Abstract In the slip casting process, the relationship between the amount of plaster and water used in the production of molds influences the production of ceramic materials, because the higher the water content in the mixture, the lower the mechanical strength of the mold and higher the water absorption rate. In order to evaluate the influence of the variation in the plaster/water (P/W) ratio in the production of ceramic pieces, plaster molds with P/W ratios of 2.0, 1.67, 1.43, and 1.25 (100 parts of plaster/50, 60, 70, and 80 parts of water by weight) were manufactured and used in the production of ceramic pieces. It was found that the fluidity, density, flexural and compressive strength of the molds decreased with the increase of water content. For pieces sintered at 1050 °C, higher density and lower porosity were observed for ceramic materials obtained with molds with higher plaster/water ratios.

Abstract The self-healing capacity of a ceramic material produced by uniaxial pressing with alumina (Al2O3), silicon carbide (SiC), and magnesium oxide (MgO) was evaluated. To assess self-healing, a discontinuity was generated on the surface of the specimens. The healing time in the oven, at a temperature of 1000 ºC, was 1, 30, and 60 min. The specimens were analyzed by physical and mechanical tests. The results showed that, for the mixture containing 15% SiC, the specimens healed at 60 min had an increase in flexural strength of 84.9% when compared to the specimens that were only indented while for the specimens containing 20% SiC, this increase was 61.1% at 30 min. For the 30 min healing time, there was a reduction in the size of the discontinuity in the specimens by about 19.1% and 14.8%, for the formulation containing 15% and 20% of SiC, respectively.

Resumo Materiais rochosos artificiais (ASM) foram produzidos com rejeito de minério de ferro (IOT) proveniente do rompimento da barragem de rejeitos do Fundão, localizada em Mariana-MG, Brasil. O IOT foi separado em três pós com diferentes tamanhos de partículas: DAG (<600 μm), DAR (600 a 75 μm) e DSA (<75 μm); em seguida cada pó foi caracterizado e misturado com uma resina polimérica (poliéster ou epóxi). Amostras de ASM foram preparadas usando a técnica de moldagem por transferência; a tecnologia de vibração a vácuo também foi aplicada à metade das amostras. Após a cura, as amostras de ASM foram caracterizadas quanto às propriedades mecânicas e parâmetros físicos. A microestrutura de amostras de ASM polidas também foi analisada por microscopia eletrônica de varredura. Todos os resultados indicaram que as amostras de ASM produzidas com resina epóxi foram superiores às amostras feitas com resina poliéster. As características encontradas para as diferentes composições e condições de preparação para as amostras de ASM produzidas podem permitir várias aplicações para esses materiais alternativos na indústria da construção, como na forma de revestimentos verticais e horizontais, proporcionando um meio de reduzir a quantidade de IOT depositada em barragens de rejeito e agregando valor econômico para este rejeito.

Abstract Artificial stone materials (ASM) were produced with an iron ore tailing (IOT) from the disruption of Fundão’s tailing dam, located in Mariana, Minas Gerais State, Brazil. The IOT was separated in 3 powders with different particle sizes: DAG (<600 μm), DAR (600 to 75 μm), and DSA (<75 μm); then, each powder was characterized and mixed with a polymer resin (polyester or epoxy). ASM samples were prepared using the transfer molding technique; vacuum vibration technology was also applied to half of the samples. After curing, the ASM samples were characterized for mechanical properties and physical parameters. The microstructure of polished ASM samples was also analyzed by scanning electron microscopy. All results indicated that ASM samples produced with epoxy resin were superior to the samples made with polyester resin. The features found for the different compositions and shaping conditions for the produced ASM samples can allow various applications for these alternative materials in the construction industry, such as floor and wall tiles, providing a means of reducing the amount of IOT deposited in the tailing dams and adding economic value to this waste.

O tratamento de efluentes contendo cádmio é de grande interesse devido à persistência desse contaminante no meio ambiente e às graves doenças que pode causar ao homem. No presente trabalho, foi utilizado o compósito magnético Mn3O4/Fe3O4 como adsorvente do íon cádmio (II) em meio aquoso. O material adsorvente foi sintetizado e caracterizado segundo as técnicas de difração de raios X (DRX), espectroscopia Raman, microscopia eletrônica de transmissão e sorção de N2 (BET). Ênfase foi dada à quantificação das fases do compósito pela análise de DRX combinada ao método Rietveld. O estudo de adsorção foi realizado variando o pH do meio e a concentração do íon cádmio em solução. A análise dos resultados possibilitou verificar que a remoção de Cd(II) utilizando compósito magnético Mn3O4/Fe3O4 em meio aquoso é dependente do pH duplicando a medida que o pH varia de 3 para 7. O estudo de imobilização do íon contaminante em solução apresentou valores significativos de capacidade máxima de adsorção, de 12,3 mgCd/g no pH 6 e 13,6 mgCd/g no pH 7, indicando uma remoção de até 98% para concentrações baixas do íon, sugerindo que o adsorvente apresenta elevado potencial para remoção de Cd(II) em meio aquoso.

The treatment of wastewater containing cadmium is of great interest because of its persistence in the environment and the serious diseases that it can cause to humans. In the present work, the magnetic composite Mn3O4/Fe3O4was used as adsorbent of cadmium ion in aqueous medium. The adsorbent material was synthesized and characterized according to the XRD, Raman, TEM and N2adsorption (BET) techniques. Emphasis was given to the quantification of the phases of the composite by XRD analysis combined with the Rietveld method. The adsorption study was carried out varying the aqueous medium pH and the concentration of cadmium ions in solution. The results show that the cadmium removal by the Mn3O4/Fe3O4magnetic composite in aqueous medium is pH-dependent duplicating as the pH varies from 3 to 7. The study of immobilization of the contaminant in solution showed significant amounts of adsorption, 12.3 mgCd/g at pH 6 and 13.6 mgCd/g at pH 7 indicating a removal of up to 98% for low ion concentrations, suggesting that the adsorbent has a high potential for removing Cd(II) in aqueous medium.