Preparation of high-purity fluorite and nanoscale calcium carbonate from low-grade fluorite

Flotation separation of calcite from fluorite is a challenge on low-grade fluorite flotation that limits the recovery and purity of fluorite concentrate.A new acid leaching–flotation process for fluorite is proposed in this work.This innovative process raised the fluor-ite’s grade to 97.26wt%while producing nanoscale calcium carbonate from its leachate,which contained plenty of calcium ions.On the production of nanoscale calcium carbonate,the impacts of concentration,temperature,and titration rate were examined.By modifying the process conditions and utilizing crystal conditioning agents,calcite-type and amorphous calcium carbonates with corresponding particle sizes of 1.823 and 1.511μm were produced.The influence of the impurity ions Mn^(2+),Mg^(2+),and Fe^(3+)was demonstrated to reduce the particle size of nanoscale calcium carbonate and make crystal shape easier to manage in the fluorite leach solution system compared with the calcium chloride solution.The combination of the acid leaching–flotation process and the nanoscale calcium carbonate preparation method improved the grade of fluorite while recovering calcite resources,thus presenting a novel idea for the effective and clean usage of low-quality fluorite resources with embedded microfine particles.

Geotechnical investigation of low-plasticity organic soil treated with nano-calcium carbonate

Soil stabilization using nanomaterials is an emerging research area although,to date,its investigation has mostly been laboratory-based and therefore requires extensive study for transfer to practical field ap-plications.The present study advocates nano-calcium carbonate(NCC)material,a relatively unexplored nanomaterial additive,for stabilization of low-plasticity fine-grained soil having moderate organic content.The plasticity index,compaction,unconfined compressive strength(UCS),compressibility and permeability characteristics of the 0.2%,0.4%,0.6%and 0.8%NCC-treated soil,and untreated soil(as control),were determined,including investigations of the effect of up to 90-d curing on the UCS and permeability properties.In terms of UCS improvement,0.4%NCC addition was identified as the optimum dosage,mobilizing a UCS at 90-d curing of almost twice that for the untreated soil.For treated soil,particle aggregation arising from NCC addition initially produced an increase in the permeability coef-ficient,but its magnitude decreased for increased curing owing to calcium silicate hydrate(CSH)gel formation,although still remaining higher compared to the untreated soil for all dosages and curing periods investigated.Compression index decreased for all NCC-treated soil investigated.SEM micro-graphs indicated the presence of gel patches along with particle aggregation.X-ray diffraction(XRD)results showed the presence of hydration products,such as CSH.Significant increases in UCS are initially attributed to void filling and then because of CSH gel formation with increased curing.

Calcium titanate corrosion inhibitor enabling carbon as inert anode for oxygen evolution in molten chlorides

The corrosion inhibition efficacy of titanate(CaTiO_(3))for carbon anodes in molten salts was investigated through various analytical techniques,including linear sweep voltammetry,X-ray diffraction,scanning electron microscopy,and energy dispersion spectroscopy.The results demonstrate that the addition of CaTiO_(3)corrosion inhibitor efficiently passivates the carbon anode and leads to the formation of a dense CaTiO_(3)layer during the electrolysis process in molten CaCl_(2)-CaO.Subsequently,the passivated carbon anode effectively undergoes the oxygen evolution reaction,with an optimal current density for passivation identified at 400 m A/cm~2.Comprehensive investigations,including CaTiO_(3)solubility tests in molten CaCl_(2)-CaO and numerical modeling of the stability of complex ionic structures,provide compelling evidence supporting“complexation-precipitation”passivation mechanism.This mechanism involves the initial formation of a complex containing TiO_(2)·nCaO by CaTiO_(3)and CaO,which subsequently decomposes to yield CaTiO_(3),firmly coating the surface of the carbon anode.In practical applications,the integration of CaTiO_(3)corrosion inhibitor with the carbon anode leads to the successful preparation of the FeCoNiCrMn high-entropy alloy without carbon contamination in the molten CaCl_(2)-Ca O.

The Influence of Carbon Nanotubes and Nano-Silica Fume on Enhancing the Damping and Mechanical Properties of Cement-Based Materials

This paper conducted experimental studies on the damping and mechanical properties of carbon nanotube-nanosilica-cement composite materials with different carbon nanotube contents. The damping and mechanical properties enhancement mechanisms were analyzed and compared through the porosity structure test, XRD analysis, and scanning electron microscope observation. The results show that the introduction of nanosilica significantly improves the dispersion of carbon nanotubes in the cement matrix. At the same time, the addition of nanosilica not only effectively reduces the critical pore size and average pore size of the cement composite material, but also exhibits good synergistic effects with carbon nanotubes, which can significantly optimize the pore structure. Finally, a rationalization suggestion for the co-doping of nanosilica and carbon nanotubes was given to achieve a significant increase in the flexural strength, compressive strength and loss factor of cement-based materials.

Crystalline-magnetism action in biomimetic mineralization of calcium carbonate

The influence of minor environmental factors,such as the geomagnetic field,on the biomineralization of nacres,is often ignored but a great deal of research has confirmed its important role in the normal mineralization of calcium carbonate.Although the geomagnetic field is weak,its cumulative effects need to be considered given that the biomineralization process can take years.Accordingly,the authors of this paper have investigated the effects of weak magnetic fields(25 Gs or 50 Gs)on calcium carbonate mineralization and analyzed the mechanism involved.The results show that even a weak magnetic field conduces to the formation of vaterite or aragonite,in the induction order of precursor→vaterite→aragonite.The stronger the magnetic field and the longer the time,the more obvious the induction effect.The effect of a magnetic field is strongest in the aging stage and weakest in the solution stage.Inductions by egg-white protein and by a magnetic field inhibit each other,but they both restrict particle growth.These findings highlight the importance of minor environmental factors for biomineralization and can serve as a reference for biomimetic preparation of a CaCO_(3)nacre-like structure and for anti-scale technology for circulating cooling water.

A Primary Study on Mechanical Properties of Heat-Treated Wood via in-situ Synthesis of Calcium Carbonate

This study aims to improve the value of fast-growing wood and extend the heat-treated wood utilization using inorganic calcium carbonate(CaCO_(3))crystals via an in-situ synthesis method.CaCl_(2)and Na 2CO_(3)solutions with a concentration ratio of 1:1 were successively introduced into the thermally modified poplar wood obtained by steam heat treatment(HT)at 200℃for 1.5 and 3 h,resulting in the in-situ synthesis of CaCO_(3)crystals inside the heat-treated wood.The filling effect was best at the concentration of 1.2 mol/L.CaCO_(3)was uniformly distributed in the cell cavities of the heat-treated wood,and some of the crystals were embedded in the fissures of the wood cell walls.The morphology of CaCO_(3)crystals was mainly spherical and rhombic polyhedral.Three main types of CaCO_(3)crystals were calcite,vaterite,and aragonite.The HT of poplar wood at 200℃resulted in degrading the chemical components of the wood cell wall.This degradation led to reduced wood mechanical properties,including the surface hardness(HD),modulus of rupture(MOR),and modulus of elasticity(MOE).After CaCO_(3)was in-situ synthesized in the heat-treated wood,the HD increased by 18.36%and 16.35%,and MOR increased by 14.64%and 8.89%,respectively.Because of the CaCO_(3)synthesization,the char residue of the 200℃heat-treated wood samples increased by 9.31%and the maximum weight loss rate decreased by 19.80%,indicating that the filling with CaCO_(3)cannot only improve the mechanical properties of the heat-treated wood but also effectively enhance its thermal stability.

Optimization of growth medium for microbially induced calcium carbonate precipitation(MICP) treatment of desert sand

Wind-induced sand erosion is a natural process, and can have several negative impacts on human health, environment, and economy. To mitigate the wind-induced sand erosion, an environmental friendly technique that helps to bind soil particles is desirable. The microbially induced calcium carbonate precipitation(MICP) treatment has lately become renowned and a viable alternative to enhance the binding of sand particles(especially against wind erosion). The efficiency of Sporosarcina pasteurii bacteria in inducing calcite formation can be influenced by various factors, including the type of growth media used for bacterial culture. Most of the studies have mainly validated the efficiency of S. pasteurii bacteria usually under single growth media for the MICP treatment. However, the efficiency of S. pasteurii under different growth media on calcite formation is rarely explored. The current study explores the effect of S.pasteurii bacteria on calcite formation under the presence of three different growth media, namely,molasses(MS), tryptic soy broth(TB), and nutrient broth(NB). The three growth media have been applied in the laboratory with and without bacterial solution(control samples). Altered cementation media concentrations(0.5 and 1.0 M) with different pore volumes(PVs), namely, 0.25, 0.50, and 1.00 PV were used in sand-filled tubes for 7 and 14 treatment cycles(1 cycle=24 h). The pH and EC were measured for 12-h period in every 2 h interval, to monitor values at the time of treatment at room temperature. The calcite precipitation was confirmed using SEM(scanning electron microscope), PXRD(powder X-ray diffraction), and calcimeter tests. It was observed that MS generates lower calcite precipitation as compared with NB and TB. However, MS has the advantage of being more economical and abundant(waste product from sugar mills and refineries) as compared with other growth media(NB and TB). It was observed that the minimum and the maximum calcite precipitation using MS is 5% and 12%, respectively.The findings using MS in the present study was compared with the literature and found that precipitation of calcite using MS is effective to stabilize soil against wind erosion.

Comparative Study of Effect of Addition of Calcium Carbonate and Clay on the Performance Properties of Polyvinyl Acetate Wood Glue

Polyvinyl alcohol (PVA) stabilized Polyvinyl acetate (PVAc) dispersions-based wood adhesive has poor water and heat resistance. Recently, the addition of fillers in the wood adhesive is one of the most effective ways to enhance the performance of PVAc wood adhesive. Inorganic fillers have unique characteristics to improve the performance of adhesive, such as small size, high surface energy and surface hardness. Hence, the present work investigates the applicability of calcium carbonate and clay incorporated 3% in situ emulsion polymerization PVAc wood adhesive. Effect on physical, thermal and mechanical properties was studied by viscosity, pH, contact angle measurement, differential scanning calorimetry (DSC) and pencil hardness test of films. Emulsions with 3% calcium carbonate and 3% clay were prepared and the shear strength of the applied adhesive on wood was measured. The viscosity of the adhesives was reduced in the case of the addition of calcium carbonate and increased in the case of clay. The mechanical properties like tensile strength of adhesives with calcium carbonate and clay were measured by a universal tensile machine (UTM). Thermal stability was studied by differential scanning calorimetry (DSC). The tensile shear strength demonstrates that clay can improve bonding strength as compared to calcium carbonate of PVAc adhesive in wet conditions. The hardness of PVAc films was also changed positively by the addition of calcium carbonate and clay. Thermal stability of PVAc was significantly improved as calcium carbonate and clay were added to PVAc. Here, we did a comparative study of the effect of the addition of calcium carbonate and clay filler materials in situ polymerization of PVAc on their different properties.

Optimization by the Taguchi Method of a Robust Synthesis Protocol of Calcium Carbonate Phosphate

The experimental processes are difficult to model by physical laws, because a multitude of factors can intervene simultaneously and are responsible for their instabilities and their random variations. Two types of factors are to be considered;those that are easy to manipulate according to the objectives, and those that can vary randomly (uncontrollable factors). These could eventually divert the system from the desired target. It is, therefore, important to implement a system that is insensitive to fluctuations in factors that are difficult to control. The aim of this study is to optimize the synthesis of an apatitic calcium carbonate phosphate characterized with a Ca/P ratio equal to 1.61 by using the experimental design method based on the Taguchi method. In this process, five factors are considered and must be configured to achieve the previously defined objective. The temperature is a very important factor in the process, but difficult to control experimentally, so considered to be a problem factor (noise factor), forcing us to build a robust system that is insensitive to the last one. Therefore, a much simpler model to study the robustness of a synthetic solution with respect to temperature is developed. We have tried to parameterize all the factors considered in the process within a wide interval of temperature variation (60˚C - 90˚C). Temperature changes are no longer considered as a problem for apatitic calcium carbonate phosphate synthesis. In this finding, the proposed mathematical model is linear and efficient with very satisfactory statistical indicators. In addition, several simple solutions for the synthesis of carbonate phosphate are proposed with a Ca/P ratio equal to 1.61.

Effects of Nano Calcium Carbonate on Strength and Microstructure of Corundum-based Castables

The castables specimens were prepared using white fused alumina particle and powder, α-Al2O3 micropowder, hydrated alumina, nano calcium carbonate or calcium aluminate cement as starting materials. Effects of nano calcium carbonate addition on phase compositions, strength and microstructure of corundum based castables were studied. The calcium aluminate cement-containing corundum based castables with the same CaO amount was also tested for comparison. The results show that, when temperature is higher than 900 ℃ , the phase compositions of nano CaCO3-containing mixture and the calcium aluminate cement containing mixture are the same, but the forming mechanism, modality and distribution of new phases in the castables are different. With temperature rising, the hydration cement dehydrates and reacts inside cement forming calcium aluminate until the alumina in cement is not enough for the reaction （ternperature is 91 400 ℃ ） , then reacts with the surrounding alumina forming cluster CA6 in the castables. The change process of nano CaCO3 in corundum based enstables is that nano calcium carbonate decomposes to CaO after firing at 800℃ which reacts with Al2O3 forming amorphous calcium aluminate that causes an in-situ bonding. With temperature rising, the formed calcium aluminate reacts with Al2O3 in matrix and wholly forms tabular CA6 at 1 600 ℃ , which distributes uniformly in the castables. The cold and hot strength of the castables with nano calcium carbonate are obviously higher than those of the castables without nano calcium carbonate, especially at 800 -1 000 ℃ due to smaller size and higher dispersion of the nano calcium carbonate and its different reaction mechanism with Al2O3.

Preparation of poly （methyl methacrylate）／nanometer calcium carbonate composite by in-situ emulsion polymerization

Methyl methacrylate (MMA) emulsion polymerization in the presence of nanometer calcium carbonate(nano-CaCO3) surface modified with γ-methacryloxypropyltrimethoxysilane (MPTMS) was carried out to prepare poly (methyl methacrylate) (PMMA)/nano-CaCO3 composite. The reaction between nano-CaCO3 and MPTMS, and the grafting of PMMA onto nano-CaCO3 were confirmed by infrared spectrum. The grafting ratio and grafting efficiency of PMMA on nano-CaCO3 modified with MPTMS were much higher than that on nano-CaCO3 modified with stearic acid. The grafting ratio of PMMA increased as the weight ratio between MMA and nano-CaCO3 increased, while the grafting efficiency of PMMA decreased. Transmission electron micrograph showed that nano-CaCO3 covered with PMMA was formed by in-situ emulsion polymerization.

Kinetics and Mechanism of Decomposition of Nano-sized Calcium Carbonate under Non-isothermal Condition

Experiments on thermal decomposition of nano-sized calcium carbonate were carried out in a thermo-gravimetric analyzer under non-isothermal condition of different heating rates (5 to 20K·min-1). The Coats and Redfern's equation was used to determine the apparent activation energy and the pre-exponential factors. The mechanism of thermal decomposition was evaluated using the master plots, Coats and Redfern's equation and the kinetic compensation law. It was found that the thermal decomposition property of nano-sized calcium carbonate was different from that of bulk calcite. Nano-sized calcium carbonate began to decompose at 640℃, which was 180℃lower than the reported value for calcite. The experimental results of kinetics were compatible with the mechanism of one-dimensional phase boundary movement. The apparent activation energy of nano-sized calcium carbonate was estimated to be 151kJ·mol-1 while the literature value for normal calcite was approximately 200kJ·mol-1. The order of magnitude of pre-exponential factors was estimated to be 10~9 s-1.

REINFORCEMENT OF POLYDIMETHYLSILOXANE NETWORKS BY NANOCALCIUM CARBONATE

Although a number of investigations have been devoted to the analysis of silica or carbon black filled elastomer networks,little work has been done on the reinforcement of CaCO_3 filled elastomer network.In this work,the reinforcement of polydimethylsiloxane(PDMS)network by using CaCO_3 nano-particles was investigated.We have found a simultaneous increase of tensile strength,modulus and elongation with the increase in nano-CaCO_3 content,which suggests that nano- CaCO_3 particles can indeed be used as a reinforcing agent,just like silica or carbon black.Interestingly,the tensile strength, modulus and elongation were seen to leave off for the first time when the content of nano-CaCO_3 particles reaches to 80%. PDMS also showed an enhanced elastic modulus and storage modulus with the increase in nano-CaCO_3 content,particularly for samples with high nano-CaCO_3 content.SEM was used to investigate the dispersion of the filler in PDMS matrix.A better dispersion was found for samples with high nano-CaCO_3 content.A great increase of viscosity was found for samples with higher filler content,which is considered to be the reason for the good dispersion thus the reinforcement,because high viscosity will be helpful for breaking the agglomerates of fillers into small size particles under effect of shear.Our work provides a new way for the reinforcement of elastomer by using an adequate amount of nano-CaCO_3 particles instead of a small quantity of silica,which is not only economically cheap but also very effective.

ELECTRICAL RESISTIVITY,CRYSTALLIZATION AND MECHANICAL PROPERTIES OF POLYPROPYLENE/MULTI-WALLED CARBON NANOTUBE/CALCIUM CARBONATE COMPOSITES PREPARED BY MELT MIXING

Polypropylene (PP)/multi-walled carbon nanotube (MWCNT)/calcium carbonate (CaCO(3)) composites are prepared by melt mixing using two types of CaCO(3) of different sizes. The electrical resistivities of the composites with the two types of CaCO(3) are all lower than those of the corresponding PP/MWCNT composites at various MWCNT loadings (1 wt%-5 wt%). The morphology of the composites is investigated by field emission scanning electron microscopy (FESEM). The crystallization behavior of PP in the composites is characterized by differential scanning calorimetry (DSC). The storage modulus, as measured by dynamic mechanical analysis (DMA), increases significantly by the presence of CaCO(3).

Effect of Nano Calcium Carbonate on Properties of Corundum-spinel Castables

Using sintered corundum as aggregate, white fused corundum powder, fused spinel powder, ultra-fine a-A12 0 3, nano calcium carbonate and hydrated alumina as matrix, effects of nano calcium carbonate additions （0. 4%, O. 8%, 1.2%, 1.6% and 2. 0% in mass, the same hereinafter） on modulus of rupture, thermal shock resi.~tanee and slag resistance of corundum -spinel castables after treating at different temperatures were studied. The results show that nano calcium carbonate decomposes at high temperatures and in-situ forms ealci- ant aluminates, which can significantly increase the CMOR and HMOR of the castables after treating at 800 -1 400 ℃ ; adding nano calcium carbonate obviously improves the thermal shock resistance of the castables, and has little influence on the high basicity slag resist- ance, however, significantly decreases the corrosion and penetration resistance to low basicity slag.

Modification of nanometer calcium carbonate for water-borne architectural coatings

A kind of modifier was synthesized to modify the surface of nanometer calcium carbonate （abbreviated as nano-CaCO3）, which is used in architectural coatings. The modification technology of the nano-CaCO3 was studied through orthogonal experimental methods. The factors studied were rotation speed, modifier dosage, emulsification temperature, emulsification time and heat aging time after emulsification. Optimized conditions for modification of the surface were： rotation speed 16000 r/min; modifier dosage 3%; emulsification temperature 75 ℃; emulsification time 60 min and aging time 40 min. The modified nano-CaCO3 was also studied by size-distribution measurements, transmission electron microscopy, infrared spectroscopy and thermal analysis. The results show that the size distribution of the modified nano-CaCO3 is uniform and that there are chemi-sorption and physi-sorption between the nano-CaCO3 and the modifier. Compared to traditional architectural coatings without nano-CaCO3, the nanometer composite coatings are obviously improved in respect to dirt resistance, scrub resistance, thixotropy, water resistance, alkalinity resistance and aging resistance.

Determination of Crystallization Kinetics and Size Distribution Parameters of Agglomerated Calcium Carbonate Nanoparticles during the Carbonation of a Suspension of Lime

The reaction studied in this work is the synthesis of nanometric size calcium carbonate by carbonation of a suspension of lime, which represents the most common industrial route. The carbonation was proceeded in a pilot batch reactor. This article presents a method for the determination of nucleation and crystal growth rates of calcium carbonate by following two macroscopic parameters: the mass production rate by precipitation and the specific surface area. The results give a constant nucleation rate around 4 × 1015m-3 ·s-1 and a decreasing crystal growth rate between 0.2 and 2 × 10-10 m·s-1. It also provides the main characteristics of the monoparticle size distributions (i.e. the mean particle sizes and in situ coefficient of variation) in the agglomerates, which cannot be obtained by other known methods. For the carbonation carried out in this work, the mean mass particle size at the end of the reaction is about 300 nm and the coefficient of variation of 0.28 indicates a narrow particle size distribution of the monoparticles.

The Influence of Creep on the Mechanical Properties of Calcium Carbonate Nanofiller Reinforced Polypropylene

The study focused on experimental and classical data to establish some mechanical properties for optimum design of new polypropylene components to serve under creep environment. The creep studies recorded stress limits that never exceeded 24.19MPa and maximum creep modulus that never exceeded 1.49GPa as against the predictions of classical equations that gave 2.0GPa for PPC0 and 2.46GPa for PPC2 at ambient conditions. The shear modulus and shear strength of the PPC0 and the PPC2 are predicted as 0.75GPa and 120MPa respectively and 0.92GPa and 150MPa respectively while the yield strengths found to be about 13.19MPa and 13.20MPa respectively for PPC0 and PPC2 at elastic strains 0.008 and 0.009 respectively. Further found are that as the material deforms the stiffness or modulus decrease, at low strains there is an elastic region, as temperature and applied stress increase the material becomes more flexible characterized with reduction in moduli. Plastic deformation at strains above 0.01 resulted to strain- hardening or strain-strengthening that manifested as the increasing area ratios and associated creep cold work. Also established by this study is a computational model for evaluating the elastic modulus of polypropylene matrix based material as expressed in equation (6). Both the Halphin-Tsai and the Birintrup equations for elastic modulus of unidirectional fibre composites were confirmed to be appropriate for prediction of elastic modulus of nanofiller composites with polymer matrix.

Separation of manganese from calcium and magnesium in sulfate solutions via carbonate precipitation

The separation of manganese from sulfate solutions containing 14.59 g/L Mn2+, 1.89 g/L Mg2+ and 1.54 g/L Ca2+ was preformed successfully by carbonate precipitation. The results of thermodynamic analysis and tests indicate that carbonate precipitation holds better selectivity for manganese over magnesium than hydroxide precipitation and the feeding method is the most critical factor for minimizing the co-precipitation of calcium and magnesium. Furthermore, with adding MnSO4 solution to NH4HCO3 solution, the effects of the initial NH4HCO3 concentration, NH4HCO3 amount, solution pH value, reaction temperature and time on carbonate precipitation were evaluated and the optimum precipitation conditions were obtained. Under the optimum conditions, the precipitation rates of Mn2+, Ca2+ and Mg2+ are 99.75%, 5.62% and 1.43%, respectively. Moreover, the prepared manganese carbonate was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX). The results demonstrate that the product can be indexed to the rhombohedral structure of MnCO3.

Evolution Mechanism of Calcium Carbonate in Solution

Calcium carbonate was synthesized in a CaCl2/NaCO3 mixed solution by using ethylenediaminetetraacetic acid （EDTA） as an additive. The thermodynamics and kinetics analyses indicate that although the driving force of amorphous calcium carbonate （ACC） precipitation is always less than that of calcite and vaterite precipitation, the nucleation rate of ACC is greater than that of calcite and vaterite at the initial stage of the precipitation reaction. With the increasing incubation time, vaterite and calcite particles nucleate heterogeneously by using the as-formed particles as active sites. Scanning electron microscopy images indicate that the transformation mechanism of ACC and vaterite to calcite is the dissolution-recrystallisation reaction. The presence of EDTA not only improves the stabilities of ACC and vaterite, but also leads to forming enlongated, connected rhombohedral calcite crystals after incubation 7 days in solutions. The ACC and vaterite are stabler in air than in solutions at room temperature, although the dissolution-recrystallisation reaction occurs on the surface.