Titânio em turmalinas pretas foi analisado por espectrofotometria entre 12500 e 27000 cm -1 (800-370 nm) em um microscópio MPV-5P, Leitz (Alemanha), e analisado quimicamente em uma micro-sonda eletrônica Camebax Microbeam, Cameca (France) (WDS-mode). Quatorze turmalinas orientadas com faces paralelas ao eixo trigonal, cortadas e polidas até espessuras finas mostraram, em espectros polarizados, duas bandas largas de absorbância a aproximadamente 14000 cm -1 (715 nm) e 24000 cm -1 (417 nm). Medidas de espessura das amostras foram usadas no cálculo de coeficientes de absorção α (cm -1 ). Para a banda em torno de 24000 cm -1 (417 nm), foi observada uma correlação linear entre α e a concentração em massa de TiO 2 (%). Outra regressão foi observada entre α e o produto da concentração em massa de TiO 2 (%) e FeO (%). Cátions localizados em grupos de octaedros Y e Z conectados através dos seus lados podem contribuir para as transferências de carga Ti 3+ -Ti 4+ , Fe 2+ -Ti 4+ , Ti 3+ -Ti 4+ -Fe 3+ .Titanium was examined in different black tourmalines by spectrophotometric analyses in the region between 12500 and 27000 cm -1 (800-370 nm) using a microscope spectrophotometer MPV-5P, Leitz (Germany), and chemically analyzed on an electron microprobe Camebax Microbeam, Cameca (France) in WDS Mode. Fourteen tourmaline samples with their face oriented parallel to the principal axis, cut and polished down to thin sections, showed polarized spectra of two broad absorption bands at approximately 14000 cm -1 (715 nm) and 24000 cm -1 (417 nm). Precision thickness measurements were used to calculate the absorption coefficients α. For the absorption around 24000 cm -1 , a linear correlation was observed between α and the TiO 2 content (mass %). Another linear regression was observed between α and the product of TiO 2 and FeO (%) contents. Cations located in the Y-and Z-octahedrons of the structure that are connected over edges might contribute to intervalence charge transfer transitions (IVCT) between Ti 3+ -Ti 4+ , Fe 2+ -Ti 4+ and Ti 3+ -Ti 4+ -Fe 3+ .

Sugarcane bagasse is commonly combusted to generate energy. Unfortunately, recycling strategies rarely consider the resulting ash as a potential fertilizer. To evaluate this recycling strategy for a sustainable circular economy, we characterized bagasse ash as a fertilizer and measured the effects of co-gasification and co-combustion of bagasse with either chicken manure or sewage sludge: on the phosphorus (P) mass fraction, P-extractability, and mineral P phases. Furthermore, we investigated the ashes as fertilizer for soybeans under greenhouse conditions. All methods in combination are reliable indicators helping to assess and predict P availability from ashes to soybeans. The fertilizer efficiency of pure bagasse ash increased with the ash amount supplied to the substrate. Nevertheless, it was not as effective as fertilization with triple-superphosphate and K2SO4, which we attributed to lower P availability. Co-gasification and co-combustion increased the P mass fraction in all bagasse-based ashes, but its extractability and availability to soybeans increased only when co-processed with chicken manure, because it enabled the formation of readily available Ca-alkali phosphates. Therefore, we recommend co-combusting biomass with alkali-rich residues to increase the availability of P from the ash to plants.