CO2 capture at high temperature using calcium-based sorbents

Calcium-based sorbents synthesized from CaO, CaCO₃, and Ca(OH)₂ precursors were demonstrated as high-temperature CO₂ capture materials. The effect on CO₂ capture capability of calcium-based sorbents receiving different activations was also investigated. After proper activation, the best carbon capturing material is CaO that captured 75% of available CO₂ in nine cyclic tests and captured 61% even after 40 cyclic experiments. The correlation of the structural difference in the three activated sorbents and CO₂ conversion has been discussed. The sintering effect is presumably a major cause for activity decline of calcium-based sorbents… after cyclic carbonation/decarbonation runs.     

稻壳基白炭黑的制备研究

以炭化稻壳为原料,Na2CO3为活化剂,采用沉淀法对稻壳基白炭黑的制备工艺进行了研究.结果表明沉淀法制备白炭黑的最佳工艺条件为:反应温度100℃,Na2CO3溶液浓度为13％(w/w),稻壳灰与Na2CO3溶液质量配比为1:40,反应时间4h,提取率可以达到93％以上.整个工艺流程中,Na2CO3溶液循环回用,有利于工业化放大,产品的相关质量检测均符合国家标准.     

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.     

Creep analysis of concrete containing rice husk ash

This paper presents an experimental study on the mechanical properties of concrete added with rice husk ash (RHA) as a supplementary cementitious material. The compressive strength, modulus of elasticity and creep were obtained experimentally from specimens with different RHA contents (0%, 10%, 15% and 20% of binder). The results show that the addition of RHA in concrete can improve both the compressive strength and modulus of elasticity and reduce the creep of concrete. The examination of pore micro-structure of hardened concrete using both the mercury intrusion porosimetry and scanning electron microscope techniques demonstrates that RHA particles can react with calcium hydroxide originated from cement hydration to produce additional C-S-H, which can fill voids and large pores and thus reduces the porosity related to capillary pores and voids. In addition, the release of absorbed water, which is retained in the small pores of RHA particles at early days, can improve cement hydration and thus reduce the porosity related to gel pores.     

Coral-like hydroxy sodalite particles from rice husk ash as silica source

Coral-like hydroxy sodalite (HS) particles were prepared from rice husk ash as silica source in the presence of other aqueous-based precursor materials following a simple process under hydrothermal condition at 90 °C for 15 h. The particles obtained at 90 °C for different times (6, 10 and 15 h) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). The HS crystals along with a small amount of zeolite A particles were observed at 90 °C/6 h while phase pure HS particles were obtained at 90 °C for 10 and 15 h. The characteristic vibration bands of the HS particles were confirmed by FTIR spectroscopy. FESEM images showed that the HS particles obtained at 90 °C/15 h were coral-like morphology which were formed through the self-assembly of the smaller particles generated at the initial stage of reaction (6 and 10 h) under the same experimental conditions. A proposed mechanism for the formation of coral-like HS particles was also illustrated.     

Optimum production conditions for reactive rice husk ash

Addition of pozzolanic admixtures generally enhances the performance of concrete and in particular the durability. If rice husk ash (RHA) is incinerated in controlled conditions, it can exhibit high pozzolanicity. Significant amount of work has already been reported on the production methodologies of reactive RHA. However, the optimum conditions which will result in highly reactive amorphous ash with minimum production energy have not yet been established. In the present experimental work, RHA samples are produced under various conditions of incineration using laboratory box furnace. Energy consumption has been examined in this study. Reactivity of ash has been established by various techniques, such as X-ray diffraction (XRD), scanning electron microscopic study (SEM), analytical method and conductometric test. RHA-OPC reactivity has also been studied in this work. Based on the experimental investigations on fineness, amorphous silica content, energy consumption and reactivity of ash, the optimum production conditions of reactive RHA have been identified.     

Preparation of an efficient humidity indicating silica gel from rice husk ash

An efficient humidity indicating silica gel was prepared using rice husk ash as a raw material via sodium silicate extraction and acid neutralization method. Cobalt chloride was impregnated into the silica gel as a colour indicating material. A low concentration of cobalt chloride solution (0·0005 mol dm^?3) was used for the impregnation. The effect of pH of the impregnating solution on the colour development behaviour of the gel was investigated. The specific surface area of the gel was determined by Brunauer-Emmett-Teller method. The gel has been characterized using X-ray diffraction, scanning electron microscopy and visible spectroscopy. The moisture adsorption and desorption kinetics of the desiccant were evaluated using simultaneous thermogravimetry and differential scanning calorimetry.     

Synthesis and surface characteristics of nanosilica produced from alkali-extracted rice husk ash

Rice husk is a form of agricultural biomass that provides an abundant silicon source. This study used rice husk as a raw material to prepare nanosilica without adding an extra surfactant. This work investigated a dissolution-precipitation technique as a function of acid treatment, sodium silicate concentration, gelation pH, aging temperature, and aging time to establish optimum conditions for preparing silica nanoparticles. Experimental results showed that silica produced by hydrochloric acid possesses higher surface area than that of sulfuric, oxalic, and citric acids. Surface characteristics of the sample depend mainly upon gelation pH. The highest surface area and pore volume of silica samples were 634 m²/g and 0.811 cm³/g. Pore diameters were controllable from 3 to 9 nm by adjusting the solution pH value. Particles had a uniform size of 5-30 nm. The objective of this study was to develop a method of nanosilica preparation that enhances the economic benefits of re-using rice husk waste.     

Properties of geopolymer with seeded fly ash and rice husk bark ash

In the present work, compressive strength of inorganic polymers (geopolymers) produced of seeded fly ash and rice husk bark ash has been investigated. Different specimens made from a mixture of fly ash and rice husk bark ash in fine and coarse form were subjected to compressive strength tests at 7 and 28 days of curing. The curing regime was different: one set of the specimens were cured at room temperature until reaching to 7 and 28 days and the other sets were oven cured for 36 h at the range of 40-90 °C and then cured at room temperature until 7 and 28 days. The results indicate that in both 7 and 28 days regimes, the highest strengths are related to the specimens by SiO₂/Al₂O₃ ratio equals 2.99 cured at 80 °C. For these specimens, those contained finer fly ash particles show more compressive strength. Thermogravimetric analysis and Fourier transform infrared spectroscopy both also are in agreement with the obtained results from compressive strength tests. In addition, SEM micrographs of the specimens show that the finer the particle size of the utilized ashes, the denser the microstructure which confirms the results obtained by the strength tests.     

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.     

Removal of fluoride from drinking water using aluminum hydroxide coated rice husk ash

Fluoride content in groundwater that is greater than the WHO limit of 1.5mg/L, causes dental and skeletal fluorosis. In India, several states are affected with excess fluoride in groundwater. The problem is aggravated due to the lack of appropriate and user friendly defluoridation technology. Several fluoride removal techniques are reported in the literature amongst which the Nalgonda technique and use of activated alumina have been studied extensively. However a simple, efficient and cost effective technology is not available for widespread use in many affected regions. In this paper, we present a novel cost effective defluoridation method that is based on surface modification of rice husk ash (RHA) by coating aluminum hydroxide. RHA is obtained by burning rice/paddy husk which is an abundantly available and is an inexpensive raw material. The results showed excellent fluoride removal efficiency and the adsorption capacity was found to be between 9 and 10mg/g.     

The sorption of lead(II) ions on rice husk ash

Present study deals with the adsorption of Pb(II) from aqueous solution on rice husk ash. Rice husk is a by-product generally obtained from rice mill. Rice husk ash is a solid obtained after burning of rice husk. Batch studies were performed to evaluate the influences of various experimental parameters like pH, initial concentration, adsorbent dosage, contact time and the effect of temperature. Optimum conditions for Pb(II) removal were found to be pH 5, adsorbent dosage 5 g/L of solution and equilibrium time 1h. Adsorption of Pb(II) followed pseudo-second-order kinetics. The effective diffusion coefficient is of the order of 10(-10)m(2)/s. The equilibrium adsorption isotherm was better described by Freuindlich adsorption isotherm model. The adsorption capacity (q(max)) of rice husk ash for Pb(II) ions in terms of monolayer adsorption was 91.74 mg/g. The change of entropy (DeltaS(0)) and enthalpy (Delta H(0)) were estimated at 0.132 kJ/(mol K) and 28.923 kJ/mol respectively. The negative value of Gibbs free energy (Delta G(0)) indicates feasible and spontaneous adsorption of Pb(II) on rice husk ash. The value of the adsorption energy (E), calculated using Dubinin-Radushkevich isotherm, was 9.901 kJ/mol and it indicated that the adsorption process was chemical in nature. Application study was also carried out to find the suitability of the process in waste water treatment operation.     

Effect of rice husk ash on the properties of bricks made from fired lateritic soil-clay mix

The effects of rice husk ash (RHA) on the various properties of lateritic soil-clay mixed bricks were studied. The effect of firing duration (at a firing temperature of 1000°C) on the properties of bricks was also studied. The measured properties were linear shrinkage, unit weight, compressive strength, 24-hour immersion water absorption and 5-hour boiling water absorption. Both linear shrinkage and unit weight of bricks decreased with increase in the percentage of RHA content. The compressive strength of lateritic soil-clay mixed bricks increased almost linearly with increase in the percentage content of RHA. The bricks which received a 4-hour at 1000°C attained maximum compressive strength. Both 24-hour immersion and 5-hour boiling water absorptions of the bricks were within the permissible limits. The strengths of the bricks were compared with British statutory minimum compressive strengths of bricks for various walls. The bricks are recommended or load-bearing walls.     

Hardened properties of self-consolidating high performance concrete including rice husk ash

This paper mainly presents the key hardened properties of self-consolidating high performance concrete (SCHPC). Various SCHPCs were produced with different water/binder (W/B) ratios, rice husk ash (RHA) contents, and air contents. The required filling ability and air content were achieved in all freshly mixed SCHPCs. The hardened SCHPCs were tested for compressive strength, ultrasonic pulse velocity, water absorption, total porosity, and true electrical resistivity. The effects of W/B ratio, RHA content, and air content on these hardened properties were observed. Test results revealed that the compressive strength, ultrasonic pulse velocity, and electrical resistivity increased whereas the water absorption and total porosity decreased with lower W/B ratio and higher RHA content. In addition, the air content decreased the compressive strength, ultrasonic pulse velocity, water absorption, and total porosity but increased the electrical resistivity. Based on the overall effects of rice husk ash, the optimum RHA content for SCHPC has been defined.     

Use of rice husk ash in sandcrete blocks for masonry units

Different mix proportions of sand, cement and rice husk ash (RHA) were studied for use in sandcrete blocks. Optimum water/(cement+RHA) ratios were determined at different mix proportions. Compressive strengths of various mix proportions at 7, 28 and 60 days were also determined. The optimum water/(cement+RHA) ratio increased with rice husk ash contents. Test results showed that up to 40% RHA could be added as a partial replacement for cement without any significant change in compressive strength at 60 days. Compressive strengths of various mix proportions were compared with British Statutory minimum compressive strengths of bricks for various walls and it was found that sandcrete blocks of 1∶5 mortar mixes with 40% RHA (by weight of cement) could be used in both load and non-load bearing walls.     

A sustainable route for the preparation of activated carbon and silica from rice husk ash

An environmentally friendly and economically effective process to produce silica and activated carbon form rice husk ask simultaneously has been developed in this study. An extraction yield of silica of 72-98% was obtained and the particle size was 40-50 nm. The microstructures of the as-obtained silica powders were characterized by X-ray diffraction (XRD) and infrared spectra (IR). The surface area, iodine number and capacitance value of activated carbon could achieve 570 m(2)/g, 1708 mg/g, 180 F/g, respectively. In the whole synthetic procedure, the wastewater and the carbon dioxide were collected and reutilized. The recovery rate of sodium carbonate was achieved 92.25%. The process is inexpensive, sustainable, environmentally friendly and suitable for large-scale production.