Size Of Calcium Carbonate Crystals Research Articles

An adjustable bio-sealing method for rock fracture leakage mitigation

This study proposed a repeated adjustable mixture injection strategy (RAM) based microbial induced carbonate precipitation (MICP) for efficient mitigation of rock fracture leakage. Granite fractures with small apertures were investigated, and bio-sealing experiments were conducted using five different cementation solution (CS) concentrations (0.25−2 M). The results showed that the RAM-based bio-sealing method can seal and bond the small aperture rock fractures with high efficiency and uniform precipitation by adjusting the CS concentration. The RAM-based bio-sealing mechanism is attributed to the following four stages: (1) fixation of bacterial flocs onto the fracture surfaces, (2) precipitation of CaCO3 onto the fracture surfaces, (3) growth of pre-precipitated CaCO3 and adhesion of new-suspended CaCO3, and (4) bridging and clogging processes. The optimal CS concentration of 1 M resulted in a fracture filling rate up to 85%, a transmissivity reduction of 4 orders of magnitude, and a shear strength ranging from 512 kPa to 688 kPa. The bio-sealing effect was found to be influenced by the CS concentration on bacterial attachment, calcium carbonate yield and calcium carbonate bulk density. The CS concentration of 1 M promoted bacterial attachment, and increased calcium carbonate yield as well as calcium carbonate bulk density, while concentrations above 1 M had the opposite effect. The bulk density of calcium carbonate played a crucial role in the sealing and bonding performance of bio-sealed fractures, particularly at comparable filling ratios and bridging areas. The bulk density was regulated by the size of calcium carbonate crystals and was determined by Ca2+ concentration in the CS. This study provides valuable insights into the RAM-based bio-sealing method, highlighting its potential for efficient rock fracture leakage mitigation through precise control of CS concentration and understanding the underlying mechanisms.

Uncovering the Mechanism of the Role of Fly Ash in the Self-Healing Ability of Mortar with Different Curing Ages.

As an admixture of cement-based materials, the reaction of fly ash (FA) usually takes place in the late age of curing, so FA will affect the self-healing ability of long-age cement-based materials. The self-healing potential and the characteristics of self-healing products of cementitious materials before and after crack healing were analyzed by microscopic tests, and the mechanism of the effect of fly ash on the self-healing performance of cementitious materials was revealed. The results showed that the increase in fly ash content promoted the improvement of the self-repair performance of cracked specimens at 28 d, especially when the fly ash dosage was 40%, the crack opened after 30 d of healing in water was completely closed, the UPV value after recovery was close to 3000 m/s, the self-repair efficiency of maximum amplitude and main frequency amplitude was up to more than 60%, and the recovery rate of compressive strength was increased to more than 30%. However, the increase in fly ash content was not conducive to the self-repair of cracked samples at 210 d, and with the increase in fly ash content, the crack closure effect weakened, the UPV value after recovery decreased, the crack repair rate based on ultrasonic transmission decreased to about 20%, and the compressive strength recovery rate increased slightly. In addition, calcium carbonate precipitation was the main repair product of crack filling and healing, including calcite and spherulite. With the increase in fly ash content, the content of element C in the self-repair products of 28-day-old specimens gradually increased, and the size of calcium carbonate crystals gradually decreased, but the filling was denser, whereas the calcium carbonate crystals in the self-repair products of 210 d specimens gradually became fine and loose.

Studies of Morphology and Size of Calcium Carbonate Crystals Nucleating on Surfaces of Various Materials

The effects of material surface characteristics on the morphology and size of calcium carbonate crystals nucleating under cold wall pipe flow conditions were studied. We found that high surface energy materials could accelerate the conversion of crystals from vaterite to calcite, and the crystal size increased. Aragonite was found to be absent throughout the experiment. The deposition of calcium carbonate crystals is a layer-over-layer formation process. In the initial deposition period, the crystals are large and continue to grow until covering the material surface. At subsequent stages, the crystals forming on the existing fouling become much smaller. Studying the influence of material surface on the morphology and size of calcium carbonate crystals is important both for the reasonable selection of industrial materials and for the synthesis of calcium carbonate crystals with certain morphology and size.

Effect of sodium-carboxymethylcellulose on inhibition of scaling by calcium carbonate and sulfate

Sodium-carboxymethylcellulose inhibits the crystallization of calcium carbonate and sulfate on the surface of stainless steel in a supersaturated aqueous solution at 80°C. An increase in the size of calcium carbonate crystals and a change of their structure is observed in the presence of sodium-carboxymethylcellulose. The data obtained indicate that development of new “green” reagents for oil and gas extraction, scale inhibitors, on the basis of sodium-carboxymethylcellulose is promising.

Arabinogalactan as effective inhibitor of calcium carbonate scaling

Arabinogalactan inhibits the crystallization of calcium carbonate on the surface of stainless steel in a supersaturated aqueous solution at 80oC. In the presence of arabinogalactan, the size of calcium carbonate crystals decreases and their structure changes. Arabinogalactan is a “green” scaling inhibitor.