Recycling of bentonites after their use in wastewater treatment: a review of environmental, sustainability and science

This paper reviews current trends in the reuse and effective disposal of bentonite clay sorbent (montmorillonite, as the main mineral in bentonite and palygorskite clays) after its application in wastewater treatment systems. Special attention is given to its potential applications in construction and polymer composites. A comparative analysis of the advantages and limitations of various approaches to bentonite regeneration, reuse possibilities, and effective disposal of the spent sorbent is conducted. The specifics of using spent bentonite are determined based on the nature of the pollutants sorbed onto the clay mineral surface. Important aspects of using montmorillonite clays, both pristine and pollutant-saturated, are discussed from the perspective of their natural sources, chemical structure, physical and chemical properties. Useful properties for industrial applications include, among others, particle size and layered structure, molecular structure and cation exchange effect, barrier properties, and water absorption. The presented data on the use of spent montmorillonite clays are based on products classified by their industrial application. Most discussions are supported by specific studies and their results.