A new type of geopolymer composite was synthesized from two industrial wastes, red mud (RM) and rice husk ash (RHA), at varying mixing ratios of raw materials and the resulting products characterized by mechanical compression testing, X-ray diffraction, and scanning electron microscopy to assess their mechanical properties, microstructure, and geopolymerization reactions. Prolonged curing significantly increases the compressive strength and Young’s modulus, but reduces the ductility. Higher RHA/RM ratios generally lead to higher strength, stiffness, and ductility, but excessive RHA may cause the opposite effect. The compressive strength ranges from 3.2 to 20.5 MPa for the synthesized geopolymers with nominal Si/Al ratios of 1.68–3.35. Microstructural and compositional analyses showed that the final products are mainly composed of amorphous geopolymer binder with both inherited and neoformed crystalline phases as fillers, rendering the composites very complex composition and highly variable mechanical properties. Uncertainties in the composition, microstructure, the extent of RHA dissolution, and side reactions may be potential barriers for the practical application of the RM–RHA based geopolymers as a construction material.

Synthesis and characterization of red mud and rice husk ash-based geopolymer composites

In order to arrest the incidence of global warming brought about by the emission of greenhouse gases notably CO 2 into the atmosphere, the use of materials that can substitute the material responsible for greenhouse gases is being promoted world-wide. One of these is rice husk ash (RHA) which has been found suitable by researchers to partially replace Portland cement in the production of concrete. This paper presents a comprehensive and up-to-date review of the work of numerous researchers on structure and properties of concrete containing rice husk ash (RHA) as partial replacement of ordinary Portland cement. Some of the findings are: (i) controlled incineration is required to produce RHA with structure that can result in structural concrete, (ii) the use of RHA resulted in increased water demand, (iii) up to 10% cement replacement with RHA will result in strength development comparable to the control specimens, and (iv) the use of RHA in concrete result in impervious RHA-concrete microstructure to agent of degradation like, sulphate attacks, chloride ingress, etc., as well as good shrinkage properties, and thus produce durable concrete when used. However, some areas such as the bending and shear responses (and allied properties) of reinforced concrete slabs and beams with RHA are presently not yet covered by researchers; they are therefore recommended for future investigation.

Structure and properties of mortar and concrete with rice husk ash as partial replacement of ordinary Portland cement – A review

Applications of rice husk ash as green and sustainable biomass

The sources of contamination of fresh and seawater are most often spills of oil and oil products by accidents with tankers or underwater pipes, as well as offshore oil platforms and oil refineries. Moreover the ships produce a large amount of oily wastewater such as bilge water which needs to be treated prior to being discharged. The bilge water is a difficult wastewater to treat as it contains seawater, particulates, used oils and detergents. Micro- and ultrafiltration are often the methods of choice to treat this water. The pretreatment of this oily wastewater prior to ultrafiltration is desirable, as the used oils and particulates can block the feed channels of the ultrafilters spiral and hollow fiber modules. In this reason, at the last time different hybrid adsorbents with high adsorption capacity and appropriate porous structure are used. The present study is an attempt to establish the possibilities to obtain black rice husk ash (BRHA) and white rice husks ash (WRHA) via pyrolysis of raw rice husks in a pilot plant fluidized-bed reactor at different conditions. The products obtained are characterized using X-ray diffraction patterns, scanning electron microscopy, FT-IR spectroscopy, thermal analysis, and low temperature nitrogen adsorption. Using batch adsorption technique, the kinetics was studied and the adsorption capacities of crude oil and diesel fuel at different temperatures as well as some hydrocarbons at 298 K onto BRHA and WRHA are determined. It was established that BRHA have been higher adsorption capacity than WRHA. At a given temperature, BRHA sorbed more crude oil than diesel fuel. The results obtained showed that the material studied has high adsorption capacity and low cost and may successfully be used as an effective adsorbent to cleanup of bilge water and spills of oil and oil products in water basins. Because the saturated BRHA with crude oil, diesel fuel or different hydrocarbons are characterized with high calorific, they can be burnt in incinerators, industrial ovens or steam generators. By this way we attain not only ecological but also economical effect.

Cleanup of water polluted with crude oil or diesel fuel using rice husks ash

Background: In the present study, three ionic liquids, namely 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), and 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM]DEP), were used to partially dissolve rice husk, after which the cellulose were regenerated by the addition of water. The aim of the investigation is to examine the implications of the ionic liquid pretreatments on rice husk composition and structure. Results: From the attenuated total reflectance Fourier transform-infrared (ATR FT-IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) results, the regenerated cellulose were more amorphous, less crystalline, and possessed higher structural disruption compared with untreated rice husk. The major component of regenerated cellulose from [BMIM]Cl and [EMIM]DEP pretreatments was cellulose-rich material, while cellulose regenerated from [EMIM]OAc was a matrix of cellulose and lignin. Cellulose regenerated from ionic pretreatments could be saccharified via enzymatic hydrolysis, and resulted in relatively high reducing sugars yields, whereas enzymatic hydrolysis of untreated rice husk did not yield reducing sugars. Rice husk residues generated from the ionic liquid pretreatments had similar chemical composition and amorphousity to that of untreated rice husk, but with varying extent of surface disruption and swelling. Conclusions: The structural architecture of the regenerated cellulose and rice husk residues showed that they could be used for subsequent fermentation or derivation of cellulosic compounds. Therefore, ionic liquid pretreatment is an alternative in the pretreatment of lignocellulosic biomass in addition to the conventional chemical pretreatments.

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Elucidation of the effect of ionic liquid pretreatment on rice husk via structural analyses

The increasing demand for producing durable construction materials is the outcome of the fast polluting environment. Supplementary cementitious materials prove to be effective to meet most of the requirements of durable concrete. Rice husk ash is found to be superior to other supplementary materials like slag silica fume and flyash. Due to its high pozzolanic activity both strength and durability of concrete are enriched. Unlike other industrial by-products rice husk ash has to be produced out of the ra w agricultural waste, husk. The quality ofash is greatlyinfluencedbyits method of production. To convert this ash into an active pozzolanic material, certain controlled conditions of production and processing methods have to be followed, which are yet to be fully understood and evolved. This paper presents various applications of rice husk ash in general and as pozzolana in particular. Works done on ash production methods have been critically reviewed. Possible areas of research have also been identified.

S. Kothandaraman

Papers

Rice Husk Ash -Properties and its Uses : A Review