A R&D trial tested biochar, produced by pyrolysis at 600°C of boric acid flame retardant treated cellulosic insulation material (produced from recycled paper, Isocell Austria), as a boron fertiliser in pot trials with rape and sunflower. Such boron-treated flame retardant cellulose can be recycled as building insulation material only a few times because of deterioration in fibre length. The pyrolysis reduces the solubility of the boric acid, which is important because boron is a necessary micronutrient for plants, but is toxic if released too rapidly. Challenges to possible industrial implementation include collection of spent insulation material without contamination, PAH (naphthalene) levels in the biochar and regulatory status of the product (end-of-waste, fertiliser authorisation).
“Functional recycling of biobased, borate-stabilized insulation materials as B fertilizer”, O. Duboc, J. Santner et al., Environ. Sci. Technol 2019, 53, 24, 14620-14629, https://doi.org/10.1021/acs.est.9b04234 19 DOPO – nitrogen – silicon FR for cotton