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The magnetic properties of sintered samples of cobalt-zinc ferrites produced from the corresponding coprecipitate were calculated based on hysteresis curves (Hc). The Hc values confirmed that soft ferrites were obtained by the procedure. A possible relation between the magnetic hysteresis curves and the microstructure of the sintered samples was investigated. X ray diffraction, thermal analysis and scanning electron microscopy were used to characterize the microstructure and the phases present in the sintered ceramic pieces, as well as those of their coprecipitated tri-metallic hydroxide precursor powders. It was found that sintering of Co0.5Zn0.5Fe2O4 at 1400 °C led to "honeycombing" of the ferrite grains and that there was no single phase in the microstructure of a sample sintered at 1400 °C. Thus, a more complete study was made of the behavior of the microstructure at lower sintering temperatures, i.e., in the 1100-1350 °C range

RESUMO Este estudo avaliou as propriedades físico-químicas envolvidas no processo de adsorção para subsidiar o potencial uso de biocarvão produzido com folhas secas de amendoeira-da-praia, Terminalia catappa, como remediador em águas contaminadas com metais. O biocarvão utilizado foi produzido por conversão à baixa temperatura e caracterizado por apresentar bandas de O-H, CH2, C-O e C-O-C; teores de 48,8% de carbono, 46,6% de oxigênio, 3,3% de hidrogênio e demais entre enxofre e nitrogênio; presença de macroporos e passado em peneira (100 mesh). Para o estudo, preparou-se um coquetel de radiotraçadores (Co-57, Mn-54 e Zn-65), que foi adicionado à água deionizada e massas de biocarvão com o objetivo de obter parâmetros tais como pH, tempo de equilíbrio e capacidade de adsorção por meio das isotermas de Langmuir e Freundlich. O detector de Germânio Hiperpuro foi utilizado para quantificar as atividades dos radiotraçadores por meio da técnica de espectroscopia gama para geração e tratamento de dados. Os resultados obtidos mostraram aumento na adsorção do pH 3,8 em diante e tempo de equilíbrio de 30 minutos ou mais. As isotermas de Langmuir e Freundlich construídas apresentaram bons ajustes, com valores de n maiores que 1, indicando preferência dos metais pelo material adsorvente. Além disso, levando-se em conta a competição pelos sítios ativos e a concentração inicial das soluções (ordem de picogramas), foram encontradas capacidades de adsorção de 1,273 ng.g-1 para o Zn-65, de 3.271 ng.g-1 para o Co-57 e de 9,026 ng.g-1 para o Mn-54.

Currently epiphytes have been considered an important type of passive biomonitors for its high spread in the forests of tropical countries. The Rhipsalis lindbergiana is a typical epiphyte in the Atlantic Forest of Brazil, but there is no data available to establish its role as a metal traces bioaccumulator. In this way, this work has succeeded in elementar characterization of the Rhipsalis lindbergiana samples collected in Niterói City, RJ. It was applied Optical Spectrometry in order to evaluate the amounts of major - Ca, K, Mg and Na - and trace elements - Fe, Al, Mn, Zn, Cu, Co, Ni, La and Y. The results showed the average ratio Ca / K = 0.59 ± 0.27, with range between 1.16 and 0.19. The Al normalization showed enrichment of Zn and Cu in the sites of UFF’s Chemistry Institute; Zn, Cu and Ni in the most polluted sites next to town. Furthermore, enrichment of Mn was observed in the sample of green area collected during the fructification season. An inconsistency was found about low values of the enrichment factor of La and Y and the distribution of these elements in the samples. This suggests that the applied algorithm is not yet the best parameter to evaluate the accumulation of these elements in this type of environmental matrix. Pearson's test pointed out a significant positive correlation between the elements Na, Ca, Cu and Fe and a negative correlation with Na and Mn. Positive correlations were also found between Co and K,  La and Al. Three aspects can be taken into account from the results obtained: the morphology of the Rhipsalis; the influence of some ion concentration on absorption of other ions; the deposition of sea spray on the plants.