Amorphous Rice Husk Ash Research Articles

Optimising Factors for the Production of Amorphous Rice Husk Ash via Combustion Process for Sustainable Construction: A Review

Optimising Factors for the Production of Amorphous Rice Husk Ash via Combustion Process for Sustainable Construction: A Review

Synergistic effects of amorphous porous materials and anhydrous Na2CO3 on the performance of bricks with high municipal sewage sludge content

The shortage of land resources around the world has led to the increasing pressure of clay brick production in recent years. On the other side, as a by-product of the sewage treatment, the mineral crystalline phase and chemical composition of municipal sewage sludge (MSS) are similar to those of clay, which also need to be treated urgently. Owing to the porous structure originating from large amounts of organics evaporation at elevated temperature in MSS, it can be utilized as the thermal insulation bricks. However, the component complexity of MSS will result in the decrease of strength and durability of bricks, thus the replacement amount of MSS was generally less than 30%. To achieve optimal experimental conditions for thermal insulation bricks with large amounts of MSS, up to 40% dried MSS, amorphous rice husk ash (RHA) and anhydrous Na2CO3 (ANC) as the raw materials in this work, the dosage and temperature were set as variable parameters. The results showed that 0.178 W/(m•K) of thermal conductivity of bricks with 9.6 MPa of compressive strength, and 1336.2 kg/m3 of bulk density were obtained under the optimal conditions: 4: 5: 1 of the weight ratio of MSS: Clay: RHA, 3% of additional dose of ANC, 1075 °C of sintering temperature. The obtained bricks revealed excellent durability and sorption properties for heavy metals through the freeze-thaw cycle test and leachability test. Overall results manifested one effective approach for solid waste treatment through cleaner production and paved one way for sustainable, economical and energy-saving construction.

Development of magnesium-silicate-hydrate (M-S-H) cement with rice husk ash

Rice husk ash (RHA) is a waste material obtained from the combustion of rice hulls. The properties of RHA, such as its crystallinity and reactivity, depend on the combustion conditions. This study investigated the use of RHA as a silica source in MgOSiO2 samples. Two different RHA sources (crystalline and amorphous) were used in comparison to microsilica (MS), which is commonly used in MgOSiO2 formulations to form magnesium silica hydrate (M-S-H). Isothermal calorimetry and pH measurements were used to analyze the progress of hydration. In addition to compressive strength measurements, microstructural analysis was performed via XRD, TG/DTG, FTIR and FESEM. Samples containing amorphous RHA as the silica source achieved the highest compressive strengths at early ages (34 MPa at 7 days), whereas those containing MS revealed the highest strengths in the long term (47 MPa at 56 days). This was in line with the faster dissolution rate of amorphous RHA in comparison to MS, as observed in pH measurements. The formation of M-S-H was clearly observed in all samples containing amorphous RHA and/or MS. The use of crystalline RHA led to low strengths, which was provided by brucite in the absence of M-S-H. Combination of amorphous RHA with MgO resulted in M-S-H formation, which was accompanied with a notable mechanical performance. Utilization of amorphous RHA in MgO systems could not only lead to strength gain, but also bring environmental and economic benefits.

Synthesis of nano-sized zeolite-Y functionalized with 5-amino-3-thiomethyl 1H-pyrazole-4-carbonitrile for effective Fe(III)-chelating strategy

Zeolite crystals having faujasite-type (FAU) topology in the nanometer range were first synthesized from amorphous rice husk ash at a low temperature of 363 K under autogenous pressure. Following this, surface functionalization of the produced zeolite with 5-amino-3-thiomethyl 1H-pyrazole-4-carbonitrile (pyrazole; Py) was carried out by two different methods, namely liquefied-period adsorption of Py (Py/Yim) and a flexible ligand method (Py/Yss). The latter provides a larger amount of Py formed into as-made zeolite-Y. The sorption of Fe(III) onto Py/NaY afforded large meso–macroporosity introduced by the aggregation–assembly between Fe(III)Py complexes and NaY zeolite, which was typically evidenced for Fe(III)Py/Yss. The materials were characterized by XRD, FT-IR spectroscopy, thermal analysis (TGA) and porous structure by N2 adsorption–desorption at 77 K. The XRD evaluation showed that the zeolite structure was managed right after adding Fe(III) to Py/Y, although a change in intensity of the zeolite reflections on complex formation was noticed. The FT-IR spectrum of Fe(III)Py/Yss exhibited two bands at 3594 and 3542 cm−1 assigned to bridging hydroxyl groups associated with a Bronsted site, which did not exist in the spectra of Fe(III)Py/Yim and Fe(III)-exchanged as-made NaY zeolite. This effect was ascribed to the induced greater electronegativity of the ligand towards Fe(III) species in dissociation of water molecules, producing acidic protons that are potential Bronsted acid sites. It was also evident that the Fe(III) adsorption capacity on Py/Yss is greater than on as-made NaY zeolite and Py/Yim, owing most likely to the increasing concentration of the incorporating Py ligand which leads to an increase in the number of binding sites. The Fe(III) adsorption onto Py/Yss was well described by the pseudo-second-order kinetic model. Density functional theory (B3LYP/6-311G*) was performed to understanding the interaction mode of the ligand and complex with zeolite. The QSPR was calculated depending on the optimization geometries, frontier molecular orbitals, thermodynamic parameters, and global chemical reactivates, which were discussed for the studied compounds. The HOMOs, LUMOs and molecular electrostatic potentials were plotted to elucidate the interaction manner of the tested compounds with the zeolite. The nonlinear optical properties were elucidated via 1st and 2nd hyper-polarizabilities. The auto-degradation behavior was predicted for the complex, based on the ionization optional and bond dissociation enthalpy. The interactions between Py and Fe(III)Py with the zeolite surface have been described with molecular dynamics using a Monte Carlo simulation.

Production of amorphous rice husk ash in a 500 kW fluidized bed combustor

A 500kW rice husk-firing fluidized bed combustor was designed for obtaining low carbon and high silicon ash in the amorphous form. The influence of operating condition (temperature, fluidizing velocity) on combustion efficiency and rice husk ash quality was experimentally investigated. Furthermore, the quality of rice husk ash collected from inner bed, two-stage cyclones and bag-house was analyzed using XRD, TEM and SEM instruments, in terms of amorphous silicon dioxide and unburnt carbon content. Comparative study was carried out between the rice husk ash produced in an electronic oven and that produced in the above-mentioned fluidized bed combustor. The results show that quality of ash from the industrial-scale fluidized bed is even better than that from electronic oven. Temperature of 660–720°C and fluidization velocity of 1.0–1.2ms−1 appear to be the favoring parameters for producing high quality rice husk ash with amorphous structure of silicon dioxide content over 93.8wt.% and unburnt carbon context less than 4.5wt.%. The fluidized bed combustor also assures combustion efficiency ∼90% in all test runs. This research indicates amorphous structure of silicon dioxide may be economically promisingly produced from the self-designed rice husk combustor.

Rice husk ash as both pozzolanic admixture and internal curing agent in ultra-high performance concrete

The present study investigated the effects of mesoporous amorphous rice husk ash (RHA) on compressive strength, portlandite content, autogenous shrinkage and internal relative humidity (RH) of ultra-high performance concretes (UHPCs) with and without ground granulated blast-furnace slag (GGBS) under different treatments. The results were compared with those of UHPCs containing silica fume (SF). Because of the mesoporous structure, RHA can absorb an amount of aqueous phase to decrease the free water content and to supply thereafter water for further hydrations of cementitious materials. Hence, compressive strength of RHA-blended samples is enhanced. The highly water absorbing RHA delays and slows down the decrease in the internal RH (self-desiccation) of UHPCs, and hence strongly mitigates autogenous shrinkage of UHPCs compared to SF. The combination of GGBS and RHA or SF improves the properties of UHPC. These results suggest that RHA acts as both highly pozzolanic admixture and internal curing agent in UHPC.

Pozzolanic reactivity of mesoporous amorphous rice husk ash in portlandite solution

Pozzolanic reactivity of rice husk ashes (RHA) and silica fume (SF) was assessed by measuring electrical conductivity, concentration of silicon, calcium ions and pozzolanic reaction product in saturated portlandite solution at 40°C. The differences in surface structure, alkali content and possible difference in nature of dissolved Si between RHA and SF are important parameters influencing their Ca ion adsorption, dissolution–precipitation process, and hence electrical conductivity of portlandite-pozzolan suspensions. The variation in electrical conductivity after 2min or 210min of hydration of portlandite-pozzolan suspensions is not appropriate to compare the pozzolanic reactivity of RHA and SF which possess different Ca ion adsorption capacity. The electrical conductivity reduction rate of portlandite-pozzolan suspensions between 30 and 210min is a suitable parameter for comparing the pozzolanic reactivity of RHA and SF. SF possesses a higher pozzolanic reactivity than RHA. The higher the specific surface area of RHA, the more the pozzolanic reactivity.

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.

Influence of bed height on the quality of rice husk ash in a fluidised bed combustor

The purpose of this study was to investigate the effect of bed height on the quality of rice husk ash in a 210-mm diameter pilot scale fluidised bed combustor. The degree of rice husk burning in the fluidised bed could be deduced from the temperature of the combustor and the particle size of the resulting ash. The turbulence in the bed would break down the char skeleton of the rice husk into finer size. From this study, the bed height of 0.5 Dc was found to give the lowest residual carbon content in the ash (1.9%) and the highest bed temperature (670°C). Moreover, the problem of contamination of amorphous rice husk ash with sand increased as the bed height was increased. Nevertheless, the results from the current study need to be validated in larger-scale fluidised beds to determine whether the bed height of 0.5 Dc is still applicable.

Effect of Uncontrolled Burning Rice Husk Ash in Foamed Concrete

Recently, foamed concrete has become a popular construction material that can be used in wide range of constructions application. Whilst the Rice Husk Ash (RHA) as agro-waste is contain high amount of silicon dioxide. RHA is produced in significant amount every year from agriculture countries. RHA has potential as a material to produce foamed concrete. In this research RHA has been used as a replacement for fine aggregate which used in construction as ordinary concrete material. In this study, foamed concrete with target density 1400, 1600 and 1800 kg/m3 has been produced. The compressive strength of foamed concrete with RHA has been tested. Concrete with Ratio 1:3 of RHA/Sand has higher compressive strength than ratios 3:1 and 2:2 of RHA/sand for every density. XRD and XRF test has been used to determinate chemical composition and crystalline structure of RHA. The result showed that RHA is an amorphous material which amorphous is important thing to pozzolanic process when hydration of cement paste. SEM and EDS test has been conducted to determine microstructure and chemical composition on microstructure of RHA foamed concrete. Amorphous RHA incorporating cement paste produces pozzolanic reaction. It is reduces the porosity and width of interfacial zone in such a way the density is increase.

Effect of silica forms in rice husk ash on the properties of concrete

The strength and durability properties of concrete with or without three types of rice husk ash (RHA), namely, amorphous, partial crystalline, and crystalline RHA, were investigates. The three types of RHA were added into concrete at a 20% replacement level. Consequently, the pozzolanic reactivity of amorphous RHA was higher than that of partial crystalline and crystalline RHA. Concrete added with amorphous RHA showed excellent characteristics in its mechanical and durability properties. The results showed that the higher the amount of crystalline silica in RHA, the lower the concrete resistivity value became. When compared with each other, concretes with 20% of the cement replaced with these types of RHA achieved similar ultrasonic pulse velocity values, but all were lower than that of the control concrete. The incorporation of these kinds of RHA significantly reduced chloride penetration. The results not only encourage the use of amorphous materials, they also support the application of crystalline or partial crystalline RHA as mineral and pozzolanic admixtures for cement.

Fluidized bed combustion of rice husk to produce amorphous siliceous ash

This paper presents research work on producing amorphous siliceous ash with low carbon content through combustion of rice husk in a fluidized bed combustor. Preparation of high-purity amorphous siliceous ash through the conventional alkaline extraction method is time-consuming and costly. Various drawbacks are associated with the preparation of siliceous rice husk ash via thermal treatment of rice husk in existing thermal treatment technologies, the main being the formation of crystals, high residual carbon in ash and long reaction time. Fluidized bed technology is capable of producing amorphous rice husk ash with very low carbon content in a very rapid reaction time due to its high combustion intensity and good mixing behaviour. The achievements and potential areas for development of the current research are also presented. Lastly, the quality of ash has been given particular attention in terms of amorphous nature and carbon content.

Effect of fluidising velocity on the combustion of rice husk in a bench-scale fluidised bed combustor for the production of amorphous rice husk ash

This study was focused on investigating the optimum fluidising velocity during the combustion of rice husk in a bench-scale fluidised bed combustor (ID 210 mm) to obtain low carbon ash in the amorphous form. When all other parameters are held constant, the optimum fluidizing velocity aids in almost complete combustion, thereby releasing the entrapped carbon for further conversion. This results in ash with consistently low carbon content (less than 2 wt%). The range of fluidising velocities investigated was from as low as 1.5 U mf to as high as 8 U mf. It was found that the optimum fluidising velocity was approximately 3.3 U mf as the mixing of rice husk with the bed was good with a high degree of penetration into the sand bed. The resulting ash retained its amorphous form with low residual carbon content (at 2.88 wt%) and minimal sand contamination as shown by the X-ray diffraction analysis.

Mechanical Properties of Rice Husk Ash/Polypropylene Composites

The technical viability of using rice husk ashes (RHA) as alternative fillers in polypropylene was studied. Three types of RHA, white rice husk ash (WRHA), black rice husk ash (BRHA) and amorphous rice husk ash (AMRHA) at 10—40 wt% filler loading were investigated. The RHA composites were compounded by twin screw compounders and the mechanical properties of the composites evaluated. Incorporation of the RHA fillers increased the flexural modulus of the composites, particularly the BRHA composities. Modulus of the RHA composites were found to be in good agreement with theoretical values predicted by equation of Lewis and Nielsen. The increase in modulus was offset by lowering of the tensile strength, elongation at break and impact properties. Theoretical treatments of the ultimate tensile strength performed based on the model proposed by Nicolai and Nicodemo showed reasonably good agreement. The mechanical properties of the RHA composites were of comparable values with the prepared polypropylene composites filled with commercial Neuburg silica. Transformation of the crystalline RHA to amorphous RHA resulted in composites with improved tensile strength. No coupling agent was used in this study.