Optimization of phosphate recovery from monkfish, Lophius vomerinus, processing by-products and characterization of the phosphate phases.

Background: Fish-processing by-products represent an increasing proportion of wastes globally. Valorizing offers a sustainable alternative by harnessing high-value products through process development. This study aimed to develop and optimize a demineralization process to recover minerals from fish bones with subsequent recovery of phosphates from the resulting solution.

Results: The demineralization process was optimized under the following conditions: 5% H PO concentration (v/v), four extractions and solvent to feed ratio (v/w) of 5:1 at ambient temperature of 17 °C. This resulted in an ossein containing 2.0 ± 1.2 g kg ash and 71.5 ± 3 g kg hydroxyproline and mineral liquor. The phosphate precipitation from the mineral liquor was further optimized resulting in > 99% total P recovery at 75 °C reaction temperature and 1 mol L Ca(OH) to mineral liquor ratio(v/v) of 0.95:1 for a reaction time of 17 min, per 150 mL starting mineral liquor. The precipitate contained 215.2 ± 3.0 g kg dicalcium phosphate dihydrate (DCPD) with a net contribution of 17.2% P from the fishbones, and 25 ± 0.2 g of octacalcium phosphate (OCP) was precipitated from 150 mL starting mineral liquor at 25 °C reaction temperature, (1.2:1) 1 mol L Ca(OH) to mineral liquor ratio (v/v) and reaction time of 17 min. The X-ray spectra confirmed the DCPD structure and Fourier transform infrared spectroscopy (FTIR) spectra indicated OCP precipitation.

Conclusion: This work successfully illustrated the recovery of minerals from fish bones and the subsequent production of different high-quality phosphates from fish-processing by-products, thus indicating a potential source for high-value products. © 2018 Society of Chemical Industry.