Yerba mate waste: Transformation to magnetic composites for the adsorption of chemically diverse pollutants

Abstract

Biochar (BC) from yerba mate waste was produced as sorbent material contributing to the circular economy. The BC was magnetized through the nucleation of Fe oxides. Three different magnetic composites were synthesized: BC2.5-Fe (2.5 g of BC), BC1.25-Fe (1.25 g of BC), and BC0.625-Fe (0.625 g of BC). The resulting BC consisted of carbon (C) and oxygen (O), with a BET surface area of 2 m2/g. It exhibited various functional groups and whewellite was identified. Comparing with BC, the BET surface area of the composites increased whereas the number of functional groups decreased. Meanwhile, whewellite was chemically destroyed. Magnetite/maghemite were the main magnetic iron oxides, which imparted a magnetic response. The saturation magnetization for BC0.625-Fe was 30.3 Am2/kg. The BC and the composites were tested against various types of pollutants found in wastewater, including emerging pollutants, oxyanions and dyes. The increases of the BET area and the change of surface properties lead to a higher adsorption efficiency of the composites, when compared to the BC. The magnetic properties of the composites and the magnetic force studies revealed that these materials can be used in water treatment systems based on magnetic recuperation of the sorbent materials. The finding highlights the need to design adequate geometries for the indirect manipulation of these types of sorbent materials when usingthem in practical applications. This study makes a significant contribution to the circular economy by providing an efficient method for recycling the yerba mate waste and a sustainable solution for water remediation processes. Besides, the developed materials allow their indirect manipulation by means of magnetic fields, which decrease the health risk of operators by reducing their exposure to pollutants such as drugs, oxyanions, and dyes.