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Phosphorus (P) fertilisation recommendations rely primarily on soil content of plant available P (Pavl) that vary spatially within farm fields. Spatially optimized P fertilisation for precision farming requires reliable, rapid and non-invasive Pavl determination. This laboratory study aimed to test and to compare visible-near infrared (Vis–NIR) and mid-infrared (MIR) spectroscopy for Pavl prediction with emphasis on future application in precision agriculture. After calibration with the conventional calcium acetate lactate (CAL) extraction method, limitations of Vis–NIRS and MIRS to predict Pavl were evaluated in loess topsoil samples from different fields at six localities. Overall calibration with 477 (Vis–NIRS) and 586 (MIRS) samples yielded satisfactory model performance (R2 0.70 and 0.72; RPD 1.8 and 1.9, respectively). Local Vis–NIRS models yielded better results with R2 up to 0.93 and RPD up to 3.8. For MIRS, results were comparable. However, an overall model to predict Pavl on independent test data partly failed. Sampling date, pre-crop harvest residues and fertilising regime affected model transferability. Varying transferability could partly be explained after deriving the cellulose absorption index from the Vis–NIR spectra. In 62 (Vis–NIRS) and 67% (MIRS) of all samples, prediction matched the correct Pavl content class. Rapid discrimination between high, optimal and low P classes could be carried out on many samples from single fields thus marking an improvement over the common practice. However, Pavl determination by means of IR spectroscopy is not yet satisfactory for determination of precision fertilizer dosage. For introduction into agricultural practice, a standardized sampling protocol is recommended to help achieve reliable spectroscopic Pavl prediction.

Soil P testing has been widely used to predict crop yields, P uptake, and fertilizer demands in agriculture. Diffusive gradients in thin films (DGT) provides a zero-sink soil P test which mimics diffusion-controlled plant uptake and has previously been found to predict P availability to crops better than conventional quantity-based P tests in highly weathered Australian, though not in European soils. Here we tested the performance of DGT and the Austrian and German standard P quantity test calcium acetate lactate (CAL) to explain the variation of crop yield and P uptake response of winter wheat ( Triticum aestivum L.) and spring barley ( Hordeum vulgare L.) in long-term P fertilization experiments at four different sites in eastern Austria. Phosphorus extracted with DGT (P-DGT) and CAL (P-CAL) correlated well in similar soils but not across sites with large variation in soil and site properties such as carbonate equivalent and water availability. The predictive power of DGT for barley (R 2  = 0.42) and wheat grain yield (R 2  = 0.32), and P uptake in wheat grains (R 2  = 0.36) was clearly superior to that of the CAL, and less dependent on soil properties. The better performance of DGT compared to the quantity test is consistent with diffusion-limited P uptake in the water-limited cultivated soils of eastern Austria. The critical values of P deficiency derived from the Mitscherlich-type fits for barley and wheat at 80% relative yield are 64.9 and 26.2 µg L −1 , respectively, consistent with differential P demands of the crops.

Waste biogenic materials derived from seafood exploitation represent valuable resources of new compounds within the blue bioeconomy concept. Here, we describe the effectiveness of Raman technology implementation as an in-line tool for the demineralization process control of crustaceans or gastropods. Transparent chitin polymeric foils and calcium acetate by-products were obtained from three waste crustacean shells (C. sapidus, S. mantis, and M. squinado) using a slow, green chemical approach employing acetic acid. Progressive mineral dissolution and increasing of the Raman characteristic signal of chitin is shown in a time-dependent manner using NIR-Raman spectroscopy, while resonance Raman shows intact carotenoids in reacted shells after 2 weeks. Chitin foil products are species-specific, and the demineralization bath of the waste shell mixture can be effectively tracked by Raman tools for solvent control and decision making for the recovery of calcium acetate by-products. Comparatively obtained calcium acetate from Rapana venosa snail shells, the subject of Raman analyses, allowed assessing by-product identity, hydration status, purity, and suitability as recrystallized material for further use as a pharmaceutical compound derived from different crustaceans or gastropod species. Cross validation of the results was done using FT-IR, XRD, and SEM-EDX techniques. A hand-held flexible TacticID Raman system with 1064 nm excitation demonstrated its effectiveness as a rapid, in-line decision making tool during process control and revealed excellent reproducibility of the lab-based instrument signal, suitable for in situ evaluation of the demineralization status and solvent saturation control.

A large number of discarded eggshells bring serious environmental pollution and waste of resources. To solve this problem, raw product of calcium acetate was prepared from waste eggshell by the ultrasonic assisted neutralization method, thus, the best material ratio of calcium and magnesium, a non-chloride environment-friendly snow melting agent, which took calcium acetate as raw material by optimizing the experimental conditions, was determined. In this paper, the eggshell powder with a recovery rate of 90% was firstly obtained through the separation of eggshells and shell membrane; then, calcium acetate was prepared with a high yield of about 95.29% using ultrasonic neutralization treatment and suction filtration, and its properties including the calcium content, pH, moisture determination, sulfate, chloride, etc. were characterized with satisfaction according to the national standard, China (GB/T 23851-2009, China), the U.S. Pharmacopeia and related literature. Furthermore, different ratios of calcium and magnesium products were prepared and its properties on the pH, freezing point, dissolution rate, ability to melt snow and ice, concrete corrosion rate, carbon steel corrosion rate and plant salt tolerance test, were compared with commercially available snow melting agents. The best snow melting agent with calcium to magnesium ratio of 5:5 was picked over to be a substitute for the chlorine salt snow melting agent which can reduce the environmental pollution by discarded eggshells caused. The results obtained also provided a new theoretical basis and credible experimental data for the preparation of environmentally friendly snow melting agents. Graphic Abstract

To explore the optimized design of bio-mediated soil enhancement, the influence of different calcium sources (i.e., calcium acetate, calcium nitrate, and calcium chloride) and magnesium ion concentrations (to simulate the seawater environment) on calcareous sand treated with microbially induced carbonate precipitation (MICP) technique was investigated. Unconfined compression tests and carbonate content tests were conducted to characterize the mechanical strength and carbonate amounts, respectively. The changes of calcium ion concentration and electrical conductivity of the MICP solution were monitored in the bio-mineralization process. Scanning electron microscopy (SEM) observation reveals the carbonate crystal morphologies and X-ray diffraction (XRD) analysis quantifies the mineral compositions of carbonate precipitations. The experimental results show that the bio-cemented samples treated with calcium acetate achieve higher carbonate content, while those treated with calcium nitrate or calcium chloride give higher strength. The addition of 0.05 M magnesium ions (i.e., close to the magnesium ion concentration in seawater) enhances the mechanical strength of the bio-cemented samples treated with each calcium source. When magnesium ion concentration increased to 0.5 M, the bio-cemented samples treated with calcium chloride achieve the highest strength and the highest carbonate content. Moreover, calcium source type affects the MICP reaction rate and additional magnesium ion could slow down the reaction rate of calcium ions. SEM and XRD analysis results highlight the strong dependence of the morphological features and mineral compositions of carbonate precipitations on calcium source and magnesium ion concentration.

Calcium acetate lactate (CAL) was rapidly synthesized for the first time using the reaction between the scallop shell-derived calcium carbonate (CaCO3) and the binary phase of acetic and lactic acids. Calcium acetate (CA) and calcium lactate (CL) synthesized from the reaction of scallop shell-derived CaCO3 with each acid by similarity routes are compared with the obtained CAL product. The production yields are 88.24, 79.17, and 96.44%, whereas the solubilities are 93.77, 90.18, and 95.08% for CA, CL, and CAL, respectively. All the synthesized CA, CL, and CAL samples were characterized and confirmed by X-ray fluorescence (XRF) to examine the calcium main element and other impurities of minor elements, X-ray diffraction (XRD) to investigate the crystallography, Fourier transform infrared (FTIR) to characterize the vibrational characteristics of the functional groups, scanning electron microscope (SEM) to observe the sample morphologies, and the thermogravimetric analysis (TGA) to investigate the thermal decomposition processes of samples. The experimental results pointed out that the synthesized CA, CL, and CAL were the monohydrate, pentahydrate, and dihydrate forms with chemical formulae of Ca(CH3COO)2·H2O, Ca(CH3CHOHCOO)2·5H2O, and Ca(CH3COO)(CH3CHOHCOO)·2H2O, respectively. The final thermal decomposition product of all calcium compounds was calcium oxide (CaO). The CAL sample’s vibrational characteristics, crystal phases, and morphologies show the binary acetate and lactate anion phases, confirming the new binary anionic calcium acetate lactate obtained. In conclusion, this research proposes an easy and low-cost technique to prepare a new valuable CAL compound using scallop shell waste as a cheap and renewable calcium source.

In nature, remarkable geological structures, such as stromatolites, thrombolites, and beachrocks, are formed through biocementation, a process involving the successive dissolution and reprecipitation of CaCO 3 . This research demonstrates mimicking natural cement via bio-sintering of limestone, a process that involves successive dissolution and reprecipitation of limestone facilitated by bacteria under ambient environmental conditions. When the bacterium Acetobacter aceti (ATCC 15973) was introduced into a mixture of ethanol and limestone powder, the pH dropped rapidly, leading to the dissolution of limestone into calcium acetate. After ethanol was fully consumed, the pH gradually increased due to acetate oxidation, causing biocement crystals to precipitate. All reaction rates were measured, and the products characterized through Fourier transform infrared spectroscopy, scanning electron microscopy, quantitative X-ray diffraction, and a particle size analyzer. The detailed characterization indicates that the precipitate is mainly calcite and that the dissolved calcium carbonate sinters microbially. This pathway offers new opportunities in biocementation research by using limestone as a direct calcium source, reducing the overall carbon footprint, and eliminating the need for urea or other chemical additives. The biocement produced shows potential for practical applications in soil stabilization, eco-concrete, and other sustainable construction solutions, providing a foundation for environmentally conscious alternatives in next-generation construction.  Key points • Novel bio-sintering emulates natural CaCO 3 cementation via microbial action. • Acetobacter aceti mediates limestone dissolution and calcite precipitation . • The process forms calcite without urea or synthetic additives . Graphical Abstract

Most concrete produced includes chemical admixtures such as air entrainers, set modifiers, water reducers, etc., many of which include organic molecules. Hydroxycarboxylic acids, in particular, retard portland cement hydration. The interaction of such acids with hydrating cement phases is a complex, multi-parameter problem. To elucidate the interaction of hydroxycarboxylic and carboxylic acid retarders on hydration of cement, a combined experimental and molecular-computational approach was used. Glycolic acid, acetic acid, calcium glycolate and calcium acetate were used as model compounds. Molecular dynamics simulations were performed to simulate the interactions of select test compounds with the (001) surface of the portlandite crystal (calcium hydroxide) and the (040) surface of the tricalcium silicate crystal. Hydrogen bond density profiles and binding energies were evaluated. The adsorption isotherm for chelate complexes was determined experimentally by equilibrating aqueous solutions of the agents in the presence of various amounts of solid-phase calcium hydroxide. Finally, isothermal calorimetry experiments were used to quantify effects on hydration rate. The glycolic acid shows significant cement retardation, whereas acetic acid does not retard. Glycolic acid was found to retard hydration via calcium chelation and surface adsorption that involves the adsorption of the calcium chelate complex preferentially on tricalcium silicate. Simulation results reveal that calcium glycolate forms a strong hydrogen bonding network near to calcium hydroxide and hydrated tricalcium silicate surfaces and are responsible for its strong adsorption on these surfaces. While acetic acid forms a strong calcium chelate, it does not associate with calcium hydroxide or unhydrated or hydrated tricalcium silicate surfaces.

Transitioning to a resource-efficient and sustainable circular economy is vital for tackling climate- and environmental-related challenges. This study demonstrates a closed-loop strategy for upcycling agricultural biowaste eggshells. Water- insoluble proteins were extracted from both shell membranes and shell fragments by boiling in water using protein denaturants. The ground eggshells also were used to prepare calcium acetate (Ca(CH 3 COO) 2 ) and to treat Scots pine ( Pinus sylvestris L. ) sapwood. Mineralisation of the wood was achieved by performing a two-step impregnation process using aqueous solutions of ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ) and Ca(CH 3 COO) 2 salts. Morphological studies revealed the relatively low saturation of wood matrix with mineral, with cell lumina mostly unfilled, while elemental mapping confirmed homogeneous distribution of Ca and P within the wood matrix. Powder X-ray diffraction (XRD) analysis revealed that wood treatment resulted in the in-situ co-precipitation of low-crystallinity hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ), and spectroscopic analysis indicated carbonate substitution within the Ca 10 (PO 4 ) 6 (OH) 2 crystal lattice, suggesting the formation of carbonated hydroxyapatite (Ca 10-x (PO 4 ) 6-x (CO 3 ) x (OH) 2-x-2y (CO 3 ) y ). Microscale combustion calorimeter (MCC) and cone calorimeter (CC) measurements of mineralised wood revealed a reduction in the total heat release (THR) compared with untreated wood, indicating potential for further optimisation of wood modification process. Results suggest that the proposed aqueous solution-based processing approach for converting an abundant resource, chicken eggshells, into value-added products has potential for new technology and bioeconomy development and represents a promising pathway towards improved sustainability.

Waste oyster shells were utilized to produce calcium carbonate (CaCO3) by grinding. This CaCO3 was then reacted with acetic acid to yield calcium acetate monohydrate (Ca(CH3COO)2·H2O). Both CaCO3 and Ca(CH3COO)2·H2O were used as precursors for synthesizing calcium oxide (CaO) through thermal decomposition at 900 °C and 750 °C, respectively. The yields of CaO from both precursors, determined through calcination experiments and thermogravimetric analysis (TGA), exceeded 100% due to the high purity of the raw agents and the formation of calcium hydroxide (Ca(OH)2). X-ray fluorescence (XRF) analysis revealed a CaO content of 87.8% for CaO-CC and 91.5% for CaO-CA, indicating the purity and contamination levels. X-ray diffraction (XRD) patterns confirmed the presence of CaO and minor peaks of Ca(OH)2, attributed to moisture adsorption. Fourier-transform infrared (FTIR) spectroscopy identified the vibrational characteristics of the Ca-O bond. Scanning electron microscopy (SEM) showed similar morphologies for both CaO-CC and CaO-CA, with CaO-CA displaying a significant amount of rod-like crystals. Based on these results, calcium acetate monohydrate (CA) is recommended as the superior precursor for synthesizing high-purity CaO, offering advantages for various applications.