PERFILAGEM ELÉTRICA DE DESAGUAMENTO DE AREIA INDUZIDO POR VIBRAÇÃO

Resumo: A perfilagem eletrorresistiva da umidade no leito de areia quartzosa sobre tela vibratória em escala piloto foi tratado aqui. No que tange à configuração do eletrodos para medição de eletrorresistividade, o arranjo Wenner alfa clássico foi usado, exigindo espaçamento igual entre os eletrodos e  mesma profundidade de penetração e alinhamento corretos. Aqui, a influência de pequenas variações na profundidade de penetração e falta de colinearidade dos eletrodos nas leituras de umidade, usando um eletrorresistivímetro digital e eletrodos de cobre, foi avaliada. As profundidades de penetração estudadas foram de 50 mm e 55 mm. Por sua vez, o desalinhamento testado dos eletrodos foi de 10 mm. O único fator que causou efeito estatisticamente significativo nas medições foi a profundidade de penetração de eletrodo, ao menos na faixa aqui estudada.Title: ELECTRICAL PROFILING OF VIBRATION-INDUCED DEWATERING OF SANDAbstract: Electrorresistive profiling of moisture inside a quartz sand bed on a pilot-scale vibrating screen was treated here. As electrode or probe configuration for resistivity measurement is concerned, the classical Wenner ? array was used, requiring equal electrode spacing, and correct penetration depth and alignment. Here, the influence of small variations in penetration depth and lack of probe collinearity on the moisture readings, using a digital earth resistance tester and copper wires as probes, was evaluated. The penetration depths studied were 50 mm and 55 mm. In turn, the electrode misalignment tested was 10 mm. The only factor that has caused a statistically significant effect in measurements was probe penetration depth, at least under the range tested here

Multivariable control strategy for a bucket wheel reclaimer / Estratégia de controle multivariável de retomadora de roda de alcatruzes

Mining operations are generally done by large machines working in very harsh environments and historically having shy embedded technology. The use of control strategies, in many cases, dramatically increases the operating efficiency without large financial investments. In this context, this paper presents the method of choice and practical application of a multivariable control strategy for a bucket wheel ore reclaimer. This strategy adopts PI and PID controllers following a type override strategy acting on the manipulated variable: the slewing angular velocity. This manipulated variable was chosen because its actions affect the controlled variable very fast, so, allowing correcting disturbances in an adequate time. In addition, a fuzzy type controller was implemented to act on a second manipulated variable: the translation step. The second manipulated variable aims at taking the first one (angular speed) out of saturation states. When working together, these controllers seek to increase the equipment and process performance, taking into account, however, their operating limitations. Finally, a statistical analysis of results was performed in order to validate the feasibility of the implanted strategy when compared with the method previously in operation

AVALIAÇÃO ESTEREOTÔMICA DE TEORES VIA MÉTODO DE MONTE CARLO

A utilização de gabaritos visuais de teores é uma ferramenta por vezes utilizada, principalmente em atividades de campo, para a avaliação prévia e estimativa de teores e concentração de fases visualmente distintas. Estes padrões geométricos de superfície podem ser simulados com métodos estatísticos, possibilitando a utilização eficaz de outras ferramentas, como a análise computacional de imagens. Neste trabalho propõe-se a utilização do método de Monte Carlo para a simulação destes padrões (gabaritos), usando-se previamente a modelagem matemática das fases mineralógicas/tipológicas imersas no maciço. Apenas alguns parâmetros das distribuições estatísticas associadas à distribuição espacial das fases constituintes são alterados, permitindo uma correlação entre valores desses parâmetros e o padrão dos gabaritos. Tal ferramenta serve, por exemplo, para estimação expedita de teor de blocos de lavra, a partir da análise visual das faces expostas da bancada, bem como para análise petrográfica ou metalográfica

PROPRIEDADES DE ÓLEOS EMPREGADOS EM FLOTAÇÃO

Neste trabalho se buscou a sistematização das características de quatro amostras de óleos vegetais e uma amostra de sebo bovino, no que concerne a suas propriedades físico-químicas como com o fito de estabelecer padrões de comportamento e de desempenho em sistemas de flotação. Os óleos vegetais estudados foram: de arroz refinado, de rícino, de semente de uva e de soja refinado, usualmente empregados em operações de tecnologia mineral, com ênfase em seu uso em sistemas de flotação em espuma. As massas específicas determinadas foram: 930 kg/m³ para o óleo de semente de uva; 950 kg/m³ para o óleo de rícino; 910 kg/m³ para o óleo de arroz refinado; e 920 kg/m³ para o óleo de soja. Quanto à tensão superficial foram realizados 26 ensaios para cada amostra de óleo vegetal sendo que os valores variam de 0,0323 N/m a 0,0334 N/m. Viscosidade dinâmica aparente, tensão superficial, índice de refração e valores de umidade também foram levantados. Os resultados permitiram aceder às propriedades das amostras e confrontá-las com as que se descrevem na literatura, servindo, assim, como subsidio ao entendimento da influência destas propriedades na flotação

Remediation alternatives for an abandoned gold mine contaminated with mercury in Brazil / Alternativas para descontaminação de mina de ouro abandonada contaminada com mercúrio no Brasil

Heavy metal contamination of soils has generated two major problems, namely, loss of land value and health risk for people near contaminated sites. Studies on soil remediation are typically conducted on a pilot scale under very controlled conditions. This is a misleading approach, once the complexity of the actual biogeochemical soil conditions may causes inefficiency in full scale real-world application. In addition, environmental impacts of remediation practices themselves are often ignored, which may make them unfeasible. In 2002, an occurrence of mercury in an abandoned old gold mine was detected in a rural area of Descoberto, Brazil. In 2014, the State Public Prosecutor required from the responsible State Environment Agency, a remediation project to the area. This study compares alternatives for remediation of the contaminated area. Also a historical approach on mercury amalgamation in gold mining in the region, in order to estimate the amount of mercury remaining in the site. The geochemical characterization of the contaminated area was performed to describe the contamination process.  The results were compared with the remediation proposal advocated by the Brazilian Ministry Public, and some alternatives for decontamination of the area were studied. The electrokinetic method has displayed the lowest overall unit cost, between US$120.00/t and US$ 260.00/t. The residual Hg concentration after four cycles of the electrokinetic technique was estimated at 1.28 mg (Hg)/kg (soil), slightly higher than the intervention value for agricultural soil, which is 1.20 mg (Hg)/kg (soil)

Long-term evolution of heap surface of paste tailings under erosion / Evolução a longo prazo de pilha da pasta de rejeitos sujeita a erosão

Many mines are moving from conventional tailings storage facilities to filtered tailings disposal systems. The benefits of these systems include increased water recovery, reduced size of containment landfills, improved facility safety, and reduced environmental impact. In geotechnical terms, the challenges are to find the correct way of waste disposal: whether in piles of dry sandy tailings or co-disposal waste rock. The long-term evolution of the surface of fine and sandy tailings stockpiles is a matter of concern. The goal of this study was to quantitatively evaluate the temporal evolution of a paste tailings pile, using a computational model of landscape evolution. For this, SIBERIA, a simulator of the evolution of landscapes under the action of runoff and erosion, was used. The effect of erosion on a trunk-pyramidal tailings pile with about 21% of slope after long periods of decommissioning (100 and 250 years) was studied. The SIBERIA modelling data considered the surface roughness and the average diameter of the sediment particles and the typical properties of iron ore tailings. The results indicate that for a lower Manning roughness coefficient and larger average apparent diameter of the sediment particles (or clods), the lower the sediment transport will be and, therefore, in the long term, the greater will be the integrity of the tailings pile

Characterization and prospecting of graphite-gneisses of the Jequitinhonha Complex

O advento da tecnologia do grafeno vem destacando ainda mais a importância da grafita no panorama industrial moderno, tornando esse mineral estratégico. Os novos campos de sua utilização tornaram a explotação de grafita cristalina (flake) economicamente atrativa. Os gnaisses kinzigíticos do Complexo Jequitinhonha contêm mineralizações de grafita e têm sido objeto de estudos recentes. A compreensão do comportamento da mineralização por meio da caracterização permite o avanço nas técnicas para sua prospecção e exploração. Estabelecer a influência dos contaminantes do meio geológico e as características que esses conferem à mineralização é importante para a padronização dos procedimentos de prospecção e beneficiamento. Este estudo permitiu determinar o padrão resistivo/condutivo da mineralização em função de seus contaminantes, estabelecendo as características inerentes à mineralização de grafita que permitem padronizar critérios de prospecção e posterior utilização industrial do minério.The advent of graphene technology has highlighted the importance of graphite in the modern industrial landscape, making this mineral strategic. The new fields of its use have made the exploitation of flake graphite economically attractive. The kinzigitic gneisses of the Jequitinhonha Complex contain graphite mineralizations and have been the object of recent studies. Understanding the behavior of mineralization, through characterization, allows advancement in the techniques for its exploration and exploration. Establishing the influence of the contaminants from the geological environment and the features they impart to the mineralization is important in order to standardize prospecting and processing procedures. This study allowed determining the orebodies resistive/conductive patterns as a function of petrological contaminants, defining the inherent characteristics of the graphite mineralization that make possible the standardization of the prospecting criteria and later the industrial use of the ore

On bed porosity of multisized spheroidal particles / Da porosidade de partículas esferoidais polidispersas

In numerous instances of engineering the problem to quantify the porosity of polydisperse systems arises. Despite its great importance, the theoretical predictability of the bed porosity is still problematic. In the field of ceramics, classically, Furnas' studies on porosity are quoted, where he has studied void fraction resulting from blending two distinct particle sizes in various proportions. Less often, ternary diagrams plotting porosity isovalues for spherical particles beds are used to characterize ternary mixtures of distinct monosized particulate systems (usually in ceramics industry). Although similar studies using polydisperse systems have been conducted, a lot of improvement is yet to be achieved. This article falls in this context and aims at contributing to this field of technical and economic impact. Synthetic samples with controlled particle size distribution were used. The resulting porosity of those glass beads random packs (mimicking several size distributions described by Rosin–Rammler equation) has been experimentally determined under a standardized compaction level. The main result was to obtain an equation for the porosity forecast for bead beds inside spheroidal containers, as a function of the sharpness parameter, n, from Rosin–Rammler distribution. An accurate extrapolation to systems well described by the Whiten sigmoidal distribution was achieved as well. A generalization of the Ergun equation is presented at the end of the article, as an application example