Process of Removing Ions From Solutions by Forming a Complex With a Sulfur Containing Hydrocarbon Covalently Bonded to Silica

The present invention has composition and process aspects.

The composition aspect relates to two classes of new organic compounds:

A. an intermediate sulfur-containing hydrocarbon covalently bonded to a trialkoxysilane, and

B that class of intermediates covalently bonded to silica e.g., sand or silica gel.

The process aspect comprises two processes, viz., (1) a process for making the two new organic compounds and (2) the process of removing and concentrating certain ions, such as noble metal ions and other transition metal ions, from solutions thereof admixed with other ions which may be present in much higher concentrations, by forming a complex of the desired ions with a compound of class B, e.g., by flowing such solutions through a chromatography column packed with a compound of class B, breaking the complex. e.g., by flowing a receiving liquid in much smaller volume than the volume of solution passed through the column to remove and concentrate the desired ions in solution in the receiving liquid, and recovering the desired ions from the receiving liquid.

The intermediates comprising sulfur-containing hydrocarbons covalently bonded to a trialkoxysilane are shown in Formula 1. ##STR1## A, B and D=any combination of O or OCH.sub.2 or S or SCH.sub.2, but B or D must be S or SCH.sub.2 ; E=H, SH, OH, lower alkyl, or SCH.sub.2 CH(R.sup.1)CH.sub.2 O(CH.sub.2).sub.a SiXYZ; X=Cl, OCH.sub.3 or OC.sub.2 H.sub.5 ; Y and Z=Cl, OCH.sub.3, OC.sub.2 H.sub.5, methyl, ethyl, or halogenated substituents thereof; R.sup.1 =H, SH, OH, loweralkyl or aryl such as phenyl, naphthyl or pyridyl; R.sup.2 =H or lower alkyl; a=2 to about 10; b=0 or 1; c=1 to about 5; d=0 to about 5.

The sulfur containing intermediates covalently bonded to silica, e.g., sand or silica gel, are shown in Formula 2. ##STR2## A, B and D=any combination of O or OCH.sub.2 or S or SCH.sub.2, but B or D must be S or SCH.sub.2 ; E=H, SH, OH, lower alkyl, or SCH.sub.2 CH(R.sup.1)CH.sub.2 O(CH.sub.2).sub.a SiYZ(O-silica); Y and Z=Cl, OCH.sub.3, OC.sub.2 H.sub.5, methyl, ethyl or halogenated substituents thereof, or O-silica; R.sup.1 =H, SH, OH, lower alkyl or aryl such as phenyl, naphthyl or pyridyl; R.sup.2 =H or lower alkyl; a=2 to about 10; b=0 or 1; c=1 to about 5; d=0 to about 5.

Where silica=sand or silica gel

The process of producing the new compounds of Formula 1 and Formula 2 are described fully hereafter.

The process of selectively and quantitatively removing and concentrating a selected ion or group of ions of the noble metal type, e.g , gold, silver; the platinum metals, e.g., platinum, palladium, rhodium and iridium; and, when noble and platinum metals are not present, ions of mercury, lead, zinc and other transition metals present at low concentrations from a plurality of other ions in a multiple ion solution in which the other ions may be present at much higher concentrations comprises bringing the multiple ion solution into contact with a compound of Formula 2 of the invention which causes the desired ion(s) to complex with said compound, breaking the complex with a receiving liquid which takes the ion(s) into solution, and recovering the ion(s) therefrom.

The preferred embodiment disclosed herein involves carrying out the process by bringing a large volume of the multiple ion solution into contact with a compound of the invention as a compound covalently bonded to sand or silica gel in a separation column through which the mixture is first flowed to complex the desired ion or ions with said compound followed by the flow through the column of a smaller volume of a receiving liquid such as aqueous NH.sub.3, for example, to break the complex by chemical or thermal means, dissolve the desired ions and carry them out of the column. Other equivalent apparatus may be used instead of a column, e.g., a slurry which is filtered, washed with a receiving liquid to break the complex and recover the desired ion. The desired metal ions are then recovered from the receiving phase by well known procedures.

More particularly, the process comprises forming a covalent chemical bond between silica, preferably sand or silica gel, and at least one of the compounds of Formula 1, placing the resulting bonded silica compound of Formula 2 in a contacting device such as a tall column, causing a large volume of the mixture of ions to flow through the column where the desired metal ions complex with the bonded silica which separates them from the rest of the mixture which flows out of the column, then flowing a small volume of the receiving liquid through the column to break the complex and dissolve and carry out of the column the desired metal ion(s). The desired metal ions are then recovered from the receiving liquid by well known procedures.

The process of making the compounds represented by Formula 1 and Formula 2 is also part of the invention.

The fact is known that macrocyclic polythioethers and certain other sulfur-containing hydrocarbon ligands present as solutes in a solvent such as water are characterized by their ability to selectivity form strong bonds with the noble metal, platinum group metal, and mercury ions or groups of these ions present as solutes in the same solvent as described in articles by R. M. Izatt, R. E. Terry, L. D. Hansen, A. G. Avondet, J. S. Bradshaw, N. K. Dalley, T. E. Jensen and J. J. Christensen, A CALORIMETRIC TITRATION STUDY OF UNI- AND BIVALENT METAL ION INTERACTION WITH SEVERAL THIA DERIVATIVES OF 9-CROWN-3, 12-CROWN-4, 15-CROWN-5, 18-CROWN-6, 24-CROWN-8 AND WITH SEVERAL OXATHIAPENTADECANES IN WATER OR WATER-METHANOL SOLVENTS AT 25.degree. C., Inorganica Chemica Acta, 1978, Vol 30, 1-8 for the complexation of silver and mercury ions by open chain sulfur-containing hydrocarbons and by S. R. Cooper, CROWN THIOETHER CHEMISTRY, Accounts of Chemical Research, 1988, Vol 21, 141-146 for the complexation of rhodium and silver ions by macrocyclic sulfur-containing ligands. However, researchers have not previously been able to incorporate sulfur-containing hydrocarbon ligands into separation systems where the behavior of the sulfur-containing ligands in the separation systems in comparison to that of the sulfur-containing ligand as a solute is unchanged and/or the sulfur-containing ligand will remain in the separation system. Articles such as those entitled SILANE COMPOUNDS FOR SILYLATING SURFACES by E. P. Plueddemann, in "Silanes, Surfaces and Interfaces Symposium, Snowmass, 1985," Ed. by D. E. Leyden, Gordon and Breach, Publishers, 1986, pp. 1-25 and SILANE COUPLING AGENTS by E. P. Plueddemann, Plenum Press, 1982 pp. 1-235 list many different types of organic materials which have been attached to silane compounds and discusses some of their properties. The preparation and uses of sulfur-containing hydrocarbons attached to silane or silica have not been disclosed in the above mentioned article or in any existing patents. Thus, the unique complexing properties of certain sulfur containing hydrocarbons and the ability to attach these sulfur-containing complexing agents to sand or silica gel without reducing their ability to complex certain metal ions is of utmost importance in the industrial use of the sulfur-containing hydrocarbon ligands. The process of the present invention accomplished this feat.

The compounds of the present invention comprise certain sulfur-containing hydrocarbon ligands covalently bonded to silica. e.g., sand or silica gel. The compounds are identified above in Formula 2. The process of the present invention uses the compounds, which are characterized by high selectivity for and removal of desired metal ions or groups of metal ions such as the noble metal ions present at low concentrations from the source phase containing a mixture of these metal ions with the ions one does not desire to remove present in much greater concentrations in the solution, in a separation device such as a column through which the solution is flowed. The process of selectively removing and concentrating the desired ion(s) is characterized by the ability to quantitatively complex from a large volume of solution the desired ion(s) when they are present at low concentrations. The said ions are recovered from the separation column by flowing through it a small volume of a receiving phase which contains a solubilized reagent which need not be selective, but which will strip the ions from the ligand quantitatively. The recovery of the desired metal ions from the receiving phase is easily accomplished by well known procedures. The process of producing the compounds of Formula 1 and Formula 2 are an important part of the present invention.

The invention will be described and illustrated by reference to a drawing in which:

FIG. 1 represents schematically a suitable column for holding the silica bonded sulfur-containing hydrocarbon ligand material through which a solution of metal ions can be flowed to complex selectively with a desired ion or group of ions in accordance with the invention.

The preferred embodiment of the ion recovery process of the invention utilizes the new compounds represented by Formula 2. The process of producing these new compounds and the intermediates represented by Formula 1 are an important aspect of the invention.

Sulfur-containing hydrocarbon ligands must be covalently bonded to the sand or silica gel in accordance with the invention. The compounds of Formula 1 satisfy this requirement because they can be bonded to sand or silica gel. One method of preparing the compounds of the class represented by Formula 1, for example, is to react mercapto forms of the sulfur-containing hydrocarbon with a silane-containing epoxide such as glycidoxypropyltrimethoxysilane shown in Equation 1. ##STR3##

As a specific example, .gamma.-glycidoxypropyltrimethoxysilane and 1,2-ethanedithiol are used which are commercially available compounds. In the above reaction both mercaptan groups react with epoxides to form a compound containing two trimethoxysilane functions. The reaction can be carried out with a molar ratio of one mole of epoxide to one mole of mercaptan to give (CH.sub.3 O).sub.3 Si(CH.sub.2).sub.3 OCH.sub.2 CH(OH)CH.sub.2 SCH.sub.2 CH.sub.2 SH where the sulfur-containing hydrocarbon is 1,2-ethanedithiol.

The following two examples are given to illustrate compounds which have been made in accordance with Formula 1 of the present invention. These examples are illustrative only, and are not comprehensive of the many different compounds which have been or can be made within the scope of the present invention.

In this example a sulfur-containing hydrocarbon bonded to a trialkoxysilane was made wherein a=3, b=1, c=1, d=0, R.sup.1 =hydroxy, R.sup.2 =hydrogen, A=oxygen, B=sulfur, D is not present since d=O, E=SCH.sub.2 CH(OH)CH.sub.2 O(CH.sub.2).sub.3 Si(OCH.sub.3).sub.3, and X, Y and Z=methoxy groups in Formula 1.

1,2-Ethanedithiol (5.0 g, 0.05 mole) (Aldrich) was added to a stirred solution of 25.5 g (0.11 mole) of 3-glycidoxypropyltrimethoxysilane (Aldrich) in about 250 ml of toluene. A catalytic amount (1 ml) of freshly prepared 10% sodium methoxide in methanol was added to the solution and the solution was refluxed for 6 hours. The infrared spectrum of this mixture showed the absence of peaks at 2570 cm.sup.-1 (SH) and greatly diminished peaks at 950 and 840 cm.sup.-1 (epoxide) indicating that all the mercaptans had reacted with the slight excess of epoxide. This material was not further purified but was used in Example 3.

In this example, a sulfur-containing hydrocarbon bonded to a trialkoxysilane was made wherein a=3, b=1, c=1, d=1, R.sup.1 =hydroxy, R.sup.2 =hydrogen, A=oxygen, B=sulfur, D=sulfur, E=SCH.sub.2 CH(OH)CH.sub.2 O(CH.sub.2).sub.3 Si(OCH.sub.3).sub.3, and X, Y and Z=methoxy groups in Formula 1.

2-Mercaptoethyl sulfide (0.71 g, 4.6 mmole) (Aldrich) was added to a stirred solution of 2.2 g (10 mmole) of 3-glycidoxypropytrimethoxysilane in 250 ml of toluene. A catalytic amount (1 ml) of freshly prepared 10% sodium methoxide in methanol was added to the solution and the solution was refluxed for 6 hours. The infrared spectrum indicated that the reaction was completed as mentioned in Example 1. This material was used without purification in Example 4 below.

The compounds of Formula 1 are covalently bonded to sand or silica gel by heating to effect a covalent bond as shown in Equation 2. ##STR4## The reaction can take place by first, dissolving the compound of Formula 1 in a low boiling solvent such as methylene chloride, adding the sand or silica gel, removing the low boiling solvent then heating the coated sand or silica gel at about 120.degree. C. for 3 to about 18 hours. A second procedure to cause the compounds of Formula 1 to react with sand or silica gel is to heat the mixture of sand or silica gel and compound of Formula 1 in a high boiling solvent such as toluene.

The following two examples are given to illustrate compounds which have been made in accordance with Formula 2 of the present invention. These examples are illustrative only, and are not comprehensive of the many different compounds which have been or can be made within the scope of the present invention. cl EXAMPLE 3

In this example a sulfur-containing hydrocarbon bonded to silica gel was made wherein a=3, b=1, c=1, d=0, R.sup.1 =hydroxy, R.sup.2 =hydrogen, A=oxygen, B=sulfur, D is not present since d=0, E=SCH.sub.2 CH(OH)CH.sub.2 O(CH.sub.2).sub.3 -Si(O-Silica Gel).sub.3, and Y and Z=O-silica gel in Formula 2.

The toluene solution containing the compound of Example 1 was placed in a 1000 ml 3-necked sound bottom flask equipped with a mechanical stirrer and the solution was diluted to 400 ml with additional toluene. Silica gel (132 g, 60-200 mesh) was added to the solution and the resulting mixture was slowly stirred and refluxed for 12 to about 24 hours. The sulfur-containing hydrocarbon bonded silica gel was filtered and air dried.

In this example, a sulfur containing hydrocarbon bonded to silica gel was made wherein a=3, b=1, c=1, d=1, R.sup.1 =hydroxy, R.sup.2 =hydrogen, A=oxygen, B=sulfur, D=sulfur, E=SCH.sub.2 CH(OH)CH.sub.2 O(CH.sub.2).sub.3 Si(O-Silica Gel).sub.3, and Y and Z=O-silica gel in Formula 2.

The toluene solution containing the compound of Example 2 was treated as above in Example 3 to give 20 g of silica gel bound to the sulfur-containing material of Example 2.

The metal ion recovery and concentration process of the invention relates to the selective recovery of desired metal ions from mixtures thereof with other metal ions using the compounds of Formula 2 of the invention as defined above. Effective methods of recovery and/or separation of metal ions, particularly the noble metal ions and platinum group metal ions, from other metal ions in water supplies, waste solutions, deposits and industrial solutions and silver recovery from waste solutions, e.g , from emulsions on photographic and X-ray film, represent a real need in modern technology. These ions are typically present at low concentrations in solutions containing other ions at much greater concentrations. Hence, there is a real need for a process to selectively recover and concentrate these metal ions. The present invention accomplishes this separation effectively and efficiently by the use of compounds selected from the families represented by Formula 2.

The silica gel material of Formula 2 is placed in a column as shown in FIG. 1. An aqueous solution containing the desired ion or ions, in a mixture of other ions which may be in a much greater concentration is passed through the column. The flow rate for the solution may be increased by applying pressure (with a pump) on the top of the column or applying a vacuum in the receiving vessel. After the solution has passed through the column, a much smaller volume of a recovery solution, i e. aqueous Na.sub.2 S.sub.2 O.sub.3, aqueous NH.sub.3, or aqueous NaI, which forms a stronger complex with the desired noble metal ions, is passed through the column. This recovery solution contains only the desired metal ions in a concentrated form.

The following examples of separations of noble metal ions by the silica gel-bound sulfur-containing materials of Examples 3 and 4 are given as illustrations. These examples are illustrative only, and are not comprehensive of the many separations of noble metal, platinum group, and in some cases transition metal ions that are possible using the materials made within the scope of this invention.

In this example, 2 grams of the silica gel-bound sulfur-containing hydrocarbon of Example 3 was placed in a column as shown in FIG. 1. A 1000 ml solution of 3 ppm of Ag.sup.+ in 1M aqueous MgCl.sub.2 was passed through the column using a vacuum pump to increase the flow rate. A 10 ml solution of 1M aqueous Na.sub.2 S.sub.2 O.sub.3 was passed through the column. An analysis of the recovery solution by atomic absorption spectroscopy (AA) showed that greater than 90% of the silver ions originally in the 1000 ml silver solution was in the 10 ml recovery solution.

A 1000 ml solution of 20 ppm Au(III) in saturated aqueous sodium chloride was passed through the column mentioned in Example 5. A 10 ml recovery solution of 5M aqueous NaI was passed through the column. An analysis of the recovery solution by AA spectroscopy showed that greater than 99% of the gold ion present in the original 1000 ml gold solution was in the recovery solution.

The experiment of Example 6 was repeated with 10 ppm Au(III) in an aqueous solution of 0.1M FeCl.sub.3, saturated NaCl and 1M HCl. Again, greater than 99% of the gold ion in the original solution was found in the recovery solution.

The experiments of Examples 5, 6 and 7, using 2 grams of silica gel-bound sulfur-containing hydrocarbon of Example 4 rather than the sulfur material of Example 3, were repeated. In each case, greater than 99% of the silver or gold ions were found in the recovery solution.

The sulfur materials of Examples 3 and 4 have also been used to make separations among noble metal and platinum metal ions in solution. An example of this is the separation of Au(III) from Ag(I) in either 1M HNO.sub.3, 1M HCl, or in saturated NaCl. By running the solution through the column until all of the ligand sites could potentially be filled with Au(III) a near quantitative separation was accomplished. No Ag(I) was detected in the regeneration solution of NaI. When a second column of Example 2 or 3 material was placed after the first column and where the ligand sites of the first column were filled with Au(III), Ag(I) ions can be isolated in the regeneration solution of the second column.

From the foregoing, it will be appreciated that the sand or silica gel-bound sulfur-containing hydrocarbon ligands of Formula 2 of the present invention provide a material useful for the separation and concentration of the noble metal cations from mixtures of those cations with other metal cations. The noble metals can then be recovered from the concentrated recovery solution by standard techniques known in the science of these materials. Similar examples have also been successfully established for platinum group metal ions, and in the absence of noble and platinum metal ions for other transition metal ions.

Although the invention has been described and illustrated by reference to certain specific silica gel-bound sulfur-containing hydrocarbon ligands of Formula 2 and processes of using them, analogs of these sulfur-containing hydrocarbon ligands are within the scope of the compounds and processes of the invention as defined in the following claims.