Optimizing woodchip biochar for adsorption of inorganic metal ion contaminants

Ugbomeh, Ify Leonard ORCID: 0000-0002-6002-4843 (2024). Optimizing woodchip biochar for adsorption of inorganic metal ion contaminants. University of Birmingham. Ph.D.

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Abstract

Affordable, reliable, and low-cost methods for removal of oil-associated heavy metal contaminants (Ni\(^{2+}\) and Pb\(^{2+}\)) from the environment are urgently needed. The use of adsorbent’s produced from organic biomass which is a renewable feedstock has gained attention recently. In this work, seven woodchip biomass samples (Ash, Apple, Alder, Beech, Birch, Cherry and Oak) were characterized in terms of their surface area, pore size, pore volume , elemental composition (Carbon, Nitrogen, Hydrogen, Oxygen), moisture, volatile substances, heat content , and metal ion concentrations (Mg, Mn, P, Ca, Co, Cu, Cr, Fe, Ni, Cd, Pb) and statistically compared using Pairwise non-parametric Kruskal-Wallis one-way ANOVA) to identity a subset based on significantly (<0.05) different parameters for conversion to biochar. Based on this analysis, four biomass samples were selected (Ash, Apple, Beech, and Birch) and subjected to pyrolysis at 550°C for 5 hrs to produce its derived biochar (Bc-Ash, Bc-Apple, Bc-Beech, and Bc-Birch). The Biochar samples had large surface areas: 307.3 ± 7.31m\(^2\)/g, 314.2 ± 7.31m\(^2\)/g, 305.1 ± 7.28m\(^2\)/g and 287.3 ± 6.77m\(^2\)/g for Bc-Ash, Bc-Apple, Bc-Beech, and Bc-Birch, respectively and were evaluated in terms of their efficacy for sorption of Ni\(^{2+}\) and Pb\(^{2+}\). Sorption results for Ni\(^{2+}\) (0.7977 - 0.8124 mg/g biochar) and Pb\(^{2+}\) (0.7958 – 0.8073 mg/g biochar) were slightly below expectation with hydrogen bonding/ electrostatic being the only binding mechanism identified for all 4 biochar types. To improve sorption capacity and possibly introduce an additional sorption mechanism, the Bc-Beech was functionalised with nanoscale materials to create hybrid biochar. Three functionalization routes were explored: Hydroxyapatite-Biochar (HA-Bc), Magnetic-Biochar (MBc), and Magnetic-Hydroxyapatite-Biochar (MHA-Bc). These hybrid Biochar samples were characterised and found to have surface areas of 141.1 ± 1.95 m\(^2\)/g (HA-Bc), 190.64 ± 4.11 m\(^2\)/g (MBc) and 104.5 ± 0.11 m\(^2\)/g (MHA-Bc) and interacted effectively in both mono (Ni\(^{2+}\) or Pb\(^{2+}\)) and binary (Ni\(^{2+}\) and Pb\(^{2+}\)) exposure modes with the target pollutants. MBc (0.25 mg/g) had better affinity for Ni2+ than HA-BC (0.24 mg/g), MHA-Bc (0.24 mg/g) had the highest affinity for Pb\(^{2+}\), while in the binary system the total amount of pollutants bound decreased in the order MBc (0.49 mg/g) > MHA-Bc (0.49 mg/g) HABc> (0.49 mg/g). Nanomaterial functionalization of biochar reduced the number of active sites for sorption but added a new attachment mechanism (complexation) to the existing one (precipitation), thereby enhancing the overall adsorption efficiencies.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):