X-ray diffraction analysis of silicon prepared from rice husk ash

Polycrystalline silicon has been prepared by metallothermal reduction of rice husk ash, which contains a considerable amount of amorphous silica. Acid-leached rice husk was burnt at a temperature of 620° C to obtain rice husk ash (RHA). RHA was then reduced with magnesium and major impurities were minimized or removed by an acid leaching process. The end-product was analysed using X-ray diffraction and mass spectrometric techniques. It was found that the powdered silicon obtained from magnesium reduction of RHA had a very low impurity concentration indicating that rice husk, which is an agricultural waste, is a potential source of metallurgical and solar-grade silicon.     

Characterization of Biogenic Silica Generated by Thermo Chemical Treatment of Rice Husk

This study presents two routes to produce amorphous silica from an Egyptian rice husk under conditions optimized for least environmental impact and low cost. The first route includes thoroughly washing of the husk sample with water, dry milling and leaching with citric acid. The leaching process was applied in two stages, that is, at 323 K for 180 min and then at 353 K for 60 min. After washing and drying, the leached sample was subjected to a heat treatment in a muffles furnace at four sequential steps. The second route includes all the previously mentioned steps, except the citric acid leaching. The final products were characterized using x-ray fluorescence analysis, carbon content analysis, x-ray diffraction, differential thermal analysis, nitrogen adsorption, mercury intrusion, and scanning electron microscopy. The results show that the citric acid leaching has many advantages with respect to silica yield and porosity as well.     

Crystalline rice husk silica reinforced AA7075 aluminium chips by cold compaction method

Aluminium matrix composite is highly demanded in various industries due to its low density and good mechanical properties as most commonly studied for metal matrix composite. The properties of the composite be improved with the addition of reinforcement significantly such as silicon carbide, aluminium oxide, and boron carbide that can be mixed easily to metal matrix composite. The study of crystalline rice husk silica reinforced AA7075 aluminium chips on mechanical properties were investigated. The rice husk ash was burned at 1200 °C and it was characterized in the crystalline phase by conducting x-ray diffraction test. The mechanical properties of aluminium matrix composite were obtained by microhardness and compression tests. Results of mechanical properties for the addition of rice husk silica up to 7.5 wt.% composition of crystalline rice husk silica showed increase value of microhardness and compression strength which are the highest value of 75.94 HV 0.1 and 443 MPa, respectively compared to another aluminium matrix composite. Hence, based on investigation to crystalline rice husk silica reinforced aluminium, it has good potential to improve the mechanical properties of aluminium matrix composite which were dependent to the composition of crystalline rice husk silica reinforcement in aluminium matrix composite.     

Effect of amorphous silica by rice husk ash on physical properties and microstructures of recycled aluminium chip AA7075

High strength to weight ratio of aluminium reinforced as metal matrix composites is a well known material used in automotive application. The effects of recycled aluminium chips AA7075 with amorphous silica by rice husk ash on the physical properties and microstructure were investigated. Recycled aluminium chip AA7075 was reinforced with agro waste of amorphous silica rice husk ash i. e., 2.5 %, 5 %, 7.5 %, 10 % and 12.5 %. Samples of these metal matrix composites were prepared by cold compaction method due to the lower energies consumption and operating cost compared to conventional recycling by casting. Physical testing of density, apparent porosity, water absorption and hardness tests of the metal matrix composites samples were examined in the current study. The density of metal matrix composites was increased up to 5 % of amorphous silica, and then decreased with increasing mass fraction of amorphous silica. Porosity and water absorption of metal matrix composites were significantly consistent at increasing mass fraction of amorphous silica, while the hardness of metal matrix composites was increased at increasing amorphous silica. Consequently, the microstructures of metal matrix composites were observed via optical microscope to analyze the dispersion of the reinforced composites. The microstructures of metal matrix composites were found non‐homogeneous and random distribution of amorphous silica and aluminium chip AA7075 compared to 100 % recycled aluminium chip AA7075. Based on investigation to aluminium reinforced rice husk ash composites, it has good potential to improve the material behavior of metal matrix composites by appropriate composition amorphous silica to composite.     

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.     

Effect of calcination temperature and heating rate on the optical properties and reactivity of rice husk ash

Rice husk is an agricultural waste and its conversion to value added products makes it a secondary resource material. On heating, rice husk gives ash with >90% by weight of silica with some carbon and other nonmetallic and metallic impurities. Silica of high purity, chemical reactivity and white color can be produced from rice husk by controlling the heating conditions and this material finds wide industrial applications. Properties of the ash depend upon various pretreatments and calcination conditions. The present work deals with the investigation on a rice husk sample from the state of Andhra Pradesh in India. The raw husk and its acid treated form were calcined at different conditions such as temperatures, soaking periods and heating rates. Lime reactivity, surface area, brightness and color values of the ash samples were measured. The high potassium content in the husk has been found to inhibit the carbon removal during ashing which affected the color as well as reactivity of the ash. Properties of the ash samples from the untreated and acid treated husk have been compared and correlated with the formation conditions.     

Effect of organic acid treatment on the properties of rice husk silica

Rice husk, an agro waste material, contains about 20% ash which can be retrieved as amorphous, chemically reactive silica. This silica finds wide applications as filler, catalyst/catalyst support, adsorbent and a source for synthesizing high performance silicon and its compounds. Various metal ions and unburned carbon influence the purity and color of the ash. Controlled burning of the husk after removing these ions can produce white silica of high purity. The present paper deals with the investigation carried out on two rice husk samples of different origin, one from the state of Andhra Pradesh (APRH) in the central part of India and the other from Kerala (KRH) the southern most part of the country. Leaching the husk with acetic and oxalic acids was attempted for the first time and the improvement in properties of the ash was studied. The husk samples were also treated with hydrochloric and nitric acids of different concentrations for comparison. The ashes produced by controlled burning of these samples before and after acid treatment, were characterized for the optical properties in addition to the chemical and physical nature. The APRH ash was found to be inferior to the KRH ash in all properties. Pretreatment of the husks with the organic acids improved the properties of ashes and the effect was comparable to that achieved by mineral acid leaching. Amorphous, reactive and high purity silica with high surface area and pore volume and good optical properties could be prepared from both the husks under specific conditions.     

Nature and reactivity of silica available in rice husk and its ashes

Scanning electron microscopy, reactivity and surface area measurements of rice husk and its ashes reveal the gradual formation of amorphous silica during ashing. The reactivity of the silica thus formed is found to be at its maximum for ashing temperatures between 400 and 600°C and hold-time from 6 to 12 h. The reactivity of the ash is found to decrease with increasing temperature (⩾ 600°C) and hold-time. IICT Communication No. 2375.     

低温稻壳灰可控制备及复合水泥研究

采用可控式低温稻壳灰制备装置研究了各种因素对稻壳灰产品的影响;X射线及SEM表征表明,制得的低温稻壳灰为无定形态,且颗粒粒度范围为50～100nm.将低温稻壳灰作为水泥掺合料,与硅灰和粉煤灰对比得到:低温稻壳灰对混凝土强度具有明显的提高效用;当水灰比一定,低温稻壳灰掺入量小于20%(质量分数)时,硅灰与稻壳灰的增强效果相近,可以用稻壳灰代替硅灰.     

Characterization of a Mineral Synthesized by Availing Silica from Plant Source

Rice husk was used to prepare the silica of amorphous nature being several times more reactive than that obtained from the mineral kingdom. Number of rice husk batches were pyroprocessed under varying time-temperature parameters for this purpose. The ash resulting from a batch pyroprocessed at 500~C for 8 h contained 92.01% silica. It was upgraded to 98.50% by applying physicochemical purification procedures. The mineral, wollastonite (CaSiO3), was synthesized from thus prepared silica and limestone containing 55.91% CaO. Solid state reaction, between CaO and SiO2 was attempted at different temperatures in the presence of a mineralizer. The sintering temperature,for affecting the said synthesis, was ranged between 900℃ to 1300℃ with the steps of 100℃. Specific chemical analysis techniques were applied to determine the effectiveness of carried out reaction and promising batches were subsequently subjected to XRD investigations. The produced mineral was also characterized regarding its physical properties like: colour, hardness, melting point and specific gravity. Percent yield of the produced wollastonite was also estimated and compared with that of obtained by other researchers who synthesized it by using silica from mineral kingdom. Batches sintered at 1200℃ and 1300℃ for 1 h showed the overall best results.     

Synthesis and characterization of high-purity silica nanosphere from rice husk

The work reports the synthesis, characterization, and the properties of high-purity silica nanospheres from low-cost rice husk. Primarily, the rice husk was washed with distilled water (DW) and subjected to acid leaching to remove the impurities. The treated rice husk was annealed at different temperatures (620 and 900 degrees C) for varied time periods to achive the desirable silica nanospheres. The annealing temperature and time considerably affected the properties of the synthesized silica nanospheres. The morphology studies confirmed that the size of nanospheres were of approximately 50-60 nm. The photoluminesence studies revealed that the synthesized silica nanospheres showed less structural defects and good optical properties. On the basis of the formation and the characterization of silica nanospheres a possible mechanism was suggested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis confirmed that the synthesized silica nanospheres contained approximately 99.93% purity.     

Review Processing, properties and applications of reactive silica from rice husk—an overview

Rice husk is an abundantly available waste material in all rice producing countries. In certain regions, it is sometimes used as a fuel for parboiling paddy in the rice mills. The partially burnt rice husk in turn contributes to more environmental pollution. There have been efforts not only to overcome this but also to find value addition to these wastes using them as secondary source of materials. Rice husk contains nearly 20% silica, which is present in hydrated amorphous form. On thermal treatment, the silica converts to crystobalite, which is a crystalline form of silica. However, under controlled burning conditions, amorphous silica with high reactivity, ultra fine size and large surface area is produced. This micro silica can be a source for preparing advanced materials like SiC, Si₃N₄, elemental Si and Mg₂Si. Due to the high pozzolanic activity, this rice husk silica also finds application in high strength concrete as a substitute for silica fume. Possibility of using this silica as filler in polymers is also studied. The present paper is an attempt to consolidate and critically analyse the research work carried out so far on the processing, properties and application of rice husk silica in various laboratories and also highlighting some results on the processing and characterization of RHA and reactive silica obtained from it in the authors' laboratory.     

高灰分碳粉的碱酸法提纯

对某电解铝企业废旧阴极材料进行浮选-酸洗-磨碎处理后获得含灰分高达27.3%的碳粉,然后采用加NaOH焙烧活化-水洗-盐酸酸浸-水洗工艺对该碳粉进行除灰提纯研究。考察了氢氧化钠加入量、焙烧温度、焙烧时间、盐酸酸浸温度对碳粉灰分脱除的影响。结果表明:当设定氢氧化钠/碳粉为0.4,在1000℃焙烧1h,然后采用浓度为1mol/L的盐酸在60℃酸浸1h,可使碳粉中的灰分由27.3%降低到4.04%,碳含量由68.4%提高至94.6%,处理后的碳粉可重返阴极配料利用。     

High-purity amorphous silica originated in rice husks via carboxylic acid leaching process

The environmentally benign, harmless to human, and economically effective process to produce high-purity amorphous SiO₂ materials from rice husks has been established by using a carboxylic acid leaching, not the conventional strong acids. TG-DTA measurement and GCMS analysis indicated that the leaching was effective for the hydrolysis of celluloses and hemicelluloses contained in rice husks at 473–873 K, which produced the same results in using the conventional sulfuric acid. In particular, the formation of furfurals and levoglucosans occurred via the hydrolysis at 473 K and 673 K, respectively, when using rice husks leached by citric acid solutions. The metallic impurities could be also removed from the husks via a chelate reaction between carboxyl groups (–COOH) and the metal elements. Concerning the burning conditions of rice husks after the acid leaching, it was necessary to supply a suitable amount of air to completely combust organics; for example, it required air supplement of 50 mL/min or more. High-purity amorphous silica materials with 99 wt% or more were prepared from rice husks by applying the citric acid leaching treatment and burning process at 1073 K in air.     

粉煤灰提取白炭黑和氧化铝的研究

粉煤灰是我国当前排量最大的工业废渣之一,年排渣量已达3亿t以上,大量堆积的粉煤灰会对自然生态环境造成严重的危害。综合利用粉煤灰,实现粉煤灰的资源化利用,对于治理粉煤灰的污染具有十分重要的意义。文章提出先采用碱液常压浸出粉煤灰,生产白炭黑,然后采用碱石灰烧结法生产氧化铝,可实现粉煤灰的经济综合利用。研究表明：用苛性碱液在常压（＜125 ℃）下浸取粉煤灰45 min,粉煤灰中硅的提取率达到72.5 %以上,而氧化铝的总溶出率＜1.2 %;碳分浸取得到的硅酸钠溶液,可以生产氧化硅含量＞99 %的优质白炭黑,溶液中氧化硅转化率＞98 %;浸取硅后的渣中氧化铝含量＞55 %,氧化硅含量＜20 %,铝硅比≥2.7,适宜采用碱石灰烧结法生产氧化铝。碱石灰烧结法适宜的配方为：碱比 0.95～1.0,钙比 1.8～2.0;烧结温度宜为1 200～1 250 ℃;熟料溶出温度75～85 ℃,时间10～20 min,氧化铝回收率＞86 %。综合利用粉煤灰生产白炭黑和氧化铝,经济效益和社会效益显著。     

The quantitative estimation of silica in rice husk ash by titrimetric method: A case study for uncertainty calculation

Silicon is an essential element found in cereals, fruits, vegetables pasta, rice, etc. Rice husk ash is one of the most silica rich raw materials after complete combustion among the family of agro wastes. For the preparation of pure activated silica rice husk are now widely used as raw material. Rice husk ashes are now used by various industries for different applications due to its important properties. The exact quantity of silica in the rice husk ash is therefore essential to know before further research. Keeping these facts an attempt has been made to determine the silica content by titrimetric method followed by quantification of uncertainty budget in four different variety of rice husk ash. The major sources of uncertainty in the measurement have been identified as contributions from repeatability, standardization of sodium hydroxide, titration, weight of the sample taken, volume measurement by volumetric flask, burette, pipette, weighing balance etc. All major sources of uncertainty have been identified and combined following the EURACHEM guidelines.     

Investigation of the effect of rice husk derived Si/SiC on the morphology and thermal stability of carbon composite aerogels

Highly porous carbon aerogels were prepared by pyrolyzing the novolac–silica aerogels. The silica phase was extracted from rice husk ash (RHA). The polymer aerogel was synthesized via the novel method of sol–gel polymerization in solvent vapor-saturated atmosphere. This method removes the need for supercritical drying and reduces the shrinkage of aerogels during drying stage and also has much lower process time compared to the conventional sol–gel method. In the next step, polymer composite aerogels become carbon/silica and carbon/silica/silicon carbide composites in pyrolysis (800 °C) and carbothermal reduction (1500 °C) stages, respectively. The characterization of the prepared composite aerogels was performed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses, respectively. Thermal and mechanical properties of the samples were investigated by differential scanning calorimetry (DSC) and compressive strength analysis. The resultant composite aerogels show a nanostructure with high porosity (above 82%) and low density (below 0.3 g cm^− 3). Si mapping images showed the good distribution of silica phase throughout the carbon matrix. Also the rate of oxidation for carbon composites decreased by silica incorporation and oxidation temperature increased about 20% by adding RHA silica. Compressive strength of composite samples increased about 25% by increasing RHA silica phase content.     

Thermal treatment of the precipitated solid material (PSM) from the waste black liquor (WBL)

Preciptated solid materials (PSM) from waste black liquor (WBL), at pH 8·5–9·0, produced from cooking of rice straw in paper mill factories were thermally treated. The cooking process led to decrease in organic material and partial substitution in silica structure. During this cooking process, three probable stages of mass loss comprise removal of moisture, volatile release, and combustion. The chemical analysis depicts the cooking effect on leaching either the high percentage elements (Ca, Na, and K) or some metallic cations (Mn, Cd, Zn and Cu) in the parent rice straw. Silica hydrate, amorphous silica and crystalline silica were obtained at <600°C, 600–700°C and at>800°C, respectively. The infrared spectra show gradual removal of the hydrocarbon bond (C–H), molecular H₂O, and sianol group (Si-OH) with temperature. TG, DTA, XRD and SEM were used in this study.     

The effects of a hydrochloric acid pre-treatment on the physicochemical properties and pozzolanic performance of rice husk ash

This paper investigates the effects of acid normality (0.01–6 N HCl) and combustion retention time (0.25–16 hours) on the pozzolanic properties of pre-combustion acid-treated rice husk ash. The pozzolanic reactivity was quantified by adding ground ash to saturated Ca(OH)₂ solutions and monitoring the time-dependent electrical conductivity and pH of the solutions. Also, the strength activity of ashes from different processes was measured by testing the compressive strength of mortars. It was observed that acid treatment results in ashes with higher SiO₂ content, lower alkali and unburned carbon content, better grindability, and smaller particle size, in comparison with ash from non-acid treated husks. Acid leaching increased the lime reactivity of the ashes and decreased their sensitivity to prolonged combustion times. Further, acid treatment with 0.01 N HCl was found to be sufficient, as the use of stronger acids did not considerably improve the pozzolanic reactivity of rice husk ash.     

Assessing the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste

This study assesses the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste. rice husk ash (RHA), palm oil fuel ash (POFA) and river sand (RS) were ground to obtain two finenesses: one was the same size as the cement, and the other was smaller than the cement. Type I Portland cement was replaced by RHA, POFA and RS at 0%, 10%, 20%, 30% and 40% by weight of binder. A water to binder ratio (W/B) of 0.35 was used for all blended cement paste mixes. The percentages of amorphous materials and the compressive strength of the pastes due to the hydration reaction, filler effect and pozzolanic reaction were investigated. The results showed that ground rice husk ash and ground palm oil fuel ash were composed of amorphous silica material. The compressive strength of the pastes due to the hydration reaction decreased with decreasing cement content. The compressive strength of the pastes due to the filler effect increased with increasing cement replacement. The compressive strengths of the pastes due to the pozzolanic reaction were nonlinear and were fit with nonlinear isotherms that increased with increasing fineness of RHA and POFA, cement replacement rate and age of the paste. In addition, the model that was proposed to predict the percentage compressive strength of the blended cement pastes on the basis of the age of the paste and the percentage replacement with biomass ash was in good agreement with the experimental results. The optimum replacement level of rice husk ash and palm oil fuel ash in pastes was 30% by weight of binder; this replacement percentage resulted in good compressive strengths.