Removal of chromium (VI) from electroplating wastewater using an anion exchanger derived from rice straw

Abstract

An anion exchanger from rice straw was used to remove Cr (VI) from synthetic wastewater and electroplating effluent. The exchanger was characterized using Fourier transform infrared (FTIR) spectrum and scanning electron microscopy (SEM), and it was found that the quaternary amino group and hydroxyl group are the main functional groups on the fibrous surface of the exchanger. The effect of contact time, initial concentration and pH on the removal of Cr (VI), and adsorption isotherms at different temperature, was investigated. The results showed that the removal of Cr (VI) was very rapid and was significantly affected by the initial pH of the solution. Although acidic conditions (pH=2−− 6) facilitated Cr (VI) adsorption, the exchanger was effective in neutral solution and even under weak base conditions. The equilibrium data fitted well with Langmuir adsorption model, and the maximum Cr (VI) adsorption capacities at pH 6.4 were 0.35, 0.36 and 0.38 mmol/g for 15, 25 and 35°C, respectively. The exchanger was finally tested with real electroplating wastewater, and at sorbent dosage of 10 g/L, the removal efficiencies for Cr (VI) and total Cr were 99.4% and 97.8%, respectively. In addition, the positive relationship between adsorbed Cr (VI) and desorbed Cl⁻ suggested that Cr (VI) was mainly removed by ion exchange with chlorine.

Keywords:

• Chromium (VI)
• anion exchanger
• electroplating wastewater
• agricultural waste modification
• rice straw

Acknowledgements

The authors thank Zhen-Pei Liu from XDY Environmental Protection Company for providing the electroplating wastewater samples. The National Natural Science Foundation of China (Nos. 40730741 and 41073088), National Special Science and Technology Project on Treatment and Control of Water Pollution of China (No. 2008 ZX07211-001), and the Natural Science Foundation of Guangdong Province (No. 9351064101000001) financially supported this work.