Removal of basic dyes from aqueous solution by sorption on phosphoric acid modified rice straw

In this article, rice straw was chemically modified by means of phosphorylation, and then the phosphoric acid modified rice straw was further loaded with sodium ion in order to yield potentially biodegradable cationic sorbent. The feasibility of the modified product as cationic dye sorbent for removing basic dyes from aqueous solution was investigated. Two basic dyes, basic blue 9 (BB9) and basic red 5 (BR5), were used as sorbates. The effects of various experimental parameters (e.g. initial pH, sorbent dosage, dye concentration, ion strength, contact time) were examined and optimal experimental conditions were decided. The BB9 and BR5 removal ratios came up to the maximum value beyond pH 4. The 1.5 g/l or more sorbent could almost completely remove BB9 and BR5 from 250 mg/l of dye solution. The ratios of BB9 and BR5 sorbed were kept above 96% over a range from 50 to 350 mg/l of dye concentration when 2.0 g/l of sorbent was used. Increase in ion strength of solution induced decline of BB9 and BR5 sorption. The isothermal data fitted the Langmuir model. The sorption processes followed the pseudo-first-order rate kinetics. The results in this research confirmed that the phosphoric acid modified rice straw was an excellent basic dye sorbent.