Hydration Characteristics and Mechanical Properties of Cement-Based Materials Modified by Calcined Zeolite and Montmorillonite

Montmorillonite and clinoptilolite zeolite were used as representative materials to prepare calcined clay-cement binary cementitious materials in order to study the effect of calcination treatment on the activation of clay minerals and the activity difference between layered and framed clays in this research.The influence of different calcined clay content(2%,4%,6%,8%,10%)on the fluidity,compressive strength,microstructure,phase change,and hydration heat of cement-based materials were analyzed.The calcined clay improves the fluidity of cement-based materials as compared with the uncalcined group.The addition of calcined montmorillonite(CMT)improves the development of mechanical strength,and the optimal compressive strength reaches 85 MPa at 28 days with 8%CMT.However,the activity of calcined clinoptilolite zeolite(CZL)is weak with few reaction sites,which slightly reduced the mechanical strength as compared to the blank sample.The addition of CMT changes the microscopic morphology of hydration products such as C-S-H and C-A-H,leading to the formation and transformation of ettringite in the early stage.It promotes the gradual polymerization of Si-O bonds into Si-O-Si bonds simultaneously,which accelerates the early hydration process.However,CZL acts mainly as a filling function in the cementitious system.In brief,CMT as an admixture can improve the mechanical properties of cement,but CZL has little effect.This work provides a guideline for the applications of calcined clay in cement,considering the influence of clay type on workability and mechanical strength.

A Comparative Study of Transesterification of Hydnocapus weightiana Seed Oil Using Calcined and Acid Activated Natural Heterogeneous Catalyst and Its Kinetic Study

The world’s total fossil fuel consumption has been significantly increasing with consequential increased environmental catastrophes. A hunt for an alternate energy source was stimulated. Biofuel is a plausible option in this pursuit due to its ideal qualities which included but are not limited to renewability and environmental friendliness. However, the pump price of biodiesel is still very high due mainly to the high cost of the production of the commodity which is influenced by the feedstock and the homogeneous nature of catalyst used. Heterogeneous catalyst was prepared by using Pila globosa sea snail shells prepared by calcination (CP8) and by acid activation (PTW1M). Hydnocapus weightiana seed oil (Non-edible feedstock) was extracted using the soxhlet extraction method and was used for biofuel production with a methanol oil ratio of 3:1. Agitation speed 800, 600 rmp, reaction temperatures of 70°C, 60°C, catalyst concentration (3.00, 2.00 wt%) and reaction time (70 and 60 min) was maintained for CP8 and PTW1M respectively. The rate of the reaction followed a reversible second-order reaction rate. Re-usability accessed. From TGA analysis, the best calcination temperature was 800°C. SEM results showed improved surface morphology after calcination, especially for CP8. FTIR analysis showed the elimination of volatiles and formation of CaO and CaO4Te after calcination. The reaction rate constant at different temperatures was 0.0287 at 30°C, 0.1200 at 50°C and 0.1142 at 70°C and activation energy of the ethyl ester was 49.49 KJ/mol. Using CP8. Most of the fuel properties met with ASTM 6751 standard. The result of the re-usability showed that the biodiesel yield declined as follows: 92, 86, 80, 73 and 69 % for CP8 and 85, 84, 81, 76, 65. For PTW1M. After the fifth regeneration cycle, both CP8 and PTW1M samples of Pila globosa sea snail shell catalyst proved effective in transesterification reaction of Hydnocapus weightiana seed oil using ethanol. It was observed that the calcined catalyst (CP8) showed a superior catalytic performance.

Production of an Eco-Cement by Clinker Substitution by the Mixture of Calcined Clay and Limestone, Songololo (DR Congo)

Ordinary Portland Cement (OPC) is by mass the largest manufactured product on Earth, responsible for approximately 6% - 8% of global anthropogenic carbon dioxide emissions (CO2) and 35% of industrial CO2 emissions. On average 0.8 to 0.9 ton of CO2 is emitted to produce one ton of OPC. In this paper, partial substitution of clinker (30% - 35%) by the calcined clay-limestone mixture was investigated in order to produce an eco-cement (LC3). Analyzes by XRF, XRD and ATG/ATD have characterized different components, determined the calcination temperature and selected the right clay which can act as effective Supplementary Cementitious Material (SCM). Mechanical tests on mortar carried out over a period of 90 days. The WBCSD/WRI “Greenhouse Gas Protocol” methodology then allowed the calculation of CO2 emissions into the atmosphere. Three types of clay are available in the Songololo Region. The kaolinite is the principal clay mineral and its content varies from 27% to 34%. The sum of kaolinite and amorphous phase which enable clay to react with cementitious material ranges from 57% to 60%. The SiO2 content ranges from 33% to 76%, the Alumina content from 12% to 20% so that the ratio Al2O3/SiO2 is on the higher side (0.17 - 0.53). The calcination window is between 750°C and 850°C and the best clay which can act as SCM identified. The clinker’s substitution reduced CO2 emissions from 0.824 ton of CO2 for one ton of OPC to 0.640 ton of CO2 for one ton of LC3, means 22% less emissions. The compressive strengths developed by LC3 vary from 8.91 to 57.6 MPa (Day 1 to Day 90), exceed those of references 32.5 cement and are close to 42.5 cement. In view of the results, LC3 cement can be considered for industrial trials.

Properties and Hydration Mechanism of Cementitious Materials Prepared from Calcined Coal Gangue

The preparation of cementitious materials by replacing part of the cement with activated coal gangue is of great significance to the cement industry in terms of carbon reduction and coal-based solid waste utilization.For this paper,cementitious material was prepared by firing activated coal gangue under suspension conditions and batching it with limestone powder using Inner Mongolia coal gangue as raw material.The optimal ratio was determined by testing the strength changes of the cementitious material at 3,7,and 28 days of hydration,and the hydration process and mechanism were explored by combining the pore structure,heat of hydration,chemical composition,phase composition,and microscopic morphological characteristics of the hydration products.The results showed that the active materials formulated from activated gangue and limestone powder can be used to prepare cementitious materials with good performance at the level of 30%–50%replacement of cement.The optimal ratio was 30%replacement of cement,and the mass ratio of calcined gangue to limestone powder was 2:1.The 3 days compressive strength of this ratio was 28.8 MPa,which was only slightly lower than that of cement.However,the 28 days compressive strength of samples reached 67.5 MPa,which was much higher than that of the reference cement.In the hydration of this cementitious material,not only does the activated coal gangue react with the Ca(OH)_(2)formed by hydration to form C–S–H gel,but CaCO3 also participates in the reaction to form a new phase of carbon aluminate,and the two effects together promote the development of the later strength of the samples.This paper can provide a reference for carbon reduction in the cement production process and comprehensive utilization of coal gangue.

Element distribution of high iron-bearing zinc calcine in high gradient magnetic field

High gradient magnetic separation was conducted in order to separate insoluble zinc ferrite from zinc calcine before acid leaching of hydrometallurgical process. Chemical composition and structural characterization of zinc calcine were studied via inductively coupled plasma （ICP）, X-ray diffraction （XRD）, Mossbauer spectra, scanning electron microscopy （SEM） and laser particle analysis （LPA）. The parameters of magnetic separation which affect the distribution of zinc ferrite and undesired elements, such as calcium, sulfur and lead in magnetic concentrate were investigated. The results of high gradient magnetic separation indicate that more than 85% of zinc ferrite is distributed into magnetic concentrate from the zinc calcine under the magnetic induction of 0.70 T. In addition, about 60% of calcium and 40% of sulfur distribute in non magnetic phases of tailings during magnetic separation process. Most of lead distributes uniformly along the zinc calcine in superfine particle size.

Adsorption of glutamic acid from aqueous solution with calcined layered double Mg-Fe-CO_3 hydroxide

Layered double Mg-Fe-CO3 hydroxide （Mg-Fe-LDH） with a mole ratio of Mg to Fe of 3 was synthesized by coprecipitation method and calcined product Mg-Fe-CLDH was obtained by heating Mg-Fe-LDH at 500 ℃ for 6 h. The as prepared Mg-Fe-LDH and calcined Mg-Fe-CLDH were used for removal of glutamic acid （Glu） from aqueous solution, respectively. Batch studies were carried out to address various experimental parameters such as contact time, pH, initial glutamic acid （Glu） concentration, co-existing anions and temperature. Glu was removed effectively （99.9%） under the optimized experimental conditions with Mg-Fe-CLDH. The adsorption kinetics follows the Ho’s pseudo second-order model. Isotherms for adsorption with Mg-Fe-CLDH at different solution temperatures were well described using the Langmuir model with a good correlation coefficient. The intraparticle diffusion model fitted the data well, which suggests that the intraparticle diffusion is not only the rate-limiting step.

Potential for Use of Iron Mining Tailings Calcined in a Flash Furnace as Pozzolanic Material

This paper presents a study of the potential use of iron mining tailings as artificial pozzolan (metakaolin) after their submission to thermal treatment via calcination in a flash furnace. The research consists of the characterization of the tailings before and after calcination, chemical, mineralogical, thermogravimetric, and mechanical strength analyses were conducted. The results were compared with those for commonly used pozzolans, metakaolin, and similarities were identified. The study of the morphology of the particles before and after calcination was conducted through analyses of images obtained by scanning electronic microscope. The pozzolanic activity of the fine mining tailings calcined with flash technology was evaluated in uniaxial compression trials, which showed excellent results.

Preparation and mechanical properties of polypropylene fiber reinforced calcined kaolin-fly ash based geopolymer

To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3%(mass fraction) fly ash by steam curing at 80 ℃ for 6 d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.

Effect of Heat Treatment Temperature on Properties of Chinese Calcined Flint Clay Based Plastic Refractories

Effects of different heat treatment temperatures on properties of Chinese calcined flint clay based plastic refractories were investigated using Chinese calcined flint clay as starting material, aluminum sulfate and fireclay as binding system. The results showed that with temperature rising, Chinese calcined flint clay based plastic refractories shrinked firstly and then expanded. The modulus of rupture （MOR） and the cold crushing strength （CCS） inereased firstly and then decreased from 110 ℃ to 600 ℃ , then increased obviously. Thermal expansion coefficient increased from 110 ℃ to 760 ℃, decreased from 760 ℃ to 1 300 ℃ , and increased from 1 300 ℃ to1500 ℃.

Differences of cyanide leaching between calcine and dust from refractory gold concentrates

Differences of cyanide leaching between the calcine and the dust from a refractory gold concentrate were investigated by comparative method. Results showed that gold leaching efficiencies of the calcine and the dust were 85.31% and 54.30%, respectively, with direct cyanidation. Contents and existing forms of arsenic and carbon were the main reasons for those differences. The maximum gold leaching efficiencies of the calcine and the dust were 87.70% and 58.60%, respectively, with cyanidation after NaOH pre-leaching. Harmful elements removal, gold loss in NaOH pre-leaching and iron oxides hindrance codetermined gold leaching efficiencies of the calcine and the dust. After H2SO4 pre-leaching, the maximum gold leaching efficiencies of the calcine and the dust achieved 94.96% and 80.40%, respectively. The effect of carbonaceous matter was the main reason for differences for leaching efficiencies of the calcine and the dust. Based on those differences, two proper gold extraction processes were put forward, and gold leaching efficiencies for the calcine and the dust achieved 94.91% and 91.90%, respectively.

Synthesis of Refractory Cordierite from Calcined Bauxite, Talcum and Quartz

A cordierite was synthesized from calcined bauxite, talcum, and quartz. The properties and microstructure of the cordierite sintered samples were characterized by Archimedes＇ method, thermal dilatometry, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and so on. The experimental results showed that calcined bauxite could broaden the range of synthesizing temperature from 1300 ℃ to 1420 ℃ and get pure cordierite. The bulk density and linear thermal expansion coefficient of the sample synthesized at 1420 ℃ for 2 h were 1.97 g·cm^-3 and 2.1×10^-6 ℃^-1, respectively. The XRD analysis showed that the major crystalline phase was a-cordierite with almost no glassy matters, the SEM images illustrated a small vent hole and the size were 5 -100 μm, the well-grown hexagonal and granular cordierite grains had the sizes distributed among 0.1-8 ;xm, and providing high mechanical strength and lower linear thermal expansion coefficient.

Sulfuric acid leaching of high iron-bearing zinc calcine

Sulfuric acid leaching of high iron-bearing zinc calcine was investigated to assess the effects of sulfuric acid concentration, liquid-to-solid ratio, leaching time, leaching temperature, and the stirring speed on the leaching rates of zinc and iron. The results showed that the sulfuric acid concentration, liquid-to-solid ratio, leaching time, and leaching temperature strongly influenced the leaching of zinc and iron, whereas stirring speed had little influence. Zinc was mainly leached and the leaching rate of iron was low when the sulfuric acid concentration was less than 100 g/L. At sulfuric acid concentrations higher than 100 g/L, the leaching rate of iron increased quickly with increasing sulfuric acid concentration. This behavior is attributed to iron-bearing minerals such as zinc ferrite in zinc calcine dissolving at high temperatures and high sulfuric acid concentrations but not at low temperatures and low sulfuric acid concentrations.

Characterization of Calcined Kaolin/TiO_2 Composite Particle Material Prepared by Mechano-Chemical Method

Calcined kaolin/TiO2 composite particle material （CK/TCPM） was prepared with TiO2 coating on the surfaces of calcined kaolin particles by the mechano-chemical method. X-ray diffraction （XRD） and scanning electron microscope （SEM） were used to investigate the microstructures and morphologies, respectively. The mechanism of the mechano-chemical reaction between calcined kaolin and TiO2 was studied by infrared spectra （IR）. The results show that TiO2 coats evenly on the surfaces of calcined kaolin particles by Si-O-Ti and Al-O-Ti bonds on their interfaces. The hiding power and whiteness of CK/TCPM are 17.12 g/m^2 and 95.7%, respectively, presenting its similarity to TiO2 in pigment properties.

Ceramification of Composites of MgO-Al_(2)O_(3)-SiO_(2)/Boron Phenolic Resin with Different Calcine Time

The ceramifiable polymer composite of MgO-Al_(2)O_(3)-SiO_(2)/boron phenolic resin(MAS/BPF)with 40wt%of inorganic fillers was calcined at 1200℃for different time to promote ceramification of ceramifiable composite and improve heat resistance.The effects of different calcine time on the macroscopical morphology,mass loss,phase evolution,microstructure and chemical bond evolution of MAS/BPF composites were characterized by XRD,XPS,and SEM analyses.The experimental results reveal that the increase of calcine time result in the fewer holes,relatively denser and smoother top layer of MAS/BPF composites and protect the interior from deeper decomposition.The final residues of composites are amorphous carbon and C-O-Si-Al-Mg ceramic.And MAS/BPF composites show excellent mass stability,low shrinkage and self-supporting features after 2 h holding compared with BPF composites without 40wt%of inorganic fillers.

Comprehensive recovery of Fe,Zn,Ag and In from high iron-bearing zinc calcine

A beneficiation-metallurgy combination process is developed to recover Zn, Fe and to enrich In, Ag from high iron-bearing zinc calcine based on our former researches. In gaseous reductive roasting process, the roasting conditions were tested by magnetic separation of roasted product. It is found that the V_(CO)(P_(CO)/(P_(CO+CO_2)) in roasting atmosphere should be maintained below 30% to avoid the generation of zinc iron solid solution(Fe_(0.85-x)Zn_xO), which can bring a decrease of iron recovery in magnetic separation. After roasting, acid leaching and multistage magnetic separation are carried out for the recovery of Zn, Fe and enrichment of Ag and In. About 90% of zinc is extracted and 83% of iron is recovered in the whole process. The Ag mainly enters the tailings with a recovery of 76%, the Ag grade increases from 0.12 g/t in raw materials to 1.18 g/t in the tailings. However, the In mainly enters the iron concentrations and the recovery reaches 86%. This process was proved to be technically feasible and may be a favorable option in the treatment of high iron-bearing zinc material with high Ag or In content.

Thermodynamic and Kinetic Studies of Effective Adsorption of 2,4,6-trichlorophenol onto Calcine Mg/Al-CO_3 Layered Double Hydroxide

Adsorption of 2, 4, 6-trichlorophenol（TCP） onto the calcined Mg/Al-CO_3 layered double hydroxide（CLDH） was investigated. The prepared Mg/Al-CO_3 layered double hydroxide（LDH） and CLDH were characterized by powder X-ray diffraction（XRD） and thermo gravimetric analyzer-differential scanning calorimeters（TG-DSC）. Moreover, 2,4,6-trichlorophenol（TCP） was removed effectively（94.7% of removal percentage in 9h） under the optimized experimental conditions. The adsorption kinetics data fitted the pseudosecond-order model well. The Freundlich, Langmuir, and Tempkin adsorption models were applied to the experimental equilibrium adsorption data at different temperatures of solution. The adsorption data fitted the Freundlieh adsorption isotherm with good values of the correlation coefficient. A mechanism of the adsorption process is proposed according to the intraparticle diffusion model, which indicates that the overall rate of adsorption can be described as three steps.

Isothermal reduction kinetics of zinc calcine under carbon monoxide

The reduction kinetics of zinc calcine under a CO atmosphere was evaluated by isothermal reductive roasting in a temperature range of 600-800℃.The extent of reaction of zinc calcine was measured using thermogravimetry(TG),and the decomposition mechanism of zinc ferrite in zinc calcine was analyzed based on variations in the soluble zinc and ferrous contents.The results indicate that the reaction was controlled by the nucleation of the products,with an apparent activation energy of 65.28 k J/mol.The partial pressure of CO affected the reaction rate more strongly than the CO intensity(defined as PCO/(PCO+PCO2)).The generation rate of zinc oxide was higher than that of ferrous oxide;therefore,the nucleation of ferrous oxide is the rate-determining step of the reaction.

Dissolution properties of calcined gangue

To study the dissolution mechanism of gangue, dissolution characteristics of the gangue samples calcined at different temperatures in alkaline solutions and alkali metal silicate solutions with respect to Si and Al ions were analyzed by identical coupled plasma optical emission spectroscopy （ICP）. The results show that the extent of dissolution of Al and Si varies with calcination temperature. It shows that the samples have a higher degree of dissolution in NaOH than in KOH medium. Si and Al appear to have synchro-dissolution behavior in alkaline solution, which means that Si and Al could dissolve from the mineral surface in certain linked forms. The result that a higher degree of dissolution exists in sodium silicate solution and a lower degree of dissolution exists in sodium-potassium silicate solution of Al is proved by the 29Si NMR spectra and the mean connectivity degree of these alkali metal silicate solutions.

The Adsorbing Effect of Calcined Layered Double Hydroxide for Chloride Ions in Simulated Concrete Pore Solutions

The adsorbing effect of calcined layered double hydroxide （CLDH） for chloride ions in simulated concrete pore （SCP） solutions was investigated with the potentiodynamic polarization method, impedance measurement, ion selective electrode analysis and XRD. CLDH could effectively adsorb Cl^- and increase pH value in SCP solutions containing NaCl. The chloride to hydroxyl ions ratio （[C1^-]/[OH^-]） of the solution greatly decreased by CLDH treatment. In CLDH treated SCP solution with CI-, the pitting potential of carbon steel notably increased, and the surface impedance was much higher, indicating strengthened passivation. The process of CLDH adsorbing chloride ions from SCP solutions was accompanied with the reconstruction of the layered structure.

Sulfate Ions Immobilization of Calcined Layered Double Hydroxides in Hardened Cement Paste and Concrete

The sulfate ions immobilization behavior of calcined layered double hydroxides(CLDHs) in the hardened cement paste was investigated. The experimental results show that the sulfate ions in cement paste are immobilized by CLDHs to reconstruct the layered structure and aggregate around CLDHs. The immobilization amount of sulfate ions by CLDHs reaches 4.74×10^-3 mol/g, while the increasing amount indicates non-linear relation with the addition of CLDHs. The incorporation of CLDHs decreases the amount of ettringite formed to limit the expansion of cement paste, which decays the sulfate reaction to enhance the sulfate resistance of concrete.