Valorisation of agricultural biomass-ash with CO2.

This work is part of a study of different types of plant-based biomass to elucidate their capacity for valorisation via a managed carbonation step involving gaseous carbon dioxide (CO2). The perspectives for broader biomass waste valorisation was reviewed, followed by a proposed closed-loop process for the valorisation of wood in earlier works. The present work newly focusses on combining agricultural biomass with mineralised CO2. Here, the reactivity of selected agricultural biomass ashes with CO2 and their ability to be bound by mineralised carbonate in a hardened product is examined. Three categories of agricultural biomass residues, including shell, fibre and soft peel, were incinerated at 900 ± 25 °C. The biomass ashes were moistened (10% w/w) and moulded into cylindrical samples and exposed to 100% CO2 gas at 50% RH for 24 h, during which they cemented into hardened monolithic products. The calcia in ashes formed a negative relationship with ash yield and the microstructure of the carbonate-cementing phase was distinct and related to the particular biomass feedstock. This work shows that in common with woody biomass residues, carbonated agricultural biomass ash-based monoliths have potential as novel low-carbon construction products.

Offsetting anthropogenic carbon emissions from biomass waste and mineralised carbon dioxide.

The present work investigates biomass wastes and their ashes for re-use in combination with mineralised CO2 in cement-bound construction products. A range of biomass residues (e.g., wood-derived, nut shells, fibres, and fruit peels) sourced in India, Africa and the UK were ashed and exposed to CO2 gas. These CO2-reactive ashes could mineralise CO2 gas and be used to cement 'raw' biomass in solid carbonated monolithic composites. The CO2 sequestered in ashes (125-414 g CO2/kg) and that emitted after incineration (400-500 g CO2/kg) was within the same range (w/w). The CO2-reactive ashes embodied significant amounts of CO2 (147-424 g equivalent CO2/kg ash). Selected ashes were combined with raw biomass and Portland Cement, CEM 1 and exposed to CO2. The use of CEM 1 in the carbonated products was offset by the CO2 mineralised (i.e. samples were 'carbon negative', even when 10% w/w CEM 1 was used); furthermore, biomass ashes were a suitable substitute for CEM 1 up to 50% w/w. The approach is conceptually simple, scalable, and can be applicable to a wide range of biomass ashes in a closed 'emission-capture' process 'loop'. An extrapolation of potential for CO2 offset in Europe provides an estimate of CO2 sequestration potential to 2030.

Sorption kinetics of zinc and nickel on modified chitosan.

This study was conducted to evaluate the effect of equilibration time on adsorption of zinc [Zn(II)] and nickel [Ni(II)] on pure and modified chitosan beads. The initial adsorption of Zn(II) was high on molybdenum (Mo)-impregnated chitosan beads (MoCB) during the initial 60 min. However, after 240 min, Zn(II) adsorption occurred more on single super phosphate chitosan beads (SSPCB), followed by monocalcium phosphate chitosan beads (MCPCB), untreated pure chitosan beads (UCB), and MoCB. Similarly, Ni(II) adsorption was greatest on MoCB during the initial 60 min. At the conclusion of the experiment (at 240 min), the greatest adsorption was occurred on MCPCB, followed by MoCB, UCB, and SSPCB. Chemical sorption and intra-particle diffusion were probably the dominant processes responsible for Zn(II) and Ni(II) sorption onto chitosan beads. The results demonstrated that modified chitosan beads were effective in adsorbing Zn and Ni and hence, could be used for the removal of these toxic metals from soil.