Cd(II) Adsorption on Different Modified Rice Straws under FTIR Spectroscopy as Influenced by Initial pH, Cd(II) Concentration, and Ionic Strength

Shuai Wang, Wanhong Li, Xinhua Yin, Nan Wang, Shuai Yuan, Ting Yan, Shuang Qu, Xiangbo Yang and Dianyuan Chen
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Shuai Wang: College of Agriculture, Jilin Agricultural Science and Technology University, Jilin 132101, China
Wanhong Li: College of Agriculture, Jilin Agricultural Science and Technology University, Jilin 132101, China
Xinhua Yin: Department of Plant Sciences, The University of Tennessee, Knoxville, TN 37996, USA
Nan Wang: College of Agriculture, Jilin Agricultural Science and Technology University, Jilin 132101, China
Shuai Yuan: College of Agriculture, Jilin Agricultural Science and Technology University, Jilin 132101, China
Ting Yan: College of Agriculture, Jilin Agricultural Science and Technology University, Jilin 132101, China
Shuang Qu: College of Agriculture, Jilin Agricultural Science and Technology University, Jilin 132101, China
Xiangbo Yang: College of Agriculture, Jilin Agricultural Science and Technology University, Jilin 132101, China
Dianyuan Chen: College of Agriculture, Jilin Agricultural Science and Technology University, Jilin 132101, China

IJERPH, 2019, vol. 16, issue 21, 1-15

Abstract: Rice straw is a kind of low-cost biosorbent. Through mechanical crushing, pyrolysis, incineration, and citric acid (CA) modification, it could be converted to rice straw powder (Sp), biochar (Sb), ash (Sa), and modified rice straw (Ms) accordingly. Using rice straw as an adsorbent, the influence of pH value (2, 4, and 9), initial Cd(II) concentration (0, 200, and 800 mg/L), and ionic strength (0, 0.2, to 0.6 mg/L) on the adsorption capacity for Cd(II) were examined with three replicates, and the relevant mechanisms were explored using Fourier transform infrared (FTIR) technology. Results showed that the modifications could improve the adsorption capacity of Cd(II) by changing their chemical structures. The products (Sb and Sa) of the pyrolysis and incineration of rice straw contained fewer hydroxyl and alkyl groups, but more Si–O groups. Citric acid modification removed a portion of silica in rice straw, increased its carboxylic content, and made more –OH groups exposed. Compared with Sp, Sb, Sa, and Ms were more likely to act as π donors in the Cd(II) sorption process and exhibited more carboxyl binding. The bands of C = C, –O–CH 3 , and the O–H, carboxyl, Si–O–Si or Si–O groups were involved in the Cd(II) sorption process. The adsorption amount of Cd(II) by the four adsorbents increased with the increase in the pH value of the solution and the initial Cd(II) concentration. Affected by pH in a solution, ion exchange, surface complexation, and precipitation were the major adsorption mechanisms. Further, under the influence of the initial Cd(II) concentration, electrostatic attraction played a leading role. With no interference by ionic strength, all the adsorbents had the greatest adsorption amount of Cd(II), and the intensity of O–H vibration was also the weakest; ion exchange was the most important mechanism in this process. Regardless of the influencing factors, Sa, with the greatest specific surface area, had an absolute advantage in the adsorption capacity of Cd(II) over Sp, Sb, and Ms.

Keywords: rice straw; Cd(II); FTIR; adsorption; influencing factor (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2019
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