Production Of Amorphous Silica Research Articles

Integrated Recovery of Iron and Nickel from Olivine Ores Using Solvent Extraction: Synergistic Production of Amorphous Silica and Carbonates through pH Adjustment and Carbon Mineralization

Integrated Recovery of Iron and Nickel from Olivine Ores Using Solvent Extraction: Synergistic Production of Amorphous Silica and Carbonates through pH Adjustment and Carbon Mineralization

HYDROFLUORIDE PROCESSING OF TAILINGS FROM WET MAGNETIC SEPARATION OF TITANOMAGNETITE TO OBTAIN AMORPHOUS SILICON DIOXIDE

A method for the opening of silicon-containing technogenic feedstock using an aqueous solution of ammonium bifluoride (NH4HF2) with subsequent production of amorphous silica has been developed. In this work we examined wet magnetic separation tailings (WMST) – iron titanium-magnetite ore enrichment rejects that are formed in huge quantities and stored in sludge depositories at concentrating plants. The main rock-forming minerals of WMST are resistant silicates – pyroxene, amphibole, plagioclase and olivine with the total SiO2 content of about 50%. It was established that fluorination of silicon-containing minerals begins during mechanical dispersion of a dry reaction mixture at room temperature. The thermodynamic calculations confirm active interaction of components in the composition of mineral complexes already at 25 ℃, some of the processes being exothermic with entropy reserve. When the temperature increases to 90 ℃ and the duration of leaching to 5 h, the extraction of silicon in the form of soluble ammonium fluorosilicate grows. Insoluble calcium and magnesium fluorides and sparingly soluble under leaching conditions ammonium fluorometallates, as well as a part of unreacted rock are formed in the insoluble residue. Under the most effective desilication conditions (20% NH4HF2 solution, L:S=4:1, 2 h), the residual content of SiO2 decreases to 1–2%. The synthesis of finely dispersed amorphous silica (SiO2) was performed by hydrolytic deposition when the value of рН of clarified ammonium fluorosilicate solution was reduced by adding ammonia. It was shown that gradual introduction of hydrous ammonia (5 ml/h) into diluted fluorosilicate solution with a concentration of less than 5 g/l Si while constant stirring leads to the formation of spherical silica nanoparticles. The degree of silica extraction from tailings in the process of hydrofluorination of 20% NH4HF2 solution at 90 ℃ for 2 h was 98%, and the content of impurities in amorphous silica did not exceed 1–2%. Separation of finely dispersed suspension of insoluble fluorides and hydroxide impurities formed during stepwise hydrolysis of fluorosilicate solution to рН value less than 5 is a necessary condition for producing pure silica SiO2. The final product, similar to “white soot” in properties, is characterized by predominant particle size in the interval of 2-20 nm, a large surface area 230-360 m2/g and a low pycnometric density 1.62 g/cm3. For citation: Medyankina I.S., Pasechnik L.A. Hydrofluoride processing of tailings from wet magnetic separation of titanomagnetite to obtain amorphous silicon dioxide. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 2. P. 70-77. DOI: 10.6060/ivkkt.20236602.6706.

Thermo-kinetic modelling of the acidic leaching of anorthosite: Key learnings toward the conception of a sustainable industrial process

• Specific ion Interaction Theory model can suitably describe the electrolyte solution. • Geochemical simulation gives conditions for Al 3+ extraction & SiO 2 (am) precipitation. • Gudvangen anorthosite dissolution proves to proceed in chemical reaction regime. • Kinetic model helps refining process parameters (incl. particle size distribution). • The counter-current configuration can outperform the batch performance. The world is facing critical technological and environmental challenges in the production of basic materials in high demand, such as aluminium and silica, whose processes were developed long ago. New production routes, involving using alternative resources and innovative technological solutions, are needed to secure access to these base materials at a lower cost to the environment, in terms of waste and carbon footprint. The European project AlSiCal is currently investigatingan environmentally friendly multi-step process for producing alumina and silica from anorthosite, an abundant feldspar mineral. The present paper focuses on the modelling strategy of the dissolution of anorthosite in concentrated hydrochloric acid, which is the first step of the AlSiCal process. The objectives of this study are (i) to give a reliable first-level prediction of the product speciation in the aqueous and solid phases, (ii) to provide the sensitivity of the process to key operating variables, and finally, (iii) to evaluate the performance of both batch and continuous leaching processes. The proposed methodology is based on the coupling of geochemical equilibrium simulations and particle reaction models, using different computational tools and relevant literature data. This makes it possible to select the favourable operation window and process configuration for the quantitative extraction of aluminium in solution and the production of amorphous silica with an acceptable purity for large-market applications.

Erianthus Plant: A Rich Silica Source for Extraction of Amorphous Silica

In this paper, Erianthus plant, a grass type of lignocellulosic biomass, is presented as an alternative source for the production of amorphous silica. Thermal treatment (combustion) of Erianthus plant under a controlled temperature of 600–900°C produces Erianthus Ash (EA). Then, silica powder was extracted from EA by the chemical extraction method. In this work, the effect of treatment temperature on the preparation of EA and extracted silica is studied. The EA samples and extracted silica are noted as EA600 – EA900 and Si600 – Si900 respectively with respect to the treatment temperature. To evaluate the effect of the concentration of NaOH solution on the purity of silica, NaOH solution (2–3 N) is verified in this work. The results revealed that the pure amorphous silica can be extracted using a 2.5 N NaOH solution from EA800. The percentage of amorphous silica with a purity of about 99% was confirmed by X-Ray Fluorescence (XRF).

Production of amorphous silica and activated carbon from rice husk char obtained from two stage gasification process

In this study the rice husk has been subjected to two-stage gasification to obtain syngas, tar and char. The rice husk char is subjected to alkaline extraction to obtain amorphous silica and activated carbon. The products have been characterized by methods such as BET, FTIR and XRF. The silica obtained from acid leached rice husk has BET specific surface area of 311.68 m 2 /g and purity of 88.85%. The BET specific surface area of activated char increase from 102.49 m 2 /g to 567.03 m 2 /g after the activation process. The silica extraction using carbon dioxide (CO 2 ) precipitation is found to be more profitable than acid precipitation.

Mesoscale experimental investigation of thermomechanical behaviour of the carbon textile reinforced refractory concrete under simultaneous mechanical loading and elevated temperature

In comparison with carbon fiber reinforced polymer material, the carbon textile reinforced concrete (TRC) is usually coted to have a better fire behaviour. The aim of this paper is to analyse the elevated temperature behaviour of TRC. This paper presents the experimental results conducted on carbon TRC at mesoscale in the range of temperature from 25 °C to 700 °C. The carbon TRC consists of refractory matrix and carbon textile which has been treated with amorphous silica products for a good bond with the cement matrix. As a result, carbon TRC showed the strain-hardening behaviour with different phases and brittle behaviour depending on the temperature. The evolution of carbon TRC properties with elevated temperature (the ultimate stress, the crack stress, the initial stiffness) was experimentally identified. The mechanical property evolution of carbon textile and refractory concrete (the ultimate strength, the Young’s modulus) depending on temperature was also presented. The thermal tests on carbon TRC cylinder specimens were also performed to identify the diffusivity coefficient of this composite. All results obtained were analyzed in order to find the contribution of carbon textile and refractory matrix to fire resistance of carbon TRC. Its ultimate strength has been improved about 2 times compared with non-reinforced matrix at elevated temperature ranging from 25 °C to 400 °C. The efficiency coefficient of carbon textile could be calculated in this study.

Efficient Physicochemical Treatment Technology for Nepheline Concentrates

The processes of physicochemical treatment of nepheline concentrates are studied theoretically and experimentally, and the optimal conditions are determined for the integrated fluoride–ammonium recovery of different useful components. The enabling innovative technology is proposed for the production of amorphous silica, alumina, red iron oxide, calcium fluoride and other marketable products.

Upgrading the rice husk char obtained by flash pyrolysis for the production of amorphous silica and high quality activated carbon

The overall valorization of rice husk char obtained by flash pyrolysis in a conical spouted bed reactor (CSBR) has been studied in a two-step process. Thus, silica has been recovered in a first step and the remaining carbon material has been subjected to steam activation. The char samples used in this study have been obtained by continuous flash pyrolysis in a conical spouted bed reactor at 500°C. Extraction with Na2CO3 allows recovering 88% of the silica contained in the rice husk char. Activation of the silica-free rice husk char has been carried out in a fixed bed reactor at 800°C using steam as activating agent. The porous structure of the activated carbons produced includes a combination of micropores and mesopores, with a BET surface area of up to 1365m2g−1 at the end of 15min.

Utilization of amorphous rice husk ash for the synthesis of ZSM-5 zeolite under low temperature

The present study deals with the production and characterization of ZSM-5 zeolite under low temperature using amorphous rice husk ash as an alternative cheap silica source. Rice husk was combusted at various temperatures for the production of amorphous silica. The resulted amorphous silica ash was then utilized without any other treatment as a starting material for the synthesis of ZSM-5 zeolite using low temperature and under atmospheric pressure. For comparison, the high-temperature synthetic approach, the hydrothermal treatment under high temperature and autogenous pressure with the autoclave process, was also applied for the synthesis of ZSM-5 zeolite. The low-temperature method led successfully to the synthesis of highly siliceous zeolite of type ZSM-5. The produced materials were characterized using a variety of analytical techniques, including X-ray diffraction, Fourier transformation infrared spectroscopy, thermogravimetry–differential thermogravimetry analyses, scanning electron microscopy, electron dispersion X-ray analysis and nitrogen porosimetry. The results show that the utilization of an industrial by-product in abundance as a starting material can lead through a simple inexpensive technique to the synthesis of a high value added microporous material with many potential applications.

Valorisation of Rice Husk by Chemical and Thermal Treatments

In the industrial production of rice, large quantities of rice husk are generated constituting a residue with costs for the companies, which must be appropriately managed. The high grade of silica in the rice husk opens a possibility for its valorisation, through the production of amorphous silica with high porosity and potential application as ligand in construction materials, as catalyst support, as metals adsorbent, among others. In this research work a process was developed for the production of silica with amorphous properties from rice husk waste, and the products formed were characterised. The process involved three main operations: water washing for removal of some impurities, acid leaching with HCl or H2SO4 solutions for dissolution of contaminating metals and incineration for organics decomposition. The washing operation let a partial purification of the husk, allowing removal of 46-60% of contaminating metals such as K, Fe Mn and Zn. The leaching with 0.4M HCl and 0.2M H2SO4 allowed obtaining high metals removal efficiency, namely >99% for potassium, 85-90% for iron, >96% for manganese and >80% for zinc. The final composition of the leached husk was 0.003-0.006% K, 0.016-0.025% Fe, <0.001% Mn and <0.0007% Zn. The incineration of the rice husk after previous purification was performed at 540°C, by using samples obtained in the several chemical treatment conditions, and using different heating and cooling rates. As a result, a white colored final husk ash was produced, rich in quasi-amorphous silica (confirmed by X-ray diffraction). The analysis by scanning electron microscopy revealed that the organics removal allowed the formation of voids in the rice husk material, which became very porous and presented an alveolar morphology.

Comprehensive utilization of silica raw material of the upper and Mid-Amur River basins

The analysis of physical-chemical processing of silica-containing raw material has revealed optimal conditions for production of amorphous silica, ammonium hexafluorosilicate, mullite-siliceous refractory, and other commercial products. Using ammonium hydrodifluoride, the authors have developed efficient technologies for complex extraction of valuable components from silica-containing raw material.

Production of amorphous silica nanoparticles from rice straw with microbial hydrolysis pretreatment

An enzymatic hydrolysis approach was used in order to develop a less aggressive process for production of amorphous silica from rice straw. In the process, rice straw was firstly hydrolyzed either with a microbial isolate ( Trichoderma reesei TISTR 3080) or a microbial community (LDD1), followed by a heat treatment at 500 °C for 8 h. After hydrolysis, the rice straw was decomposed by T. reesei and by LDD1 to 59.6% and 45.2% of the initial weight, of which 12% and 23% ash content was respectively determined by thermogravimetric analysis. X-ray diffraction and transmission electron microscopy analysis confirmed that the major constituent in the ash to be amorphous silica with a particle size ranges between 50 and 80 nm. The silica content in the T. reesei pretreated ash was 82.5%, whereas the content of the LDD1 pretreated ash was 73.6%. Relatively high levels of impurities such as manganese and phosphate, associated with microbial activity were detected in both pretreated ash samples.

Mechanical fragmentation of precipitated silica aggregates

A common inorganic process for the production of amorphous silica involves acidifying a sodium silicate solution in a semi-batch reaction. Even after gelation, stirring and addition of reactants are continued. The gel is fragmented and the flocs densify until a suspension is obtained. Control of size and structure of the resulting aggregates is desirable as these strongly influence product properties. The aim of this study is to understand the destruction of the gel by mechanical energy input and to thus contribute to controlling the size of the fragments. Beside the energy input, the size of the gel fragments strongly depends on the gel's mechanical properties, which in turn depend on its age, solids content, pH, salt content and temperature. The influence of these parameters was investigated for a batch process in a continuously stirred tank and a Taylor–Couette reactor and by ultrasound dispersion. It can be shown that, in terms of breakage mechanics, the gel observes the same laws as a highly viscous liquid.

Effective technologies for complex processing of non-bauxite ores

As a result of investigation of complex processing of non-bauxite ores by the methods of segregation, extraction, and electrolysis, chemical and metallurgical conditions promoting the contrast distribution of aluminum, silicon, and their compounds between coexisting phases are revealed. Effective technologies for obtainment of aluminum and alumina and for complex processing of non-bauxite ores with the production of amorphous silica, silicon, and other useful components are developed.

Synthesis of Mesoporous Amorphous Silica via Silica-Polyviologen Hybrids Prepared by the Sol−Gel Route

A range of polyviologens synthesized by the Menshutkin reaction have been successfully incorporated into silica hybrids using the hydrolytic sol−gel route. Transparent hybrids can be obtained with up to 75% polyviologen content, indicating a likely nanoscale morphology. Hybrids were calcined at 650 °C to remove the polymer, forming porous amorphous silica products. Nitrogen adsorption−desorption studies have been undertaken on the hybrids and the calcination products, and the results are analyzed by the modeless method of Brunauer et al. for mesopore size distributions and a micropore analysis method based on t-curves. The hybrids are mostly mesoporous solids, but porosities are very low at high polymer contents. Calcination leads to silicas which are mainly mesoporous with varying degrees of microporosity depending on the nature and concentration of the polyviologen (PV) used. Poly(hexyl viologen ditosylate) produces high surface area silicas with >98% mesoporosity. The results may provide evidence for an influence of the PV on the structure of the forming silica, which is proposed to occur through electrostatic interactions between the quaternary nitrogen atoms of the polymer and the silanol oxygen atoms in the growing silica network.

Production of amorphous silica and combustible gas from rice straw

Results of the thermogravimetric analysis of untreated and 1 n HCl-treated rice straw reveal that mass loss occurred in three distinct stages: removal of moisture; release of volatile matter and oxidation of fixed carbon. The rate of combustion of fixed carbon of acid-treated straw was faster than that of untreated straw. Studies on the combustion of large samples of straw in a vertical electric furnace showed that both amorphous silica and combustible gas could be produced simultaneously under certain conditions. Acid treatment of straw prior to combustion helped in producing a white ash in a short period. The silica produced at a furnace temperature of 500°C with a maximum bed temperature of 720°C was amorphous in nature. The low-calorie combustible gas could be produced when straw containing 6.5–7.5% moisture was fed to the furnace set at a temperature above 450°C. The flame temperature, as well as the duration of the flame, increased as the bed thickness increased. A furnace temperature of 450°C, a bed depth of 20 cm and a combustion period of 3 h are considered as optimum for the production of white amorphous silica from 1 n HCl-acid-treated straw.

Conversion of rice husk into amorphous silica and combustible gas

Results of the studies on thermogravimetric analysis (TGA) of raw and 1(N) HCl acid treated rice husk (in still air) reveal that its thermal degradation takes place in three main stages of mass loss, namely (i) drying, (ii) devolatilization and (iii) slow oxidation of fixed carbon. Hydrochloric acid leaching of husk at 75° for 1 h prior to combustion is necessary for production of amorphous silica of complete white colour. For production of low calorie-combustible gas along with amorphous silica from the rice husks containing 5.5–7% (wb) moisture, a furnace set temperature of 450°C appears to be optimal.

Investigation of combustion of raw and acid-leached rice husk for production of pure amorphous white silica

The effects of various acid treatments of rice husk on removal of its metallic ingredients and different combustion temperatures on production of amorphous silica (white ash) were studied. Leaching of husk in dilute HCI (1 N) was proved to be effective in substantially removing most of the metallic ingredients and producing ash completely white in colour. Irrespective of the treatments given, the minimum temperature required for complete combustion within a reasonable period was found to be 500° C. The combustion time varied from 5 h at 500°C to 1.5 h at 700° C. The ash residues obtained from complete combustion of acid-treated husk samples were completely white in colour. On the other hand, under similar conditions, the ash residues obtained from untreated husk remained light brown. The acid treatment of husk did not affect the amorphicity of the silica.

Investigations on the production of silicon from rice husks by the magnesium method

The burning of dirt-free rice husks in a furnace at around 300°C results in the production of amorphous silica. The acid leaching of the ash so produced leads to very high purity amorphous silica. This amorphous silica can be reduced to polycrystalline silicon by magnesium at a comparatively low temperature (about 600°C). The differential thermal analysis and thermogravimetric analysis of various mixtures of silica, magnesium and magnesium oxide indicate that the reduction of silica proceeds via a gas-solid reaction. The purity of the polycrystalline silicon obtained suggests the possibility of manufacturing large quantities of solar grade silicon at a low cost and a low energy consumption.

Effect of the combustion process on the structure of rice hull silica

The study was carried to clarify the effect of thermal decomposition of rice hulls on the amorphous structure of silica ash. The ash obtained by thermal decomposition of hulls at temperatures in the range 500–1150°C for one hour was evaluated by X-ray diffraction. The ash prepared at comparatively lower temperatures (500–600°C) still consists of amorphous silica. Cristobalite was detected at 800°C. At 1150°C, both cristobalite and tridymite were present. The ash produced by combustion of rice hulls in a fixed bed at different air rates was evaluated. The amorphous structure of silica was present in the case of combustion at low air rates. At comparatively higher air rates, crystallization of silica takes place. The results obtained clarify the optimum conditions for production of amorphous silica by combustion of rice hulls in fixed beds.