Preparation and application of Zero Valent Iron immobilized in Activated Carbon for removal of hexavalent Chromium from synthetic effluent

Abstract Unlike organic contaminants, heavy metals are not biodegradable and tend to accumulate in living organisms; they are also recognized for being toxic or carcinogenic. The use of nanoparticles of zero-valent iron (nZVI) is reported as an alternative technique with high potential for in situ and ex situ remediation of contaminated matrices with this metal, mainly due to its large active surface area and significant adsorption capacity to consolidate into a simple and efficient method of treatment. In this study, ZVI particles were synthesized by the chemical reduction method using hydrated ferrous sulfate (FeSO4.7H2O) and sodium borohydride (NaBH4) with subsequent aggregation to powdered activated carbon (PAC), forming the adsorbent PAC-ZVI, which was characterized by the techniques of XRD and SEM, which revealed the integration of the catalyst to the activated carbon matrix. Finally, developed kinetic studies revealed that the adsorption kinetics was better adapted to a pseudo second order model, the isotherms were better represented by the Freundlich model and the thermodynamic results showed that the adsorption reaction occurred through a spontaneous process with endothermic interaction between Cr (VI) and PAC-ZVI with increase in the randomness of the system.摘要 与有机污染物不同，重金属无法生物降解且易于在生物体内蓄积，同时被证实具有毒性或致癌性。有研究表明，零价铁纳米颗粒（nanoparticles of zero-valent iron, nZVI）是一种极具应用潜力的替代技术，可用于受该类重金属污染基质的原位与异位修复，这主要得益于其庞大的活性比表面积与优异的吸附性能，可构建简便高效的重金属处理工艺。本研究采用化学还原法，以七水合硫酸亚铁（FeSO₄·7H₂O）与硼氢化钠（NaBH₄）为原料合成零价铁颗粒，随后将其与粉末活性炭（powdered activated carbon, PAC）复合得到吸附剂PAC-ZVI。通过X射线衍射（X-ray diffraction, XRD）与扫描电子显微镜（scanning electron microscope, SEM）对该吸附剂进行表征，结果证实催化剂已成功整合至活性炭基质中。最终开展的动力学研究表明，该吸附过程的动力学行为更符合准二级动力学模型（pseudo second order model）；等温吸附曲线更适配弗伦德里希（Freundlich）模型；热力学分析结果显示，六价铬（Cr(VI)）与PAC-ZVI之间的吸附反应为自发的吸热过程，且反应过程中体系的无序度有所提升。