Waste animal bone as a low-cost precursor for bonechar in xylene adsorption

This study focuses of the bonechar prepared from diverse animal waste bones by microwave pyrolysis, with the aim of determining its chemical and structural properties and application potential for xylene adsorption. It was revealed that the type of raw bone itself is more significant for the pyrolysis bonechar yield than the microwave power. Beef bones produced the highest amount of bonechar (∼60 wt.%), which can be attributed to the high levels of fixed carbon (∼4 wt.%) and ash (∼50 wt.%) in the raw material. The bonechar is, in fact, a composite material composed of dominant hydroxyapatite and minor carbon, showing a well-defined mesoporous-macroporous structure with S BET and V net decreasing as the Ca/P molar ratio in hydroxyapatite increases. Xylene adsorption capacity of the bonechar is affected by the inter-play of following factors: the porous structure, fixed carbon content, degree of carbon graphitisation and the presence of surface CaO and Ca²⁺ cations. These findings are supported by force-field based molecular modelling. Bonechars prepared from fresh beef bones exhibited the highest xylene adsorption capacity, characterized by the medium porosity (S BET ≈95 m 2 ·g -1 ), high fixed carbon content (∼16 wt.%), pronounced graphitisation (I D /I G ≈1.00-1.06) and elevated surface content of CaO (∼72 at.% of present as CaO). Overall, the order of bonechars adsorption capacities from various animal bones in xylene adsorption is following: fresh beef bones (∼46 mg xylene ·g -1 ) > boiled beef bones ∼ boiled pork bones ∼ boiled chicken bones (14-24 mg xylene ·g -1 ). • Bonechar is a composite composed of dominant hydroxyapatite and minor carbon. • Hydroxyapatite interacts with xylene more strongly than carbon surface. • Ca 2+ -decorated carbon surface and calcium oxide interacts with xylene more strongly than hydroxyapatite.