Technical Field

[0001] The following disclosure relates to a process for extracting zirconium, in particular from a pregnant leach solution.

Background of the Disclosure

[0002] Zirconium is used in a variety of applications, for example in the formation of advanced ceramics, precision casting, electronic sensors, water treatment, corrosion resistant alloys, catalysts, nuclear materials such as fuel rod cladding, and other advanced materials such as dental implants.

[0003] The primary mineral source of zirconium is zircon (ZrSiCL) and baddeleyite (ZrCh), with most commercial exploitation being directed towards zircon. Zircon is commonly recovered as a by-product of mining and processing of mineral sands containing ilmenite (FeTiCh) and rutile (TiCL). Zircon may also be recovered as a by-product of tin mining.

[0004] A possible alternative source of zirconium is from low grade ores or concentrates (containing > 1% ZrCL). This could provide an alternative production route independent of the zircon supply chain. However, recovering zirconium from low grade ores or concentrates presents a challenge because the zirconium must be separated from a wide range of elements such as niobium, rare earths, uranium, iron and aluminium, which may not be present in zircon mineral concentrates.

[0005] One general method of separating metals is by solvent extraction (SX). In these methods, the metal ore is prepared for SX by being dissolved and subjected to a leaching process to form a solution or liquor (commonly referred to as a pregnant leach solution (PLS)). Example preparation processes include acid baking and water leaching or caustic digestion and acid leaching. SX is then carried out by bringing the PLS into contact with a solvent chosen to cause a transfer of the desired metal species into the solvent. The metal species can then be removed from the solvent and transferred to a strip liquor for further processing such as precipitation.

[0006] Solvent extraction industrial processes specifically targeted at zirconium however, have focused on separating hafnium and zirconium. This is useful because nuclear industry based applications of zirconium require very low hafnium content. These processes are typically carried out on liquors derived from zircon or downstream zirconium chemicals derived from zircon rather than low grade zirconium containing ores. As a result, these liquors do not contain base metals, rare earths, or other elements that may be present in low grade ores which may complicate or inhibit zirconium extraction when attempting to separate it by solvent extraction. An example of a commercially used method of zirconium extraction is through a methyl isobutyl ketone (MIBK)/thiocyanate/chloride based process. This process is disadvantageous because it requires a chloride media saturated with thiocyanic acid, which may not be compatible with the treatment of low grade ores. Additionally, MIBK is also highly volatile, flammable, and toxic, necessitating further costs in proper handling and disposal.

[0007] Other examples of zirconium solvent extraction industrial processes include those using tri-butyl phosphate (TBP) as a reagent, which has been used to preferentially separate zirconium from hafnium in concentrated nitric acid solutions, and those using a tertiary amine reagent to separate zirconium and hafnium from a sulfuric acid solution. In both cases, the pregnant leach solutions are derived from zircon mineral concentrates rather than low grade zirconium containing ores. These processes thus do not account for the possibility of a wider range of elements being present in the solution along with zirconium and hafnium.

[0008] Accordingly, the present disclosure seeks to provide a solvent extraction process which provides good zirconium recovery even in the presence of other metals in the pregnant leach solution.

Summary of the Invention

[0009] According to a first aspect, there is provided a process for extracting zirconium including the steps of: a) contacting a pregnant leach solution containing at least zirconium and niobium with a solvent to create a zirconium loaded solvent and a raffinate; b) precipitating at least a portion of the niobium from the raffinate to create a barren liquor; c) contacting the barren liquor with a secondary solvent to form a partially loaded solvent; wherein the partially loaded solvent following step c) is then used as at least part of the solvent in step a). [0010] In certain embodiments, the chloride concentration in the solvent in step a) is controlled to suppress niobium transfer to the zirconium loaded solvent.

[0011] In certain embodiments, the process further includes the step of: d) washing the zirconium loaded solvent.

[0012] In certain embodiments, the zirconium loaded solvent is washed with a sodium sulfate solution in step d).

[0013] In certain embodiments, the process further includes the step of: e) stripping the zirconium loaded solvent to recover zirconium.

[0014] In certain embodiments, the zirconium loaded solvent is stripped using sodium chloride in step e).

[0015] In certain embodiments, the process further includes the step of: f) reducing or removing the chloride content of at least part of the stripped solvent.

[0016] In certain embodiments, the chloride content is reduced or removed by contacting the part of the at least part of the stripped solvent with an alkali.

[0017] In certain embodiments, the alkali is sodium carbonate.

[0018] In certain embodiments, the stripped solvent is split into two streams following step e), a first stream which is optionally reused as at least a portion of the solvent in step a) and a second stream which proceeds to step f), wherein the second stream is then used as at least part of the solvent in step c).

[0019] In certain embodiments, the chloride concentration in the solvent in step a) is controlled to suppress niobium transfer to the zirconium loaded solvent by varying the amount of the first stream being reused in step a).

[0020] In certain embodiments, at least part of the first stream and/or the second stream is subjected to a reprotonation process prior to being used in step c).

[0021] In certain embodiments, the pregnant leach solution is sulfate based. [0022] In certain embodiments, the solvent includes an amine based reagent.

[0023] In certain embodiments, the pregnant leach solution is derived from a low grade ore.

[0024] According to a second aspect, there is provided a process for extracting zirconium from a pregnant leach solution, including the steps of contacting the pregnant leach solution with a solvent to at least partially remove zirconium from the pregnant leach solution to form a zirconium loaded solvent; wherein the chloride concentration in the solvent is controlled to suppress niobium transfer to the zirconium loaded solvent from the pregnant leach solution.

[0025] According to a third aspect, there is provided a system for extracting zirconium from a pregnant leach solution, comprising: a primary extraction circuit which receives the pregnant leach solution and contacts the pregnant leach solution with a primary solvent to form a loaded solvent; a niobium precipitation circuit which receives a raffinate from the primary extraction circuit and which at least partially removes niobium from the raffinate to form a barren liquor; a secondary extraction circuit which receives the barren liquor from the niobium precipitation circuit and contacts the barren liquor with a secondary solvent; a wash circuit for removing entrained pregnant leach solution from the loaded solvent; a stripping circuit for transferring zirconium from the loaded solvent to form a stripped solvent and a loaded strip; where in the system is adapted to allow the secondary solvent to flow to the primary extraction circuit for use as the primary solvent.

[0026] In certain embodiments, the system further comprises: a zirconium precipitation circuit for removing zirconium from the loaded strip.

[0027] In certain embodiments, the system further comprises: a regeneration circuit which at least partially removes chloride from the stripped solvent to form a regenerated solvent, wherein the system is configured to allow the regenerated solvent to flow to the primary and/or secondary extraction circuits.

[0028] In certain embodiments, the system further comprises: a regeneration bypass circuit, which allows a portion of the stripped solvent to flow to the primary extraction circuit, the system being configured to allow varying amounts of stripped solvent to flow into the regeneration bypass circuit. [0029] In certain embodiments, the system further comprises: a reprotonation circuit between the regeneration circuit and the secondary extraction circuit which reprotonates the regenerated solvent.

[0030] In certain embodiments, the primary solvent is counter-currently contacted with the pregnant leach solution in the primary extraction circuit, and/or the secondary solvent is counter-currently contacted with the barren liquor in the secondary extraction circuit.

[0031] In certain embodiments, the system according to the third aspect is configured to carry out a process according to the first or second aspect.

[0032] Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of the inventions disclosed.

Brief Description of the Figures

[0033] The present disclosure will become better understood from the following detailed description of various non-limiting embodiments thereof, described in connection with the accompanying figures, wherein:

[0034] FIGURE 1 is a graph showing the effect of niobium concentration on zirconium extraction.

[0035] FIGURE 2 shows a process diagram of an embodiment of the present disclosure.

[0036] FIGURE 3 shows a process diagram of an alternative embodiment of the present disclosure.

Detailed Description

[0037] The inventors have found that a problem with attempting to extract zirconium from liquors derived from low grade ores and concentrates is the presence of niobium alongside zirconium. This niobium content results in un-extractable zirconium speciation occurring, preventing high zirconium extraction when attempting to use existing solvent extraction processes. [0038] To remedy this, the inventors have created a solvent extraction process including a primary zirconium extraction step, a niobium removal step and then a secondary zirconium extraction step. In this manner, comparatively high zirconium extraction can be achieved relative to existing processes, especially for liquors derived from low grade ores and concentrates. The solvent used in the secondary extraction can be then used in the primary extraction step to produce a single zirconium loaded stream for further processing. In preferred embodiments, the liquor is in the form of a sulfate based pregnant leach solution.

[0039] The process may be further optimized by control of the chloride in the primary zirconium extraction. The inventors have found that niobium rejection increases with increasing chloride content in the solvent. However, increasing chloride content also suppresses the zirconium transfer to the solvent. To counteract this side effect, the remaining zirconium content in the leach liquor is at least partially recovered by including a secondary extraction step, which preferably has a solvent with a lower chloride concentration relative to the primary extraction. As the niobium content is reduced or removed in the primary zirconium extraction step, a solvent with a lower chloride concentration can be used in the secondary extraction to allow for higher zirconium transfer to the solvent.

[0040] Alternatively, the control of chloride in the primary zirconium extraction circuit may be used in isolation to inhibit niobium reporting to the solvent while still allowing zirconium to report to the solvent for further processing.

[0041] The zirconium loaded solvent can be further processed by including a washing step to remove entrained liquor, a stripping step where the zirconium in the loaded solvent is transferred to a strip liquor, and zirconium precipitation step from the loaded strip. If a chloride ion containing liquor (such as a sodium chloride strip liquor) is used, then a portion of the stripped solvent can be recycled into the primary extraction so as to provide and maintain the desired chloride content. By varying the portion that is recycled into primary extraction, the chloride concentration in the primary extraction may be controlled. The remainder of the solvent can be regenerated to remove the chloride content and recycled to the secondary extraction. Controlling the chloride content is important as an overly large chloride concentration will lead to increased suppression of zirconium extraction and thus a lower zirconium rate, while a low chloride content will allow niobium to transfer to the solvent, also suppressing zirconium extraction, as shown in the following experiments. [0042] The inventors have carried out experiments to verify the effect of niobium concentration on zirconium extraction. In these experiments, the PLS was derived from a zirconium ore containing - 2% ZrCL and -0.45% Nb20s sourced from a trachyte deposit. The PLS was produced by a sulfuric acid roasting and water leaching process. The results are shown in FIGURE 1, which shows a graph of zirconium in the aqueous phase (raffinate) vs zirconium in the organic phase (solvent) when using an N,N-dioctyl-l-octanamine (also known under the trade name Alamine 336) based solvent. In this experiment, the solvent was a mixture of 10 vol% Alamine 336 and 10 vol% tributyl phosphate (TBP) in a kerosene based diluent. Figure 1 shows that as the niobium concentration decreases, the equilibrium curve moves towards the y-axis. Otherwise stated, lower niobium concentrations result in lower concentrations of zirconium in the raffinate and higher concentrations in the solvent, promoting higher zirconium recovery.

[0043] In a related experiment, the inventors maintained the niobium concentration in the zirconium extraction circuit while varying the amount of chloride in the solvent feeding the zirconium extraction to characterise the effect of chloride on the amount of niobium reporting to the product stream. The process was operated so that the zirconium loaded strip underwent a stripping process where the zirconium in the solvent transferred to a chloride containing strip and chloride transferred to the solvent. A varying amount of the stripped solvent (containing chloride) was fed back into the zirconium extraction to achieve the required chloride concentrations. The results are shown in the table below.

[0044] The results show that with increasing chloride concentration present in the zirconium extraction circuit, the amount of niobium in the reporting product stream can be greatly reduced. However, the addition of chloride to zirconium solvent extraction streams is known to suppress the zirconium extraction. This detrimental side effect may be mitigated by subjecting the raffinate to a second extraction process in order to recover the remaining zirconium following the removal of niobium. Chloride may thus be added to the primary zirconium extraction in such systems without causing an appreciable reduction in the overall amount of recovered zirconium.

[0045] The present disclosure will become better understood from the following examples of non-limiting embodiments.

[0046] FIGURE 2 shows a process diagram of an embodiment of a process for extracting zirconium in accordance with the present invention. A pregnant leach solution (1), also referred to as a liquor, is passed into a primary extraction circuit (12). In this embodiment, it is envisioned that the pregnant leach solution is obtained from a low grade ore containing > 1 % ZrCh, as well as other elements including at least some of niobium, rare earths, uranium, iron and aluminum, though it will be understood that the pregnant leach solution may also be obtained in other embodiments from other known zirconium sources. In particularly preferred embodiments, the pregnant leach solution has been obtained by subjecting the low grade ore to a sulfuric acid bake/water leach process, resulting in a sulfate based pregnant leach solution.

[0047] In the primary extraction circuit (12), the sulfate based pregnant leach solution is contacted with a solvent (10). In this embodiment, it is envisioned that a tertiary amine based solution is used owing to its preferential extraction of zirconium and hafnium from sulfate based media. In other embodiments, other solvents, such as primary or secondary amine based reagents, or other known reagents may be used instead, provided that they provide satisfactory separation of zirconium and hafnium from other elements in the leach solution. In this embodiment, the tertiary amine based solvent is counter-currently contacted with the pregnant leach solution. It will be understood that other contact methods may be used in other embodiments. The main purpose of the primary extraction circuit is to extract zirconium and reject other elements, in particular niobium from the pregnant leach solution. The solvent is also preferably chosen to reject other unwanted elements in the solution. For example, the solvent used in the experiments described above utilized a solvent containing Alamine 336, which rejects elements such as rare earths, aluminium, thorium, iron, and magnesium when operated in acidic sulfate media. The chloride concentration present in the primary extraction circuit is controlled and adjusted to ensure that niobium is rejected by the solvent, which is explained further in relation to the regeneration bypass circuit (8). [0048] The raffinate (2) from the primary extraction circuit (12) moves to a niobium precipitation circuit (13). The purpose of this circuit is to remove niobium from the raffinate and creating a niobium barren solution. This may be carried out through any known niobium precipitation process but in its simplest form the temperature is increased above 80°C. As a beneficial side effect, the niobium precipitated may be sold, further processed, and/or made into products. This provides an alternative process route to purify and isolate niobium to conventional processes which are carried out on pyrochlore ore. Zirconium is not found within these ores and these processes are very different from those used for zirconium recovery.

[0049] The niobium barren solution (3) then proceeds to a secondary extraction circuit (14), where zirconium can be further extracted into solvent (9) to form a partially loaded solvent (10) and a secondary raffinate (4). This is useful as the chloride present in the primary extraction circuit (12) suppresses zirconium extraction. The remaining zirconium remaining in the pregnant leach solution can be extracted in this secondary circuit (14). The solvent used in this circuit, which is only partially loaded with zirconium, is then sent to be used as the solvent (10) in the primary extraction circuit (12).

[0050] Following the secondary and primary extraction circuits, the zirconium loaded solvent (5) is passed to a wash circuit (15) to remove entrained pregnant leach solution. In this embodiment, sodium sulfate is envisioned as the wash solution (20), however it will be understood that in other embodiments, other wash solutions may be used to remove entrained pregnant leach solution can also be used without departing from the scope of the invention.

[0051] The washed solvent (6) then proceeds to a strip circuit (16), where zirconium is recovered in this embodiment by contacting the washed solvent with a sodium chloride wash

(21) to transfer chloride to the solvent (7) and zirconium to the loaded strip. The loaded strip

(22) can then proceed to a zirconium precipitation circuit (17) to remove the zirconium metal for sale or further processing. Any known method of precipitating zirconium from the strip can be used without departing from the scope of the invention.

[0052] The stripped solvent (7) is then split into two streams. The first stream enters a regeneration bypass circuit (8) which brings solvent to the primary extraction circuit (12) for reuse. The solvent which enters the regeneration bypass circuit (8) has a high chloride concentration owing to the chloride transfer in the stripping circuit (16). The second stream proceeds to a regeneration circuit (18), where an alkali (23) (in this embodiment, sodium carbonate) is used to remove chloride from the second stream. The regenerated second stream (9) then proceeds to the secondary extraction circuit (14) and then the primary extraction circuit (12). By varying the amount of the first stream that proceeds to the primary extraction circuit, the chloride concentration in the primary extraction can be controlled. Accordingly, the primary extraction circuit can be configured to optimize the chloride concentration and thus the niobium rejection of the circuit. Splitting the stripped solvent between the regeneration bypass circuit and the regeneration also results in a differential in chloride concentration between the primary and secondary extraction, allowing greater recovery of zirconium in the secondary extraction circuit and thus overall extraction is improved.

[0053] FIGURE 3 shows a process diagram of an alternative embodiment of the process. This embodiment bears a lot of similarity to the embodiment shown in FIGURE 2, also including a primary and secondary extraction circuit (12, 14 respectively) with a niobium precipitation circuit (13) between them, as well as wash, stripping and regeneration circuits (15, 16, 18 respectively). This embodiment further includes a reprotonation circuit (19) between the regeneration circuit and the secondary extraction. In this embodiment, this is carried out through the addition of sulfuric acid (H2SO4). The reprotonated solvent (11) can then be reused in the secondary extraction circuit (14).

[0054] In summary, the process for extracting zirconium as exemplified by these examples has a number of benefits over existing solvent extraction methods. The process rejects base metals, rare earths, alkali earth metals and niobium to the raffinate. The rejection of niobium in particular is important as the presence of niobium causes un-extractable zirconium speciation to occur, reducing high zirconium recoveries. The present process overcomes this problem by providing a controlled amount of chloride in the primary extraction step to reject niobium from reporting to the solvent, performing a niobium removal step and then performing a second extraction step, preferably with a lower chloride content solvent, to extract remaining zirconium in the raffinate following the niobium removal step.

[0055] In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. [0056] In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of’. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

[0057] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0058] In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

[0059] Furthermore, invention(s) have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.