| With the rapid development of textile and dyestuff industries, the pollution of dye wastewater becomes more and more serious. Dye wastewater discharged from textile and dyestuff industries should be treated due to their impacts on water bodies and particularly growing public concern over their toxicity and carcinogenicity. It has large quantity, dark chroma, high concentration, strong toxicity, complicated constituents and usually contains various kinds of dyes. Therefore, it is a kind of wastewater difficult to be degraded and hard to be treated. The conventional physical-chemical methods for treating dye wastewater are coagulation or flocculation, oxidation or ozonation and membrane separation etc. The effectiveness of these conventional treatment technologies is not significant in decolorizing because of the complex molecular structure of the dyes. The adsorption could remove effectively ionic dyes from water. The utilization of activated carbon is limited because of its relatively higher price, higher operating costs and problems from regeneration, though it is the most popular and widely used sorbent. In recent years, it has been increasingly noticeable to find economical, renewable, locally available and highly effective materials as sorbent for the dye removal. Developing efficient, economic and easily available sorbents of agricultural products or agricultural waste byproducts will be the direction of dyeing wastewater treatments. Rice husk is an agricultural byproduct from the cereal processing industry and it is widely available in large quantity in China. And the structure of rice hull is very particular, one of the major components is element Silicon (14%~16%), which is distributed with the form of the network, and cellulose and ligin are packed among them. Therefore, rice husk is very suitable for processing sorbent. In this paper, the studies on adsorption of dye removal from aqueous solution by raw granular rice husk were carried out under varying experimental conditions of contact time, dye concentration, adsorbent dose, partical size and pH value, etc. The functional groups were chemically modified in order to determine their contribution to the dye binding process. Batch experiments were performed with the modified biomass. The mechanism of rice husk absorbing ionic dyestuffs was investigated by SEM and IR spectrum. The results were as follows: 1. Solution pH value was one of the important influence factors which rice husk sorbent absorbed the ion dyestuffs. The cation dyestuff AO, NR, MB could be removed effectively above pH 4, the anionic dyestuff Am, SY and SF were absorbed best at pH 2. 2. The size of the absorbent particle was negatively related with the absorbing rate of dyestuffs 3. As the sorbent dosage increased, the removal rate of cationic dyestuffs and anionic dyestuffs increased too, until reaching the balance. 4. The removal effect appeared best when cationic dye concentration was at 100mg/L and anionic dye concentration was at 50mg/L. The isothermal data of cationic dye adsorption coincided with the Freundlich models, while that of the anionic followed Langmuir models, however, that of SY followed the above two models. 5. The absorbing course could be divided into three stages: absorbing fast stage, absorbing slowly stage and balanced stage, the adsorption processes conformed to the pseudo-first-order rate kinetics. The cationic dyestuffs absorption reached balance in 12h, while the anionic dyestuffs absorption in 24h. 6. The treated sorbent by NaOH obviously improved the absorbing rate of the two kinds of ionic dyestuffs. The carboxyl group was major functional group in the adsorption of cationic dyes, but inhibited the adsorption of anionic dyes. The hydroxyl group was important functional group in both the adsorption of cationic and anionic dyestuffs. The effect of methylation of amino group on ionic dye adsorption wasn't significant. 7. Rice husk with high dye removal capacity is a locally available, low cost and untried botanic material in China. It could reduce the operatin...
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