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THIS INVENTION relates to extractive metallurgy and to molecular recognition resins used therein. In particular, the invention relates a process for improving the loading capacity of a molecular recognition ("MR") resin, a method for synthesizing a molecular recognition ("MR") resin and to a MR resin synthesized in accordance with said method. The invention also extends to a method for the removal and concentration of desired ions such as Pd ²⁺ from a multiple ion source solution which may contain larger concentrations of other undesired ions.

BACKGROUND TO THE INVENTION

Platinum group metals ("PGMs") have enormous economic value; therefore, improved processes or methods for the recovery and/or separation of these metals are of great importance. In particular, molecular recognition ("MR") as an extractive metallurgical method plays an important role as one of these recovery methods.

Broadly speaking, MR involves bringing a source solution containing multiple ions, some of which may be desired PGM ions while others are undesirable, into contact with an MR resin. The MR resin has functional groups that are chemically bound to a surface of a macroporous support or matrix. The matrix is usually particle based and selected from the group consisting of sand, silica gel, glass, glass fibres, aluminium, zirconium, titanium and nickel oxide or other hydrophilic inorganic supports and mixtures thereof. During precious metal refining, contact between functional groups of the MR resin and, for example, a palladium-rich chloride-based solution occurs when said solution is passed through cylindrical glass columns holding the MR resins. Functional groups of the MR resin selectively bind palladium thereby removing it from the chloride-based solution, now being a palladium-lean solution. After the palladium-lean solution is washed out, the loaded palladium can be removed from the loaded MR resin by the passage of a so-called eluent, or stripping solution, with chemical properties suitable for this task. PGM ions, other than palladium, can also be extracted in a similar way.

Two important parameters determining the economic feasibility of the MR resin are its loading capacity, which is expressed in terms of grams of metal per column litre of MR resin, and its loading capacity decay, expressed as a loss of grams of metal per column litre of resin per cycle of operation. The economic value of the MR resin is determined by the extent to which it loads metal and the extent to which it chemically ages and declines to load metal, or decays, with use.

More particularly, for palladium extraction it is known that the MR resin comprises a sulphur and electron withdrawing group containing ligand covalently bonded through an organic spacer silicon grouping to a solid inorganic macroporous support or matrix such as a silica particle. The sulphur and electron withdrawing group containing ligand portions of the MR resin has an affinity for the desired palladium ions in the source solution and, when contacted therewith, form a palladium complex on the surface of the MR resin thereby removing the desired palladium ions from the source solution. Thereafter, desired palladium ions are removed from the MR resin by contacting the MR resin with a much smaller volume of the eluent having a greater affinity for the desired palladium ions than does the sulphur and electron withdrawing group containing ligand portion of the MR resin. The particular MR resin described in the above paragraph is synthesized by a standard resin synthesis whereby silica particles are reacted with functional group molecules, i.e. the sulphur and electron withdrawing group containing ligand portion, dissolved in an organic solvent. After the reaction, the MR resin, being functionalized silica, is separated from the solvent, air dried and packaged for use in metal refining.

The physical nature of the silica matrix of any MR resin is that it has a very high surface area of the order of hundreds of square meters per gram. This derives from its highly porous internal structure. Although the porous structure can be fairly well filled with the solvent and functional group molecules, it can retain air in its pores. Air in the pores prevents the solvent fully contacting the entire surface area of the silica. Consequently some parts of the available surface area will not be functionalized. Surface area is, thus, effectively wasted.

At least one of the objects of this invention is to provide an MR resin adapted to at least in part address the above mentioned problem by providing increased contact area on a surface of the MR resin for locating functional group molecules so that more reactions can occur between functional group molecules and desired Palladium-chloro complex ions in a source solution during extraction.

The invention also aims to provide an improved method for the removal and concentration of desired ions such as Palladium ions from a multiple ion source solution, which may contain larger concentrations of other undesired ions.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a process for improving the loading capacity of a molecular recognition ("MR") resin, the process including subjecting the MR resin to ultrasound treatment. In particular, provision is made for the process to include fitting an ultrasonic transducer to a MR resin synthesis reactor assembly; and connecting an external ultrasonic generator to the ultrasonic transducer to provide sound waves of suitable frequency to clear air from the porous structure of the MR resin.

The process may include producing sound waves having a frequency of between about 15000Hz and 40000Hz; preferably, sound waves having a frequency of about 19950Hz are produced. In an embodiment of the invention, the process including subjecting the MR resin to ultrasound treatment for about 30 to 60 minutes.

The invention also extends to a method for synthesising a molecular recognition ("MR") resin, the method comprising: preparing a transitional compound having functional group molecules for reacting with a macroporous matrix, the functional group molecules being in the form of sulphur and electron withdrawing group containing ligand portions having a high selectivity for the removal of ions or groups of ions containing Pd ²⁺ even when present at low concentrations from a source solution containing a mixture of these metal ions with ions that are not desirable to be removed ; immersing the macroporous matrix in a solution of the transitional compound to form a slurry; subjecting the slurry to ultrasound treatment to remove air from pores of the macroporous matrix; and reacting the transitional compound with the macroporous matrix in the treated slurry to form a MR resin having the functional group molecules attached thereto. Provision is made for the method to include fitting an ultrasonic transducer to a resin synthesis reactor assembly in which the transitional compound is reacted with the macroporous matrix; and connecting an external ultrasonic generator to the ultrasonic transducer to provide sound waves of suitable frequency to clear air from the porous structure of the macroporous matrix.

Further provision is made for the method to include producing sound waves having a frequency of between about 15000Hz and 40000Hz; preferably, sound waves having a frequency of about 19950Hz.

In an embodiment of the invention, the method includes subjecting the MR resin to ultrasound treatment for about 30 to 60 minutes. In a further embodiment of the invention, the method includes stirring the ultrasound treated slurry and reacting same for about 12 hours at a temperature between 60 °C to 80 °C before a product of the reaction, constituting the synthesized MR resin, is filtered and dried. The method includes utilizing a macroporous matrix selected from the group consisting of sand, silica gel, glass, glass fibres, aluminium, zirconium, titanium and nickel oxide or other hydrophilic inorganic supports and mixtures thereof.

The method further includes utilizing a macroporous matrix comprising particles having a particle size ranging between about 250μηη and 500μηη.

The invention further extends to a molecular recognition ("MR") resin which has been exposed to ultrasound treatment and which is ready for use in an extractive metallurgical separation device.

The invention yet further extends to a method for removal and concentration of desired ions such as Pd ²⁺ even when present at low concentrations from a source solution containing a mixture of these metal ions with ions that are not desirable to be removed, which method includes: passing a desired ion rich source solution through a separation device containing a MR resin which has been exposed to ultrasound treatment to contact functional group molecules, which are in the form of sulphur and electron withdrawing group containing ligand portions, with ions or groups of ions containing Pd ²⁺ in the desired-ion rich solution to form a Pd ²⁺ complex on the surface of the MR resin thereby removing desired ions from the source solution; removing the desired ions from the MR resin by contacting the MR resin with a smaller volume of an eluent having a greater affinity for the desired ions than does the sulphur and electron withdrawing group containing ligand portion of the MR resin; and recovering desired ions from the receiving solution by use of known extraction methods.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is now described, by way of example, with reference to the accompanying non-limiting diagrammatic drawings. In the drawings:

Figure 1 shows a block diagram of a method for synthesising a molecular recognition ("MR") resin in accordance with an embodiment of the invention; Figure 2 shows a graph of loading capacity performance of a MR resin according to the invention compared to that of a known MR resin; and Figure 3 shows a graph of loading capacity performance using data of

Figure 2 extrapolated to 220 cycles.

DETAILED DESCRIPTION OF THE DRAWINGS

This description is presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how at least one of the several forms of the invention may be embodied in practice.

Referring to Figure 1 , a method 10 for synthesising or manufacturing of a molecular recognition ("MR") resin in accordance with an embodiment of the invention is shown.

Firstly, a transitional compound is produced, the compound typically having general formula (i) as represented herebelow, for reacting with a macroporous matrix. The transitional compound is prepared to have functional group molecules, which are in the form of sulphur and electron withdrawing group containing ligand portions (the A-Q portion of (i)) with a high selectivity for and removal of ions or groups of ions containing Pd ²⁺ even when present at low concentrations from a source solution containing a mixture of these metal ions with ions that are not desirable to be removed.

Formula (i)

The 3-glycidoxypropyltrimethoxysilane portion of (i) acts as a spacer grouping, which is sufficiently hydrophilic to function in an aqueous environment to separate the A-Q portion of (i) from a surface of a matrix, with which the transitional compound (i) will bind in a subsequent reaction, to maximize the interaction between the A-Q portion of transitional compound (i) and a desired ion being separated from a source solution containing both desired Pd ²⁺ ions and non-desirable ions. It will be appreciated that spacer groupings, other than 3- glycidoxypropyltrimethoxysilane, may also be used such as, for example, glycidoxypropyl, ethyl, propyl, phenyl and methacryl.

In one example, transitional compound (i), which contains the functional group molecules (the A-Q portion), is prepared by dissolving 2 grams of reagent grade thiophenol in 10 mL of methanol in which had been dissolved 0.2 g of sodium metal. The mixture is slowly added to a three-necked round bottom flask equipped with a mechanical stirrer containing 20 mL of toluene and 4.3 g of 3- glycidoxypropyltrimethoxysilane at 75° C. The reaction is allowed to proceed for about 12 hours and consequently forms a transitional compound (i), in which A is sulphur (S) and Q is phenyl. Before thiophenol, as the A-Q portion of transitional compound (i), is attached via chemical reaction according to step 18 to porous surfaces of silica gel particles, having a particle size of between about 250μηη - 500μηη, steps 14 and 16 as shown in Figure 1 , are effected. Step 14 involves the immersion of the silica gel particles in the transitional compound (i) to form a slurry. The slurry is then subjected to ultrasound treatment according to step 16 in order to remove air from pores of the silica gel particles, which particles will form a macroporous matrix for the MR resin after reaction with the transitional compound (i) according to step 18.

In laboratory tests, silica gel particles immersed in the transitional compound (i) were subjected to 1 0 minutes of ultrasound having a frequency of 43,000Hz. Air trapped in the silica was observed to rapidly escape as an abundance of small bubbles. It will be appreciated that high frequency (typically over 1 9,000Hz) sound waves that are above human hearing are used during step 16. The ultrasound vibrates the slurry at high frequency. These vibrations have the ability to continually distort micro-sized air bubbles trapped within pores of the macroporous structure of the silica gel particles. The vibrations, thus, weaken and break the bubbles' adhesion to surface areas of the macroporous structure of the silica gel particles. Trapped air is thereby vibrated out of the porous structure and replaced with the functional group-bearing transitional compound (i). Step 16, thus, maximizes the contact between the surface area of the silica gel particles and the functional group-bearing transitional compound (i), ultimately enabling more functional groups to be chemically bound to the silica gel particles in the subsequent reaction step 18. The effect is that Pd ²⁺ loading capacity of the newly synthesized MR resin is increased.

Scaled up industrial scale test work has shown similar results when a resin synthesis reactor assembly was fitted with an internal ultrasonic transducer in the form of a so-called sonotrode, which in turn was connected to an external ultrasonic generator. A titanium horn of the transducer produced ultrasound having a frequency of around 19,950Hz. After immersing the silica gel particles in the functional group-bearing transitional compound (i) according to step 1 6, the reaction mixture was subjected to ultrasound treatment for 30 to 60 minutes prior to the synthesis reaction according to step 18. The addition of steps 14 and 16 considerably improved contact between available surface area of the silica gel particles and the functional group-bearing transitional compound (i) and so enhanced the subsequent binding of the functional groups to the surface.

Penultimately, step 18 includes reacting 1 8 g of silica gel particles, which had been subjected to treatment according to step 16, with the transitional compound (i), in which A is typically sulphur (S) and Q is typically phenyl while stirring and heating the slurry at 60-80 °C for about 12 hours.

Finally, in step 20, the final product was isolated by filtration and dried before testing for capacity as a newly synthesized MR resin for selective Palladium removal.

Test results of the newly synthesized MR resin according to the invention showed that the resin's loading capacity had been noticeably (more that 10%) improved and that no damage to the silica gel matrix had occurred. The loading capacity was high and the loading capacity decay low. However, selectivity for palladium loading over platinum loading remained unchanged.

Comparative performance testing of an MR resin not including step 16 (COMPARATIVE) and one that includes step 16 when it is prepared (INVENTION) was performed over 20 cycles to determine reliable loading capacities and capacity decay factors. The experimental data is provided in Table 1 and illustrated graphically in Figure 2 of the drawings.

Loading Capacity (g/lt.)

Cycle

COMPARATIVE INVEhiTiON

1 27.32 31.71

2 27.36 31.19

3 27.S6 30.85

4 2 /.21 0.b4

5 26.79 30.91

6 27.14 3D.22

7 27.12 30.10

8 2G.S9 30.00

9 26.71 29.70

10 26.41 30.12

11 26. SS 30.31

12 26.39 30.08

13 26.56 30.17

14 26.64 29.97

15 26.07 29.79

16 26.26 29.81

17 26.44 30.23

18 25.99 30.13

19 ♦ 30.17

20 25.88 30.39

♦ Sample lost during the ex eriment

Table 1

Data of Table 1 was then extrapolated to 220 cycles which is the usual period of use for an MR resin in a resin column in the industrial application.

The comparative analysis (Figure 3) showed that palladium loading capacity for the MR resin according to the invention was 31 % more than the standard or comparative MR resin over the projected normal lifetime of the resin. This was due both to a 12% higher starting capacity (based on extrapolation) and a 30% lower loading capacity decay rate. Economic benefits from using the MR resin according to the invention over the standard or comparative MR resin are that less resin is required, lower volumes are generated in use, less boiling down of liquors is required (a time and energy saving), less waste solution and salt is generated in the process and less apparatus maintenance is required.

The experimental results, thus, indicate that the invention extends to a method for the removal and concentration of desired ions such as Pd ²⁺ even when present at low concentrations from a source solution containing a mixture of these metal ions with ions that are not desirable to be removed. The method includes passing a desired ion rich source solution through a separation column having MR resins according to the invention to contact functional group molecules of the MR resins, which molecules are in the form of sulphur and electron withdrawing group containing ligand portions, with ions or groups of ions containing Pd ²⁺ in the desired-ion rich solution to form a Pd ²⁺ complex on the surface of the MR resins thereby removing the desired ions from the source solution.

Thereafter, the desired Palladium ions are removed from the MR resin by contacting the MR resin with a smaller volume of a known eluent having a greater affinity for the desired ions than does the sulphur and electron withdrawing group containing ligand portion of the MR resin. Finally, the desired ions can be recovered from the eluent by use of known PGM refining methods.