The effect of frother blends on the flotation performance of selected PGM bearing ores

Concentrators processing PGM bearing ores make use of polysaccharide depressants to reduce the recovery of the undesired naturally floatable gangue minerals, mainly silicates, present in the ore. Recent work has shown that high depressant dosages can completely depress naturally floatable gangue and thus prevent it from reporting to the concentrate. These high depressant dosages can, however, have a negative effect on the recovery of valuable minerals present in the ore by reducing the stability of the froth. In order to counterbalance the effects of depressant addition, frothers are added. It is, however, preferable to maintain independent control over bubble size and froth stability which is difficult to achieve with only one frother. An alternative strategy is to use a blend of frothers, e.g. a weaker frother in combination with a stronger frother. Such a system allows an additional degree of freedom: changing the ratio of the two frothers provides more independent control of bubble size and froth stability. This study demonstrates through the use of batch flotation tests how blending low molecular weight alcohols with commercially available frothers impacts the solids and water recovery, as well as the valuable mineral recovery and concentrate grade in different PGM ores. Higher water and solids recoveries together with higher valuable mineral recoveries (>90% copper and >70% nickel) were obtained from tests using frother blends.     

Comparison of the kinetics and composition of ethoxylated methyl dodecanoate and ethoxylated dodecanol with narrow and broad distribution of homologs

Broad- and narrow-range dodecanol ethoxylates were obtained with sodium hydroxide and a proprietary calcium-based catalyst, respectively. The proprietary catalyst was also used for direct ethoxylation of methyl dodecanoate ester. Natta-Mantica distribution coefficients were calculated from the fractional content of the reaction products. A specific sequence of the distribution coefficients was observed in each case. A superior activation of the second addition step in ethoxylation of the methyl dodecanoate ester was noted. The kinetic pattern of the reaction resulted in a product distribution specifically related to the average degree of oxyethylation degree.     

Frother structure–property relationship: Effect of alkyl chain length in alcohols and polyglycol ethers on bubble rise velocity

In mineral flotation, frothers are used to produce fine bubbles, reduce bubble rise velocity, and stabilize the froth, three properties that enhance the flotation process. These properties depend on the frother structure and this paper is part of an investigation into the frother structure-property relationship. The property here is bubble rise velocity and the structural variation is alkyl chain length of two frother families, alcohols and polyglycols. Single bubble rise velocity profiles were determined in a 350 cm column. Velocity at 300 cm as a function of concentration is determined and as a measure of the impact of structure on reduction in bubble rise velocity the concentration at minimum velocity (CMV) is estimated. The effect of increasing alkyl chain length is to decrease CMV by about ca. 90% in alcohols and ca. 70% in polyglycols for every one carbon addition. Taking log CMV as a function of the number of carbons in the alkyl chain gives a series of self-similar linear plots. An argument relating bubble rise velocity to surfactant molecule packing on the bubble surface is proposed.     

Structural and magnetic properties of CoFe2O4 nanopowders,prepared using a modified Pechini method

Cobalt ferrite nanopowders were synthesized by means of the sol-gel method, using citric acid as a chelating agent, and various alcohols as gelling agent: ethanol (ET), ethylene glycol (EG), polyvinyl alcohol (PVA), 1,3 propanediol (PD) and a mixture of PVA and EG. The simultaneous TG/DTA analysis revealed different thermal behaviours of the synthesized gels, depending on the gelling agent. The powders obtained at 500 °C and annealed at 700 °C and 1000 °C contain a single CoFe₂O₄ phase. Scanning electron microscopy (SEM) revealed the influence of the gelling agent on the morphology of cobalt ferrite particles. The coercivity and the saturation magnetization of the powders obtained at 500 °C showed a strong dependence on the crystallite size, determined by the nature of the gelling agent.     

Alcohol combustion chemistry

Alternative transportation fuels, preferably from renewable sources, include alcohols with up to five or even more carbon atoms. They are considered promising because they can be derived from biological matter via established and new processes. In addition, many of their physical-chemical properties are compatible with the requirements of modern engines, which make them attractive either as replacements for fossil fuels or as fuel additives. Indeed, alcohol fuels have been used since the early years of automobile production, particularly in Brazil, where ethanol has a long history of use as an automobile fuel. Recently, increasing attention has been paid to the use of non-petroleum-based fuels made from biological sources, including alcohols (predominantly ethanol), as important liquid biofuels. Today, the ethanol fuel that is offered in the market is mainly made from sugar cane or corn. Its production as a first-generation biofuel, especially in North America, has been associated with publicly discussed drawbacks, such as reduction in the food supply, need for fertilization, extensive water usage, and other ecological concerns. More environmentally friendly processes are being considered to produce alcohols from inedible plants or plant parts on wasteland. While biofuel production and its use (especially ethanol and biodiesel) in internal combustion engines have been the focus of several recent reviews, a dedicated overview and summary of research on alcohol combustion chemistry is still lacking. Besides ethanol, many linear and branched members of the alcohol family, from methanol to hexanols, have been studied, with a particular emphasis on butanols. These fuels and their combustion properties, including their ignition, flame propagation, and extinction characteristics, their pyrolysis and oxidation reactions, and their potential to produce pollutant emissions have been intensively investigated in dedicated experiments on the laboratory and the engine scale, also emphasizing advanced engine concepts. Research results addressing combustion reaction mechanisms have been reported based on results from pyrolysis and oxidation reactors, shock tubes, rapid compression machines, and research engines. This work is complemented by the development of detailed combustion models with the support of chemical kinetics and quantum chemistry. This paper seeks to provide an introduction to and overview of recent results on alcohol combustion by highlighting pertinent aspects of this rich and rapidly increasing body of information. As such, this paper provides an initial source of references and guidance regarding the present status of combustion experiments on alcohols and models of alcohol combustion.     

Pervaporation for Drying and Dewatering

Dewatering denotes moisture removal from materials and it is a more general term than drying. In dehydration and drying technology, a growing role of modern techniques used either separately or in hybrid solutions is observed. Membrane techniques find many industrial applications in this field. Based on available literature, examples of dehydration on membranes, important from the viewpoint of energy saving, environmental protection, and recoverable energy sources, are presented in this study. Special attention is given to the process of pervaporation as the most modern and promising technique for azeotropic mixture separation to be used in dehydration of solvents, including alcohols, and removal of volatile organic compounds from sewage, concentration of aromas, and separation of multicomponent systems.     

Kinetic Analysis On The Effects Of Dissolved Inorganic And Organic Substances In Raw Water On The Ozonation Of Geosmin And 2–MIB

The kinetics of geosmin and 2–MIB decomposition by ozonation in the presence of dissolved inorganic and organic substances were studied. As a first approximation, the decomposition rate of geosmin and 2–MIB were analyzed as a first–order reaction with respect to their concentration. The first–order rate constants decreased significantly with increase in the concentration of carbonate ion, free chlorine, alcohols and volatile fatty acids. Small amounts of humic acids or fulvic acids, however, enhanced the rate of decomposition. It was also demonstrated that the decomposition rates in natural waters were influenced mainly by the concentrations of carbonate and humic substances.     

Formation of oxygenated compounds from isooctane flames

The formation of three families of oxygenated compounds is studied in the case of isooctane combustion. Stoichiometric, lean and rich conditions are studied at different distances from a flat burner. Nine carbonyl compounds, five alcohols and three organic acids are found in detectable concentrations in the combustion products. These oxygenated compounds are formed very quickly, their concentrations increase or remain constant for about 2-3 mm and then they fall to zero. Generally, in accordance with the results of a spark ignition engine, the oxygenated compounds have a maximum concentration at stoichiometry or under lean conditions. Some combustion products are well correlated, indicating that they are formed in parallel, or one is the precursor of the other.     

Pervaporation for Drying and Dewatering

Dewatering denotes moisture removal from materials and it is a more general term than drying. In dehydration and drying technology, a growing role of modern techniques used either separately or in hybrid solutions is observed. Membrane techniques find many industrial applications in this field. Based on available literature, examples of dehydration on membranes, important from the viewpoint of energy saving, environmental protection, and recoverable energy sources, are presented in this study. Special attention is given to the process of pervaporation as the most modern and promising technique for azeotropic mixture separation to be used in dehydration of solvents, including alcohols, and removal of volatile organic compounds from sewage, concentration of aromas, and separation of multicomponent systems.