Acid mine drainage (AMD) in the coal mining industry is recognized as one of the major sources of environmental damage. The active treatment of AMD involves adding alkaline reagents to wastewater so as to raise pH and to precipitate dissolved metals in the form of oxides/hydroxides. Studies have shown that yellow pigment (goethite) can be produced from the iron present in AMD. However, the presence of other metals can prevent the formation of pigment. Therefore, this paper seeks to evaluate several processes for purifying iron sludge so as to obtain raw material that can be recovered from AMD and thereby obtain a good quality of yellow pigment. The experiments were carried out by causing precipitation with strong and weak bases and removing other metals from the sludge by washing and filtering the sludge or by centrifugation. The results show that the color, type and morphology of the compounds changed, depending on the number of contaminants, and that these factors are strongly dependent on the type of reagent and less dependent on the separation process and the repetition of washes.

Coal is an abundant resource which can be used to produce low-cost energy; however, its usage causes great environmental damage. Before mineral coal can be used, it must be processed to remove coal tailings. These tailings contain pyrite and accumulate in large dumps, presenting significant environmental liabilities, such as acid mine drainage. Another industry that generates environmental liabilities is the chrome-plating industry, mainly because it produces hexavalent chromium (Cr6+) waste. The main aim of this work was to evaluate Cr6+ as a reduction agent in trivalent chromium (Cr3+) conversion in the leaching of coal-mine waste containing pyrite. Cr3+ is about 100 times less toxic than Cr6+ and can be easily removed from industrial effluents by alkaline precipitation. There are several sources of effluents containing Cr6+—a compound which is known worldwide to be toxic, carcinogenic, and mutagenic. A leaching and treatment device was developed and tested for waste treatment. The results indicated that the developed treatment system reduced 100% of Cr6+ to Cr3+ through pyrite leaching in a Cr6+ wastewater sample from the electroplating industry. In addition, the chromium sludge resulting from the treatment process, after calcination, was tested in a ceramic glaze as a pigment and, when compared with an industrial pigment, showed similar mineralogical characteristics.

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Os blocos de concreto celular cada vez mais vêm ganhando mercado devido as suas características de isolamento térmico, de isolamento acústico, de baixa densidade, entre outras. Uma propriedade relevante é a resistência à compressão, a qual limita algumas aplicações deste tipo de material, por exemplo, a utilização em paredes estruturais (paredes que venham a ser submetidas a deformações impostas ou a cargas de ocupação mais significativas), as quais exigem uma resistência à compressão mínima de 3 MPa. Devido ao aumento da utilização do concreto celular nas construções, este trabalho teve como objetivo a avaliação das propriedades físicas e mecânica de dois tipos de blocos celulares comercializados na região de Passo Fundo/RS, Brasil. Ensaios experimentais foram realizados para determinar as seguintes propriedades: densidade seca, a densidade saturada, os índices de vazios, a absorção de água, a condutividade térmica e a resistência à compressão foram realizados. Os resultados mostraram que o concreto celular autoclavado apresentou melhores propriedades físicas e mecânicas quando comparado com o concreto celular espumígeno, isto é, o bloco de concreto celular autoclavado teve maior resistência à compressão, menor condutividade térmica, menor densidade e poros distribuídos de forma mais homogênea, porém os valores encontrados para a resistência à compressão de ambos os blocos foram inferiores aos determinados pelos fabricantes destes blocos. Portanto, os blocos de concreto autoclavado podem ser utilizados para alvenaria de vedação nas construções, pois atingiu a resistência à compressão mínima necessária para este tipo de parede. Já os blocos de concreto celular espumígenos, em média, apresentaram valores de resistência à compressão muito abaixo (0,6 MPa) dos valores exigidos para paredes de alvenaria de vedação (1,5 MPa), exigindo que o fabricante revise a formulação dos traços desses blocos.

Fiber-reinforcement has been reported as an effective and cost-attractive technique to improve the mechanical behavior of cemented soils. However, the dosage methodologies for these mixtures are still limited, especially regarding dynamic loading. The objective of this research was to analyze the dynamic response and strength behavior of fiber-reinforced cement-treated sand. In this sense, fatigue life, unconfined compressive strength, and split tensile strength tests were conducted. Results indicated that the mechanical behavior of the soil-cement mixtures was governed by fiber content, cement content and void ratio. The presence of fibers, the increase in cement content and the decrease in void ratio improved the overall mechanical behavior of all specimens. The porosity/cement content index resulted in a viable dosage method to predict both the monotonic and cyclic behavior of the mixtures. Lastly, the statistical analysis of variance corroborated the experimentally observed findings.

The increasingly strong search for alternative materials to Portland cement has resulted in the development of alkali-activated cements (AAC) that are very effective at using industrial by-products as raw materials, which also contributes to the volume reduction in landfilled waste. Several studies targeting the development of AAC—based on wastes containing silicon and calcium—for chemical stabilization of soils have demonstrated their excellent performance in terms of durability and mechanical performance. However, most of these studies are confined to a laboratory characterization, ignoring the influence and viability of the in situ construction process and, also important, of the in situ curing conditions. The present work investigated the field application of an AAC based on carbide lime and glass wastes to stabilize fine sand acting as a superficial foundation. The assessment was supported on the unconfined compressive strength (UCS) and initial shear modulus (G0) of the developed material, and the field results were compared with those prepared in the laboratory, up to 120 days curing. In situ tests were also developed on the field layers (with diameters of 450 and 900 mm and thickness of 300 mm) after different curing times. To establish a reference, the mentioned precursors were either activated with a sodium hydroxide solution or hydrated with water (given the reactivity of the lime). The results showed that the AAC-based mixtures developed greater strength and stiffness at a faster rate than the water-based mixtures. Specimens cured under controlled laboratory conditions showed better results than the samples collected in the field. The inclusion of the stabilized layers clearly increased the load-bearing capacity of the natural soil, while the different diameters produced different failure mechanisms, similar to those found in Portland cement stabilization.

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