Mass transport process for the adsorption of Cr(VI) onto water-insoluble cationic starch synthetic polymers in aqueous systems
✍ Scribed by Wu-Chung Chan; Jyh-Chi Ferng
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 225 KB
- Volume
- 71
- Category
- Article
- ISSN
- 0021-8995
No coin nor oath required. For personal study only.
✦ Synopsis
Dynamic adsorption behaviors between Cr(VI) ion and water-insoluble amphoteric starches was investigated. It was found that the HCrO 4 Ϫ ion predominates over the initial pH ϳ 2-4, the CrO 4 Ϫ2 ion predominates over the initial pH ϳ 10 -12, and both ions coexist over the initial pH ϳ 6 -8. The sorption process occurs in two stages: the external mass transport process occurs in the early stage and the intraparticle diffusion process occurs in the long-term stage. The diffusion coefficient of the early stage (D 1 ) is larger than that of the long-term stage (D 2 ) for the initial pH 4 and pH 10. The diffusion rate of HCrO 4 Ϫ ion is faster than that of CrO 4 Ϫ2 ion for both processes. The D 1 and D 2 values are ϳ 1.38 ϫ 10 Ϫ7 -10.1 ϫ 10 Ϫ7 and ϳ 0.41 ϫ 10 Ϫ7 -1.60 ϫ 10 Ϫ7 cm 2 s Ϫ1 , respectively. The ion diffusion rate in both processes is concentration dependent and decreases with increasing initial concentration. The diffusion rate of HCrO 4 Ϫ ion is more concentration dependent than that of CrO 4 Ϫ2 ion for the external mass transport process. In the intraparticle diffusion process, the concentration dependence of the diffusion rate of HCrO 4 Ϫ and CrO 4
Ϫ2
ions is about the same. The external mass transport and intraparticle diffusion processes are endothermic and exothermic, respectively, for the initial pH 4 and pH 10. The k d values of the external mass transport and intraparticle diffusion processes are ϳ 15.20 -30.45 and ϳ Ϫ3.53 to Ϫ12.67 kJ mol Ϫ1 , respectively. The diffusion rate of HCrO 4 Ϫ ion is more temperature dependent than that of CrO 4 Ϫ2 ion for both processes.