Abstract
Animal flour ash, rich in phosphorous, calcium and alkaline oxides, has been used to formulate (i) controlled-release fertilizers, since they manage to release the nutrient elements (P, K) at a low rate, and (ii) bioactive glasses.(i) Four formulations were tailored using different amounts of animal flour ash (35–48wt%), potassium carbonate (10–25wt%) and a fixed amount of glassy sand (40wt%) in order to get glasses and glass-ceramics. The materials were characterised from a chemical (XRF), crystallographic (XRD) and microstructural (SEM/EDS) point of view. Moreover, in order to check the ability to release the macro- and micro-nutrients, tests were conducted to determine the kinetics of glass dissolution in different media (2% citric acid solution, 1% hydrochloric acid solution and ammonium citrate solution). The results obtained allowed to confirm all samples show a very low solubility in water (less than 1%) and high values (>40%) of P, Ca, K and Na in the other media.(ii) The rich content of phosphorous and calcium oxides makes the animal waste-derived ash a potential low-cost raw material to produce bioactive glasses. The analysis was focused on a bioactive glass, named BG_Ca, whose composition comes from the standard Bioglass® 45S5, got by increasing as much as possible the CaO content to combine a controlled behaviour during processing and a good apatite-forming ability in a simulated body fluid (SBF).This preliminary investigation shows that animal flour ash is a versatile material, which may be successfully used for several applications as various as the production of fertilisers and the preparation of bioactive glasses.
Highlights
The slaughter bovine industry generates a significant amount of residues and by-products of animal origin that could be enhanced through recovery process and/or further transformation instead of being disposed as waste.On the other hand, the National and European legislation in force since 2002 has allowed very limited technological options for the treatment of waste from animal origin.Normally, animal by-products are generated on a regular basis throughout the year and they are only transformed into flour
The asreceived ash contains an unburned fraction of organic carbon corresponding to 4.64% and a percentage of inorganic carbon of 1.02%
The particle size distribution of the glassy sand supplied by the producer indicates that the 90% has a diameter lower than 710 μm and the 50% of the particles present a diameter lower than 283 μm and only a small fraction of particles is below 73 μm
Summary
The slaughter bovine industry generates a significant amount of residues and by-products of animal origin that could be enhanced through recovery process and/or further transformation instead of being disposed as waste. Raw materials on the market usually ensure a very controlled purity grade, but they are quite expensive For this reason, in the present contribution a bioactive glass of known composition was formulated by using the animal flour ash in substitution of commercial tricalcium phosphate (Ca3(PO4)2) with a consequent economical and environmental saving. The analysis was focused on Na, Ca, Si, K, Mg, Fe, Al. the nominal composition of the glass includes Na, Ca, and Si, whereas the presence of K, Mg, Fe, Al in the glass and the possible release of such elements in SBF may result from the use of the animal flour ash as a raw material (see following section). The concentration of chlorides was evaluated with the Mohr titration method (method sensibility+0.6%)
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