Arsenic removal from lead concentrate by ozone treatment and reverse flotation

Abstract

Method for removing arsenic mineral from a lead concentrate by reverse flotation with an ozone pre-treatment. The method comprises the steps of: receiving a slurry of the lead concentrate that has previously undergone flotation processes, bubbling ozone into the slurry of the lead concentrate to remove reagents used in previous flotation processes, adding a sulfide salt to the slurry to depress lead mineral, adding an alkali to increase the pH of the slurry, adding a collector and then a frother to the slurry for a reverse flotation processing and floating the arsenic mineral out of the lead mineral to obtain a now-purified lead concentrate.

Claims

1. A method for removing arsenic mineral from a lead concentrate by reverse flotation with an ozone pre-treatment, the method comprising the steps of: a) receiving a slurry of the lead concentrate that has previously undergone flotation processes; b) bubbling ozone into the slurry of the lead concentrate to remove reagents used in previous flotation processes; c) adding a sulfide salt to the slurry to depress lead mineral; d) adding an alkali to increase the pH of the slurry; e) adding a collector and then a frother to the slurry for a reverse flotation processing; and f) floating the arsenic mineral out of the lead mineral to obtain a now-purified lead concentrate.

2. The method of claim 1, wherein the reagents used in the previous flotation processes include dithiophosphinate.

3. The method of claim 1, wherein the sulfide salt is selected from NaSH, Na.sub.2S, SO.sub.2 gas, or combination thereof.

4. The method of claim 1, wherein the alkali is lime.

5. The method of claim 1, wherein the redox potential of the slurry after the step b) of adding the sulfide salt is from about 500 mV to about 300 mV.

6. The method of claim 1, wherein the pH of the slurry after the step c) of adding the alkali is between about 9.0 and about 11.5.

7. The method of claim 1, wherein the pH of the slurry after the step c) of adding the alkali is between about 10.0 and about 11.0.

8. The method of claim 1, wherein the collector is a short carbon-chain anionic collector.

9. The method of claim 8, wherein the short carbon-chain anionic collector comprises 1 to 6 carbon atoms (i.e., C.sub.1 to C.sub.6).

10. The method of claim 9, wherein the short carbon-chain anionic collector is PEX.

11. The method of claim 1, wherein the frother is MIBC.

12. The method of claim 1, wherein the arsenic mineral is arsenopyrite (FeAsS).

13. The method of claim 1, wherein the lead mineral is galena (PbS) that contains silver.

14. The method of claim 1, wherein the lead mineral is galena (PbS) that does not contain silver.

15. The method of claim 1, further comprising the step of: retaining the slurry for a contact time with ozone sufficient in length to maintain the slurry have no more foaming appears at the surface during the step a) of bubbling ozone gas into the slurry.

16. The method of claim 15, wherein the contact time is about 10 to about 20 minutes.

17. The method of claim 1, further comprising the step of adding N.sub.2 or sulfite salts to the slurry after the step of b) to de-aerate the slurry and keep a dissolved oxygen concentration in the slurry less than about 1 mg/L.

18. The method of claim 1, further comprising the step of adding N.sub.2 or sulfite salts to the slurry after the step of b) to de-aerate the slurry and keep a dissolved oxygen concentration in the slurry less than about 0.5 mg/L.

19. The method of claim 1, wherein an arsenic content in the now-purified lead concentrate is about 0.66% or less.

20. A method of for removing arsenic mineral from a lead concentrate by reverse flotation with an ozone pre-treatment, the method comprising the steps of: a) receiving a slurry of the lead concentrate that has previously undergone flotation processes; b) bubbling ozone into the slurry of the lead concentrate to remove dithiophosphinate used in previous flotation processes; c) adding NaHS to the slurry to depress lead mineral; d) adding lime to increase the pH of the slurry; e) adding PEX and then MIBC to the slurry for a reverse flotation processing; and f) floating the arsenic mineral out of the lead mineral to obtain a now-purified lead concentrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

(2) FIG. 1 shows the results achieved by the disclosed methods; and

(3) FIG. 2 shows a block flow diagram of an exemplary embodiment for arsenic removal from lead concentrate.

DESCRIPTION OF PREFERRED EMBODIMENTS

(4) Disclosed are methods and processes for removing arsenic mineral from a lead concentrate through a reverse flotation using ozone treatment, More specifically, the methods and processes disclose use of ozone as an oxidizing agent to remove residual reagents including residual collectors and frothers from a slurry of the lead concentrates that were used in previously flotation process. An exemplary of the residual collector is Aerophine 3418A. The residual collector exists on the particles surface and exists in the water of the slurry. In the disclosed methods and processes, by removing the residual collector, sulfurizing and alkalizing the slurry, the arsenic existing in the slurry is floated out of the lead concentrate, and a now-purified lead concentrate is produced. The ozone advantageously oxidizes the previously used collector still existing on the particles surface and existing in the water of the slurry.

(5) Here, the now-purified lead concentrate refers to an arsenic content in the lead concentrate of about 0.66% or less. The reverse flotation is a process where desired minerals are depressed, while undesired minerals are floated with the help of some reagents, as opposed to a conventional flotation where the desired minerals are floated.

(6) Aerophine 3418A is an aqueous solution of sodium diisobutyldithiophosphinate. Aerophine 3418A is one of the strongest and most common collectors on the market for lead flotation. Aerophine 3418A collector is a dithiophosphinate-type, as opposed to an existing dithiophosphate-type, such as disclosed in U.S. Pat. No. 7,152,741 issued to Jara et al. The structure of Aerophine 3418A is as follows.

(7) ##STR00001##

(8) Certain embodiments of the present invention remove one of the strongest collectors for the lead concentrate, Aerophine 3418A, using ozone treatment. Certain embodiments of the present invention show a reverse flotation of an undesirable material arsenopyrite from the lead concentrate, following the cleaning action of ozone treatment. This is in stark contrast to the methods known heretofore, which fail to show removal or destruction of the residual collector Aerophine 3418A from the particles surface and flotation of arsenic out of the lead concentrate through a reverse flotation for taking a final lead concentrate.

(9) The challenges for removing arsenic mineral from a lead concentrate include i) removal of residual dithiophosphinate-type collector (such as Aerophine 3418A) left from the previous flotation from the particles surface of the slurry; ii) the selective flotation of arsenic (the undesirable element) while depressing lead (reverse flotation), which is the desirable element.

(10) In certain embodiments, the conditions to achieve these results can include: ozone treatment to remove residual collector, frother and other chemicals used in the previous flotation steps from the particles surface and the water, followed by an addition of sodium hydrosulfide that results in the depression of the lead mineral.

(11) Here, the arsenic impurity may be arsenopyrite. The lead concentrate may be a galena concentrate. A pH range of 9.5 to 11.0 and a redox potential range from 500 to 350 mv are preferable for an optimum flotation of the arsenopyrite from the galena concentrate. Here the galena may contain silver or may not contain silver.

(12) FIG. 1 is a block flow diagram of an exemplary embodiment of a system for removing arsenic mineral from a lead concentrate in a continuous mode. As shown, a slurry of a lead concentrate containing residual reagents from the previous flotation is fed to a tank 102 where ozone is injected. The lead concentrate may contain about 50% to about 90% lead and about 2% to about 10% arsenic. The residual reagents includes a collector, a frother and other chemicals. An exemplary collector is Aerophine 3418A.

(13) The lead concentrate can include a residual of collector such as Aerophine 3418A from the previous flotation, which is adsorbed on particles surface of the slurry and exists in the water of the slurry. In one embodiment, the pH of the fed lead concentrate in tank 102 is approximately 9.5. The injected ozone is oxygen gas, which preferably contains 3 to 12% by weight of ozone. Ozone is injected into tank 102 for a sufficient amount of time, preferably about 10 to 20 minutes, until no more foaming appears on the slurry surface. Ozone as an oxidizing agent destroys the residual collector Aerophine 3418A contained in the lead concentrate, thus, the particles surface of the slurry are cleaned and Aerophine 3418A in the slurry after the ozone treatment in tank 102 is removed. After the ozone treatment, the pH of the slurry is preferably reduced to about 4 to 5, and the redox potential is in the rage of about 600 to about 200 mv.

(14) The cleaned slurry after the ozone treatment is then pumped to tank 104 where a sulfidizing agent is added to the slurry to depress the lead mineral. The sulfidizing agent may be sodium hydrosulfide (NaHS) or any other sulfidizing agents. For example, a dosage of about 2 to about 10 kg/ton, preferably about 4 to about 6 kg/ton, of NaHS is added for about 20 min. Alternatively, a dosage of NaHS is added to the slurry until the slurry pH increases to about 8 and redox potential reaches about 500 to about 300 mv, preferably about 450 to about 350 mv.

(15) Nitrogen gas or sulfite salts, such as Na.sub.2SO.sub.3, may also be added into tank 104 to de-aerate the slurry of the lead concentrate and maintain the dissolved oxygen in the slurry to less than about 1 mg/L, preferably less than about 0.5 mg/L. An alkali may be added to tank 104 to adjust the pH value of the slurry. The slurry pH may range from about 9.0 to about 11.5, preferably about 9.5 to about 11, more preferably about 10.0 to about 11.0. The alkali may be lime, soda ash, or sodium hydroxide. Preferably, the alkali is lime. For example, 2 ml lime is added to the slurry for 2 min.

(16) Thereafter, the slurry is pumped to tank 106 where a suitable collector and frother are added for flotation. The suitable collectors may be a short carbon-chain anionic collector, more selective in floating arsenopyrite (small quantity) from galena (large quantity). The suitable collectors may be selected from a sulfhydryl, xanthogenate, dithiophosphate or combination thereof. Furthermore, a collector that has a carbon chain length comprising about 1 to 6 carbon atoms (i.e., C.sub.1 to C.sub.6) may be used. The molecules having the short carbon-chain are preferred for high selectivity of a little mass of arsenic impurity versus a large mass of lead. For example, a short carbon-chain potassium ethyl xanthate (PEX), opposed to a long carbon-chain potassium Amyl Xanthate (PAX), used herein, favorites the selectivity of the little mass of arsenic impurity versus the large mass of lead mineral.

(17) The slurry in tank 106 is mixed with the collector PEX for a sufficient conditioning time, for example, 10-30 min, preferably 10-20 min, to allow the collector PEX to form a hydrophobic layer on arsenopyrite particles surface in the lead concentrate. After the conditioning time with the collector, a suitable frother is added. The suitable frothers can include high molecular-weight alcohols, such as methyl isobutyl carbinol (MIBC), and polyglycol ethers, such as, marketed as Dowfroth 250, Cyanamid R65, and Union Carbide PG400. Other frothers known to one skilled in the art are also suitable for use. When MIBC is used as a frother, MIBC is added at a dosage of 5 to 50 g/ton, preferably 10 to 20 g/ton.

(18) The mixing time between the slurry and the frother is about 1-30 min, preferably about 5-10 min, to allow a stable froth during concentrate recovery. N.sub.2 is optional for this step. If air gets in, 02 may kill NaSH. So adding N.sub.2 or any sulfite salts to remove O.sub.2 may be extremely beneficial for this step.

(19) The slurry is then pumped to flotation cell 108 for a reverse flotation where air or nitrogen is injected to float hydrophobic arsenopyrite, FeAsS (concentrate) from hydrophilic galena, PbS (tailings). A now-purified lead concentrate is recovered from the bottom of the flotation cell 108 and arsenic mineral is collected from the top of the flotation cell 108. The now-purified lead concentrate, recovered through the tailings of the flotation cell 108, containing approximately 2000 g/ton of silver and about 0.66% arsenic, is directed to the existing lead thickener 110, where the slurry density will be increased significantly before feeding to a filter press 112.

(20) A resulting cake from the filter press 114 is then dried and stockpiled. The arsenopyrite concentrate from the flotation cell 108, containing approximately 20 g/t gold, is directed to the existing arsenopyrite line, for thickening, filtering and drying. In summary, the suitable pH for the reverse flotation disclosed herein may range from 10 to 11. The suitable redox potential for the reverse floatation disclosed herein may range from 350 to 450 mv.

(21) In certain embodiments, the method for removing arsenic mineral from a lead concentrate can include the steps of: receiving a slurry of the lead concentrate that has previously undergone flotation processes, bubbling ozone into the slurry of the lead concentrate to remove reagents used in previous flotation processes, adding a sulfide salt to the slurry to depress lead mineral, adding an alkali to increase the pH of the slurry, adding a collector and then a frother to the slurry for a reverse flotation processing, and floating the arsenic mineral out of the lead mineral to obtain a now-purified lead concentrate.

(22) The advantages of the disclosed methods include i) reducing or eliminating penalty charges when selling the final lead concentrate to the smelters; ii) acting as a buffering step: extra arsenic will be eliminated or reduced from the final concentrate when run-of-mine (ROM) ore with unusual high-arsenic content is accidentally processed upfront. In addition, since arsenopyrite is in the similar family to pyrite, pyrrhotite and the like, the disclosed method for removing arsenic mineral from a lead concentrate using a reverse flotation may also be applied to removing FeS.sub.2 or FeS from a lead concentrate.

EXAMPLES

(23) The following non-limiting examples are provided to further illustrate embodiments of the invention. However, the examples are not intended to be all-inclusive and are not intended to limit the scope of the inventions described herein.

Example 1

(24) A feed material of lead concentrate having about 53% lead and about 2.7% arsenic was mixed with water to obtain about 20% solid density of a slurry of a concentrate. The pH of the slurry was about 7 to 9. Adding an ozonated gas containing 10% O.sub.3 by weight into the slurry for about 20 min to remove reagents including collectors, such as Aerophine 3418A, left from previous flotation processes. The pH was reduced to about 4 to 5. The redox potential was about 300 to 200 mv. Thereafter, adding 30 ml NaSH in to the slurry and remaining it for about 20 min. The pH was then increased to 8.3. The redox potential was 496 mv. After that, adding 2 ml lime to the slurry for about 2 minutes to toss the pH up to 10.3.

(25) The redox potential was then in a range between 460 to 520 mv. Then, adding 3 ml PEX to the slurry and after 10 min adding 3 ml MIBC to the slurry for a reverse flotation process. The pH now was 10.33 and the redox potential was about 510 mv. A now-purified lead concentrate is produced from the reverse flotation containing 0.66% arsenic. The mineral contents contained in the lead concentrates before and after the reverse flotation process are shown in FIG. 2. Using ozone treatment followed by addition of sodium hydrosulfide, at alkaline condition and low redox potential, initial around 3% arsenic in the lead concentrate was reduced to around 0.66% after the reversed flotation with the ozone treatment, which is close to the industry target of 0.5% arsenic content and falls in the lowest penalty range for arsenic content of 0.5% to 1.0%.

(26) Reference herein to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the invention. The appearances of the phrase in one embodiment in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term implementation.

(27) As used in this application, the word exemplary is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as exemplary is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion.

(28) Additionally, the term or is intended to mean an inclusive or rather than an exclusive or. That is, unless specified otherwise, or clear from context, X employs A or B is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then X employs A or B is satisfied under any of the foregoing instances. In addition, the articles a and an as used in this application and the appended claims should generally be construed to mean one or more unless specified otherwise or clear from context to be directed to a singular form.

(29) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(30) About or around or approximately in the text or in a claim means10% of the value stated.

(31) Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of comprising. Comprising is defined herein as necessarily encompassing the more limited transitional terms consisting essentially of and consisting of; comprising may therefore be replaced by consisting essentially of or consisting of and remain within the expressly defined scope of comprising.

(32) Note that herein, the terms lead concentrate and lead mineral may be used interchangeably. It is understood that a lead concentrate may correspond to, or related to a lead mineral, and that the lead mineral may refer to the lead concentrate.

(33) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(34) It will be understood that many additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above and/or the attached drawings.

(35) While embodiments of this invention have been shown and described, modifications thereof may be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and not limiting. Many variations and modifications of the composition and method are possible and within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims,