Investigation of ammonia gas sorption on heat-treated struvite using STA-PTA-FTIR

摘要

Investigation of ammonia gas sorption on heat-treated struvite using STA-PTA-FTIR Agricultural techniques including composting and nitrogen (N)-based fertilizer application are significant sources of ammonia gas (NH3(g)) emissions to the atmosphere [1-3]. This is due to N-transformations that lead to N-volatilization as NH3(g), exacerbating nutrient loss from soils to the environment [4]. To mitigate NH3(g) loss, adsorbents such as zeolites, metal organic frameworks, and biochars are typically used. Another potential sorbent is struvite (MgNH4P04 6H2O). Struvite crystallization has been used to recover phosphorous (P) and N from wastewaters, for subsequent re-application as fertilizer, thus promoting valorization [5]. To determine if struvite (S-25) and heated struvite solids (HTS55-300) would be effective sorbents for NH3(g)compared to biochars (BC) a simultaneous thermal analysis-pulse thermal analysis-Fourier transform infrared spectroscopy (STA-PTA-FTIR) technique was used. The HTS substrates were prepared by heating commercial struvite in the range 55-300 C, to remove structural NH3(s) and H2O(s)[6]. Thermogravimetric analysis (TG) indicated mass gain (4.09 (S-25) - 50.6 (BC-B) mg NH3(g)/g sorbent) occurred for all substrates until steady state was achieved, i.e., sorption sites were filled. The HTS-150 (dittmarite, MgNH4P04 H2O) sorbent had the highest HTS uptake at 23.5 mg NH3(g)/g. The sorption enthalpies recorded by DSC ranged from -4.6 to -118 J g-1. Desorption revealed partial reversibility in the uptake. The mass of sorbate remaining after desorption was BC-B > HTS-150 > HTS-250 > HTS-200 > HTS-300 > HTS-100 > BC-A > HTS- 55 = S-25 [4]. The investigation of NH3(g) sorption by struvite recovered from dairy (DW) and swine (SW) effluents reacted at 15-68 min retention times was also investigated. Both untreated DW and SW solids, and solids heat-treated to either 150 C or 300 °C were assessed. The sorption capacities for DW and SW solids ranged from 9.9 to 49.9 mg NH3/g sorbent. The SW15(150°C) sorbent had the highest uptake. Exothermic sorption enthalpies ranged from -21.4 to -131.0 J/g. Upon desorption, 100 to 44 % of total sorbate was found to be reversibly bound. These results showed struvite treated at temperatures of 100-300 C could be effective for amelioration of compost and fertilizers by retaining N-NH3 [7].