Abstract
This work describes the preparation of the cellulose phosphate with high ion exchange capacity from rice straw and bagasse for removal of heavy metals. In this study, rice straw and bagasse were modified by the reaction with phosphoric acid in the presence of urea. The introduced phosphoric group is an ion exchangeable site for heavy metal ions. The reaction by microwave heating yielded modified rice straw and modified bagasse with greater ion exchange capacities (∼3.62 meq/g) and shorter reaction time (1.5–5.0 min) than the phosphorylation by oil bath heating. Adsorption experiments towards Pb2+, Cd2+, and Cr3+ ions of the modified rice straw and the modified bagasse were performed at room temperature (heavy metal concentration 40 ppm, adsorbent 2.0 g/L). The kinetics of adsorption agreed with the pseudo-second-order model. It was shown that the modified rice straw and the modified bagasse could adsorb heavy metal ions faster than the commercial ion exchange resin (Dowax). As a result of Pb2+ sorption test, the modified rice straw (RH-NaOH 450W) removed Pb2+ much faster in the initial step and reached 92% removal after 20 min, while Dowax (commercial ion exchange resin) took 90 min for the same removal efficiency.
Highlights
Rice straw and sugarcane bagasse are abundant agroresidues in Thailand
The effect of pretreatment methods on ion exchange capacity of the sample was tested by using dimethyl formamide (DMF) or NaOH solution
For the modified rice straw, the samples which were pretreated by DMF (RSDMF oil 2 hr, RS-DMF 300 W, RS-DMF 450 W, RS-DMF 600 W, RS-DMF 800 W) showed slightly lower ion exchange capacity than the no pretreatment samples (RS-oil 2 hr, RS 300 W, RS 450 W, RS 600 W, and RS 800 W)
Summary
Rice straw and sugarcane bagasse are abundant agroresidues in Thailand. The sugarcane bagasse is currently used as a biofuel and in the manufacture of pulp and building materials. Commercial ion exchange resins are petroleum based polymers so that the cost is relatively high Since they are nonbiodegradable, the environmental impact for disposal is larger than the use of biosorbents. The phosphoric acid modified rice straw showed high ability for dyes removal from aqueous solution [9]. It was found that cellulose phosphate in modified rice straw prepared by conventional heating could remove almost 100% of Cd2+ [10]. Rice straw and sugarcane bagasse contain approximately 30–35% and 32–43% cellulose, respectively [11]. Of hydroxyl groups in bagasse by phosphoric acid in the presence of urea leads to the formation of cellulose phosphate: H3PO4 + H–O–cellulose → cellulose–O–PO3H2 (1). The feasibility of the modified product as cationic sorbents for removing Cd2+, Cr3+, and Pb2+ from aqueous solution was investigated
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