US3656938A

US3656938A - Treatment of bituminous sands for recovery of heavy metals therefrom

Info

Publication number: US3656938A
Application number: US886746A
Authority: US
Inventors: Stephen Penzes
Original assignee: Canada Cities Service Ltd; Imperial Oil Ltd; Royalite Oil Co Ltd; Atlantic Richfield Co
Current assignee: Petro Canada Exploration Inc; Gulf Canada Ltd; Canada Cities Service Ltd; Imperial Oil Ltd; Royalite Oil Co Ltd
Priority date: 1969-12-19
Filing date: 1969-12-19
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18
Also published as: CA927983A

Abstract

Heavy metals, especially zircon, may be recovered from bituminous sands by introducing a fluid slurry of bituminous sand into a body of water whereby a froth containing bitumen and solids floats to the top of the water and is recovered therefrom. Solids are recovered from this froth and the recovered solids are treated with sodium hydroxide and then subjected to a flotation treatment using aeration gas. During the flotation treatment, solids other than heavy metal are selectively floated and heavy metals, especially zircon, remain in the bottom of the flotation zone from which they may be recovered.

Description

ijnited States Patent Penzes [151 3,656,938 [451 Apr. 18, 1972 [54] TREATMENT OF BITUMINOUS SANDS FOR RECOVERY OF HEAVY METALS THEREFROM [72] Inventor: Stephen Canada [73] Assignees: Canada Cities Service, Ltd., Alberta, Canada; Imperial Oil Limited; Atlantic Richiield Corporation; Royalite Oil Company, Limited, part interest to each [22] Filed: Dec. 19, 1969 [21] App1.No.: 886,746

Penzes, Edmonton, Alberta,

[52} U.S.Cl ..75/10l,75/2, 75/121, 208/11, 23/24 Z, 23/202 [51] lnt.Cl. ..C22b 61/02 [58] Field ofSearch ..75/2,101,121;208/11;23/18, 23/22, 24 Z, 110,140,182, 200, 202; 209/171, 167,

[56] References Cited UNITED STATES PATENTS 3,330,757 7/1967 Bichard ..208/11 3,338,814 8/1967 Given et a1... ..208/11 2,696,425 12/1954 Kistler ..23/140 2,082,383 6/1937 Corbett.... ....209/I66 X 2,792,940 5/1957 Baarson ..209/166 Primary Examiner-L. Dewayne Rutledge Assistant ExaminerG. T. Ozaki Attorney-J. Richard Geaman [5 7] ABSTRACT 4 Claims, No Drawings TREATMENT OF BITUMINOUS SANDS FOR RECOVERY OF HEAVY METALS THEREFROM Large deposits of bituminous sand are found in various localities throughout the world. The term bituminous sand is used herein to include those materials commonly referred to as oil sand, tar sand and the like. One of the most extensive deposits of bituminous sand occurs, for instance, in the Athabasca district of the Province of Alberta, Canada.

Typically, the composition of these sands by weight is: from about 5% to about 20% of oil; from about 1% to about by water; and from about 70% to about 90% of inorganic solids. The specific gravity of the bitumen varies from about 1.0 to about 1.05. (The specific gravity of the bitumen as well as all other values of specific gravity given herein are taken at 60 F.) The major portion of the inorganic solids, by weight, is fine grain quartz sand having a particle size greater than about 45 microns and less than 2,000 microns. The remaining inorganic solid matter has a particle size of less than 44 microns and is referred to as fines. The fines content typically varies from about 5% to about 30% by weight of the solid inorganic content of bituminous sand. However, the composition of bituminous sand can vary from the above-mentioned ranges and this is not too uncommon. Also, in mining the bituminous sand, clay which is found in layers of varying thickness in such sand areas, may be admixed with the the inorganic solids content and particularly the fines content of the material to be processed.

Various methods have been proposed for separation of bitumen from bituminous sand. The two best known methods are often referred to as the hot water method" and the cold water method. In the former, the bituminous sand is jetted with steam or hot water and mulled with a small proportion of water at about 175 F., and the pulp is then dropped into a turbulent stream of circulating water and carried through a separation cell maintained at an elevated temperature of about 180 F. In the separation cell, entrained air causes the oil to rise to the top in the form of a froth rich in bitumen which is then drawn off. Sand settles to the bottom and may be removed therefrom.

The so called cold water method does not involve heating the bituminous sand other than whatever heating might be required to conduct the operation at room temperature. The process involves mixing the bituminous sand with water, soda ash and an organic solvent such as kerosene. The mixture is then permitted to settle at room temperature. A mixture of water and bitumen dissolved in the organic solvent rises to the top of the settling zone and is recovered.

While the presence of zirconium and titanium in very minor quantities in coarse grains of bituminous sands has been previously recognized, these metals have not appeared to be present in economically recoverable concentrations. The present invention provides a means for concentrating and recovering such metals, especially zirconium, from bituminous sands.

It has been found that when bituminous sand containing minor quantities of heavy metals, especially metals of Group NE of the periodic table of elements (titanium, zirconium and hafnium), and particularly zirconium, is treated for recovery of bitumen by processes such as the above described hot and cold water methods, the heavy metals concentrate in the bituminous froth recovered from the body of hot water to an extent such that recovery of the metals from the froth becomes economical. The concentration of metals in such froth has been found to be at least 10 and frequently as much as 40 or 50 times that of the corresponding metals in the raw bituminous sand. In the case of titanium, the concentration in the froth is usually about times that in the raw sand while zirconium is usually found in the froth in about forty times the concentrations found in the original bituminous sand. While references are made herein to the heavy metals themselves, it should be understood that such metals are frequently present in the form of oxides, silicates, etc. and when present in these forms, may be recovered as such materials rather than as pure metal. Zirconium, for instance, is typically present primarily in bitumen, thus increasing the form of zircon (zirconium silicate) while titanium may be present as ilmenite (iron-titanium oxide) or rutile (titanium oxide). Zircon, is usually enriched with minor amounts such as l to 5 weight percent (wt.%) of hafnium. Concentrations of zirconium in raw bituminous sand are frequently between about 0.01 and about 0.1 wt.% and the concentrations of titanium between about 0.05 and about 0.5 wt.%. ln accordance with the present invention, it is possible to recover at least about 30% and frequently as much as about of these metals in froth recovered from water separation processes of the type described above. The solids content of such froth usually contains at least about 3 wt. of such heavy metals, frequently in excess of 5 wt.%.

The present invention contemplates recovery of heavy metal, especially zircon, from bituminous sands by introducing a fluid slurry of bituminous sand containing heavy metal and other solids into a body of water whereby a froth containing bitumen, heavy metal and other solids rises to the top of the body of water and sand settles to the bottom thereof. Heavy metal and other solids are recovered from the froth and contacted with an alkali metal hydroxide after which the solids are contacted with aeration gas in a flotation zone to preferentially float solids other than heavy metal and form a lower layer rich in heavy metal from which heavy metal may then be recovered by conventional techniques.

In accordance with a preferred embodiment of the invention, bituminous froth containing concentrations of heavy metals is produced from bituminous sand by the hot water method referred to briefly above. In this process, raw bituminous sand is mixed with warm water in a mixer such as a conventional rotating cylindrical tumbler having perforations for the slurry to drop out and provision for rejecting oversized rocks and lumps of sand which cannot be broken down. The slurry produced in the mixer is preferably at a temperature between about and about F. The slurry temperature may be controlled by control of the temperature of the water added to the mixer or by direct addition of steam to the mixer or by other suitable means. Average residence time of bituminous sand in the mixer is preferably between about 0.5 and about 5 minutes. Sufficient water is normally added in the mixer to form a slurry containing between about 20 and about 40 wt.% water. After leaving the mixer the slurry is usually flooded with additional water to bring its water content to between about 40 and about 60 wt.% and the flooded slurry is then introduced into a body of warm water maintained at a temperature between about 140 and about 200 F. If desired, aeration gas may be added to the hot water to assist in separation of bitumen from sand particles. Air entrained in the slurry during the mixing step as well as any introduced into the separation zone causes bitumen to rise to the upper surface of the water to form a froth while sand is allowed to settle to the bottom. Sand tailings may be withdrawn from the bottom of the separation zone while froth containing bitumen, heavy metals and other solids is recovered from the upper portion of the separation zone.

Following recovery from the hot water separation zone, the froth containing bitumen, heavy metals and other solids is treated for recovery of bitumen and metals therefrom. In a preferred embodiment of the invention, the froth is subjected to thermal dehydration treatment to evaporate water therefrom and is then subjected to gravity treatment as in a cyclone separator to obtain an overhead stream containing the majority of the bitumen and an underflow stream containing most of the solids and substantially all of the heavy metals. if desired, the underflow stream may be filtered to further separate liquid and solids. The solids from the underflow stream are then preferably dried as in a rotary kiln.

Solids recovered from bituminous sand froth, as described above, are generally in the size range between about 20 and about 44 microns and contain concentrated amounts of heavy metals. In accordance with the present invention, such solids are further treated with alkali metal hydroxide followed by flotation with aeration gas to further concentrate the heavy metals and especially the zirconium present in the form of zircon. The alkali metal hydroxide is preferably in the form of an aqueous solution and, while the strength of the solution is not considered especially important, concentrations of between about 5 and about 30 mol percent of the alkali metal hydroxide are commonly used. When treating the solids with the alkali metal hydroxide, enough liquid should be used to completely wet the solids and maintain a continuous liquid phase. This may usually be accomplished with the use of at least 3 volumes of liquid per volume of solids with liquid to solids ratios in the range of about 3 to about 20 being most usual. While any alkali metal hydroxide may be used, sodium hydroxide has been found to be especially useful.

While the mechanism by which the process of the present invention results in selective flotation of solids other than heavy metal is not completely understood, it is believed to be due to the selective action of the alkali metal hydroxide in stripping naturally occurring surfactants from heavy metal solids in preference to stripping of such surfactants from the other solids such as silica present in the solids recovered from the bituminous froth. Thus, when the solids are subjected to conventional flotation operation with aeration gas, the solids other than heavy metals which are still coated with naturally occurring surfactants are floated in preference to the heavy metals which have been stripped clean of naturally occurring surfactants by the action of the alkali metal hydroxide. This operation is thus in contrast to conventional ore flotation operations in which special additives must be used either to suppress flotation effects on certain components of the solids mixture or to enhance the flotation of some components, or both. In practicing the present invention, it is merely necessary to treat the solids with the alkali metal hydroxide and no additives need be used in the flotation portion of the process. Also, in conventional ore flotation processes, it is usual to preferentially float the desired product solid, whereas in the present metals recovery process, the undesired solids, i.e., silica and other non-heavy metal solids, are floated while the desired heavy metal components are concentrated in the lower portion ofthe flotation zone.

While the alkali metal hydroxide preferentially cleans the natural surfactants from the heavy metal solids and especially zircon, these hydroxides do have some effect upon other solids and, accordingly, it is preferred to limit the time of contact of the alkali metal hydroxide with the solids so that surfactants are not substantially stripped from solids other than heavy metals. Also, since the temperature maintained during the contact effects the rate of stripping of surfactants, relatively higher temperatures are preferred in order to expedite the process and minimize equipment investment. Preferred conditions for the contacting of the alkali metal hydroxide with solids recovered from froth in accordance with the invention include temperatures in the range between about 50 and about 210 F., more usually between about 100 and about 200 F., and a contact time between about minutes and about 2 hours. Preferred contact times in the 100 to 200 F. temperature range are from about 15 minutes to about 1 hour.

Once heavy metal solids have been concentrated in the lower portion of the flotation zone, as described above, they may be recovered therefrom and the heavy metal recovered in accordance with standard metal recovery techniques.

One suitable method for recovering zirconium (with or without hafnium enrichment) and titanium from such solids involves first passing the dried solids through magnetic separation equipment to recover ilmenite therefrom. The tailings from the magnetic separation step are then passed across a conventional shaking table to remove light solids, leaving zircon and rutile. These may be treated in conventional flotation equipment with a soap collector such as sodium oleate and a frothing additive to obtain separation of zircon from rutile. It should be understood that the zircon may be enriched with minor amounts of hafnium such as up to about 5% by weight ofthe zircon.

A typical example of recovery of heavy metals from tar sands in accordance with the present invention involves recovery of such metals from bituminous sand having the following composition:

Ingredients wt.% Solids 86.12 Bitumen l0.43 Water 3.45 Hafnium Enriched Zirconium (as Zr) 0.05 (as Zircon) 0. l0 Titanium (as Ti) 0.21 (as Rutile) 0.35

This tar sand is mixed with water to form a flooded slurry containing 60 wt.% water and is then introduced into a hot water separation zone containing a body of hot water maintained at a temperature of 159 F. Froth recovered from the upper portion of the separation zone contains 22.14 wt.% water, 68.50 wt.% bitumen, and 9.36 wt.% solids. Zirconium is present in the solids in this froth to the extent of 1.95 wt.% based on Zr and 3.92 wt.% based on Zircon. Titanium is present in the solids in the froth to the extent of 4.04 wt.% on Ti and 6.74 wt.% based on rutile. Following thermal dehydration and cycloning, the underflow solids from the cyclone contain 70 to wt.% of the solids present in the froth except that about of the rutile, ilmenite and hafnium enriched zircon is present in the solids recovered from the cyclone underflow stream due to the relatively high gravity of these materials. The underflow solids from the cyclone are then treated with 5 volumes of 10 mol percent aqueous solution of sodium hydroxide for a period of one-half hour at a temperature of 190 F. and are subsequently contacted with upflowing air in a flotation zone for one-half hour to preferentially float solids other than heavy metals. This results in a concentrated layer of heavy metal solids in the bottom of the flotation zone and the solids are then removed and heavy metals recovered therefrom by the metal recovery techniques described above.

While the invention has been described above with respect to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

lclaim:

1. A process for the recovery of heavy metal compounds selected from the group consisting of titanium, zirconium, and hafnium metals, compounds, and combinations thereof from bituminous sand which process consists essentially of:

mixing the bituminous sand with water at a temperature between about and about F. to form a fluid slurry; introducing the fluid slurry of bituminous sand containing said metals and compounds thereof into a body of hot water maintained at a temperature between about 140 F. and 200 F., whereby a froth containing bitumen, said metals and other solids rises to the top of said body of water and sand settles to the bottom thereof; separating said metals and other solids from said forth by thermally dehydrating the froth to remove water therefrom, and gravimetrically separating said dehydrated froth into said metals and other solids, and into a bitumen stream; mixing said separated metals and other solids with an aqueous solution of an alkali metal hydroxide at a ratio of liquid to solids of at least 3 to 1, while maintaining said mixed solution and solids at a temperature in the range of between about 50 and about 210 F.;

then contacting said separated mixed metals and compound thereof, and other solids in a flotation zone with an upwardly flowing aeration gas to thereby preferentially float the solids other than said metals and compounds thereof and form a concentration in said floatation zone of a lower layer rich in said metals and compounds thereof; and

and other solids is at a temperature of between 200 hour.

4. The process of claim 3 in which the metal compound is in the form of zircon.

and about F. and for a time between about 15 minutes and about 1

Claims

2. The process of claim 1 in which the alkali metal hydroxide is sodium hydroxide.
3. The process of claim 2 in which mixing between the sodium hydroxide solution and the metals and compounds thereof and other solids is at a temperature of between 100* and about 200* F. and for a time between about 15 minutes and about 1 hour.
4. The process of claim 3 in which the metal compound is in the form of zircon.