Pyrolysis of biomass with phosphate compound is a promising method to improve biochar characteristics. However, how phosphate compound affects the three components of biomass during the biochar formation is still unclear. In this study, a typical phosphate compound, calcium dihydrogen phosphate (Ca(H 2 PO 4 ) 2 ), was premixed with cellulose, hemicellulose, and lignin reagent, at the ratio of 20% (w/w) for biochar production through pyrolysis, aiming to investigate the effects of Ca(H 2 PO 4 ) 2 addition on biochar formation. Results show that, with Ca(H 2 PO 4 ) 2 additions, carbon retention of biochars from cellulose (MCBC) and hemicellulose (MHBC) increased by 63.4% and 48.3%, respectively, but that of lignin (MLBC) decreased by 6.7% due to the reactions between lignin and Ca(H 2 PO 4 ) 2 . Moreover, the stable carbon proportion in the biochar decreased by 10.2% for MCBC, almost unchanged for MHBC, and increased by 6.15% for MLBC based on the potassium dichromate oxidation. During the pyrolysis process, Ca(H 2 PO 4 ) 2 addition fixed more volatile and/or labile carbon in biochar, resulting in greater carbon retention. Declined carbon stability of biochar might be caused by the inhibited formation of aromatic-C, evidenced by the Fourier transform infrared spectroscopy analysis. This study highlights the importance and potential mechanisms of calcium dihydrogen phosphate influencing the carbon retention and stability of biochar derived from three biomass components.
Huan Li,Shuijin Hu,Matthew L. Polizzotto,Xiaoli Chang,Qirong Shen,Wei Ran,Guanghui Yu
Highly reactive nano-scale minerals, e.g., short-range-ordered minerals (SROs) and other nanoparticles , play an important role in soil carbon (C) retention. Yet, the mechanisms that govern biomineralization from bulk minerals to highly reactive nano-scale minerals remain largely unexplored, which critically hinders our efforts toward managing nano-scale minerals for soil C retention. Here we report the results from a study that explores structural changes during Aspergillus fumigatus Z5 transformation of montmorillonite and goethite to SROs. We examined the morphology and structure of nano-scale minerals, using high-resolution transmission electron microscopy , time-resolved solid-state 27 Al and 29 Si NMR, and Fe K-edge X-ray absorption fine structure spectroscopy combined with two dimensional correlation spectroscopy (2D COS) analysis. Our results showed that after a 48-h cultivation of montmorillonite and goethite with Z5, new biogenic intracellular and extracellular reactive nano-scale minerals with a size of 3–5 nm became abundant. Analysis of 2D COS further suggested that montmorillonite and goethite were the precursors of the dominant biogenic nano-scale minerals. Carbon 1s near edge X-ray absorption fine structure (NEXAFS) spectra and their deconvolution results demonstrated that during fungus Z5 growth, carboxylic C (288.4–289.1 eV) was the dominant organic group, accounting for approximately 34% and 59% in the medium and aggregates, respectively. This result suggested that high percentage of the production of organic acids during the growth of Z5 was the driving factor for structural changes during biomineralization. This is, to the best of our knowledge, the first report of the structural characterization of nano-scale minerals by 2D COS, highlighting its potential to elucidate biomineralization pathways and thus identify the precursors of nano-scale minerals.
Molten salt electrorefining offers a promising approach for green and efficient recycling of waste cemented carbides. However, the conventional halide-based electrolytes suffer from volatile tungsten halide losses and only recover metallic tungsten, necessitating energy-intensive carburization to recover tungsten carbide (WC). Herein, we propose a novel electrolytic refining and recovery method based on an oxygen-containing CaCl 2 -CaO molten salt electrolyte. The introduction of CaO suppresses the formation of volatile tungsten halides, enabling simultaneous dissolution of carbon (C) and tungsten (W) in the WC-Co anode to non-volatile CaCO 3 and CaWO 4 , respectively. Retention of Co in the anode slime is achieved through controlling anodic potential, realizing component separation. The dissolved CaCO 3 and CaWO 4 are reduced at the cathode, resulting in the generation of WC powder. This work accomplishes the direct recycling of WC from spent cemented carbides without intermediate stages. The composite products of WC and carbon are deposited on the cathodes, of which morphologies are comprised of granular aggregates and flakes. The presence of carbon suppresses the formation of W 2 C and W. However, the residual carbon does not affect hard alloy reprocessing since the W/C ratio can be adjusted via controlled W addition during subsequent alloying. This paper proposes a novel short-process green recycling technology for strategic tungsten resources.
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