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Ind. Eng. Chem. Res. 2009, 48, 5584–5589
Sphalerite Flotation Using an Arylhydroxamic Acid Collector: Improving Grade while Using a Reduced Amount of Copper Sulfate for Activation Daniel Hamilton, Ramanathan Natarajan,1 and Inderjit Nirdosh Department of Chemical Engineering, Lakehead UniVersity, 955 OliVer Road, Thunder Bay, Ontario, Canada, P7B 5E1
N-Hydrocinnamoyl-N-phenylhydroxylamine (HCNPHA) was determined to float sphalerite without copper sulfate activation. However, the concomitant flotation of sulfidic (pyrite) and nonsulfidic gangue (silica) minerals significantly reduced the grade of the float concentrate. The addition of only 200 g/t copper sulfate, which is ∼20% of that which is being used currently in the xanthate reagent scheme, improved the grade and the recovery. Seven different types of carboxymethylcellulose (CMC-1-CMC-7) were tested. CMC-1 was found to be the best as a depressant of gangue flotation. Copper sulfate appeared to differentiate the sphalerite surface well and facilitated chelation while the CMC changed the frothing characteristics of the slurry and prevented entrainment of gangue into float concentrate (froth). Studies on flotation kinetics also confirmed the improved selectivity attained by using copper sulfate and a CMC. The selectivity index (SI) for sphalerite, with respect to pyrite, improved from 0.88 to 2.35 when copper sulfate was added, and that for nonsulfidic gangue increased from 1.93 to 6.29 when CMC was added. Introduction Sphalerite is commonly activated with copper sulfate to facilitate xanthate adsorption by forming a more-stable and lesssoluble chemical compound on the mineral surface. The amount of copper sulfate needed for activation is dependent on the zinc grade of the ore. Although copper sulfate is not a specialty chemical such as collectors and frothers, its large consumption makes it the most expensive auxiliary chemical used in the processing of zinc ores. Natarajan and co-workers1-5 tested several alternative collectors to eliminate copper sulfate in the flotation of sphalerite. Cupferron derivatives were determined to float sphalerite without activation by copper sulfate.2,5 However, the toxic nature of cupferrons and the concomitant flotation of pyrite placed major limitations on the modified Cupferron reagents. Hydroxamic acids (R1N(OH)C(dO)R2) are structurally more similar to Cupferron and belong to the O-Otype chelating reagent. The chemistry of hydroxamic acids and their ability to form chelates with several metal ions have been well-documented in the literature.6-9 They are more selective than carboxylic acids and the stability constants of the chelates formed by hydroxamates have the following order: alkalineearth metals < transition metals < rare earths < cations with charges of >2. Because of their capacity to form more-stable complexes with transition metals and rare-earth metals, N-alkylhydroxamic acids and their sodium or potassium salts were tested as mineral collectors to float oxidized copper minerals and rare-earth minerals by Fuerstenau and co-workers.10-13 Russia and China were using hydroxamic acids for a long time under the commercial name IM-50.14 Although the potential of alkyl hydroxamates as mineral collectors was explored extensively, Marabini15 tested an arylhydroxamic acidsnamely, N-benzoylN-phenylhydroxyl amine (NBPHA)sfor the flotation of rutile. Based on the studies on the use of hydroxamic acids as mineral collectors and the structural similarity with Cupferron, Natarajan and Nirdosh4 switched over to N-arylhydroxamic acids from Cupferrons. Unlike alkylhydroxamic acids, there is a wider 1 To whom correspondence should be addressed. Tel.: +1 807 343 8754. Fax: +1 807 343 8928. E-mail address:
[email protected].
scope for structural variation in the case of N-arylhydroxamic acids and thus pKa could be varied. The effect of substituents on the flotation of sphalerite by N-arylhydroxamic acids was studied by testing 31 synthesized compounds, and N-hydrocinnamoyl-N-phenylhydroxyl amine (HCNPHA) was determined to give the best results.3 Although they achieved the flotation of sphalerite without using copper sulfate for activation, a concomitant flotation of pyrite affected the grade of the zinc concentrates, as observed in the previous study using heptylcupferron.2 The formation of foam by alkyl hydroxamates at alkaline pH is a known phenomenon.16 Because of the similar behavior by HCNPHA, a thick froth was formed while floating sphalerite at pH 9, and this seemed to be the main reason for entraining silica into the float. Research work was conducted on a lead-zinc ore obtained from Teck Cominco, where lead is first floated with potassium ethyl xanthate (PEX) and sphalerite from the lead rougher tails is floated with potassium amyl xanthate (PAX) using 1 kg/t copper sulfate but no carboxymethylcellulose (CMC). Note that the industry (Teck Cominco) uses 200 g/t potassium amyl xanthate (PAX) as the collector and copper sulfate (1 kg/t) as an activator for sphalerite. The industry is able to achieve ∼94% sphalerite recovery, and the grade of the concentrate is 65% sphalerite. In the present study, lead rougher was obtained as per the protocol employed by the mill, using potassium ethylxanthate (PEX), and a new collector was used to float sphalerite from the tails of the lead rougher stage without adding any copper sulfate activation. However, the concomitant flotation of pyrite and the entrainment of other gangue minerals into the thick forth prohibited any promise for a commercial application. To alleviate these limitations, auxiliary chemicals were added to improve the recovery and grade of the zinc concentrate. This paper reports the results of flotation tests performed using various CMCs and outlines the improvement of zinc grade during the flotation of sphalerite using HCNPHA as the collector, with and without the addition of copper sulfate. Experimental Section Materials and Methods. HCNPHA was synthesized using a reported procedure17 and purified by crystallization from an
10.1021/ie900305r CCC: $40.75 2009 American Chemical Society Published on Web 05/19/2009
Ind. Eng. Chem. Res., Vol. 48, No. 12, 2009
ethanol-water mixture (3:1 by volume). The purity of HCNPHA was ascertained via C, H, and N elemental analysis and hydrogen-1 nuclear magnetic resonance (1H NMR) spectroscopy. A stock solution of HCNPHA (1% by weight) was prepared in water, and 1% sodium hydroxide solution was added dropwise to achieve complete dissolution. A lead-zinc ore with an average composition of 7%-8% lead, 20-22% zinc, and 5%-6% iron was provided by Teck Cominco (British Columbia, Canada). Potassium ethyl xanthate (PEX) and potassium amyl xanthate (PAX) were provided by Prospec Chemicals (Alberta, Canada), and CMCs were supplied by Cambrian Chemicals (Oakville, Ontario, Canada). A solution of each CMC was prepared by dissolving the appropriate amount in water at pH 11, and freshly prepared solutions were used because the viscosities of the solutions changed upon storage. Zinc sulfate, sodium metabisulfite, and sodium cyanide were used; all were reagent grade. A polyurethane-lined rod mill with size-graded stainless steel rods as grinding medium was used. A Denver laboratory flotation system that was fitted with an external air supply was used to conduct the flotation tests. Flotation Tests. The ore (350 g) was grinded in the rod mill at 67% solids and the rod mill discharge was 80% solids passing through 63 µm. Zinc sulfate (100 g/t) and sodium metabisulfite (68 g/t) were added during grinding. Two-stage floation tests that were comprised of lead rougher (Pb-R) and zinc rougher (Zn-R) stages were conducted at 35% solids in a slurry. In the lead-rougher stage (Pb-R), galena was floated using 100 g/t potassium ethyl xanthate (PEX) and 10 g/t methylisobutyl carbinol (MIBC) as the collector and frother, respectively. Zinc sulfate (30 g/t) and sodium cyanide (50 g/t) were used to suppress sphalerite in the Pb-R stage. In the Pb-R stage, no pH modifier was used and the flotation was conducted at the natural pH (∼6.4) of the laboratory water. In the second stage of flotation (the zinc-rougher (Zn-R) stage), the slurry pH was adjusted to 9.0 and 200 g/t HCNPHA was added as a collector while the frother was MIBC (10 g/t). In addition to the collector and frother, copper sulfate (activator) and/or CMC (suppressant) were added, based on the nature of the tests. The flotation samples (floats and tails) were acid-digested using a HNO3-HF mixture in Teflon crucibles and analyzed for the presence of lead, zinc, and iron by inductively coupled argon plasma atomic emission spectrometry (ICAP). Reagents additions were scaled up for tests conducted with 1 kg ore samples (see the sections entitled “Effect of Copper Sulfate” and “Flotation Kinetics”, presented later in this paper). The flotation kinetics was studied only for the zinc rougher stage by collecting timed float samples. While calculating the recoveries and grades, an iron content of 3% was assumed to be associated with zinc, as suggested by Teck Cominco, and the remainder was considered to be pyritic iron. The mass percentage of nonsulfidic gangue (NSG) was calculated by subtracting the sum of galena (Ga), sphalerite (Sp), and pyrite (Py) from 100%.
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the iron content, based on the assumption that 3% of the iron was associated with zinc. There was no significant improvement in recovery beyond an air flow rate of 1.5 Lpm. An optimum air flow rate of 2.5 Lpm was used in subsequent tests, because of the better sphalerite recovery, as shown in Figure 1. Effect of Collector Concentration. The effect of collector concentration was studied by varying HCNPHA dosages from 50 g/t to 250 g/t, and, in all tests, an air flow rate of 2.5 Lpm was maintained as noted previously. The results of flotation tests on collector dosage are given in Figure 2. In the Zn-R concentrates, the sphalerite grade remained almost constant (∼45%) and was not affected by the amount of collector added. However, the sphalerite recovery increased as the collector dosage increased. This indicated that there was no enrichment of sphalerite in the float, probably because of the concomitant flotation of gangue minerals that is caused by a thick froth formed during flotation. It was decided to use 200 g/t HCNPHA and improve the grade of the float concentrate by adding
Figure 1. Effect of air flow rate on mineral recovery.
Figure 2. Effect of collector dosage on sphalerite recovery and grade.
Results and Discussions Effect of Air Flow. To fix variables such as the rate of air flow and the collector dosage, a set of preliminary flotation tests were conducted using 350 g of the ore for each test. The effect of air flow rate on the recovery of sphalerite was studied by varying the air flow from 0.5 Lpm to 3.0 Lpm. In these tests, 200 g/t HCNPHA was used, and this dosage was fixed to be consistent with the amount of potassium amyl xanthate (PAX) used by Teck Cominco. The results of the air flow rate on the recovery of sphalerite, pyrite, and nonsulfidic gangue are shown in Figure 1. Note that the amount of pyrite was calculated from
Figure 3. Effect of copper sulfate on the overall grades of the float concentrates.
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Table 1. Effect of Carbomethylcellulose (CMC) on Suppression of Ganguea Grade (wt %)b stagec
mass (g)
Ga
Sp
Recovery (%)b
Py
NSG
Ga
Sp
Py
NSG
wt %
54.4 37.1 8.5 100
9.6 86.7 3.7 100
8.9 63.0 28.1 100
6.7 41.2 52.1 100
9.5 52.6 37.9 100
58.5 32.6 9.0 100
8.8 84.4 6.8 100
8.8 59.9 31.4 100
6.5 41.3 52.2 100
9.3 52.4 38.4 100
52.7 40.0 7.3 100
8.4 86.7 4.8 100
8.5 67.5 24.0 100
6.8 47.0 46.2 100
10.5 57.0 32.4 100
51.8 39.8 8.4 100
8.4 86.9 4.7 100
8.7 64.3 27.0 100
6.9 47.4 45.6 100
11.2 57.0 31.8 100
52.1 41.4 6.5 100
7.4 87.5 5.1 100
8.2 67.7 24.1 100
7.1 53.3 39.6 100
12.7 61.1 26.2 100
53.2 39.5 7.3 100
8.3 86.1 5.6 100
8.8 65.2 26.0 100
6.9 46.6 46.5 100
11.1 56.3 32.6 100
46.9 42.9 10.2 100
8.3 81.4 10.3 100
7.9 63.0 29.1 100
7.1 40.2 52.7 100
10.7 52.1 37.2 100
42.2 49.9 7.9 100
7.9 89.2 3.0 100
8.1 74.4 17.5 100
8.5 59.6 31.9 100
11.2 67.7 21.1 100
Baseline Pb-R Zn-R tail feed
32.9 182.2 131.1 346.2
23.9 2.9 0.9 4.2
28.6 46.6 2.8 28.3
13.1 16.8 10.4 14.1
Pb-R Zn-R tail feed
31.5 177.7 130.2 339.4
28.7 3.0 1.1 4.6
26.6 47.4 5.2 29.3
13.2 16.7 11.9 14.5
Pb-R Zn-R tail feed
37.4 202.2 115 354.6
25.6 3.2 1.0 4.8
27.5 45.9 4.5 30.5
13.7 17.7 11.1 15.1
Pb-R Zn-R tail feed
39.5 200.5 111.9 351.9
25.5 3.2 1.2 5.1
27.6 46.8 4.6 31.2
14.3 17.4 13.1 15.7
34.3 33.6 85.9 53.5 CMC-1 31.5 32.9 81.7 51.5 CMC-2 33.3 33.3 83.4 49.5 CMC-3 32.6 32.6 81.1 48.0 CMC-4
Pb-R Zn-R tail feed
44.2 212.4 91.1 347.7
29.8 3.7 1.3 6.4
26.0 47.8 6.5 34.2
14.6 18.7 15.5 17.3
Pb-R Zn-R tail feed
38.6 194.9 112.9 346.4
26.7 3.3 1.1 5.2
26.5 46.3 5.2 30.7
14.1 17.7 12.1 15.5
Pb-R Zn-R tail feed
36.7 179.1 127.8 343.6
26.9 4.5 1.5 5.8
27.7 49.8 8.9 32.2
13.6 20.0 13.0 16.7
Pb-R Zn-R tail feed
38.2 231.4 72.1 341.7
19.1 3.2 1.6 4.7
29.1 47.0 5.0 36.1
13.6 17.7 13.4 16.4
29.5 29.9 76.7 42.1 CMC-5 32.7 32.7 81.6 48.6 CMC-6 31.7 25.6 76.6 45.2 CMC-7 38.2 32.1 79.9 42.9
a Error between repeat tests was observed to vary over a range of 4%-8% for grade (wt %) and 2%-3% for recovery (%). sphalerite; Py ) pyrite; NSG ) nonsulfidic gangue. c Pb-R ) lead rougher stage; Zn-R ) zinc rougher stage.
Table 2. Ratio of Sp Grade to Py Grade or NSG Grade in the Float Concentrate Grade Ratio CMC
Pya
NSGb
CMC-1 baseline CMC-3 CMC-7 CMC-5 CMC-2 CMC-4 CMC-6
2.84 2.77 2.69 2.65 2.62 2.60 2.56 2.49
1.44 1.38 1.44 1.46 1.42 1.38 1.60 1.95
a The notation Py means with respect to pyrite. denotes with respect to nonsulfidic gangue.
b
The notation NSG
reagents that would change the frothing characteristics of the pulp, such that the gangue did not end up in the float. Effect of Copper Sulfate. In all the preliminary tests, sphalerite was floated without adding copper sulfate and the grades were very poor. Sphalerite was suppressed in the Pb-R stage and it was believed that it perhaps required reactivation
b
Ga ) galena; Sp )
to facilitate differential flotation. Copper sulfate is known to adsorb preferentially on zinc sulfide (ZnS); therefore, the effect of adding copper sulfate in the Zn-R stage was studied. For this, varying amounts of copper sulfate were added in the Zn-R stage while using HCNPHA as the collector. Unlike the preliminary tests, in each of these tests 1 kg ore was used and the floats were collected in four cuts (Zn-R1, 0-1 min; Zn-R2, 1-2 min; Zn-R3, 2-4 min; Zn-R4, 4-8 min). A baseline test without any copper sulfate was also conducted to compare the results. Sphalerite grades and recoveries of these tests are given in Figure 3. There was no significant improvement, either in grade or recovery, up to 100 g/t copper sulfate. However, sphalerite recovery increased from 50% to 80% upon the addition of 200 g/t copper sulfate and the grade improved to 54%. However, the addition of more copper sulfate was not observed to improve either sphalerite recovery or grade. The results indicated that 200 g/t copper sulfate was the minimum required dosage for the efficient flotation of sphalerite using HCNPHA. In the case
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Table 3. Effect of CMC-1 Dosage Grade (wt %)a stageb
mass (g)
Ga
Sp
Recovery (%)a
Py
NSG
Ga
Sp
Py
NSG
mass
50.9 36.8 12.3 100
7.5 79.2 13.3 100
7.4 55.5 37.1 100
6.7 37.2 56.0 100
9.8 49.5 40.7 100
50.6 36.7 12.7 100
7.8 75.0 17.2 100
7.6 53.5 38.9 100
6.8 32.7 60.5 100
9.9 45.0 45.0 100
52.9 33.5 13.6 100
8.6 73.2 18.2 100
8.0 48.4 43.6 100
6.5 28.7 64.8 100
9.7 41.0 49.3 100
[CMC-1] ) 150 g/t Pb-R Zn-R tail feed
34.2 172.6 142.2 349.0
30.2 4.2 1.7 5.7
26.3 53.2 10.9 33.3
12.6 18.0 14.6 16.1
Pb-R Zn-R tail feed
35.0 158.9 158.9 352.8
28.1 4.2 1.5 5.3
27.1 53.8 12.4 32.5
12.7 18.4 13.4 15.6
Pb-R Zn-R tail feed
33.4 141.2 169.6 344.2
28.9 4.3 1.4 5.3
27.6 54.6 11.3 30.7
12.7 17.7 13.3 15.1
30.9 24.6 72.9 44.9 [CMC-1] ) 200 g/t 32.1 23.6 72.8 46.6 [CMC-1] ) 250 g/t 30.9 23.4 74.0 49.0
a Ga ) galena; Sp ) sphalerite; Py ) pyrite; NSG ) nonsulfidic gangue. b Pb-R ) lead rougher stage; Zn-R ) zinc rougher stage; feed ) calculated feed assay.
Figure 4. Time-cumulative recovery plots for the zinc rougher stage using 200 g/t HCNPHA as the collector: (a) without adding any CuSO4 for activation, (b) after activating sphalerite with 200 g/t CuSO4, (c) 250 g/t CMC was added in addition to CuSO4 (the slurry was conditioned first with CMC and then with CuSO4); and (d) swapping the order of conditioning with CuSO4 and CMC (the slurry was conditioned first with CuSO4 and then with CMC).
of the xanthate reagent scheme, copper sulfate is known to facilitate the flotation of sphalerite by forming a more hydrophobic and stable surface compound. This did not seem to be the phenomenon responsible when using HCNPHA, because the stability constants of the Zn2+ and Cu2+ complexes with several N-arylhydroxamic acids do not differ significantly. Effect of CMCs on the Suppression of Gangue. After achieving significant improvement in grade and overall recovery of sphalerite using copper sulfate, additional tests were conducted with the objective of reducing the entrainment of gangue by changing the frothing characteristics of the pulp in the Zn-R
stage. For this purpose, seven CMCs that differ in their molecular mass, because of substitution and the degree of branching, were used. For proprietary reasons, the exact composition and details of the CMCs are not discussed here. In each of these batch flotation tests using 350 g ore and 200 g/t HCNPHA, an arbitrary amount of 100 g/t CMC was tested individually. The results of these tests are shown in Table 1. The purpose of these tests was to improve the grade without affecting the recovery. To compare the results, a new measure called grade ratio (GR) was used. GR is the ratio of the grade of a valuable mineral (sphalerite) to that of a gangue mineral
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Table 4. Flotation Kinetics Parameters Selectivity Index, SI mineral
k (min-1)
R∞
Km
with respect to NSG
with respect to Py
6.67 7.56 3.46
1.93
0.88
15.52 8.72 4.16
3.73
1.78
4.37
1.63
6.29
2.35
Test 4a sphalerite, Sp pyrite, Py nonsulfidic gangue, NSG
0.125 0.151 0.113
53.4 50.1 30.6
sphalerite, Sp pyrite, Py nonsulfidic gangue, NSG
0.186 0.150 0.112
83.4 58.1 37.2
sphalerite, Sp pyrite, Py nonsulfidic gangue, NSG
0.151 0.152 0.119
67.8 41.3 19.7
sphalerite, Sp pyrite, Py nonsulfidic gangue, NSG
0.203 0.144 0.100
73.7 44.2 23.9
Test 4b
Test 4c 10.24 6.28 2.34 Test 4d
(pyrite or nonsulfidic gangue such as silica) in the float concentrate. Grade ratios of the tests using the CMCs are given in Table 2, and the results are arranged in the descending order of GR, as calculated with respect to pyrite. Based on the grade ratios in Table 2, CMC-1 and CMC-6 showed promise among the seven CMCs tested. The best pyrite suppression was obtained with CMC-1, whereas, for nonsulfidic gangue suppression, it was obtained with CMC-6. CMC-1 was preferred to CMC-6, because of higher sphalerite recovery (for CMC-1, the sphalerite recovery was 84.4%; for CMC-6, the sphalerite recovery was 81.4%), and the consequent decrease in the rejection of sphalerite to the tails was observed (CMC-1 left 6.8% sphalerite in the tails, whereas CMC-6 left 10.3% in the tails). Additional tests were conducted using CMC-1, because it showed promise in pyrite suppression, and the results of these tests are given in Table 3. Higher dosages of CMC-1 were not tested, because a decrease in sphalerite recovery was observed; moreover, CMCs are known to increase slurry viscosity at higher concentration. Hence, the decision was made to use 250 g/t of CMC-1, because it seemed to be optimum to suppress gangue. Flotation Kinetics. Flotation kinetics was studied only for the zinc rougher stage, to understand the differential flotation of various minerals. The following tests on flotation kinetics were conducted using 200 g/t HCNPHA as the collector: (i) baseline test using only HCNPHA, without adding copper sulfate or CMC-1; (ii) HCNPHA with 200 g/t copper sulfate; and (iii) HCNPHA with 200 g/t copper sulfate and 250 g/t CMC-1. It was observed that the addition of copper sulfate appreciably improved the recovery of sphalerite (see Figures 4a and 4b), without a significant change in the recovery of other minerals, and this resulted in a better sphalerite grade of the float concentrates. This was consistent with the results of experiments that were conducted to test the effect of copper sulfate; these results are discussed in the section “Effect of Copper Sulfate”, presented earlier in this paper. The maximum sphalerite recovery (R∞) increased from 53% to 83% (a 30% increase), whereas the increase in R∞ for pyrite and nonsulfidic gangue was ∼8%; this result supports the preferential adsorption of copper sulfate on zinc sites and the facilitation of chelation by HCNPHA. While testing the effect of CMC-1 on the flotation kinetics, two possible options were open, because of the order of adding copper sulfate and CMC-1, and both of them were tried. It was interesting to note that swapping the order of addition of copper sulfate and CMC-1 significantly influenced the recoveries (see Figures 4c and 4d). Conditioning with CMC-1 prior to that with
14.96 6.36 2.38
copper sulfate was detrimental (see Figures 4b and 4c), and this might be due to the indiscriminate masking of sites by CMC-1. This could be inferred from the decrease in the recoveries of all the minerals. On the other hand, in the experiment in which CMC-1 was added after conditioning with copper sulfate, sphalerite recovery was almost equal to that with experiment 4b (see Figure 4b and Table 4); however, the overall grade of the float concentrate improved, because of the suppression of nonsulfidic gangue (compare Figure 4b with Figure 4d). Although some qualitative observations to compare the effects of auxiliary chemicals could be made with the time recovery plots and the grades of the concentrates, quantitative estimation of increase or decrease in selectivity for a given mineral was not possible. Selectivity of a collector for a certain mineral over others, under given experimental conditions, is dependent on the value of maximum recovery (R∞) and the first-order rate constant (k) for flotation. Hence, it becomes difficult to interpret the change in selectivity between a valuable mineral and a gangue mineral from the R∞ values alone. To overcome this, Xu18 suggested a modified rate constant (Km), which is a combination of R∞ and k, and is given by the equation Km ) R∞ × k
(1)
The modified rate constants were then used to define the selectivity index (SI) or the rate constant of one mineral (M1) relative to that of the other mineral (M2). The selectivity index is given by the following expression: SI(M1/M2) )
Km of M1 Km of M2
(2)
Thus, the selectivity index between a valuable mineral M and a gangue mineral G may be calculated by the equation SI(M/G) )
KmM Km G
(3)
SI is the quantification of the selectivity of a collector for a particular mineral over another mineral under the given set of process variables. Therefore, it is helpful to identify the factors that have positive effects on SI, to maximize the separation between the two minerals. The modified first-order rate equation for the flotation kinetics (eq 4) is given below:
Ind. Eng. Chem. Res., Vol. 48, No. 12, 2009
Rt ) R∞[1 - e
-k(t+φ)
]
(4)
where Rt is the cumulative recovery at time t, R∞ the maximum recovery or the cumulative recovery at time ∞, k the first-order rate constant, and φ the time correction factor. The data for the flotation kinetics (Rt, t) were used as input parameters in eq 4 to fit the time-recovery plots (Figures 4a-d), and the freeware CurveExpert 1.319 was used to obtain the first-order rate constant k, the maximum recovery of a mineral (R∞), and the time correction factor (φ). Values of the modified rate constant Km and the selectivity index SI were computed using eqs 1 and 3. The parameters calculated from flotation kinetics data are given in Table 4. The addition of 200 g/t copper sulfate increased the selectivity of the collector, with respect to pyrite, from 0.88 to 1.78 and that for nonsulfidic gangue increased from 1.93 to 3.73. There is an apparent suppression of gangue minerals; however, a closer inspection of the first-order rate constant k reveals that k remains almost unaltered for both pyrite (k ≈ 0.150 min-1) and nonsulfidic gangue (k ≈ 0.113 min-1) but it increased significantly for sphalerite (from 0.125 min-1 to 0.186 min-1). Hence, it is evident that copper sulfate preferentially modified the sphalerite surface from other minerals’ surfaces and facilitated differential flotation. The modified rate constant Km for pyrite decreased from 8.72 to 6.36 (an ∼25% decrease), whereas Km for NSG decreased from 4.16 to 2.38 (an ∼50% decrease) for experiments 4b and 4d. This revealed that CMC-1 helped to suppress NSG more than pyrite. Conclusions N-Hydrocinnamoyl-N-phenylhydroxylamine (HCNPHA) was able to float sphalerite through the use of ∼20% of the copper sulfate required for processing a similar ore in the xanthate reagent scheme. The collector concentration and the optimum airflow for flotation were determined to be 200 g/t and 2 to 3 Lpm, respectively. The addition of copper sulfate increased not only the recovery but also the flotation kinetics of sphalerite. Copper cation species adsorb chemically on the sphalerite surface and facilitated surface chelation. In the case of xanthates, copper sulfate activates sphalerite by forming a more-stable and less-soluble surface complex, and this does not seem to be the mechanism of activation while using HCNPHA, because the stability constants of copper and zinc complexes of hydroxamic acids do not differ very much. The foaming characteristic of HCNPHA at pH 9, and the consequential entrainment of gangue minerals into the float was alleviated by a considerable extent, using a modified carboxymethylcellulose (CMC). Acknowledgment This research was funded by Natural Sciences and Engineering Research Council of Canada (NSERC). Thanks are due to
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Teck Cominco (Trail, British Columbia, Canada), for the kind support and supply of ore samples; Prospec Chemicals (Fort Saskatchewan, Alberta, Canada), for xanthates; and Cambrian Chemicals (Oakville, Ontario, Canada), for free samples of CMCs. Literature Cited (1) Natarajan, R. Synthesis of Cupferron-derivatives as mineral collectors for ore-beneficiation, Ph.D. Thesis, Bharathidasan University, Tiruchirapalli, India, 1995. (2) Nirdosh, I.; Natarajan, R. p-Heptylcupferron as collector for flotation of zinc from a Canadian copper-rougher-tails. Metall. 2002, 6, 366–371. (3) Natarajan, R.; Nirdosh, I. New collectors for sphalerite flotation. Int. J. Miner. Process. 2006, 79 (3), 141–148. (4) Natarajan, R.; Nirdosh, I. N-Arylhydroxamic acids as mineral collectors for ore beneficiation. Can. J. Chem. Eng. 2001, 79, 941–945. (5) Natarajan, R.; Nirdosh, I.; Muthuswami, S. V. Flotation of a copperzinc ore using p-nonylcupferron as collector. DeV. Chem. Eng. Miner. Process. 1997, 5, 183–193. (6) Agrawal, Y. K.; Tandon, S. G. Metal-ligand stability constants of hydroxamic acids. J. Inorg. Nucl. Chem. 1974, 36 (4), 869–873. (7) Agrawal, Y. K. Hydroxamic Acids and Their Metal Complexes. Russ. Chem. ReV. 1979, 48 (10), 948–963. (8) Yale, H. L. The Hydroxamic Acids. Chem. ReV. 1943, 33 (3), 209– 256. (9) Chatterjee, B. Donor properties of hydroxamic acids. Coord. Chem. ReV. 1978, 26 (3), 281–303. (10) Barbaro, M.; Herrera Urbina, R.; Cozza, C.; Fuerstenau, D.; Marabini, A. Flotation of oxidized minerals of copper using a new synthetic chelating reagent as collector. Int. J. Miner. Process. 1997, 504, 275–287. (11) Fuerstenau, D. W. Equilibrium and Nonequilibrium Phenomena Associated with the Adsorption of Ionic Surfactants at Solid-Water Interfaces. J. Colloid Interface Sci. 2002, 256 (1), 79–90. (12) Pradip; Fuerstenau, D. W. The adsorption of hydroxamate on semisoluble minerals. Part I: Adsorption on Barite, Calcite and Bastnaesite. Colloids Surf. 1983, 8 (2), 103–119. (13) Pradip; Fuerstenau, D. W. Adsorption of hydroxamate collectors on semisoluble minerals. Part II: Effect of temperature on adsorption. Colloids Surf. 1985, 15, 137–146. (14) Nagaraj, D. R. The chemistry and applications of chelating or complexing agents in minerals separations. In Reagents in Mineral Technology; Somasundaran, P.; Moudgil, B. J., Eds.; Marcel Dekker: New York, 1987; pp 257-334. (15) Marabini, A. M. Criteria for the design and synthesis of chelating reagents for flotation. In Emerging Separation Technologies for Metals and Fuels; Lakshmanan, V. I., Bautista, R. G.; Somasundaran, P., Eds.; The Mineral, Metals & Materials Society: Warrendale, PA, 1993; pp 141-152. (16) Gorlovskii, S. I.; Ustinov, D. I. Anomalous foam-forming properties of alkylhydroxamic acids. Kolloid Zh. 1973, 35 (5), 1011. (17) Tandon, S. G.; Priyadarshini, U. Preparation and properties of some N-aryl hydroxamic acids. J. Chem. Eng. Data 1967, 12 (1), 143–144. (18) Xu, M. Q. Modified flotation rate constant and selectivity index. Miner. Eng. 1998, 11 (3), 271–278. (19) Available via the Internet at http://userpages.xfoneusa.net/∼dhyams/ cftp.htm.
ReceiVed for reView February 23, 2009 ReVised manuscript receiVed April 21, 2009 Accepted May 2, 2009 IE900305R
