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Use of High-Pressure CO2 for Concentrating CrVI from Electroplating Wastewater by Mg–Al Layered Double Hydroxide

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journal contribution
posted on 13.11.2013, 00:00 by Xiangying Lv, Zhi Chen, Yongjing Wang, Feng Huang, Zhang Lin
The desorption of CrVI from CrVI-adsorbed layered double hydroxide (CrVI-LDH) and the recycling of LDH adsorbent are the bottlenecks that limit the practical application of LDH in treating CrVI-containing industrial wastewater. Given the strong affinity of LDH for CO2, we studied desorption and enrichment of CrVI from CrVI-LDH as well as recycling of LDH in the presence of high-pressure CO2. Results showed that CrVI solution with concentration of 500 mg/L could be enriched more than 20 times in each adsorption–desorption cycle. The regenerated LDH maintained the layer structure and the sheets as revealed by XRD and TEM patterns. FT-IR data showed CO2 formed HCO3 at high pressure. The transformation from CO2 to HCO3 followed by the anion-exchange with CrO42– was the critical factor for CrVI desorption and LDH regeneration. A pilot-scale experiment was carried out with 20 L CrVI-containing electroplating wastewater. The concentration of the desorbed CrVI solution could reach up to 10000 mg/L, which could be used in electroplating after appropriate adjustment. The main advantages of this method are high concentration of CrVI, direct reuse of enriched CrVI, and efficient regeneration of LDH adsorbent. This method showed promises in recycling CrVI and regenerating LDH in treating industrial wastewater.