Abstract
AbstractThe properties of rice husk biochar during the ageing process in soil and the resulting impacts on sorption capacity with respect to Cu(ii) were assessed. Rice husk-derived biochar was placed in fabric bags and buried in a plastic incubator filled with soil for 0–240 d. The aged biochar was then characterised and its sorption capacity compared with control (unaged) biochar in batch sorption experiments. The structural composition and morphology of the biochar before and after ageing were analysed based on element composition, scanning electron microscopy (SEM) coupled with energy X-ray dispersive spectroscopy (EDS), diffuse reflectance infrared Fourier transform infrared spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS). The concentration of O, atomic O/C ratios, and carboxyl and hydroxyl functional groups increased at the surface of the biochar during ageing, which together indicated oxidation. Within the biochar particles, O/C ratios progressively increased towards their outer surfaces. Furthermore, ageing for more than 120 d facilitated Cu(ii) sorption as oxygen-containing groups were able to develop. The maximum adsorption capacity (qm) of biochar increased by 1.24 ∼ 1.32 times after ageing in the soil for 240 d. It is suggested that biochar surface properties were gradually altered during environmental exposure and the aged rice husk biochar showed increased performance in Cu(ii) adsorption. However, the performance of aged biochar as a soil remediator or conditioner will be affected by the ageing process and interactions among different soil components. As such, further research is required to evaluate these complex effects.
Highlights
Biochar is a carbon-rich solid by-product produced from biomass pyrolysis and has remarkable environmental properties [1,2,3]
The present study evaluate the effects of ageing on rice husk-derived biochar and its sorption capacity with respect to Cu(II)
The observed increase in the O content and decrease in the C content of the aged biochar, and increase in atomic O/C ratios, indicated that the biochar surfaces became more oxidised during the ageing process
Summary
Biochar is a carbon-rich solid by-product produced from biomass pyrolysis and has remarkable environmental properties (e.g., porous structure, large surface area, high aromaticity) [1,2,3]. Physical, biological and chemical methods have been used to artificially age biochar. This includes using physical wetting/drying and freezing/thawing cycles, which can modify the stability of biochar after field exposure [13,14]. Different chemical oxidants such as oxygen, hydrogen peroxide, nitric acid, acidified potassium dichromate, ozone and even air alone have been used as ageing reagents in biochar experiments [15,16,17,18,19]. Biological mineralisation of biochar has been investigated by incubating biochar with sand, soil, inoculum solution and specific nutrients [20,21,22,23]
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