Production of silicon compounds and fulvic acids from cotton wastes biochar using chemical depolymerization

• The chemical depolymerization of cotton wastes biochar was evaluated.
• FT-IR and UV–vis spectroscopy were used to describe the biochar depolymerization.
• The KMnO4 treatments produced the largest biochar depolymerization.
• It is possible to repetitively depolymerize the gasification biochar.
• Silicon compounds and fulvic acids were purified from the depolymerized liquid phase

This study evaluated the depolymerization of biochar from cotton wastes gasification using three chemical agents (KMnO4, H2SO4, and NaOH). The experiment was carried using a factorial design 3 × 3 × 2 with three concentrations (2.5, 5, and 10% w/v) and two environmental conditions (autoclave and without autoclave). After the chemical treatments, the liquid and solid phase obtained was analyzed using UV–vis and FT-IR spectroscopy, and ultimate and proximate analysis. The sulfuric acid treatments performed the largest transformations of the biochar’s solid phase; meanwhile, the KMnO4 treatments achieved the largest depolymerizations followed by the NaOH experiments. The methanol precipitation of the ATC–KMnO4 [10%] treatment’s products generated two silicon related compounds and a brown liquid associated with fulvic acids. This is the first research showing the possibility of transform cotton wastes biochar into profitable products as silica or fulvic acids.