The removal of heavy metals from water is one of the major challenges that humanity must address to avoid negative potential impacts on the environment and human health. During the last few years, several adsorbents have been examined, in a search for highly efficient and cost-effective materials. In this work, we investigated the use of laurel, canelo and eucalyptus lignocellulosic sawdust residues (LRs) impregnated with magnetite nanoparticles (MNP), to remove Cr6+ ions. Each LR was added to an aqueous solution in which MNP were being synthesized by coprecipitation. Two composite adsorbents were obtained, with LR:MNP ratios of 1:1 and 3:1. The materials obtained were characterized by X-ray diffraction, scanning and transmission electron microscopy, and infrared and Raman spectroscopy. The results obtained showed that the laurel composite was the best adsorbent, reaching a maximum removal efficiency and capacity of 99.8 % and 30.5 mg/g, respectively. The optimal contact time was 30 min and the process fitted the Langmuir isotherm model, showing small effects of the fraction of sawdust residues used to support the MNP. Further studies will be performed to optimize the composition of the composites aiming to reduce the amount of costly MNP used while ensuring a high removal performance.

The degradation of Reactive Red 120 dye (RR-120) in synthetic waters was studied. Two processes were considered: homogeneous sono-Fenton with iron(II) sulfate and heterogeneous sono-Fenton with synthetic goethite and goethite deposited onto silica and calcite sand (modified catalysts GS and GC, respectively). In 60 min of reaction, the homogeneous sono-Fenton process allowed a degradation of 98.10 %, in contrast with 96.07 % for the heterogeneous sono-Fenton process with goethite at pH 3.0. The removal of RR-120 increased when the modified catalysts were used instead of bare goethite. Chemical oxygen demand (COD) and total organic carbon (TOC) measurements showed that the highest TOC and COD removals were achieved with the homogeneous sono-Fenton process. Biochemical oxygen demand (BOD 5) measurements allowed confirmed that the highest value of BOD 5 /COD was achieved with a heterogeneous sono-Fenton process (0.88±0.04 with the modified catalyst GC), demonstrating that the biodegradability of the residual organic compounds was remarkably improved.