Adsorption of chromium(VI) from saline wastewater using spent tea-supported magnetite nanoparticle

Spent tea-supported magnetite (ST/Mag) nanoparticles were synthesized as an adsorbent for the removal of hexavalent chromium [Cr(VI)] from saline wastewater. Prepared ST/Mag adsorbent was characterized using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. Various factors affecting the uptake behavior such as pH, contact time, initial concentration of metal ions, adsorbent dose, coexisting ions, and desorption behavior were studied using batch tests. The results revealed that adsorption of Cr(VI) was highly pH dependent and the kinetics of the adsorption followed by the Avrami fractional-order and pseudo-second-order kinetic models. The results showed that the adsorption isotherms were more accurately represented by Langmuir and Liu isotherm models with a sorption capacity of 30.0 mg g−1. Adsorption experiments with co-ions indicated that the adsorptive removal of Cr(VI) ions was slightly decreased. Desorption studies using alkaline eluents showed maximum recovery of ST/Mag and only 10% decrease occurring in maximum adsorption capacity after five cycles. The ST/Mag nanoparticles proved to be a very prospective adsorbent for Cr(VI) uptake from industrial high-TDS effluents.

废茶负载型磁铁矿（ST/Mag）纳米颗粒被制备为吸附剂，用于脱除含盐废水中的六价铬[Cr(VI)]。采用X射线衍射（X-ray diffraction）、扫描电子显微镜（scanning electron microscopy）与傅里叶变换红外光谱（Fourier transform infrared spectroscopy）对制备得到的ST/Mag吸附剂进行了表征。通过批量吸附实验，考察了影响Cr(VI)吸附性能的各类因素，包括pH值、接触时间、金属离子初始浓度、吸附剂投加量、共存离子以及脱附行为。研究结果表明，Cr(VI)的吸附过程显著依赖于pH条件，其吸附动力学符合Avrami分数阶动力学模型与准二级动力学模型。结果显示，吸附等温线可更为精准地由Langmuir模型与Liu等温模型拟合，其最大吸附容量达30.0 mg·g⁻¹。共存离子吸附实验表明，Cr(VI)离子的吸附去除率略有降低。采用碱性洗脱剂开展的脱附实验显示，ST/Mag的回收率可达最优水平，且经过5次循环后其最大吸附容量仅下降10%。实验证实，ST/Mag纳米颗粒是一种极具应用前景的吸附剂，可用于从工业高总溶解固体（total dissolved solids, TDS）废水中吸附去除Cr(VI)。