Preparation and Properties of SiO&lt;sub&gt;2&lt;/sub&gt; from Rice Hulls

Nakata, Yoshinori; Suzuki, Masaaki; Okutani, Takeshi; Kikuchi, Masanobu; Akiyama, T.

doi:10.2109/jcersj.97.842

Cited by 65 publications

(62 citation statements)

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“…7, which hinders a eutectic reaction with silica to cause its liquid phase. This result corresponds well to those in the previous reports, [28][29][30] showing that crystallization of silica to cristobalite or tridymite when burning over 1127 K.…”

Section: Resultssupporting

confidence: 93%

Process Parameters Optimization in Preparing High-Purity Amorphous Silica Originated from Rice Husks

2007

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Rice husk, one of the main agricultural disposals in Japan, China, India, and South-east Asian countries, is employed as useful renewable resources to produce energy and high-purity silica (SiO 2 ), because it consists of 70% organics and about 20% SiO 2 . The latter, SiO 2 is obtained by burning rice husks in air. The purity of rice husk ashes, however, is reduced by the remains of both carbon contents originated in organics and original metallic impurities such as K, Na, Ca, P, Al, etc. In the previous works, the utilization of the leaching methods by strong acids with a high concentration for both the remove the metallic impurities and the fragmentation of silica structural network was suggested. As their results, the thermal resolution mechanism of organics was discussed by using TGA showing the mass loss behavior during heating. The objective in this study is to clarify the mechanism of the removal of organic components when applying a dilute H 2 SO 4 leaching treatment with 15% solution concentration. In particular, from a viewpoint of the investigation on molecule structural changes of organics, GCMS (Gas Chromatograph Mass Spectrometer) analysis is carried out on acid-leached rice husks. When using only 1% concentration H 2 SO 4 solution leaching, a change of cellulose of polysaccharides to levoglucosan via glucose of monosaccharide by hydrolysis and condensation reactions occurred. This reaction accompanied with dehydration always served en endothermic heat, which was found in DTA profile of acid leached rice husk materials. It was also clarified that such a low concentration H 2 SO 4 solution was enough to remove alkali metal elements contained in husks. By optimizing the combustion temperature of rice husks after acid leaching, completely amorphous silica ashes, composing of 99.3% SiO 2 and 0.04% carbon, were obtained.

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Section: Resultssupporting

confidence: 93%

Process Parameters Optimization in Preparing High-Purity Amorphous Silica Originated from Rice Husks

2007

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“…6,12 At calcination temperatures above 1173 K, the SiO 2 in RHA would consist phases of cristobalite and some tridymite because of the melting of the surfaces of ash silica particles and bonding of particles together. 14 This behavior was demonstrated in the calcination applied here even though the as-received rice husk ash was found to be already in crystalline form according to its XRD spectrum ( Figure 1). The as-received RHA only have defined Bragg's peaks at 2θ value of 21.9˚ and some distinct peaks at 20.9, 26.6 and 36.0˚.…”

Section: Properties and Solubility Of Rhs And Rhasmentioning

confidence: 56%

Properties of silica from rice husk and rice husk ash and their utilization for zeolite y synthesis

2011

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Recebido em 21/12/10; aceito em 22/3/11; publicado na web em 10/6/11This study compared properties of silica (SiO 2 ) from rice husk (RH) and rice husk ash (RHA) extracted by acid-and heat-treatment. The SiO 2 from RH was in amorphous phase with nearly 100% purity while that from RHA was in crystalline phase with 97.56% purity. Both extracted SiO 2 were used in the synthesis of zeolite NaY but that from RH was better due to the efficiency in product recovery and simplicity of extraction. After the NaY was exchanged to NH 4 Y and calcined to convert to HY, the product did not carry over the textural properties of the parent NaY and NH 4 Y.

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“…It contains 13-29% inorganic components, of which 87-97% is SiO 2 (silica) 3) in an amorphous state. The use of silica from the residual rice husk has been a major concern of many researchers.…”

Section: Introductionmentioning

confidence: 99%

“…The use of silica from the residual rice husk has been a major concern of many researchers. Their approach may be classified into two categories: 1) purification or modification of rice husk to produce highly pure silicon and silica compounds [3][4][5][6] , 2) utilizations as an economic source of silica for the cement industry, lightweight construction products, abrasives and absorbents 7,8) . In the latter category, rice husk is usually burnt to white ash to obtain and use the silica it contains.…”

Section: Introductionmentioning

confidence: 99%

“…The presence of amorphous silica, crystalline silica or both in RHA depends on the temperature of heating used in this process. of tridymite and cristobalite 3,6,8) . Although there are many studies dealing with the transformation of amorphous silica to tridymite and cristobalite at around 1,000°C [9][10][11] , quite a few studies have examined the quantities and characteristics of the crystalline phase in heated silica 11,12) .…”

Section: Introductionmentioning

confidence: 99%

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Quantitative Analysis of Tridymite and Cristobalite Crystallized in Rice Husk Ash by Heating.

2004

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The quantities of two forms of crystalline silica, tridymite and cristobalite, in heated rice husk ash (RHA) samples were determined by X-ray diffraction (XRD) and chemical methods. Two RHA samples, containing 93% SiO 2 and 2-3% K 2 O, were prepared from charcoaled rice husk products and heated to above 900°C. The crystalline silica made up over 60-80% of the total silica in the heated RHA samples based on the XRD analysis. The crystalline phases in the two samples were somewhat different: The sample heated in the temperature range of 900 to 1,200°C contained 52-62% cristobalite and 10-17% tridymite, but the other sample heated at a comparable temperature, above 1,100°C, contained 46-66% tridymite and 37-16% cristobalite. Based on a correlation of lower tridymite crystallization temperature with higher potassium content, it was concluded that higher potassium levels were responsible for this difference. The pyrophosphoric acid analysis did not give exact results in the evaluation of total crystalline silica content in these RHA samples. As the combustion of rice husk was considered to cover the demands for energy and silica resource in Asian countries, cristobalite and tridymite crystallized in RHA by burning of rice husk should be assessed precisely by XRD analysis and the airborne dust in relevant workplace be controlled.

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Preparation and Properties of SiO<sub>2</sub> from Rice Hulls

Cited by 65 publications

References 0 publications

Process Parameters Optimization in Preparing High-Purity Amorphous Silica Originated from Rice Husks

Process Parameters Optimization in Preparing High-Purity Amorphous Silica Originated from Rice Husks

Properties of silica from rice husk and rice husk ash and their utilization for zeolite y synthesis

Quantitative Analysis of Tridymite and Cristobalite Crystallized in Rice Husk Ash by Heating.

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