151 research outputs found
Influence of particle size and contact angle on the flotation of chalcopyrite in a laboratory batch flotation cell
No full textAbstract not availableS. Muganda, M. Zanin, S.R. Gran
Producción, precios e integración de los mercados regionales de grano en la España preindustrial
No full textEditada en la Fundación Empresa PúblicaEste trabajo aborda la integración de los distintos mercados regionales
de grano en España durante el Antiguo Régimen. Haciendo uso de series
de precios y de producción de diversa procedencia, el autor emplea técnicas
de estimación relativamente sencillas, desde correlaciones y desviaciones típicas
de series sin tendencia hasta modelos de retardos distribuidos. Estas técnicas
revelan la existencia de una covariación entre los precios de granos
en distintos mercados regionales, así como la existencia de efectos simultáneos
y retardados de la producción de granos sobre el precio de los mismos en
mercados locales y bastante más lejanos. El autor concluye que existía una
integración modesta pero en aumento de los distintos mercados en la Península,
sobre todo durante el siglo XVIII, y que las instituciones eran capaces
de amortiguar en parte los efectos de una cosecha fallida. El trabajo concluye
apuntando el calendario posible de la progresiva integración de los mercados
de grano ocurrida a lo largo de buena parte del siglo XIX en España.The present paper deals with regional grain market integration in Spain
during the Old Regime. Using mostly published price and production seríes,
the author employs straightforward statistical techniques, rangíng from correlations
and standard deviations of detrended series to distributed lag models.
These techniques show the existence of a clear covariation in the price of
grain on different regional markets, as well as both simultaneous and delayed
effects of grain production on prices both locally and at considerably greater
distances. The author concludes that regional grain markets on the peninsula
were modestly but increasingly integrated over the period, especially during
the eighteenth century, and that existing institutions were a partial buffer
for the immediate effects of harvest failures. The paper concludes by suggesting
the potential timing for the progressive intergration of grain markets taking
place throughout much of the nineteenth century in Spain.Publicad
Agricultural Genetics and Plant Breeding in Early Twentieth-Century Italy
No full textThis thesis is about plant breeding in Early 20th-Century Italy. The stories of the two most prominent Italian plant-breeders of the time, Nazareno Strampelli and Francesco Todaro, are used to explore a fragment of the often-neglected history of Italian agricultural research. While Italy was not at the forefront of agricultural innovation, research programs aimed at varietal innovation did emerge in the country, along with an early diffusion of Mendelism. Using philosophical as well as historical analysis, plant breeding is analysed throughout this thesis as a process: a sequence of steps that lays on practical skills and theoretical assumptions, acting on various elements of production. Systematic plant-breeding programs in Italy started from small individual efforts, attracting more and more resources until they became a crucial part of the fascist regime's infamous agricultural policy. Hybrid varieties developed in the early 20th century survived World War II and are now ancestors of the varieties that are still cultivated today. Despite this relevance, the history of Italian wheat hybrids is today largely forgotten: this thesis is an effort to re-evaluate a part of it. The research did allow previously unknown or neglected facts to emerge, giving a new perspective on the infamous alliance between plant-breeding programs and the fascist regime. This thesis undertakes an analysis of Italian plant-breeding programs as processes. Those processes had a practical as well as a theoretical side, and involved various elements of production. Although a complete history of Italian plant breeding still remains to be written, the Italian case can now be considered along with the other case-studies that other scholars have developed in the history of plant breeding. The hope is that this historical and philosophical analysis will contribute to the on-going effort to understand the history of plants
Regrinding sulphide minerals - Breakage mechanisms in milling and their influence on surface properties and flotation behaviour
No full textChanges in surface properties with grinding and regrinding play a key role in mineral flotation performance. Different particle breakage mechanisms in grinding mills may change the mineral surface properties in different ways, possibly leading to different mineral floatabilities depending upon the predominant breakage mechanism. The Magotteaux Mill® and IsaMill were selected as representations of a tumbling and a stirred mill, respectively. The latter has a greater contribution to particle size reduction from the abrasion mechanism than the former which also has contributions from impact breakage.X. Ye, S. Gredelj, W. Skinner, S.R. Gran
The surface dilational viscosity of polypropylene glycol solutions and its influence on water flow and foam behavior
No full textThe non-equilibrium interfacial properties of a homologous series of aqueous polypropylene glycol solutions (400-2000 g/mol) were investigated as a function of concentration to understand their role in determining foam behavior. The overflowing cylinder technique was used to generate a continually expanding surface. Static and dynamic surface tensions, as well as the surface velocity of the expanding surface, were characterized. The surface dilational viscosity was compared to water flow rate and foam retention time of the polypropylene glycol solutions reported in the literature. This study suggests that the surface dilational viscosity is a key parameter in the Marangoni effect which retards water drainage, resulting in wetter foam and increased water recovery across flowing foams.S.N. Tan, A. Jiang, J.J. Liau, S.R. Grano, R.G. Hor
Quantifying contributions to froth stability in porphyry copper plants
No full textA method to describe froth stability in industrial flotation cells, and its link with froth recovery, is discussed in this paper. The direct measurement of froth stability in industrial flotation cells is still controversial, and different techniques have been developed. In this paper, the froth half-life time and bubble size on the top of the froth are discussed as indicators for froth stability. Experiences at two flotation concentrators treating porphyry copper ore are compared. The relative contributions to froth stability from frother in solution and solids loading in the froth were investigated in both concentrators, and links were found between both the froth half-life and bubble size on the top of the froth and the amount and nature (hydrophobicity) of particles in the concentrate. The comparison also suggests how two significantly different operating strategies for the froth phase may lead to similar outcomes in terms of froth recovery. © 2008 Elsevier B.V. All rights reserved.M. Zanin, E. Wightman, S.R. Grano, J.-P. Franzidi
Detachment of coarse particles from oscillating bubbles-The effect of particle contact angle, shape and medium viscosity
No full textThis paper examines the detachment of coarse particles from oscillating bubbles as a function of particlehydrophobicity and shape, as well as medium viscosity. The detachment experiments were conducted using anovel electro-acoustic technique for both ground quartz particles and spherical glass beads of various diameters and hydrophobicity. The detachment force for both types of particles, calculated from the maximum vibration amplitude at which a particle detaches from a bubble, increased with an increase in the contact angle of particles and viscosity of the suspending medium. At low vibration frequencies, the quasistatic model predicts the experimental detachment force reasonably well. In contrast, at high vibration frequency and, particularly, in high viscosity medium, the quasi-static model does not predict the experimental detachment force. It is hypothesised that the magnitude of the detachment force is determined by the dynamic contact angle, which is governed by the velocity of movement of the three phase contact line. Larger detachment forces were observed for the quartz particles compared to that of the spherical glass beads of the same size range and similar contact angle value. The stability of the bubble-particle aggregates at high viscosity has been related to the dynamic contact angle of particles. At high viscosity, the rate of movement of the three phase contact line, which governs thedynamic contact angle, is reduced thus resulting in more stable bubble-particle aggregates.D. Xu, I. Ametov and S.R. Granohttp://www.journals.elsevier.com/international-journal-of-mineral-processing
Benchmarking the flotation performance of ores
No full textA porphyry copper ore containing chalcopyrite as the principal copper bearing mineral, and pyrite as the only other sulphide mineral, was treated in batch flotation tests under well defined physical conditions. The size-by-size flotation response was benchmarked against established calibration curves to infer an operational contact angle of the sulphide minerals as a function of particle size. The inferred operational contact angle values of the sulphide minerals were validated by independent measurements of contact angle on the concentrates and, in the case of chalcopyrite, by an indirect approach using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Recovery, flotation rate, and inferred operational contact angle increased with collector addition across all size fractions, with the intermediate and coarse size fractions benefitting the most from increased collector addition. The directly measured and inferred operational contact angles were in reasonable agreement, with an R2 value of 0.7 across all size fractions. There was good agreement between the advancing contact angle values determined using ToF-SIMS and those calculated from direct contact angle measurement on the 53-75 μm size fraction for the case of chalcopyrite. A method for benchmarking flotation response has been developed, which may lead to better flotation process diagnostics and modelling.S. Muganda, M. Zanin, S.R. Gran
Pyrrhotite Depression for Enhanced Pentlandite/Pyrrhotite Selectivity at the 153 Strathcona Concentrator, Falconbridge Limited, Canada
No full text5th progress report for Amira P260E Improving Sulphide Mineral Flotation (chapters 2, 5, ans 6)
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