Rock dust has been historically applied to mitigate the coal dust explosion in either dry or wet form. Dry rock dust performs best in inerting the potential coal dust explosion due to the greatest dispersive properties. However, it undesirably exposes underground coal miners to respirable dust particles which imposes a severe health danger. Wet dust application is able to significantly reduce the floatable dust particles but another problem associated with caking is predominant. Caking phenomenon is usually used to describe the change of free-flowing bulk solids into agglomerated chunks. Unfortunately, the environmental conditions of an underground mine have the potential to cause caking of the rock dust, especially for wet dust application, which reduces the dispersive characteristics needed for effective explosion mitigation and is also the focus of the present study. Surface modification of rock dust to generate a hydrophobic surface is believed to alleviate the caking problem by allowing instant water drainage and eliminating the formation of water and solid bridges. Surface modification of rock dust was evaluated in the present study with a series of potential modifying reagents including oleic acid, sodium oleate and stearic acid. The modification efficiency in terms of measured contact angle, zeta potential and dispersibility values was investigated with sodium oleate generating the best modification effect. Dispersants were investigated as well in the present work aiming to further increase the particles dispersibility in addition to the excellent hydrophobization effect generated by sodium oleate. However, dispersibility test results indicated that the adsorption of dispersant and sodium oleate was competitive. The preferential adsorption of dispersants over oleate deteriorated the surface hydrophobicity of particles and the dispersibility was decreased as a result. As anticipated, dry rock dust always provided the best dispersibility with almost 95% of the dust remaining in suspension at a dispersion time of 30 seconds. The percentage dust dispersion values of sodium oleate treated rock dust was increased to as high as 71% in contrast to 47% of untreated wet rock dust and the explosion potential was correspondingly reduced by almost 83%. The effect of sodium oleate was further studied as a function of reagent concentration to determine the optimum application condition. The dispersibility of rock dust particles was initially increased until the application of 0.1 wt% sodium oleate, after which it slightly decreased up to 0.5 wt% oleate. When the concentration was above 0.5 wt%, the dispersibility of dust particles substantially decreased to a value lower than the value obtained for regular wet dust. The optimum sodium oleate concentration was thus determined at approximately 0.1 by weight of rock dust particles with a corresponding contact angle of around 110 degrees. The pivotal of rock dust modification efficiency is its long-term stability which can be corroborated by irreversible chemical adsorption rather than the short-term physical adsorption. Therefore, the fundamental adsorption mechanism of sodium oleate on rock dust surface was continuously investigated by means of using surface tension measurements, FTIR, Thermogravimetric, SEM analyses and constructing the species distribution diagram. Based on the surface tension measurements and calculated apparent surface area occupied by per oleate molecule, the monolayer adsorption of oleate on dust surface was proposed with oleate concentration falling between 0.1-0.15 wt% which guarantees the long-term surface modification efficiency. Calcium oleate started precipitating out of bulk solution and depositing on the dust surface when the oleate concentration was above 0.15 wt% which became more predominant under high oleate concentration. Super hydrophobic particles together with nucleated calcium oleate nanoparticles tend to increase particles aggregation significantly through attractive hydrophobic particle-particle interactive force, which renders the particles more agglomerated instead of dispersed. Systematic and economic evaluation of the wet form rock dusting process in underground coal mine applications was conducted at the end to determine the safety effects, potential benefits and improvement for future implementation. Suggestions for future work were given as well to shed light on the dusting process together with rock dust surface chemistry modification.

Made available in DSpace on 2014-08-20T14:33:00Z (GMT). No. of bitstreams: 1 Dissertacao_Marcia_Beatriz_Vasconcelos.pdf: 2622303 bytes, checksum: fc997b6c1682e74631f3ca53318515e1 (MD5) Previous issue date: 2011-12-19 / The Family Farm has a great capacity for productive conversion and management, fitting the best possible economic, social and cultural rights, including the market in an effective and dynamic, but facing some problems to absorb new technologies to increase productivity. There is the great importance of developing technologies for family farms, covering their needs and demands of economically and efficiently. Therefore this study aimed to develop a prototype feeder fertilizer that meets the two sowing lines simultaneously, and to verify the functionality of the design principles of the chosen solution. We evaluated the performance of the prototype with four types of fertilizer, three conditions for opening the dispenser system (430, 839 and 1.270mm ²) and three speeds (2.5, 5.0 and 7.5 rpm) of the active organ. The performance of the fertilizer metering mechanism was judged satisfactory for granulated products, but should be improved to avoid disrupting the flow of materials in powder form at low speeds. It was possible to obtain flow rates of fertilizer between 14 and 100 g / s, which meet the needs of family farmers. / A Agricultura Familiar apresenta uma grande capacidade de reconversão produtiva e de gestão, se adequando às melhores possibilidades econômicas, sociais e culturais, inclusive de mercado de maneira eficaz e dinâmica, porém enfrentam alguns problemas para absorver novas tecnologias para o aumento de sua produtividade. Verifica-se a grande importância de desenvolvimento de tecnologias voltadas a agricultura familiar, que contemple suas necessidade e demandas de forma econômica e eficiente. Com isso o presente trabalho objetivou desenvolver um protótipo de dosador de fertilizante que atende a duas linhas de semeadura simultaneamente, bem como verificar a funcionalidade dos princípios de solução da concepção escolhida. Avaliou-se o desempenho do protótipo com quatro tipos de fertilizantes, três condições de abertura no sistema dosador (430, 839 e 1.270mm²) e três rotações (2,5; 5,0 e 7,5 rpm) do órgão ativo. O desempenho do mecanismo dosador de fertilizante foi julgado satisfatório para os produtos granulados, porém deve ser melhorado para evitar a interrupção do fluxo dos materiais na forma de pó em baixas rotações. Foi possível obter vazões de fertilizantes entre 14 e 100 g/s, as quais atendem às necessidades dos agricultores familiares.

The purpose of this thesis is to examine the potential of a novel method for analysis and characterization of coal mine dust. Respirable dust has long been an industry concern due to the association of overexposure leading to the development occupational lung disease. Recent trends of increased incidence of occupational lung disease in miners, such as silicosis and Coal Workers Pneumoconiosis, has shown there is a need for a greater understanding of the respirable fraction of dust in underground coal mines. This study will examine the development of a comprehensive standard methodology for characterization of respirable dust via thermogravimetric analysis (TGA). This method was verified with laboratory-generated respirable dust samples analogous to those commonly observed in underground coal mines. Results of this study demonstrate the ability of the novel TGA method to characterize dust efficiently and effectively. Analysis of the dust includes the determination of mass fractions of coal and non-coal, as well as mass fractions of coal, carbonate, and non-carbonate minerals for larger respirable dust samples. Characterization occurs through the removal of dust particulates from the filter and analysis with TGA, which continuously measures change in mass with specific temperature regions associated with chemical changes for specific types of dust particulates. Results obtained from the verification samples reveal that this method can provide powerful information that may help to increase the current understanding of the health risks linked with exposure to certain types of dust, specifically those found in underground coal mines. / Master of Science

To produce enough food for a growing population, soil remediation is crucial unless more forests are to be cleared to make way for agriculture land. Finely ground rocks have been proposed as a soil amendment for highly weathered soils. In Chontales, Nicaragua most of the forest has been converted to cattle pasture. In fertile soils, crop agriculture is more lucrative per unit of area than cattle grazing, but the low nutrient content of Chontales soils makes it uneconomic. The purpose of the study was to examine whether incorporation of rock dust is a sustainable way to increase the fertility in Chontales and thus can be part of a strategy that encourages farmers to adopt crop agriculture as an alternative to animal husbandry. A field experiment was conducted in which basaltic rock dust and compost was applied to soil for cultivation of common beans. Three sustainability parameters were analyzed and the diffusion potential of the proposed technology was assessed. The experiment failed to confirm the positive result obtained in previous studies on yield in similar soils and no correlation between pest resistance and rock dust applications was found. The failure to produce a confident result on yield was partly due to a leaf hoppers invasion and harm caused by intruding calves into the experiment site. Rock dust was found to be typically free of toxic agents and little environmental damage is associated with the practice, provided that the source of extraction is close to the application site. The relative disadvantage in terms of social prestige and incompatibility with the current cattle oriented production system were found to be the main obstacles for diffusion of the technique in Chontales.