US3773637A - Method of dissolution of metals using thermogalvanic cells - Google Patents

Abstract

Thermogalvanic cells comprising two half cell units each containing an inert electrode, e.g., graphite the half cells being connected at their upper and lower portions by conduit means; cell adapted to dissolution of metals, e.g. stainless steel - in operation, electrode and metal to be treated charged to each half cell and heat applied to first half cell, continuous convection circulation of electrolyte as dissolution occurs.

Description

United States Patent Decrosta Nov. 20, 1973 [54] METHOD OF DISSOLUTION OF METALS 1,160,400 11/1915 Goldschmidt..... 204/146 USING THERMOGALVANIC CELLS 3,198,720 8/1965 Knippers et al... 204/146 3,194,750 7/1965 Knippers et al... 204/146 6] Inventor: Edward Decrosta, 7 James 1,511,967 10 1924 Holland 204 146 Hudson, N.Y

[22] Filed; Nov, 2, 1970 Primary Examiner.lohn H. Mack Assistant ExaminerT Tufariello [21] Appl' 86318 AttorneyRobert A. Burroughs Related US. Application Data [62] l3)i5v;s7io9n7; f Ser. No. 607,241, Jan. 4, 1967, Pat. No. 57 ABSTRACT Y I Thermogalvanic cells comprising two half cell units 52 US. Cl. 204/146, 204 249 each Containing an inert electrode, -ggraphite the 511 1111.01 B0lk 1/00, BOlk 3/03 half cells being Connected at their upper and lower [58] Field of Search 204/146, 248, 140, PortionS by conduit means; adapted to dissolution 204/249 of metals, e.g. stainless steel in operation, electrode and metal to be treated charged to each half cell and [56] References Cited heat applied to first half cell, continuous convection UNITED STATES PATENTS circulation of electrolyte as dissolution occurs.

718,927 1 1903 Gould 204/248 8 Claims, 1 Drawing Figure METHOD OF DISSOLUTION OF METALS USING THERMOGALVANIC CELLS This application is a division of my copending application, Serial No. 607,241 filed January 4, 1967 and now Patent No. 3,537,972.

The present invention relates in general to thermogalvanic cells and more particularly to thermogalvanic cells capable of providing an exceptional efficiency level of energy utilization, said cells being uniquely and beneficially adapted for use in connection with a wide variety of industrial operations such as metals reclaiming and salvaging gas generation, the production of electricity, monitoring techniques and the like.

As will be appreciated, a significant number of commercial activities depend critically for feasible and economic practice upon the availability of low cost energy sources, the diversion of such energy to useful purposes requiring, of necessity, relatively specific means. In this regard, exemplary reference may be made to the metals reclamation industries wherein metal dissolution comprises a vital phase of the processing. Although the industrial applications involving the implementation of methods designed to effect metal dissolution are legion those peculiar to the basic metal processing industries in particular have assumed a position of premier importance. Metal dissolution, in some form, is, of course, a necessary adjunct to a vast number of commercial operations associated with metal reclaiming, salvaging, polishing, as well as techniques evolved for purposes of reducing a metal to its component constituents, i.e., the extraction of component metals from parent alloys and the like. The extent of metal dissolution will depend primarily on the nature of the operation; thus, in the case metal polishing or other operations involving the removal of spurious coatings or other surface deposits, the dissolution effects with correspondingly be confined to the surface portions of the metal article in question. In general, the techniques heretofore promulgated for such purposes and based upon the use of various forms of mechanicalabrasion, e.g., rubbing, griiiding, etc., have proved notably deficient and have thus necessitated resort to more palatable. chemical means, the latter techniques invariably being based upon the utilization of solvent media, e.g., acid baths to accomplish the requisite degree of metal dissolution. As will be recognized, with methods of the foregoing type it is only necessary that dissolution be carried out to a predetermined depth of the metal article being treated.

The technology surrounding the efficacious practice of metal dissolution techniques has perhaps assumed paramount industrial importance in connection with metal extraction, salvaging, reclamation, and similar operations. The term metal extraction" as used herein is intended to connote those unit processes and operations which may be resorted to for purposes of reclaiming one or more constituent metals of a' parent alloy; thus, metal dissolution as an operative technique in this regard signifies conversion of the base material to a form which permits expeditious separation, isolation and recovery of the various metal ingredients. The burgeoning industrial importance of metal dissolution methodology as a means for achieving metal reclamation is, of course, well established and may be efficaciously employed in the treatment of scrap materials as well as native ores.

Despite the relatively widespread industrial exploitation of metal dissolving processing to accomplish the aforestated objectives, serious disadvantages have nevertheless been encountered in its practice which in the main have tended to retardor otherwise abate even further commercialization. In many instances, such processing provides but marginal advantage and especially when considered from an economic standpoint. Thus, even slight variations in market value of the metal sought to be reclaimed may militate against the propriety of a given operative technique. In fact, it may well be necessary to discard a considerable portion of the raw material metal supply should the metal composition,'i.e., content of valuable metal, fail to justify the cost increment incurred as a concomitant of the required processing. As a practical matter, the prohibitive economics involved has lead to vast stock pilings of raw material reserves considered economically unworthy of metal extraction treatment. The minimization of the cost factor at each and every step of metals extraction processing is quite obviously a matter of critical import.

Considerable effort has thus been expended by skilled investigators and practioners pursuant to the obtention of means whereby metals-extraction processing could be beneficially implemented with respect to raw material metals containing but minimal quantities of valuable metal ingredients. Despite the meritorious achievement which has typified suchinvestigation, the economic problems continue to persist and have heretofore represented a seemingly insurmountable challenge to metals reclamation technology. The situation has been particularly problematical with respect to the reclamation of nickel from stainless steel alloys. It is a matter of common knowledge that nickel lends itself admirably to a wide variety of commercial uses and particularly'with reference to catalysis, e.g., the polymerization of organic monomeric materials such as the alpha, beta-ethylenically unsaturatedmaterials commonly referred to as vinyl monomers; alkylation, isomerization, cracking and the like. In view of the commercial importance of nickel, its efficient reclamation has become a matter of primary industrial importance. The

foregoing represents, of course, but one .particularized example of the urgency characterizing metals reclamation andmay well be extended to other metals including the reclamation of copper, manganese, tin from tinplate, etc.

The methods heretofore evolved which purportedly enable the attainment-of metal extraction, dissolution,

etc., at least insofar as describedin the published literature both patent and otherwise, usually involves some type of electrolysis treatment wherein the metal to be treated is subjected to electrolysis in an appropriate electrolyte. Typically, the vast majority of such methods invariably require the utilization of a direct current source independent of the energy generated during the course of the metal dissolution reaction. Although the costs attributable to the necessity of furnishing electrical energy may appear to be somewhat minimal in the agglomerate, it should be realized that the total profitloss picture characterizing processes of this type is highly tenuous and it is thus incumbent upon the processor to mitigate such expenses to the greatest extent possible. Further refinements and ramifications of the basic electrolysis process have included various means for accelerating or otherwise expediting the metal dissolution reaction. For example, the utilization of heat, e.g., steam sparge, introduced directly into the electrolyte medium is pretty much standarized procedure and provides a satisfactory measure of improvement as regard augmenting the metal electrolysis reaction. However, implementation of the aforedescribed reactionaccelerating embodiments has tended to severely restrict the processor in his scope of operation, i.e., imposed rather stringent limitations as regards the choice of reaction parameters including temperature, quantity of reactants and the like. Thus, in order to assure optimum realization of any possible advantage peculiar to such techniques, it has been imperative in practice to employ highly elevated temperatures, i.e., temperatures which materially promote electrolyte corrosivity, as well as other deleterious effects and thus make mandatory the use of specific and relatively costly materials of construction. Moreover, since the electrolyte media is in many instances comprised of highly volatile acidic substances having relatively low salt concentrations and thus exhibit comparactively high vapor pressures at ambient temperatures, the useof closed systems for carrying out the electrolysis reaction correspondingly requires the employment of container materials structurally adapted to Withstand any pressure build-up which might accompany the reaction. Other disadvantages which have tended to detract considerably from the commercial feasibility of the metal extractiontechniques heretofore promulgated, in the art include the requirement for using exceedingly high-energy electrolyte media, i.e., solutions containing an inordinately high concentration of electrolyte. The use of such high concentration baths tends to aggravate problems of the type previously stated and in some cases imposes intolerable requirements on the processor as regards the selection of parameters for conducting the electrolysis reaction in question.

Thus, it is not surprising to find even today that many of the metal dissolution techniques practiced on a commercial scale, albeit somewhat more sophisticated, nevertheless constitute ramifications of the basic, nonelectrolytic acid-treatment process, e.g., the dissolution of copper scrap in sulfuric acid at elevated temperatures, the latter being effected by the use of a steam sparge, for example. The latter has proved to be a somewhat effective method since it combines thereaction-accelerating effects resulting from the influence of higher temperatures with those attributable to agitation effects which of course, are promotive of more efficient acid-metal contacting. Although other metal dissolution systems have been proposed which ostensibly capitalize on the advantageous features inherent in both electrolytic and non-electrolytic processes, such systems are uniformly characterized in that successful operation invariably requires materials of construction, operating parameters or specific modes of operation which militate against feasible commercial practice.

It is thus manifestly clear that there exists in the art a distinct need for an efficient energy-producing cell beneficially adapted for use in connection with the broad spectrum of operations incident to, for example, metals extraction, metals reclaiming, as well as other operations and wherein the energy requirements for efficacious operation are reduced significantly.

In accordance with the discovery forming the basis of the present invention it has been ascertained that the basic principle governing the operation of thermogalvanic cells as distinguished from cells principally electrolytic in nature, can be synergistically modified to advantage to provide a cell of novel construction and operation, such cell being uniquely and beneficially adapted to a plurality ofindustrial applications and particularly those relating to metals dissolution processing.

The construction and operation of thermogalvanic cells is well known in the art, being extensively described in the published literature both patent and otherwise. Perhaps the primary utility of cells of this type relates to the production of electrical energy. Thus, such cells, each cell being composed in turn of two half-cells, can be provided in battery form utilizing series or series-parallel arrangements to make possible the production of useful quantities of electrical energy. In essence, thermogalvanic cells operate on the principle of mass flux against a temperature gradient which in turn gives rise to the formation of a concentration difference across each of the half cells comprising the basic cell unit. The concentration differences thus formed lead to the generation of an electromotive force and the consequent flow of electricity in a first or primary electric circuit. lons generated and discharged at each of the electrodes contained in the respective half cells are transported between the half cells to form an internal or secondary electric circuit. Thus, with oxidation occurring at the anode, electrons are given up by a substance which becomes ionized, and solvated in an electrolyte medium which can be solution, a molten salt, or, an ionized gas molecule. The electrons flow in the external circuit to the cathode, where positively charged ions recombine with the electrons to form electrically neutral materials. Under the influence of a temperature-induced concentration gradiant, diffusion of the electrically-neutral species occurs, and the process is repeated.

Each of the electrodes employed in the aforedescribed cell structure is of course of the non-consumable type, i.e., undergoes substantially no net change in mass. It is recognized that some loss in electrode mass may possibly be experienced due to what can perhaps best be described as wear and tear; consequently some degree of electrode dissolution, though minimal, may inevitably occur. It is axiomatic, however, that efficient thermogalvanic cell operation requires the observance of procedures designed to minimize electrode loss and especially that which might otherwise occur through dissolution. To this extent, then, the electrodes can be regarded as permanent.

As sources of electrical energy, thermogalvanic cells are commonly recognized as providing a satisfactory level of operational efficienty. Heretofore, the principal of operation characterizing such devices has been confined for the most part to the production of electrical energy. As will be made apparent in the discussion which follows, thermogalvanic cells fabricated in accordance with the present invention not only exhibit a manifold increase in operational efficiency, i.e., the total energy requirements for effective operation are reduced to an extent heretofore considered unattainable, but, in addition, due to novel aspects of construction, are peculiarly adapted to a mode of operation which greatly extends their field of use.

Thus, a primary object of the present invention resides in the provision of a thermogalvanic cell wherein the foregoing and related disadvantages are eliminated or at least mitigated to a substantial degree.

Another object of the present invention resides in the provision of a thermogalvanic cell characterized by an exceptional efficiency level of energy utilization.

A further object of the present invention resides in the provision of a thermogalvanic cell which affords exceptional means for effectuating the rapid dissolution of metals with the use of but moderate conditions of temperature, electrolyte concentration and the like.

A still further object of the present invention resides in the provision ofa thermogalvanic cell which is highly economical in construction and operation to thereby make possible the realization of substantial savings.

Other objects and advantages of'the present invention will become more apparent from the following description and accompanying drawings.

The attainment of the foregoing and related objects is made possible in accordance with the present invention, which in its broader aspects includes the provision of a novel thermogalvanic cell comprising as essential components a first half cell and a second half cell each of said half cells comprising container means having disposed therewithin an inert unreactive electrode, a first conduit means interconnecting the upper regions of each of said container means, a second conduit means interconnecting the lower regions of said container means and wherein each of said conduit means communicates with the internal portions of said container means.

The particular manner in which the improvements described herein may be realized can be perhaps best illustrated by reference to the accompanying drawing which illustrates schematically the unique arrangement of parts comprising the thermogalvanic cell structure. Each of the half cells constituting the basic cell unit is represented generally at 1 and 2. Conduit means interconnection the upper and lower regions of each of the half cells and serving as electrolyte bridges are represented at 3 and 4, respectively. lnert unreactive' electrodes 5 and 5', e.g., graphite, are situated in such manner that at least a portion thereof protrudes internally of the half cells. The sole criticality with regard to the exact positioning of the respective inert electrode members 5 and 5' is such that it permits the establishment and maintenance of adequate electrical contact therebetween via a suitable electrically conductive path represented at 8 and coupled through switch 7, the latter permitting insertion of voltmeter or ammeter A into the conductive path i.e., primary circuit 8. Thus, as illustrated in the drawing, a portion of such electrodes projects externally of the half cell housings, this being generally preferred since it affords ready access to at least two essential points of electrical contact which serves to expedite any troubleshooting operaelectrodes, owing to their solubility in the acidic electrolyte media which during cell operation would fill the respective half cells 1 and 2, can be characterized as consumable, as distinguished from inert electrodes 5 and 5' which, of course, are substantially immune to the dissolution effects of the electrolyte. Each of half cells 1 and 2 may be further provided with suitable wells, (not shown), to accommodate thermometers represented by T to permit necessary temperature readings. vent lines 29 and 30 provided with valves 24 and 28 provide means for allowing gases to escape to the atmosphere during acid introduction.

l-lalf cells 1 and 2, via conduit lines 9 and 10 communicate with container means 11, the latter serving as a gas liquid trap and allows for the separation of entrained electrolyte from the gases evolved from each of the half cells. Conduit line 13 interconnecting trap 11 and gas collecting tank 12 is provided with valve means 14 and permits removal of gaseous material evolved in the system. Entrained electrolyte may be returned to the lower electrolyte bridge line 4 through line 15 provided with valve means 16. Half cell communicates with acid reservoir tank,17 thru line 27 provided with valve means 18. The upper electrolyte bridge, i.e., conduit line 3, is provided with valve means 19 to permit either continuous or intermittent withdrawal of product solution, i.e., electrolyte containing dissolved metal salts which result from continued dissolution of consumable electrodes 6 and 6'. The product may be directed to hold up tank 22 through line 21 to await further handling. Further valve means 20, 23, and. 25 and 26 are positioned at various points of the apparatus whereby to afford complete control of fluid flow throughout the system. Valves 23 and 26 in upper and lower electrolyte bridges 3 and 4 respectively permit each half cell to be isolated should chemical analyses, i.e., quantitative, qualitative, etc. of the process stream be desired.

Operation of the aforedescribed apparatus, specific reference being made again to metals dissolution processing, may be effected in the following manner. The metal selected for dissolution treatment is introduced into each of half cells 1 and 2. Suitable means may be provided for accomplishing this step in either batch or continuous fashion. Thus, in those instances wherein the metal to be treated is provided in bulk form, a suitable feeding hopper (not shown) may be positioned adjacent each of the half cells to enable metered feeding. Alternatively, the raw material metal may be provided insolution-form in which case feeding may beaccomplished via a suitable conduit line (-not shown).provided with valve means. ln anyevent, the manner in which metal feeding is accomplished is not a particularly critical factor in the practice of the present invention, depending solely upon the requirements of the processor, e.g., whether continuous or batch operation is desired.

. The metal thus introduced comes to rest in contact system through valve 18 to an extent sufficient to fill each of the half cells as well as the appertaining conduit lines. The acid materials may be any of those conventionally employed in the metal processing industries for accomplishing electrolytic dissolution of raw material metals, with typical representatives including, without necessary limitation, sulfuric acid, hydrochloric acid,

etc; in some instances the use of organic acids may be dictated such as citric acid and the like. The particular acids selected will of course depend primarily on the dissolution rates desired by the processor. The concentration of the acid solution may vary ranging from about 10 to about 80% by volume with a range of about -30 percent being particularly preferred. In general, it is found that the use of acid solutions having a pH ranging from about .1 to 2 are admirably suited to the purposes of the present invention. Vent valves 24 and 28 which remain open throughout the acid introduction are at this point closed. The metal dissolution reaction rate depends of course, to a great extent upon the susceptibility of the metal to acid attack, i.e., its reactivity which in turn is influenced by the previous history of the metal, its extent of oxidation, corrosion and the like. I

The thermal gradient across half cells 1 and 2 essential to the practice of the present invention is established by merely supplying heat to half cell 1, hereinafter referred to as the hot half cell. This can be accomplished by conventional means, i.e., most any of the systems promulgated in the art for effecting efficient heat transfer. For example, the hot half cell may be provided with a heating jacket to provide an annular space surrounding the cell which serves to accommodate a heating fluid which may be in either vapor or liquid form. Alternatively, thermal energy may be supplied by means of an external heat exchanger or by radiant energy transmission. In any event, the exact nature of the heating means adopted is significant only insofar as design considerations promotive of maximum energy utilization are deemed significant. As will be noted from the drawings, the mutual physical arrangement of half cell 2 hereinafter referred to as the cold half cell and the acid reservoir respectively may be such as to permit gravity feed of the acid material into the system, i.e., by syphon effects. Such an arrangement correspondingly reduces pumping requirements thereby minimizing the cost involved. The contacting of the acid medium with the stainless steel electrodes is accompanied practically simultaneously by the initiation ofthe metal dissolution reaction. The net effect of supplying thermal energy to the hot half cell is the creation of a'concentration'difference across the respectivehalf cells which can apparently be explained by reference to two mechanisms; firstly, the increased metaldissolution reaction rate occurring in the hot half cell due to the reaction accelerating effects of the higher temperature generates correspondingly, a higher concentration of dissolved metal salts; secondly, the thermogradient established across the respective half cells likewise gives rise to a further increment of concentration gradient.

Each of the foregoing effects is operative in the creation of an electromotive force and correspondingly the production of direct current electricity.

Considerable experimental investigation, study and evaluation suggests the conclusion that the manifold increase in metal dissolution reaction rate made possible by the present invention cannot be explained by reference to the harnessing of those particular energy values attributable solely to the-effects of temperature and concentration differences. Without intending to be bound by any theory, it has nevertheless been postulated in explanation of such phenomena that the following situation obtains. Each of the thermal and concentration gradients created across the respective half cells represents a source of free energy, the approximate value of either being capable of mathematical resolution although somewhat approximate. In this connection, the Nerst theorum is deemed va1id.

However, the present invention is uniquely typified in that a still further source of free energy results from the difference in the relative metal-dissolution reactions occurring in the half cells. This can be explained asfollows: The reaction occurring in each of the half cells is identical and can be explained by the following equations:

(cold half cell) M+HA R: M* +A H (hot half cell) M+HA B; M +A [-1 wherein M represents the metal being treated, HA represents a suitable acid of the typementioned hereinbefore, M and A represent theproducts of acid ionization and R and R connote' suitable indicia reflecting the reaction rate involved. v

As will be readily obvious R, is necessarily greater by a considerable margin than R the disparity between becoming many times greater with increased heat inputs to the hot half cells, i.e., as the temperature gradient across the half cells is increased. A qualitative realization of the extent of the differential in reaction rates can be appreciated by reference to the rule of thumb" to the effect that the rate of a chemical reactionis approximately doubled for each 10 rise in temperature. The difference in reaction rates which can be represented by A R gives rise to a further free energy source whose energy contribution to the metals dissolving sytemcan be at least as significant as those energies derived from the concentration and thermal gradients. In fact, the energy provided by the AR value can exceed significantly the energy values attributable to the concentration gradient, i.e., AC, and thermal gradient AT in view of the aforedescribed temperature-sensitivity of the reaction rate; otherwise stated, the temperature coefficient characterizing the mathematical statement defining the AR value would be relatively large and thus relatively slight changes in temperature would have considerable impact on the respective half cell reaction rate and thus the'AR. Thus, the therinogalvanic electrolytic cells described herein utilize 3 variables i.e., temperature difference AT, concentration difference AC1 and reaction rate differences AR to achieve useful ends.

It is important to note at this point, that the desired metal dissolution reaction occurs in each of the half cells, i.e., oxidation occurs at each of the electrodes. Within the context of the present invention, the hot half cell described herein can be regarded as an anode equivalent due to the fact that the electromotive force generated thereby is positive relative to the cold half cell in the sense that a more accelerated metal dissolution reaction rate occurs thereat. This particular observation has been confirmed gravimetrically by weight loss measurements of the metal in each half cell. Thus, the metal being treated, i.e., each of the consumable electrodes, is simultaneously undergoing dissoultion. I

The significance of this particular aspect of the present invention cannot be emphasized too strongly. Heretofore, the energies diverted to useful purposes in the operation of metal-dissolving electrolytic cells were in large part derived from competing reactions, i.e., oxidation and reduction respectively, one of the electrode members being of the inert type. With respect to metals dissolution, such methods possess the obvious and inherent limitation that purposive ends, i.e., the solubilization of metal, are achieved at one electrode only. The present invention thusprovides what must be considered a vital advance in the art in that the necessity for the use of competing reactions, i.e., redox, in the operation of electrolytic type cells for purposes of accumulating energies is completely obviated. Although the basic operative principle characterizing the mechanism of oxidation-reduction cells is involved, i.e., to the extent that a source of e.m.f. is established by virtue of an electrical difference in potential across the respective half cells, the anode-cathode relationship results solely from a simultaneous occurrence of identical reactions albeit at different rates.

Optimization of the'improvement described herein are obtained by maintaining hot half cell temperature within the range of from about50 C. to about 70 C. and preferably from 58 C. to 65 C. During actual cell operation, valves 24 and 28 in vent lines 29 and 30 remain closed, while valves 25and 26 remain open in order to permit gaseous electrolysis products to be expelled into gas collecting tank 11. Although suitable pumping means may be employed if desired for purposes of accelerating or otherwise expediting the flow of fluid throughout the system, any such means will usually not be required for most applications. Actually, the combined effects of heat input to the hot half cell, the heat loss experienced via radiation and convection (whether natural or induced) from the cold half cell serve to promote a density gradient across the half cells, such density gradient providing the driving means for initiating as well as sustaining the necessary fluid flow volecity; the directional flow of fluid occurring in an upwardly direction through the hot half cell through the upper electrolyte bridge downward through the cold half cell and thereafter to the bottom of the hot half cell through lower electrolyte bridge 4. The continuous convection circulation of electrolyte aids considerably in minimizing the possibility of cell polarization which might otherwise occur and thusto this extent en'- hances the metal-electrolyte rate of reaction.- Other means may be resorted to whereby to establish some degree of fluid turbulence in the immediate vicinity of the consumable .metal electrodes-in order to combat cides with that point in the processing corresponding to 7 total consumable electrode. Such terminal point can be detected according to a number of methods, e.g., colorimetrically, increase in electrolyte density, chemical analysis-qualitative and/or quantitative, decrease in the weight of metal added initially, etc. Continuous processing may be effected, of course, simply by introducing the metal to be treated into each half cell on a periodic basis, as previously described. The prescribed intervals maybe readily determined by correlating the rate of metal dissolution with the mass of metal to be treated.

' The salt' solution obtained as a result of metal dissolution is preferably withdrawn continuously from the system with suitable valve means being provided for such purposes as indicatedat 19. The temperature of the product solution withdrawn from upper electrode bridge 3 will be lower than the temperature prevailing in the hot half cell. Such solution is then directed through conduit means 21 into product storage tank 22 and allowed to cool. Crystallization of solid salts will accompany solution cooling. Supernatant liquor i.e., saturated salt solution may be re-cycled to cold half cell 2. Salt recovery may be effected by several techniques. Quite naturally, some salt will precipitate on cooling i.e., crystallization. With mixed salts, such as would be the case when treating alloys, separative recovery is best effected by redissolving such salts and adding specific chemicals to preferentially precipitate the respective metals. Other techniques'which may be resorted to V ment is given solely for purposes of exemplifying a specific arrangement of parts found to be convenient in practicing the present invention. Regardless of the particular form ofapparatus employed, the essential units comprise, respectively, the hot and cold half cells, a first electrolyte bridge interconnecting the upper portionsof each of said half cells, a second electrolyte bridge interconnecting the lower portions of said half cells, and inertelectrodes-disposed within each half cell. The foregoing elements comprise the essential components ofthe apparatus described herein. Such items as gas-collecting tank acid reservoir tank, etc., can be regarded as being auxiliary in nature and merely provide convenient means forcarrying out themetals dissolution processing. During actual cell operation of prises a highly effective source of hydrogen gas,i.e.,

due to the accelerated electrolysis reaction involved as well as the highly efficient utilization of the energies generated, the cost of hydrogen gas generation can be reduced to an extent never before realized. This aspect of the present invention isof the first order of commercial significance in view of the fact that hydrogen is a highly valuable raw material for many industrial processes; thus, its economic production for use in conventional fuel cells continues to remain one of the unsettled problems of modern technology. The present thermogalvanic cells are likewise extremely useful as a test device whereby to determine rates of galvanic corrosion. This affords ready means for determining the applicability of a given metallic substance to uses which involve significant risks of corrosion. Another highly important utility characterizing the thermogalvanic cells described herein relates to their use as generators of electricity. As previously described, since cell operation proceeds as a result of the respective energy contributions attributable to differences in concentration, temperature, and reaction rates, and since each of such energy contributions is operative in the formation of an emf, the electrical energy realizable thereby greatly exceeds the corresponding energy outputs of prior devices proposed for similar purposes.

Nevertheless, the utilization of the aforedescribed energy quantities to metals dissolution processing has provided a particularly fruitful area of utility.

The following examples are given for purposes of illustration only and are not to be regarded as necessarily constituting a limitation on the scope of the present invention.

In each of the examples which follow, the apparatus employed was Comprised of the following arrangement of parts:

Hot Half Cell: 6 inch glass test tube, circular crosssection, 2 inch diameter having open ends, each of said ends fitted with a 3-hold rubber stopper and a 2-hole rubber stopper, respectively;

Cold Half Cell: same as hot half cell;

Acid Reservoir: 1,000 ml. glass flask fitted with 2-hole rubber stopper;

Gas Collecting Bottle-trap: one liter flask open at one end and fitted with a 2-hole rubber stopper.

The above described component parts are interconnected in the following manner. Each of the half cells is disposed vertically with a 3-hole stopper end facing upward. The glass tube serving as the cold half cell is disposed approximately 8 inches higher than the glass tube serving as the hot half cell. This arrangement is preferred since it permits the utilization of siphon effects whencharging the apparatus with the acidic electrolyte. The upper ends of each of half cells are provided with an interconnecting glass tubing approximately inches in length (V4 inch diameter), such line serving as the upper electrolyte bridge. The end portion of such electrolyte bridge in the immediate vicinity of the cold half cell is fitted with a T-joint which connects respectively with (l) the cold half cell, (2) the upper bridge line, and (3) the acid reservoir flask, the latter through a length of glass tubing measuring approximately 48 inches in length (V4 in diameter) and provided with a polypropylene stopcock to permit control over acid flow into the system. The end portion of the upper electrolyte bridge in the immediate vicinity of the other half cell, is likewise provided with a T-joint provided with a polypropylene stopcock, (2) the hot half cell, and (3) the upper electrolyte bridge. The cold half cell is further provided with a length of glass tubing measuring approximately 40 inches in length (V4 inch diameter) which connects with the gas collecting bottle or trap disposed vertically above each of the half cells. This line serves as a conduit for transporting effluent gases evolved during the electrolysis reaction to the trap. The upper end of the hot half cell connects with this line through a lingth of glass tubing approximately 22 inches in length (V4 inch diameter). Each of the upper ends of the half cells is provided with a thermometer whereby necessary temperature measurement may be taken. The lower ends of the half cells are interconnected in the following manner. A length of glass tubing (V4 inch diameter) disposed horizontally beneath the half cells and serving as the lower electrolyte bridge and measuring approximately 15 inches in length is joined to the hot half cell by a vertical length of glass tubing extending upwardly and measuring approximately 2% inches in length (V4 inch diameter) and to the cold half cell by a vertical length of glass tubing extending upwardly and measuring approximately 1 1 inches in length (V4 inch diameter). The lower electrolyte bridge line is provided with a polypropylene stopcock in the line connecting the aforedescribed vertical tube lengths, as well as in each of its end portions extending outwardly of each of the vertical leg connecting points. The latter valves permit withdrawal of electrolyte solution from the system as desired. Each of the bottom ends of the half cells is further provided with a carbon electrode of substantially circular cross-section measuring 2% inches in length and 5/16 inch in diameter. Each of the electrodes protrudes approximately V2 inchinto the internal portions of the half cells. The electrodes are electrically connected through a length of copper wire measuring approximately 47 inches in length and coupled through a single-pole-single-throw (SPST) switch which permits a voltmeter or ammeter to be inserted into the line to thereby permit the desired current or e.m.f. measurements. Each of the voltmeter (0.3 volts) and ammeter (0-500 milliamps) is provided with a double-pole-single-throw (DPST) switch which allows electrical continuity to be established as'desired thereacross. The hot half cell is immersed in a water-filled aluminum tank equipped with an immersion heater (1,000 watts).

EXAMPLE 1 chromium 18% nickel 8% manganese 2% iron 72% Electrical continuity across the carbon electrodes is established by closing the SPST switch. At this stage of the operations, the vent line connected to the cold half cell as well as the intermediate stopcock valve in the lower electrolytic bridge are open. Sufficient acid from the acid reservoir flask is charged to the system whereby to fill each of the half cells and the upper and lower electrolytic bridge lines. The acid employed in this example comprises aqueous sulfuric acid (10 percent H 50 by volume) having a pH between 1 and 2. The temperature of the'hot half cell is raised to approximately 28 C. by heating the water in which it is immersed. At this temperature, the stainless steel dissolution reaction accelerated visibly. The reaction was allowed to proceed unabated for a period of 3 hours with voltmeter and ammeter readings being taken periodically.

EXAMPLES 2 and 3 Example I is repeated except that the concentration of sulfuric acid is increased to 20 percent 58 10 percent by volume respectively. The results obtained are summarized in the following table:

TAB LE I sitating resort to the use of special, high-pressure equipment, It is further quite possible that adjustments in the composition of the electrolyte may be necessary, e.g., the use of additional ingredients to surpress vapor pressure. In any event, the salient point to be noted concerns the fact that the reduced temperature pro- Wgt. stainless steel As the data in the above table clearly indicates, acid concentrations, by volume, approximating 20-30 percent provide exceptionally high metals dissolution rates thereby enabling the dissolution of approximately 70 percent by weight of the original metal charge in a period of only 3 hours. The significance of this data can be made readily manifest by comparison with the results obtained utilizing more standardized techniques previously resorted to for effecting metals dissolution. For example, experimental runs'based on simple acid immersion were conducted employing identical stainless steel samples and sulfuric acid at varying concentrations as the electrolyte medium. In each case, the period of immersion in the acid was in excess of 3 hours. The results obtained are summarized in the following table.

TABLE [1 Acid Concentration Wt. Stainless Steel (grams) %(Vol Initial Dissolved l0 1.05 0.01 20 1.02 0.0] 40 1.02 0.01 8 0 1.1 1 0.01

The dissolution rates obtainable with simple immersion techniques as clearly indicated in Table II above are intolerably low and would scarcely suffice for commercial requirements. The use of elevated acid temperatures provide some degree of improvement however, of vital importance is the fact that in each .case, utilizing acid concentrations, by volume of 10 percent, percent, 40 percent and 80 percent, respectively,

t mp atu es in. exc spflfiqflwe necess n.

order to obtain metals dissolution reaction rates which would even begin to compare with those typifying the process and apparatus of the present invention. This is to be contrasted with the temperature values characterizing operation of the subject cell in the foregoing examples, i.e., on the order of 55 C. to 63 C. The extremely high temperatures required for feasible practice of prior art techniques such as typified by the aforedescribed acid immersion treatement make mandatory the use of highly costly, temperature-resistant materials of construction specifically adapted to withstand the corrosive nature of high temperature acidic media. As a matter of pure economics, the cost involved can be prohibitive. Furthermore, since the operating temperatures employed would of necessity exceed 100 C. and thus the normal boiling point of water, the maintenance of constant electrolyte solution concentrations can be somewhat problematical. Operation at higher pressure may well be dictated thus necescessing characterizing the present invention greatly increases the operators scope of operations.

The product solution obtained in the foregoing examples upon completion of dissolution operation was determined by analysis to comprise a mixture of metallic sulfates, i.e., CrSO FeSO NiSO and MnSO As previously described, separation of the salt mixture into its various components may be readily and easily accomplished by, for example, re-dissolution followed by preferential precipitation. Alternatively, fractional crystallization or resin bed absorption may be resorted to such purposes.

Results similar to'those described above are obtained when the procedures exemplified are repeated by employing in lieu of stainless steel equivalent quantities of 10,10 scrap, iron, zinc, etc.

It will also be observed from the foregoing examples that optimum metals dissolution reaction rates are obtained with the use of acid concentrations ranging from 20-30 percent by volume. This can probably be explained by reference to the fact that the degree of acid dissociation increases with increased dilution within, of course, certain limits. With acid solutions of high dilution, i.e., on the order" of 10 percent by volume, solution activity is apparently decreased to the extent that the degree of acid dissociation becomes relatively insignificant. In any event, the aforestated acid concentrations, namely, 20-30 percent by volume, are found to be'admirably suited to the purposesof the present invention and particularly within the temperature ranges extant during actual cell operation.

The various container means comprising the several components of the apparatus described herein as well as the conduit lines, valves, etc. must of course, be resistant to acidic solutions having a pH as low as 1. A wide variety of materials are readily available commerically in this regard. However, particularly beneficial results are obtained with many of the synthetic, organic plastic materials currently on the market, e.g., polyethylene, Materials of this type possess excellent structural ability, are substantially inert i.e., in no way deleteriously affect the electrolyte solution, while exhibiting exceptional resistance to/the corrosive effects of the acidic electrolyte. Such materials are, in addition, desirable from an economic standpoint since they are relatively inexpensive both in cost and maintenance.

The sizes of the various apparatus components will depend primarily on the volume requirements of the processor as well as the flow characteristics of the process stream. Such considerations are not particularly critical factors in the practice of the present invention and are readily capable of determination byrather routine means. For example, it will usually be advisable to maintain linear as opposed to turbulent flow in the connecting conduit lines, this being more conducive to efficient transport of the ionic species between the respective half cells.

This invention has been described with respect to certain preferred embodiments and there will become obvious to persons skilled in the art other variations, modifications, and equivalents which are to be understood as coming within the scope of the present invention.

What is claimed is:

l. A process for effecting the rapid dissolution of metals in an acid solution which comprises placing the metal to be treated in contact with a first inert unreactive electrode and a second inert unreactive electrode, each of said electrodes being situated in physically separate first and second container means, said container means being interconnected at their upper regions by a first conduit means serving as an upper electrolyte bridge and at their lower regions by a second conduit means serving as a lower electrolyte bridge whereby to provide a continuous flow path between said container means, said first container means being maintained at a higher temperature than said second container means the concentration of acid being from about 10 to 80 percent by volume.

2. A process according to claim 1 wherein said acid solution comprises sulfuric acid.

3. A process according to claim 1 wherein said metal comprises stainless steel.

4. A process according to claim 1 wherein the acid is at least one member selected from the group consisting of sulfuric acid, hydrochloric acid and organic acids.

5. A process according to claim 1 wherein the pH of said acid solution is from about 1 to about 2.

6. A process according to claim 1 wherein the temperature maintained in said first container means is from about 50 C. to about C.

7. A process according to claim 6 wherein the temperature maintained in said first container means is from 58 C. to 65 C.

8. A process according to claim 1 wherein the concentration of acid is from 20 to 30 percent by volume.

Claims (7)

1. 2. A process according to claim 1 wherein said acid solution comprises sulfuric acid.
2. 3. A process according to claim 1 wherein said metal comprises stainless steel.
3. 4. A process according to claim 1 wherein the acid is at least one member selected from the group consisting of sulfuric acid, hydrochloric acid and organic acids.
4. 5. A process according to claim 1 wherein the pH of said acid solution is from about 1 to about 2.
5. 6. A process according to claim 1 wherein the temperature maintained in said first container means is from about 50* C. to about 70* C.
6. 7. A process according to claim 6 wherein the temperature maintained in said first container means is from 58* C. to 65* C.
7. 8. A process according to claim 1 wherein the concentration of acid is from 20 to 30 percent by volume.

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