US3463632A

US3463632A - Metal recovery method

Info

Publication number: US3463632A
Authority: US
Inventors: Jack W Petty
Original assignee: JACK W PETTY
Current assignee: JACK W PETTY
Priority date: 1967-02-24
Filing date: 1967-02-24
Publication date: 1969-08-26
Anticipated expiration: 1986-08-26

Description

' Aug. ze, 1969 J. w. Pam 3,463,632 i METAL RECOVERY METHOD Filed Feb. 24. 1967 smfa//f Mazza-W 54H5 aar INVENTOR [f4/02651 swva/x/Wsfgz/ United States Patent O 3,463,632 METAL RECOVERY METHOD Jack W. Petty, 1115 Arbor Dell Road, Los Angeles, Calif. 90041 Filed Feb. 24, 1967, Ser. No. 618,458 Int. Cl. C22b 1]/02, 7/02; C10b 57/04 U.S. Cl. 75-83 4 Claims ABSTRACT OF THE DISCLOSURE A method of obtaining precious metals by heating oil shales to drive off oily vapors containing precious metals and bubbling the vapors through a bath of a molten alkali metal chloride.

Background of the invention This invention relates to the metallurgical art and more particularly to a method of recovering metals from oil shales (kerogen), tar sands, carbonaceous material, and natural petroleum. When oil shales are mentioned hereinafter, tar sands, natural petroleum, and carbonaceous materials are included in this phrase.

Although the present invention should not be limited to those uses specifically described herein, it has been found to have exceptional utility in recovering gold, silver, and other precious metals from vapors, gases, entrained liquids and solids obtained by heating and retorting oil shale (kerogen), tar sands, carbonaceous materials, and natural petroleum. When the term vapors is mentioned hereinafter, it is taken also to include gases,

3,463,632 Patented Aug. `26, 1969 remove carbon, coke, adventitious mineral particles, and the like which may enter the system from the retort. The filtered molten salt is returned to the bubble tower at a convenient point above the molten salt level in the bubble tower. l

Types of retorts other than retort 3, such as the U.S. Bureau of Mines gas combustion type,Union Oil Company rock pump gas combustion retort, etc., which depend upon partial burning of the oil shale may also be used. The oily vapors and combustion products formed are collected at the retort vapor exit 6 and then through tube 6 into the molten salt bath. AnotherI suitable method is to maintain a partial vacuum in the bubble tower so that oily vapors, etc. are drawn through the molten salt.

In the event that natural petroleum is being processed, hot vapors, liquids, etc. from the pipe still are forced through the molten salt in the bubble tower. However,

@trained liquids, and solids. 1t has been discovered that such vapors contain gold and silver.

Summary of the invention In accordance with the present invention, gold and silver are removed from such vapors to reduce production costs of petroleum compounds. The method of the invention includes the step of contacting a molten alkali metal chloride in a liquid state with an oily vapor derived from oil shale wherein the molten chloride salt has the capacity of combining with the metals to be recovered.

The above-described and other advantages of the present invention will be better understood from the following description when considered in connection with the accompanying drawings.

Brief description of the drawing In the drawing, the view is diagrammatic of the apparatus employed with the method of the present invention.

Description of the preferred embodiments In the drawing, an oil shale retort 3 is located in a furnace 1. Retort 3 has an inlet passageway 4 and an out let passageway 5. Shale is heated in retort 3 and vapors collected and transmitted via a pipe 6 to the bottom of a bubble tower 7 containing a molten chloride salt. Tower 7 has an inlet at 8 and an outlet at 9. A condenser 10 is provided to condense oily vapors that are passed from tower 7 to condenser 10. Bubble tower 7 s heated in a furnace 2.

In the tube leading from the bubble tower 7 to condenser 10, a vacuum pump 13 is incorporated. The vacuum pump 13 is used to facilitate the liow of oily vapors through the molten salt. Also, after passage through the molten salt, oily vapors are quickly transferred to the condenser, thereby reducing the tendency of the oily vapor to form coke in the bubble tower above the molen salt.

At a convenient place in the bubble tower near the bottom, provision is made to circulate the molten salt by means of a suitable pump 12 through a filter 1.1 to

the temperatures employed are generally in the range of 400 F. to 1000 F. or more. After passage through the molten chloride salt, the vapors and hot petroleum are led into a fractionating column for further processing. See also Petroleum Products Handbook, Virgil B. Guthrie (McGraw-Hill, 1st edition, 1960, pages 1-11).

The molten salt bath in tower 7 may contain one or more of the molten chloride salts of the.` metals in Groups I-A and II-A of the Periodic Table as set forth on page 59 of Handbook of Chemistry sixth edition, by N. A. Lange (Handbook Publishers, Inc., 1946, Sandusky, Ohio). Modifying salts, such as NaOH, Na2CO3, NaCN, etc., and their potassium counterparts, may also be used in order to control molten salt temperatures, viscosities, and pH values.

Alternatively, the molten salt path in tower 7 may actually be two or more salts. Thesel salts may be in the said groups of the Periodic Table aforesaid. For example, KCl and NaCl chlorides may be used together. Li, Na and K chlorides may also be used together.

Example Oil shale is heated in retort 3 to a temperature of 850" F. or more. The oil shale temperature should be sufficiently high to drive off oily vapors and yet be low enough to minimize breakdown of the oily vapors. Li, Na and K salts are then used in tower 7, in proportions of 50%, 25% and 25% by weight, respectively. They are also heated to a temperature of 850 F. or more, their melting point being approximately 760 F. LiCl, NaCl and KCl are used.

It will be noted that the temperatures employed for this or any other embodiment of the invention are not critical although best results are obtained Within the range of I850" F. to 1700 F. or more, such as that obtained in gas combustion retorts.

When NaCl or KCl is used, each one is preferably heated to a temperature in excess of 1475 F. or more. The melting point of NaCl is 1472 F. When KCl is used in tower 7, it is heated to a temperature of 1430 F. or more, its melting point being 1429" F. Lower salt melting temperatures may be obtained by using approximately a 50-50 percent mixture of KCl and NaCl. The melting point of this combination is approximately 1250o F.

None of the salt temperatures listed herein are critical. The salt bath simply needs to be maintained in a molten state.

After petroleum vapors have been bubbled through the said molten salts in tower 7, the molten salt is drawn off at 9 and allowed to cool to a solid state. Gold and silver may be recovered from the salt which is removed from tower 7. Gold and silver in the product may then be recovered in any conventional manner. One method of recovery is to dissolve the chloride salts in water and then filter (step one). Some silver chloride will be found in the filtered material. The resultant silver chloride may be recovered from the filtered material by dissolving in NH4OH and then retiltering. Addition of HNO3 to the above ltrate will then reprecipitate AgCl. Metallic silver may then be produced by cupelling the AgCl with lead. The filtrate from the initial lilter operation (step one), is acidied with HC1 and precious metals are precipitated with zinc precipitate dust. Recovery of gold and silver from the Zinc produced may then be done in any standard manner as normally employed in the mining industry for recovery of silver and gold.

The economics of the inventive process are attractive. For example, Colorado shale oil has a gold and silver content of approximately fty cents per barrel. Brea, Calif., natural petroleum approximately twenty-five cents per barrel, and Santa Maria, Calif., tar sands approximately forty-six cents per barrel. It is my experience that when proceeding in accordance with the invention, a substantial proportion of the gold and silver contained in the kerogen content of the oil shale appears in the oily vapors issuing from the retorting process, and in turn, a substantial portion of that is captured by the molten salt and eventually made available as saleable metallic gold and silver. It may be observed that my inventive process can be carried out withno real interference with conventional methods for recovering oil from oil shale, and from the standpoint of heat consumption, the operating costs are low indeed. The salts used can readily be recovered substantially by evaporation completely from the step wherein the gold and silver is extracted so that makeup quantities from the system as a whole are low. It will be appreciated that my process is equally adaptable to processes in which oil shale is retorted and the oil therefrom is not necessarily recovered as a valuable constituent per se. This may occur with oil shales of high gold and silver content and relatively undesirable oily constituents, or where the retorted shale is the primary product of the process, being useful, for example, asa lightweight aggregate for concrete or for solid fuel.

What is claimed is:

1. The method of obtaining a precious metal, said method comprising the steps of: heating a precious-metalbearing oil shale to drive olf oily vapors containing a precious metal; bubbling said vapors through a bath containing a major amount of a molten alkali metal chloride; cooling said bath to a solid state; and recovering said previous metal from said cooled bath.

2. The method of claim 1 wherein said precious metal is gold or silver.

3. The method of obtaining a precious metal, said method comprising the steps of contacting a bath containing a major amount of a molten chloride of at least one metal from Group I-A or II-A of the Periodic Table with an oily vapor containing the precious metal to be recovered; and recovering said precious metal from said bath.

4. The method of claim 3 wherein said metal is gold or silver and said bath contains lithium chloride, sodium chloride, and potassium chloride in proportions of 25% and 25%, respectively, by Weight, said chlorides being in the molten state.

References Cited UNITED STATES PATENTS RICHARD O. DEAN, Primary Examiner U.S. Cl. X.R. -118