The Role of Oxygenated Functional Groups on Cadmium Removal using Pyrochar and Hydrochar Derived from Guadua angustifolia Residues

In the Ecuadorian Amazonia, there is a concern about the presence of high concentrations of cadmium (Cd) in rivers and sediments because of changes in land use and anthropogenic activities, e.g., mining and oil exploitation. Hence, the research related to water treatment processes to meet environmental standards has gained relevance. The use of biochar (BC) as adsorbent is considered a promising and low-cost alternative to improve the water quality in developing countries. In this work, lignocellulosic wastes from Guadua angustifolia were transformed through thermochemical treatments, into a promising carbonaceous material, such as BC. BC samples were prepared by pyrolysis (termed pyrochar, PC) and hydrothermal carbonization (termed hydrochar, HC). Their physicochemical properties were correlated with the Cd adsorption removal performance, analyzing the effect of adsorbent dosage, initial solution pH, adsorption kinetics and adsorption isotherms. HC showed the highest Cd adsorption performance, due to the presence of a higher number of oxygenated functional groups, as confirmed by FTIR, XPS and Raman spectroscopy. This research has proposed a sustainable alternative for the recovery of an available waste, contributing to mitigate the effects of the presence of metals on the health and economy of the most vulnerable sectors of society.