Sorption of copper (II) and sulphate to different biochars before and after composting with farmyard manure

Abstract

Biochar application has been suggested for reducing toxic levels of metals in contaminated soils and enhancing nutrient retention in agro‐ecosystems. We studied sorption of copper (Cu(II)) and sulphate‐sulphur (SO4‐S) to charcoal, gasification coke and flash‐pyrolysis biochar in order to relate sorption to char properties. Furthermore, we investigated the effect of composting of charcoal and gasification coke on sorptive properties. Langmuir sorption affinity coefficients for Cu(II) for non‐composted biochars increased in the order flash‐pyrolysis char < charcoal < gasification coke. The sorption capacity for Cu(II) of the chars decreased in the order gasification coke (629 mg kg−1) > flash‐pyrolysis char (196 mg kg−1) > charcoal (56 mg kg−1). Composting significantly increased the sorption affinity coefficient approximately by a factor of 5 for charcoal (up to 1.1 l mg−1) and by a factor of 3–4 for gasification coke (up to 3.2 l mg−1). Whereas Cu(II) sorption to gasification coke (composted or not) was largely irreversible, sorption to flash‐pyrolysis char and charcoal showed higher reversibility. Relationships between Cu(II) sorption and biochar properties such as cation exchange capacity, specific surface area or aromaticity suggest that sorption was largely determined by complexation with organic matter. Sorption of SO4‐S was negligible by non‐composted and composted biochars. Composted gasification coke might be suited to reducing toxic Cu(II) concentrations in contaminated soils. Composted charcoal can potentially improve Cu(II) retention in a plant available form in acidic, sandy soils with small organic matter contents. Transient effects of biochars on soil pH can over‐ride the influence of sorption to biochars on concentrations of trace elements in soil solution and their availability to plants.

Biochar and forest restoration: a review and meta-analysis of tree growth responses

“…The sorptive properties of biochars are commonly responsible for biochar's capacity to mitigate the impacts of plant stress by reducing exposure of plants to stress agents (Yu et al 2009;Beesley et al 2010Beesley et al , 2011Buss et al 2011). Studies have documented reduced bioavailability of heavy metals and sulfates in the presence of biochar incorporated in contaminated soils (Beesley et al 2010;Borchard et al 2012). One study has also documented strong hysteresis in sorption, approaching a state of irreversible sorption, of Cu(II) ions in certain biochars (Borcard et al 2012).…”

Contrasting effects of organic amendments on phytoextraction of heavy metals in a contaminated sediment

“…The high P content would promote precipitation or co-precipitation of heavy metals (Liu The adsorption of heavy metals onto organic materials like biochars and manures involves several mechanisms such as electrostatic interactions, ion exchange (including protons), and/or complexation via chemical ligand binding (Uchimiya et al 2012). Ion exchange may be a prevalent mechanism of adsorption for organic materials which are attributed to various functional groups (Borchard et al 2012;Uchimiya et al 2011a). This helps to explain the decreasing pH during adsorption processes (Fig.…”

Review Paper: The Fundamentals of Biochar as a Soil Amendment Tool and Management in Agriculture Scope: An Overview for Farmers and Gardeners

“…Biochar can offer additional environmental advantages, containing: 1) Decrease nutrient pollution in water bodies; 2) Biochar may decrease the production of greenhouse gases by soil; 3) Impacts of biochar on the bio-availability and movement of heavy metals have been extensively reported [25] [26] [27] [28]. So biochar can decrease the bio-availability and mobility of pesticides and heavy metals in soil [11] [12].…”