KLINGBERG, Anders (Ödsmål 145, Henån, S-473 93, SE)
LANNEFORS, Christina Josefin (Norra Skeppspromenaden 13, Göteborg, S-417 63, SE)
GUSTAFSSON, Jan Olof (Olserödsgatan 47, Kungälv, S-442 42, SE)
KLINGBERG, Anders (Ödsmål 145, Henån, S-473 93, SE)
LANNEFORS, Christina Josefin (Norra Skeppspromenaden 13, Göteborg, S-417 63, SE)
| CLAIMS
1. A process for enriching an iron mineral from a silicate-containing iron ore containing coarse silicates having K 8 o ≥ 110 μm by reverse flotation of the ore using a collecting composition comprising a) one or more compounds having the formula R 1 O-A-NH(CH 2 ) n NH 2 (I) wherein R 1 is a straight or branched hydrocarbyl group with 12-15 carbon atoms, A is a group -CH 2 CHXCH 2 -, wherein X is hydrogen or a hydroxyl group, preferably hydrogen, and n is a number 2-6, preferably 2-3, and most preferably 3; and b) a compound selected from the group of compounds described by the formulae
R 2 (0-A) x -NH 2 (II) wherein R 2 is a straight or branched hydrocarbyl group with 12-24, preferably 12-18, and most preferably 13-18 carbon atoms, x = 0 or 1 , and A is as described above; and
R 3 (O-A) y -NH(CH 2 ) n NH 2 wherein R 3 is a straight or branched hydrocarbyl group with 16-24, preferably 16-18 carbon atoms, y = 0 or 1 , and A and n are as described above; and wherein the weight ratio between a) and b) is 1 :5 to 5:1.
2. A process according to claim 1 wherein b) is III and the weight ratio between a) and b) is 1 :4 to 1 :1.
3. A process according to claim 1 -2 comprising a further component c) which is a depressing agent for the iron mineral.
4. A process according to claim 3 wherein the depressing agent is chosen from the group of hydrophilic polysaccharides.
5. A process according to claims 1 -4 wherein the first component a) of the formulation is described by the formula
R 1 OC 3 H 6 NHC 3 H 6 NH 2 (Ia) wherein R 1 is a straight or branched hydrocarbyl group with 12-15 carbon atoms, and the second component b) of the formulation is selected from the group of compounds described by the formulae
R 2 NH 2 (Ha), R 3 NHC 3 H 6 NH 2 (Ilia),
R 2 OC 3 H 6 NH 2 (Mb), and
R 3 OC 3 H 6 NHC 3 H 6 NH 2 (MIb)
wherein R 2 is a straight or branched hydrocarbyl group with 12-24 carbon atoms and R 3 is a straight or branched hydrocarbyl group with 16-24 carbon atoms.
6. A process according to claims 1 -5 wherein component b) has formula Ma or Ilia.
7. A process according to claims 1 -6 wherein the collecting composition further contains a frother.
8. A process according to claim 7 wherein the frother is 2-ethylhexanol.
9. A process according to claims 1 -8 wherein the amine components in the collecting composition are present as ammonium salts in an amount of at least 20% by mole.
10. A process according to claims 1 -9 where the collecting composition comprises a) N-(3-isothdecoxypropyl)-1 ,3-propane diamine, b) a fatty monoamine of formula Ma, wherein R 2 is a hydrocarbyl group with 12-18 carbon atoms, and c) a hydrophilic polysaccharide.
11. A process according to claim 10 wherein component c) is starch. |
AMINE FORMULATIONS FOR REVERSE FROTH FLOTATION OF SILICATES FROM IRON ORE
The present invention relates to a reverse froth flotation process for removal of silicates from iron ore having K 8 o ≥ 110 μm using formulations comprising alkyl ether diamine and alkyl ether monoamine, alkylamine or alkyl diamine.
Iron ore often contains considerable amounts of silicates. The presence of silicates has a detrimental effect on the quality of the iron, and it is therefore essential that the silicate content of the iron mineral can be considerably reduced. A common process of removing silicates from iron ore is reversed froth flotation, where the silicates are enriched in the flotate and leave the system with the froth, and the iron ends up in the bottom fraction. When using reverse froth flotation, generally the iron ore bottom fraction either contains a low level of SiO2 and has a low recovery of iron, or it contains a high level of Siθ2 and has a high recovery of iron. In particular, the presence of coarse silicates (particle size > 110 μm) in the system has a negative effect on the iron recovery. Various solutions have been proposed in the prior art to increase iron recovery and reduce SiO2 levels. Very often these solutions have involved grinding the ores to fine particles.
Grinding (also referred to as milling) is thus an important step of the flotation process, which step is necessary to liberate the valuable species in the ore. The particle size to which an ore must be size-reduced in order to liberate the mineral values from associated gangue or non-values is called the liberation size, and this will vary from ore to ore. In theory, the ore should not be ground further when the liberation size of the ore has been reached, since this will unnecessarily consume more energy and produce comparatively larger fractions of the very fine particles which are detrimental to the flotation process. However, as is stated in Mineral Processing Technology, sixth edition, by B.A. Wills, page 278, "...the optimum grinding size of the particles depends not only
on their grain size, but also on their floatability. Initial examination of the ore should be made to determine the degree of liberation in terms of particle size in order to estimate the required fineness of grind. Testwork should then be carried out over a range of grinding sizes in conjunction with flotation tests in order to determine the optimum mesh of grind. In certain cases, it may be necessary to overgrind the ore in order that the particles are small enough to be lifted by the air-bubbles." Accordingly, it is not uncommon to mill ores to particle sizes below the liberation size in order to improve the flotation process, particularly to reduce the SiO2 level in the iron-fraction. It is clear that from an energy and milling-efficiency point of view, such overmilling is undesired.
It is noted that in order to describe the distribution of particle sizes in an ore, the K 8 O value is generally used. The factor K 8 o is defined as the sieve opening through which 80% by weight of the material of the mineral sample passes. If an ore has a K 8 o value of 110 μm, this means that 80% by weight of the material in the mineral sample will pass through a 110 μm sieve, and thus 20% by weight of the material of the sample will consist of particles having a diameter that is larger than 110 μm.
US 6,076,682 discloses a process for enriching iron mineral from a silicate- containing iron ore by carrying out a reverse froth flotation in the presence of a silicate collecting agent containing a combination of at least one primary ether monoamine and at least one primary ether polyamine, where each of the ether amines contains an aliphatic hydrocarbyl group having 6-22 carbon atoms and the weight ratio of ether monoamine to ether polyamine is 1 :4-4:1 , and a depressing agent for the iron mineral. The working examples were performed with an iron ore having a K 80 of about 75 μm.
SE 421 177 discloses a way to enrich oxidic minerals, especially iron minerals, by separation of silicate-containing gangues by foam flotation using a collector that is a combination of C8-C24 alkyl, preferably C10-C16 alkyl, fatty amines
(mono-, di- or polyamines) and C8-C24 alkyl, preferably C8-C14-alkyl, ether diamines. The weight ratio of ether diamine to fatty amine is defined to be larger than 1.1 :1. The K 8 o for the iron ore used in the working examples of this patent publication is 85 μm. CA-A1 -2 205 886 relates to compositions of matter comprising a blend of (a) an amine component, which is one or more compounds selected from the group consisting of alkyl amines, alkyl diamines, alkyl polyamines, ether amines and ether polyamines and mixtures thereof; and (b) a C3-C24 carboxylic acid or mixtures thereof; for use e.g. in the froth flotation of silica from iron ore. This patent publication is silent about the K 8 o-value of the mineral samples flotated.
In all this art the ores were milled to relatively small particles, most likely to facilitate the flotation process in order to optimize SiO2 removal. The presence of very small particles also indicates that the ore is milled to below the liberation size. However, there is still a desire to be able to flotate silicate-containing iron ores having a K 8 o ≥ 110 μm, since there will be less energy consumption if the ores to be flotated do not need to be ground to a smaller size and because it was found that the liberation size is often greater than 110 μm. Furthermore if the ore is less finely ground, there will be lower iron fine particle losses, further increasing the iron yield.
When evaluating iron ores with a K 8 o ≥ 110 μm it was observed that the collectors used in the prior art for the more finely ground ores do not work very well, which again explains why traditionally smaller particle sizes were used. Therefore, there still is a need for a process wherein ores with a K 80 ≥ 110 μm, comprising an iron-mineral, can be reverse flotated to effectively remove silicate, using collecting agents that at the same time will not have a negative effect on the recovery of iron.
Now it has surprisingly been found that low silicate levels as well as high recovery of iron can be achieved for silicate-containing iron ores having K 8 o ≥ 110 μm, preferably > 115 μm and most preferably > 120 μm, by reverse flotation of the ore using a specific collecting composition comprising a) one or more C12-C15 alkyl ether diamines b) one or more C12-C24, preferably C12-C18, and most preferably C13-C18, alkyl ether monoamines, one or more C12-C24, preferably C12-C18, alkyl monoamines, one or more C16-C24, preferably C16-C18, alkyl ether diamines or one or more C16-C24, preferably C16-C18, alkyl diamines, or mixtures thereof c) and optionally a depressing agent for the iron mineral, wherein the weight ratio between a) and b) is 1 :5 to 5:1 , preferably 1 :4 to 4:1 , more preferably 1 :4 to 3:1.
This surprising effect is probably due to the fact that this mixture of flotating aids is capable of flotating larger silicate particles in these reverse flotation processes.
The maximum K 8 o value from a mineralogical point of view is determined by the milling needed to liberate the minerals. Thus, the less milling needed, the higher the value of K 8 o- Preferably, the K 8 o of the ore to be processed in accordance with the invention is at most 200 μm, more preferably at most 180 μm, even more preferably at most 160 μm, and most preferably at most 150 μm.
The first component a) is described by the general formula R 1 O-A-NH(CH 2 ) n NH 2 (I) wherein R 1 is a straight or branched hydrocarbyl group with 12-15 carbon atoms, A is a group -CH 2 CHXCH 2 -, wherein X is hydrogen or a hydroxyl group, preferably hydrogen, and n is a number 2-6, preferably 2-3, and most preferably 3;
the second component b) of the formulation is selected from the group of compounds described by the formulae
R 2 (0-A) x -NH 2 (II) wherein R 2 is a straight or branched hydrocarbyl group with 12-24, preferably 12-18, and most preferably 13-18 carbon atoms, x = O or 1 , preferably O, and A is as described above; and
R 3 (O-A) y -NH(CH 2 )nNH 2 (III) wherein R 3 is a straight or branched hydrocarbyl group with 16-24, preferably 16-18 carbon atoms, y = 0 or 1 , preferably 0, and A and n are as described above; and wherein the weight ratio between a) and b) is 1 :5 to 5:1.
In another embodiment, the first component a) of the formulation is of the formula R 1 OC 3 H 6 NHC 3 H 6 NH 2 (Ia) wherein R 1 is a straight or branched, preferably branched, hydrocarbyl group with 12-15 carbon atoms, and the second component b) of the formulation is selected from the group of compounds described by the formulae R 2 NH 2 (Ma),
R 3 NHC 3 H 6 NH 2 (Ilia),
R 2 OC 3 H 6 NH 2 (Mb), and
R 3 OC 3 H 6 NHC 3 H 6 NH 2 (MIb), wherein R 2 is a straight or branched hydrocarbyl group with 12-24, preferably 12-18, and most preferably 13-18 carbon atoms, and R 3 is a straight or branched hydrocarbyl group with 16-24, preferably 16-18 carbon atoms.
Most preferred are the embodiments where component b) has formula Ma or Ilia.
For any embodiment the weight ratio between a) and b) is 1 :5 to 5:1 , preferably 1 :4 to 4:1 , and most preferably 1 :4 to 3:1.
In embodiments where b) is a compound of formula (III) it is especially preferred that the weight ratio between a) and b) is < 1 :1 , preferably in the range 1 :4 to 1 :1 , but for the other embodiments the wider range is more applicable.
The use of alkyl monoamines according to formula (Ma) as component b) could be advantageous for economic reasons, since alkyl monoamines generally are cheaper than alkyl diamines and alkyl ether mono- and diamines. The compositions containing (Ma) also are easy to formulate, and the collecting compositions are very effective.
Compositions where component b) is an alkyl diamine according to formula (Ilia) are also effective, but in this case compounds having saturated alkyl chains have a greater risk of precipitating, and thus compounds having unsaturated alkyl chains are more suitable.
Compositions where b) is an alkyl ether monoamine according to formula (Mb) or an alkyl ether diamine of formula (MIb) can suitably be used at low temperatures, compounds having branched alkyl chains in particular will confer desirable physical properties on the compounds, such as lower pour points.
Suitable examples of groups R 1 are dodecyl, 2-butyloctyl, methyl-branched C13-alkyl (isothdecyl), tetradecyl, and methyl-branched C15-alkyl. Compounds having a branched alkyl group are especially preferred. Suitable examples of groups R 2 are dodecyl, 2-butyloctyl, methyl-branched C13-alkyl (isotridecyl), tetradecyl, C14-C15-alkyl, methyl-branched C15-alkyl, hexadecyl, C16-C17-alkyl, octadecyl, tallow alkyl, rapeseed alkyl, soya alkyl, oleyl, and erucyl.
Suitable examples of groups R 3 are hexadecyl, octadecyl, C16-C17-alkyl, tallow alkyl, rapeseed alkyl, soya alkyl, oleyl, linoleyl, linolenyl, erucyl, and behenyl. Compounds having branched alkyl groups are especially preferred, and among
the compounds derived from natural sources those having unsaturated alkyl chains are especially preferred, because they are easier to formulate.
Examples of suitable alkyl ether diamines to be used in the collecting compositions as component a) are N-[3-(dodecoxy)propyl]-1 ,3-propane diamine, N-[3-(2-butyloctoxy)propyl]-1 ,3-propane diamine, N-[3-(tridecoxy)- propyl]-1 ,3-propane diamine, N-[3-(tetradecoxy)propyl]-1 ,3-propane diamine, and N-[3-(C15-alkoxy)propyl]-1 ,3-propane diamine. Examples of suitable alkyl ether amines to be used in the formulations are 3- (dodecoxy)propylamine, 3-[(coco alkyl)oxy]propylamine, 3-(2-butyloctoxy)- propylamine, 3-(isothdecoxy)propylamine, 3-(tetradecoxy)propylamine, 3-(C14- C15-alkoxy)propylamine, 3-(hexadecoxy)propylamine, 3-(octadecoxy)propyl- amine, 3-[(rapeseed alkyl)oxy]propylamine, 3-[(soya alkyl)oxy]propylamine, 3- (octadecenoxy)propylamine, 3-[(tallow alkyl)oxy]propylamine, and 3-(erucoxy)- propylamine.
Examples of suitable alkyl monoamines to be used in the formulations are n- dodecyl amine, (coco alkyl)amine, n-tetradecyl amine, n-hexadecyl amine, n- octadecyl amine, oleyl amine, (tallow alkyl)amine, (rapeseed alkyl)amine, (soya alkyl)amine, and erucyl amine. Examples of suitable alkyl diamines to be used in the formulations are N- hexadecyl-thmethylene diamine, N-octadecyl-thmethylene diamine, N-oleyl- trimethylene diamine, N-(rapeseed alkyl)-thmethylene diamine, N-(soya alkyl)- trimethylene diamine, N-(tallow alkyl)-thmethylene diamine, N-linoleyl- trimethylene diamine, N-linolenyl-thmethylene diamine, N-erucyl-trimethylene diamine, and N-behenyl-thmethylene diamine.
Unprotonated amines with the formulae described above (formulae I-V) are difficult to disperse in mineral/water systems without the aid of heating or vigorous stirring. Even with heating and stirring, the dispersions are not stable. A common practice for improving the dispersibility of amines is to prepare the
corresponding ammonium salts by adding acid to the amine, forming at least 20% by mole ammonium salt, preferably before the amine compounds are diluted with water. Examples of suitable acids are lower organic acids, such as formic acid, acetic acid, and propionic acid; and inorganic acids, such as hydrochloric acid. Complete formation of ammonium salt is not needed to form a stable dispersion. In an aqueous mixture the amine compounds are therefore suitably present partly as ammonium salts. For example, 20-70, preferably 25- 50% of the amine groups are transferred to ammonium groups, which may be achieved by adding c. 10% by weight acetic acid to the amine compounds of the invention.
Preferably, the flotation is performed in the conventional pH-range of 8-11 in order to obtain the right surface charge of the minerals.
A conventional depressing agent, such as a hydrophilic polysaccharide, e.g. different kinds of starches, may be used in a conventional quantity sufficient to cover the iron ore surface in the amount needed. The depressing agent is normally added in an amount of 10 to 1 ,000 g per tonne of ore.
An additional way of improving the efficiency of the system according to the invention is to add a froth regulator. Although froth regulators such as methylisobutyl carbinol and alcohols having a C6-C12 alkyl chain, such as 2- ethylhexanol, and alcohols alkoxylated with ethylene oxide and/or propylene oxide, e.g. propoxylated methanol and other ethoxylated/propoxylated short- chain alcohols, are conventionally used, the addition of a froth regulator to the flotation systems comprising our claimed collectors will surprisingly result in a better iron recovery. This is in contrast with prior art flotation compositions containing compounds having shorter chain lengths. For such systems we found that frothers typically have an adverse effect.
Further conventional additives may be added to the flotation system, such as pH-regulating agents, co-collectors, and extender oils.
The principal ores of iron which are suitable for treatment according to the invention are hematite and magnetite ores.
The present invention is further illustrated by the following examples.
EXAMPLES
General Experimental
Flotation preparation
Collector (a+b) + frother
1 g of collector + frother (0.9 g amino compounds (a+b) neutralized with 10% by weight of acetic acid + 0.1 g frother) was diluted with 99 g of distilled water. The solution was stirred for at least 30 min before use.
In all formulations containing frother, 2-ethylhexanol is used as the frother in an amount of 10% by weight. Frother is added to all formulations below unless otherwise stated. Depressant (c) (optional) 1 % by weight solution of depressant was used. 4 g of unmodified regular corn starch containing approximately 73% amylopectin and 27% amylase (Sigma Aldrich) were diluted in 56 g of distilled water. 20 g of 5% by weight NaOH solution were added slowly. The solution was stirred until a gel formed and then an additional 320 ml of distilled water were added. Flotation procedure
The ground ore sample (770 g) was (optionally) conditioned with depressant c for 5 min in the flotation cell at a concentration of 60% by weight of solid in water, and then additional water was added until the concentration of solid was 40% by weight (= 40% pulp density). All water added during the flotation was tap water. The speed of the rotor was 1 ,000 rpm. The pH of the 40% pulp was
then adjusted to 10.5 with 5% NaOH solution, after which the components a + b of the collector composition + frother were added as a 1 % by weight water solution. The actual dosages are described in each of the examples. The dosages are chosen according to recommendations for the specific ore samples used. The alkaline pulp with the added components was conditioned for 1 min before the air and the automatic froth scrapers were turned on. The flotation was performed at 20-25 0 C using an air flow of 3 l/min and a scraping frequency of 15 scrapes/min. The pulp level was kept constant by the addition of water below the pulp surface. The flotation was continued until complete exhaustion of mineralized froth was achieved.
The flotation was performed in a sequence with three additions of collector and optional frother followed by a flotation step after each addition, so called stepwise rougher flotation. Each froth product was dried, weighed, and analyzed with respect to Siθ 2 content. After completion of the flotation, the bottom concentrate was withdrawn, dried, and analyzed with respect to SiO2 content and Fe 2 Os content. For each completed flotation experiment the mass balance and SiO2 grades were used to calculate the iron recovery and Siθ2 grade in each flotation step, and these results were then plotted in a grade-recovery graph. From this graph the iron recovery was determined by interpolation at a given SiO2 grade for this specific flotation experiment. In the Tables below, this SiO 2 grade is set at 2.0%.
Sieve analyses
The sieve analyses of the mineral samples were performed in accordance with BS 1796 and DIN 66165, with the sieves used conforming to the standard DIN ISO 3310/1. BS 1796 generally describes a sieve analysis using a shaking machine, the latter being adapted in accordance with DIN 66165. A detailed description of the sieve analysis, based on BS 1976, is found in B.A. Wills,
Mineral Processing Technology, 6 th Ed, 1997, pages 96-100.
Example 1
Iron ore containing 73.3% Fe 2 O 3 and 24.8 % by weight of SiO 2 was used in this
Example to illustrate the invention.
The sieve analysis for this ore is displayed in Table 1.
Table 1
Example 1a
In this example formulations containing an ether diamine and an ether monoamine are used for flotating the ore exhibiting the sieve analysis of Table 1. All formulations contain 10% by weight of 2-ethylhexanol as a frother. The used dosage levels are 50, 30, and 30 g/t of ore (corresponding to 34.7, 20.8, and 20.8 mg of components a+b and 3.9, 2.3, and 2.3 mg of frother added to the flotation cell, respectively).
Table 2
Flotations Nos. 120, 52, and 54 show that a better effect is obtained when the ether monoamine component has a hydrophobic group containing 12 or more carbon atoms.
Example 1b
In this example formulations containing an ether diamine and an alkyl monoamine or alkyl diamine are used for flotating the ore exhibiting the sieve analysis of Table 1. All formulations contain 10% by weight of 2-ethylhexanol as a frother. The used dosage levels are 50, 30, and 30 g/t of ore (corresponding to 34.7, 20.8, and 20.8 mg of components a+b and 3.85, 2.3, and 2.3 mg of frother added to the flotation cell, respectively).
Table 3
*For the comparison experiment it was not possible to perform the flotation due to the weak foam formation, the oleyl group is derived from rapeseed oil
Flotations Nos. 29, 55, 76, and 75 show that a synergistic effect is achieved by using a combination of an alkyl ether diamine and an alkyl diamine in the collecting composition, as compared to using the single compounds. Flotations Nos. 29, 121 , 122, and 126 show that the use of collecting compositions containing an alkyl ether diamine and an alkyl diamine where a higher amount of the alkyl diamine is present is beneficial, but that the use of the alkyl diamine alone is detrimental.
Flotations Nos. 29, 87, 114, and 113 show that the use of collecting compositions containing an alkyl ether diamine and an alkylamine where a higher amount of the alkylamine is present is beneficial, but that the use of the alkylamine alone is detrimental.
Flotations Nos. 123, 124, 125, and 50 show that when using a collecting composition containing an ether diamine and an alkyl diamine where the alkyl diamine has a coco alkyl hydrophobic group (which is about C12C14) or lower, the iron recovery is not very good, whereas for a collecting composition containing an alkyl ether diamine and an alkyl monoamine, a coco alkyl hydrophobic group is sufficient to obtain a good iron recovery.
Example 2 A comparison test was performed using an ore sample where the ore having the sieve analysis displayed in Table 1 had been further sieved to remove the coarser particles. The sieve analysis of this sample is displayed in Table 6. The ore sample displayed in Table 6 contains 72.1 % Fe 2 Os and 26.5% by weight of SiO 2 .
Table 6
In this example formulations containing an alkyl ether diamine and an alkyl monoamine or an alkyl ether diamine and an alkyl ether monoamine are used for flotating the coarser particle ore (C) exhibiting the sieve analysis of Table 1 (K 8 O = 124 μm) as compared to the finer particle ore (F) exhibiting the sieve analysis of Table 6 (K 8 o = 79.5 μm). All formulations contain 10% by weight of 2-ethylhexanol as a frother. The used dosage levels are 50, 30, and 30 g/t of ore (corresponding to 34.7, 20.8, and 20.8 mg of components a+b and 3.9, 2.3, and 2.3 mg of frother added to the flotation cell) for the ore sample described in Table 6.
Table 7
For the comparison experiment it was not possible to perform the flotation due to the weak foam formation. Experiment performed on the finer particle ore 4 Experiment performed on the coarser particle ore
In all cases the specific collecting compositions according to the present invention work better for the coarse ore (K 8 o = 124 μm) than for the fine ore (K 80 = 79.5). For the collecting compositions outside the scope of the present invention, there is no difference between the flotations performed on fine and coarse ores, and the Fe-recovery is smaller than for the compositions according to the invention.
Example 3
In this example the effect of adding a frother to the collecting compositions is investigated.
The ore of Table 1 was used. The used dosage levels when 10% frother (2- ethylhexanol) is used are 50, 30, and 30 g/t of ore (corresponding to 34.7, 20.8, and 20.8 mg of components a+b and 3.85, 2.3, and 2.3 mg of frother added to the flotation cell, respectively). The used dosage levels when no frother is added are 50, 30, and 30 g/t (corresponding to 38.6, 23.1 , and 23.1 mg of components a+b added to the flotation cell).
Table 8
This example shows that for the composition according to the invention, it is advantageous to add a frother, whereas for the comparison compositions containing compounds having shorter chain lengths, it is more advantageous not to add a frother.