Estudo de pastas de cimento Portland com adição de sílica extraída de cinzas de casca de arroz para a imobilização de cromo hexavalente

Abstract

The extensive generation of waste associated with human activities demands studies on treatment techniques and final disposal. The solidification stabilization process (S/S process) becomes relevant, especially when using Portland cement as a low-cost binder and which has wide alternatives of improving properties, such as the use of silica (SiO2) extracted from rice husk ash (RHA), an agrosilvopastoral residue. Thus, this work aims to report the evaluation of the mechanical properties, the hydration development and the capacity of Cr(VI) retention of pastes produced with Portland cement (PC) and the addition of SiO2 extracted from RHA. Initially, SiO2 was obtained, followed by steps of characterization of the starting materials, moving on to the step of production of PC pastes with additions in the proportions of 0,0%SiO2-0,0%K2Cr2O7, 0,0%SiO2-2,5%K2Cr2O7 and 0,6%SiO2-2,5%K2Cr2O7. In the next step, tests about resistance to compression, solubilization and characterization tests of the pastes were performed, among them scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-VIS spectrophotometry and Fourier-transform infrared spectroscopy (FTIS). Regarding the outcomes, the XRD and the SEM of SiO2 indicated predominantly amorphous characteristics and grains mostly in the PC dimension range, respectively. The resistance to compression of the different traits, at the same ages (7, 28 or 91 days), in statistical terms, showed that the additions did not bring significant differences. The XRD of the pastes with K2Cr2O7 showed changes in the hydration process, especially in relation to the ettringite and portlandite phases, while the SEM of the pastes showed mainly the identification of acicular phases. The FTIS of the pastes of all the traces at all ages allowed us to observe typical bands, the main ones being related to the Si-O bond in the calcium silicate phases, Si-O in the C-S-H, bonds in the CO3 -2 functional group of calcite and O-H bonds in the Ca(OH)2. Despite presenting immobilization efficiencies between 99.82% and 99.87%, in the solubilization test, in statistical terms, there was no improvement of the property through the addition of SiO2 extracted from RHA, both at 7 days and at 28 days. Thus, considering the procedures and traces, it was concluded that the research objectives were met and it is suggested that the SiO2 extracted from RHA did not improve the pastes with K2Cr2O7, in relation to the analyzed parameters.