Amount Of CaCO3 Research Articles

Applying steel slag leachate as a reagent substantially enhances pH reduction efficiency for humidification treatment.

A cost-effective, easy-to-implement, and sustainable approach is needed to mitigate the production of alkaline leachate from steel slags that are reused or disposed in the environment. To address this issue, a humidification treatment process, which is operated by wetting a stack of steel slag using aqueous reagents and letting atmospheric CO2 to be passively diffused into the slag pores to induce slag carbonation reaction, was previously developed. In this study, we demonstrate that the leachate of raw steel slag can be recycled and used as a humidification reagent to substantially enhance the treatment efficiency as well as to enable operating the process with neither synthetic chemical consumption nor wastewater discharge. In a 24-h study, a 0.61-unit reduction in slag pH is achieved using a raw slag leachate as a reagent, which is substantially greater than a 0.28-unit reduction using deionized water. The net amount of CaCO3 produced during an extended humidification duration of 4weeks is increased by 2.7-fold when the leachate is used instead of deionized water. A series of systematically designed experiments demonstrates that the pH (11.0) and ionic strength (0.0048) are the two major characteristics of the raw slag leachate that contribute to the enhanced efficiency of humidification treatment. With further demonstration at larger scales in follow-up studies, the novel humidification process that utilizes the leachate generated on-site as a reagent is expected to be a feasible alternative for alkali waste treatment prior to its reuse or disposal.

Preparation of near net size porous alumina‐calcium aluminate ceramics by gelcasting‐pore‐forming agent processs

AbstractIn the processing of porous ceramics, shrinkage from green body to sintered compact during drying and sintering is one of the key concerns which affect microstructure and properties of porous ceramics. Through releasing gases from the burning of the pore forming agents, and volume expansion from the formation of low density resultants during sintering, the sintering shrinkage can be effectively compensated and near net size preparation can be achieved. Herein, near net size porous alumina‐calcium aluminate ceramics with controllable shrinkage have been prepared using a combination of gelcasting and pore‐forming agent process by adjusting the amount of CaCO3 and polymethyl methacrylate (PMMA) microspheres added. Al2O3 and CaCO3 were used as raw materials, PMMA microspheres were used as pore‐forming agent, isobutylene/maleic anhydride copolymer (Isobam104) was used as gelling agent and dispersing agent. The effects of the addition amounts of CaCO3 and PMMA in the slurry on the phase composition, shrinkage, porosity, and strength of porous alumina‐calcium aluminate ceramics were investigated. The results show that as the CaCO3 addition amount increases from 0 to 20 wt%, the shrinkage of the samples gradually decreases from 7.3% to −1.4%, and the consequent porosity increases from 58% to 66%, while the compressive strength increases from 5.9 to 15.5 MPa. When PMMA content increases from 10 to 50 wt%, the shrinkage of the samples decreases first and then increases, the porosity increases from 51% to 74%, and the compressive strength decreases from 12.5 to 5.3 MPa. The mechanisms for controlling shrinkages during preparation of porous alumina‐calcium aluminate ceramics can be attributed to the following aspects: on one hand, gas release from burning of PMMA and decomposition of CaCO3 during sintering; on the other hand, volume expansion due to the formation of lower density calcium aluminates which come from the reactions between CaO and Al2O3. The near net size preparation technique is of great significance for the manufacture of porous ceramics since the subsequent machining cost can be effectively reduced.

An Alternative Biotechnological Tool for Magnesite Enrichment: Lactic Acid Bacteria Isolated from Soil

Calcium carbonate (CaCO3) is found in different polymorph structures such as aragonite, vaterite, and calcite. The most common and stable form of CaCO3, calcite, which is abundant in sedimentary rocks as magnesite ore. Magnesite has application areas in many industrial fields including paper, pharmaceutical and refractory materials. Magnesite is theoretically formulated MgCO3, but contains many impurities (silicium, iron, and also calcite), that limits its usability and applicability. In this research, we aimed to investigate the decalcification possibility of the raw magnesite material through application of Enterococcus feacelis (EF) with CaCO3 dissolution ability. The exact mechanism of CaCO3 dissolution was investigated by carbonic anhydrase enzyme assay and HPLC analysis of organic acids produced by EF. Consequently, EF reduced the amount of CaCO3 from 2.94% to 0.49% which means a reduction (≈83.33%) in the rate of CaCO3 percentage. As a result of the experiments, it was observed that different organic acids produced by bacteria reacted with CaCO3 and removed the lime of magnesite ore. The bacteria used in the study did not show any pathogenic properties in rats, thus, it can be used safely for the industrial applications.

Pedogenesis in a karst environment in the Cerrado biome, northern Brazil

Karst terrains in tropical regions are object of few studies on soil properties and pedogenesis. In this study, soils pedogenesis was evaluated in a karst environment in the Cerrado biome, northern region of Brazil. The assumption is that even in the Cerrado conditions the characteristics of the soils are similar to other limestone soils in arid and semi-arid climates. Six soil profiles along a toposequence were sampled in trenches located at the summit (P1), shoulder (P2), backslope (P3), footslope (P4) and toeslope (P5 and P6) positions. The profiles were described, and their morphological (macromorphology and micromorphology), physical, chemical, mineralogical and organic matter attributes analyzed. The soils were classified as Calcic Luvisol (P1), Calcaric Eutric Cambisol (P2), Haplic Kastanozem (P3), Calcic Pellic Vertisol (P4), Orthofluvic Gleyic Calcaric Eutric Fluvisol (P5), Orthofluvic Calcaric Eutric Fluvisol (P6). Melanization and calcification are the main pedogenic processes, and they are controlled by the nature of parent material and the landscape position of the soil profile. The profiles P1, P2 and P3, at footslope and toeslope, show higher values of weathering ratios, which indicates the presence of clay minerals with a higher SiO2/Al2O3 ratio. They also have the highest amounts of CaCO3 which are associated with precipitation and neoformation of calcite. Although soils in the Cerrado biome are mostly highly weathered and with low natural fertility, the soils in the study area show accumulation of carbonates, high levels of exchangeable calcium and magnesium, pH values and base saturation that are associated with specific pedo-environments. The combination of the soil forming factors parent material and karst terrain controlled the dynamics of carbonates, leading to their accumulation in soils, regardless of the regional climatic conditions of the Cerrado biome.

Experimental evaluation of oxygen isotopic exchange between inclusion water and host calcite in speleothems

Abstract. The oxygen and hydrogen isotopic compositions of water in fluid inclusions in speleothems are important hydroclimate proxies because they provide information on the isotopic compositions of rainwater in the past. Moreover, because isotopic differences between fluid inclusion water and the host calcite provide information on the past isotopic fractionation factor, they are also useful for quantitative estimation of past temperature changes. The oxygen isotope ratio of inclusion water (δ18Ofi), however, may be affected by isotopic exchange between the water and the host carbonate. Thus, it is necessary to estimate the bias caused by this postdepositional effect for precise reconstruction of paleotemperatures. Here, we evaluate the isotopic exchange reaction between inclusion water and host calcite based on a laboratory experiment involving a natural stalagmite. Multiple stalagmite samples cut from the same depth interval were heated at 105 ∘C in the laboratory from 0 to 80 h. Then, the isotopic compositions of the inclusion water were measured. In the 105 ∘C heating experiments, the δ18Ofi values increased from the initial value by 0.7 ‰ and then remained stable after ca. 20 h. The hydrogen isotope ratio of water showed no trend in response to the heating experiments, suggesting that the hydrogen isotopic composition of fluid inclusion water effectively reflects the composition of past drip water. We then evaluated the process behind the observed isotopic variations using a partial equilibration model. The experimental results are best explained by the assumption that a thin CaCO3 layer surrounding the inclusion reacted with the water. The amount of CaCO3 that reacted with the water is equivalent to 2 % of the water inclusions in molar terms. These results suggest that the magnitude of the isotopic exchange effect has a minor influence on paleotemperature estimates for Quaternary climate reconstructions.

A cascading influence of calcium carbonate on the biogeochemistry and pedogenic trajectories of subalpine soils, Switzerland

Soil research in temperate to cool and humid regions has typically focused on acidic soils; there has been relatively little investigation of the effects of calcium carbonate (CaCO3) on unamended soil properties or function in these environments. The object of this study was to characterise the effects of small amounts of CaCO3 on pedogenic trajectories and soil biogeochemistry in a humid subalpine valley of Switzerland. To isolate the influence of CaCO3, six profiles were selected that had developed under almost identical conditions for soil formation, i.e. climate, topography, vegetation structure, time since deglaciation, silicate mineralogy and texture. The main difference between the profiles was that three contained a small quantity of CaCO3 (<6.2%; thereafter, ‘CaCO3-bearing’) while the remaining three contained no detectable CaCO3 (thereafter, ‘CaCO3-free’). The presence of CaCO3 was associated with cascading changes in soil biogeochemistry. These changes included higher pH, an order of magnitude higher extractable Ca and twice as much soil organic carbon (SOC). CaCO3-bearing profiles also displayed a higher proportion of poorly crystalline Fe forms. The higher pH at the CaCO3-bearing site was attributable to the weak buffering provided by CaCO3 dissolution, which in turn maintained the relatively higher extractable Ca. Exchangeable Ca (CaExch) and other reactive Ca forms could help stabilise SOC, contributing to its accumulation through processes such as flocculation and subsequent occlusion within aggregates and/or sorption to mineral surfaces. The increased SOC, CaExch and pH at the CaCO3-bearing site could in turn be inhibiting the crystallisation of disordered Fe forms, but further research is required to confirm this effect and isolate the exact mechanisms. Overall, this study shows that the presence of small amounts of CaCO3 in humid environments has a far-reaching influence on soil biogeochemistry and further supports the idea that indicators of Ca prevalence have the potential to improve regional SOC estimates.

Rheological and Mechanical Performance of Asphalt Binders and Mixtures Incorporating CaCO3 and Lldpe

This study was conducted to assess the performance of modified asphalt binders and engineering properties of mixtures prepared with incorporation 3 vol% and 6 vol% of calcium carbonate (CaCO3), linear low-density polyethylene (LLDPE), and combinations of CaCO3 and LLDPE. The rheological properties of control and modified asphalt binders were evaluated using a series of testing such as rotational viscometer (RV), multiple stress creep recovery (MSCR) and bending beam rheometer (BBR) tests. Meanwhile, four-point beam fatigue test, the dynamic modulus (E*) test and tensile strength ratio (TSR) test were conducted to assess the engineering properties of asphalt mixtures. Based on the findings, the RV and MSCR test result shows that all modified asphalt binders have improved performance in comparison to the neat asphalt binders in terms of higher viscosity and improved permanent deformation resistance. A higher amount of CaCO3 and LLDPE have led modified asphalt binders to better recovery percentage, except the asphalt binders modified using a combination of CaCO3 and LLDPE. However, the inclusion of LLDPE into asphalt binder has lowered the thermal cracking resistance. The incorporation of CaCO3 in asphalt mixtures was found beneficial, especially in improving the ability to resist fatigue cracking of asphalt mixture. In contrast, asphalt mixtures show better moisture sensitivity through the addition of LLDPE. The addition of LLDPE has significantly enhanced the indirect tensile strength values and tensile strength ratio of asphalt mixtures.

Carbonation Resistance Performance and Micro-Structure Analysis of Glazed Hollow Bead Insulation Concrete

In this paper, the carbonation depths of glazed hollow bead insulation concrete (GHBC) and normal concrete (NC) at different carbonation ages are tested. The microstructure of GHBC and NC before and after carbonation were observed and compared by mercury intrusion porosimetry (MIP), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The results showed that NC had better carbonation resistance than GHBC, and GHBC had a carbonation depth of 1.61 times than that of NC at 28 days accelerated carbonation experiment. The microstructural analysis showed that with the decrease of porosity of the samples, the carbon content and CaCO3 content increased after carbonation. The porosity of NC decreased from 14.36% to 13.53%, the carbon content increased from 4.42% to 5.94%, and the CaCO3 content increased from 18.5% to 56.0%. The porosity of GHBC decreased from 22.94% to 20.71%, the carbon content increased from 4.97% to 5.31%, and the CaCO3 content increased from 70.0% to 82.0%. The above results showed that carbon reacts with hydration products 3CaO·SiO2, 2CaO·SiO2, and Ca(OH)2 to produce a large amount of CaCO3 which causes a large amount of pores to be filled and refined hence the porosity and pore size were reduced leading to increase in the compactness of the material. From the results obtained, the carbonation depth prediction formula of glazed hollow bead insulation concrete was developed, and carbonation life was predicted.

Estimating CO2 degassing effect on CaCO3 precipitation under oil well conditions

To act effectively in the prevention of calcium carbonate precipitation, it is necessary to know the contribution of each causing factor. Many thermodynamic models, including the codes of scale software, just predict the total amount of CaCO3 precipitated. A study was developed to model the two major causing factors of calcite precipitation when the fluids experience a pressure drop. The effects of depressurization were investigated, first on calcite precipitation thermodynamics and second on CO2 degassing thermodynamics. It has been found that CO2 outgassing produces an expressive amount of scale, contributing from 60% to 90% on total calcite precipitation under the investigated conditions. That is, considering these results, it may be more efficient to work to keep CO2 in solution than to try to avoid the calcium carbonate nucleation.

Influence of temperature on microbially induced calcium carbonate precipitation for soil treatment.

Microbially induced calcium carbonate precipitation (MICP) is a potential method for improvement of soil. A laboratory study was conducted to investigate the influence of temperatures for soil improvement by MICP. The ureolytic activity experiments, MICP experiments in aqueous solution and sand column using Sporosarcina pasteurii were conducted at different temperatures(10, 15, 20, 25 and 30°C). The results showed there were microbially induced CaCO3 precipitation at all the temperatures from 10 to 30°C. The results of ureolytic activity experiments showed that the bacterial had higher ureolytic activity at high temperatures within the early 20 hours, however, the ureolytic activity at higher temperatures decreased more quickly than at lower temperatures. The results of MICP experiments in aqueous solution and sand column were consistent with tests of ureolytic activity. Within 20 to 50 hours of the start of the test, more CaCO3 precipitation was precipitated at higher temperature, subsequently, the precipitation rate of all experiments decreased, and the higher the temperature, the faster the precipitation rate dropped. The final precipitation amount of CaCO3 in aqueous solution and sand column tests at 10 °C was 92% and 37% higher than that at 30 °C. The maximum unconfined compressive strength of MICP treated sand column at 10 °C was 135% higher than that at 30 °C. The final treatment effect of MICP at lower temperature was better than that at high temperature within the temperature range studied. The reason for better treatment effect at lower temperatures was due to the longer retention time of ureolytic activity of bacteria at lower temperatures.

Self-propagating High-temperature Synthesis of Materials Based on Tungsten Carbide for One-Pot Hydrolysis-Hydrogenolysis of Cellulose Into Ethylene Glycol and 1,2-Propylene Glycol

Catalytic systems based on tungsten carbide (WnC) containing mainly W2C were obtained by the method of self-propagating high-temperature synthesis from a mechanochemically activated mixture of tungsten oxide, metallic magnesium, carbon black and CaCO3. The phase composition of the formed materials was shown to depend on the amount of CaCO3. The catalytic properties of the materials were tested in the hydrolysis-hydrogenation of cellulose to ethylene glycol (EG) and 1,2-propylene glycol (PG). It was established that in the presence of WnC the main products of the reaction were EG and PG with a ratio of PG/EG – 1.5-1.8. The deposition of nickel nanoparticles on the WnC surface increased the reaction rate and product yields. The maximum total yield of diols was 47.1 mol. %.

Formation of $${\text {CaCO}}_3$$ varieties from a carbonated aqueous solution

Experimental studies have been conducted to clarify the paragenetic conditions of CaCO3 varieties, calcite and aragonite formed from the same wall rock. In addition, the solubility dependence of calcite, aragonite, and limestone formed from limestone cave in CO2 -saturated solutions was compared with the previous studies. First, the calcite and aragonite were powdered to below 200 meshes. In addition, the powders were, respectively, added into the CO2 -saturated distilled water at 8, 13, 18, and 22∘C and were kept constant for 15 days. The amount of dissolved CaCO3 was then measured. The solubility of aragonite was higher than that of calcite, and the solubility decreased exponentially with increasing temperature. Simultaneous production and growth of calcite and aragonite proceeded only when the saturation of aragonite was reached in aqueous carbonate solution. Conversely, when the dissolved amount of CaCO3 has not been reached, calcite is only formed and grown. In these solutions, aragonite crystals dissolve and calcite crystals grow. The degree of saturation of aragonite can be reached by rapid evaporation of solvent, CO2 gas degassing, and the presence of Mg. However, paragenesis of calcite and aragonite in natural caves can be explained by rapid evaporation of the solvent. A rapid evaporation of the solvent may occur at a place, where a small amount of karst solution flows and a large amount of air flows. In such places, paragenesis of calcite and aragonite is possible.

Piezoelectric 3-D Fibrous Poly(3-hydroxybutyrate)-Based Scaffolds Ultrasound-Mineralized with Calcium Carbonate for Bone Tissue Engineering: Inorganic Phase Formation, Osteoblast Cell Adhesion, and Proliferation.

Elaboration of novel biocomposites providing simultaneously both biodegradability and stimulated bone tissue repair is essential for regenerative medicine. In particular, piezoelectric biocomposites are attractive because of a possibility to electrically stimulate cell response. In the present study, novel CaCO3-mineralized piezoelectric biodegradable scaffolds based on two polymers, poly[( R)3-hydroxybutyrate] (PHB) and poly[3-hydroxybutyrate- co-3-hydroxyvalerate] (PHBV), are presented. Mineralization of the scaffold surface is carried out by the in situ synthesis of CaCO3 in the vaterite and calcite polymorphs using ultrasound (U/S). Comparative characterization of PHB and PHBV scaffolds demonstrated an impact of the porosity and surface charge on the mineralization in a dynamic mechanical system, as no essential distinction was observed in wettability, structure, and surface chemical compositions. A significantly higher (4.3 times) piezoelectric charge and a higher porosity (∼15%) lead to a more homogenous CaCO3 growth in 3-D fibrous structures and result in a two times higher relative mass increase for PHB scaffolds compared to that for PHBV. This also increases the local ion concentration incurred upon mineralization under U/S-generated dynamic mechanical conditions. The modification of the wettability for PHB and PHBV scaffolds from hydrophobic (nonmineralized fibers) to superhydrophilic (mineralized fibers) led to a pronounced apatite-forming behavior of scaffolds in a simulated body fluid. In turn, this results in the formation of a dense monolayer of well-distributed and proliferated osteoblast cells along the fibers. CaCO3-mineralized PHBV surfaces had a higher osteoblast cell adhesion and proliferation assigned to a higher amount of CaCO3 on the surface compared to that on PHB scaffolds, as incurred from micro-computed tomography (μCT). Importantly, a cell viability study confirmed biocompatibility of all the scaffolds. Thus, hybrid biocomposites based on the piezoelectric PHB polymers represent an effective scaffold platform functionalized by an inorganic phase and stimulating the growth of the bone tissue.

Specifications for carbonate content quantification in recent marine sediments using Rock-Eval pyrolysis

The amount of CaCO3 in sediments and/or sedimentary rocks is usually measured by calcimetry while the nature of the carbonates is determined by X-ray diffraction. Recently, a carbonate recognition method based on the results of Rock-Eval pyrolysis was proposed in 2014 by Pillot et al. [1]. Rock-Eval pyrolysis is also widely used for the characterization of recent sediments. However, later in 2015 Baudin et al. [2] noticed that some of the characteristics of recent sediments tended to produce different results from those of more classical Rock-Eval analyses, causing bias in interpretations.In this study, the thermal stability of fossil and recent marine carbonated sediments was analyzed to identify differences in carbonate decomposition and to underline the importance of accounting for them in Rock-Eval analyses. The state of calcite preservation in recent marine sediments and sedimentary rocks at temperatures between 400 °C and 600 °C was characterized using different techniques (calcimetry, XRD, SEM imaging, etc.) for better interpretation of data obtained with Rock-Eval.Our results highlight a clear difference in the range of calcite decomposition temperatures during Rock-Eval analysis: between 550 °C and 775 °C for bulk clayey hemipelagic sediments versus 650 °C–840 °C after the same sediments were rinsed to get rid of the salt. During heating, water and hydroxide anions are released from clay minerals and react with salt crystals to form acid vapor. This acid vapor reacts with carbonates to produce CO2. The chemical decomposition of carbonate starts at temperatures that are lower than the typical range of decomposition temperatures, leading to overestimation of mineral carbon content (overestimation of the S5 peak) and to underestimation of organic carbon content (underestimation of the S4CO2 peak) with the Rock-Eval method. In the absence of clay minerals, such as in recent marine pure carbonate oozes, there is no evidence for this effect. It is therefore essential to prepare and rinse recent clay-rich carbonated sediment samples before Rock-Eval analysis to avoid misinterpretation.

Controlling the Distribution of Microbially Precipitated Calcium Carbonate in Radial Flow Environments.

Bacterially driven reactions such as ureolysis can induce calcium carbonate precipitation, a well-studied process called microbially induced calcium carbonate precipitation (MICP). MICP is of interest in subsurface applications such as sealing leaks around wells. For effective field deployment, it is important to study MICP under radial flow conditions, which are relevant to near-well environments. In this study, a laboratory-scale radial flow reactor of 23 cm diameter, with a 1 mm glass bead monolayer serving as a porous medium, was used to investigate the effects of fluid flow rates and calcium concentrations on the mass and distribution of MICP by the ureolytic bacterium Sporosarcina pasteurii. Experiments were performed at hydraulic residence times of 14, 7, and 3.5 min and calcium to urea molar ratios of 0.5:1, 1:1, and 2:1. The total amount of CaCO3 precipitated in the reactor increased with increasing residence time and with decreasing Ca2+ to urea molar ratios. Increased bacterial attachment and increased CaCO3 precipitation were observed with distance from the center inlet of the reactor in all experiments. More uniform calcium distribution was achieved at lower flow rates. The relationship between reaction and transport rate (i.e., the Damköhler number) is identified as a useful parameter for the prediction of MICP in radial flow environments.

Effect of Morphology of Calcium Carbonate on Toughness Behavior and Thermal Stability of Epoxy-Based Composites

In this study, the modification of an epoxy matrix with different amounts of cube-like and rod-like CaCO3 nanoparticles was investigated. The effects of variations in the morphology of CaCO3 on the mechanical properties and thermal stability of the CaCO3/epoxy composites were studied. The rod-like CaCO3/epoxy composites (EP-rod) showed a higher degradation temperature (4.5 °C) than neat epoxy. The results showed that the mechanical properties, such as the flexural strength, flexural modulus, and fracture toughness of the epoxy composites with CaCO3 were enhanced by the addition of cube-like and rod-like CaCO3 nanoparticles. Moreover, the mechanical properties of the composites were enhanced by increasing the amount of CaCO3 added but decreased when the filler content reached 2%. The fracture toughness Kic and fracture energy release rate Gic of cube-like and rod-like CaCO3/epoxy composites (0.85/0.74 MPa m1/2 and 318.7/229.5 J m−2, respectively) is higher than the neat epoxy (0.52 MPa m1/2 and 120.48 J m−2).

Thermal behaviors of a porous calcium silicate material prepared from coal-bearing strata kaolinite

The thermal behaviors of a porous calcium silicate (PCS) material prepared from coal-bearing strata kaolinite were investigated by thermogravimetry and derivative thermogravimetry (TG–DTG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, and Brunauer–Emmett–Teller method. The XRD results showed that the PCS was determined as calcium silicate hydrates (C–S–H) and a small amount of CaCO3, which transformed to an orderly crystal structure of wollastonite approximately at 700 °C. The TG–DTG results indicated that the dehydration was observed until 300 °C and the dehydroxylation presented at 728 °C. The PCS exhibited a large number of pores with a fibrous flake network structure, which disappeared at 800 °C. The BET data showed that the specific surface area of material decreased as the temperature increased. The high-temperature phase transformation of PCS underwent the following transformation: active calcium silicate → dehydrated calcium silicate → dehydroxylated calcium silicate → wollastonite.

Experimental Study on the Fine-Grained Uranium Tailings Reinforced by MICP

Sporosarcina Pasteurii was chosen for the experiment to study the effect and mechanism of fine-grained uranium tailings reinforced by MICP. The biochemical characteristics of strains and microbial immobilization in uranium tailings were analyzed. The results showed that the CaCO3 production rate is positively correlated with the physiological activity of Sporosarcina Pasteurii and the concentration of calcium sources, and the higher the solution concentration of CaCl2, the lower the discharge rate of bacterial liquid from the sand column, but high concentration of CaCl2 solution will affect the uniform distribution and migration of bacteria in the uranium tailings. After 16 days, the direct shear was used to test the reinforcement effects of fine-grained uranium tailings by MICP. The cohesive force and the internal friction angle of fine-grained uranium tailings were increased by 140.1% and 46.7%. The production amount of CaCO3 is 138.89 kg/m3. The results showed that the MICP-reinforced technology can effectively improve the shear strength of the uranium tailings, and the experiment provides a new method for the reinforcement of the fine-grained uranium tailings dam.

Single and competitive adsorption isotherms of some heavy metals onto a light textured calcareous soil amended with agricultural wastes-biochars

ABSTRACTThis study investigated the adsorption behavior of selected heavy metals (Pb, Cu, and Ni) under single and multi-metal conditions by a light textured calcareous soil amended with plant residue biochars (corn straw, wheat straw, rice husk and licorice root pulp each at 3% w/w). The Freundlich isotherm best described the heavy metal adsorption suggesting multilayer adsorption. For all treatments under both adsorption conditions, the heavy metal adsorption capacity followed the order of Pb > Cu > Ni, which was associated with the hydrolysis constant, ionic radius, and electronegativity of these metals. Simultaneous presence of multiple metals decreased the adsorption capacity for each metal and the sequence was in the order of Ni > Pb > Cu. The corn straw biochar (CSB) had the highest adsorption capacity (Freundlich Kf (mg g−1) for Ni = 0.23, Cu = 1.41 and Pb = 2.73) and medium distribution coefficient (Kd medium(L kg−1) for Ni = 59.30, Cu = 1961.00 and Pb = 2602.00), indicating the CSB is the best treatment for stabilization of heavy metals in the soil. This was associated with the chemical characteristics of the CSB (high amounts of CaCO3 and P) and the greatest increase in soil pH value.

Fabrication of aluminum foams by using CaCO3 foaming agent

Since TiH2 is widely used as a foaming agent to generate gas bubbles in the melt, but it has some disadvantages and difficulties that studying another foaming agent instead TiH2 is of great interest. In this work, pure aluminum foams were produced by a foam melting method using CaCO3 as a foaming agent. In this regard, the process parameters were optimized to fabricate the homogeneous foam based on its structure. The effect of Ca addition on the density and porosity of foams has been investigated. In addition, the influence of CaCO3 as a foaming agent and stirring speed on density and porosity has been studied. The mechanical response of the foam obtained at optimum condition was evaluated by uniaxial compression test. The results showed that by adding 1.5 wt% Ca, a uniform structure and an optimum viscosity can be achieved with a maximum porosity of 70% and minimum density of 0.8 g cm−3. Moreover, it was found that by increasing the amount of CaCO3 up to 2 wt% and increasing of the stirring speed up to 2000 rpm, the porosity increased and the size of cells decreased. The optimum values for Ca amount, CaCO3 value, and stirring speed was found as 1.5 wt%, 1 wt%, and 1400 rpm, respectively. The produced foam at optimum condition had a density of 0.9 g cm−3 with spherical cell morphology, and revealed compressive strength of 8 MPa and energy absorption of 1.12 kJ. It was successfully concluded that CaCO3 can be used as a foaming agent instead of TiH2 to produce aluminum foams in order to reduce the cost of manufacture, density of foam, and generation of harmful and H2 gas.