Feedstock recycling of secondary raw materials is the backbone of the Circular Economy (CE). The efficient recovery of resources, energy, along with achieving minimal environmental impact is mandatory for the successful realization of CE. Chicken manure is an interesting waste stream due to its content of nutrients, in particular of phosphorus, which makes it a suitable feedstock for fertilizer applications. However, the contamination caused by antibiotics, organic pollutants, and sanitary aspects demand the manures treatment before further recycling. Thermochemical treatment based on intermediate pyrolysis targets decentral application to produce carbonized solids for fertilizer application. This work evaluated pyrolysis char from the pyrolysis of chicken manure in comparison to the original feedstock using state-of-the-art thermal treatment, i.e., combustion in grate furnaces. The samples were evaluated in terms of chemical and mineralogical composition by applying several analytical techniques. Bio-availability of the main nutrients (NPK) was assessed by adopting standard methods. Additionally, the effect on toxicity was discussed by means of heavy metals analysis, as well as of pot tests. Results showed, that pyrolysis had a far more positive effect on nutrient availability compared to combustion, and it provided a suitable method for the thermal treatment of contaminated feedstocks.

Herein, composite nanofiber membranes (CNMs) derived from UiO-66 and UiO-66-NH₂ Zr-metal-organic frameworks (MOFs) were successfully prepared, and they exhibited high performance in adsorptive fluoride removal from aqueous media. The resultant CNMs were confirmed using different techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Brunauer–Emmett–Teller (BET) in addition to Fourier-transform infrared spectroscopy (FTIR). The parameters that govern the fluoride adsorption were evaluated, including adsorbent dose, contact time, and pH value, in addition to initial concentration. The crystalline structures of CNMs exhibited high hydrothermal stability and remained intact after fluoride adsorption. It could also be observed that the adsorbent dose has a significant effect on fluoride removal at high alkaline values. The results show that UiO-66-NH₂ CNM exhibited high fluoride removal due to electrostatic interactions that strongly existed between F⁻ and metal sites in MOF in addition to hydrogen bonds formed with MOF amino groups. The fluoride removal efficiency reached 95% under optimal conditions of 20 mg L⁻¹, pH of 8, and 40% adsorbent dose at 60 min. The results revealed that UiO-66-NH₂ CNM possesses a high maximum adsorption capacity (95 mg L⁻¹) over UiO-66 CNM (75 mg L⁻¹), which exhibited better fitting with the pseudo-second-order model. Moreover, when the initial fluoride concentration increased from 20 to 100 mg/L, fluoride adsorption decreased by 57% (UiO-66 CNM) and 30% (UiO-66-NH₂ CNM) after 60 min. After three cycles, CNM revealed the regeneration ability, demonstrating that UiO-66-NH₂ CNMs are auspicious adsorbents for fluoride from an aqueous medium.

This study provides an insight into possible recycling processes for autoclaved aerated concrete (AAC) at low temperatures (<1000 °C). Belite binders were synthesized from wastes of AAC by the addition of CaCO₃ and adaption of the molar CaO/SiO₂ (C/S ratio) in the range of 2 to 2.5. An in situ XRD study performed during heating up to 1000 °C and subsequent quenching to room temperature evidenced the formation of ternesite besides C₂S in sulfate-containing systems. Several factors influencing the reaction kinetics and the evolution of the phase composition were investigated thoroughly. Increased sulfate content and dwelling time during heating increase the ternesite content and promote the formation of highly crystalline α’H-C₂S. The C/S-ratio of the starting materials has to be adjusted to the sulfate content in order to prevent the formation of ternesite at the expense of C₂S. Ternesite remains stable during quenching to room temperature or even increases in amount, except in cases of very low cooling rates or high residual quartz contents (C/S-ratio ≤ 2). Temperature and range of α’H-C₂S to β-C₂S phase transition on quenching strongly depend on the cooling rate. The onset temperature for β-C₂S formation varies between 540 °C (slow quench) and 450 °C (fast quench). Thermal expansion coefficients of ternesite are calculated showing similarity with C₂S. The incorporation of CaSO₄ modules in the structure switches the direction of maximum compression.

The suitability of CaCl₂ as a mineralizing agent in the synthesis of a low-temperature C₂S-cement clinker from wastes of autoclaved aerated concrete was investigated. As chlorellestadite is a potential host mineral for the immobilization of chlorine, the formation conditions for the highest joint content of chlorellestadite and C₂S were studied in samples with different sulfate contents. Oven experiments were conducted at temperatures between 700 and 1200 °C. The samples were analyzed by X-ray diffraction in combination with chemical and thermal analysis and Raman spectroscopy. Calculation of the yield of C₂S and ellestadite for all samples proves the optimum temperature range for the C₂S-ellestadite clinker from 950 to 1000 °C. At lower temperatures, the formation of a carbonate-rich halogenide melt promotes the crystallization of a significant amount of spurrite at the expense of C₂S. Ellestadite formation mainly depends on the sulfate content and to a lesser extent on the synthesis temperature. However, at higher temperatures, with ternesite another sulfate coexists in sulfate-rich samples at the expense of ellestadite. In addition, distinct evidence for non-stoichiometry and carbonate substitution in the structure of low-temperature ellestadite was found. Low sulfate content leads to the crystallization of Ca₁₀[Si₂O₇]₃Cl₂ at higher temperatures. In all samples treated at temperatures above 1000 °C chlorine loss starts. Its extent decreases with increasing sulfate content.

Phosphorus (P) is an essential macronutrient, playing a role in developmental and metabolic processes in plants. To understand the local and systemic responses of sorghum to inorganic phosphorus (P_i) starvation and the potential of straw and ash for reutilisation in agriculture, we compared two grain (Razinieh) and sweet (Della) sorghum varieties with respect to their morpho-physiological and molecular responses. We found that P_i starvation increased the elongation of primary roots, the formation of lateral roots, and the accumulation of anthocyanin. In Razinieh, lateral roots were promoted to a higher extent, correlated with a higher expression of SbPht1 phosphate transporters. Infrared spectra of straw from mature plants raised to maturity showed two prominent bands at 1371 and 2337 cm⁻¹, which could be assigned to P-H(H₂) stretching vibration in phosphine acid and phosphinothious acid, and their derivates, whose abundance correlated with phosphate uptake of the source plant and genotype (with a higher intensity in Razinieh). The ash generated from these straws stimulated the shoot elongation and root development of the rice seedlings, especially for the material derived from Razinieh raised under P_i starvation. In conclusion, sorghum growing on marginal lands has potential as a bio-economy alternative for mineral phosphorus recycling.

The synthesis of low-temperature belite (C₂S) clinker from wastes of autoclaved aerated concrete and limestone was studied in the presence of CaCl₂ as a mineralizing agent. Synthetic chlorellestadite (SCE; Ca₁₀(SiO₄)₃(SO₄)₃Cl₂) forms in experiments at temperatures between 700 and 1200 °C. Samples were investigated by X-ray diffraction and Raman spectroscopy. In general, the amount of SCE depends mainly on the sulfate content and to a lesser extent on the synthesis temperature. At lower temperatures of formation, a non-stoichiometric SCE seems to crystallize in a monoclinic symmetry similar to hydroxylellestadite. Rietveld refinements revealed the presence of chlorine and calcium vacancies. Raman spectroscopy proved the partial substitution of sulfate by CO₃²⁻ groups in ellestadites formed at 800 °C and 900 °C in air. Incorporation of CO₃ results in a shorter unit cell parameters and smaller cell volume similar to CO₃₋apatite. At low temperatures, SCE coexists with spurrite intermixed on a very fine nm scale. At temperatures above 900 °C in air, ellestadite is carbonate-free and above 1000 °C chlorine loss starts in all samples.