Effect of Temperature on Calcium Carbonate Precipitation in Biomimetic Calcium Chloride Solution

In the present work, the effect of temperature on calcium carbonate precipitation in the biomimetic calcium chloride solution was investigated. A spontaneous calcium carbonate precipitate was formed in the biomimetic calcium chloride solution as a result of the carbon dioxide hydration process. The reaction was conducted at different temperature range vary from 30°C to 100°C. The mass of the calcium carbonate precipitate and the pH solution was measured in the study. The finding indicated that an increment of the temperature has led to the fast pH reduction of the solutions to 7.0. However, the process has retarded the calcium carbonate precipitation process. The optimum temperature for higher calcium carbonate precipitation has occurred at the temperature range of 47.5°C – 65°C which gave the highest calcium carbonate precipitate at 0.121g. The addition of Tris buffer into the calcium chloride solution in this study did not gave an inhibition effect on the calcium carbonate precipitate. Based on the results, an operating condition at 47.5°C – 65°C was recommended to be used in mineral carbonization of CO2 using the biomimetic calcium chloride solution.

Synthesis and Characterization of Calcium Carbonate Nanoparticles via Bacterial Mineralization in Steel Slag Comprising Cementitious Materials

Bacteria-induced mineralization is a new technique to produce calcium carbonate in steel slag for the preparation of building materials. Calcium carbonate nanoparticles were precipitated as a result of the enzymatic activity of Bacillus mucilaginous subtilis in steel slag. The crystal structure and morphology of the calcium carbonate precipitate were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), while thermal properties were studied by thermogravimetric-differential scanning calorimetry (TG-DSC) analysis. The experimental results showed that the microstructure of calcium carbonate precipitate induced by the reproductive enzymes of Bacillus mucilaginous differs from the chemical precipitation in simulated pore solution of steel slag. Powder XRD patterns confirmed the formation of Bacillus mucilaginous subtilis-induced calcium carbonate with an average particle size of 42.1 nm, while the average particle size of the chemically synthesized calcium carbonate was 59.3 nm. Compared with the chemical synthesis, we found that the decomposition temperature of calcite by bacterial precipitation was higher than that for the chemically-precipitated calcite. The compressive strength improved with the amount of bacterial content. Bacterial mineralization could accelerate the rate of carbon sequestration in the mineralization process. The content of calcium carbonate in microbial mineralized steel slag increased obviously. The compressive strength of steel slag mortar with 1.5% bacterial reached up to 51.5 MPa, the compressive strength increased over 50% compared with the carbonized steel slag mortar. The micron-size calcite by bacterial mineralization resulted in a more compact structure. Our study suggests that microbial mineralization technology is a good method to utilize steel slag for building materials.

Formate Oxidation-Driven Calcium Carbonate Precipitation by Methylocystis parvus OBBP

ABSTRACTMicrobially induced carbonate precipitation (MICP) applied in the construction industry poses several disadvantages such as ammonia release to the air and nitric acid production. An alternative MICP from calcium formate byMethylocystis parvusOBBP is presented here to overcome these disadvantages. To induce calcium carbonate precipitation,M. parvuswas incubated at different calcium formate concentrations and starting culture densities. Up to 91.4% ± 1.6% of the initial calcium was precipitated in the methane-amended cultures compared to 35.1% ± 11.9% when methane was not added. Because the bacteria could only utilize methane for growth, higher culture densities and subsequently calcium removals were exhibited in the cultures when methane was added. A higher calcium carbonate precipitate yield was obtained when higher culture densities were used but not necessarily when more calcium formate was added. This was mainly due to salt inhibition of the bacterial activity at a high calcium formate concentration. A maximum 0.67 ± 0.03 g of CaCO3g of Ca(CHOOH)2−1calcium carbonate precipitate yield was obtained when a culture of 109cells ml−1and 5 g of calcium formate liter−1were used. Compared to the current strategy employing biogenic urea degradation as the basis for MICP, our approach presents significant improvements in the environmental sustainability of the application in the construction industry.

Morphological Investigation of Calcium Carbonate during Ammonification-Carbonization Process of Low Concentration Calcium Solution

Ultrafine calcium carbonate is a widely used cheap additive. The research is conducted in low degree supersaturation solution in order to study the polymorphic phases’ change and its factors of the calcium carbonate precipitate in the ammonification-carbonization process of the solution with calcium. Fine particles of calcium carbonate are made in the solution containing 0.015 mol/L of Ca2+. Over 98% of the calcium carbonate precipitate without ammonification resembles the morphology of calcite, while the introduction of ammonia can benefit the formation of vaterite. It was inferred that the main cause should be serious partial oversaturation or steric effects. Ammonia also helps to form the twin spherical calcium carbonate. However, particles formed in the process of ammonification-carbonization in solution with low concentration degree of calcium are not even with a scale of the particle diameter from 5 to 12 μm. Inorganic salts, alcohol, or organic acid salts have significant controlling effect on the particle diameter of calcium carbonate and can help to decrease the particle diameter to about 3 μm. Anionic surfactants can prevent the conglobation of calcium carbonate particles and shrink its diameter to 500 nm–1 μm.

Characterization of calcium carbonates used in wet flue gas desulphurization processes

This paper presents an experimental characterization of two sources of calcium carbonate, limestone and calcium carbonate precipitate (CCP) used in wet flue gas desulphurization processes. Characterization of the two carbonate sources was carried out by chemical analysis, IR spectra, thermal behavior, particle size distribution for CCP, BET surface area and absorption capacity of SO2 in calcium carbonate suspensions. The absorption temperature, suspension concentration and carbonate grain size were found to be the most influential parameters in the absorption capacity measurements.