Addition Of Calcium Carbonate Research Articles

Calcium Carbonate as Dephosphorization Agent in Direct Reduction Roasting of High-Phosphorus Oolitic Iron Ore: Reaction Behavior, Iron Recovery, and Dephosphorization Mechanism

Calcium carbonate, renowned for its affordability and potent dephosphorization capabilities, finds widespread use as a dephosphorization agent in the direct reduction roasting of high-phosphorus oolitic hematite (HPOIO). However, its precise impact on iron recovery and the dephosphorization of iron minerals with phosphorus within HPOIO, particularly the mineral transformation rule and dephosphorization mechanism, remains inadequately understood. This study delves into the nuanced effects of calcium carbonate on iron recovery and dephosphorization through direct reduction roasting and magnetic separation. A direct reduction iron (DRI) boasting 95.57% iron content, 93.94% iron recovery, 0.08% phosphorus content, and an impressive 92.08% dephosphorization is achieved. This study underscores how the addition of calcium carbonate facilitates the generation of apatite from phosphorus in iron minerals and catalyzes the formation of gehlenite by reacting with silicon dioxide and alumina, inhibiting apatite reduction. Furthermore, it increases the liquid phase, enhancing the dissociation of metallic iron monomers during the grinding procedure, thus facilitating efficient dephosphorization.

Low-Temperature Water Electrolysis Under a Sustained pH-Gradient for the Electrochemically-Induced Decarbonation of Limestone into Hydrated Lime

Conventional low-temperature water electrolysis processes operate either at high or low pH to enhance conductivity, minimizing electrical resistance. Neutral water electrolysis in a buffer solution is considered non-competitive due to higher energy consumption. Nevertheless, interest in water electrolysis using a salt-based electrolyte has grown due to its ability to generate a pH gradient inside the cell. Electrolysis using a neutral salt-based electrolyte has higher operating costs due to its higher standard equilibrium potential (due to the pH gradient) and lower conductivity. Although this approach incurs higher operating costs, it presents a unique advantage: the production of additional valuable elements thanks to the pH gradient generated.In 2019, Ellis & al. [1] highlighted the possibility to use this pH gradient to electrify the production of hydrated lime (calcium hydroxide). Lime has applications in different areas such as the removal of impurities during steel production and aqueous or gaseous effluent treatments. It can also be used as a precursor of cement. Cement production is accounting for 8% of global CO2 emissions. The acidity generated by water oxidation at the anode dissolves the calcium carbonate inserted. Carbon dioxide from the dissolution is recovered with the oxygen generated. The calcium cations migrate through the cationic membrane towards the cathodic compartment to react with the hydroxide ions generated by water reduction at the cathode. Calcium hydroxide is finally collected after precipitation. Figure 1 compares the conventional process with the electrochemical way and describes more precisely the steps involved in Figure 1. More recently, another way of exploiting this gradient has been proposed by Ni & al. [2] for the recycling of spent Li-ion batteries. With the growing interest in process electrification, other applications may emerge.In this paper, this hybrid electrochemical system for the simultaneous production of hydrogen, oxygen and calcium hydroxide has been intensively studied. Water electrolysis has been performed in a two-compartment cell at different applied currents. Calcium concentration and pH measurement enabled the study of the sub-step efficiencies and equilibria in anodic and cathodic chambers. Perfect faradic efficiencies were obtained with perchlorate salt electrolytes and platinum-free electrodes. The establishment of the pH gradient has been proven and correlated with the transport number of protons through the cationic membrane. Finally, the kinetics of calcium ion migration and calcium hydroxide precipitation have been investigated as well. Continuous addition of calcium carbonate as opposed to a single excess addition was shown to be able to tune the working pH in the anodic compartment and thereby reducing the risk of precipitation on the membrane. Our experimental results lead to the formulation of practical recommendations for achieving optimal reaction stoichiometry in each stage. These findings pave the way for scaling up a promising new sustainable process for lime and cement production.[1] L. D. Ellis, A. F. Badel and M. L. Chiang, "Toward electrochemical synthesis of cement," PNAS, vol. 117, no. 23, pp. 12584-12591, 2019.[2] N. Jihong, Z. Jiayin, B. Jinhong and G. Xiaofei, "Recycling the cathode materials of spent Li-ion batteries in a H-Shaped neutral water electrolysis cell," Separation and Putification Technology , vol. 278, p. 119485, 2022. Figure 1 - Conventional and electrochemical production route of Ca(OH)2 and a simplified scheme of the hybrid electrolyzer used in this work, with the reactions involved. Figure 1

Crude oil removal from water: Influence of organic phase composition and mineral content

AbstractThe effect of organic and inorganic compounds, commonly present in the mineralogy of crude oil and/or added in the washing processes of extracted crude, on the removal efficiency of emulsified oils present in waste washing waters was investigated by means of flocculation. Approximately 90% of the emulsified oil could be removed using an anionic flocculant, providing a residual turbidity below 100 NTU. The yield depended on the nature of the organic and inorganic components present. The higher the chain length of the main organic component, the greater the flocculant concentration required to remove the oil. Several components had an effect of emulsification (e.g., octane, decane), some of which rendered de‐oiling process completely ineffective (e.g., naphthenic acids). Aliphatics were the most difficult to eliminate, requiring flocculant levels in the 200–300 ppm range. This is in contrast to 75–100 ppm levels which were required to remove bi‐ and poly‐cyclic aromatics. Heavy oils were more difficult to remove than light oils. There was a strong effect of the pH of the aqueous phase. The optimum was pH = 2.0. Virtually all inorganic compounds reduced the efficiency of removing oil from water when spiked at 1%. The only exception was sodium carbonate which acted as a de‐emulsifier. Monovalent salts have a minor effect on de‐oiling, with efficiencies remaining at 80%. Divalent chlorides reduced the de‐oiling efficiency to 70% while sulphates had a more severe influence. The de‐oiling efficiency was lowered substantially with the addition of clays, zinc, cadmium, ferric oxide, calcium carbonate, and dibenyhlthiophene.

Thermal Decomposition of Bio-Based Plastic Materials.

This research delves into a detailed exploration of the thermal decomposition behavior of bio-based polymers, specifically thermoplastic starch (TPS) and polylactic acid (PLA), under varying heating rates in a nitrogen atmosphere. This study employs thermogravimetry (TG) to investigate, providing comprehensive insights into the thermal stability of these eco-friendly polymers. In particular, the TPS kinetic model is examined, encompassing the decomposition of three distinct fractions. In contrast, PLA exhibits a simplified kinetic behavior requiring only a fraction described by a zero-order model. The kinetic study involves a systematic investigation into the individual contributions of key components within TPS, including starch, glycerin, and polyvinyl alcohol (PVA). This detailed analysis contributes to a comprehensive understanding of the thermal degradation process of TPS and PLA, enabling the optimization of processing conditions and the prediction of material behavior across varying thermal environments. Furthermore, the incorporation of different starch sources and calcium carbonate additives in TPS enhances our understanding of the polymer's thermal stability, offering insights into potential applications in diverse industries.

Sustainable biomaterials for tissue engineering: electrospun polycaprolactone fibers enriched with freshwater snail calcium carbonate and waste human hair keratin

AbstractThis study focuses on developing a sustainable and biocompatible polycaprolactone (PCL)‐based scaffold for bone tissue engineering through electrospinning, utilizing calcium carbonate (CaCO3) from Pomacea canaliculata shells and keratin from human hair, known for stimulating bone regeneration. The isolated CaCO3 has been identified to demonstrate two polymorphs, vaterite and calcite, as determined by X‐ray diffraction. The isolation of keratin from human hair was confirmed through sodium dodecyl sulfate polyacrylamide gel electrophoresis and Fourier transform infrared spectroscopy analysis, revealing the presence of α‐keratin structures around 45–50 kDa and β‐keratin structures around 55–60 kDa. According to scanning electron microscope observations, the addition of keratin to PCL fibers reduced their diameter from 457 ± 345 to 371 ± 103 nm. Further addition of calcium carbonate led to a mean diameter of 258 ± 76 nm. The melting temperature of PCL fibers containing keratin and CaCO3 was determined to be 76.17 °C via differential scanning calorimetry, while thermogravimetric analysis, conducted at temperatures up to 600 °C, revealed a remaining ash content of 9.59%. Calcium phosphate accumulation was observed to initiate on PCL fibers containing keratin and CaCO3 following a 7‐day exposure to simulated body fluid. The fibers exhibit cytocompatibility, showing no toxicity while supporting the growth and proliferation of Saos‐2 osteosarcoma cells. The results suggest that the innovative incorporation of keratin and CaCO3 into PCL nanofibers could serve as a bioactive matrix compared to pure PCL matrices, thereby offering enhanced potential for bone tissue engineering applications. © 2024 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Addition of calcium carbonate in the synthesis of flexible polyurethane foams

Within all their variability, foams constitute the largest segment in the polyurethane industry. Polyurethane is composed mainly of isocyanate (-N=C=O) and polyol (-OH) functional groups, presenting different characteristics by adding fillers. This polymer has a wide range of applications such as adhesives, coatings, varnishes, elastomers and foams. Aiming improvements in its thermal properties, calcium carbonate addition was investigated in proportions of 12.5%, 25% and 37.5% (w/w). This filler is widely used to change the properties of polymers, as it is easily found in nature and has a low cost. For the synthesis of polyurethane samples, isocyanate and polyol were reacted using "one shot" process. The obtained results demonstrated the change in the glass transition temperatures (Tg) of the material to higher values, which indicates a decrease in the mobility of the polymer chains. Also, an increase in decomposition temperature was observed via differential scanning calorimetry (DSC). With Fourier transform infrared spectroscopy (FTIR) analysis, it was possible to analyze that the material was successfully synthesized by the appearance of the characteristic bands of PU foams. Furthermore, with the addition of calcium carbonate, it was possible to identify the presence of two phases, which indicate that the material underwent changes in its crystallinity, identified through X-ray diffraction (XRD) analysis. Finally, it was possible to observe via optical microscopy (OM) analysis that the addition of filler significantly changed the morphology of the foams.

Preparation of nanocellulose-based flexible calcium carbonate to improve filler retention and combustion performance of cigarette paper

The addition of calcium carbonate to cigarette paper can enhance its combustion performance and apparent properties. However, it does come at the cost of reduced paper strength. In this study, a flexible calcium carbonate (FCC) was developed through the in-situ formation of calcium carbonate on nanocellulose surfaces. The incorporation of FCC into cigarette paper offered the potential to improve filler retention and combustion performance while maintaining high paper strength. The results of the study demonstrated that when compared to the addition of 30% precipitated calcium carbonate (PCC), the filler retention rate in cigarette paper increased by 31.5% when 30% FCC was used. Scanning electron microscopy images showed that only a minimal number of inorganic particles were observed between the fibers in the FCC-containing paper, indicating appropriate air permeability and fiber-fiber bond strength. Furthermore, when compared to PCC-containing paper, the FCC-containing paper exhibited an 8.8% increase in tensile strength and a 7.5% increase in folding resistance. Additionally, thermogravimetric analysis of the cigarette paper revealed that the incorporation of flexible calcium carbonate effectively lowered the thermal decomposition temperature, leading to a 10.3% increase in the combustion rate of FCC-containing paper. The inclusion of FCC into paper fibers has the potential to enhance air permeability and regulate cigarette burning performance. Consequently, the FCC developed in this study holds promise as a substitute for traditional calcium carbonate fillers in cigarette paper applications.

Quality of skipjack surimi (Katsuwonus pelamis) with addition of calcium carbonate (CaCO3)

This study aims to determine the effect of the addition of CaCO3 as a whitening agent on the quality properties of the skipjack surimi. The functional properties were evaluated using physical and chemical tests, including white degree analysis, folding test, texture test, water holding capacity, and fat content analysis. Skipjack surimi was carried out in four treatments: 0%, 0.5%, 1%, and 1.5% CaCO3 in a completely randomized design (CRD). The results revealed that adding 1.5% CaCO3 achieved the highest white degree value of 54.22. The folding test values increased with higher CaCO3 concentrations, ranging from 1.57 (control) to 2.05 (1.5% CaCO3). Surimi fat content analysis showed no significant differences (P>0.05) between treatments, varying from 1.16% in the control to 1.51% in the 1.5% CaCO3 treatment. Furthermore, the WHC of skipjack surimi was significantly different (P<0.05) between treatments and increased with the addition of CaCO3: 52.44% (0% CaCO3), 66.42% (0.5% CaCO3), 74.57% (1 % CaCO3), and 79.96 % (1.5% CaCO3). However, sensory color tests showed a significant difference (P<0.05) between the treatments. In conclusion, the incorporation of 1.5% CaCO3 as a whitening agent resulted in an optimal treatment with a folding test value of 2.05 and a WHC value of 79.96%. These findings suggested the potential use of CaCO3 to enhance the functional properties of skipjack surimi during production.

Influence of Calcium Carbonate Flour on Hydration, Strength, and Rheology of fast setting CSA based mortars

AbstractCalcium Sulfoaluminate cements (CSA) are a more sustainable alternative to Portland Cement (PC). On top of that, they can outperform PC in mortars application. The addition of calcium carbonate to such a system is beneficial as it improves workability, accelerates the setting time, and stabilizes the ettringite in the hardened mortar. In this paper, we are investigating the influence of fine calcium carbonate flour on CSA‐C$‐based mortars. The hydration course was traced by the means of isothermal microcalorimetry. It was observed that with the addition of fine calcium carbonates the heat release due to the hydration of CSA started earlier and resulted in the higher hydration peak. Higher hydration degree was able to partially compensate for additional water used to maintain workability. The rheological properties were measured with the rotational viscometer. The results were compared to the mortars of the same composition where fine calcium carbonate was replaced with the ground quartz sand of similar particle size distribution. Surprisingly, no differences in rheology and mechanical parameters between these flours were found.

Performance and VOCs emission inhibition of high-content waste rubber powder modified asphalt and its mixture

ABSTRACT The high-content waste rubber powder (WRP)-modified asphalt (WRMA) has poor storage stability and tends to produce many volatile organic compounds (VOCs). This study aimed to research the influence of incorporating high-content WRP on the performance enhancement and VOCs emission of asphalt and its mixtures. The storage stability, rheological properties and cracking resistance of WRMA were tested. Further, the high and low-temperature properties of WRMA mixtures were evaluated. Additionally, the VOCs emission characteristics of WRMA mixtures were analysed . The results indicate that activated WRP has good compatibility with asphalt. The high-content of WRP can significantly enhance the high-temperature rheological properties and low temperature cracking resistance of asphalt binder, and the addition of nanometre calcium carbonate (B3) adsorbent can further enhance the physicochemical properties of asphalt binder. Moreover, compared with 70# asphalt mixture, the dynamic stability of WRMA mixture increases by about 50%, and the immersion residual stability and freeze–thaw splitting strength values increase by 6.34% and 5.98%, respectively. In addition, the B3 adsorbent can significantly reduce the VOCs emission from WRMA mixtures. The corresponding conclusions could provide guidance for the large-scale application of high-content WRMA mixtures and promote cleaner and greener products.

Improved ettringite stabilization by calcium carbonate and calcium nitrate additions in ternary PC-CSA-C$ systems

Mixing Portland cement (PC) and calcium sulfoaluminate (CSA) cement can provide several advantages for specific applications. However, the stability of ettringite has a significant impact on ettringite-rich cements properties. This study aims to investigate the impact of calcium nitrate (Ca(NO3)2 = CN) and calcium carbonate (CaCO3 = CC) on the performance evolution and stabilization mechanism of PC-CSA-C$ systems. The experimental results demonstrate that the incorporation of CC and CN has a significant impact on the early hydration kinetics. A second exothermic peak appears indicates the depletion of the calcium sulfate, and its appearance time is related to the amount of CC and CN added. The blended system containing CN exhibited the highest early and late compressive strength, as well as excellent volume stability. Compared with CC, CN was confirmed to be more effective in stabilizing ettringite in the PC-CSA-C$ system and preventing its conversion into monosulfate. Furthermore, the analysis of the pore structure reveals a significant increase in the proportion of pores with diameters ≤50 nm in the systems containing CN. In particular, CN displays a stronger ability to stabilize ettringite to reduce chemical shrinkage and increase the content of C-(A-)S-H gel, and the 28-day compressive strength was approximately 10 MPa higher compared to the control group.

Formulation of inexpensive and green reactive powder concrete by using milled-waste-glass and micro calcium-carbonate – A multi-criteria optimization approach

In view of its high strength and durability, reactive powder concrete (RPC) is a promising construction material. The replacement of cement and silica fume with sustainable alternatives to RPC may provide significant benefits, however, there are challenges to overcome. In this study, calcium carbonate and ground waste glass powder were introduced as mineral mixtures to develop an environmentally friendly and cost-effective RPC mixture. The best flowability, proper compressive strength, and reduced cement content were achieved using a multi-objective simultaneous optimization approach based on the Derringer & Suich methodology. As a result of the study, 603 kg/m3 of cement was determined as the most suitable dosage for RPC. Additionally, the optimized mix contained 368 kg/m3 of waste glass and 118 kg/m3 of calcium carbonate, which had a beneficial impact on both cost and environmental considerations. As a result of numerous experimental tests, including compressive strength, elasticity modulus, chloride ion penetration, and drying shrinkage, the developed RPC's properties were validated and were comparable to the control mixture while showing superior drying shrinkage behavior. A further benefit of adding these admixtures was the reduction of superplasticizer dosage. Despite the optimized RPC's lower mechanical and chloride ion penetration performance at early ages, the performance discrepancy diminished over time due to the pozzolanic properties of waste glass powder. A significant characteristic of the optimized RPC was its superior drying shrinkage behavior throughout the testing period resulting from its reduced water dosage. Ultimately, the study highlights the potential of the addition of calcium carbonate and waste glass powder to RPC for sustainable concrete production at a low cost.

TENSILE STRENGTH AND HARDNESS OF POLYPROPYLENE-BAMBOO/KENAF HYBRID COMPOSITE AFTER OPTIMIZATION OF PRODUCTION PROCESS

While in use and when not, engineering materials occasionally exhibit poor characteristics and perform poorly as a result of internal or external factors. Therefore, there is a need to improve the protection of the composites from the various agents and improve their mechanical properties. This study's objective was to assess the impact of bamboo/kenaf hybrid fibres, Maleic Anhydride Grafted Polypropylene (MAHgPP), Hinder Amine Light Stabiliser (HALS), and Calcium Carbonate (CaCO3) additions on tensile strength and hardness at various levels, as well as their interactions on polypropylene (PP) composites. The manufacturing of the composites was accomplished through the compression molding process. The study was conducted using Taguchi orthogonal array L27 with fiber, MAHgPP, HALS, and CaCO3 as input parameters. A robust optimization technique for product and process design (Taguchi method ) was used to optimize the parameter settings for the tensile strength and hardness of the composite. Results showed that the tensile strength of the resultant composite ranged from 37.60 MPa to 53.57 MPa; while the hardness value ranged from 70.32 (Shore A) to 93.03 (Shore A). The optimized composite had a tensile strength of 49.12 MPa and a hardness of 79.85 (Shores A). The factors settings that gave the combined optimum tensile strength and hardness for the bamboo/kenaf fiber are 36.87% fiber, 5% MAHgPP, 1% HALS, and 3% CaCO3. therefore the best tensile strength and hardness performance of the composite was obtained from the optimum setting.

Optimizing the addition of calcium carbonate (CaCo3) on the growth and survival of glass eel (Anguilla sp.)

The development of eel fish cultivation has quite good business opportunities and prospects. However, the main obstacle in cultivating eel fish is the high mortality in the glass eel phase, so it has a survival rate of 30-50% and slow growth, namely less than 3.1%. One effort to maximize glass eel maintenance is through optimizing alkalinity as a buffer for water quality. The alkalinity level in the maintenance medium can be regulated by adding calcium carbonate (CaCO3). This research aims to determine the effect of adding CaCO3 to the rearing media on glass eels' growth and survival rate. The study was conducted for 14 days in March 2023. The method was wholly randomized with three replications in 3 treatments (P1=0 mg L-1, P2=50 mg L-1, P3=100 mg L-1). Analysis of research data used the ANOVA test. Adding CaCO3 produced a natural effect on length growth with a value of 0.16 cm, weight growth of 0.73 mg L-1, and a survival rate of 74%. The treatment did not naturally affect the alkalinity levels in the glass eel maintenance media. The best treatment effect was found in P2 (50 mg L-1). These results show that adding CaCO3 to the glass eel-rearing media decreased but did not naturally affect alkalinity levels.

Ca2+ addition facilitates the shell repair with eggs production of Pomacea canaliculata through biomineralization and food intaking regulation

Pomacea canaliculata was by far one of the most harmful invasive organisms in the world, causing serious harm to aquatic crops and ecosystem. Calcium carbonate is a common component of aquatic environment, which is important for the growth of Pomacea canaliculata. Therefore, the objective of this study was to investigate the response characteristics of P. canaliculata suffered shell breakage to the addition of calcium carbonate in water environment. In this experiment, we explored the effects of calcium carbonate addition on the P. canaliculata shell repair rate, food intake, egg production, shell strength, and calcium content through breaking the snails shell and the addition of calcium carbonate treatment. The results showed that snail broken-shell repaired mostly within 21 days. The snails experienced a significant increase in shell repair rates during earlier days of the treatment, especially for female snails. Food intake of snails exhibited different patterns when their shells were broken and calcium carbonate was added. Shell breakage treatment combined with calcium carbonate addition significantly increased the diameter of snail eggs compared with the control and the calcium carbonate addition treatment without shell-broken snail group. There was no significant difference in shell strength or calcium content of male snails between the treatments. The study suggests that P. canaliculata exhibits a sex-dependent response pattern when subjected to shell damage and calcium carbonate addition. The findings can provide some references to better understand the invasion mechanism and survival strategy of the P. canaliculata.

Possibility of Using Different Calcium Compounds for the Manufacture of Fresh Acid Rennet Cheese from Goat's Milk.

Calcium can be added to cheese milk to influence the coagulation process and to increase cheese yield. Calcium compounds used in the dairy industry show substantial differences in their practical application. Therefore, this study aimed to evaluate the potential use of 0, 5, 10, 15, and 20 mg Ca 100 g-1 of milk in the form of calcium gluconate, lactate, and carbonate as alternatives to calcium chloride in manufacturing fresh acid rennet cheese from high-pasteurized (90 °C, 15 s) goat's milk. The pH value of the cheese was reduced most strongly by the addition of increasing doses of calcium lactate (r = -0.9521). Each cheese sample showed increased fat content with the addition of calcium. Only calcium chloride did not reduce protein retention from goat's milk to cheese. The addition of 20 mg Ca 100 g-1 of milk in the form of gluconate increased cheese yield by 4.04%, and lactate reduced cheese yield by 2.3%. Adding each calcium compound to goat's milk significantly increased Ca and P levels in the cheese (p ≤ 0.05). The highest Ca levels were found in cheese with the addition of 20 mg Ca 100 g-1 of milk in the form of lactate. In all groups, similar contents of Mn, Mo, and Se were found. Calcium addition significantly affected cheese hardness, while higher calcium concentrations increased hardness. Carbonate caused the greatest increase in the cohesiveness of cheese. The addition of calcium compounds increased the adhesiveness and springiness of cheese compared to controls. The cheese with calcium chloride had the highest overall acceptability compared to the other cheese samples. The addition of calcium carbonate resulted in a lower score for appearance and consistency, and influenced a slightly perceptible graininess, sandiness, and stickiness in its consistency, as well as provided a slightly perceptible chalky taste.

Foam Glass Fabrication from End-of-Life Blended LCD Screen, Photovoltaic Glass Cullet and Flat Glass

End-of-life LCD screens from various waste steam have been used to formulate foam glass, aiming for use as light weight, high compressive strength, and insulation purposes. Via conventional ball milling, the foam glass powder was mixed with a binder and fabricated through compaction under 5-10 MPa using stainless steel press moulds to give green samples in cubic and plate shapes. Firing the samples at 1000 – 1050 °C for 0.5-4 hours allowed the construction of foam glass structure, giving low densities of 0.15-0.23 g/cm3. Additions of cordierite, calcium carbonate, graphite and borax determined the phases and composition of the final recycling products. Cristobalite appeared as the main phase along with anorthite were found to give high compressive strength of 1.10-4.22 MPa to the foam glass. The foam glass possessed thermal conductivity in a range of 0.1004-0.1183 W/m K, which can be used for insulation purposes. Different foam glass formulation and geometries required different firing temperature and time to acquire suitable foam glass structure for specific purposes of compressive and thermal insulation properties.

The Taxonomic Composition Changes of Bacteria and Fungi in Plant Residue Composts Induced by Biochar and Calcium Carbonate Application

Plant residues are the main source of humus and some nutrients in soils. The composting of organic waste using modifiers is a promising way to obtain high-quality organic fertilizers. Here, the effect of biochar and calcium carbonate on the abundance and taxonomic composition of bacteria and fungi in mature plant compost has been studied using metagenomic analysis. Plant materials with different initial C:N ratios—low (22, clover), medium (38, rye) and high (68, oats)—served as composting materials in the pot experiment. The plant material mixed with sterile sand was modified by the addition of biochar or calcium carbonate. Both ameliorants increased pH values and humic acid content in composts irrespective of plant material composition. Representatives of the phyla Proteobacteria, Actinobacteriota and Firmicutes dominated among bacteria and representatives of the division Ascomycota dominated among fungi in the mature composts, as in the initial plant samples. The abundances of bacteria and fungi in the cereal composts were higher than in the composts with clover. The effect of biochar and calcium carbonate on the number and taxonomic composition of bacteria and fungi in composts from the same plant material was similar, while the effect of reagents in composts from different raw materials was ambiguous. No one dominant group of bacteria was found to develop in response to biochar or calcium carbonate application in any of the types of composts studied. However, the structure of the fungal community both at the phylum and genus levels changed significantly under the influence of these additives. The addition of calcium carbonate and biochar led to an increase in the abundance of the same groups of fungi, but this increase was different for composts made from different plant materials.

Mechanisms of mitigating nitrous oxide emission during composting by biochar and calcium carbonate addition

To investigate the mechanisms underlying effects of biochar and calcium carbonate (CaCO3) addition on nitrous oxide (N2O) emissions during composting, this paper conducted a systematic study on mineral nitrogen (N), dissolved organic carbon (C) and N, sources of N2O, and functional genes. Biochar and CaCO3 addition decreased N2O emissions by 26.5–47.8% (9.5–96.9 mg N kg−1 dw) and 13.9–37.4% (12.0–121.0 mg N kg−1 dw) compared to the control (14.3–179.7 mg N kg−1 dw), respectively. The mitigation of N2O emission was caused by decreased contribution of ammonia-oxidizing bacteria (AOB) and fungi to N2O production due to diminished AOB amoA, fungal nirK and P450 gene abundances, or by stimulated N2O reduction to N2 owing to increased abundances of nosZⅠ and nosZⅠⅠ genes under biochar and CaCO3 addition. The findings suggest that the addition of biochar or CaCO3 is effective in mitigating N2O emission during composting.

Biochar as a soil conditioner for common bean plants

Biochar is a carbon-rich material produced during organic waste pyrolysis. In this context, two experiments were performed to evaluate the effect of biochar produced from rice husks and cattle manure on soil fertility and common bean production, as well as to identify the optimal dose of cattle manure biochar to be applied. The first experiment (Experiment I) was conducted according to a completely randomized design (factorial scheme 2 × 2 × 2 + 1) with six replicates: two types of biochar (cattle manure biochar and rice husk biochar), with and without acidity correction [addition of calcium carbonate and magnesium carbonate (PA) in a proportion of 4:1 (Ca:Mg) to raise the soil base saturation to 60%], with or without the addition of 120 mg dm-3 of phosphorus (P) as ammonium phosphate, and a control treatment (without biochar, acidity correction, and P). Based on the results of Experiment I, a second experiment was conducted according to a completely randomized design, with five treatments (doses of biochar from cattle manure) and four replications. Rice husk biochar, as a conditioner of soil chemical properties, had less prominent effects than cattle manure biochar. Cattle manure biochar functioned as a corrective for soil acidity and a source of nutrients (mainly phosphorus). The dose corresponding to 5.46% of the soil volume led to the maximum grain production by common bean plants.