Tannin-based biosorbents for environmental applications – A review

• Literature review on the synthesis of tannin-based biosorbents.
• Discussion about the factors affecting the performance of tannin-based biosorbents.
• Overview of the use of tannin-based biosorbents for water decontamination.
• Overview on the use of tannin-based biosorbents for critical metals recovery.

Adsorption has been proved as an efficient process to remove a multiplicity of solutes from aqueous solution. Various biosorbents have found promising applications in wastewater treatment and in the recovery of critical metals that is, nowadays, the spotlight due to the promotion of environmental and economic sustainability. Tannins are excellent candidates to produce biosorbents. These ubiquitous and inexpensive natural biopolymers are of easy extraction and conversion into insoluble (tannin gels and tannin foams) or immobilized matrices. Tannin-based adsorbents (TBAs) have a natural affinity to uptake heavy metals, dyes, surfactants and pharmaceutical compounds from contaminated waters, and to accumulate selectively precious and critical metals from aqueous streams. Furthermore, chemically modified forms, such as iron-loaded and amine-modified tannin gels can be produced with relative ease and enhance the adsorption ability of many substances. In this paper, the literature about the production of different types of TBAs (resins, foams, immobilized tannins on support matrices, iron and amine treatments) is revised. The actual state of knowledge, in respect to TBAs application for water remediation and recovery of substances is presented.