An alternative to conventional methods for mine tailings disposal is stabilization with alkali-activated binders (AABs), developed from agro-industrial waste. Despite increasing interest in this topic, there is still a lack of studies focusing on the stabilization of iron ore tailings (IOTs) using AABs, particularly those that combine the characterization of cementitious gels with an evaluation of leaching behavior. This study assessed the strength, mineralogy, and leaching performance of IOTs stabilized with AABs formulated from rice husk ash (RHA) and hydrated eggshell lime (HEL), using sodium hydroxide as the alkaline activator. Tests included unconfined compressive strength (UCS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and metal leaching analyses. The IOT–AAB mixture with the highest AAB content and dry unit weight achieved an average UCS of 2.14 MPa after 28 days of curing. UCS increased with AAB content, followed by dry unit weight and curing time, the latter showing a non-linear influence. The formation of C–S–H gel was confirmed after 28 days, while N–A–S–H gel was detected as early as 7 days of curing. The cemented IOT–AAB mixtures showed no metal toxicity and effectively encapsulated barium originating from the RHA.

The foundry industry generates large amounts of residual byproducts, such as waste foundry sand (WFS). This high generation has motivated studies concerning the disposition of WFS, which in turn can be used for road subbases. Nevertheless, paving applications are still limited, especially regarding the behavior of WFS when added to a mixture of crushed materials. Hence, the objective of this study was to evaluate WFS reuse in mixtures with crushed materials, applied as granular layers of granulometric stabilized pavements. The crushed materials and WFS were characterized by size distribution, physical aspects, and different mixtures, and later submitted to mechanical testing. Initial tests were utilized to define mixtures (crushed material + WFS) that fulfilled the technical requirements for road subbases. California bearing ratio and resilient modulus tests indicated that WFS additions up to 12% for “A” grading improved the bearing capacity of the mixture; while in “E” grading, WFS additions up to 38% resulted in no expressive improvement in bearing characteristics. Thus, for both gradings, a structure with high density, strength, and low susceptibility to deformations can be used for road subbase construction without technical issues. Finally, the highest WFS content (38%) mixture was environmentally classified as a Class II A non-inert waste, indicating its environmental viability for road applications.

A indústria de processamento de papel está entre as três maiores produtoras de águas residuais de significativa contaminação ambiental. Com o objetivo de minimizar os impactos nos corpos d’água e se adequar aos padrões exigidos pela legislação, são necessárias soluções avançadas de tratamento. Neste trabalho, uma membrana cerâmica de microfiltração foi desenvolvida, tendo como base 60% da composição correspondente ao resíduo de cinza de casca de arroz e 40% de Caulim, para ser aplicada como pré-tratamento do efluente real da indústria de papel. A membrana foi obtida por compactação uniaxial a 27 MPa em uma prensa elétrica, com posterior sinterização em mufla a 1.200°C por 1 hora. Os materiais foram caracterizados por análises químicas e físicas. A membrana apresentou porosidade aparente de 34,59%, densidade de 1,30 g/cm³, retração linear de diâmetro e espessura de 1,7 e 2,5%, respectivamente, perda ao fogo de 9,3% e boa estabilidade química em ácido e base. A permeabilidade hidráulica correspondeu a 11,3 × 10^-3 m³/m² s MPa^-1, com diâmetro hidráulico de poros de 2,29 μm e tamanho médio de poros de 1,727 μm. A caracterização do efluente bruto revelou altos teores de demanda química de oxigênio (1.125,4 mg•L^-1), turbidez (1.300 UNT) e cor (253,8 UC). O estudo de filtração indicou resultados satisfatórios de eficiência da membrana, com remoção de turbidez (99,3%), demanda química de oxigênio (95,7%), cor (83,0%), compostos fenólicos (82,1%) e sólidos (85,1 a 90%). O uso da cinza de casca de arroz desempenhou a função de agente formador de poros e adsorvente de compostos fenólicos, representando promissora alternativa para a incorporação do resíduo ao ciclo produtivo.