2-MERCAPTO-BENZOXAZOLE DERIVATIVES AS COLLECTORS FOR THE SELECTIVE FLOTATION OF METAL ORES

Abstract: 2-mercapto-benzoxazole derivatives, having formula (I): wherein: R, R1, R2 and R3, being the same or different, are each H, or a straight or branched alkyl, alkoxyl or hydroxalkyl group with up to 12 carbon atoms; and M is H, Na, R, Li, Cs or NH4; are employed as collectors for the selective flotation of sulphide ores to separate mineral salts containing copper, zinc and silver.

Description: 2-MERCAPTO-BENZOXAZOLE DERIVATIVES AS COLLECTORS FOR THE SELECTIVE FLOTATION OF METAL ORES SPECIFICATION This invention concerns the use of 2-mercapto≡ benzoxazole derivatives as collectors for the selective flotation of metal ores, as well as the related flotation process. More particularly, this invention relates to the selective flotation of those ores which are substantially in form of sulphides, to separate materials containing copper, zinc and silver. As known in the art, flotation techniques use the selective activity of some special reagents on the various mineral components in order to separate one of said components or to provide an enrichment of the product in one of such components. The reagents employed for this purpose are commonly referred to as flotation "collectors", or "collecting agents" (or "collection agents"). The known or used collectors of the existing art are classified in two main classes, depending upon their ionic or nonionic nature. The use of non-ionic oily or neutral collectors is generally restricted to the flotation of non polar minerals, whilst the ionic collectors are used for all the other ore types. The ionic collectors are absorbed on the ore surface through an essentially chemical bond. The conventional collectors suitable for the sulphide mineral flotation are mercaptan-based (i.e. thiol type) compounds and, among them, xanthates are the most widespread. However, such agents are effective on the whole sulphide class, without showing any specific selectivity within the said class. While in most cases this property does not involve any problem, in some specific cases the composition of the ore to be treated is such that the use of modifying compounds is needed to make the collecting activity more specific. Actually, the ore could contain a number of different commercially valuable sulphides forming an intimate admixture with each other and with the gangue, and each one of said sulphides could be present in such amount as to justify its recovery. For example, this occurs with complex sulphide ores consisting of intimate associations of chalcopyrite (CuFeS-) , sphalerite (ZnS) and galena (PbS) into a pyrite matrix, which associations could also contain a valuable amount of silver and, in some cases, of gold. The use of modifiers often causes strong problems without giving the desired results, particularly when treating ores of a complex composition, whose surface features are not sufficiently defined. It is clear from the foregoing that the use of collectors capable of bonding given sulphides in a selective way with respect to other sulphides would be highly recommended in some cases. The use of such collectors would limit the inclusion of undesired materials, thus resulting in higher recoveries of the desired metal(s), at higher concentrations. According to this invention, it has been found that a class of mercapto-benzoxazole compounds shows superior selectivity in sulphide mineral flotation, thus affording effective separation between minerals of this category. Compounds having some analogy with the compounds of this invention, specifically some mercapto-benzo≡ thiazole derivatives, are disclosed in Italian patent 1,181,890 as used in the selective flotation of lead and zinc ores. Such disclosure generically refers to both oxide and sulphide ores and evidences the ability of mercapto-benzot iazoles to separate lead ores, such as galena (PbS), from zinc ores, such as sphalerite (ZnS), by selectively floating the former with respect to the latter. To this regard it should be noted that, according to the known art, zinc can be floated only when previously activated by treatment with copper sulphate, in order to enrich the ore particle surface in copper salts. However, the mercapto-benzothiazole-based collectors showed a comparable effectiveness, for instance, in selectively floating chalcopyrite (CuFeS-), and consequently they cannot be used to separate the latter from galena when raw ores comprising both materials are to be treated. On the contrary, the mercapto-benzoxazole derivatives of this invention have the ability to float sulphides of copper and silver, as well as zinc sulphides that have been previously properly activated, but they are unable to float lead and iron sulphides, nor zinc sulphides that have not been previously activated. It is evident that such ability allows to obtain single-metal concentrates by flotation also when starting from complex sulphides, without needing to use any modifier. Therefore, the present invention specifically provides the use of 2-mercapto-benzoxazole derivatives of the formula: wherein: R, R,, R 2 and R 3 , being the same or different, are each H, or a straight or branched alkyl, alkoxyl or hydroxalkyl group with up to 12 carbon atoms; and M is H, Na, K, Li, Cs or NH ή ; as collectors for the selective flotation of metal ores of the sulphide type, for the separation by flotation of minerals containing copper, zinc and silver. Although some of the compounds according to this invention are known per se, the use thereof in the field of ore processing does not appear to have been suggested before, nor does, specifically, the use as selective flotation collectors. According to a preferred embodiment, the invention provides the use, as selective flotation collectors for obtaining the separations mentioned before, of 2-mercapto-benzoxazoles having an alkyl group with 1-9 carbon atoms, preferably linked at the 5- or 6-positions on the benzoxazole ring, and more preferably linked at the 5-position. The collectors of this invention are advantageously employed to process materials containing chalcopyrite (CuFeS 2 ), covellite (CuS), chalcocite (Cu 2 S), sphalerite (ZnS), galena (PbS), pyrite (FeS-,), silicate and/or carbonate-based gangues and mixtures thereof. As the collectors of this invention float copper sulphides but do not float iron or lead sulphides, nor the not previously activated zinc sulphides, a separation of the various desired components fr -n raw ores comprising complex sulphides could be obtained by recovering copper as a first step, by means of the collector of this invention, followed by a lead recovery, using the collectors of the existing art, and then by a zinc recovery, after having activated the remaining slurry with copper sulphate. For instance, this procedure could be satisfactorily used to process ores comprising chalcopyrite in a mixture with galena and sphalerite, together with pyrite and other gangues, when it is desired to recover all of the first three named minerals. In this case, the use of the ercapto-benzotiazole derivatives of the prior art as collecting agents would not afford the desired separation of chalcopyrite from galena. Moreover, when the ore to be processed comprises an appreciable silver amount, the collectors of this invention allow, because of their selectivity for silver, to recover silver in the floating material, together with the copper compounds, if any. The collectors of this invention can also be used in a mixture with other conventional collectors, such as xanthates, as well as with the zinc activators, if any, in order to obtain a bulk concentrate, e.g. a concen= trate of copper, lead and zinc minerals. The process using the collectors of this invention is particularly efficient when carried out at a pH range from 4 to 12, particularly from 6 to 10, by using the collector at a rate of 10 to 200 g per kg of the ore to be floated. In such conditions the metal recovery is close to 100%. The ercapto-benzoxazole compounds of this invention have preferably an alkyl, alkoxyl or hydroxyalkyl chain linked to the benzoxazole ring, preferably at the 5- or 6-positions. Said chain provides the molecule with some hydrophobic character, which is advantageous in the flotation process. Actually, besides being an organic chelating agent, a flotation collector must also pro≡ vide an adequate hydrophoby level, in order to facili≡ tate the flotation of the ore particles which it bonds during the process. However, the balance between chelating and hydrophobic properties must be such as to avoid any ore particle erosion due to a too strong bonding of the collector on the mineral surface. It is clear that the various features that a collector must have in order to perform its selective activity are strictly depending upon the nature of the ore to be floated. The methods for preparing some of the collectors of this invention are described in the following examples, which are intended for the purpose of illustration only. EXAMPLE 1 Preparation of a collector having the following formu≡ la: 22 parts of (85%) potassium hydroxide was added dropw≡ ise to 90 parts of water. 12.3 parts of para-methyl- ortho-aminophenol was then added at room temperature. Stirring was carried out for 1 hour at 25°C, then 8.36 parts of carbon sulphide was added dropwise. Stirring was carried out for 2 hours at 25°C, followed by heati≡ ng at 45°C. The mixture was allowed to react for 2 hours. The development of the reaction was monitored by chromatography on a silicagel thin layer, with 8:2 by volume, normal exane/ethyl acetate mixture as eluent (the salt-free product obtained by treatment with acetic acid showed a Rf = 0.4). When the reaction was completed, the product was filtered and the mother liquor was removed from the precipitated product on the filter, using 20 parts of methyl alcohol. The product was dried in oven under vacuum at appr. 50°C-, obtaining finally 18.4 parts of dried raw material. 2 g of such product was dissolved in water and its pH was adjusted to 5, using acetic acid, providing "1.6 g of: which is insoluble in the medium. The product obtained is unitary when analyzed by TLC, and has a melting point 216.5-217°C. Based on the above data, the purity of the technical product is 80 %. EXAMPLE 2 Preparation of a collector having the following formu≡ la: To 300 parts of 95% ethanol 41.1 parts of 4-ethyl≡ 2-aminophenol was added, as well as 45 parts of water and 52.8 parts of potassium ethyl-xanthate. The mixture was refluxed for 3 hours and the solvent was distilled off when the reaction was completed. The solid product was treated with 50 parts of acetone, then filtered, and the solid product was treated again with 30 parts of acetone. Finally, the material was dried in a vacuum oven at 50°C, giving 52.2 parts of the dried product. The HPLC analysis of the final product showed a 78 % titer. EXAMPLE 3 Preparation of a collector having the following formu≡ la: 30 parts of (85%) potassium hydroxide was added to 30 parts of water. 15.3 parts of 2-amino-5-etoxyphenol was added at room temperature. Stirring was carried out for 1 hour at 25°C, then 8.6 parts of carbon sulphide was added dropwise in 40 minutes. The mixture was heated at 45°C for 2 hours, then the reacted product was filte= red, and the mother liquor was removed from the precis pitated product with 50 parts of 10% brine. The product was dried in a vacuum oven at 50°C yield≡ ing 19.5 parts of dried product. The HPLC analysis showed a 87.2% titer. A small amount of the product, which was dissolved in water and treated with acetic acid at pH of about 5, precipitated. After filtration and drying, the salt- free product showed 214°C as melting point. FLOTATION TESTS The. properties of the compounds according to this invention in the selective flotation of ores essen≡ tially comprising sulphides are shown in the following practical examples. The general conditions of the flotation tests, as described in the examples, were as follows: -Grinding: from a fractured material which was granu= lated to a size lower than 3 mm, a 900 g sample was picked up, placed into a laboratory rod mill together with. 900 g of mains water and the mixture was ground for a time sufficient to reduce 90% of the sample to sizes able to release ia v.seful minerals; then the sample was extracted and diluted with 2 litres of water. -Flotation: the sample was introduced into the 2 litre cell of a Denver flotation equipment, and was stirred by the equipment rotor. While keeping the air inlet valve closed, one of the collectors under test was added and allowed to condition for 2 minutes. There≡ after, a foaming agent (frothing agent) was added. At the end of the conditioning time, during which the pH was continuously controlled, the air suction valve was opened and the rotor speed was adjusted to 1200 r.p.m., thus providing a foam carrying the mineral. The foam was removed by a hand shovel until exhaustion thereof, or, in case of persistency, till the complete removal of the mineral from the foam. Methyl-isobuthylcarbinol (MIBC) was used as foaming agent in all of the tests reported below. EXAMPLE 4 In order to carry out a comparative test between the compound of Example 1 and a conventional collector, i.e. potassium amylxanthate, the test was carried out on a raw ore which is currently treated with said known collector, in order to recover copper therefrom. Raw material analysis: Cu 0.65%, substantially as chalcopyrite; Pb 2%, substantially as galena; Zn 5.2%, substantially as sphalerite; Fe 35.2%, substantially as pyrite; Flotation granulometry: d 80 43 p; Collector: potassium amylxanthate? 80 mg/kg, pH 7 Weight (%) Cu (%) Recov.'d Cu (%) Floating material 25.15 2.11 73.5 Waste 74.85 0.25 26.5 Collector: as per Example 1; 80 mg/kg, pH 7 Weight (%) Cu (%) Recov.'d Cu (%) Floating material 7.65 7.14 73.9 Waste 92.35 0.21 26.1 From the above results it may be noted that, at the same recovery rate, the Cu contents of the flotation product obtained according to this invention is more than 3 times that obtained using the prior art product. EXAMPLE 5 A comparative test as the previous one was carried out on a raw material having the same composition, but with coarser granulometry. Flotation granulometry: d 80 56 um; Collector: potassium amylxanthate; 80 mg/kg, pH 9. Weight (%) Cu (%) Recov.'d Cu (%) Floating material 15.04 3.06 66.0 Waste 84.96 0.28 34.0 Collector: as per Example 1; 80 mg/kg, pH 9 Weight (%) Cu (%) Recov.'d Cu (%) Floating material 9.57 5.04 66.5 Waste 90 . 43 0. 27 33 . 5 Also in this case it may be noted that, at the same recovery rate, the collector of this invention provides a higher Cu enrichment. Furthermore, the above data show the importance of the mineral releasability, which is associated to the ground granule size. EXAMPLE 6 In order to illustrate the properties of the colle≡ ctors of the closest prior art, i.e. erca≡ pto-benzothiazoles, the results of two flotation tests with 6-propyl-mercapto-benzothiazole are summarized below. Flotation granulometry: d 80 100 ^u ; Collector: 6-propyl-mercaptobenzothiazole; 40 g/t Raw material A analysis: Cu 3.2% as chalcopyrite, associated with pyrite, quartz, dolomite and chlorite; Cu contents (%) Recovered Cu (%) Floating material 17 82 Raw material B analysis: Pb 2.2%, essentially as galena; Zn 5.7%, essentially as sphalerite, associated with pyrite, quartz, siderite, mica, calcite and dolo≡ mite; Pb contents (%) Recovered Pb (%) Floating material 14 85 The above results show that the mercapto-benzothiazole derivative is equally effective in the flotation of both chalcopyrite and galena. Therefore, as previously - indicated, mercapto-benzothiazoles do not possess the necessary selectivity to effectively treat a raw ore comprising both the above-mentioned sulphides. EXAMPLE 7 A mercapto-benzoxazole with an alkyl chain of 9 carbon atoms, i.e. 5-nonyl-mercapto-benzoxazole, was tested as selective flotation agent according to this invention, with the following results: Raw material analysis: Cu 1.07%; Zn 2.49%; Pb 0.89 %; Ag 23 ppm; pyrite; Flotation granulometry: d 80 65 urn; Collector: 5-nonyl-mercaptobenzoxazole, 110 g/t; Weight Cu cont.'s Recoy.Cu Ag cont.'s Recov.Ag (%) (%) (%) (ppm) (%) Float.mat. 19.09 4.31 76.62 54.29 44.62 Residue 80.91 0.49 36.89 19.00 66.18 As shown above, an appreciable amount of silver was recovered in the floating material, together with a considerable fraction of the copper ore. EXAMPLE 8 The selective ability of the collectors of this inve≡ ntion in silver ore recovery is further illustrated in the following example. Raw material analysis: Cu 1.18%; Zn 2.30%; Pb 0.87%; Ag 21 ppm, in a pyrite gangue; Flotation granulometry: d 80 48 um; Collector: compound as per Example 1; 110 g/t; Weight Cu cont.'s Recov.Cu Ag cont.'s Recov.Ag (%) (%) (%) (ppm) (%) Float.mat. 8.20 12.07 84.02 123 47.11 Residue 91.80 0.22 16.98 13 52.89 EXAMPLE 9 The possibility of separating by means of a sequence flotation not only copper, but also zinc, by using the collectors of this invention, is illustrated by the following experimental results. The process steps are described further on. Raw material analysis: Cu 0.9%, essentially as chalco≡ pyrite; Pb 0.63%, essentially as galena; Zn 9.83% as sphalerite; gangue consisting of pyrite, chlorite and silicates. Weight (%) Cu (%) Pb (%) Zn (%) Zn recov.(%) Cu product 8.57 6.10 Pb " 10.25 Zn " 25.42 31.78 81.83 Waste 55.76 0.17 0.14 2.0 11.54 The Cu ore flotation was carried out at neutral pH, using the derivative of Example 2 as collector. From the resulting slurry the lead ore was separated by a further flotation, after having raised the pH, using a conventional collector, such as potassium amylxanthate. After flotation of the Cu and Pb materials, the slurry had a pH 9.9. Then 300 g/t of CuSO, was added, in order to activate the zinc sulphide flotation, and the mixture was allowed to react under stirring for 5 minutes; thereafter, lime wash was added to adjust the pH to 10.3. The of Example 2 was added at a rate of 80 g/t. This mixture was allowed to react for 2 minutes and, following the foaming agent addition, a 5 minutes flotation was carried out. As showed by the results in the foregoing table, the treatment allowed to recover 81.83% of the original zinc contents, besides recovering copper and lead sulphides. EXAMPLE 10 Another advantageous use of the collecting agents of this invention is for recovering zinc from the residues of the Cu and Pb separation, irrespective of how said minerals were separated. A feed of the kind previously described gave the following Analysis: Cu 0.33%; Zn 2.5%; Pb 0.61%; Ag 22 ppm. Activator: CuSO.; 400 g/t; pH 12, using CaO; Collector: compound of Example 1; 110 g/t Weight (%) Zn cont.'s (%) Rec.'d Zn(%) Floating material 5.02 33.14 65.81 Residue 94.98 0.91 34.19 The present invention has been disclosed with specific reference to some preferred embodiments thereof, but it is to be understood that modifications and changes can be brought to it by those who are skilled in the art without departing from its true spirit and scope.

Claims: CLAIMS 1. Use of 2-mercapto-benzoxazole derivatives having the formula: wherein: R, R,, R 2 and R-,, being the same or different, are each H, or a straight or branched alkyl, alkoxyl or hydroxalkyl group with up to 12 carbon atoms; and M is H, Na, K, Li, Cs or NH 4 ; as collectors for the selective flotation of metal ores of the sulphide type. 2. Use according to claim 1 for the separation by flotation of minerals containing copper, zinc and silver. 3. Use according to claims 1 or 2, wherein R, R 2 and R 3 are hydrogen and R, is an alkyl group with 1-9 carbon atoms. 4. Use according to claims 1 or 2, wherein R, , R-, and R 3 are hydrogen and R is an alkyl group with 1-9 carbon atoms. 5. Use according to any one of • the preceding claims, for the selective flotation of materials containing chalcopyrite (CuFeS-), covellite (CuS), chalcocite (Cu 2 S), sphalerite (ZnS), galena (PbS), pyrite (FeS.,), silicate- and/or carbonate-based gangues or mixtures thereof. 6. Use according to any one of the preceding claims for obtaining single metal concentrates by selective flot≡ ation. 7. Use according to any one of claims 1-4, wherein the said derivative is used in a mixture with other collec≡ tors and/or activating agents. 8. Use according to claim 7 for obtaining multimetal concentrates by selective flotation. 9. Use according to any one of the preceding claims, wherein said selective flotation is carried out at a pH comprised between 4 and 12. 10. Use according to claim 9, wherein the pH is compri≡ sed between 6 and 10. 11. Use according to any one of the preceding claims, wherein the said collector is added in an amount comp≡ rised between 10 and 200 mg per kg of the material to be processed. 12. A process for the selective flotation of metal ores in the form of sulphides, comprising the addition of an effective amount of one or more collectors having the formula: S-M wherein: R, R, , R~ and R^, being the same or different, are each. H, or a straight or branched alkyl, alkoxyl or hydroxalkyl group with up to 12 carbon atoms; and M is H, Na, K, Li, Cs or NH 4 ; to a suspension of said ores. 13. Process according to claim 12 for the separation by flotation of minerals containing copper, zinc and silver. 14. Process according to claims 12 or 13 wherein R, R 2 and R 3 are hydrogen and R, is an alkyl group with 1-9 carbon atoms. 15. Process according to claims 12 or 13 wherein R-, R 2 and R 3 are hydrogen and R is an alkyl group with 1-9 carbon atoms. 16. Process according to any one of the preceding claims, for the selective flotation of materials cont≡ aining chalcopyrite (CuFeS 2 ), covellite (CuS), chalco≡ cite (Cu-S), sphalerite (ZnS), galena (PbS), pyrite (FeS-), silicate- and/or carbonate-based gangues or mixtures thereof. 17. Process according to any one of the preceding claims for obtaining single metal concentrates by selective flotation. 18. Process according to any one of claims 11-15, wherein the said derivative is used in a mixture with other collectors and/or activating agents. 19. Process according to claim 18 for obtaining multim≡ etal concentrates by selective flotation. 20. Process according to any one of the preceding claims, wherein said selective flotation is carried out at a pH comprised between 4 and 12. 21. Process according to claim 20, wherein the pH is comprised between 6 and 10. 22. Process according to any one of the preceding claims, wherein the said collector is added in an amount comprised between 10 and 200 mg per kg of the material to be processed.

Inventors: ALESSE VITTORIO, BERGAMINI FABRIZIO, BORNENGO GIORGIO, MARABINI ANNA, ALESSE, VITTORIO, BERGAMINI, FABRIZIO, BORNENGO, GIORGIO, MARABINI, ANNA
Applicants: CONSIGLIO NAZIONALE RICERCHE, CONSIGLIO NAZIONALE DELLE RICERCHE
Application year: 1992
Main classification: B03D1
IPC codes: B03D1, B03D101, B03D103