial and municipal wastes enhance plant growth and soil functions in potentially toxic elements-polluted environments

“…Because of these physico-chemical properties, MSWC could be a strategic resource for the improvement of soil functionality and plant growth in PTE-contaminated soils (Castaldi et al, 2005(Castaldi et al, , 2018Garau et al, 2020). Moreover, humic substances of MSWC can immobilize PTE forming complexes of different strengths and reducing their mobility and bioavailability in soil (Paradelo et al, 2012;Silvetti et al, 2017). This is due to a high surface charge density of humic substances and to their functional groups such as carboxyl, phenolic, hydroxyl, carbonyl, and sulfhydryl which are particularly active in the formation of metal-organic complexes.…”