The invention relates to functionalised materials and their uses, and in particular a treatment involving a metal scavenger and a process to selectively remove one of more specific metal species from a stream containing a range of metal ions and complexes.

Precious metals including platinum, rhodium, palladium, ruthenium, iridium and gold are a limited resource and are used extensively in numerous different applications across a vast array of industries. In addition more and more applications are being found and developed where precious metals are required. Thus there is a growing need to develop or improve systems and processes where the losses of precious metals are minimised. Losses can occur both in their application and in the refining and purification of precious metals. In such cases the precious metal is typically present in either a solid or a liquid. Systems have been developed to manage the former. However recovering precious metals from liquid streams remains a significant challenge given the wide range of formulations and compositions that are used for a diverse range of applications.

Functionalised materials are one of several systems that are being developed to remove precious metals from organic and aqueous liquids. In this approach a liquid containing one or more precious metals is passed through a material, often described as a metal scavenger, which contains a functional group that possesses an affinity for precious metals. Depending on the structural nature of the precious metal in solution it is possible to design suitable functionalised materials to remove the desired metal species. However precious metals are generally found in the presence of further metal species and in a vast range of different chemical environments. These conditions pose significant technical challenges and improved removal and selectivity to particular metals is desirable.

In the refining and purification of precious metals as well as in a number of other applications precious metals may be present at low concentrations, for example 0.5 to 2000 ppm along with further metal species at higher concentrations for example 500 to 50,000 ppm. The treatment of these streams with functionalised materials typically results in some initial removal of some of the precious metals present and then the removal of these metals stops. The overall results are very low removal of the desired precious metals from the stream, very low loading of the desired precious metals on the metal scavenger and a very high concentration of the further metal ions on the metal scavenger. Currently a high percentage of these precious metal streams are not being treated in a satisfactory manner or at all and so significant quantities of precious metals are not recovered. In addition to the economic loss of a limited essential resource, their removal from process streams is desirable from an environmental and health perspective or for reasons of quality control, for example in the pharmaceutical industry. New functionalised materials and processes are thus required to improve the capture of these limited and valuable resources.

The inventors have devised a treatment involving the use of a functionalised material which has a high and selective affinity for precious metals and a low affinity for further metals along with a periodic washing process that in combination selectively removes the desired precious metal to a high level from a stream containing a high concentration of further metals and complexes for example base and transition metals. The invention provides both a process for treating a feed material comprising a precious metal or a range of precious metals to be removed and further metals or complexes, the further metal species being present in concentrations ranging from 0.3 to 10 ^s times the combined concentration of the precious metals, the process comprising contacting the feed material and a metal scavenging compound or mixture of compounds to selectively remove the precious metal or metals to be removed from the feed material in the presence of further metals or complexes along with a periodic washing process and optionally a pH adjustment of the feed stream that in combination produces a feed material depleted in the removed precious metal or metals, the metal scavenging compounds include functionalised materials and polymers where the framework is an organic polymer such as polystyrene or polyolefin; or an inorganic framework such as silica or alumina, and a functional group is attached to the framework; and the use of a metal scavenging compound or mixtures of said compounds for the recovery of precious metal or metals from a feed material comprising the precious metal and further metals and complexes. A metal scavenging compound of particular interest is a compound of General Formula A being:

A composition [0 _4/ 2Si] _a [0 _3/ 2SiCH ₂ (CR ³ R ⁴ ) _m X] _b [0 _3/ 2SiCH ₂ (CR ³ R ) _n Y] _c [0 _3/ 2SiV] _d

wherein X is selected from NRR ² , NR[(CH ₂ ) _p NR ¹ ]iR ² , SR, S(CH ₂ ) _e SR, S(CH ₂ ) _f U, S[(CH ₂ )jS],R, S[(CH ₂ ) _e S] _t (CH ₂ ) _s Z, NRC(S)NR H, SCH ₂ CH(NHR)C0 ₂ E, SCH2CH(C0 ₂ E)CH ₂ C0 ₂ E, S(CH ₂ )|OR, S(CH ₂ ) _u C(0)W, S(CH ₂ ) _j NRC(S)NR ¹ H and OCH ₂ CH(OH)CH ₂ NR[(CH ₂ ) _p NR ¹ ]iR ³ where U is a heteroaromatic ring, Z is Si0 _{3 2} or a heteroaromatic ring, E is a H, C-MO alkyl or a metal ion M and W is OH, OR, OM or and when c is greater than 0, Y is selected from NRR ² , NR[(CH ₂ ) _p NR ¹ ]iR ² , SR, S(CH ₂ ) _e SR, S(CH ₂ ) _f U, S[(CH ₂ ) _j S],R, or S[(CH ₂ ) _e S] _t (CH ₂ ) _s Z;

R, R , R ³ and R ⁴ are independently selected from hydrogen, C _-22 -alkyl group, C _1-22 -aryl group and a C _1-22 -alkylaryl group; R ² is selected from hydrogen, C _-22 -alkyl group, or a C ₂ . ₁₀ - alkyl Si(0) _3/2 group, I, s, t and u are independently integers from 1 to 100; i is an integer from 1 to 10,000; m is an integer from 1 to 100; n is an integer from 1 to 100 and e, f, j, p are independently integer from 2 to 20;

V is a group which is optionally substituted and selected from a C _1-22 -alkyl group, C ₂ . ₂₂ - alkenyl group, a C _2-22 -alkynyl group, an aryl group a C _-22 -alkylaryl group, a Ci_ ₂₂ -alkyl group substituted with or containing as part of a chain a sulfide, a sulfoxide, a sulfone, an amine, a polyalkyl amine, a phosphine or other phosphorous containing group; M is a metal ion including base and transition ions; the free valences of the silicate oxygen atoms are saturated by one or more of:

a silicon atom of other groups of General Formula A, hydrogen, a linear or branched C _1-22 - alkyl group, an end group R ⁵ ₃ M ¹ 0 _1/2 , a cross-linking bridge member or by a chain R^M^OR^ _g Owa or AI(OR ⁶ ) ₃ - _h O _h/2 or R ⁵ AI(OR ⁶ ) ₂ . _r O _r/2 ;

wherein

M ¹ is Si or Ti;

R ⁵ and R ⁶ are independently selected from a linear or branched C _1-22 alkyl group, an aryl group and a C^-alkylaryl group;

k is an integer from 1 to 3, q is an integer from 1 to 2 and g is an integer from 0 to 2 such that g + k + q = 4;

h is an integer from 1 to 3; and

r is an integer from 1 to 2;

or an oxo metal bridging systems where the metal is zirconium, boron, magnesium, iron, nickel or a lanthanide;

a, b, c and d are integers such that the ratio of b:a is from 0.00001 to 100000 and a and b are always greater than 0 and when c is greater than 0 the ratio of c to a+b is from 0.00001 to 100000 and when d is greater than 0 the ratio of d to a+b is from 0.00001 to 100000. The term "metal" as employed herein includes any species of the metal whether solid metal, a complex or any other form of the metal.

Where an end group and/or cross linker and/or polymer chain is used, it is preferred that the ratio of end group, cross linker or polymer chains to a+b+c+d is from 0 to 999:1 preferably 0.001 to 999:1 and especially 0.01 to 99:1.

The removal of the precious metals from the feed material may be due to the precious metals being bound through donor interactions with the functional groups of the metal scavenging compound such as a functionalised polystyrene or polyolefin or a composition of General Formula A, or may be as a result of an ion exchange process.

Suitably, the process of the invention is carried out to achieve a pre-determined loading of the desired precious metal or metals on the metal scavenger. The loading of the desired precious metal or metals will be influenced by the available time to treat the feed material. High loadings up to 10% weight are preferred but levels of between 0.4 to 6% weight is acceptable.

The feed material may be a continuous stream for example a continuous process reaction feedstock, or may be in the form of a batch of material for discrete treatment. The feed material, for example a waste water or a waste process stream or a product stream, may be treated to selectively remove components of the feed material in the presence of similar or higher concentration of other components. The removed component may be a desirable or an undesirable material in the feed material. This process may be used for example in removing desired species such as precious metals from a feed material in a refining or purification process prior to disposal or use of the feed material. The process can also act to provide a desired composition for the feed material that has been depleted in the selectively removed component or components after contact with the metal scavenger. Known metal scavengers typically comprise a functional group attached to a solid organic or inorganic framework. Examples of organic polymer frameworks include polystyrene, polyaromatic or polyolefin resins or fibres. An example of a polyolefin framework is the Smopex® range of metal scavengers. Examples of functional groups include carboxylic acids and salts, pyridine, sulfonics acids, amines, sulfides and mercapto containing compounds as well as combination of these functional groups. Preferred compounds of General Formula A include those wherein: X is selected from NRR ² , NR[(CH ₂ ) _p NR ]iR ² , SR, S(CH ₂ ) _e SR, S[(CH ₂ ) _j S],R, S[(CH ₂ ) _e S] _t (CH ₂ ) _s Z, NRC(S)NR ¹ H, S(CH ₂ ) _u C(0)W, S(CH ₂ ) _j NRC(S)NR ¹ H and OCH ₂ CH(OH)CH ₂ NR[(CH ₂ ) _p NR ¹ ]iR ³ where Z is Si0 _3/2 or a heteroaromatic ring and W is NR[(CH ₂ ) _p NR ¹ ]jR ² .

In a preferred embodiment, when c is greater than 0, Y is selected from NRR ² , NR[(CH ₂ ) _p NR ¹ ]iR ² , SR, S(CH ₂ ) _e SR, S[(CH ₂ ) _j S],R, or S[(CH ₂ ) _e S],(CH ₂ ) _s Z;

Preferably, R, and R ¹ are independently selected from hydrogen, C^o-alkyl group, Ci_ ₂₂ -aryl group and a C _1-22 -alkylaryl group; R ² is selected from hydrogen, C _{1 -2} 2-alkyl group, or a C ₂ _i ₀ - alkyl Si(0) _3/2 group, R ³ and R ⁴ are hydrogen; s, t and u are independently integers from 1 to 20; i is an integer from 1 to 10,000; m is an integer from 1 to 10; n is an integer from 1 to 10 and e, j, p are independently integer from 2 to 20. Preferably, V is a group which is optionally substituted and selected from a C _-22 -alkyl group, C _2-22 -alkenyl group, a C _2-22 -alkynyl group, an aryl group a Ci_ ₂₂ -alkylaryl group, a ₂₂ -alkyl group substituted with or containing as part of a chain a sulfide, a sulfoxide, a sulfone, an amine, or a polyalkyl amine. Preferably, the free valences of the silicate oxygen atoms are saturated by one or more of: a silicon atom of other groups of General Formula A, hydrogen, a linear or branched C _1-10 - alkyl group, an end group R ⁵ ₃ M ¹ Oi ₂ , a cross-linking bridge member or by a chain R ⁵ _q M ¹ (OR ^e ) _e Ow2 or AI(OR ⁶ ) ₃ - _h O _h/2 or R ⁵ AI(OR ⁶ ) ₂ . _r O _r/2 ;

wherein

M ¹ is Si or Ti;

R ⁵ and R ⁶ are independently selected from a linear or branched Ci. ₂ alkyl group, an aryl group and a C^o-alkylaryl group;

k is an integer from 1 to 3, q is an integer from 1 to 2 and g is an integer from 0 to 2 such that g + k + q = 4;

h is an integer from 1 to 3; and

r is an integer from 1 to 2;

or an oxo metal bridging systems where the metal is zirconium, boron, magnesium, iron, nickel or a lanthanide.

Preferably, a, b, c and d are integers such that the ratio of b:a is from 0.00001 to 100 and a and b are always greater than 0 and when c is greater than 0 the ratio of c to a+b is from 0.00001 to 100 and when d is greater than 0 the ratio of d to a+b is from 0.00001 to 00. In an especially preferred embodiment, the composition comprises in combination two or more of these preferred features. In a particularly preferred embodiment, the composition comprises in combination all of these preferred features. Where an end group and/or cross linker and/or polymer chain is used, it is preferred that the ratio of end group, cross linker or polymer chains to a+b+c+d is from 0 to 999:1 preferably 0.001 to 999:1 and especially 0.01 to 99:1.

Particularly preferred compounds of General Formula A include those wherein: X is selected from NRR ² , NH[(CH ₂ ) _p NH]iR ² , SR, S(CH ₂ ) _e SH, S[(CH ₂ ) _j S],H, S[(CH ₂ ) _e S] _t (CH ₂ ) _s Z, NHC(S)NR ¹ H, S(CH ₂ ) _u C(0)W, S(CH ₂ ) _j NRC(S)NR H and OCH ₂ CH(OH)CH ₂ NH[(CH ₂ ) _p NH]iH where Z is Si0 ₃₂ or a heteroaromatic ring and W is NH[(CH ₂ ) _p NH]iH; and when c is greater than 0, Y is selected from NRR ² , NH[(CH ₂ ) _p NH]iR ² , SR, S(CH ₂ ) _e SH, S[(CH ₂ ) _j S] _t H, or S[(CH ₂ ) _e S] _t (CH ₂ ) _s Z;

R and R are independently selected from hydrogen, C _1-10 -alkyl group, C _1-22 -aryl group and a C _1-22 -alkylaryl group; R ² is selected from hydrogen, d.i ₂ -alkyl group, or a C ₃ -alkyl Si(0) _3/2 group, R ³ and R ⁴ are hydrogen; s, t and u are independently integers from 1 to 10; i is an integer from 1 to 10,000; m is an integer from 1 to 5; n is an integer from 1 to 5 and e, j, p are independently integer from 2 to 20;

V is a group which is optionally substituted and selected from a Ci_i ₂ -alkyl group, C _2-22 - alkenyl group, a Ci. ₂₂ -alkyl group substituted with or containing as part of a chain a sulfide, or an amine; the free valences of the silicate oxygen atoms are saturated by one or more of:

a silicon atom of other groups of General Formula A, hydrogen, a linear or branched C _1-10 - alkyl group, an end group R ⁵ ₃ M ¹ 0i ₂ , a cross-linking bridge member or by a chain or AI(OR ⁶ ) ₃ . _h O _h/2 or R ⁵ AI(OR ⁶ ) ₂ . _r O _r / ₂ ;

wherein

M ¹ is Si;

R ⁵ and R ⁶ are independently selected from a linear or branched C _1-6 alkyl group, and an aryl group;

k is an integer from 1 to 3, q is an integer from 1 to 2 and g is an integer from 0 to 2 such that g + k + q = 4;

h is an integer from 1 to 3; and r is an integer from 1 to 2;

or an oxo metal bridging systems where the metal is zirconium, boron, magnesium, iron, nickel or a lanthanide; a, b, c and d are integers such that the ratio of b:a is from 0.00001 to 10 and a and b are always greater than 0 and when c is greater than 0 the ratio of c to a+b is from 0.00001 to 10 and when d is greater than 0 the ratio of d to a+b is from 0.00001 to 10.

Where an end group and/or cross linker and/or polymer chain is used, it is preferred that the ratio of end group, cross linker or polymer chains to a+b+c+d is from 0 to 999:1 preferably 0.001 to 999:1 and especially 0.01 to 99:1.

Suitably, the process comprises passing the feed material through a fixed bed containing one or more metal scavengers. The feed material suitably comprises an aqueous solution and may range in pH between 0 and 10. The feed material may comprise an acid, for example hydrochloric acid, nitric acid and sulfuric acid or a mixture of acids. The pH of the feed material may optionally be adjusted using either acid or base to increase the desired metal uptake. The feed material may be passed either up or down through a fixed bed containing a metal scavenger at flow rates suitable for the efficient removal of the desired component. Whilst passing the feed material through a fixed bed of a metal scavenger the stream may be held for a period of time ranging from 1 second to 48 hours so as to ensure effective contact with the desired component to be removed. After contacting the feed material with a metal scavenger for an effective amount of time ranging from 1 second to 48 hours under such conditions to remove the desired component, the fixed bed of a metal scavenger is preferably washed with a suitable compatible solvent to remove the build up of the unwanted ions and complexes around the metal scavenger. Where the feed material contains precious metals along with unwanted base and transition metals then suitably, the functional group of the metal scavenger possesses a differential affinity, suitably a very high affinity for precious metal as compared to further metals.

Suitably, the flow rate and washing frequency and volume will depend on the volume of feed material to be treated, the nature, combination and concentrations of the precious metals, the concentration of the further metal ions and complexes and the nature of the feed material such as solvent and pH. Flow rate values are preferably from 0.1 to 2000 litres/hour and more preferably 0.1 to 50 litres/hour. The washing volume is suitably from 1 to 1000 Bed Volumes of solvent with desirably 1 to 10 Bed Volumes. The washing frequency preferably is from 30 minutes to 4 days. Suitable washing solvents include water, deionised water, aqueous formulations, alcohols, hydrocarbons, aromatics, and polar solvents. Where water or an aqueous formulation is used the pH may range from 0-10 with 4-8 preferred. The washing solvent may be passed either up or down through the metal scavenger at flow rates suitable for the efficient removal of the unwanted ions and complexes. The washing solvent may be held in the metal scavenger for a period of time so as to ensure effective washing. The period of time may range from 1 second to 24 hours. The overall process may be conducted at temperatures from 5 to 80°C and pressures up to 10 bar. Preferred temperatures are in the range of 10-60°C. The process also encompasses recycling the feed material through the metal scavenger where necessary or desirable with the aim of removing higher levels of precious metal species as compared to a single pass and loading onto the metal scavenger. In one embodiment a combination of different composition of metal scavengers and in particular of General Formula A may be employed to selectively remove different precious metals for example where different ions, oxidation states and complexes may be present. Thus the invention also encompasses the use of a combination of compositions of metal scavengers to remove a range of specific metals from the feed material. In particular the invention also encompasses the use of a combination of metal scavengers with compositions of General Formula A to remove a range of precious metals species from the feed material.

In the metal refining and purification industry metals such as but not limited to aluminium, iron, copper, bismuth, nickel, selenium and zinc are found or used to aid separation, in similar or higher concentrations than the desired precious metal species. Examples of process streams include but not limited to a combined precious metal content of 1-500 ppm along with metal ions such as iron, copper, nickel, aluminium and zinc ranging from 100- 50,000 ppm.

Removal of the precious metal species from the feed material may be improved by including a periodic washing step in which a wash liquid is contacted periodically with the metal scavenger including a composition or a mixture of compositions of General Formula A. In a preferred embodiment the washing step is carried out using a ratio of Bed Volume of wash liquid to Bed Volumes of feed material of at least 1 to 100, preferably at least 1 to 80, and desirably at least 1 to 50. By way of example in a preferred process, treatment of an acidic process stream where the combined precious metal concentration is less than 100 ppm, for example less than 20 ppm and further metals, for example zinc, nickel or iron, are present at as level in excess of 1000 ppm, for example at 11 ,000 ppm with a compound of General Formula A [Si0 ₂ ] [0 _3/ 2SiCH2CH2SCH2C(=0) H(CH2CH ₂ NH)4H] provides for selective removal of the precious metal in combination with a washing process involving passing 8 Bed Volumes of deionised water through the material, after every 400 Bed Volumes of process stream has passed through, then the average reduction in metal content of the treated feed material was platinum - 99%; palladium - 99% and rhodium - 70%. In another example compositions of General Formula A [Si0 ₄ ,2][0 _3/ 2SiCH ₂ CH2SCH ₂ C(=0)NH(CH ₂ CH ₂ NH) ₄ H], [Si0 _4/ 2][0 _3/ 2SiCH ₂ CH ₂ CH ₂ SH],

[SiO^fO^SiCHzCHzSCHzCHzCHzSHKOa^SiCHzCHzSCHzCHsCHzSCHzCHzSiO ad and [Si0 _4/2 ][0 _3/2 SiCH ₂ CH ₂ SH] each in combination with an aqueous washing cycle can selectively remove platinum, palladium, rhodium, gold and ruthenium at a total concentration of 500 ppm from a solution also containing 3500 ppm nickel.

In a large scale operation an aqueous acidic stream (5,600 L) containing platinum (2 ppm), palladium (3 ppm) and rhodium (0.6 ppm) complexes and a mixture of zinc, copper, sodium and iron (total 8,000 ppm) was passed through sequentially two fixed beds (0.9 kg per bed) containing compounds [Si0 _4/2 ] [C^SiC^C^SH] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ CH ₂ CH ₂ SH] and [0 _3/2 SiCH ₂ CH ₂ SCH2C(=0)NH(CH ₂ CH ₂ NH)4H] [Si0 _4/2 ] in a 2:1 weight ratio . The flow rate varied between 14-17 Litres/hour and the washing process involving passing 9 Bed Volumes of deionised water through the material after every 8 hours. The process was conducted at ambient temperature. The average reduction in metal content of the treated stream was platinum - 80%; palladium - 92% and rhodium - 40%.

The invention will now be described in detail with reference to illustrative examples of the invention.

Example 1

12.5 L of a 0.2M HCI solution containing 11000 ppm of zinc ions, 5 ppm each of platinum and palladium ions and 1 ppm rhodium ions was passed through a fixed bed of metal scavenger [0 ₃₂ SiCH ₂ CH2SCH2C(=0)NH(CH2CH2NH)4H][Si0 ₄ 2] (13.29 g) at a flow rate of 0.3 Uh. Deionised water (250 ml_, 8 Bed Volumes) was passed through the fixed bed. Then a further 12.5 L of the same 0.2M HCI solution was passed through the fixed bed at the same flow rate of 0.3 Uh . Samples of the treated feed material were taken every 50 mL and metal content was measured by ICP-OES using standard methodology. The average reduction in metal content of the treated solution was platinum - 99%; palladium - 99% and rhodium - 70%. Example 2

12.5 L of a 0.2M HCI solution containing 6,000 ppm of zinc ions and 2,000 ppm of iron ions, 4 ppm each of platinum and palladium ions, 2 ppm of iridium and 1 ppm of rhodium ions was passed through a fixed bed of metal scavenger [SiO^HOa^SiCh^CI-^SH] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ CH ₂ CH ₂ SH] (14.2 g) at a flow rate of 0.9 L/h. Deionised water (250 ml_, 8 Bed Volumes) was passed through the fixed bed. Then a further 12.5 L of the same 0.2M HCI solution was passed through the fixed bed at the same flow rate of 0.9 L/h. Samples of the treated feed material were taken every 50 mL and metal content was measured by ICP- OES using standard methodology. The average reduction in metal content of the treated solution was platinum - 99%; palladium - 99%, iridium - 80% and rhodium - 75%.

Example 3

12.5 L of a dilute sulfuric acid solution containing 14,000 ppm of zinc ions, 6 ppm each of platinum and ruthenium ions and 1 ppm of rhodium ions was passed through a fixed bed of metal scavenger [Si0 _4/2 ] [0 ₃₂ SiCH ₂ CH ₂ SCH ₂ CH ₂ NH ₂ ] (14.08 g) at a flow rate of 0.1 L/h. Deionised water (250 mL, 8 Bed Volumes) was passed through the fixed bed. Then a further 12.5 L of the same dilute sulfuric acid solution was passed through the fixed bed at the same flow rate of 0.1 L/h. Samples of the treated stream were taken every 50 mL and metal content was measured by ICP-OES using standard methodology. The average reduction in metal content of the treated solution was platinum - 99%; ruthenium - 99% and rhodium - 60%.

Example 4

12.5 L of a solution containing 9,000 ppm of combined zinc and sodium ions, 5 ppm each of platinum and palladium ions and 1 ppm of rhodium ions was passed through a fixed bed of a mixture of metal scavengers [Si0 _4/2 ] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ C(=0)NH(CH ₂ CH ₂ NH) ₄ H] and [Si0 _4/2 ][0 _3/2 SiCH ₂ CH ₂ SH] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ CH ₂ CH ₂ SH] (1 :2 ratio, 13.81 g) at a flow rate of 0.6 L/h. Deionised water (250 mL, 8 Bed Volumes) was passed through the fixed bed. Then a further 12.5 L of the same solution was passed through the fixed bed at the same flow rate of 0.6 L/h. Samples of the treated stream were taken every 50 mL and metal content was measured by ICP-OES using standard methodology. The average reduction in metal content of the treated solution was platinum - 99%; palladium - 99% and rhodium - 70%. Example 5

12.5 L of a solution containing 9,000 ppm of combined zinc and iron ions, 8 ppm each of platinum and palladium ions, 3 ppm of ruthenium ions and 1 ppm of rhodium ions was passed through a fixed bed of a mixture (1 :2 ratio) of metal scavengers [Si0 _{4 2} ] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ C(=0)NH(CH ₂ CH ₂ NH) ₄ H] and [Si0 _4/2 ] [0 _3/2 SiCH ₂ CH ₂ SH] [0 ₃ / ₂ SiCH ₂ CH ₂ SCH ₂ CH ₂ CH ₂ SH] (13.81 g combined weight) at a flow rate of 0.6 L/h. Deionised water (250 mL, 8 Bed Volumes) was passed through the fixed bed. Then a further 12.5 L of the same solution was passed through the fixed bed at the same flow rate of 0.6 IJh. Samples of the treated stream were taken every 50 mL and metal content was measured by ICP-OES using standard methodology. The average reduction in metal content of the treated solution was platinum - 99%; palladium - 99%, ruthenium - 70% and rhodium - 70%.

Example 6

20.5 L of a solution containing 1 1 ,000 ppm of zinc and iron ions, 8 ppm each of platinum and palladium ions, 3 ppm of ruthenium ions and 1 ppm rhodium ions was passed through a fixed bed of a mixture of metal scavengers [Si0 _4/2 ] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ CH ₂ NH ₂ ] and [Si0 _4/2 ] [0 _3/2 SiCH ₂ CH ₂ SH] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ CH ₂ CH ₂ SH] (1 :2 ratio, combined weight 14.2 g) at a flow rate of 0.6 Uh. Deionised water (250 mL, 8 Bed Volumes) was passed through the fixed bed. Then a further 20.5 L of the same solution was passed through the fixed bed at the same flow rate of 0.6 L/h. Samples of the treated stream were taken every 50 mL and metal content was measured by ICP-OES using standard methodology. The average reduction in metal content of the treated solution was platinum - 99%; palladium - 99%, ruthenium - 70% and rhodium - 70%.

Example 7

23 L of a solution containing 14,000 ppm of combined zinc and iron ions, 2 ppm each of platinum and palladium ions, 3 ppm of ruthenium ions and 1 ppm rhodium ions was passed through a fixed bed of a mixture (1 :2 ratio) of metal scavengers [Si0 _{4 2} ] [0 _3/2 SiCH ₂ CH ₂ CH ₂ SH] and [Si0 _4/2 ] [0 _3/2 SiCH ₂ CH ₂ CH ₂ NH ₂ ] (13.81 g, combined weight) at a flow rate of 0.6 U . Deionised water (250 mL, 8 Bed Volumes) was passed through the fixed bed. Then a further 23 L of the same solution was passed through the fixed bed at the same flow rate of 0.6 Uh. Samples of the treated stream were taken every 50 mL and metal content was measured by ICP-OES using standard methodology. The average reduction in metal content of the treated solution was platinum - 99%; palladium - 99%, ruthenium - 60% and rhodium - 70%. Example 8

An aqueous acidic stream (5600 L) containing platinum (2 ppm), palladium (3 ppm) and rhodium (0.6 ppm) complexes and a mixture of zinc, copper, sodium and iron (total 8,000 ppm) was passed through sequentially two fixed beds (0.9 kg per bed) containing metal scavengers [Si0 _{4 2} ] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ C(=0)NH(CH ₂ CH ₂ NH) ₄ H] and [Si0 _4/2 ] [0 ₃ / ₂ SiCH ₂ CH ₂ SH] [0 _3/2 SiCH ₂ CH ₂ SCH ₂ CH ₂ CH ₂ SH] ₂ in a 1 :2 weight ratio. The flow rate varied between 14-17 LJh and the process was conducted at ambient temperature. After every 8 hour continuous operation the fixed beds were washed with deionised water (20 L, 9 Bed Volumes) at a flow rate of 60 Uh. Samples of the treated feed material were taken every 120 L and metal content was measured by ICP-OES using standard methodology. The average reduction in metal content of the treated solution was platinum - 80%; palladium - 92% and rhodium - 40%.