F.F. Aplan

The effect of clay slimes on coal flotation, part I: The nature of the clay

Abstract The role of slimes in coal flotation has been the subject of controversy in the literature, and the present study is designed to determine the effect of the nature of the clay on coal flotation. Kaolinite and illite, which do not significantly depress coal flotation, contaminate the floated clean coal largely by carry-over with the froth, though electrostatic attachment to the coal contributes in a lesser way to the ash content of the froth. Bentonite greatly depresses all but the most hydrophobic of coals by armour-coating of the bubbles, preventing coarse particle attachment, and increasing slime coatings, all because of its high surface area, charged sites, and ion-exchange-capacity. Common clay dispersants were found to depress coal flotation. Fuel oil improves coal recovery in the presence of clay slimes, but the ash and pyrite content of the floated coal also increases.

The effect of clay slimes on coal flotation, part II: The role of water quality

Abstract Suspended clay solids, ions, pH and humic acid are shown to have a significant influence on coal flotation. Coal flotation is greater in tap than in distilled water. This is believed due to instability and thinning of the hydrated layer at the surface of the coal particle when ions are present. The loss of recovery in the presence of clay slimes is more pronounced in distilled water than when ions are present. In both cases coal depression is much greater with bentonite than with kaolinite or illite clays. The greater surface area, surface-charged sites and ion-exchange-capacity enables bentonite coatings to be established by electrostatic attraction of the clay to the coal. The presence of humic acids is shown to depress coal readily in either distilled or ion-contaminated water.

Evaluation of flotation collectors for copper sulfides and pyrite, III. Effect of xanthate chain length and branching

Abstract The flotation of four copper sulfide minerals (chalcopyrite, chalcocite, bornite, covellite) and pyrite with xanthates shows that a minimum in the collector concentration necessary for flotation usually occurs at about C-5 (amyl) to C-8 (octyl) for the straight chain xanthates. Comparison of straight-chain and branched-chain compounds demonstrated that while short, branched chain xanthates out perform their straight chain analogs, above ∼ C-5 the branched-chain xanthates are less effective as compared to the straight chain form. When Cu2+ is added to the flotation system, it was found that a minimal amount will often produce an enhanced flotation recovery, while greater amounts will either produce essentially no effect or may cause a slight decrease in flotation.

Use of xanthogen formates as collectors in the flotation of copper sulfides and pyrite

Abstract Though xanthogen formates have long been used as sulfide mineral collectors, they have been largely ignored by the research community. The flotation of chalcopyrite, chalcocite, covellite, bornite and pyrite with this class of collector has been evaluated using a variety of hydrocarbon constituent groupings, in both the xanthogen and the formate positions. In addition to being stable in acidic circuits, xanthogen formates are shown to be effective copper sulfide collectors over a broad pH range (5.0–10.5). In general, many of the nine especially synthesized xanthogen formates were found to discriminate against the flotation of pyrite. It is possible to tailor make these compounds to enhance or diminish the flotation of pyrite.

The flotation of chrysocolla by mercaptan

Abstract Laboratory experiments have demonstrated that chrysocolla and malachite can be floated with a mercaptan as collector. In contrast, even when used in large quantities, the higher xanthate homologs (hexyl, dodecyl) will float malachite but not chrysocolla. The flotation of chrysocolla with mercaptan is readily accomplished in a pristine system, but in the presence of finely ground gangue particles, additions of the mercaptan to the grinding mill gave superior recoveries to those achieved when the mercaptan is added to the flotation cell. A model for the attachment of the mercaptan to the chrysocolla surface is proposed which involves the reaction of molecular mercaptan with the copper sites. This results in the formation of copper mercaptide at the surface and the splitting off of a molecule of water. By extension, this model should describe the reaction of mercaptan with any base metal oxide or sulfide mineral where the metal mercaptide is relatively insoluble.

Evaluation of chemical and operational variables for the flotation of a copper ore Part I — Collector concentration, frother concentration, and air flow rate

Abstract The flotation process may be considered an interactive system consisting of many chemical, operational, and equipment variables. Changing any one of these variables causes an overall system response change. This study examines the effects of simultaneously changing the operating variables of: (1) frother concentration and air flow rate, and (2) frother concentration and collector concentration. It is part of a comprehensive study to look at how changes in several of the major variables may be used to produce interactions which will allow the rougher flotation process to be optimized. Ultimate recovery, flotation rate, concentrate grade and froth qualities are used as the major evaluative criteria.

The influence of point defects on the floatability of cassiterite, I. Properties of synthetic and natural cassiterites

Abstract Cassiterite is an n-type semiconductor whose properties may be altered by aliovalent doping. Such changes are noted in color, electrical conductivity, electrokinetic behavior and, as will be demonstrated in Parts II and III, by flotation behavior. The isoelectric point (IEP) of synthetic cassiterites is found to depend on both electronic (i.e. dopants) and atomic (i.e. oxygen vacancies) defects. The temperature of cassiterite formation has a profound influence on the IEP with most samples reaching a limiting value at pH ∼6.5. Two natural samples showed similar values.

The influence of point defects on the floatability of cassiterite, III. The role of collector type

Abstract While electrostatic attraction between mineral and collector is an underlying mechanism for the flotation of cassiterite with the collectors studied here, a number of other mechanisms, often determining, are superimposed on this basic mechanism. Other mechanisms such as the hydrophilic effect which controls the ease of water removal from the surface during collector attachment, electron transfer between collector and mineral, chelation, activation, chemisorption and doping also appear to be operating. In sum, these mechanisms produce the following general order of flotation of cassiterite with the collectors tested: Fe 3+ -doped > undoped > Sb 5+ -doped SnO 2 The Fe 3+ -doped cassiterite typically floats at about one-tenth the collector concentration required to float the Sb 5+ -doped material.

The influence of point defects on the floatability of cassiterite, II. Electrostatic collector interactions

Abstract Cassiterite flotation, irrespective of trace element dopant, follows the electrostatic theory of flotation with sodium dodecyl sulfate and dodecyl ammonium acetate collectors. This appears to be the underlying mechanism for cassiterite flotation with a broad variety of collectors, though other attachment mechanisms are frequently superimposed on this basic mechanism. The flotation of cassiterite with these collectors is strongly influenced by the dopant present, with the ease of flotation following the pattern: Fe 3+ -doped > undoped > Sb 5+ -doped SnO 2 The Fe 3+ -doped material floats at about one-tenth the collector concentration required to float the Sb 5+ -doped material.