Rice hull ash

Industrial by-products are becoming more widely used as raw materials for cement, eg, slags contain carbonate-free lime, as well as substantial levels of silica and alumina. Fly ash from utility boilers can often be a suitable feed component, because it is already finely dispersed and provides silica and alumina. Even vegetable wastes, such as rice hull ash, provide a source of silica. Probably 50% of all industrial by-products are potential raw materials for Pordand cement manufacture. 

The Langmuir equation has been used to describe adsorption of p carotene from solution onto activated bleaching clays (8) and free fatty acid from isooctane solution by acid-washed rice hull ash (9). Likewise, isotherm analysis of the commercial bleaching of rubber and melon seed oil by Fullers earth, activated carbon, and Fullers earth/activated carbon mixture (10) followed Langmuir behavior at 55°C and 80°C, suggesting the possibility of monolayer adsorption with little competition. This behavior was not observed at 30°C where the isotherm no longer applies, because of desorption. The amount of adsorbent was kept constant while varying... 

Property/sample Permeate After Treatment with Rice Hull Ash After Treatment with Bleaching Earth After Physical Refining... 

Another version of Portland cement mortar or concrete is the replacement of some of the Portland cement with rice hull ash. This ash additive markedly improves the resistance of the mortar or concrete to food acids and similar chemicals. Flyash (pozzolanic admixture) meeting ASTM C618 has also been widely used to improve the properties and sulfate resistance of Portland cement... 

Other materials used as filter aids include asbestos, cellulose, rice hull ash, paper fibers, etc. 

Cellulose is widely used for filtration of products that cannot tolerate silica. The filterability of cellulose is not as good as DE or perlite, but cellulose can be incinerated. Calcined rice hull ash and fibers from used newspapers are newly available filter aids. They are used for wastewater sludge dewatering as well as other applications. 

Rice hull hydrocarbons supply the carbon source and rice hull ash the silicon source. This is an early carbothermal process (Equ. 10a). At <900°C, coking (Equ. 10b and 10c) removes water and organics and yields a mixture of silica and carbon, and at <1700°C, pyrolysis yields silicon carbide whiskers (Equation lOd). The overall yield is 1 percent. Three variants of the rice hull process are known. Compacted rice hulls can be pyrolized at 1600°C without coking [14], thus directly yielding a mixture of graphite and SiC whiskers, 10-200 pm in length and... 

Chaudhary DS, Jollands MC, Cser F (2002) Understanding rice hull ash as fillers in polymers a review. Silicon Chem 1 281-289... 

Chaudhary DS, Jollands MC (2004) Characterization of rice hull ash. J Appl Poiym Sci 93 1-8... 

Rodrigues FA, Monteiro PJM (1999) Hydrothermal synthesis of cements from rice hull ash. J Mater Sci Lett 18 1551-1552... 

At present, some of the brand new works conducted on the silica system in aqueous solution concern the use of agricultural wastes, such as rice hull ash, as an inexpensive silica source [15, 16]. 

Tang Q, Wang T (2005) Preparation of silica aerogel from rice hull ash by supercritical carbon dioxide drying. 

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