DNI, sorry i missed your p.m.
:arrow:
The invention relates to a method for the interseparation of noble metals from a gold-free halide solution containing at least two noble (PGMs), wherein said solution is passed through at least one chromatographic column containing a solid adsorbent with a "distribution coefficient" Kd, above 1, which adsorbs the PGMs, and subsequently the loaded adsorbent is eluted by a halide salt solution, obtaining thereby well spaced fractions, each containing only one single noble metal and emerging in the order: Ru, Rh, Pd, Pt, Ir and Os. In this manner the noble metals are interseparated in a very pure state with very great efficiency.
According to a preferred embodiment the feed solution consists of PGM chlorides in hydrochloric acid in an overall concentration of 5 g/l. Preferably, the eluant comprises a halide salt together with a mineral acid, the latter being most preferably hydrochloric acid.
In case gold is also present with the noble metals, it should be removed prior to the noble metals (PGMs) adsorption operation. It was unexpectedly found that gold does not migrate through the adsorbent, being held up at the top of the column. The removal of gold may be carried out in any manner known to the art. According to a most preferred embodiment, the gold separation according to the present invention is carried out in the same apparatus, which consists of at least two chromatographic columns connected in series. The first column contains an absorbent only for gold and the second column one for the other noble metals. In this manner, the gold-free solution containing the noble metals will pass onto the second chromastographic column, wherein an inter-separation thereof occurs as described above.
A most preferred adsorbent for gold is polystyrene divinyl resin (sold on the market under the Trade Mark Ambrelite XAD-7, produced by Rhom and Haas) in the water-swollen condition.
The solid adsorbents to be used in the present invention are selected from chromatographic reagents used for gel permeation but should possess a chromatographic coefficient of at least 1 and preferably above 4. Typical examples of suitable adsorbents are gels of polysaccharide of the polydextran type (known on the market by their Trade Mark Sephadex) and crosslinked polyacrylamide gel (known on the market by its Trade Mark Biogel). The degree of crosslinking controls the porosity and ability to swell in a solution: the higher the crosslinking, the smaller pores and the lower the swelling. There are several types of Sephadex adsorbent gels, such as: Sephadex G-10, Sephadex G-15, Sephadex G-25 and Sephadex G-50. The numbers of the gels indicate their porosity. The higher the number, the bigger the pores and the faster does migration take place, but then the lower is the resolution of the different PGMs. The kind of Sephadex actually chosen will therefore depend on considerations affecting the specific industrial or other application of the method according to the present invention. The adsorption of the dissolved noble metal components onto the dextran gel is explained by the generation of hydrogen bonds with the hydroxyl groups present in the gel. Also, the high hydrophilic property of the dextran imparted by the OH groups makes it most suitable for the present invention.
The interseparation between the noble metals is quite unexpected in view of the weak bonding of Pt to the gel. The Inventor explains the matter by the polarizability of the metal halide bond which influences the hydrogen bond of the gel and enables the noble metals to be selectively separated. In the case of Biogel the interseparation is based on the electcrostatic interactions of PGM complexes with the amide group of the gel, which are electrostatic and depend on the ion charge. In the case of Sephadex, the interactions of the complexes are of a bipolar type, being weaker than those of the electrostatic type but more selective.
The retention times of the platinum metals on the Sephadex gel are in the following order: Ru(IV)<Rh(III)<Pd(II)<Pt(IV)<Ir(IV)<Os(II).
This order was determined by means of the adsorption of each of the metals to the gel in accordance with its interaction with the gel.
The high selectivity of the gel adsorbents according to the present invention for the platinum metals enables good separation to be obtained without the need for establishing any selective conditions for each of the metals to be separated, as is usually the case in these separations with ion exchangers.
It was found that the adsorption of the anionic complexes of the PGMs are bound to the gel more strongly than their counter cations.
One of the advantages of the method are the relatively high concentrations of the PGMs which can be processed. This, of course, is of great importance from the economic point of view.
While the invention will now be described in connection with certain preferred embodiments in the following Examples, it will be understood that it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended Claims. Thus, the following Examples which include preferred embodiments will serve to illustrate the practice of this invention, it being understood that the particulars described are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention without being limited thereto.
EXAMPLE 1
This Example describes the separation of the four noble metals: gold, platinum, iridium and palladium, from base metals when all are dissolved in an acidic solution, and the subsequent interseparation of the noble metals from each other by the method of the invention.
2 ml of an acidic solution comprising: 3.12 mg/ml Au, 24.2 mg/l Pt, 2.08 mg/ml Ir, 1.33 mg/ml Pd, 2,8 mg/ml Cu, 3.3 mg/ml Fe and 0.4 mg/ml Ni, all dissolved in 2N HCl, were used in the experiment.
The solution was first introduced into a vertical column (inner diameter 10 mm, length 250 mm) filled with the polymeric adsorbent resin Amberlite XAD-7 (Trade Mark, produced by Rohm and Haas) in the water-swollen condition. The depth of the resin bed was 15 cm, and the flow rate at which the solution was made to run through the bed was 1 ml/min. After the entire quantity of the solution had been introduced into the resin bed, partly replacing the water held therein, a solution of 1N HCl was introduced at the flow-rate stated before until the entire quantity of the solution had been washed out. The brown-coloured mixture thereupon emerging, as well as a quantity of the HCl washing solution immediately following, were analyzed and tested for the presence of gold, but no traces thereof could be detected in any of them. The emerging mixture was also analyzed for the presence of Pt and Pd, and it was found that there had been no less of these elements to the resin phase, since they were completely present in the mixture analyzed.
The gold was then eluted from the
XAD-7 resin by passing an eluant mixture of acetone and concentrated HCl (in the volume ratio of 9:1) through the column, replacing the 1N HCl solution present therein. It was found that the entire quantity of 6.24 mg gold originally present in the first solution was collected in 25 ml of the eluent, so that there were no losses to the resin phase. Metallic gold was recovered from the eluant by adding a reducing agent --FeSO 4 in one experiment, hydroquinone in another--and distilling away the acetone and the HCl.
The remaining solution was introduced into a second chromatographic column (inner diameter 10 mm, length 300 mm), containing the water-swollen polydextran gel (known under its Trade Mark name of Sephadex G-10) to a bed-depth of 25 cm. The flow-rate maintained was 0.5 ml/min. After the solution had been fully adsorbed on the gel, elution was commenced by adding 1N HCl as eluting agent. A fraction collector was adjusted to collect 5-ml fractions of the liquid emerging from the column, and each such fraction was analyzed by atomic absorption sepectroscopy for the presence of Pd, Pt, Ir and base metals. The first five fractions (each 5 ml) were discarded, since they did not contain any traces of metal ions whatsoever, whereas the subsequent fractions emerging from the column, produced the analysis shown in the graph of FIG. 1. As appears from the Figure there is a noticeabls time-gap between the emergence of the solution fraction containing the base metals and those containing the PGMs. In the time-gap, a colourless HCl solution left the column. Following this, a fraction of a yellowish hue emerged which upon examination was found exclusively to contain Pd. After the cessation of the flow of Pd solution, a large fraction containing only Pt appeared, and this in turn was followed by the metal most strongly on the gel, namely Ir, in a dark brown solution. The separation between the four groups--base metals, Pd, Pt and Ir--is seen to be complete, as indicated by the well-spaced peaks and the negligible overlap of the bottom portions.
) I soaked them in HCL to remove some stuff from them and after 2 days with a tiny bit of agitation, i took them out and rinsed them off. When i did that the green mask came off easily...
