Application of zeolites for efficient tannery wastewater remediation

Leather manufacturing is the process of converting raw animal hides or skins into finished leather. The complex industrial procedures result in a tanning effluent composed of chemical compounds with potentially hazardous impacts on humans and ecosystems. Among the traditional and efficient wastewater treatments, adsorption is an effective and well-known approach, able to manage a wide range of contaminants from wastewater. Among the plethora of adsorption substrates used on an industrial scale, zeolites have traditionally shown remarkable performances. Differently from other types of adsorbents, zeolites can also work as cation exchangers, which can remove cationic contaminants without influencing the anionic content of the effluent and (in specific cases) also when the removal process is endothermic. Zeolites are minerals naturally present in the environment, but they can be also easily synthesized and modified to enhance their water remediation features. However, the removal efficiency of zeolites is strictly dependent on the type of target contaminant because its uptake capacity is linked to its chemical and physical characteristics, especially on the surface interlayer. This review intends to present a general description of the tannery process to understand the origin and characterization of tanning wastewater. The core of the study aims to approach the most significant studies about zeolite applications in the removal of tanning contaminants. Drawbacks of the reviewed literature are further discussed, and some potential future research content is eventually revealed by identifying the issues that need further investigation.