Insight into evolution of chemical structure and mineralogy to reveal the mechanism of temperature-dependent phosphorus release from hydrochars

Abstract

Shrimp shell (SS) is sustainable biomass with abundant minerals and developable phosphorus (P) resource. Hydrothermal carbonization of SS can solve the shortage of P resources and the utilization of waste. However, few studies on the application of SS hydrochar as fertilizer have been conducted. Having an insight into the evolution of chemical structure and mineralogy could understand the mechanism of P release. In this study, Olsen method was employed to determine the available P (AP) release, and the temperature-dependent evolution of crystalline phase, carbon skeleton structures and surface functionalities were characterized by XRD, XPS, FTIR and TG. The results of AP release from SS hydrochar showed the following temperature (120−280 °C in 20 °C intervals) dependence: 120 °C derived hydrochars (2.30 mg/g) >feedstock (1.51 mg/g) > 160−280 °C derived hydrochars. In addition, AP dissolution kinetic data were well fitted to pseudo-second-order equation (R2 >0.999). Two-dimensional correlation spectroscopy revealed that phosphate crystallinity degree was negatively corresponding to release behavior. Meanwhile, calcite crystal growth and the transformation of P species influence the P bioavailability of SS hydrochar. Therefore, hydrochar with lower phosphate crystalline could benefit the P fertilizing efficiency.