Chemical Kinetic Aspects of Solid State Reaction Producing Wollastonite from Rice Husk Silica and Limestone

An industrial mineral wollastonite (CaSiO3) was produced under solid state conditions from rice husk silica and limestone. Reaction was carried out at 900'C to 1300'C for 1 h. The product batches were subjected to XRD and chemical analysis techniques specific for wollastonite. Mole fractions of different product batches were calculated on the basis of accumulated data to study the kinetics. Specific rate constants and reaction rate were also found out. Various probable models of mechanism for reaction were considered and testified with the laid down criterion for suggesting the suitable one. The resulting data were treated with Arrhenius equation as well and activation energy was calculated--therefrom. In addition to finding it's value from the slope of Arrhenius curve, an alternate method was also applied for this purpose. Both of the values were observed to be comparable. The activation energy required for performed reaction was found to be almost one third of that reported for synthesizing CaSiO3 by using quartz. This referred to the economical preparation of wollastonite by using rice husk as a source of silica instead of quartz.

Synthesis and Structural Characterization of Hydroxyapatite-Wollastonite Biocomposites, Produced by an Alternative Sol-Gel Route

Hydroxyapatite is a type of calcium phosphate-based material with great interest for biomedical applications, due to the chemical similarity between this material and the mineral part of human bone. However, synthetic hydroxyapatite is essentially brittle;the practice indicates that the use of hydroxyapatite without additives for implant production is not efficient, due to its low strength parameters. In the present work, biocomposites of hydroxyapatite-wollastonite were synthesized by an alternative sol-gel route, using calcium nitrate and ammonium phosphate as precursors of hydroxyapatite, and high purity natural wollastonite was added in ratios of 20, 50 and 80 percent by weight immersed in aqueous medium. Formation of hydroxyapatite occurs at a relatively low temperature of about 350?C, while the wollastonite remains unreacted. After that, these biocomposites were sintered at 1200?C for 5 h to produce dense materials. The characterization techniques demonstrated the presence of hydroxyapatite and wollastonite as unique phases in all products.

New Discovery of Shizhushan Superlarge Wollastonite Deposit in Xinyu City, Jiangxi Province

Objective The Mengshan area of the Xinyu City, Jiangxi Province is an important wollastonite production base in China. As early as the 90s of the 20th century, more than ten medium to small-sized wollastonite deposits, such as the Yueguangshan and Caofangmiao Deposits were discovered in the outer contact zone of the Mengshan rock mass. After that, no more progress was achieved in wollastonite prospection. In 2016, the project funded by the Geological Prospecting Fund of Jiangxi Province made significant breakthroughs in the ＂General Survey of the Shizhushan Wollastonite Ore in the Yushui District and Zhangmuqiao Wollastonite Ore in Shanggao County, Xinyu City, Jiangxi Province＂ in the Mengshan area. The new discovered Shizhushan Wollastonite Deposit has a scale of 50 million tons and its resources scale far exceeds that of the Seeleys Bay Wollastonite Deposit discovered in Canada.

Evaluation of Bioactive Properties of α and β Wollastonite Bioceramics Soaked in a Simulated Body Fluid

Dense natural wollastonite bioceramics (CaSiO3) were prepared by a sintering method, varying the pressing load and sintering temperature, in order to obtain different phases of wollastonite, and different physical properties in the materials. The products were characterized by TGA-DTA, XRD, FT-IR, SEM-EDS, TEM and XPS techniques. The results indicate the presence of two polymorphic phases of wollastonite, the β-wollastonite and α-wollastonite with a transition temperature of the β phase to α phase at approximately 1250℃. These materials were soaked in a simulated body fluid (SBF) during 1, 2 and 3 weeks, to study their solubility and bioactivity. The effect of different wollastonite phases on the solubility of Ca and Si, as well as the capacity of producing layers of “newly formed apatite” on the surfaces of these materials in SBF solution were analyzed.

Evaluation on Fabrication and Properties of Composite Polyurethane Coatings with Wollastonite Partially Substituting for Rutile Titanium Dioxide

This study aims to prepare a composite polyurethane coating through a facile synthesis process. Titanium dioxide, which is a component of the prepared hydroxyl acrylic resin polyurethane varnish, was partially substituted by wollastonite, and an optimal substitution ratio was obtained. Analyses based on scanning electron microscope, powder X-ray diffraction, and Raman scattering measurements demonstrated that the addition of wollastonite caused nearly no change in the basic structure of the coating. Coating with a substitution ratio of 25% showed high thermal stability, good cover effect, considerable moisture-proof and water resistance ability, great acidic and basic resistance, and improved performance and hardness in performance tests. Furthermore, the production cost was reduced significantly at this substitution ratio.

SURFACE CHEMICAL CHARACTERISTICS AND FLOATION SEPARATION OF WOLLASTONITE AND GARNET

In order to nealize the efficient floatation separation of garnet and uiollastonite , the authors studied the surface chemical charac-teristics and various floatation behaviour of the two minerals?developed acidic combination depressant FDi and introduced sodium oleate j FeCls and FDi as the flotation agent, they achieved success. In the experimental re-search on the artificiallymixed ores separation, the recovery and concentra-tion grade of the two minerals ivere both over 92% and 95% respectively. At the same time , it was found that the chemical absorption form of iron oleate presented bridge and chelating patterns on the surfaces of garnet and wollastonite activated by Fe3+.

In vitro Evaluation with 5SBF of Alloy ASTM F75 Thermally Treated with Wollastonite

Samples of a cobalt-based alloy that underwent a surface treatment were evaluated. The samples, which were obtained by casting alloy ASTM F 75, were ground and polished on one side until a mirror finish was obtained. The samples were encapsulated in wollastonite （W） using uniaxial pressure, treated at 1 220 ~C for 1 h and subsequently tempered in water. The characterisation of the sample indicated that part of the ceramic encapsulating material was mechanically incorporated on the metallic surface by growth of the oxide layer of the alloy. After thermal treatment, a series of specimens were submerged in a solution with 5-fold simulated body fluid （5SBF） for 3, 5 and 21 days. Characterisation by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD） indicated nucleation and growth of a homogenous layer of apatite, beginning on the third day when the sample was submerged.

STUDY ON SOLUTION CHEMISTRY BETWEEN TANNIC ACID AND THE FLOTATION PULP OF WOLLASTONITE AND DIOPSIDE

The mechanisms of interaction between tannic acid and calcium ions either added externally to or inherently present in the (?)olution ( dissociated from mineral surface ) , are studied by the use of Inductively Coupled Plasma Atomic Emission Spectroscopy ( ICP-AES ) , Ultraviolet Spectroscopy (UV). It is found that wollastonite has a high solubility in the concentration of calcium ions, calcium ions are able to interact with tannic acid.

EFFECT OF SOLUTION CHEMISTRY ON THE FLOTATION SEPARATION OF WOLLASTONITE FROM QUARTZ

This paper deals with the flotation separation of wollas-tonite from quartz by using Na-oleate as a collector and metallic ion as an activator. The reasons why wollastonite is difficult to separate from quartz using Na-oleate as a collector have been studied. It is found that quartz does not float well in a mixture of wollastonite and quartz because of the solution chemistry effect in a wollastonite suspension. The compositions of the wollastonite suspensions have been studied, and the?potential of the two minerals have been determined to explain the solution chemistry effects on the flotation of the respective minerals.

Reciprocity Effect between Silicate Bacteria and Wollastonite

This paper studied the reciprocity effect between wollastonite and a strain silicate bacterium from purple soil. We analyzed the changes of pH value, glucose (GLU) residual concentration, electrolyte and Mn, Si, Fe etc. in the culture liquid with wollastonite after 48 h. The results show that the GLU wastage of silicate bacteria with wollastonite is 2.5 times of the bacterial contrast. It showed wollastonite could obviously accelerate silicate bacteria growth, but bacterial cell broken and distorted badly have been found by SEM analysis. The solubilization of silicate bacteria to Si element of wollastonite reached above 10 times. At the same time, three apices in FTIR of wollastonite (898 cm-1, 925 cm-1, 962 cm-1) descended obviously after the action of silicate bacteria, which shows that a great deal of Si has dissolved out. So we can get that wollastonite has remarkable effect to the growth of silicate bacteria and silicate bacteria has obvious solubilization to Si of wollastonite.

STUDY ON THE GRAVITATION SEPARATION OF SKARN-TYPE WOLLASTONITE ORE FOR PURIFICATION

This paper introduces the common paragenetic minerals of skarn-type wollastonite ore and its principle of gravitation separation for purification. Through the separation experiment of concentrating table on the wollastonite ore from Xiaojipu Wollastonite Mine of Hubei province, the product has reached the reguirement of wollastonite powder used as the ceramic raw material.

STUDIES ON THE APPLICATION OF TOWER MILL IN THE PRODUCTION OF ULTRAFINE WOLLASTONITE

The feasibilities of ultrafine fvollastonits prnvder have been analysed based on joint considerations of satisfying product size re-quiremet, presenting the needlelike wollastonite structure, maintaining an easy operation, stable performance and simplified flowsheet, etc. Opti-mum operating conditions have been established through, systematic reseach-es on the bases of product requirements. Modern analytical technique such as light-transmission particle sizing and scanning electron spectroscopy have been used to determine the size and morphology of the product. It is found that the meedelelike structure can be preserved even dawn to the ul-trafine range by using the toiver mill. The torver mill is easy to operate, has stable performances, and can be used in open-circuit to produce re-quired products without needing for a classifier.

Raman Spectroscopy Analysis of Wollastonite/Tricalcium Phosphate Glass-Ceramics after Implantation in Critical Bone Defect in Rats

In this work wollastonite/tricalcium phosphate (W/TCP) glass-ceramics with three W/TCP weight ratios (20/80;60/40 and 80/20) were implanted in rat calvaria and the modifications taking place during implantation were studied by Raman spectroscopy. The experimental glass-ceramics were composed of different contents of βW, αW, βTCP, αTCP, and glassy phases. Materials were implanted for 7-, 15-, 45- and 120-day periods after which the implanted materials were recovered and analyzed by FT-Raman spectroscopy. The results suggested that the αW phase reabsorbs fast during implantation in the glass-ceramics 60/40 and 80/20, whereas βTCP and αTCP glass-ceramic are gradually attenuated and replaced by biological apatite-like bands. In the glass-ceramic 20/80, the bands related to the βTCP phase remained unvaried in all analyzed periods. New bands associated with the deposition of collagenous material appeared during implantation for all 60/40 and 80/20 glass-ceramics experimental groups, but important differences in intensities between both groups. The spectra corresponding to implants of 60/40 glass-ceramic at the 120-day period were very similar to those of the control group (normal cortical bone), with regards to Raman shifts and intensities, as well as in the FWHM value of the 962 cm-1 apatite band (ν1 PO4 in hydroxyapatite), evidencing that apatite deposited at the implant site has the same crystallinity than biological apatite in normal bone mineral. The glass-ceramic 20/80 behaved just as an osteoconductive filling material, while glass-ceramics 60/40 and 80/20 were able to induce deposition of organic matrix mineralized new tissue. The 60/40 glass-ceramic showed the best performance and the most similar Raman spectrum to normal cortical bone.

Tuning zinc content in wollastonite bioceramic endowing outstanding angiogenic and antibacterial functions beneficial for orbital reconstruction

Prosthetic eye is indispensable as filler after enucleation in patients with anophthalmia,whereas there are still many complications including postoperative infection and eye socket depression or extrusion during the conventional artificial eye material applications.Some Ca-silicate biomaterials showed superior bioactivity but their biological stability in vivo limit the biomedical application as long-term or permanent implants.Herein we aimed to understand the physicochemical and potential biological responses of zinc doping in wollastonite bioceramic used for orbital implants.The wollastonite powders with different zinc dopant contents(CSi-Znx)could be fabricated as porous implants with strut or curve surface pore geometries(cubic,IWP)via ceramic stereolithography.The experimental results indicated that,by increasing zinc-substituting-Ca ratio(up to 9%),the sintering and mechanical properties could be significantly enhanced,and meanwhile the bio-dissolution in vitro and biodegradability in vivo were thoroughly inhibited.In particular,an appreciable angiogenic activity and expected antibacterial efficacy(over 90%)were synergistically achieved at 9 mol%Zn dopant.In the back-embedding and enucleation and implantation model experiments in rabbits,the superior continuous angiogenesis was corroborated from the 2D/3D fibrovascular reconstruction in the IWP-pore CSi-Zn9 and CSi-Zn13.5 groups within very short time stages.Totally,the present silicate-based bioceramic via selective Zn doping could produce outstanding structural stability and bifunctional biological responses which is especially valuable for developing the next-generation implants with vascular insertion and fixation in orbital reconstruction prothesis.

CO_2 Sequestration from flue gas by direct aqueous mineral carbonation of wollastonite

Emission of carbon dioxide is considered to be the main cause of the greenhouse effect. Mineral carbonation, an important part of the CCS technology, is an attractive option for long-term CO2 sequestration. In this study, wollastonite was chosen as the feedstock and the feasibility of direct aqueous mineral carbonation in the simulated flue gas was investigated via a series of experimental studies carried in a stirred reactor. X-ray diffraction （XRD）, X-ray fluorescence spectroscopy （XRF）, ion chro- matography （IC） and thermal decomposition were used to determine the carbonation conversion. The influences of various factors, including reaction temperature, reaction pressure, solution composition, heat-treatment and particle size, were dis- cussed. Concurrently, the effects of SO2 and NO presented in simulated flue gas were also investigated and a possible mecha- nism was used to explain the results. Experimental results show that reaction temperature, reaction pressure and particle size can effectively improve the carbonation reaction. Addition of 0.6 M NaHCO3 was also proved to be beneficial to the reaction and heat-treatment is not needed for wollastonite to get a higher carbonation conversion. Compared with carbonation in puri- fied CO2 gas, CO2 sequestration directly from simulated flue gas by mineral carbonation is suggested to have a certain degree of economic feasibility in the conditions of medium and low-pressure. A highest carbonation conversion of 35.9% is gained on the condition of T=150℃, P=40 bar and PS 〈30 μ in distilled water for 1 h.

Comparative investigations of structure and properties of micro-arc wollastonite-calcium phosphate coatings on titanium and zirconiumniobium alloy

Investigation results of micro-arc wollastoniteecalcium phosphate(W-CaP)biocoatings on the pure titanium(Ti)and Zr-1wt.%Nb(Zr-1Nb)alloy were presented.The voltages of 150-300 V generate the micro-arc oxidation(MAO)process with the initial amplitude current of 150-550 A and 100-350 A for Ti and Zr-1Nb substrates,respectively.The identical dependencies of changes of the coating thickness,surface roughness and adhesion strength on the process voltage were revealed for the both substrates.The W-CaP coatings with the thickness of 10-11μm were formed on Ti and Zr-1Nb under the low process voltage of 130-150 V.Elongated wollastonite particles with the size in the range of 40-100μm were observed in such coatings.The structure of the coatings on Ti was presented by the X-ray amorphous and crystalline phases.The X-ray reflexes relating to the crystalline phases of Ti and wollastonite were observed only in XRD patterns of the coatings deposited under 130-200 V on Ti.While,the crystalline structure with phases of CaZr4(PO4)6,β-ZrP2O7,ZrO2,and Zr was detected in the coatings on Zr-1Nb.FT-IRS,XRD,SEM,and TEM data confirmed that the increase of the process voltage to 300 V leads to the dissociation of the wollastonite.No toxic effect of specimens on a viability,morphology and motility of human adipose-derived multipotent mesenchymal stem cells was revealed in vitro.

3D printing of Mg-substituted wollastonite reinforcing diopside porous bioceramics with enhanced mechanical and biological performances

Mechanical strength and its long-term stability of bioceramic scaffolds is still a problem to treat the osteonecrosis of the femoral head.Considering the long-term stability of diopside(DIO)ceramic but poor mechanical strength,we developed the DIO-based porous bioceramic composites via dilute magnesium substituted wollastonite reinforcing and three-dimensional(3D)printing.The experimental results showed that the secondary phase(i.e.10%magnesium substituting calcium silicate;CSM10)could readily improve the sintering property of the bioceramic composites(DIO/CSM10-x,x=0-30)with increasing the CSM10 content from 0%to 30%,and the presence of the CSM10 also improved the biomimetic apatite mineralization ability in the pore struts of the scaffolds.Furthermore,the flexible strength(12.5 -30 MPa)and compressive strength(14-37 MPa)of the 3D printed porous bioceramics remarkably increased with increasing CSM10 content,and the compressive strength of DIO/CSM10-30 showed a limited decay(from 37 MPa to 29 MPa)in the Tris buffer solution for a long time stage(8 weeks).These findings suggest that the new CSM10-reinforced diopside porous constructs possess excellent mechanical properties and can potentially be used to the clinic,especially for the treatment of osteonecrosis of the femoral head work as a bioceramic rod.

Effect of Applied Stresses on the Microstructure and Dissolution Behavior of Plasma Sprayed Wollastonite Coatings

Wollastonite coatings were deposited on the U-shape titanium alloy coupons by atmospheric plasma spraying.The effect of applied stresses on the microstructure and dissolution behavior of wollastonite coatings was investigated.The microstructure and composition of coatings were examined by scanning electron microscope(SEM)and electron diffraction spectroscopy(EDS).In addition,the dissolution behavior of coatings was evaluated by immersion in simulated body fluid(SBF).More apatite is observed on the surface of coatings under a tensile stress and a stress-free condition after immersion in the SBF solution,whereas almost no apatite can be found for the coatings under a compressive stress.The dissolution rate of coatings characterized by the pH changes and the ion concentration of Ca,Si and P in the SBF solution is lower under the compressive stress than those under a tensile stress or a stress-free condition.It can be concluded from the experimental results that the compressive stress inhibits the dissolution of wollastonite coatings and the formation of apatite,whereas a tensile stress enhances the two processes.

Environmentally friendly wollastonite@TiO2 composite particles prepared by a mechano-chemical method

Core-shell wollastonite@ TiO2(WOT)composite particles are prepared by a mechano-chemical method (MCM)to improve the dispersion of TiO2and reduce its dosage,and to achieve synergistic effects with the wollastonite mineral.The crystal structure,morphology,functional groups,and pigment properties of the as-prepared composite powders are determined.The W@T composite particles are formed by van der Waals force in addition to electrostatic attraction and chemical bonding.The anatase TiO2coating is anchored on the woUastonite surface by Si-O-Ti and Ca-O-Ti bonds.The W@T powders possess excellent characteristics such as whiteness of 96.6%,hiding power of 17.97g/m^2,and oil absorption of 22.72g/100g.The properties of the W@T composite are similar to those of TiO2and the former,which is much cheaper,can potentially substitute the latter as a white paint in many applications.

Formation and Biomimetic Deposition of Bone-like Hydroxyapatite on Wollastonite-gypsum Composites

Bone cements are often used for bone repair and fixation. The main objective of formulating a bone cement is to achieve structure and properties similarity to bone. In addition, bioactivity of a bone cement provides a major advantage that helps achieving better binding and interaction with the surrounding tissues. In the current study, gypsum was used as a matrix for a composite that comprises highly crys- talline prestine and acid-treated wollastonite （CaSiO3） fibers. Composites made by mixing their powder precursors with deionized water at room temperature, were investigated for their composition using X-ray diffraction （XRD） and Thermogravimetric Analysis （TGA）, for their microstructure using Scanning Electron Microscopy （SEM）, for their compressive strengths and modulus of elasticity, and for setting time measurements. In addition, cement composites were evaluated for their preliminary bioactivity in a protein-free Simulated Body Fluid （SBF） for up to 14 days. Results show the improvement of mechanical properties and bioactivity of the composites using acid-treated wollastonite fibers. This was attributed to the formation of hydrated silica layer on the surface of the acid-treated fibers which improved the binding with the gypsum matrix and provided nucleating sites for the deposition of bone-like apatite spherolites from SBF media.