Chemical exploitation of metal contaminated biomass produced in phytoextraction

Abstract

This article describes some aspects of the chemical recovery of the metal contaminated biomass produced in phytoextraction technologies. Taking advantage of the adaptive capacity of certain plants to hyperaccumulate metallic cations in their aerial parts, phytoextraction could be a sustainable way to remediate trace metals pollution. A possible exploitation of the metal contaminated biomass produced in phytoextraction is the direct use of metallic cations derived from plants as Lewis acid catalysts for organic chemistry. These original polymetallic systems serve as heterogeneous catalysts in chemical transformations enabling the synthesis of molecules with high added value. Results for Friedel-Crafts acylations and alkylations are presented in this paper: the acetylation of anisole and benzylation reactions are considered in more detail. The use of mine tailings as catalytic supports is also investigated: it could represent a new integrated outlet for tailings and phytoextraction products. Each step of the process is designed to minimise environmental impacts in accord with the principles of Green Chemistry. The process seeks to be an incentive for the economic development of phytoextraction. As phytoremediation gains momentum, it could also prove a concrete solution to the criticality of non-renewable mineral materials with new sources of zinc, nickel and other metals.

From Conventional Lewis Acids to Heterogeneous Montmorillonite K10: Eco‐Friendly Plant‐Based Catalysts Used as Green Lewis Acids

“…The yellow solution is concentrated under vacuum then filtered through a pad of Celite if a purification step is necessary. The resulting solid residue, stored in a desiccator, may be used as an ecocatalyst or may be supported on silica or MK10 …”

“…Nevertheless, classical aromatic acylation causes a general problem because it requires more than one molar equivalent of Lewis acid. Heterogeneous eco‐friendly plant‐based Lewis acids show very interesting activity in Friedel–Crafts alkylation and acylation …”

“…This reagent is a mixture of ZnCl 2 and HCl and is commonly used in the synthesis of alkyl chlorides from aliphatic alcohols on an industrial scale, but remains expensive . For this reaction, Eco‐Zn catalyst derived from T. caerulescens was produced and purified to eliminate alkali and alkaline earth cations, but was not supported on clays (Scheme ) . The green catalytic solid was mainly composed of ZnCl 2 , CdCl 2 , PbCl 2 , CaCl 2 , and FeCl 3 …”