What is the amount of CaCO3 produced by bacteria?5 answersBacteria can produce varying amounts of CaCO3. In one study, the highest amount achieved was 57.6 g/L when using purified urease enzyme or urease enzyme produced by a bacterium. Another study reported a maximum concentration of 33.78 g/L of microbial calcium carbonate. In a different experiment, a maximum amount of 15.46 g calcite was precipitated from 100 mL of solution. Additionally, bacteria were found to produce an abundant fraction of marine calcium carbonate particles in seawater, with a typical concentration of 104-105 particles L−1. The exact amount of CaCO3 produced by bacteria can vary depending on factors such as enzyme concentration, substrate concentration, and culture conditions.
How does the use of calcium carbonate affect the mechanical strength of Portland cement concrete?4 answersThe use of calcium carbonate in Portland cement concrete can have varying effects on its mechanical strength. One study found that the use of biogenic CaCO3 as a limestone filler in portland limestone cements (PLCs) led to enhanced nucleation effects and increased 7-day compressive strength compared to PLCs produced using reagent-grade CaCO3. Another study showed that the addition of fine calcite as a mineral additive in concrete mixes resulted in the possibility of achieving high compressive strength at the age of 28 days, as well as high integral waterproofing of the concrete. However, it was also observed that the products of calcium carbonate used as crack fillers were more suitable as surface consolidants rather than crack fillers. Additionally, the formation of calcium carbonate in CO2-cured cement pastes provided additional nucleation sites and improved the early compressive strength due to lower porosity. Finally, the addition of nano-CaCO3 in 3D printing cementitious materials showed improved fresh-state performances and enhanced strength compared to mixtures without nano-CaCO3.
What are the challenges of using CaO-based solids to capture CO2?5 answersCaO-based solids face several challenges in capturing CO2. One challenge is the degradation of the sorbent due to sintering-induced agglomeration, which negatively impacts the solid inventory and plant operation. Another challenge is the influence of realistic flue gas conditions, such as the presence of H2O and O2, on the performance of the sorbent. While H2O promotes the kinetics of CO2 capture, O2 oxidizes the sorbent and hinders the utilization of captured CO2. Additionally, the presence of alkali metal salt promoters, such as K2CO3, can affect the cyclic performance of CaO-based sorbents. Low amounts of K2CO3 improve the cyclic performance, but large amounts reduce the positive effect on CO2 uptake performance. Furthermore, the carbonation reactivity of CaO sorbents can decay over cycles, but this can be mitigated by using organic acid-rich torrefaction condensate (TC) as an acidification treatment. Overall, these challenges need to be addressed to enhance the CO2 capture performance of CaO-based solids.
Why does the band position of Ca-O in the FTIR spectra of CaCO3 change with temperature?5 answersThe band position of Ca-O in the FTIR spectra of CaCO3 changes with temperature due to the weakened lattice vibration caused by large crystallite strain in the nano-particle CaCO3. This strain is possibly related to the abnormal IR assimilation characteristics observed in nanocrystalline CaCO3. The FTIR absorption spectra of the samples show peaks due to M-O, which could be responsible for the observed changes in the band position of Ca-O. Additionally, the presence of excess oxygen introduced by La through CuO2 planes in BSCCO superconductors can also affect the band position of Ca-O in the FTIR spectra. However, further research is needed to fully understand the specific mechanisms behind these temperature-induced changes in the band position of Ca-O in the FTIR spectra of CaCO3.
How does nanochemistry field address CO2 emission?3 answersThe field of nanochemistry addresses CO2 emission by developing techniques and advanced nanomaterials for capturing and reducing CO2. Two-dimensional nanomaterials such as metal sulphides, carbon-based materials, and graphene oxide have shown promise in capturing CO2 from various sources. Functionalized nanoreactors based on metal organic frameworks (MOFs) have also emerged as a new dimension in catalyzing the conversion of CO2 into valuable chemicals. Nanomaterials, with their unique properties and high surface area to volume ratios, are attractive for carbon capture and storage. Additionally, carbon nanotubes have been investigated for their field emission properties, which can contribute to addressing CO2 emission. Overall, nanochemistry offers potential solutions for mitigating CO2 emission through the development of nanomaterials and catalytic systems.
Is calcium carbonate a green house gas?9 answers