Biochars produced from various agro-industrial by-products applied in Cr(VI) adsorption-reduction processes

Abstract

This study aimed to reuse different agro-industrial by-products (poultry litter, pig manure, sewage sludge and coffee husk) for biochar production and to evaluate their Cr(VI) removal capacities in aqueous medium. The biochars showed different morphologies with porous structures. The percentages of Cr(VI) removal from solution were higher in acid medium (pH = 2), reaching values up to 87%. For all biochars, Cr(VI) removal occurs via both adsorption and reduction, being a rapid (30 min) process, which fits best to the pseudo-second order kinetic model. The biochars, especially from coffee husk, were able to reduce up to 20% of Cr(VI) to Cr(III). The maximum Cr(VI) removal capacities ranged from 10.86 mg g⁻¹ (sewage sludge biochar) to 18.52 mg g⁻¹ (coffee husk biochar). Therefore, the production of biochars from the agro-industrial by-products using the same experimental conditions in one single study is important to compare the Cr(VI) removal capacities from different biomasses. Thus, this study explored the corresponding raw material without the need of further treatment. Biochars showed potential for environmental applications considering Cr(VI)-polluted environments. It is hoped to provide basis to future studies using real wastewater samples.

Keywords:

• Pyrolysis
• adsorption
• waste reuse

Acknowledgments

The authors gratefully thank the Minas Gerais State Agency for Research and Development – FAPEMIG and the National Council for Scientific and Technological Development – CNPq. This study was financed in part by the Coordination for the Improvement of Higher Education Personnel – Brazil (CAPES) – Finance Code 001. The authors acknowledged Barbara Olinda Nardis and José Ferreira Lustosa Filho for helping with biochar preparation, and Paulo Júnio Fernandes Braga for his valuable assistance.

Disclosure statement

The authors declare no competing interest.

Data availability

The authors confirm that the data supporting the findings of this study are available within the article and/or its supplementary materials.