Patent Application
20140305848
The present disclosure relates to a method of selective froth flotation of sulphide minerals using a combination of depressant reagents.
Sulphide mineral flotation has been practiced since the early 20th century. Its industrial importance is well recognized as the concentrates from flotation can be more economically smelted and refined to provide primary metals. Froth flotation is a process to selectively separate value minerals from waste gangue materials through utilizing the differences in surface hydrophobicity. In general, the flotation process involves the grinding of crushed ore in a dense slurry to liberation size, followed by its conditioning with different reagents in a suitable dilute pulp. The reagents include collectors, depressants, frothers, modifiers, etc. Collectors render the surface of desired minerals hydrophobic by physical/chemical adsorption, which facilitates the attachment of air bubbles that cause the mineral particles to float to the surface of the slurries and form a stabilized froth which is collected for further treatment. Depressants have the reverse action to collectors, causing the surface of undesired mineral particles to become hydrophilic by adsorbing hydrophilic components or by removing the active sites for the collector's adsorption, thus allowing the particles to remain in the tailings fraction. Frothers help to stabilize air bubbles of suitable sizes in the slurry in order to capture and transfer particles to the froth zone. Modifiers are usually used for pH control. The various schemes of froth flotation that are employed are generally quite complex in order to maximize grade and recovery of the valuable minerals present and to maximize rejection of rock and sulphide minerals of little commercial value.
In the processing of sulphide ores for the recovery of non-ferrous pay metals, the common value minerals treated include pentlandite and millerite, chalcopyrite and chalcocite and bornite, galena, and sphalerite for the metals Ni, Cu, Pb and Zn respectively. However, these value minerals are naturally associated with iron sulphides, namely pyrrhotite, pyrite, and marcasite, which have no commercial value and are considered as sulphide gangues. Selective rejection of iron sulphides in flotation can significantly improve the economic value of the concentrate and also reduce the SO2 emissions at smelters where the iron sulphides are significant contributors to these gaseous emissions. However, pyrrhotite rejection is challenging. It not only relates to the abundance of pyrrhotite in the ore, but also to the crystal structure of pyrrhotite (i.e. monoclinic, hexagonal or troilite). Furthermore, pyrrhotite is intimately associated with other minerals, primarily with pentlandite. Selective depression of pyrrhotite without compromising the recoveries of Cu and Ni during flotation is a key to building commercial value in an industrial mineral processing plant.
U.S. Pat. No. 5,074,993 describes a method of flotation of sulphides wherein pyrrhotite is depressed by use of a water-soluble polyamine in an amount >50 g/mt of the ground mineral mixture. The water-soluble polyamine is preferably diethylenetriamine (DETA), and can also be selected from a list that includes triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 2-[(2aminoethyl)amino]ethanol, Tris-(2-aminoethyl)amine, N-methyl ethylenediamine and 1,2 diamino 2 methylpropane.
U.S. Pat. No. 5,411,148 describes a process for the improved separation of mono- or multi-metallic sulphide minerals from iron sulphides. The process comprises a conditioning stage before flotation with at least one water-soluble sulphur-containing inorganic compound as a prerequisite step before further conditioning with a nitrogen-containing organic chelating agent which is described in U.S. Pat. No. 5,074,993. The water-soluble sulphur-containing inorganic compound is preferably sodium sulphite (Na2SO3), and can also be selected from the group consisting of sulphides, dithionates, tetrathionates, and sulphur dioxide, in an amount varying from 50 to 600 g/mt of dry solids processed. The nitrogen-containing organic chelating agent is preferably a polyethylenepolyamine such as diethylenetriamine (DETA) used at an adequate dosage for a particular flotation feed. The pyrrhotite is depressed as a result of the combined effects of the sulphur-containing compound and the nitrogen-containing organic compound, added in a particular order.
The aforementioned processes are very effective at increasing Ni and Cu concentrate grade and recovery with selective pyrrhotite depression. However, the use of DETA can complicate the operation of the wastewater treatment regarding the total (soluble and insoluble) Cu and Ni discharged in the effluent. DETA is a strong chemical chelating agent that forms stable complexes with heavy metal ions, such as Cu and Ni. These complexes cannot be precipitated out by raising the pH above 11, as is typically done in the wastewater treatment plants. Instead, a polyamine precipitating agent such as NALMET® 8702 (available from the Nalco Company, Naperville, Ill.) is added to the wastewater to react with the DETA-metal complexes and faun a precipitate. However, the precipitates are very fine particles which do not settle in the clarifier, making it difficult to effectively remove the Cu and Ni from the wastewater. In order to avoid a high level of Cu and Ni in the wastewater when using DETA, efforts are being made to identify alternative iron sulphide depressants to reduce or eliminate the use of DETA.
A recent patent from LignoTech (U.S. Pat. No. 8,221,709) describes a method of using hardwood lignosulphonates for separating gangue materials from metallic sulphide ore. The patent specifies three hardwood lignosulphonates obtained from Eucalyptus, Maple, and Birch trees with different sulphur or sulphonate contents and molecular weights, and compared their performances at dosages of ˜250-500 g/mt with NaCN additions in the flotation of a ground ore slurry which comprised copper sulphide, zinc sulphide, or lead sulphide with iron sulphides. The lignosulphonates can be added before or after other reagents and pH adjustments. However, the selectivity between Cu/Ni sulphides and pyrrhotite is not improved with the addition of lignosulphonate alone in the industrial process.
In this sense, the state of the art lacks a method for a) improving the selectivity and recovery in the flotation of Cu/Ni sulphide minerals which are associated with iron sulphides, and b) reducing or eliminating the use of problematic polyamine chemicals (such as DETA) to minimize the negative impact on the environment.
In light of the problems and unmet needs described above, the present invention discloses a method of using the synergy of multiple depressants to improve the depression of iron sulphide without compromising the recovery of the valuable sulphide minerals in the flotation of non-ferrous metal sulphides, while reducing or eliminating the use of environmentally problematic chemicals such as polyamines. The method has significant economic and environmental benefits. Included are examples of the flotation of Cu/Ni sulphide ore with pyrrhotite, either as freshly ground slurry or as a pre-treated and finely ground process intermediate during a flotation process.
The essence of the process involves the use of multiple depressants, taking advantage of the individual depression effect of each chemical, and generating a synergistic effect to improve selectivity and recovery and reduce polyamine usage by at least 50%, or eliminate it whenever possible. The three chemicals used include: 1) A polyamine, such as DETA; 2) A water-soluble sulphur-containing inorganic compound, such as sodium sulphite; and 3) A hardwood lignosulphonate product, preferably a calcium lignosulphonate with a 6 kDa molecular weight, 5% sulphonate, and 2% sugar, and specifically the D-912 product from LignoTech. Used individually, the chemicals either a) do not generate sufficient pyrrhotite depression, or b) decrease the Cu/Ni recovery, or c) cause environmental discharge problems at the wastewater treatment plant due to potentially high levels of heavy metals.
The three chemicals can be added separately at the same time, or added sequentially with no preferred order, or premixed into a single solution with a preferred ratio. Similarly, two components can be premixed into a single solution with a preferred ratio and added to the third one separately with varying amounts. The depressants can be added before or after other flotation reagents.
Aspects of the present invention promote the improvement of the selective recovery of the non-ferrous pay metals which are associated with iron sulphides.
Aspects of the present invention promote synergy between the depressants and the collector allowing for a reduction of the polyamine (i.e. DETA) dosage by at least 50% over that typically used with the DETA/Na2SO3 combination, without compromising the selectivity and recoveries during flotation.
Aspects of the current invention help avoid discharges of heavy metals and DETA at the wastewater treatment plant exceeding the mandated limits that can occur due to the formation of DETA-metal complexes.
Additional advantages and novel features of these aspects of the invention will be set forth in part in the description that follows, and in part will become more apparent to those skilled in the art upon examination of the following or upon learning by practicing the invention.
Various exemplary aspects of the systems and methods will be described in detail, with reference to the following figures but not limited to, wherein:
The following detailed description does not intend, in any way, to limit the scope, applicability or configuration of the invention. More specifically, the following description provides the necessary understanding for implementing the exemplary features of the invention. When using the teachings provided herein, those skilled in the art will recognize suitable alternatives that can be used, without extrapolating the scope of the present invention.
The present invention describes a method of using the synergistic effect of multiple depressants to selectively float sulphide minerals which contain at least one or more non-ferrous pay metals and which are associated with iron sulphides consisting mainly of pyrrhotite to obtain an excellent grade and recovery of the non-ferrous pay metal values. By taking advantage of the synergistic effect obtained by using multiple depressants, the dosage of one of the key chemicals (i.e. DETA) can be significantly reduced, thereby alleviating a potential negative impact to the environment. The method comprising:
i) Treating a sulphide ore, either freshly ground slurry or a pre-treated and finely ground process intermediate, which contains at least one or more non-ferrous pay metal sulphide minerals (Cu/Ni) with iron sulphides (pyrrhotite), in an aqueous alkaline slurry in the presence of a collector, a frother, a pH modifier, and a carrier gas distributed through the slurry, and the multiple depressants.
ii) The multiple depressants contain at least one organic polymer (calcium lignosulphonates from hardwood), at least one sulphur-containing compound, and at least one nitrogen-containing organic compound (polyamine), the latter being present at lesser amounts in the mixture than would be needed if it was being used alone or in combination with one sulphur-containing compound.
iii) The addition of multiple depressants has the following options with some conditioning time allowed:
iv) The dosages of the depressants for the synergistic effect and reduced polyamine usage will depend on the ore type, grade and its mineralogical composition and should therefore be determined experimentally. For the tested ore samples, D-912 dosages ranged from 50 to 150 g/t, Na2SO3≧100 g/t, and DETA from 0 to 50 g/t. The quoted dosages refer back to the ground ore, even for intermediate streams. The DETA dosage is kept as low as possible without compromising the overall selectivity and recovery, to avoid the high levels of heavy metals in the wastewater.
v) The collector dosage will be adjusted accordingly for the optimal metallurgy as there is competition between collectors and depressants.
In the preferred embodiments, the invention refers to a method of using the synergistic effect of multiple depressants to selectively float at least one or more sulphide minerals which contain at least one or more non-ferrous pay metals and which is/are associated with iron sulphide in a sulphide ore, the process comprising:
i) Treating a sulphide ore, either freshly ground slurry or a pre-treated and finely ground process intermediate, which contains at least one of said valuable sulphide minerals associated with at least one iron sulphide mineral, in an aqueous alkaline slurry in the presence of a collector, a frother, a pH modifier, a carrier gas distributed through said slurry, and multiple depressants selected to include at least one organic polymer, at least one sulphur-containing compound, and/or at least one nitrogen-containing organic compound; and
ii) Carrying out froth flotation to depress the iron sulphides, while allowing the flotation of the valuable non-ferrous sulphides.
In another preferred embodiment, the invention refers to a method of using the synergistic effect of multiple depressants to selectively float at least Ni/Cu/Co sulphide minerals which contain at least Ni, Cu, Co, Pt, Pd, Au, and Ag pay metals and which is/are associated with iron sulphide minerals including at least pyrrhotite in a sulphide ore, the process comprising:
i) Treating a Ni/Cu/Co sulphide ore, either freshly ground slurry or a pre-treated and finely ground process intermediate, which contains at least the minerals pentlandite and chalcocite associated with at least pyrrhotite, in an aqueous alkaline slurry in the presence of a collector, a frother, a pH modifier, a carrier gas distributed through said slurry, and multiple depressants including a calcium-lignosulphonate product (preferably a product such as D-912), a sodium sulphite (Na2SO3) and/or DETA; and
ii) Carrying out froth flotation to depress the pyrrhotite, while allowing the flotation of the valuable pentlandite and chalcocite.
Alternatively, the method of adding the three depressants may comprise 1) separately, but all at the same time; and 2) sequentially with individual conditioning.
Additionally, the depressants solution can be added before or after the collector.
The dosages of the depressants for the synergistic effect and reduced polyamine usage were found to depend on the ore type, grade and its mineralogical composition and should therefore be determined experimentally. For the tested ore samples, D-912 dosages ranged from 50 to 150 g/t, Na2SO3>100 g/t, and DETA from 0 to 50 g/t. The quoted dosages refer back to the ground ore, even for intermediate streams.
The synergistic pyrrhotite depression obtained when using multiple depressants (i.e. by combining DETA, Na2SO3 and D-912) is obtained by maximizing the pyrrhotite depression obtained with each depressant at a minimum dosage. More specifically, DETA, Na2SO3 and D-912 have their own unique functions in iron sulphide depression. Pyrrhotite flotation has three proposed mechanisms; 1) Cu activation to promote collector (xanthate) adsorption; 2) Formation of poly-sulfur to produce some hydrophobic sites on the pyrrhotite surface for the air bubble to attach to; and 3) Formation of dixanthogen for hydrophobic sites. DETA can remove or mask the Cu2+ activation sites on the iron sulphides to inhibit collector adsorption on the surface. Na2SO3 can prevent iron sulphide flotation by removing the adsorbed collector or the poly-sulfur formed on the iron sulphide surface. D-912 is a negatively charged hydrophilic polymer which can adsorb onto the iron sulphide surface through active sites (such as Fe(OH)2+, Ca2+ or Cu2+) to render its surface hydrophilic, thus depressing the iron sulphide.
With any one of the depressants used singly, no effective pyrrhotite depression is obtained without compromising pay metal recovery or causing high levels of heavy metals in the wastewater. By using three different depressants simultaneously, a synergistic effect is created. An advantage can be obtained from each of the three reagents, resulting in maximizing the iron sulphide depression while minimizing decreases in the recovery of the valuable minerals.
The following examples are meant to illustrate, and not in any way to limit the scope, applicability, or configuration of the claimed invention.
In the figures, it should be noted that short forms have been used in the axis titles for the minerals. Included are the notations: Pn (pentlandite), Cp (chalcopyrite), and Po (pyrrhotite).
The test with the collector (PAX) alone showed no pyrrhotite depression. The test with DETA/Na2SO3 represented an acceptable pyrrhotite depression and pay metal recovery.
Using the hardwood lignosulphonate product D-912 as a pyrrhotite depressant at a dosage of 25 to 50 g/t did not improve the pyrrhotite depression in comparison to the use of the combination of DETA and Na2SO3 (i.e. the “Baseline” chemicals). At a high D-912 dosage of 250 g/t, pentlandite was significantly depressed without improving the selectivity of pentlandite/pyrrhotite in comparison to the combination of DETA and Na2SO3.
The test with the collector (PAX) alone showed no pyrrhotite depression. The test with DETA/Na2SO3 represented an acceptable pyrrhotite depression and pay metal recovery.
It was demonstrated that using a dosage of 200 g/t Na2SO3 by itself had some effect on pyrrhotite depression, but the results were not as good as those obtained using the baseline chemicals DETA and Na2SO3. In the tests with D-912 and Na2SO3, some indications of pyrrhotite depression were observed when the Na2SO3 dosage was >100 g/t. When the Na2SO3 dosage was ≧200 g/t and the D-912 dosage was ≧50 g/t, similar pentlandite/pyrrhotite selectivity curves were obtained with D912/Na2SO3 as the baseline DETA/Na2SO3. Increasing the dosage of D-912 from 25 to 100 g/t and the dosage of Na2SO3 from 200 to 400 g/t did not significantly change the shape of the pentlandite/pyrrhotite selectivity curves (i.e. the pentlandite recovery dropped with a decrease in the pyrrhotite recovery).
For this feed, there was no need to add DETA, which is preferable for environmental concern.
It was observed that the selectivity was improved and even better than the DETA/Na2SO3 baseline when the D-912 dosage was ≧50 g/t with 200 g/t of Na2SO3. However, the recovery of chalcopyrite decreased by ˜15%. If the dosage of D-912 is further decreased (≦25 g/t) or the dosage of PAX is increased, the selectivity will be compromised. This is not acceptable for industrial production.
In tests in which the dosages of each chemical were fixed (T18309, T18310, T18311), the order of adding the chemicals was varied. No significant differences in the results were seen.
In tests in which the dosages of the depressants and collector were varied, either the selectivity was very good but the recoveries of pentlandite and chalcopyrite were far below target (T18309, T18310, T18311), or the recoveries of pentlandite and chalcopyrite were acceptable but the selectivity was significantly reduced (T18358, T18360).
The selectivity and recovery approached the “Baseline” results only when a balance between the collector and depressants was reached (T18359). At the proper dosages of D-912, DETA, and Na2SO3 and the collector (PAX), good selectivity and recoveries are obtained.
In the test design, the criteria for selecting the dosages included: a) The DETA dosage should be less than the level that was used in the DETA/Na2SO3 combination (i.e. usually 50 g/t); b) As previous results showed that D-912 dosages <50 g/t did not work, and the upper limit was not known, the dosages were extended to higher levels; and c) Since the results in Example 5 showed that the recoveries of pentlandite and chalcopyrite were adequate at PAX dosages of 10 to 15 g/t, there was no need to go to much higher dosages than normal (i.e. 5 g/t).
In one group with high dosages of D-912 (FD2, FD3, FD5 and FD7), a high concentrate grade with a very low pentlandite recovery (20˜50%) was obtained, indicating that a D-912 level of 150 g/t was too high. In another group with high dosages of PAX and low dosages of D-912 (FD8 and FD9), the pentlandite/pyrrhotite selectivity was reduced, resulting in a concentrate grade below the target. Using the dosages at the middle points of the ranges (FD1) produced results between these limits. It can be seen that at 10 g/t PAX, 50 g/t D-912, and 15 g/t DETA (FD6), good pentlandite/pyrrhotite selectivity was obtained with results approaching those of the DETA/Na2O3 baseline. Chalcopyrite recovery at these dosages was also very good (˜90%).
The other repeated and optimized results were all in the same pentlandite/pyrrhotite selectivity range, indicating a stable performance. It can be seen that: a) Increasing the D-912 dosage to 75 g/t decreased pentlandite and chalcopyrite recoveries by a few percentage points; b) Changing the DETA dosages from 15 to 25 and then to 35 g/t did not affect the recoveries and selectivity, so that the lower DETA dosage (15 g/t) was preferred; and c) Decreasing the PAX dosage slightly (i.e. from 10 to 7.5 g/t) did not have a significant impact on the results.
The additions of the chemicals and the conditions of the addition method to the cleaner are summarized in Table 7.
The differences in the results obtained with the various methods of adding the chemicals were not significant, as all the results showed good selectivity. Adding the three chemicals separately has the advantage of being able to adjust each dosage individually. Using a premixed solution gives a simpler solution for the arrangement of chemical storage tanks and delivery lines, which is good when the conditions have been fully established.
It is known that the different tailings solids each have specific capacities for stably adsorbing DETA. The results given in Table 9 verified that by using the combination of D-912, DETA and Na2SO3 with a reduced DETA dosage, the residual amount of DETA in the process water could be significantly decreased. This amount of DETA can be adsorbed on the tailings solids without any negative impact on the wastewater treatment plant.
This application claims priority from U.S. Patent Application No. 61/623,459, titled “A Method for Improving Selectivity and Recovery in the Flotation of Nickel Sulphide Ores that Contain Pyrrhotite by Exploiting the Synergy of Multiple Depressants,” filed on Apr. 12, 2012, and which is incorporated herein by reference in its entirety.
