Considering the increasing need for renewable products, the present work aims to evaluate the physical-chemical properties of the eucalyptus harvest residues and its constituent fractions individually (barks, leaves, and branches), through proximate, ultimate, energetic and thermal analyzes. The biomass studied was Eucalyptus saligna species, cultivated mainly for the production of pulp and paper. The proximate analysis of the residue resulted in the moisture content of 10.1%, ash content of 3.9%, volatile materials about 81.1%, and fixed carbon of 15.0%, showing similar values to the constituent fractions. The ultimate analysis of the residue resulted in 46.5% of carbon content, 5.8% of hydrogen, and 43.2% of oxygen. The high heating value (HHV) for the residue is 17.93 MJ/kg, comparable to other biomasses of importance, including eucalyptus wood, the noblest part of the forest cultivation. The thermogravimetric (TGA) and differential thermal analysis (DTA) were carried out and the resulting thermograms show three main ranges of biomass degradation. The first range, from 30 to 150 °C, corresponds to the drying of the material; in the range from 200 to 325 °C hemicelluloses degrade, with partial degradation of lignin and cellulose, and in the range from 325 to 380 °C, the majority of cellulose degradation takes place. The physical-chemical data demonstrate that the eucalyptus residue is an excellent source of biomass for thermal conversion processes. Obtaining products with higher added value from this residue contributes to the implementation of new technological practices that link economic development to environmental responsibility.

The removal of Cr(VI) from wastewater by adsorption from agro-industrial residues remain an attractive option since combines reasonable cost with the quality of effluents treated. This paper employs of parboiled-rice husk ash (RHA) and parboiled-rice husk ash chemically treated (RHAH⁺) as adsorbents for Cr(VI). The RHA and RHAH⁺ were characterized. It was studied the adsorption efficiency on adsorbent dosage, pH, chromium concentration, and interaction time. RHAH⁺ presented superior Cr(VI) removal, although both adsorbents have shown satisfactory results. The best results are obtained at pH 1.0, presenting 90.9% and 97.7% of Cr(VI) removal for RHA and RHAH⁺, respectively, in 5 mg L⁻¹ of Cr(VI) concentration at about 30 minutes. The adsorption of RHAH⁺ is governed by the Freundlich isotherm (R²_adj = 0.989) and kinetically by the pseudo-second order model (R²_adj = 0.991). The rice rusk ash represents an alternative low-cost and environment-friendly material that efficiently removes Cr(VI) from dilute aqueous solutions.