AU2013204836A1 - Method for Administering an Active Agent - Google Patents

Abstract

Abstract A method for administering an agent comprising the step of: adding an amount of the agent to an alkaline feed solution, wherein the agent chemically decomposes into one or more active species.

Description

1 "Method of Administering an Active Agent" TECHNICAL FIELD [0001] The present invention relates to a method for administering an active agent. More particularly, the active agent administered is capable of chemically decomposing into one or more active species under alkaline feed solution conditions. In one embodiment, the present invention relates to a method for administering an agent capable of decomposing into an oxalate stabiliser and an antifoaming agent in a Bayer process liquor. BACKGROUND ART [0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application. [0003] Active agents are commonly used in industrial processes to facilitate a specific and desired processing outcome. For example, in the Bayer process, numerous agents are added at different locations of the Bayer circuit in order to optimise the recovery of alumina (aluminium oxide) from bauxite. [0004] By way of background, the Bayer process involves the digestion of bauxite ore in a caustic solution at high temperatures and elevated pressure. The caustic solution dissolves aluminum hydroxide compounds, such as sodium aluminate (NaAI(OH) 4 , forming a slurry mixture. The slurry mixture is then cooled and the insoluble impurities are separated. The remaining dissolved compounds are then passed to a precipitation stage, wherein precipitation occurs through seeding with aluminium trihydroxide (AI(OH) 3 ). The precipitated product is calcined to recover alumina as a product. [0005] Sodium oxalate is one of the many organic compounds present in Bayer liquor. Due to its limited solubility, sodium oxalate can co-precipitate with aluminium trihydroxide during the precipitation stage. Uncontrolled -2 precipitation of sodium oxalate in Bayer process streams may cause processing problems, including interfering with the agglomeration of alumina leading to an increase in the concentration of alumina fines during precipitation. As such, there is a known need to control the precipitation of sodium oxalate from the Bayer process. [0006] Several methods have been proposed in the prior art to reduce or control the precipitation of sodium oxalate in a Bayer process. For example, the present Applicant's Australian Patent application 2009201264 describes a method for the removal of oxalate from Bayer process liquors using an oxalate stabiliser. While the prior art teaches the removal of oxalate with stabilisers, it is known that the efficiency of oxalate stabilisers can be influenced by the chemistry or composition of the Bayer liquor. For example, the stabiliser of Australian Patent Application 2009201264 is influenced by the presence of particular organic compounds that are present in some refinery liquors. It has previously been proposed in ["Quatemary Amines as Sodium Oxalate Seed Stabilisers in Bayer Liquor" (Sipos, Shaw, Seydel, Parkinson, McKinnon, Smith, Kildea), Fifth International Alumina Quality Workshop, 1999] that the negatively charged quaternary amine contained in the stabiliser of Australian Patent application 2009201264 forms a complex with certain humate molecules, which is then attracted to the oxalate surface resulting in poisoning of active nucleation and growth sites. The reliance on interaction with other liquor components results in an agent that is not broadly applicable to all refinery liquor types and potentially sensitive to changes in liquor chemistry at a given refinery. [0007] Furthermore, the chemical properties of oxalate stabilisers, such as their physical state and solubility, may limit their use in Bayer process circuits. For example, fatty acids are known to be effective oxalate stabilisers in Bayer liquor [Australian Patent Application 2009201264]. However, many pure fatty acids of particular interest are typically solid at ambient temperature and have low aqueous solubilities, limiting their practical dosing to the Bayer circuit. In addition, the option of using an organic solvent carrier to increase the solubility of the fatty acids is less desirable due to the presence of unwanted -3 impurities and additional measures required to ensure safe deployment.. Furthermore, fatty acids typically promote foam formation in the Bayer liquor, which presents several process issues including unwanted oxalate nucleation. [0008] It is therefore desirable to provide an alternative stabiliser that is broadly applicable to a range of Bayer refinery liquors. [0009] One object of the present invention is to therefore provide a method that overcomes substantially the abovementioned problems known in the art, or at least provide a useful alternative thereto. [0010] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. [0011] Throughout the specification unless the context requires otherwise, the term "Bayer process liquor" will be understood to mean a liquor having a pH greater than about 10. [0012] Throughout the specification unless the context requires otherwise, the term "alkaline feed solution" will be understood to mean a solution having a pH greater than about 10. [0013] Throughout the specification, unless the context requires otherwise, the term "total alkali" or "TA" represents the total alkali concentration, expressed as the sum of the "total caustic" or TC and the concentration of sodium carbonate in liquor expressed as g/L sodium carbonate (Na 2

CO

3 ), wherein the TC is the sum of the sodium hydroxide and sodium aluminate in liquor expressed as g/L sodium carbonate. SUMMARY OF INVENTION [0014] In accordance with the present invention, there is provided a method for administering an agent comprising the step of: adding an amount of the agent to an alkaline feed solution, -4 wherein the agent chemically decomposes into one or more active species. [0015] Preferably, the agent comprises a fatty acid group. [0016] Preferably, the agent further comprises a polyglycol group. [0017] Preferably, the agent chemically decomposes via an alkaline hydrolysis reaction. [0018] Preferably, the one or more active species comprises a salt of the fatty acid. [0019] Preferably, the salt of the fatty acid acts as an oxalate stabilising agent. [0020] Still preferably, the one or more active components further comprises a polyglycol. [0021] Preferably, the polyglycol acts as an anti-foaming agent. [0022] Without being bound by theory, it is understood that the agent undergoes alkaline hydrolysis under the alkaline feed solution conditions of the present invention, thereby causing the agent to chemically decompose into the salt of the fatty acid and the polyglycol group. [0023] Preferably, the pH of the alkaline feed solution is in the range of about 10 to 15. [0024] In one form of the invention, the alkaline feed solution is a Bayer process liquor. [0025] Preferably, the Bayer process liquor comprises a portion of dissolved oxalate and dissolved alumina. [0026] Preferably, the Bayer process liquor has a TA ranging between about 200 and 350 g/L [0027] Preferably, the Bayer process liquor is maintained at a temperature ranging between about 50 and 80 0C during the steps of: -5 adding an amount of the agent to a Bayer process liquor. [0028] Preferably the Bayer process liquor has a pH ranging between about 13 and 15 during the step of: adding an amount of the agent to a Bayer process liquor. [0029] Preferably, the amount of oxalate stabilising agent added to the Bayer process liquor ranges between about 0.5 and 10 ppm. [0030] Preferably, the amount of agent added to the Bayer process liquor is added under mixing conditions. [0031] Without being limited by theory, it is understood that the agent comprising the fatty acid group and the polyglycol group undergoes alkaline hydrolysis when added to the Bayer process liquor to chemically decompose to the salt of the fatty acid and the polyglycol. [0032] Advantageously, the agent of the present invention chemically decomposes to the salt of the fatty acid and the polyglycol, such that the salt of the fatty acid is capable of stabilising the dissolved oxalate and the polyglycol is capable of acting as an anti-foaming agent. Those skilled in the art would understand that due to the organic content of the Bayer liquor, foam formation may occur. Those skilled in the art will also understand that fatty acids may further promote foam formation in the Bayer liquor. [0033] In one form, the present invention further comprises the steps of: precipitating alumina hydrate from the Bayer process liquor, thereby producing a spent Bayer process liquor; removing the agent from the spent Bayer process liquor; and precipitating sodium oxalate. subsequent to the step of: adding an amount of the agent to a Bayer process liquor.

-6 [0034] In accordance with the present invention, there is further provided an agent, wherein the agent is capable of separating into one or more active components under alkaline feed solution conditions. [0035] Preferably, the agent comprises a fatty acid group. [0036] Preferably, the agent further comprises a polyglycol group. [0037] Preferably, the agent has a molecular weight ranging between about 400 and 1200 g/mol. [0038] Preferably, the agent has a fatty acid content ranging between about 20 and 70 w/w%, [0039] The fatty acid group is preferably selected from a group comprising saturated fatty acids, mono-unsaturated fatty acids, poly-unsaturated fatty acids, and mixtures thereof. Suitable examples of saturated fatty acids include, but are not limited to, butyric, valeric, caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, margaric, stearic, arachidic, behenic, lignoceric, cerotic, carboceric, montanic, melissic, lacceoic, psyllic. Suitable examples of mono-unsaturated fatty acids include, but are not limited to, obtusilic, caproleic, lauroleic, linderic, myristoleic, physeteric, tsuzuic, palmitoleic, petroselinic, oleic, vaccenic, gadoleic, gondoic, cetoleic, erucic, and nervonic. Suitable examples of polyunsaturated fatty acids include, but are not limited to, linoleic, y-linolenic, dihomo-y-linolenic, arachidonic, a linoleic, stearidonic, 7,10,13,16-docosatetraenoic, 4,7,10,13,16 docosapentaenoic, 8,11,14,17-eicosatetraenoic, 5,8,11,14,17 eicosapentaenoic (EPA), 7,10,13,16,19-docosapentaenoic (D PA), 4,7,10,13,16,1 9-docosahexaenoic (DHA), and 5,8,1 1-eicosatrienoic (Mead acid). [0040] In one form of the invention the fatty acid group is a lauric acid group. [0041] In one form of the invention, the polyglycol group may be selected from a group comprising, polypropylene glycol (PPG) and copolymers, polyethylene glycol (PEG) and copolymers thereof.

-7 BRIEF DESCRIPTION OF THE DRAWINGS [0042] The present invention will now be described, by way of example only, with reference to following embodiments thereof and the accompanying figures, in which: Figure 1 is a flow sheet showing a method in accordance with the embodiment; Figure 2 is a graph of the viscosity of Stabiliser A and Stabiliser B over range of temperatures; Figure 3 is a graph of the effect of 1mg/L lauric acid on oxalate stability in Pinjarra liquor at TA 250 g/L; Figure 4 is a graph of the effect of 3mg/L lauric acid on oxalate stability in Pinjarra liquor at TA 250 g/L; Figure 5 is a graph of the effect of lauric acid and Stabiliser A on oxalate stability in Pinjarra liquor at TA 250 g/L; Figure 6 is a graph of the effect of lauric acid, Stabiliser A and Stabiliser B on oxalate stability in Pinjarra liquor at TA 250 g/L; Figure 7 is a bar graph of the effect of Stabiliser A on oxalate yield under Pinjarra oxalate crystallisation conditions; Figure 8 is a graph of the effect of Stabiliser B on oxalate settling under Pinjarra oxalate crystallisation conditions; and Figure 9 is a graph of the effect of Stabiliser A on liquor foaming in Pinjarra liquor. BEST MODES(S) FOR CARRING OUT THE INVENTION [0043] The present invention provides a method for administering an agent comprising the step of: adding an amount of the agent to an alkaline feed solution, -8 wherein the agent chemically decomposes into one or more active species. [0044] Preferably, the agent comprises a fatty acid group. [0045] Preferably, the agent further comprises a polyglycol group. [0046] Preferably, the agent chemically decomposes via an alkaline hydrolysis reaction. [0047] Preferably, the one or more active species comprises a salt of the fatty acid. [0048] Preferably, the salt of the fatty acid acts as an oxalate stabilising agent. [0049] Still preferably, the one or more active components further comprises a polyglycol. [0050] Preferably, the polyglycol acts as an anti-foaming agent. [0051]Without being bound by theory, it is understood that the agent undergoes alkaline hydrolysis under the alkaline feed solution conditions of the present invention, thereby causing the agent to chemically decompose into the salt of the fatty acid and the polyglycol group. [0052] Preferably, the pH of the alkaline feed solution is in the range of about 10 to 15. [0053] In one form of the invention, the alkaline feed solution is a Bayer process liquor. [0054] Preferably, the Bayer process liquor comprises a portion of dissolved oxalate and dissolved alumina. [0055] Preferably, the Bayer process liquor has a TA ranging between about 200 and 350 g/L [0056] Preferably, the Bayer process liquor is maintained at a temperature ranging between about 50 and 80 0C during the step of: -9 adding an amount of the agent to a Bayer process liquor. [0057] Preferably the Bayer process liquor has a pH ranging between about 13 and 15 during the step of: adding an amount of the agent to a Bayer process liquor. [0058] Preferably, the amount of oxalate stabilising agent added to the Bayer process liquor ranges between about 0.5 and 10 ppm. [0059] Preferably, the amount of agent added to the Bayer process liquor is added under mixing conditions. [0060] Without being limited by theory, it is understood that the agent comprising the fatty acid group and the polyglycol group undergoes alkaline hydrolysis when added to the Bayer process liquor to chemically decompose to the salt of the fatty acid and the polyglycol. [0061] Advantageously, the agent of the present invention chemically decomposes to the salt of the fatty acid and the polyglycol, such that the salt of the fatty acid is capable of stabilising the dissolved oxalate and the polyglycol is capable of acting as an anti-foaming agent. Those skilled in the art would understand that due to the organic content of the Bayer liquor, foam formation may occur. Those skilled in the art will also understand that fatty acids may further promote foam formation in the Bayer liquor. [0062] In one form, the present invention further comprises the steps of: precipitating alumina hydrate from the Bayer process liquor, thereby producing a spent Bayer process liquor; removing the agent from the spent Bayer process liquor; and precipitating sodium oxalate. subsequent to the step of: adding an amount of the agent to a Bayer process liquor.

-10 [0063] In accordance with the present invention, there is further provided an agent, wherein the agent is capable of separating into one or more active components under alkaline feed solution conditions. [0064] Preferably, the agent comprises a fatty acid group. [0065] Preferably, the agent further comprises a polyglycol group. [0066] Preferably, the agent has a molecular weight ranging between about 400 and 1200 g/mol. [0067] Preferably, the agent has a fatty acid content ranging between about 20 and 70 w/w%. [0068] The fatty acid group is preferably selected from a group comprising saturated fatty acids, mono-unsaturated fatty acids, poly-unsaturated fatty acids, and mixtures thereof. Suitable examples of saturated fatty acids include, but are not limited to, butyric, valeric, caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, margaric, stearic, arachidic, behenic, lignoceric, cerotic, carboceric, montanic, melissic, lacceoic, psyllic. Suitable examples of mono-unsaturated fatty acids include, but are not limited to, obtusilic, caproleic, lauroleic, linderic, myristoleic, physeteric, tsuzuic, palmitoleic, petroselinic, oleic, vaccenic, gadoleic, gondoic, cetoleic, erucic, and nervonic. Suitable examples of polyunsaturated fatty acids include, but are not limited to, linoleic, y-linolenic, dihomo-y-linolenic, arachidonic, a linoleic, stearidonic, 7,10,13,16-docosatetraenoic, 4,7,10,13,16 docosapentaenoic, 8,11,14,17-eicosatetraenoic, 5,8,11,14,17 eicosapentaenoic (EPA), 7,10,13,16,19-docosapentaenoic (DPA), 4,7,10,13,16,1 9-docosahexaenoic (DHA), and 5,8,1 1-eicosatrienoic (Mead acid). [0069] In one form of the invention the fatty acid group is a lauric acid group. [0070] In one form of the invention, the polyglycol group may be selected from a group comprising, polypropylene glycol (PPG) and copolymers, polyethylene glycol (PEG) and copolymers thereof.

-11 [0071]One embodiment of the present invention will now be described with reference to Figure 1, in which there is shown a method 10 for administering an agent capable of chemically decomposing into one or more active species under alkaline feed solution conditions in accordance with the present invention. In the method 10, the agent 12 is added to Bayer process liquor 14 containing dissolved oxalate and dissolved alumina under mixing conditions. Precipitation of aluminium hydroxide 16 from the Bayer process liquor is facilitated thereby producing spent Bayer process liquor 18. The crystallisation of sodium oxalate 20 is induced by, for example, the addition of oxalate seed 22. Between the precipitation of alumina hydrate 16 and sodium oxalate 20, the spent liquor 18 may be concentrated by evaporation in evaporation tanks (not shown). Activated carbon 24 may be added to the system in order to mitigate the effects of the oxalate stabliser. [0072] The following non-limiting examples are intended to assist in the understanding of the parameters of the present invention. Example 1 Lauric acid based oxalate stabilisers [0073] A variety of oxalate stabilisers were studied to determine their ability to stabilise oxalate in Bayer process liquors. Table I shows the oxalate stabilisers investigated and their physical properties.

-12 Table 1: Physical properties of lauric acid based agents Molecular %w/w Physical Viscosity S.G at Agent Chemical weight lauric state at at 200C 250C (g/mol) acid 250C (cPs) (g/cm 3 ) Solid Lauric Lauric acid 200 100 (mp applicable 0.88 acid . apial 430C) Stabiliser Polypropylene Approx. 33 liquid 100 0.97 monolaurate Stabiliser Polypropylene Approx. . . B glycol - 789 51 liquid 85 0.95 dilaurate Figure 2 shows the viscosity as a function of temperature for Stabiliser A, (polypropylene glycol-monolaurate) and Stabiliser B, (polypropylene glycol dilaurate). The results show that the viscosity decreased with increasing temperature, which demonstrates that the stabilisers behave as simple liquids and are therefore advantageous in respect to their dosing in the Bayer circuit. [0074] Stock solutions of lauric acid were prepared in 1 g/L aqueous sodium hydroxide. Stock solutions of the Stabiliser A and Stabiliser B were prepared in water as emulsions, wherein the emulsions were vigorously shaken immediately prior to sampling with a pipette. Performance testing [0075] The oxalate stabilising ability for each of the oxalate stabilisers was investigated by measuring the oxalate breakpoint (in g/L sodium oxalate) of the stabiliser treated liquor concentrations at a nominal total alkali (TA) concentration versus a control liquor. The oxalate breakpoint is the highest concentration of oxalate that the liquor can tolerate before spontaneous oxalate crystallisation occurs. The difference in the two breakpoints; stabiliser treated liquor versus a control liquor, is reported as the stability increase caused by the stabiliser. The oxalate breakpoints were measured by treating portions of spent liquor to give a range of oxalate concentrations. These -13 portions were then equilibrated to target temperature and mixed with hydrate seed at temperature for a specified holding time, before the sodium oxalate concentration in the liquors was measured. Sodium oxalate concentrations were determined by gas chromatography of the dimethyl esters of oxalic acid. [0076] Figures 3 to 6 show the stabilising ability of the oxalate stabilisers in a Bayer process liquor having a total alkali (TA) content of 250 g/L. Figures 3 and 4 show that lauric acid dosed at 1 mg/L and 3 mg/L is an effective stabiliser. The oxalate stabilising ability of Stabiliser A, Stabiliser B and lauric acid was found to be comparable on a equivalent lauric acid dose basis, as can be seen with reference to Figures 5 and 6. [0077] To determine the performance and assess the variability of the investigated stabilisers over multiple experiments, the oxalate stability increase per mg/L lauric acid at both low (1 mg/L) and high (3 mg/L) stabiliser doses was calculated. These results are shown in Table 2 below. [0078] The data shows that the stabiliser performance at the low dose was variable between experiments and that there was no significant difference between the performance of lauric acid, Stabiliser A and Stabiliser B. For the high dose, the performance variability was lower, with no observable difference between the stabilisers. The results also demonstrated that the dose response is not linear with the dose response dropping with increasing dose rate.

-14 Table 2: Comparison of stabiliser performance on a lauric acid basis Chemical Liquor Stability increase per mg/L lauric acid sample 1 mg/L lauric acid 3 mg/L lauric acid Lauric acid 1 0.22 0.13 Lauric acid 2 0.34 0.15 Lauric acid 3 0.30 0.14 Lauric acid 4 0.49 0.20 Stabiliser A 1 0.15 0.14 Stabiliser A 2 0.35 0.24 Stabiliser B 1 0.30 0.20 Example 2 Oxalate Crystallisation Yield [0079] The effect of Stabiliser A on oxalate yield was tested under simulated refinery conditions. This test determined oxalate crystallisation yield after 2 hours at 590C in Pinjarra refinery liquor at TA 270 g/L seeded with 33 g/L sodium oxalate seed. The stabilisers were dosed to the liquor just prior to oxalate seed addition. Multiple tests for each condition were performed to determine the experimental variability and measurement of statistically significant changes. [0080] Figure 7 shows that a 6 mg/L dose of Stabiliser A, (equivalent to 2 mg/L lauric acid), had no measurable effect on oxalate yield. Example 3 Oxalate Settling [0081] The effect of Stabiliser B on oxalate settling rate was investigated under simulated refinery oxalate settling conditions: TA 275 g/L, temperature 590C, sodium oxalate solids 34 g/L.

-15 [0082] A stock solution of 1.8 g/L Stabiliser B was prepared in water. A Pinjarra refinery oxalate thickener feed slurry sample was collected and separated into identical 900 mL portions. Each portion was added into high density polyethylene (HDPE) bottles and allowed to equilibrate at 70 0C prior to the commencement of the oxalate settling experiments. [0083]Aliquots of the Stabiliser B stock solution were added to the slurry portions to prepare samples having 2 and 4 mg/L Stabiliser B respectively. Additional 'control' slurry samples were prepared with no stabiliser addition. The slurry samples were equilibrated at 700C for two hours prior to the performing the oxalate setting experiments. The individual slurries were then transferred into I L glass measuring cylinders in a purpose built settling apparatus and left to equilibrate at 590C for 15 minutes. 0.7 mL of a suitable flocculant solution was added to achieve 50 g/t relative to the oxalate solids and the slurry then mixed with a perforated disc plunger to uniformly disperse the oxalate solids through the cylinder. The bed height of the oxalate solids was recorded at regular time intervals throughout the experiments. In addition the settled bed height was measured after 45 minutes. A test was also performed with no stabiliser and no flocculant addition to confirm flocculant addition had been effective. [0084] The results showed that Stabiliser B had no effect on oxalate settling rate (Figure 8). The settled bed height after 45 minutes was also similar for all tests with the exception of the tests in the absence of added flocculant, which had a more compact bed typical of unflocculated settled oxalate. Example 4 Foaming The effect of Stabiliser A on liquor foam formation was examined using a Pinjarra Bayer process liquor. [0085] A laboratory method based on the Australian Standard Method ASTM D3519-1988 was used to measure the foaming tendency of various oxalate stabilisers.

-16 [0086]A Pinjarra spent liquor sample was separated into 200 mL portions, then placed into HDPE bottles and preheated to 800C. An electric blender with a glass jug was preheated with hot deionised water just prior to each experiment. The 200mL of preheated liquor and 40 g of aluminium hydroxide, (also pre-heated to 800C), were added to the pre heated blender together with an appropriate volume of Stabiliser A such that the temperature of the resulting slurry was approximately 650C. Additional 'control' slurry samples were prepared with no stabiliser addition. The slurry was mixed as vigorously as possible using the blender for 30 seconds and the contents were immediately poured into a preheated 500 mL glass measuring cylinder. The resulting foam height was then recorded at thirty second intervals. The slurry temperature during the experiment was between 60 and 650C. The results show that Stabiliser A dosed at 2 mg/L was effective at breaking down foam relative to the control tests (Figure 9). These results are similar to that achieved when a commercial antifoam is dosed into these liquors. Example 5 Pinjarra Refinery Trials [0087] In order to further assess the stabiliser performance and monitor for side effects such as foaming, a series of precipitation bank trials at the Applicant's Pinjarra refinery were performed. Two stabiliser formulations containing 33% (Stabiliser A, PPG9-monolaurate) and 50% (Stabiliser B, PPG9-dilaurate) by weight lauric acid were evaluated. [0088] The trials consisted of a series of tests in which stabiliser performance was assessed by comparing the oxalate stability between dosed and undosed banks over a three to four day test period. The banks were controlled to maintain similar conditions (flow, temperature, TA) in order to minimise variability and therefore better assess stabiliser performance. [0089] The stabiliser was dosed to first precipitator vessel overflow under mixing conditions to ensure good mixing of the stabiliser and liquor prior to entering the subsequent precipitator vessel. Slurry samples from the final -17 precipitator vessel were taken at fixed intervals during the trial and analysed to determine the oxalate stability. In addition selected slurry samples were filtered and oxalate breakpoints determined on the filtered liquor as described in Example 1. Results of stabiliser performance [0090] The performance of Stabiliser A (Table 3) and Stabiliser B (Table 4) was compared by dividing the average weekly stability change induced by the stabilisers by the average weekly dose. Table 3: Oxalate stability increase due to Stabiliser A addition where dose is as ppm Stabilser A. Stabiliser A Test Average dose Average stability increaselncremental stability increase ------- - ppm g g/L per ppm 1 6.5 i 0.37 0.057 2 6.2 0.38 0.061 3 6.8 0.24 0.035 5 5.1 0.14 0.027 6 4.1 0.32 0.078 Average 0.052 Standard deviation 0.020 RSD % 39 Table 4: Oxalate stability increase due to Stabiliser B addition where dose is as ppm Stabilser B. Stabiliser B Test Average dose Average stability increase Incremental stability increase ppm g/L g/L per ppm 7 3.6 0.13 0.036 8 4.0 0.15 0.038 9 4.4 0.76 0.174 10 4.3 0.61 0.143 11 4.8 0.32 0.067 11 2.3 0.19 0.083 - ---- -Average 0.090 Standard deviation 0.057 RSD % 63 -18 [0091] The results showed that Stabiliser A provided a stability increase of 0.052 g/L ± 0.020 per ppm stabiliser based on 13 days total testing and Stabiliser B provided a stability increase of 0.090 g/L ± 0.057 per ppm of stabiliser based on 12 days total testing. [0092] The performance of Stabiliser A and Stabiliser B were the same within experimental error on a lauric acid dose basis, Stabiliser A having provided a stability increase of 0.16g/L per ppm stabiliser and Stabiliser B a stability increase of 0.18g/L per ppm stabiliser. [0093] It is envisaged that the process 10 of the present invention may substantially reduce operating costs in relation to the recovery of alumina products, when compared to the prior art processes for alumina recovery. [0094] Advantageously, the agent of the present invention chemically decomposes to the salt of the fatty acid and the polyglycol, such that the salt of the fatty acid is capable of stabilising the dissolved oxalate and the polyglycol is capable of acting as an anti-foaming agent. Those skilled in the art would understand that due to the organic content of the Bayer liquor, foam formation may occur. Those skilled in the art will also understand that fatty acids may further aid foam formation in the Bayer liquor. [0095] The Applicant envisages that the agent 12 of the present invention will be broadly applicable to all refinery liquor types. [0096] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims (28)

1. A method for administering an agent comprising the step of: adding an amount of the agent to an alkaline feed solution, wherein the agent chemically decomposes into one or more active species.

2. A method according to claim 1, wherein the agent comprises a fatty acid group.

3. A method according to claim 1 or 2, wherein the agent further comprises a polyglycol group.

4. A method according to any one of the preceding claims, wherein the agent chemically decomposes via an alkaline hydrolysis reaction.

5. A method according to any one of the preceding claims, wherein the one or more active species comprises a salt of the fatty acid.

6. A method according to claim 5, wherein the salt of the fatty acid acts as an oxalate stabilising agent.

7. A method of any one of the preceding claims, wherein the one or more active components further comprises a polyglycol.

8. A method of claim 7, wherein the polyglycol acts as an anti-foaming agent.

9. A method of any one of the preceding claims, wherein the pH of the alkaline feed solution is in the range of about 10 to 15.

10. A method of any one of the preceding claims, wherein the alkaline feed solution is a Bayer process liquor.

11. A method of claim 10, wherein the Bayer process liquor comprises a portion of dissolved oxalate and dissolved alumina. -20

12. A method of any one of claims 10 or 11, wherein the Bayer process liquor has a TA ranging between about 200 and 350 g/L

13. A method according to any one of claims 11 to 12, wherein the Bayer process liquor is maintained at a temperature ranging between about 50 and 80 0 C during the step of: adding an amount of the agent to a Bayer process liquor.

14. A method according to any one of claims 10 to 13, wherein the Bayer process liquor has a pH ranging between about 13 and 15 during the step of: adding an amount of the agent to a Bayer process liquor.

15. A method according to any one of claims 10 to 14, wherein the amount of oxalate stabilising agent added to the Bayer process liquor ranges between about 0.5 and 10 ppm.

16. A method according to any one of claims 10 to 15, wherein the amount of agent added to the Bayer process liquor is added under mixing conditions.

17. A method according to any one of claims 10 to 16, wherein the method further comprises the steps of: precipitating alumina hydrate from the Bayer process liquor, thereby producing a spent Bayer process liquor; removing the agent from the spent Bayer process liquor; and precipitating sodium oxalate, subsequent to the step of: adding an amount of the agent to a Bayer process liquor.

18. An agent, wherein the agent is capable of separating into one or more active components under alkaline feed solution conditions. -21

19. An agent according to claim 18, wherein the agent comprises a fatty acid group.

20. An agent according to any one of claims 18 or 19, wherein the agent further comprises a polyglycol group.

21. An agent according to any one of claims 18 to 20, wherein the agent has a molecular weight ranging between about 400 and 1200 g/mol.

22. An agent according to any one of claims 18 to 21, wherein the agent has a fatty acid content ranging between about 20 and 70 w/w%.

23. An agent according to any one of claims 19 to 22, wherein the fatty acid group is selected from a group comprising saturated fatty acids, mono unsaturated fatty acids, poly-unsaturated fatty acids, and mixtures thereof. Suitable examples of saturated fatty acids include, but are not limited to, butyric, valeric, caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, margaric, stearic, arachidic, behenic, lignoceric, cerotic, carboceric, montanic, melissic, lacceoic, psyllic.

24. An agent according to claim 23, wherein the mono-unsaturated fatty acids are one or more of obtusilic, caproleic, lauroleic, linderic, myristoleic, physeteric, tsuzuic, palmitoleic, petroselinic, oleic, vaccenic, gadoleic, gondoic, cetoleic, erucic, and nervonic.

25. An agent according to claim 23, wherein the poly-unsaturated fatty acids are one or more of linoleic, y-linolenic, dihomo-y-linolenic, arachidonic, a-linoleic, stearidonic, 7,10,13,16-docosatetraenoic, 4,7,10,13,16 docosapentaenoic, 8,11,14,17-eicosatetraenoic, 5,8,11,14,17 eicosapentaenoic (EPA), 7,10,13,16,19-docosapentaenoic (DPA), 4,7,10,13,16,1 9-docosahexaenoic (DHA), and 5,8,1 1-eicosatrienoic (Mead acid).

26. An agent according to claim 23, wherein the fatty acid is a lauric acid group. -22

27. An agent according to any one of claims 20 to 26, wherein the polyglycol group may be selected from a group comprising, polypropylene glycol (PPG) and copolymers, polyethylene glycol (PEG) and copolymers thereof.

28. A method for administering an agent as herein before described with reference to Figure 1. 26. A method for administering an agent as herein before described with reference to Examples 1 to 5.