APSC 150 Lectures-Part III

APSC 150 Lectures-Part III - 1) Collectors adsorb on...

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Classification of flotation reagents 1) Collectors – adsorb on mineral surfaces, selectively render the valuable mineral surface hydrophobic and facilitate bubble-particle attachment/adhesion. 2) Frothers – adsorb primarily at the air-water interface, locally decrease water/air surface tension and thus improve bubble formation and frothing, also affect bubble size. 3) Modifying agents a) Activators – facilitate mineral-collector interaction. b) Depressants – prevent mineral-collector interaction, and/or render a mineral surface hydrophilic. When selective, depressants inhibit floatability of unwanted minerals. c) Dispersants – used to prevent fine particle aggregation, aggregation of invaluable slimes onto coarser valuable particles, by controlling surface charge. d) pH regulators – used to control the pH of mineral suspensions/pulps.
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C H 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 N + H H H C H 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 C O O - C H 3 CH 2 CH 2 CH 2 CH 2 CH 2 OH Cl - Na + + + C H 3 CH 2 CH 2 CH 2 CH 2 CH 2 O C S - S + K + C H 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Cationic amines Anionic fatty acids (carboxylates) Anionic xanthic acids (xanthates) Non-ionic (uncharged) hydrocarbon oils
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Note that the structures shown in the previous slide can generally be represented by: C n H 2n+1 – X Where X is a functional end group giving the entire molecule cationic, anionic, or non-ionic character. Note that if X = H, we have a pure hydrocarbon, C n H 2n+2 . For typical flotation reagents “n” can be anywhere between 2 (e.g., for short chain xanthates) and 24 (e.g., for some long-chain amines).
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Another way of looking at such reagents is to recognize that the end functional group is hydrophilic (polar), while the hydrocarbon chain is hydrophobic (apolar). As a result of those structural properties, flotation reagents can adsorb at various interfaces (solid-liquid, air-liquid). Because of this exceptional surface activity, these chemicals are generally referred to as surfactants – surface active agents. Flotation collectors are always charged (anionic or cationic). Frothers are practically always non-ionic (uncharged). Modifying agents can be anything from simple single ions to
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Collectors Collectors work by adsorbing primarily on mineral surfaces (at the liquid-solid interface). It should be recalled that both collectors and mineral surfaces are electrostatically charged in aqueous solutions, which in many cases leads to adsorption by electrostatic attraction (physical adsorption) between the surface and the collector (e.g., a cationic collector on a negatively charged surface, or vice versa).
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Negatively charged, hydrophilic mineral surface Cationic collector molecules Electrostatic attraction results in adsorption of collector molecules on the oppositely- charged surface. Since the hydrocarbon (hydrophobic) chain
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APSC 150 Lectures-Part III - 1) Collectors adsorb on...

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