Collector Collector Interactions

The use of mixtures of collectors has long been recognized in plant practice and has been shown to enhance flotation performance. These benefits have been reported for a wide range of collector mixtures (anionic, cationic and nonionic) and include lower dosage requirements, improved selectivity and rates and extents of recovery and an increase in the recovery of coarse particles. In many cases an optimum ratio of constituent collectors was shown to exist. Dithiophosphates are a class of thiol collectors that are so widely used in mixtures that they are known as promoters.

Using measurements obtained from experimental techniques shown in Table 1, a number of mechanisms have been proposed by various authors to

Table 1 The effects of mixing reagents in Flotation

Interactions

Reagentsa (ratios tested)b

Mineral systemsc

Techniques

Benefit ofmixture

Reference

Collector:collector Ethyl X:amylX Thiol-thiol (2:1,1:2 mass)

Arsenopyrite (P)

Ethyl X: amyl X: diethyl Arsenopyrite (P) DTP (1 : 1 mass)

Batch flotation Higher rates of Plaskin etal. (1954)

recovery with mixtures. Optimum mixtures: ethyl X: amyl X (1 : 2) for arsenopyrite and (1:1) for galena

Ethyl X: butyl X: diethyl Galena (P) DTP (1 : 1 mass)

Radiographic adsorption techniques

More even collector coverage on mineral surface with mixture

Plaskin and Zaitseva (1960)

n-propyl DTC: n-hexyl Pyrite ore with quartz Batch flotation Increased recoveries Bradshaw and

DTC : cyclohexyl DTC : di propyl DTC (10:90; 50:50; 90:10)

gangue (South Africa) (1.27% Sulfur)

Galena (P)

Adsorption Bubble pick-up for all mixtures. Optimum ratio: n-propyl DTC: cyclohexyl DTC (90: 10)

Preferential DTP adsorption from mixture with no increased mass picked up by bubble

O'Connor (1994)

Wakamatsu and Numata (1979)

Isopropyl DTC: iso propyl X (1 : 2 mass)

Di-isobutyl DTP : iso butyl X (30: 70; 50: 50; 70: 30 mass)

Platinum group metal (PGM) ore

Batch flotation

Batch flotation

Better results with DTC:X mixture than with pure DTC

Recovery improved from 73.2% for pure X to 80% with 70:30 mixture

Falvey (1969)

Mingione (1984)

Di-isobutyl DTP: SMBT Auriferous pyrite ore (50: 50 mass) (0.38 g/t Au, 1 % Sulfur)

Recovery improved from 73.8% for pure SMBT to 79.9% with mixture

Di-isobutyl DTP : SMBT Sphalerite ore (50:50; mass) (1.5% Zn)

Recovery improved from 90% for pure SMBT to 95% with mixture

Isobutyl X: cyano diethyl DTC (12: 44 mass)

Chalcopyrite/pyrite with quartz gangue (China)

Batch flotation Chalcopyrite recovery Jiwu etal. (1984) increased from 92.4% to 92.8% with 12:44 mixture

DTP: MTP (types unspecified)

Mixed copper sulfide ore

Batch flotation

Optimum recovery at 75:25 due to combination of collector properties

Mitrofanov etal. (1985)

Table 1 Continued

Interactions

Reagentsa (ratios tested)b

Mineral systemsc

Techniques

Benefit ofmixture

Reference

Ethyl X: di-ethyl DTC (80:20; 66:33; 50:50; 33: 66; 20: 80)

Hazelwoodite (SP)

Adsorption Surface tension Microflotation

Gold and arsenopyrite Batch flotation ore (France)

Critchley and Riaz (1991)

Optimum ratio: 33:66 for lower surface tension, increased microflotation recovery and extent of adsorption

Gold and arsenopyrite Van Lierde and recovery increased Lesoille (1991) with use of mixture

Collector: collector Isopropyl X:dicresyl

Thiol-thiol

Mixed copper sulfide/ oxide ore (2.9% Cu)

Batch flotation

Enhanced rate and recovery with mixture. Recovery from 80-83% Cu

Adkins and Pearse (1992)

n-butyl X : cyclohexyl DTC (95:5; 90:10; 85: 15; 50: 50)

Pyrite ore with quartz Batch flotation gangue (South Africa) (0.83% S)

Recovery increased for all mixtures. Highest recovery for 50:50 mixture

Bradshaw and O'Connor (1997)

Thiol-anionic n-butyl X : cyclohexyl DTC (90:10)

Ethyl X : sodium oleate (10:90; 20:80; 40:60; 60: 40; 80: 20)

Pyrite (P)

Bubble loading Increased bubble Thermochemical loading and heat of adsorption with mixture

Pyrite (polished section) Surface tension Largest contact angle Valdiviezo and

Gold (polished section) Contact angle corresponded to low surface tension with 3: 1 mixture

Oliveira (1993)

Thiol-anionic polymers

Ethyl X : amino acid glycine (1:1)

Microflotation

Higher recoveries obtained for all sulfides with mixture

Hanson etal. (1988)

Thiol-cationic

Butyl X: hydrolysed polyacrylamide (90:10)

Ethyl X : ammonium bromide

Mixed sulfide ore with Batch flotation gold

90 : 10 mixture increased gold recovery 3% above that obtained with pure X

Orel etal. (1986)

Surface tension Lowest surface tension Buckenham and for 1 :1 mixture Schulman

Microflotation Increased recovery (1963) with all mixtures

Collector: frother Ethyl X : alkyl alcohols Chalcocite (P)

Frothability

Enhanced frothability with X added to alcohols

Leja and

Schulman (1954)

Ethyl X : a-terpinol

Chalcocite (P)

Microflotation

Frothability

Increased recovery with increasing dosage of frother with xanthate. Only froths in 3 phase

Lekki and Laskowski (1971)

Table 1 Continued

Interactions

Reagentsa (ratios tested)

Mineral systemsc

Techniques

Benefit ofmixture

Reference

Chalcocite ore

Batch flotation

Increased recovery due to joint frother-collector interactions

Lekki and Laskowski (1975)

Butyl X:41G

Galena

(polished section)

Xanthogen formate : Copper sulfide ore MIBC (Chile)

Collector: frother Ethyl X: alkyl alcohols No mineral Range of molar concentrations

Contact angle Contact angle on Harris (1982) mineral increased with addition of frother to X Batch flotation Collector dosage Crozier and Klimpel Plant practice reduced 40% to (1989) achieve same recovery, which reduced cost and selectivity

Surface tension Reduced film Manev and Pugh

Film thickness thickness and surface (1993) tension with increasing addition of X

Frother: frother

MIBC, pine oil, cresylic acid, PPG

Various copper sulfide ores

Plant practice

Survey of 66 plants showed 37% used mixtures of frothers

Crozier and Klimpel (1989)

aReagentstested as components of the mixture are separated by a colon. Where more than two reagents are in the list, all the reagents listed have been tested at all the ratios specified in brackets.

bRatios are mole ratios unless otherwise specified as mass ratios (mass).

cIn cases where the origin or grade of the ore is not included in Table 1, this information was not available in the original reference. X, Xanthate class of reagents; DTC, dithiocarbamate class of reagents; DTP, dithiophosphate class of reagents; MTP, monothiophos-phate class of reagents; SMBT, sodium mecaptobenzonthiazole; PPG, polypropylene glycol; 41G, a proprietary frother containing triethoxybutane manufactured by NCP; MIBC, methyl isobutyl carbinol; (P), pure mineral sample with no gangue component; (SP), synthetically prepared pure mineral sample.

explain the fact that the mixtures give a flotation performance greater than that expected from the contributions of each individual component. These proposals are based on effects related to adsorption of the collectors on the surface of the particle, interactions between the reagents, either in the bulk or at the surface, or changing froth characteristics.

When using mixtures of collectors it has often been observed that there is a greater surface coverage of the adsorbed collectors on the mineral than would have been expected from their weighted averages. This could either enhance the overall hydrophobicity of the mineral surface or result in an adsorbed surface layer of collector molecules more suitable for frother-collector interactions. The increased mineral hydrophobicity could result from the formation of a more evenly distributed surface species. The change in hydrophobicity can be measured by, for example, changes in contact angle, bubble loading and ultimately the recovery in batch flotation tests. It has also been proposed that, for certain systems, when a mixture of collectors is exposed sequentially to a surface which, by definition, must have a heterogeneous distribution of energetically different sites, the weaker collector will adsorb preferentially on the strong sites and the strongly adsorbing collector, added subsequently, will adsorb on the weaker sites. In this way as many sites as possible are utilized for adsorption, thus enhancing the hydrophobicity. Single collector addition may only result in adsorption on strongly adsorbing sites, forming nonuniform coverage and thus a less than optimal adsorption capacity. It is possible that such an effect will not be observed if the collectors are pre-mixed before addition, thus emphasizing the fact that synergism may depend on the sequence of addition as much as on the presence of a mixture.

The grade of the concentrate is largely a function of the depressant used, which affects the froth zone characteristics. The presence of hydrophobic solids in the froth phase will destabilize the froth, causing bubble coalescence in the froth which results in improved drainage and consequently increased selectivity and grades. The presence of hydrophilic or only

Figure 1 The effect of mixtures of collectors on batch flotation performance of a low-grade pyrite ore at pH 4. Values measured (squares) were compared with those predicted from the linearly additive mole ratio contribution of potassium n-butyl xanthate (PNBX) and dithiocarbamate class of reagents (DTC; triangles) for (A) % sulfur recovery obtained for 25% grade; (B) % sulfur grade obtained for 80% recovery; and (C) water recovery obtained after 7 min (g).

Figure 1 The effect of mixtures of collectors on batch flotation performance of a low-grade pyrite ore at pH 4. Values measured (squares) were compared with those predicted from the linearly additive mole ratio contribution of potassium n-butyl xanthate (PNBX) and dithiocarbamate class of reagents (DTC; triangles) for (A) % sulfur recovery obtained for 25% grade; (B) % sulfur grade obtained for 80% recovery; and (C) water recovery obtained after 7 min (g).

slightly hydrophobic minerals can stabilize the froth zone and thereby decrease the grade achieved. The use of a combination of collectors resulting in both physisorbed and chemisorbed surface products can also affect the froth structure and influence the final grade achieved. It is also often observed that enhanced performance is achieved when a strong collector with no frothing properties is used with a weaker collector with frothing properties. The former increases coarse particle recovery and the latter increases fine particle recovery. This is however not a true synergistic effect since the combined effect is the sum of the individual effects.

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