AU2011236124B2

AU2011236124B2 - Method for the Control of Ammonium Sulphate Addition in the Hydrogen Reduction of Base Metals

Info

Publication number: AU2011236124B2
Application number: AU2011236124A
Authority: AU
Inventors: John O'callaghan
Original assignee: Murrin Murrin Operations Pty Ltd
Current assignee: Murrin Murrin Operations Pty Ltd
Priority date: 2010-10-21
Filing date: 2011-10-19
Publication date: 2014-10-30
Anticipated expiration: 2031-10-19
Also published as: AU2011236124A1

Abstract

- 12 Abstract 1. A method for the control of ammonium sulphate addition in the hydrogen reduction of base metals, the method comprising the steps of: (i) Adding ammonium sulphate to a metal containing solution to which 5 ammonia is also added; (ii) Measuring the density of the solution to which both ammonia and ammonium sulphate has been added in step (i); (iii) Measuring the concentration of the metal contained in the metal containing solution; and 10 (iv)Comparing the results of steps (ii) and (iii) to determine the ammonium sulphate concentration which in turn determines whether more or less ammonium sulphate is added to at step (i).

Description

I 1VV1V I ,I ,f.- I Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Murrin Murrin Operations Pty Ltd Actual Inventor John O'Callaghan Address for service is: WRAYS Ground Floor, 56 Ord Street West Perth WA 6005 Attorney code: WR Invention Title: Method for the Control of Ammonium Sulphate Addition in the Hydrogen Reduction of Base Metals The following statement is a full description of this invention, including the best method of performing it known to me:- "Method for the Control of Ammonium Sulphate Addition in the Hydrogen Reduction of Base Metals" Field of the Invention The present invention relates to a method for the control of ammonium sulphate 5 addition in the hydrogen reduction of base metals. More particularly, the method of the present invention is intended to improve the production of nickel from nickel sulphate solutions in hydrogen reduction. Background Art The process of hydrogen reduction is used for the precipitation of metal powder 10 from purified metal containing solution using hydrogen gas as the reductant. This process is typically carried out in mechanically agitated horizontal autoclaves at elevated temperature and pressure. For example, in the hydrometallurgical treatment of nickel sulphide or laterite ores to recover nickel, nickel containing ore is leached in sulphuric acid, producing a 15 pregnant leach solution that contains, amongst other things, nickel sulphate. After impurity removal a nickel sulphate containing aqueous raffinate solution is produced that is in turn passed to hydrogen reduction. In the hydrogen reduction of nickel, cobalt and other base metals from aqueous solutions, those solutions are typically contacted with ammonia to generate an 20 ammine solution, for example Ni(NH 3 )xSO 4 . However, at the elevated temperatures used in hydrogen reduction, ammonium sulphate (hereinafter "amsul") is used to stabilise nickel in the ammine solution. If there is insufficient amsul present then any of Ni(OH) 2 , basic nickel sulphates and other binary and tertiary salts may be formed. These salts may lead to fouling of piping, vessels 25 and equipment through the deposition of scale therein. This may then lead to plant downtime whilst that piping and equipment is cleaned. Dependent upon -2 plant design, this may in turn lead to production loss and/or incurring significant costs to de-scale. As such, a minimum level of amsul is required in solution in the hydrogen reduction of base metals. It is preferable to keep the amsul concentration within a relatively narrow range of 5 concentration to avoid several adverse effects. If more than the optimum level of amsul is present then dilution of nickel or other valuable metal occurs. Depending upon the configuration of the plant equipment this may lead to a potentially significant drop in metal production. In an effort to overcome these problems plant operators have previously used 10 regular laboratory analysis of manually sampled hydrogen reduction feed liquor. This analysis of amsul in feed liquor may be conducted using the Kjeldahl method, by Inductively Coupled Plasma Spectroscopy, by Atomic Absorption, or by X-Ray Diffraction. Unfortunately, as such samples are taken manually and the analysis takes several hours, there can be a substantial delay in providing the plant 15 operators with information relevant to maintaining the process chemistry within optimal parameters. Consequently, the concentration of amsul can vary significantly from the desired range. The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an 20 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. Throughout the specification and claims, 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 25 the exclusion of any other integer or group of integers.

Disclosure of the Invention In accordance with the present invention there is provided a method for the control of ammonium sulphate addition in the hydrogen reduction of base metals, the method comprising the steps of: 5 (i) Adding ammonium sulphate to a metal containing solution to which ammonia is also added; (ii) Measuring the density of the solution to which both ammonia and ammonium sulphate has been added in step (i); (iii) Measuring the concentration of the metal contained in the metal containing 10 solution; and (iv)Comparing the results of steps (ii) and (iii) to determine the ammonium sulphate concentration which in turn determines whether more or less ammonium sulphate is added at step (i). Preferably, the density measurement of step (ii) is conducted on a substantially 15 continuous basis. In one form of the present invention the density measurement of step (ii) is conducted at set times and a rolling average density calculated therefrom. Preferably, the metal containing solution of step (i) contains either no ammonium sulphate or contains very low levels thereof. 20 Still preferably, the metal containing solution of step (i) contains up to about 50 to 60 gpl ammonium sulphate.

-4 Preferably, the metal concentration measurement of step (iii) is conducted on a substantially continuous basis. The amount of ammonium sulphate added to the metal containing solution is preferably sufficient to raise the ammonium sulphate concentration thereof to 5 about 250 to 350 gpl. In one form of the present invention the metal containing solution is a nickel and/or cobalt sulphate containing aqueous solution. Preferably, the comparison of step (iv) is conducted through the application of an algorithm for the estimation of concentration of ammonium sulphate. 10 Still further preferably, the algorithm is defined as: CAm - [(1000.Ds.) D,,n -(0.60B)-(1.635B2)_1)] (0.57 + (0.60B)) Where: CAmsuI = concentration of ammonium sulphate (g/L) in the metal containing solution 15 Dsol,= density of the metal containing solution (g/mL) B = weight fraction of metal sulphate (MeSO 4 ), determined by: B- 2.63.[Me] 1 000.D,,, Where: [Me] = metal ion concentration in the metal containing solution. 20 Me = a base metal.

-5 Brief Description of the Drawings The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a portion of a metal recovery 5 flow sheet in which a method in accordance with the present invention is being applied; Figure 2 is a first plot showing amsul concentration determined by prior art methods compared with amsul concentration predicted by the method of the present invention; and 10 Figure 3 is a second plot showing amsul concentration determined by prior art methods compared with amsul concentration predicted by the method of the present invention, over a separate trial period. Best Mode(s) for Carrying Out the Invention In Figure 1 there is shown a method 10 for the control of ammonium sulphate 15 addition in hydrogen reduction. A metal containing solution 12, for example a nickel and/or cobalt sulphate containing aqueous solution, is received as a purified solution exiting an impurity removal process, for example a raffinate from a solvent extraction process step (not shown) and passed to a mixing vessel 14. The solution 12 contains either no ammonium sulphate ("amsul") or contains very 20 low levels thereof, for example up to about 50 to 60 gpl amsul. The mixing vessel 14 receives ammonia 16 in either gaseous or aqueous form. Further, amsul 18 is supplied to the mixing vessel 14, in the form of dry amsul or as a slurry or solution containing amsul, in a controlled manner. The amount of amsul added is sufficient to raise the amsul concentration to about 250 to 350 gpl. 25 It is to be understood that the amsul concentration will vary depending upon the concentration of nickel in the metal sulphate solution referred to above. For -6 example, nickel may be present at a concentration of 100 gpl in the metal sulphate solution. A mixed product 20 from the mixing vessel 14 is passed through a density measuring device 22 from which a fluid density reading 24 is obtained and passed 5 to a programmable device 26, such as a computer or similar, into which an algorithm has been programmed. This algorithm has as one relevant input the fluid density reading 24. The fluid density reading 24 is taken on a substantially continuous basis. For example, the density measuring device 22 may be provided in the form of an in-line meter that measures density continuously. It is 10 envisaged however that density may also be measured at set times and a rolling average density calculated from those set time measurements. A sample of the mixed product 20 from the mixing vessel 14, post the density measuring device 22, is passed to a device 28 for the measurement of metal concentration. A resulting metal concentration reading 30 is in turn passed to the 15 programmable device 26 as another input for the algorithm. The algorithm is defined as follows: CAmsut - [(10ooo.FD,,(XFD,, -(0.60B)-(1.635B2)-1)] (0.57 + (0.60B)) Where: CAmsuI = concentration of ammonium sulphate (g/L) in the metal containing 20 solution FDsoI 0 = fluid density of the metal containing solution (g/mL) B = weight fraction of metal sulphate MeSO 4 , determined by: B -2.63.[Me] I 00O.FD,, -7 Where: [Me] = metal ion concentration in the metal containing solution. Me = a base metal, for example Ni, Co or Cu. The programmable device 26, utilising the algorithm, calculates the amsul 5 concentration in the mixed solution 20 and provides feedback 32 to the amsul stream 18 which governs the flow of amsul to the mixing vessel 14. The influence of the calculated amsul concentration and feedback 32 on the flow of amsul 18 is either manual or, preferably, automatic. In Figures 2 and 3 there are shown the results of a series of tests in which the 10 results produced by the method 10 of the present invention have been compared with the concentrations obtained through the application of traditional techniques to the same samples. As can be noted, there is a clear or high level of correlation between the results in each of Figures 2 and 3. It may also be noted that low levels of amsul, below 200 gpl, are predicted by the algorithm and allowed 15 correction of the amsul concentration thereby avoiding prolonged operation at low amsul concentrations. As may be noted with reference to the above description, the method 10 of the present invention provides near real time information on amsul concentrations allowing either improved manual control or automated control thereof. This in turn 20 reduces the variability of amsul concentration in reduction feed liquors, minimising exposure to the formation of unwanted precipitates and scale, whilst also avoiding excessively dilute feed solution that would otherwise reduce productivity. It is understood that the term "base metal" includes, but is not limited to, nickel, cobalt, copper, magnesium, and aluminium.

-8 It is envisaged that the method of the present invention may be used to provide an estimate of amsul concentrations in other mixed salt systems, for example, caustic soda and alumina. Modifications and variations such as would be apparent to the skilled addressee 5 are considered to fall within the scope of the present invention.

Claims

1. A method for the control of ammonium sulphate addition in the hydrogen reduction of base metals, the method comprising the steps of: (i) Adding ammonium sulphate to a metal containing solution to which 5 ammonia is also added; (ii) Measuring the density of the solution to which both ammonia and ammonium sulphate has been added in step (i); (iii) Measuring the concentration of the metal contained in the metal containing solution; and 10 (iv)Comparing the results of steps (ii) and (iii) to determine the ammonium sulphate concentration which in turn determines whether more or less ammonium sulphate is added to at step (i).

2. A method according to claim 1, wherein the density measurement of step (ii) is conducted on a substantially continuous basis. 15

3. A method according to claim 1, wherein the density measurement of step (ii) is conducted at set times and a rolling average density calculated therefrom.

4. A method according to any one of the preceding claims, wherein the metal containing solution of step (i) contains either no ammonium sulphate or contains very low levels thereof. 20

5. A method according to claim 4, wherein the metal containing solution of step (i) contains up to about 50 to 60 gpl ammonium sulphate. - 10

6. A method according to any one of the preceding claims, wherein the metal concentration measurement of step (iii) is conducted on a substantially continuous basis.

7. A method according to any one of the preceding claims, wherein the amount of 5 ammonium sulphate added is sufficient to raise the ammonium sulphate concentration to about 250 to 350 gpl.

8. A method according to any one of the preceding claims, wherein the metal containing solution is a nickel and/or cobalt sulphate containing aqueous solution. 10

9. A method according to any one of the preceding claims, wherein the comparison of step (iv) is conducted through the application of an algorithm for the estimation of concentration of ammonium sulphate.

10. A method according to claim 9, wherein the algorithm is defined as: CAmu - [(OOO.D,, )(D,, -(0.60B)- (1.635B2)_ 1)] (0.57 + (0.60B)) 15 Where: CAmsuI = concentration of ammonium sulphate (g/L) in the metal containing solution Dorn= density of the metal containing solution (g/mL) B = weight fraction of metal sulphate (MeSO 4 ), determined by: 20 B- 2.63.[Me]

1000.D,, Where: - 11 [Me] = metal ion concentration in the metal containing solution. Me = a base metal.

11. A method for the control of ammonium sulphate addition in the hydrogen reduction of base metals, the method being substantially as hereinbefore 5 described with reference to the Figures.