Calcium Carbonate Content Research Articles

Valorization of purified agricultural brown eggshell by-product as filler in bio-epoxy composites

This study presents tensile, flexural and water absorption properties of composites made from bio-epoxy resin containing brown eggshell (with membrane), purified brown eggshell (without membrane) and mineral limestone at three filler levels of 5, 10 and 20 wt%. Composites were made by an open silicone mold casting method. Fourier transform infrared (FTIR) spectroscopy was used to demonstrate removal of the membrane. Inductively coupled plasma mass spectrometry (ICP-MS) indicated brown eggshells without membrane had a higher calcium carbonate content suggesting the purification technique worked well. Although composite tensile strengths and flexural strengths were lower than the pure bio-epoxy, the composites containing brown eggshells (with membrane) had slightly better strengths than composites containing purified brown eggshells (without membrane) and mineral limestone for the same particle size of 32 µm. The organic membrane contains proteins on the surface of the eggshells which may be beneficial for chemical bonding to occur with the bio-epoxy resin. Filler contents of 5–10 wt% were acceptable for tensile and flexural strengths. Scanning electron microscopy (SEM) provided visual observations of the fractured surfaces where an increase in surface roughness was related to an increase in filler loading, implying changes occurred within the composite materials. Brown eggshells can be exploited as a waste management opportunity for use as a filler in bio-epoxy composites.

Experimental study on macro-micro effectiveness of Yellow River silt solidified by using soybean-induced carbonate precipitation (SICP) technology

For a long time, the sediment problem has been regarded as the most concerning issue for the Yellow River in China. Meanwhile, the research on the resource utilization of Yellow River silt has been highly valued. In this paper, soybean-induced carbonate precipitation (SICP) technology was adopted to catalyze the formation of calcium carbonate with the view of solidifying the Yellow River silt. The sensitivity of unconfined compressive strength (UCS) of solidified Yellow River silt sample to various factors such as cementation solution concentration C, grouting times N, and relative density D r was analyzed. The influence of different bio-treatment plans considering cementation solution concentration C, grouting times N on the calcium carbonate content of Yellow River silt sample with a certain relative density was characterized. Furthermore, loading failure modes of Yellow River silt cured with different cementation solution concentration C were demonstrated. Scanning electron microscope (SEM) images were used to illustrate the microscopic mechanism of biomineralization technology. The results of this study show that soybean-induced carbonate precipitation method can provide a technical guarantee for the resource utilization of the Yellow River silt.

Carbon and Nitrogen Stocks in Topsoil under Different Land Use/Land Cover Types in the Southeast of Spain

Land use plays a crucial role in the stock of soil organic carbon (SOC) and soil nitrogen (SN). The aim of this study was to assess and characterize the effects of various soil management practices on the physicochemical properties of soil in a Mediterranean region in southeastern Spain. Texture, soil moisture, bulk density, pH, electrical conductivity, equivalent CaCO3 (%), soil organic matter and carbon, and Kjeldahl nitrogen were determined for the surface topsoil (0–5 cm, 180 samples) under three types of land cover: cropland, grassland, and urban soil. The main soil textures were silt, silt loam, and sandy loam with low percentages of soil moisture in all soil samples and lower bulk density values in cropland and grassland areas. The pH was alkaline and the electrical conductivity as well as the equivalent calcium carbonate content were moderate to high. Organic matter estimated using the LOI and WB methods varied in the order cropland > grassland > urban soil. The results obtained for SOC and SN indicate that cropland presented the highest stocks, followed by grassland and urban soil. The values determined for the C/N ratio were close to 10 in cropland and grassland, indicating that organic matter readily undergoes decomposition at these sites. Our results emphasize the importance of evaluating the effects and identifying the impacts of different soil management techniques, and further research is needed to better understand the potential to improve soil organic carbon and nitrogen storage in semiarid regions.

Microstructural Evolution of Calcium Sulfoaluminate Cement during the Wet-Carbonation Process

Calcium sulfoaluminate (CSA) cement, as a type of low-carbon cement, can contribute to further reduction in carbon emissions with carbonation technologies. However, the detailed microstructure development of CSA cement during the carbonation process has been rarely analyzed. In this paper, wet carbonation was applied to CSA cement to investigate the microstructure evolution of carbonation products and carbon absorption capacity of CSA cement by means of pH measurement, X-ray diffraction (XRD) measurement, thermogravimetric (TG) measurement, Fourier-transformed infrared spectroscopy (FT-IR) measurement and scanning electron microscope measurement. During the carbonation process, the formed ettringite product and the dicalcium silicate clinker were carbonated immediately to generate calcium carbonate crystals, silica gel and aluminum hydroxide (AH3) gel. With the trend of pH increasing first and notably decreasing later, the coupling interaction between the hydration and carbonation reactions of CSA cement was revealed. From the XRD and TG results, three types of calcium carbonate crystal forms (calcite, vaterite and aragonite) were detected, and the content of calcium carbonate increased with the increase in carbonation time. FT-IR analysis further confirmed the existence of calcium carbonate, silica gel and AH3 gel with their characteristic vibrations. Moreover, the microstructure of carbonation products with different morphologies was observed. The application of wet carbonation to CSA cement provides a more comprehensive insight to the carbonation mechanism of this low-carbon cement.

Distribution of individual mud fractions in a tidal basin of the East Frisian Wadden Sea (southern North Sea): affinities between sortable silts, aggregated particle suites, and calcium carbonate and organic matter contents

In the 1990s and early 2000s, it was recognized that marine muds consisted of sortable silt (63–8 µm) and aggregated (< 8 µm) particle suites and that these responded differentially to the hydraulic sorting process. Among the aggregated particle suite, the composition and hydraulic behavior of fecal pellets received the least attention. The present study focused on a tidal basin (~ 71 km2) of the East Frisian Wadden Sea (southern North Sea), in which the depositional patterns of both the sortable silt and aggregated mud fractions were compared with the aim of identifying similarities and/or dissimilarities. The results show essentially dissimilar trends, the sortable silt suite being characterized by two non-overlapping hydraulic populations, the aggregated particle suite by three overlapping populations with modal diameters separated by only a few microns. The depositional pattern of the latter is interpreted to suggest that the hydraulic populations relate to specific fecal pellet groups, each composed of a different discrete grain-size spectrum produced by different filter-feeding organisms. At the same time, it is demonstrated that the distribution of organic matter is closely linked to the aggregated (< 8 µm) particle suite. The CaCO3 content, by contrast, is linked to the mud fraction by a power relationship, the large data scatter suggesting multiple sources. Budget calculations show that the standing stock of mud in the uppermost 5 cm of the sediment in the tidal basin amounts to ~ 0.461 × 106 tons (9.78% of the total sediment), of which ~ 31.3 × 103 tons (0.67% of the total sediment) are contributed by organic matter.Graphical abstract

Study on influencing factors of wellbore scaling during ASP flooding

In the middle and later stages of oil and gas field development, the produced fluid carries a large amount of formation scaling ions. During the entire extraction process, changes in parameters such as temperature, pressure, and flow rate can disrupt the original equilibrium and cause collisions between scaling ions. The scale particles formed by chemical reactions aggregate and deposit on the cylinder wall, causing scaling. The accumulation of scale not only causes wellbore blockage, but also irreversible damage to the production well. In order to study the scaling problem of oil production wells, the scaling mechanism was studied through indoor experiments. On this basis, a numerical model for the formation of wellbore scaling was established, and the mass fraction distribution of CaCO3 scaling particles at different positions in the wellbore was studied. The results indicate that: (1) the main type of scale sample is calcium carbonate, and as the concentration of calcium carbonate and sulfate ions increases, the amount of scale and corrosion will increase; (2) As the concentration of bicarbonate ions increases, the amount of scaling increases and the amount of corrosion decreases. (3) The mass fraction of calcium carbonate scaling at the upper and lower parts of the oil pump cavity and the sucker rod coupling decreases with increasing temperature, decreases with increasing initial inlet speed, and increases with increasing scaling ion concentration. The research results of this paper provide theoretical and technical support for predicting the scaling law of production Wells, improving the pumping inspection period of pumping units and ensuring the safety of oil Wells.

Strength characteristics and carbonation depth evolution of modified magnesium slag based solid waste storage backfill materials

CO2 storage is one of the effective ways to achieve China's 30·60 dual carbon goal. The study of the interaction between CO2 and storage backfill material lays a foundation for the long-term stability and gas tightness of CO2 storage. Based on the modified magnesium slag-based solid waste backfill material constructed by the storage, in order to explore the strength characteristics and carbonation depth evolution of the CO2 storage backfill material, the interaction between CO2 and the storage backfill material was analyzed from the perspectives of uniaxial compressive strength, carbonation depth test, pore structure distribution, microstructure and phase composition. The results show that carbonation can significantly improve the compressive strength of the storage backfill material, and the carbonation depth increases with the increase of carbonation time, and increases slowly after complete carbonation. The later the initial carbonation age, the faster the growth rate of compressive strength and carbonation depth, and the greater the growth rate. After high concentration CO2 curing, the diffusion rate and carbonation degree of the storage backfill material gradually decreased from the outside to the inside, and the calcium carbonate content also gradually decreased. The carbonation can significantly reduce the porosity of the sample, gradually transform from large pores to small pores, and the pore size distribution and pore structure are significantly improved. Therefore, the later the initial carbonation age is, the more beneficial the carbonation effect is for the long-term stability and air tightness development of the backfill material of the CO2 storage, which provides important theoretical guidance for the construction and storage method of the CO2 storage.

Local deposition characteristics of calcium carbonate fouling in different enhanced tubes

With the development and advancements of modern industry, the application of enhanced tubes is becoming more and more extensive in various engineering domains and technological applications. When water is used as the working fluid for thermal energy utilization, there is a large chance of accumulating a large amount of fouling on the surface of the enhanced tubes. This paper establishes a mathematical model of the local fouling deposition of calcium carbonate in enhanced tubes. The model is used to simulate and compare the local fouling characteristics of CaCO3 in different tubes. In addition, a study is conducted on the effects of different inlet flow rates, water temperature, and calcium carbonate concentrations on the local fouling resistance of bellows tubes. The results showed that the local fouling resistance (average) and local fouling resistance of enhanced tubes is smaller than that of circular tubes. Additionally, the bellows tubes yielded the best scale inhibition effect. The obtained local fouling resistance is also found to change periodically along the length of the tube. The local fouling resistance decrease with an increase in the inlet flow rate and wall temperature, and increases with an increase in the calcium carbonate solution concentration.

Effect of Mussel Shells as Soil pH Amendment on the Growth and Productivity of Rosemary (Rosmarinus officinalis L.) Cultivation

Mussel shells, with their calcium carbonate content, serve as a natural pH buffer, aiding in neutralizing acidic soils and, consequently, enhancing nutrient availability for plants. The aim of this study was to evaluate the effect of treating soils with mussel shells as a soil pH amendment on the agronomic characteristics and productivity of Rosmarinus officinalis. A pot experiment was set up for two growing years. The treatments were amended using different doses of mussel shells. Overall, the treatments were the following: C: unamended soil (control); T1: 0.1%; T2: 0.3%; T3: 0.5%; T4: 1%; T5: 3%; T6: 6%. Plant height was higher in pots amended with 6% mussel shells and reached the value of 32.2 cm in the first year and 51 cm in the second. The application of mussel shells increased the branch length by 53.4–58.7% and the number of branches per plant by 61.3–62% in T6 compared to the control. The total yield of fresh and dry weight in the 1st and 2nd year was ordered as follows: T6 &gt; T5 &gt; T4 &gt; T3 &gt; T2 &gt; T1 &gt; C. In conclusion, while the established optimal quantity for neutralizing soil pH is 300 g of mussel shells per 10 kg of soil, it has been observed that a ratio of 600 g of mussel shells proves more effective in terms of both the productivity and agronomic characteristics of rosemary.

Fire-Induced Vegetation Dynamics: An In-Depth Discourse on Revealing Ecological Transformations of the Mahaban and Surrounding Forests

Since the Palaeozoic era, fire as a potent driver of environmental changes, has dramatically shaped the terrestrial ecosystems. Fire affects soil structure and composition, which in turn affects the floral diversity of an area. This research work aims to examine the impact of fire on vegetation and the physicochemical nature of the soil in fire-affected and fire-free sites across the Mahaban and the surrounding forests, Swabi District, Khyber Pakhtunkhwa, Pakistan. Quadrat quantitative ecological techniques were used for vegetation sampling in fire-free and fire-affected sites. In total, 219 plant species belonging to 173 genera and 70 families were recorded. Among the 219 plant species, 173 species were recorded from fire-free sites and the remaining 122 species were from fire-affected sites. The incidence of fire results in elevated organic matter, nitrogen, phosphorus, and lower calcium carbonate concentrations in the soil. The greatest species richness and evenness were observed across the fire-free sites. Our study concludes that the influence of edaphic and topographic factors on species richness varies between fire-affected and fire-free sites. Fire has significantly altered the nutrient availability in the studied region, and this is confirmed by soil analysis and vegetation research. It is suggested that further research in the field of fire ecology can produce valuable insights.

Influence of Forest Strips on Changes in Soil Properties in the Agrolandscape

Background: In Russia 5.2 million hectares of protective forest plantations were created on agricultural land. Forest strips optimize moisture turnover, heat and gas exchange of the territory and transform agrarian landscapes into more sustainable forest-agrarian ecosystems (agroforest landscapes). Studying the impact of shelterbelt forests on the transformation of soil properties in the context of climate change (organic carbon storage) is an important problem. The aim of our research was to study the effect of shelterbelt forests on soil indicators and to digitally map the contours of forest-meliorated soils on the test site using GIS-technology and field studies. Methods: In the present study, the methodology of soil studies in agroforested soils (1978) and the methodology of assessing the accumulation of substances in plants and soils in agroforested landscapes were used to study forest-meliorated soils. We proceeded from the position that the reclamation effect of forest belts occurs at a distance of 30 heights. The research was conducted from 2016 to 2022. Result: Research has established, that the soil profile under the forest belt has an organogenic horizon A0 (forest floor); the thickness of the humus horizon (A+B1) under the forest belt is 8-10 cm higher compared to other zones. Spatial distribution of humus content in the A+B1 horizon from the forest belt to the centers of inter-belt squares (zone 20H) is not characterized by great variability and clear patterns and on average makes 1.15-1.2%. The increase in calcium carbonate (CaCO3) content in the soil occurs in the direction from the forest belt to the 20H zone. The indicator of dense residue in terms of the content of readily soluble salts is not relevant in estimating the forest belt’s influence on transformation of soil properties. A preliminary digital map of the contours of forest-reclaimed soils has been compiled. The obtained materials will serve as a basis for modeling the spatial and temporal dynamics of soils under forest belts in the zonal section and improving soil fertility in the interstrip space.

Snail Shell Waste Threat to Sustainability and Circular Economy: Novel Application in Food Industries

Effective waste management has become an urgent societal challenge. Food waste is made up of items meant for human consumption that are lost, polluted, disposed of, or deteriorated; the reutilization of shells from mollusk waste is a severe problem in terms of environmental protection and the development of the circular economy. The properties of waste shells are presented and discussed, including their biological–natural origin and high calcium carbonate content. This could add social and innovation focus on shell waste management, getting a non-toxic, eco-sustainable, low-cost, biodegradable supplement to invest in. Furthermore, it has the potential to support the circular economy approach by creating a closed system that minimizes the use of natural resources and environmental contamination. This review explores edible mollusk shell waste sources and functional properties of inorganic components of snail shell waste like minerals and active substances like chitin, chitosan, and calcium carbonate and attempts to carry out a comprehensive analysis of the scientific literature published over the last 20 years, elucidating prominent patterns in the utilization of shell waste in food application industry, as additives and supplements development to promote both human and animal health.

Benthic fauna along sandy beaches enriched by metals after mining disaster

In 2015, 60 million tons of ore tailings from the Fundão dam failure entered the Doce River basin, Brazil, and reached surrounding sandy beaches. This study evaluated the influence of sedimentology and morphology of beaches that received mining tailings on chemical element concentrations and consequent benthic community responses. We collected sediments for physical (granulometry, heavy mineral, and calcium carbonate content) and geochemical (chemical elements) analyses and biological diversity parameters (benthic macro- and meiofauna density, richness, and composition) on 8 beaches with different morphodynamic types. Beaches with more dissipative characteristics retained the highest contents of mud, As, Fe, Mn, V, and heavy minerals, present in the tailings. We also recorded the lowest density and richness of macrofauna on these beaches, compared to more reflective beaches. These results contradict the global trend, suggesting that anthropic disturbances outweigh the effects of morphodynamics in structuring the benthic fauna community, mainly in dissipative sandy beaches.

Short- to Medium-Term Corrosion of Mild Steel in Highly Calcareous Seawaters: Effects of Calcium Carbonate Concentration, Coupon Orientation, and Nutrient Addition

Mild steels exposed to marine immersion conditions in which carbonate solubilities are exceeded, leading to deposition of calcareous material, have been shown to exhibit much-reduced corrosion rates compared with corrosion under conditions in which there is no exceedance of solubility limits and therefore no calcareous deposition. However, the differences in corrosion including the potential effect of microbiologically influenced corrosion (MIC) in these conditions have not been examined systematically in the literature. The study reported herein involves short- to medium-term marine immersion exposures (up to 18 month) of mild steel coupons in natural seawater (control) and in environments using the same seawater source dosed with (1) CaCO3, acting as an inorganic particulate suspension representative of that encountered in seawater with elevated calcareous content; and (2) a nitrate salt, acting as an industrial pollutant and bacterial nutrient source. The results show the extent to which the deposition of particulate CaCO3 from suspension in seawater onto and into the rusts reduces the rate of corrosion of mild steel; a rate that was found to be dependent on the coupon orientation within the seawater. Coupons that were permanently buried beneath a cap of settled CaCO3 particles exhibited a 70% reduction in corrosion rate compared with the representative control coupons. The results also show that for these exposure durations and conditions, while iron-related bacteria and sulfate-reducing bacteria populations were identified in high concentrations (respectively ∼1 × 106 cfu/g and ∼1 × 102 to 4 × 106 cfu/g, depending on coupon orientation) within the rust products themselves after 18 month of exposure, there was no clear evidence of MIC. These findings indicate that short and medium-term (nonaccelerated) studies of MIC for mild steel are insufficient or even misleading for the prediction of long-term corrosion rates in these environments.

Long-Term Performance of Soybean-Based Concrete Surface Protectant under Laboratory Accelerated Aging Conditions

Soy methyl ester-polystyrene (SME-PS) is an organic material derived from soybeans, which has proven to be an effective protectant for concrete surfaces. This study investigated the long-term performance of cement paste samples treated with SME-PS under laboratory accelerated aging conditions (AAC). The specimens were subjected to cyclic conditions: 8 h of UVA radiation (simulating solar radiation), followed by 6 h of darkness with water condensation and a high temperature of 40°C for 28 days. After the AAC exposure, the samples were immersed in a deicing salt solution, specifically a 29.8 wt. % calcium chloride solution, for 7 days. To evaluate the long-term behavior of SME-PS, a series of experiments, including visual observation, thermogravimetric analysis (TGA), and low-temperature differential scanning calorimetry (LT-DSC) was conducted. Visual observations revealed slight damage in SME-PS-treated samples after AAC exposure, while control samples experienced microcrack formations. SME-PS chemical compositions remained unaffected by AAC, in contrast to the control samples where a decrease in the quantity of calcium hydroxide and an increase in calcium carbonate content were observed as a result of carbonation during AAC exposure. LT-DSC results indicated that SME-PS-treated samples showed a significant reduction in the enthalpy of fusion associated with calcium oxychloride (CAOXY) formation, indicating that the SME-PS remained effective after AAC exposure, while control samples exhibited higher CAOXY enthalpy of fusion.

Towards a monitoring tool to quantify urease during biocementation treatment at microscale

Biocementation consists in using urease enzyme and a solution rich in urea and in calcium to precipitate calcium carbonate (biocement). When applying this treatment in soils, the biocement minerals bond the grains improving overall soil’s hydro-mechanical properties. For the practical use of this technique, it is necessary to be able to predict the properties of the treated soil after following specific protocols, by preference avoiding non-destructive testing such as those performed on samples extracted after the treatment. The amount of biocement precipitated depends on the amount of urease enzyme, urea and calcium. This idea has inspired the development of one magnetoresistive biosensor to detect urease, to be used as a non-destructive monitoring tool during the treatment. A magnetoresistive platform was used to quantify the signal, which is related to the urease concentration through a calibration curve. The sensor was tested to measure the enzyme present in the inflow and outflow fluids used to treat cylindrical soil samples (2.5 cm diameter and 2.0 cm height), prepared with a uniform grading size sand (D50=0.3 mm). Purified urease from Canavalia ensiformis, was used. The improvement of the biocemented sand samples was quantified through measuring the calcium carbonate content of the soil after the treatment and the values were related with the amount of enzyme retained by the soil, determined using the sensor readings. This work found, for the first time, the relationship between the measured concentration of urease retained by soil and the calcium carbonate content precipitated. This relationship is an important tool for monitoring the treatment, without the need to use destructive tests or even stop the treatment.

Development of tools to investigate biocementation - microscale analysis for studying bacterial solutions

Biocementation consists on the use of microorganisms (bacteria) to promote the precipitation of calcium carbonate (biocement). When this technique is applied in soils or fractured rocks, the biocement which is precipitated can fill voids and discontinuities, being easy to apply, not very intrusive and requiring low energy consumption. There are several aspects that must be investigated when using living microorganisms for such purpose, mainly related with ensuring the environmental conditions for their survival and the maximization of production of biocement. The age of the bacteria and the increment of biocement production after increasing the number of inoculations were investigated in the work presented in this paper. A microfluidic device was developed to visualize the production of biocement after multiple injections of bacteria and feeding solution. These devices allow for an easy and straight forward visualization of small-scale physical, chemical and biological processes. The results of injection cycles in microfluidics channel were examined with imaging techniques. In parallel, experimental tests were carried out on samples of uniform sand soil, with the objective of evaluating the penetration resistance and the calcium carbonate content that was formed, according to the number of injections. There was also a verification of the electrical conductivity of the bacterial solutions in use, to guarantee its viability. As expected, the production of biocement increased after three injections of bacteria, which is consistent with the results found in both microfluidic devices and soil samples.

Evaluating soil acidification risk and its effects on biodiversity–ecosystem multifunctionality relationships in the drylands of China

BackgroundSoil acidification caused by anthropogenic activities may affect soil biochemical cycling, biodiversity, productivity, and multiple ecosystem-related functions in drylands. However, to date, such information is lacking to support this hypothesis. MethodsBased on a transect survey of 78 naturally assembled shrub communities, we calculated acid deposition flux in Northwest China and evaluated its likely ecological effects by testing three alternative hypotheses, namely: niche complementarity, mass ratio, and vegetation quantity hypotheses. Rao's quadratic entropy and community-weighted mean traits were employed to represent the complementary aspect of niche complementarity and mass ratio effects, respectively. ResultsWe observed that in the past four decades, the concentrations of exchangeable base cations in soil in Northwest China have decreased significantly to the extent of having faced the risk of depletion, whereas changes in the calcium carbonate content and pH of soil were not significant. Acid deposition primarily increased the aboveground biomass and shrub density in shrublands but had no significant effect on shrub richness and ecosystem multifunctionality (EMF), indicating that acid deposition had positive but weak ecological effects on dryland ecosystems. Community weighted mean of functional traits (representing the mass ratio hypothesis) correlated negatively with EMF, whereas both Rao's quadratic entropy (representing the niche complementarity hypothesis) and aboveground biomass (representing the vegetation quantity hypothesis) correlated positively but insignificantly with EMF. These biodiversity–EMF relationships highlight the fragility and instability of drylands relative to forest ecosystems. ConclusionsThe findings from this study serve as important reference points to understand the risk of soil acidification in arid regions and its impacts on biodiversity–EMF relationships.

A 70 kyr Record of Monsoon-induced Marine Productivity Changes, Terrigenous Flux and Weathering Variations in the Southern Bay of Bengal

Abstract The southwest (SW) and northeast (NE) monsoon winds significantly affect the oceanographic and climatic changes over the Bay of Bengal (BoB). We present here detailed geochemical and isotopic records from two sediment cores (SK157 14; 5°11′ N: 90°5′ E and SK157-16; 8°46′ N: 90°18′ E), collected from the southern BoB. In this study, we mainly focus on variations in paleoproductivity and terrigenous fluxes introduced into the BoB since last ~70 kyr: We have reconstructed biogenic barium (Babio), calcium carbonate (CaCO3) content, and total organic content (TOC) in both sediment cores to infer paleoproductivity during the period of study. The distributions of productivity proxies in both these cores indicate that the productivity may have been significantly high during MIS 1 and MIS 3 (warmer interglacial periods), when SW monsoon was intensified. The terrigenous proxies (Al%, Ti%, d(0.9)) show that the southern BoB may have received higher terrigenous input during the MIS 2 and MIS 4 (glacial periods) coinciding with the intensification of NE monsoon. The weathering proxy (K/Al), in contrast, shows no significant changes during MIS 2, 3 and 4. However; a significant shift is seen during glacial to Holocene transition.

A numerical model of the MICP multi-process considering the scale size.

As an environmentally friendly and controllable technology, Microbially induced carbonate precipitation (MICP) has broad applications in geotechnical and environmental fields. However, the longitudinal dispersivity in MICP multi-process varies with the scale size. Ignoring the effect of the scale size of the research object on the dispersivity leads to the inaccuracy between the numerical model and the experiment data. Thus, this paper has established the relationship between the scale size and the dispersivity initially, and optimized the theoretical system of MICP multi-process reaction. When scale size increases logarithmically from 10-2 m to 105 m, longitudinal dispersivity shows a trend of increasing from 10-3 m to 104 m. The distribution of calcium carbonate is closer to the experimentally measured value when the size effect is considered. After considering the scale size, the suspended bacteria and attached bacteria are higher than the cased without considering the size effect, which leads to a higher calcium carbonate content. Scale has little effect on the penetration law of the suspended bacteria. The maximum carbonate content increases with the increase of the initial porosity, and the average carbonate shows a significant increasing trend with the increase of the bacterial injecting rate. In the simulation of the microbial mineralization kinetic model, it is recommended to consider the influence of the scale size on the MICP multi-process.