Production Of Carbonate Research Articles

Soil Nutrient Retention and pH Buffering Capacity Are Enhanced by Calciprill and Sodium Silicate

In the tropics, warm temperatures and high rainfall contribute to acidic soil formation because of the significant leaching of base cations (K+, Ca2+, Mg2+, and Na+), followed by the replacement of the base cations with Al3+, Fe2+, and H+ ions at the soil adsorption sites. The pH buffering capacity of highly weathered acid soils is generally low because of their low pH which negatively impacts soil and crop productivity. Thus, there is a need to amend these soils with the right amount of inorganic liming materials which have relatively high neutralizing values and reactivity to overcome the aforementioned problems. Soil leaching and the pH buffering capacity studies were conducted to determine whether the co-application or co-amendment of a calcium carbonate product (Calciprill) and sodium silicate can improve soil nutrient retention and pH buffering capacity of the Bekenu series (Typic Paleudults). A 30 day soil leaching experiment was carried out using a completely randomized design with 16 treatments and 3 replications after which the leached soil samples were used for a pH buffering capacity study. The Calciprill and sodium silicate treatments significantly improved soil pH, exchangeable NH4+, available P, exchangeable base cations, Effective Cation Exchange Capacity (ECEC), and pH buffering capacity in comparison with the untreated soil. The improvements were attributed to the alkalinity of Calciprill and sodium silicate due to their high inherent K+, Ca2+, Mg2+, and Na+ contents. The neutralizing effects of the amendments impeded the hydrolysis of Al3+ (96.5%), Fe2+ (70.4%), and Mn2+ (25.3%) ions resulting in fewer H+ ions being produced. The co-application of Calciprill and sodium silicate reduced the leaching of Ca2+ (58.7%) and NO3− (74.8%) from the amended soils. This was due to the ability of sodium silicate to reduce soil permeability and protect the Calciprill and available NO3− from being leached. This also improved the longevity of Calciprill to enhance the soil pH buffering capacity. However, the amounts of NH4+, P, and base cations leached from the amended soils were higher compared with the un-amended soils. This was due to the high solubility of sodium silicate. The most suitable combination amendment was 7.01 g Calciprill and 9.26 g sodium silicate (C2S5) per kilogram soil. It is possible for farmers to adopt the combined use Calciprill and sodium silicate to regulate soil nutrient retention and improve the soil pH buffering capacity of highly weathered acidic soils. This will enhance soil and crop productivity.

Trends in Carbon Dioxide Capture and Conversion

Carbon dioxide capture and conversion is gaining increased attention due to climate change issues. The direct air capture of CO2 may be accomplished with functionalized adsorbents that can work at atmospheric pressure and room temperature. The captured CO2 may be converted into fuels and chemicals. CO2 can be hydrogenated to methanol, which is a commodity used in the fuel and chemical sectors, over Cu.ZnO-based catalysts. Improvements to catalyst formulation are still needed to operate at lower temperatures. Dimethyl ether can be directly produced from CO2 and H2 through the use of bifunctional catalysts. Organic carbonates appear as promising compounds of wide use in the chemical sector. Cyclic carbonates may be produced from CO2 and epoxides with the use of Lewis acids catalyst. Zeolites impregnated with metal halides appear to be a promising system to achieve high conversion and selectivity. Aliphatic organic carbonates can be produced from CO2 and alcohols, but the reaction presents thermodynamic limitations. The role of oxygen vacancies on CeO2-based catalysts and use of dehydrating agents in the production of dimethyl carbonate will be discussed in this account. The challenges and future perspectives for the direct air CO2 capture and conversion into fuels and chemicals will be addressed.

Core-shell TiO2-x-CuyO microspheres for photogeneration of cyclic carbonates under simulated sunlight.

Propylene carbonates are important organic solvents and feedstocks for different applications, including synthesis of polymers and Li-batteries. The generation of propylene carbonate utilising anthropogenic CO2 and renewable solar energy offers an alternative sustainable process with a closed loop carbon cycle. The development of microstructured photocatalysts with desired properties, including high degree of product selectivity, wide range of optical properties, and maximised conversion yield, plays an important role for effective production of propylene carbonate from CO2. A hierachical hollow core with a double shell of TiO2-x-Cu2O-CuO was fabricated using the versatile solvothermal-microwave synthesis method. The fabricated sample revealed effective cascading of photogenerated electrons and holes that promoted the conversion of propylene carbonate (i.e., 1.6 wt%) under 1 Sun irradiation.

REUSE OF WASTE CRAB SHELLS FOR SYNTHESIS OF CALCIUM CARBONATE AS A CANDIDATE BIOMATERIAL

The crab shell (Portunus Pelagicus) wastes are constituted of major calcium carbonate (account for 70 wt. %) and have the potential to reuse as a starting biomaterial for precipitated calcium carbonate (PCC) products. The purpose of the present work was to synthesize PCC powder using crab shells based on the gas-solid-liquid carbonation route. In this experiment, crab shell powder was prepared by washing, drying, and subsequent grinding. The resulting powder was then calcined at 900 ℃ for 5 h before being used for the synthesis of the PCC product. Later, the calcined crab shell powder was dissolved with 2M HNO3 solution in a glass beaker with the pH solution of 12 set up by adding NH4OH. The solution was subsequently stirred magnetically for 30 min. The carbonation process ended when the PCC solid was obtained at a pH of 7. The crab shell powder, crab shell powder after calcination, and the obtained PCC solid were then characterized using XRD, SEM-EDX, and FTIR methods, respectively. The resulting PCC product has been shown to have calcium carbonate with the major vaterite phase. This experimental work demonstrated the potential application of crab shells for a low-cost biomaterial of future medical applications.

Ti and Zr amino-tris(phenolate) catalysts for the synthesis of cyclic carbonates from CO2 and epoxides

Herein, we report the application of four amino-tris(phenolate)-based metal complexes incorporating Ti(IV) or Zr(IV) centres (2a-3b) as homogeneous catalysts for the conversion of CO2 and epoxides into cyclic carbonates. The four complexes were synthesised, characterised and then evaluated in combination with tetrabutylammonium iodide, bromide or chloride as binary catalytic systems for the reaction of CO2 with 1,2-epoxyhexane as epoxide substrate at 12 bar CO2 pressure and 90 °C for 2 h. The catalytic systems comprising the two Ti(IV) complexes (2a and 2b) showed similar performance. One notable exception was the catalytic system consisting of titanium complex 2b, bearing an axial Cl-ligand, and tetrabutylammonium chloride, which displayed higher catalytic activity compared to other titanium-based systems. Even higher activity was achieved with Zr(IV) complex 3a, bearing an axial isopropoxide ligand, which reached turnover numbers (TONmetal) up to 1920 for the reaction of CO2 with 1,2-epoxyhexane at 12 bar CO2 pressure and 90 °C for 2 h. This performance is comparable with that of state-of-the-art catalysts for this reaction. The catalytic system consisting of complex 3a and tetrabutylammonium bromide was explored further by investigating its applicability with a broad substrate scope, achieving quantitative conversion of several epoxides with CO2 into cyclic carbonate products at 90 °C and 12 bar CO2 pressure for 18 h. The selectivity towards the cyclic carbonate products was ≥ 98% for all studied terminal epoxides and ≥ 80% for all examined cyclohexene-type epoxides.

Comprehensive investigation on the gasification reactivity of pyrolysis residue derived from Ca-rich petrochemical sludge: Roles of microstructure characteristics and calcium evolution

Pyrolysis-gasification coupling process is an effective technology that can realize the thorough reutilization and clean disposal of petrochemical sludge. However, pyrolysis residue of petrochemical sludge (PRPS) produced at different temperatures possesses obviously different structure properties, which profoundly impacts the subsequent gasification. This study reveals the effect of pyrolysis degree of PRPS on the CO2 gasification reactivity by evaluating the micromorphology, pore property, existed form of calcium mineral and carbon structural characteristics. Results demonstrate that micromorphology development of the PRPSs with diverse pyrolysis degree (PRPS prepared at 500–900 °C) has three main stages, namely, the emergence of macropores and fissures (500–600 °C), the pore development (700–800 °C), and the pore jam (900 °C). The optimal PRPS was obtained at 800 °C-pyrolysis (800-PRPS) as the maximal specific surface area and desorption pores volume were observed. In addition, Raman analysis indicated that the 800-PRPS has the best carbon activity as well. By further increasing pyrolysis temperature to 900 °C, the carbon disordering, defect, and active sites of the PRPS decreased. Moreover, results of non-isothermal PRPS-CO2 reaction indicated that the basic calcium compound carbonation, gasification, calcium carbonate decomposition regimes were involved. Compared with 800–900 PRPSs, 500–700 PRPSs were more vulnerable in the lower gasification temperature owing to the more char matrix remain. In addition, owing to the occurrence of the carbonation reaction, the calcium carbonate product layer was formed and might affect the early-age gasification.

Production of Mn3O4 nanoparticles from a manganiferous iron ore via reductive leaching, precipitation, and calcination

The synthesis of Mn3O4 nanoparticles from a manganiferous iron ore through reductive leaching, precipitation, and calcination was investigated. The reductive leaching results showed that Mn (99.9%) was almost completely extracted into the leaching solution along with a substantial amount of Mg (99.9%), Al (99.5%), Ca (80%), and Fe (22.9%) under the following conditions: 30 g/L tartaric acid as a reducing agent, 1 M HCl solution, leaching temperature of 90 °C, and leaching duration of 3 h. In the first precipitation step, Fe and Al were expelled from the pregnant leach solution by the addition of NaOH prior to conducting the precipitation experiments for the production of manganese carbonate (MnCO3) particles from the purified solution. In the second precipitation step, MnCO3 particles were produced using sodium carbonate (Na2CO3) as the precipitating agent. The effects of parameters such as reaction temperature, Na2CO3 concentration, and experimental duration were investigated using the Taguchi approach. Manganse(II) was precipitated in the form of MnCO3 particles (97.4%) under the following conditions: a temperature of 30 °C, Na2CO3 concentration of 0.014 mol/L, and duration of 30 min. The precipitate was observed to have a structure similar to that of rhodochrosite (MnCO3). Thermogravimetric/differential thermal analyses were subsequently performed in three different atmospheres (air, oxygen, and nitrogen) to select a suitable atmosphere for calcination. The experimental results indicated the formation of hausmannite (Mn3O4) with a purity of 97.5% Mn3O4, 0.42% MgO, 1.66% CaO, and 0.34% FeO. The specific surface area, particle size, Curie temperature, magnetisation, coercivity, and remanence ratio of the final product obtained via 3 h of calcination at 350 °C were estimated to be 133.3 m2/g, <142.2 nm, 56 K, 10.10 Am2/kg, 0.35 T, and 0.19, respectively. The characterisation results revealed the excellent low-temperature ferromagnetic properties of the produced Mn3O4 nanoparticles.

Application of fungal copper carbonate nanoparticles as environmental catalysts: organic dye degradation and chromate removal

Biomineralization is a ubiquitous process in organisms to produce biominerals, and a wide range of metallic nanoscale minerals can be produced as a consequence of the interactions of micro-organisms with metals and minerals. Copper-bearing nanoparticles produced by biomineralization mechanisms have a variety of applications due to their remarkable catalytic efficiency, antibacterial properties and low production cost. In this study, we demonstrate the biotechnological potential of copper carbonate nanoparticles (CuNPs) synthesized using a carbonate-enriched biomass-free ureolytic fungal spent culture supernatant. The efficiency of the CuNPs in pollutant remediation was investigated using a dye (methyl red) and a toxic metal oxyanion, chromate Cr(VI). The biogenic CuNPs exhibited excellent catalytic properties in a Fenton-like reaction to degrade methyl red, and efficiently removed Cr(VI) from solution due to both adsorption and reduction of Cr(VI). X-ray photoelectron spectroscopy (XPS) identified the oxidation of reducing Cu species of the CuNPs during the reaction with Cr(VI). This work shows that urease-positive fungi can play an important role not only in the biorecovery of metals through the production of insoluble nanoscale carbonates, but also provides novel and simple strategies for the preparation of sustainable nanomineral products with catalytic properties applicable to the bioremediation of organic and metallic pollutants, solely and in mixtures.

Reservoir Characteristics and Major Controlling Factors of the Cambrian Xixiangchi Formation, Central Sichuan Basin, Southwest China

AbstractThe Xixiangchi Formation is a significant replacement stratum for natural gas production of deep marine carbonate in the Sichuan basin, which is mainly composed of grain shoal. Basic charac...

Effect of Different CO2 Treatments on the Metal Leaching in Steel Slag Binders

Carbonation is an effective method to promote the quality of the steel slag binder. In this article, two carbonation approaches, namely hot-stage carbonation and accelerated carbonation, were employed to leach the metals, and the influence mechanism on the metal sequential leachability of the binders composed of 80 wt% of EAF slag incorporating 20 wt% of Portland cement (PC) was revealed. The carbonate products, microstructures, and chemical states were investigated, and the results indicated that chromium, vanadium, and titanium gradually transformed into inactive phases after two carbonation approaches, while zinc appeared the opposite trend. The sequential leachability of chromium declined with the increase of the carbonation efficiency, in which the exchangeable chromium decreased from 1.99 mg/kg in the A2A binder to below the detection limit in the A2C binder and C2C binder. Hot-stage carbonation treatment facilitated particle agglomeration, minerals remodeling, and calcite formation. The carbonation curing of the steel slag paste resulted in the formation of amorphous CaCO3, calcite crystalline and Si-bearing hydrates that covered the pores of the matrix, and silicate structure with a higher disorder. The hot-stage carbonation and accelerated carbonation curing methods were adopted to jointly prevent the leaching of harmful metals and facilitate promising high-volume steel slag-based binders with structural densification and CO2 storage.

Modeling and Parametric Investigation of Rotating Packed Bed Processes for CO2 Capture and Mineralisation

Rotating Packed Beds (RPB) are receiving increased attention in CO2 capture, due to their considerably lower volume compared to conventional packed-beds and their beneficial effects on process capital costs. As a result of these advantages, RPB have also been considered as a CO2 mineralisation option for the production of precipitated calcium carbonate (PCC). In the area of CO2 capture, the few model-based investigations employ either the two-film or Higbie’s penetration theory to model the gas-liquid mass transfer as the main driving force of the systems’ operation. In the area of PCC production, there is only one model type available that is based on the two-film theory. While the latter includes the limiting assumption of linear and steady-state mass transfer within the liquid film, Higbie’s theory is considerably closer to realistic operation due to the assumption of time-dependent and non-linear, gas-to-liquid mass transfer. Considering this significant advantage, this work proposes for the first time a model for RPB-based, PCC production using Higbie’s penetration theory. The model is first developed and validated considering solvent-based CO2 capture with monoethanolamine (MEA) solvent, taking advantage of the available experimental data in published literature. The model is then adapted to PCC production to perform a parametric investigation based on various performance indicators. Results indicate that the proposed model enables improved accuracy compared to the two film theory. Higher rotation speeds and liquid flowrates enable improved mass transfer, whereas PCC production can be achieved at lower energy consumption simultaneously with high CO2 capture efficiency.

Identification of Adsorbed Species and Surface Chemical State on Ag(111) in the Presence of Ethylene and Oxygen Studied with Infrared and X-ray Spectroscopies

Using a combination of two surface-sensitive spectroscopy techniques, the chemical state of the Ag(111) surface and the nature of the adsorbed species in the presence of ethylene and oxygen gases are identified. In the 10 mbar pressure range and 25–200 °C studied here, Ag(111) remains largely metallic even in O2-rich conditions. The only adsorbed molecular species with a low but discernible coverage is surface carbonate, which forms due to further oxidation of produced CO2, in a similar manner to its formation in ambient air on Ag surfaces. Its formation is also pressure-dependent, for instance, it is not observed when the total pressure is in the 1 mbar pressure range. Production of carbonate, along with carbon dioxide and water vapor as the main gas-phase products, suggests that an unpromoted Ag(111) surface catalyzes mainly the undesired full oxidation reaction.

Using hazardous barium slag as a novel admixture for alkali activated slag cement

Barium slag (BS) is a hazardous industrial solid waste formed during the production of barium carbonate. The accumulated stock of BS in China has exceeded 10 million tons, which urgently needs to be recycled in an efficient and sustainable way. BS contains a lot of soluble Ba2+ with a leaching concentration up to 2000 mg/L in water. Meanwhile, Ba2+ is an alkali-earth metal which can activate ground granulated blast furnace slag (GGBFS). This paper explores the possibility of incorporation BS as an admixture for alkali activated slag (AAS) cement. The mechanical property and microstructure evolution of AAS pastes with addition of BS are investigated in comparison with pure AAS paste. The results indicate that the addition of BS could significantly enhance mechanical strength of AAS paste, attributing to the increased hydration degree and the formation of dense pore structure. In addition, the leaching concentration of Na+ shows a significant decline by incorporation of BS in AAS paste, associated with the changed composition of hydration products. Therefore, BS is a promising admixture for AAS cement and holds great potential for promotion and application.

Fatty alcohol/water reaction-separation platform to produce propylene carbonate from captured CO2 using a hydrophobic ionic liquid

• A novel and sustainable biphasic platform to CO 2 conversion and catalyst regeneration is created. • COSMO-RS predicted a biphasic system (fatty alcohol/water) to separate propylene carbonate and catalyst. • Fatty alcohol media synergistically improves catalytic activity enhancing CO 2 conversion from 68 to 86%. • Five consecutive reaction + separation cycles validate the stability of the catalytic/separation system. • Open possibilities to integrate chemical capture and conversion with a bifunctional chemical absorbent-catalyst. The combined use of a hydrophobic ionic liquid catalyst and a fatty alcohol is presented to synergistically improve cycloaddition reaction of CO 2 to epoxides producing cyclic carbonates and envision catalyst recovery by cyclic carbonate removal using water as extracting solvent. This approach is described for the production of propylene carbonate using trihexyl(tetradecyl)phosphonium 2-cyanopyrrolide catalyst -which chemically captures CO 2 reactant- and 1-decanol/water mixture as extracting solvent. The novel use of fatty alcohols on CO 2 cycloaddition reaction not only permits the effective separation of the catalyst and the product purification, but also improves the CO 2 conversion in the reactor, and opens the challenge of process intensification by integrated CO 2 capture and conversion.

Reef accumulation is decoupled from recent degradation in the central and southern Red Sea

Reefs are biogenic structures that result in three-dimensional accumulations of calcium carbonate. Over geological timescales, a positive balance between the production and accumulation of calcium carbonate versus erosional and off-reef transport processes maintains positive net accretion on reefs. Yet, how ecological processes occurring over decadal timescales translate to the accumulation of geological structures is poorly understood, in part due to a lack of studies with detailed time-constrained chronologies of reef accretion over decades to centuries. Here, we combined ecological surveys of living reefs with palaeoecological reconstructions and high-precision radiometric (U-Th) age-dating of fossil reefs represented in both reef sediment cores and surficial dead in situ corals, to reconstruct the history of community composition and carbonate accumulation across the central and southern Saudi Arabian Red Sea throughout the late Holocene. We found that reefs were primarily comprised of thermally tolerant massive Porites colonies, creating a consolidated coral framework, with unconsolidated branching coral rubble accumulating among massive corals on shallow (5–8 m depth) exposed (windward), and gently sloping reef slopes. These unconsolidated reef rubble fields were formed primarily from ex situ Acropora and Pocillopora coral fragments, infilled post deposition within a sedimentary matrix. Bayesian age-depth models revealed a process of punctuated deposition of post-mortem coral fragments transported from adjacent reef environments. That a large portion of Saudi Arabian Red Sea reef slopes is driven by allochthonous deposition (transportation) has important implications for modeling carbonate budgets and reef growth. In addition, a multi-decadal lag exists between the time of death for branching in situ coral and incorporation into the unconsolidated reef rubble. This indicates that recent climate related degradation in the 21st century has not had an immediately negative effect on reef building processes affecting a large portion of the reef area in the Saudi Arabian Red Sea.

First-principles Study of Surface and Solution Model of Li-O2 Reactions in Lithium-air Batteries

Lithium-air batteries are promising competitors to replace traditional lithium ion batteries due to the extremely high theoretical energy density. However, the development is limited by the cathode properties, which should be stable, conductive, and reactive in oxygen-rich environments. Here, we employ two different systems of 1) Co3O4-based cathode and vacuum center, and 2) Co3O4-based cathode and DMSO electrolyte to study the mechanisms of Li-air discharge and charge reactions. The structure, stability, and electronic properties of different surface reconstructions of the Co3O4 (100) facet are investigated by static DFT calculations and ab initio Grand Canonical Monte Carlo method. The Co3O4 (100)-O (Oxidized) surface is found as the most stable one at standard conditions. In addition, the mechanisms of multi-step reactions between Li+/e- and O2 are studied, where lithium suboxide products (Li2O2 or Li3O2) are formed on the different Co3O4 (100) terminations. Finally, we also simulate reaction pathways involving only the surface (“surface model”) as well as pathways involving DMSO-based electrolyte (“solution model”) for the discharging/charging process on the Co3O4 (100) surfaces. In the co-designed system of Co3O4 (100)-O cathode and DMSO electrolyte, the solution model pathway for Li-O2 discharge reaction is energetically favorable, providing a low constant overpotential of 0.17 V for the toroid Li2O2 formation. However, the discharge overpotential will be gradually increased from 0.17 V to 0.33 V in the surface model after the cathode surface being fully covered. The charge overpotential we found at the interface of DMSO electrolyte and Co3O4 (100) surface can be low to 0 V but with slow decomposition rate. Instead, 0.36 V overpotential is always required to rapidly decompose the Li2O2 from itself surface in both solution and surface model of charging process. Moreover, a even higher charge overpotential (1 V) is always observed in experiments, which is due to the voltage demand for other side reactions (including Li2CO3 decomposition). In this aspect, increasing the stability of the aprotic electrolytes (including DMSO) is a key technical issue to prohibit the formation of side carbonate products during operation. Our results help shed fundamental insight on the electrolyte assisted Li-O2 reactions on the transition metal oxides and can potentially lead to a new nanomaterials design dimension towards Lithium batteries.

Sustainable Synthesis of Cyclic Carbonates from Terminal Epoxides by a Highly Efficient CaI2/1,3-Bis[tris(hydroxymethyl)-methylamino]-propane Catalyst.

The nonstopping increment of atmospheric carbon dioxide (CO2) concentration keeps harming the environment and human life. The traditional concept of carbon capture and storage (CCS) is no longer sufficient and has already been corrected to carbon capture, utilization, and storage (CCUS). CCUS involves significant CO2 utilization, such as cyclic carbonate formation, for its cost effectiveness, less toxicity, and abundant C1 synthon in organic synthesis. However, the high thermodynamic and kinetic stability of CO2 limits its applications. Herein, we report a mild, efficient, and practical catalyst based on abundant, nontoxic CaI2 in conjunction with biocompatible ligand 1,3-bis[tris(hydroxymethyl)-methylamino]-propane (BTP) for CO2 fixation under atmospheric pressure with terminal epoxides to give the cyclic carbonates. The Job plot detected the 1:1 Ca2+/BTP binding stoichiometry. Furthermore, formation of a single crystal of the 1:1 Ca2+/BTP complex was confirmed by single-crystal X-ray crystallography. The bis(cyclic carbonate) products exhibit potentials for components in the non-isocyanate polyurethanes (NIPUs) process. Notably, this protocol shows attractive recyclability and reusability.

Biocementation effect of high-efficiency urease-producing bacteria mutagenized from indigenous bacteria

A strain of urease-producing bacteria (UPB) was isolated from soil collected from the south of China, and a mutated strain with a high urease-producing efficiency was obtained through ultraviolet mutagenesis technology. The morphological characteristics of the isolated strain were examined under a transmission electron microscope. Numerous controlled trials were conducted to determine the optimal culture conditions of the mutated strain. Biocemented treatments were conducted on tailing sand with the mutated strain, and the uniaxial compressive strength of the biocemented samples was measured. SEM imaging and EDS were used to identify the type and morphological characteristics of calcium carbonate formed during biocementation. Results showed that the urease activity of the mutated strain was the highest at pH 9, and the optimum growth temperature was between 25°C and 35°C, which is similar to climate conditions in southern China. The urease activity of the mutated strain and the production of calcium carbonate were 2.18 and 1.16 times that of commercially used Sporosarcina pasteurii, respectively. The SEM images indicated that crystals with an unusual shape, such as long grains and broccoli shape, formed in the biocemented tailing sand. Raman test revealed that they were calcite. Therefore, using indigenous bacteria is practical and feasible, and ultraviolet mutagenesis technology has great potential for application in the improvement of the performance of isolated strains and their biocementation effect.

Multiple-phase enzyme-induced carbonate precipitation (EICP) method for soil improvement

Enzyme-induced carbonate precipitation (EICP) is a potential method to improve the mechanical properties of granular soil. The one-phase premixed percolation method using purified urease enzyme is widely adopted for in-situ EICP treatment currently, but it is expensive and uses a relatively large amount of urease. This paper proposes a multiple-phase method consisting of a percolation of premixed soybean crude urease and cementation solution followed by several percolations of cementation solution in one cycle of biocementation. The utilizing rate of urease was increased by at least four times for the production of precipitated carbonate compared with the one-phase method. The proposed method also weakened the clogging of carbonate precipitation, thus bringing out a relatively uniform EICP treatment. After four cycles of biocementation (each cycle included five applications of cementation solution), the unconfined compressive strength of EICP-treated ASTM C778-graded sand exceeded 10 MPa with a CaCO3 content of ~20%.

Investigation and characterization of high purity and nano-sized SrCO3 production by mechanochemical synthesis process

In this study, the production of strontium carbonate (SrCO3) from concentrated celestite ore (SrSO4) by mechanochemical synthesis process was investigated. Different proportions of ammonium carbonate ((NH4)2CO3) were used to convert the celestite ore to strontium carbonate. The effects of SrSO4: (NH4)2CO3 stoichiometric ratio and synthesis time on the purity of the produced strontium carbonate were examined. In the mechanochemical synthesis experiments, the stoichiometric ratios of 1:1, 1:1.5 and, 1:2 between SrSO4 and (NH4)2CO3, and synthesis times of 10, 100, and 200 min were applied. Impurities and contaminations in concentrated celestite ore were removed by acid leaching and calcination processes. DTA, TGA, XRD, SEM, EDX, TEM, and FT-IR analyzes were performed throughout the strontium carbonate production process. Experimental studies have revealed that the 1:2 stoichiometric ratio between SrSO4 and (NH4)2CO3 and 200 min synthesis time are the most suitable process parameters for the production of high purity strontium carbonate.