Feedstock doping using iron rich waste increases the pyrolysis gas yield and adsorption performance of magnetic biochar for emerging contaminants

Abstract

Magnetic carbons can significantly lower the costs of wastewater treatment due to easy separation of the adsorbent. However, current production techniques often involve the use of chlorinated or sulfonated Fe precursors with an inherent potential for secondary pollution. In this study, ochre, an iron-rich waste stream was investigated as a sustainable Fe source to produce magnetic activated biochar from two agricultural feedstocks, softwood and wheat straw. Fe-doping resulted in significant shifts in pyrolysis yield distribution with increased gas yields (+50 %) and gas energy content (+40 %) lowering the energy costs for production. Physical activation transformed ochre to magnetite/maghemite resulting in activated magnetic biochars and lead to a 4-fold increase in the adsorption capacities for two common micropollutants-caffeine and fluconazole. The results show that Fe doping not only benefits the adsorbent properties but also the production process, leading the way to sustainable carbon adsorbents.

Sorption, separation and recycling of ammonium in agricultural soils: A viable application for magnetic biochar?

“…Interestingly, the need for co-precipitation or iron solution pre-treatment has been challenged by a novel approach demonstrated by Rodriguez Alberto et al (2019) , using the digestate from an anaerobic digestion process fed by cow manure and industrial food wastes, followed by pyrolysis to produce magnetic biochar. Similarly, other iron rich waste streams have been proposed as sustainable reagents for magnetisation, with Wurzer and Mašek (2021) showing that ochre (mining waste) could be effectively used to form magnetite/maghemite impregnated biochar with increased adsorption capacity for caffeine and fluconazole. Rodriguez Alberto et al (2019) attributed the formation of magnetite particles on their biochar (approximately 3.1% Fe) to the high iron content of the solid digestate combined with the thermochemical processing parameters.…”

“…Such particles include magnetite, maghemite, hematite, and zero-valent iron, and often exist as nanoparticles bound to the surface of biochar or contained within pores. Some unmodified biochars may also be classed as magnetic, for example where feedstocks contain high concentrations of iron which successfully form magnetic particles through chemical changes induced by pyrolysis ( Rodriguez Alberto et al, 2019 ; Wurzer and Mašek, 2021 ). There is, therefore, a large variety of physical and chemical properties of magnetic biochars, as affected by the magnetic particles present and the mode of impregnation, which subsequently leads to variability in mechanisms and capacity for sorption of nitrogenous pollutants.…”

Biochar composites: Emerging trends, field successes and sustainability implications

“…For instance, Fe(II) species on the surface of FeCl 3 ‐soaked biochar were found to be responsible for Cr(VI) reduction, whereas Fe(III) species would precipitate with the as‐formed Cr(III) (Chen et al, 2020). Iron in different forms, including mining and industrial residues, can be successfully used as a dopant to improve biochar performance in the removal of contaminants, offering a potentially attractive circular economy option (Wurzer & Mašek, 2021).…”

Synthesis of magnetic date stone biochar for solid phase extraction of NSAIDs from water samples

“…Iron oxides are the most commonly used magnetic materials to endow BC with magnetic properties. 7,[12][13][14] Magnetically loaded activated carbon was used for the removal of methylene blue and aluminum from water samples. 15,16 Most articles have reported that magnetic biochar is an effective adsorbent for the removal of heavy metals, but to our knowledge, fewer studies have reported on the adsorption of pharmaceuticals.…”