Variables affecting the fine grinding of minerals using stirred mills

Base metal resources are becoming more fine-grained and refractory and minerals separation processes require these ores to be milled to increasingly finer sizes. To cope with very fine grinding to below a P-80 of approximately 15 mum stirred milling technology has been adopted from other industries Neither this technology, nor the basic concepts of fine grinding, are well understood by the minerals processing industry. Laboratory studies were therefore carried out in order to investigate fine milling using different types of stirred mills. The variables analysed were stirrer speed, grinding media type and size, slurry solids content as well as the feed and product size. The results of the testwork have shown that all of these variables affect the grinding efficiency. The ratio of media size to material size was found to be of particular significance. The results were also analysed using the stress intensity approach and the optimum stress intensity ranges for the most efficient grinding were determined. Application of the results for process optimisation in the industrial size units is also discussed in this paper. (C) 2003 Elsevier Science Ltd. All rights reserved.

Las actividades extraescolares y complementarias en el marco escolar : posibilidades educativas desde la educación física en secundaria.

La oferta de actividades extraescolares deportivas es un elemento social de primer orden que deben estar reguladas por los proyectos de centro, como elemento del papel educativo de los mismos. Se analiza el concepto de actividad extraescolar, la normativa que las regula, el papel del Ampa y criterios para su organización. Se centra en las actividades desde la educación física y en las complementarias en el entorno natural.

Percutaneous closure of patent foramen ovale: safe and effective but underutilized.

With three recently published randomized trials on patent foramen ovale (PFO) closure, the concept of PFO closure to reduce recurrent strokes has been proven; however, PFO closure is currently only considered for secondary prevention. Given the potential devastating consequences of a PFO-related event, we advocate screening for and closure of a PFO for primary prevention in high-risk populations. Such populations include patients who are suffering from a disease that is associated with PFO (e.g., migraine) or patients with high-risk hobbies/professions (e.g., weight-lifters, frequent-flyers, and deep sea divers). Looking at young people with a remaining average life expectancy of 50 years, we have to close 2.4 PFOs to prevent one stroke. This should support a more proactive attitude toward PFO screening and closure.