Characterization, Concentration of Biochar and Titanspheres and Heavy Metals Assessment of Quercus Suber Cork Powder Fly Ash Fractions

Abstract

Cork powder is categorized in the group of the biodegradable fraction of products and waste. In Portugal, the cork powder production ranges between 32 000 and 37 000 tons/year and is used as fuel, which generates ash. For this ash characterization and possible recycling, sieving (dry and wet) and pre-treatments (ultrasounds and polycarboxylate) were tested in order to concentrate biochar, titanspheres and assess the fractions more suitable for fertilizer material. The samples were characterized via a combination of techniques: SEM/EDS, RLM, XRF, MRS and ICP-MS. For size-fractionation of cork powder fly ash, dry sieving is not an efficient method, however, improved efficiency, especially in the <25 μm size-fraction, can be attained by preceding wet sieving with a combined pre-treatment of ultrasounds and polycarboxylate. A sequence method was applied for biochar concentration and purification, however the amount of final biochar obtained is very low (1%wt.). The ICP-MS results indicate that the use of cork powder ash as fertilizer material in plant crops intended for human and animal consumption is not recommended, whereas other uses in soils are possible.