The effect of temperature on the flotation of pyrite - saimm

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30 '" ci' 20 0 ';:: C\S .... ::s "0 ..c: (5 10 ..... ~ 0 This work . Gotte13 300 '" ci' 0 ';:: C\S .... 200 ::s "0 ..c: ..... 0 .... ~100 0 0 10 20 30 Temperature, °C 40 50 0 60 Fig. 8- Tests on froth stability TABLE 11 EFFECT OF COLLECTOR CONCENTRATION ON RECOVERY OF PYRITE AND GANGUE 5MBT concentration Pyrite Gangue '1' k x 1O2s-1 '1' k X 1O2s-1 g/t % % 10 91,99 7,60 13,08 1,74 20 92,65 7,59 12,47 1,40 40 90,61 7,76 12,58 1,48 100 95,04 8,68 14,44 1,50 200 94,64 7,84 11,43 1,92 TABLE V EFFECT OF ACTIVATOR CONCENTRAnON ON RECOVERY OF PYRITE AND GANGUE CUSO4 Pyrite Gangue concentration g/t %'1' k x 1O2s-1 %'1' k X IOZs-1 '1' = 'Infinite-time' - 89,37 9,33 12,14 1,56 20 88,61 9,19 12,67 1,51 50 90,25 8,52 12,9 1,26 100 89,32 8,39 11,30 1,43 recovery '1' = 'Infinite-time' recovery TABLE III EFFECT OF FROTHER CONCENTRAnON ON RECOVERY OF PYRITE AND GANGUE Pyrite Gangue DOWFROTH 250 concentration '1' kx1O2s-1 g/t '1' kx 1O2s-1 % % - 85,12 7,91 7,01 1,41 10 87,37 7,96 10,26 1,65 20 89,66 7,72 12,67 1,38 40 88,55 8,02 15,72 1,72 80 88,66 8,80 17,75 1,68 160 91,20 8,33 21,64 1,50 TABLE VI EFFECT OF AERATION RATE ON RECOVERY OF PYRITE AND GANGUE Pyrite Gangue Aeration rate l/min '1' k X 1O2s-1 '1' k X 1O2s-1 % % 3 82,31 2,38 8,93 0,17 5 86,38 5,89 8,96 0,70 7 88,55 8,02 15,72 1,72 9 91,06 10,75 19,69 1,92 '1' = 'Infinite-time' recovery TABLE IV EFFECT OF DEPRESSANT CONCENTRAnON ON RECOVERY OF PYRITE AND GANGUE Pyrite Gangue ACROL (J2P350) concentration g/t '1' k x 1O2s-1 '1' kx IOZs-1 % % - 89,37 9,33 12,14 1,56 10 86,91 8,90 11,22 1,45 20 88,00 8,11 11,55 1,17 50 90,46 7,19 11,97 0,94 lOO 89,15 6,68 9,73 0,87 '1' = 'Infinite-time' recovery TABLE VII EFFECT OF IMPELLER SPEED ON RECOVERY OF PYRITE AND GANGUE Pyrite Gangue Impeller speed r/min '1' k x 1O2s-1 '1' k X 1O2s-] % % 800 85,77 4,57 11,45 0,52 950 83,97 6,89 10,24 1,02 1100 88,11 5,97 11,04 0,68 1300 89,66 7,72 12,67 1,38 1450 89,11 8,94 11,90 1,49 1600 89,63 8,45 12,12 1,57 '1' = 'Infinite-time' recovery '1' = 'Infinite-time' recovery 392 DECEMBER 1984 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY
'"~ 0 'h .~ ~~ ";: I IcP=I.OxlO-'P..s 0 0 10 20 30 Tem"",.!u,e. "C Fig. 9- Effect <strong>of</strong> <strong>temperature</strong> on pulp viscosity lower velocity <strong>of</strong> the froth. A similar trend in the rates <strong>of</strong> flotation was observed by Klimpel12 in the flotation <strong>of</strong> silica from a taconite ore. Slightly less pyrite was recovered (92 per cent as compared with 98 per cent) when a froth phase was present, probably as a result <strong>of</strong> normal froth <strong>effect</strong>s such as crowding and bubble breakage. Lowering <strong>of</strong> the pulp <strong>temperature</strong> decreased the rate <strong>of</strong> flotation since it decreased the velocity <strong>of</strong> the froth, increased the viscosity <strong>of</strong> the pulp, and reduced the rate <strong>of</strong> mass transfer <strong>of</strong> the pyrite from the pulp to the froth. <strong>The</strong> influence <strong>of</strong> <strong>temperature</strong> on the rate <strong>of</strong> pyrite flotation was virtually the same in the presence <strong>of</strong> a froth phase as it was in its absence (Figs. 3 and 5); so the most important <strong>of</strong> these factors is probably the rate <strong>of</strong> mass transfer <strong>of</strong> the pyrite from the pulp to the froth phase. <strong>The</strong> reason for the decrease in the rate <strong>of</strong> mass transfer has not yet been identified, but this decrease may be due to one <strong>of</strong> the following factors: (a) poorer loading <strong>of</strong> bubbles as the result <strong>of</strong> decreased induction time, (b) lower rate <strong>of</strong> bubble rise, or (c) fewer bubbles per unit volume <strong>of</strong> pulp. Induction time, defined as the time necessary for the thinning <strong>of</strong> the bubble liquid layer to a critical thickness at which rupture occurs, is affected by several variables15 such as the viscosity <strong>of</strong> the bul~ liquid and the concentrations <strong>of</strong> the flotation reagents. Less collector is adsorbed at lower <strong>temperature</strong>s, but the rate <strong>of</strong> pyrite flotation is hardly affected by a change in collector concentration. <strong>The</strong>refore, the extent <strong>of</strong> collector adsorption does not appear to be responsible for the marked change in the flotation rate. <strong>The</strong> other parameters that affect induction time have yet to be evaluated. <strong>The</strong> rate <strong>of</strong> bubble rise was observed to be slower for colder pulps <strong>of</strong> higher viscosity. Although this is consistent with the observed lower rate <strong>of</strong> flotation at low <strong>temperature</strong>s, other factors, e.g. induction time, may be as important, or more important. Photographic studies showed that, at low <strong>temperature</strong>s, 40 o~. there were more bubbles per unit volume than at high <strong>temperature</strong>s. This, and the fact that the flotation rate did not vary considerably with varying quantities <strong>of</strong> frother, do not sustain the hypothesis that the slower rate <strong>of</strong> flotation at low <strong>temperature</strong> is caused by the presence <strong>of</strong> fewer bubbles per unit volume. At lower <strong>temperature</strong>s, flotation <strong>of</strong> the gangue is affected as follows. <strong>The</strong> rate <strong>of</strong> mass transfer from the pulp to the froth, the elutriation <strong>of</strong> gangue from the froth phase, and the velocity <strong>of</strong> the froth are lower, and the froth is more stable. At <strong>temperature</strong>s below lOoC, the k and 'IjJ<strong>temperature</strong> pr<strong>of</strong>iles for gangue (Figs. 4 and 5) are markedly different from those for pyrite in the presence <strong>of</strong> a froth phase, in that the rate <strong>of</strong> gangue flotation increases. This phenomenon is ascribed to the <strong>effect</strong> <strong>of</strong> the increased stability <strong>of</strong> the froth and the viscosity <strong>of</strong> the elutriating medium, which cause less gangue to return to the pulp by bubble breakage or by elutriation. In the flotation <strong>of</strong> gangue at lower <strong>temperature</strong>s, these two <strong>effect</strong>s appear to overshadow the <strong>effect</strong> <strong>of</strong> reduced froth velocity and <strong>of</strong> lower mass-transfer rates from the pulp to the froth. <strong>The</strong> different pr<strong>of</strong>iles obtained for the rate <strong>of</strong> gangue flotation in the presence <strong>of</strong> a froth phase and in its absence indicate that, with respect to the rate <strong>of</strong> gangue flotation, the <strong>effect</strong> on the froth phase at lower <strong>temperature</strong>s is most significant, resulting in greater recoveries <strong>of</strong> gangue and seriously reduced grades. This is shown clearly in Fig. 6. It has been shown 16 that the rate <strong>of</strong> adsorption <strong>of</strong> 5MBT onto pyrite decreases with <strong>temperature</strong>. Fig. 7 shows the <strong>effect</strong> <strong>of</strong> <strong>temperature</strong> on the equilibrium adsorption <strong>of</strong> 5MBT. However, in all instances, a pseudo-equilibrium adsorption <strong>of</strong> collector, approximately equivalent to a double layer <strong>of</strong> reagent molecules, is obtained after 4 minutes. Monolayer coverage is obtained at all <strong>temperature</strong>s after less than 1 minute. <strong>The</strong> adsorption isotherms show that, at higher <strong>temperature</strong>s, desorption may occur. <strong>The</strong> equilibrium adsorption at 2 °C is significantly lower than at ambient <strong>temperature</strong>, but is nevertheless adequate for flotation to occur. Hence, since adequate amounts <strong>of</strong> reagent are adsorbed within the normal conditioning time, viz 4 minutes, the rate <strong>of</strong> reagent adsorption is not considered to be rate controlling. Conclusions This study showed that the flotation rate <strong>of</strong> pyrite decreases with <strong>temperature</strong> owing to a reduction in the rate <strong>of</strong> mass transfer <strong>of</strong> pyrite from the pulp to the froth. This, in turn, is probably partly because the bubbles rise more slowly at lower <strong>temperature</strong>s, and hence higher viscosities. <strong>The</strong> <strong>effect</strong> <strong>of</strong> <strong>temperature</strong> on induction time was not investigated. It was also shown that the rate <strong>of</strong> gangue flotation is influenced mainly by the <strong>effect</strong> <strong>of</strong> <strong>temperature</strong> on the stability <strong>of</strong> the froth and the viscosity <strong>of</strong> the elutriating medium. <strong>The</strong>se <strong>effect</strong>s <strong>of</strong> a decrease in <strong>temperature</strong> cannot be overcome by changes in reagent concentrations. As this study simulated the <strong>effect</strong> <strong>of</strong> <strong>temperature</strong> on the rougher banks <strong>of</strong> flotation plants, it is concluded that, for adequate grades to be maintained at lower <strong>temperature</strong>s, the load on the cleaner will have to be increased. An increase in aera- JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY DECEMBER 1984 393
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The effect of temperature on the flotation of pyrite - saimm

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