Rice Husk at a Glance:From Agro-Industrial to Modern Applications

Excessive waste production has led to the concept of a circular bioeconomy to deliver valuable by-products and improve environmental sustainability.The annual worldwide rice production accounts for more than 750 million tons of grain and 150 million tons of husk.Rice husk(RH)contains valuable biomaterials with extensive applications in various fields.The proportions of each component depend primarily on rice genotype,soil chemistry,and climatic conditions.RH and its derivatives,including ash,biochar,hydrochar,and activated carbon have been placed foreground of applications in agriculture and other industries.While the investigation on RH’s compositions,microstructures,and by-products has been done copiously,owing to its unique features,it is still an open-ended area with enormous scope for innovation,research,and technology.Here,we reviewed the latest applications of RH and its derivatives,including fuel and other energy resources,construction materials,pharmacy,medicine,and nanobiotechnology to keep this versatile biomaterial in the spotlight.

Performance Evaluation of Novel Eco-Materials Composed of Millet Husks, Rice Husks, and Polystyrene

Managing agricultural waste and expanded polystyrene (EPS) poses significant environmental and economic challenges. This study aims to create composites from millet husks, rice husks, and recycled EPS, using a manufacturing method that involves dissolving the polystyrene in a solvent followed by cold pressing. Various particle sizes and two binder dosages were investigated to assess their influence on the physico-mechanical properties of the composites. The mechanical properties obtained range from 2.54 to 4.47 MPa for the Modulus of Rupture (MOR) and from 686 to 1400 MPa for the Modulus of Elasticity in Bending (MOE). The results indicate that these composites have potential for applications in the construction sector, particularly for wood structures and interior decoration. Moreover, surface treatments could enhance their durability and mechanical properties. This research contributes to the valorization of agricultural and plastic waste as eco-friendly and economical construction materials.

Investigation of the Fermentation Mode of Rice Husk for the Stabilization of Earth Plaster

Despite its low resistance to humidity, adobe remains the most widely used material for housing construction, particularly in developing countries. The present study aims to assess different modes of use of fermented RH and to evaluate their influence on the behavior of raw earth for application in plaster. The influences of two types of RH are evaluated: granular rice husk (RHg) and powdered RH (RHp). The clay mainly consists of clay (40%), silt (22%), and sand (38.4%), with a small proportion of gravel (0.24%). Its liquidity limit is 40% and the plasticity index is 26.5%. The mixtures were designed using earth and each of the two rice husks at the volumetric content of 10%, 15% and 20% of the total volume mixed with water 36.5%, 38.5% and 40.3% and fermented for three weeks. Each fermented mixture was added to the soil to form the paste, and 40 × 40 × 160 mm3 test speciments were made for characterization. The results generally show an improvement in the physico-mechanical properties and water resistance of the mortars containing fermented RH, with an optimal content between 10% and 15%. The powdered RH improved the performance of the mortar better than granular RH.

The Influence of Rice Husk Ash on Mechanical Properties of the Mortar and Concrete: A Critical Review

Increasing the population and infrastructure in both emerging and developed countries requires a considerable amount of cement, which significantly affects the environment. The primary materials of concrete (‘cement’) production emit a large quantity of CO2 into the environment. Also, the cost of conventional building materials like cement gives motivation to find geopolymer waste materials for concrete. To reduce harmful effects on the environment and cost of traditional concrete substance, alternative waste materials like rice husk ash (RHA), ground granulated blast-furnace (GGBS), fly ash (FA), and metakaolin (MK) can be used due to their pozzolanic behavior. RHA waste material with a high silica concentration obtained from burning rice husks can possibly be used as a supplementary cementitious material (SCM) in the manufacturing of concrete, and its strong pozzolanic properties can contribute to the strength and impermeability of concrete. This review paper highlights a summary of the positive effect of using RHA as a partial substitute for cement in building construction, as well as its optimal inclusion of enhanced mechanical properties like compressive strength, flexural strength, and split tensile strength of mortar and concrete.

Antioxidant Activities and Characterization of Polyphenols from Selected Northern Thai Rice Husks: Relation with Seed Attributes

Rice production generates a significant amount of agricultural waste. This study aimed to give results related to the existence of antioxidant phenols in agricultural waste of selected Northern Thai rice varieties. The antioxidant activities, contents of total flavonoids and phenolic compounds in the ethanolic rice husk extract were evaluated. The highest antioxidant activities were found in the variety PES1CMU, with 2,2’-azinobis-3-ethyl-benzothiazoline-6-sulfonic acid and 2,2-diphenyl-1-picrylhydrazyl as 679.66 and 4.16 mmol/(L·g) trolox equivalent, respectively, ferric reducing antioxidant power as 0.87 mmol/(L·g) Fe2+, total phenolic content as 29.90 mmol/(L·g) gallic acid and total flavonoid content as 12.16 mg/g catechin equivalent. Polyphenol compounds were identified mainly by standard polyphenols using the liquid chromatography mass spectrometry, with the highest contents of phytic acid, o-coumaric acid, naringin and kaempferol. The non-glutenous and wetland ecotypes of rice husk samples were the richest in antioxidant activities and polyphenol contents characterized by using principal component analysis. The glutenous rice husk contained higher antioxidant activities than the rest. Interestingly, quercetin is a significant phenolic compound that positively correlated with the overall antioxidant activities of rice husk. This finding will be relevant for future application of rice husk antioxidant components in the production of functional ingredients as well as for the food and pharmaceutical industries.

Mechanical properties of a clay soil reinforced with rice husk under drained and undrained conditions

Fiber-reinforced soils have been increasingly used in geotechnical engineering.Over the years,research has sought to understand and investigate the influences of fibers as reinforcement in soilefiber mixtures.This study assessed the behavior of clayey soil in the city of Curitiba(Paraná,Brazil),adding rice husk fiber(RHF),an industrial waste from Cooperativa Agroindustrial in Alegrete(Rio Grande do Sul,Brazil).To evaluate the effect of the presence of natural RHF on the mechanical behavior of compacted soil,aspects such as the influence of fiber content and the drained and undrained behaviors of the soil were evaluated through unconfined triaxial compression tests.The following tests were realized:soil granulometry,specific mass of solids and Atterberg limits.Specimens were produced in quadruplicate for the soil and mixtures using the RHF contents of 0.5%,0.75%,1%and 1.5%to determine the unconfined compressive strength(UCS).Triaxial tests were realized on a pure soil specimen and the specimens with 1%RHF under confining pressures of 50 kPa,100 kPa,200 kPa and 400 kPa.The interactions at the interface between husk surface and soil were analyzed using scanning electron microscopy(SEM).In UCS tests,specimens with RHF percentages of 1%and 1.5%presented the highest results,with an increment of 36%compared to the soil without RHF.The results of the consolidated drained triaxial compression tests show that in terms of effective stress,there was a small difference in the strength of the compacted pure soil and soil with the addition of RHF.For the undrained tests,the strength increased with the inclusion of husk,with a reduction of 50%in cohesion and an increment of 22%in friction angle for specimens containing RHF compared to the soil without RHF additions.

Effectiveness of Rice Husk and Sugarcane Bagasse Ashes Blended Cement in Improving Properties of Concrete

This paper emphasized the use of rice husk ash (RHA) and sugarcane bagasse ash (SBA) in improving concrete properties, and also their combined effects on workability, compressive strength, flexural strength, permeability and water absorption capacity. Thus, in this study, the water-to-cement ratio was kept constant (0.45), the binder materials content for conventional mix was kept constant at (350 kg/m3) and the partial replacement of cement with RHASBA used was 5%, 10%, 15%, 20%, 25%, and 30% by weight of cement. The maximum compressive strength was noted at a 5% replacement level of cement with RHASBA. The Results showed that the optimum replacement of cement with RHASBA in concrete was 5%, which was found to increase the compressive strength by 15%, flexural strength by 3.4%, lowered permeability by 50%, lowered sorptivity by 11.34% as compared with control concrete at 90 days of curing time. The micro-structural test results further established that RHA and SBA have a high content of SiO2 which enables them to be more reactive in concrete and also revealed that the presence of RHASBA depletes Ca(OH)2 crystals, converting it into CaH2O4Si (C-S-H gel) leading to the strengthening of bond within the concrete matrix.

Effectiveness of Rice Husk and Sugarcane Bagasse Ashes Blended Cement in Improving Properties of Concrete

This paper emphasized the use of rice husk ash (RHA) and sugarcane bagasse ash (SBA) in improving concrete properties, and also their combined effects on workability, compressive strength, flexural strength, permeability and water absorption capacity. Thus, in this study, the water-to-cement ratio was kept constant (0.45), the binder materials content for conventional mix was kept constant at (350 kg/m3) and the partial replacement of cement with RHASBA used was 5%, 10%, 15%, 20%, 25%, and 30% by weight of cement. The maximum compressive strength was noted at a 5% replacement level of cement with RHASBA. The Results showed that the optimum replacement of cement with RHASBA in concrete was 5%, which was found to increase the compressive strength by 15%, flexural strength by 3.4%, lowered permeability by 50%, lowered sorptivity by 11.34% as compared with control concrete at 90 days of curing time. The micro-structural test results further established that RHA and SBA have a high content of SiO2 which enables them to be more reactive in concrete and also revealed that the presence of RHASBA depletes Ca(OH)2 crystals, converting it into CaH2O4Si (C-S-H gel) leading to the strengthening of bond within the concrete matrix.

Characteristics of Rice Husk-Admixed Conplast SP 430 Concrete

Experimental work was mounted using 5.7 mL of the Conplast SP430 admixture and rice husk ash(RHA)at replacement levels of 0 to 50%at 10%intervals by wt.%of cement.It is on the performance of Conplast SP 430 admixture and its effects on concrete and concrete with rice husk ash.Concrete specimens were cast and cured for 3 to 90 days and subjected to slump and mechanical characteristics tests.Data generated from the experiments were analyzed and sensitivity analysis of the concrete mix was determined using the Minitab 18 Statistical Package.The results showed that CP with concrete improves the workability of the concrete and reduces water absorption.The reverse was the case when RHA was used with the admixture which may be an issue of compatibility.The statistical characteristics restrict good and within the specified limits.

Nano⁃Silica Production by Rice Husk Combustion in a 0.7 MW Double⁃Circulating Fluidized Bed after Acid Pretreatment

Rice husk is an organic silicon source for amorphous nano⁃silica particles.This paper reports the experimental study on the industrial production of nano⁃silica by rice husk combustion in a specially⁃designed 0.7 MW double⁃circulating fluidized bed(DCFB)based on acid pretreatment process.The physicochemical properties of RHA were characterized by various testing instruments.Results showed that acid pretreatment removed a large amount of metal impurities in the rice husk and thus inhibited the formation of crystalline silica or the agglomeration during the fluidized bed combustion process.The combustion efficiencies were as high as 99.5%.The obtained RHA comprised white fine particles and exhibited an amorphous structure,but factors such as collection point and acid type had certain influences on the quality of RHA.The highest SiO2 purity was greater than 98.6 wt.%,the lowest content of unburned carbon was 0.2 wt.%,the specific surface area reached 178 m2/g,and the pore size reached 5 nm.The circulating fluidized bed combustion of rice husk based on acid pretreatment can prepare nano⁃silica while providing heat for industrial processes,which is a highly energy⁃rich process.

Effect of grinding on chemical and physical properties of rice husk ash

The effect of grinding on the chemical and physical properties of rice husk ash was studied. Four rice husk ashes with different finenesses, i.e. coarse original rice husk ash （RHA0）, RHA1, RHA2, and RHA3 were used for the study. Ordinary Portland cement （OPC） was partially replaced with rice husk ash at 20% by weight of binder. The water to binder ratio （W/B） of the mortar was maintained at 110%±5% with flow table test. Specific gravity, fineness, chemical properties, compressive strength, and porosity test of mortars were determined. The differences in chemical composition of the rice husk ashes with different finenesses from the same batch are small. The use of RHA3 produces the mortars with good strength and low porosity. The strength of the mortar improves with partial replacement of RHA3 in comparison with normal coarse rice husk ash. The use of RHA3 results in a strong and dense mortar, which is due to the better dispersion and filling effect, as well as an increase in the pozzolanic reaction.

Pyrolysis of rice husk and sawdust for liquid fuel

The paper is focused on studying how to convert rice husk and sawdust into liquid fuel. Rice husk, sawdust and their mixture were pyrolyzed at the temperature between 420℃ and 540℃, and the main product of liquid fuel was obtained. The experimental result showed that the yield of liquid fuel heavily depended on the kind of feedstock and pyrolysis temperature. In the experiments, the maximum liquid yields for rice husk, sawdust and their mixture were 56% at 465 ℃, 61% at 490℃ and 60% at 475℃ respectively. Analysis with GC-MS and other apparatus indicated that the liquid fuel is a complicated organic compound with low caloric value and can be directly used as fuel oil without any up-grading. As a crude oil, the liquid fuel can be refined to be vehicle oil.

Preparation of fly ash and rice husk ash geopolymer

The geopolymer of fly ash （FA） and rice husk ash （RHA） was prepared. The burning temperature of rice husk, the RHA fineness and the ratio of FA to RHA were studied. The density and strength of the geopolymer mortars with RHA/FA mass ratios of 0/100, 20/80, 40/60, and 60/40 were tested. The geopolymers were activated with sodium hydroxide （NaOH）, sodium silicate, and heat. It is revealed that the optimum burning temperature of RHA for making FA-RHA geopolymer is 690oC. The as-received FA and the ground RHA with 1%-5% retained on No.325 sieve are suitable source materials for making geopolymer, and the obtained compressive strengths are between 12.5-56.0 MPa and are dependent on the ratio of FA/RHA, the RHA fineness, and the ratio of sodium silicate to NaOH. Relatively high strength FA-RHA geopolymer mortars are obtained using a sodium silicate/NaOH mass ratio of 4.0, delay time before subjecting the samples to heat for 1 h, and heat curing at 60oC for 48 h.

Application of Rice Husk Biochar for Achieving Sustainable Agriculture and Environment

This paper critically reviewed the current knowledge and challenges of rice husk biochar(RHB)production and its effects on soil properties,plant growth,immobilization of heavy metals,reduction of nutrient leaching and mitigation of greenhouse gas emissions.The characteristics of RHBs produced at various pyrolysis temperatures were discussed and compared to biochars derived from other agro-industrial wastes.RHBs produced at higher pyrolysis temperatures show lower hydrogen/carbon ratio,which suggests the presence of higher aromatic carbon compounds.The increase of pyrolysis temperature also results in production of RHBs with higher ash content,lower yield and higher surface area.RHB usually has higher silicon and ash contents and lower carbon content compared to biochars derived from other feedstocks at the same pyrolysis conditions.Although it depends on soil type,RHB application can improve soil organic carbon content,cation exchange capacity,available K concentration,bulk density and microbial activity.The effect of RHB on soil aggregation mainly depends on soil texture.The growth of different crops is also enhanced by application of RHB.RHB addition to soil can immobilize heavy metals and herbicides and reduce their bioavailability.RHB application shows a significant capacity in reduction of nitrate leaching,although its magnitude depends on the biochar application rate and soil biogeochemical characteristics.Use of RHB,especially in paddy fields,shows a promising mitigation effect on greenhouse gas(CH4,CO2 and N2O)emissions.Although RHB characteristics are also related to other factors such as pyrolysis heating rate and residence time,its performance for specific applications(e.g.carbon sequestration,pH amendment)can be manipulated by adjusting the pyrolysis temperature.More research is needed on long-term field applications of RHB to fully understand the advantages and disadvantages of RHB as a soil amendment.

Production of porous silica by the combustion of rice husk ash for tundish lining

In order to study the production of porous silica compacts by the combustion of rice husk ash （RHA） for tundish lining, the experimental design technique was used to evaluate the effect of firing temperature, soaking time and compaction pressure on controlling both the porosity degree and compressive strength of rice husk ash compacts. The results revealed that while the porosity degree of the compacts decreased with the increase in the entire studied parameters, the compressive strength exhibited another trend especially at a lower soaking time. At a lower soaking time, the increase in firing temperature led to a slight decrease in compressive strength and then increasing thereafter. The porous silica compacts having 30% porosity and 〉 2.5 MPa compressive strength suitable for tundish lining could be obtained from the combustion of rice husk ash compacts.

Activated Carbon from Rice Husk with One-Step KOH Mechanical Mixing Activation as Adsorbent for Treating Phenolic Wastewater

This study investigates how large-surface-area biocarbons with high phenolic adsorption capacities can be obtained from cheap and abundant rice husk(RH).The RH is directly mixed with potassium hydroxide(KOH)and activated in a flowing N_(2) atmosphere,and the effects of the pyrolysis temperature and KOH to RH ratio on the structure of the obtained activated carbon adsorbents and their adsorption of p-nitrophenol and phenol are studied.The results show that the optimum pyrolysis temperature of RH is 750℃,whereby the highest surface area of 2047 m^(2)/g and best adsorption performance are obtained with a KOH to RH ratio of 3:1.Moreover,the obtained biocarbons achieve a maximum adsorption capacity of 175 mg/g for phenol and 430 mg/g for p-nitrophenol,which are higher than most previously reported data.

Development of high volume rice husk ash alumino silicate composites

The development of high volume rice husk ash （RHA） alumino silicate composites （ASC） was studied. RHA was used as the source of silica and aluminium in the ASC. The mass ratios of RHA：Al（OH）3 of 70：30 to 99：1 were tested. The results indicate that the obtained ASC mortars are not stable and disintegrate in water. Boric acid was introduced to the mixture to overcome this problem. Stable ASC mortars with high RHA：Al（OH）3 mass ratios of 90：10 to 97.5：2.5 were obtained with the use of boric acid and 115oC curing. The compressive strength of the mortar of 20 MPa was gained. The immersion test indicates that high volume RHA ASC mortars show good resistance in 3vol% H2SO4 solution, but is slightly less durable in 5wt% MgSO4 solution.

Preparation and characterization of rice husk/ferrite composites

A novel ferrite composite using rice husk as substrate has been prepared via high temperature treatment under nitrogen atmosphere.The rice husk substrate consists of porous activated carbon and silica,where spinel ferrite particles with average diameter of 59 nm are distributed.The surface area of the composite is greater than 170 m^2 g^(-1) and the bulk density is less than 0.6 g cm^(-3).Inert atmosphere is indispensable for the synthesis of pure ferrite composites,while different preparation temperatures ...

Controllable conversion of rice husks to Si/C and SiC/C composites in molten salts

Direct conversion of biomass to functional materials is an ideal solution to relieve challenges in environmental and energy sustainability.We herein demonstrate a molten salt thermoelectrolysis of rice husks(RHs)mainly consisting of organic mass and biosilica to achieve high-efficiency and upgraded utilization of both Si and C in RHs.By coupling pyrolysis of organic mass with electrochemical reduction of silica in molten salts,the thermoelectrolysis of RHs in molten CaCl_(2)-NaCl at 800℃ refines the RHs and acidleached RHs to SiC nanowire/C(SiC-NW/C)and Si nanoparticle/C(Si-NP/C),respectively.The present study highlights the molten salt thermoelectrolysis for reclamation of biomass wastes in an affordable and controllable manner.

Rice Husk Templated Mesoporous ZnO Nanostructures for Ethanol Sensing at Room Temperature

Mesoporous zinc oxide nanostructures are successfully synthesized via the sol-gel route by using a rice husk as the template for ethanol sensing at room temperature. The structure and morphology of the nanostructures are characterized by x-ray diffraction, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and nitrogen adsorption-desorption analyses. The mechanism for the growth of zinc oxide nanostructures over the biotemplate is proposed. SEM and TEM observations also reveal the formation of spherical zinc oxide nanoparticles over the interwoven fibrous network. Multiple sized pores having pore diameter ranging from 10- 4Ohm is also evidenced from the pore size distribution plot. The larger surface area and porous nature of the material lead to high sensitivity （40.93% for 300 ppm of ethanol）, quick response （42s） and recovery （40 s） towards ethanol at 30014. The porous nature of the interwoven fibre-like network affords mass transportation of ethanol vapor, which results in faster surface accessibility, and hence it acts as a potential candidate for ethanol sensing at room temperature.