US1314236A - arnold - Google Patents

Description

E. E. ARNOLD. I SYSTEM FOR RECOVERING CYANIDS AND THE LIKE FROIII OYANID BEARING MATERIAL.

APPLICATION FILED FEB. I6. \9I8I Patented Aug. 26, 1919,

I 2 SHEETS-5HEET 2.

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I I l H II I ll II I I I I: I: I I I l I 'I' l I I I1 I I l I l l I I I l I i II II I II I l :1 I I: I I" 'I 'II I II I II I \II UNKTED STATE EDWARD E. ARNGLD, OF GREENE, CUVEHTRY, RHQDE ISLtND, ASSIG NQBJ T0 NITEQGEN @RODUCTS COMPANY, OF PROVIDENCE, RHODE ISLAND, A. CORPGRATIQH 9F RHQIDE ISLAND.

SYSTEM. RECOVERIKG-CYMIDS AND THE'LKKE $126M QYlNID-EEA ENG I MATERIAL.

specification oi Letters Patent.

Patented Aug. 26,

Application mes February is, rare. Serial No. 5217,4584.

the like from material which contains, intil mately mixed with said cyanid, a material from which the cyanid is to be separated, the invention having for one of its principal objects the eifecting of economies in time and in apparatus needed for the extraction and recovery of, for example, sodium cyanid from material containing such cyanid intimately mixed withother substances, such as sodium carbonate. Another object of my invention is to provide apparatus for economically handling a vo-latilizable solvent, especially as regards its application to the ma terial to be treated, whereby to more efiicaciously dissolve the solute, and as regards speeding up or accelerating the subsequent yolatilization of such solvent.

1 further aim to effect economies in converting the solvent'fl'om its gaseous to its liquid. phase, and in the time hitherto lost in eliminating occluded solvent from the pores or interstices of the leached or lixivia'ted mass, after the bulk of the solvent has Jeen withdrawn.

These and other objects of my invention will be hereinafter referred to and the novel combination of means and elements comprised in my improved apparatus, will be more particularly pointed out in the claims appended hereto.

In the drawings, which form parts hereof and in which like reference characters designate like parts throughout the several views, I have exemplified a preferred apparatus in which the process (described and claimed in my co-pending application Serial No. 26%,924, filed Dec. 2, 1918, as a division hereof) may be efiectuate'd, and I have herein described the preferred mode of efi'ectua't- 511g said process in said apparatus; but as I am aware of various changes and modifications which may be made both in said process and apparatus, I desire to be hunted only by the scope of the claims.

Referring to the drawings:

Figure 1 is a diagrammatic representat on of a preferred embodiment of my liuiviating and evaporating system.

Fig. 2 is a front elevation, partly broken away, of, and more fully showing, the lixiviator which appears in the diagrammatic representation aforesaid.

Fig. 8 is a vertical detail section, taken on the line HI-HI of Fig. 2.

Fig. 3 is a fragmentary detail section, taken on the line HI1H of Fig. 3.

Fig. 4 is a section taken on line IV-IV of Fig. 3; and showing in plan the lockingor hook-plate for the closure or plug of the lixiviator; and

a Fig. 5 is a front elevation of the condenser, the latter being partly broken away to show pipe connections.

In the U. S. patent to John E. Bucher, No. 1,120,682, dated December 15, 1914, there is disclosed a process for forming alkali metal cyanogen compounds, such as sodium cyanid; the material in which the cyanogen compound forming reaction is to be effected, being preferably, although not necessarily, briqueted. This material comprises asubstance capable of acting as the source of the base of the cyanogen compound to be formed, c. 9., sodium carbonate, intimately mixed with suitable carbonaceous material, such as powdered coke, charcoal, or the like, or a mixture of such carbonaceous material.

There is also prefz'erablypresent in said mass, catalytic material, such. as finely divided iron or the like, and after materials have been briqueted (or not, as the case may be), they are subjected to nitrogen gas, or to a gas such as producer gas, comprising nitrogen, and also to heat.

The temperature at which the reaction may be eiiected may be considerahly varied, but is preferably in the neighborhood of 1000 C.

In the hereindescribed process, the cyanized material resulting from this or a sinus lar reaction, is prefer ated with. a

eotvent, such as ely leached or liaia i.

' liquid ammonia, which solvent should preferreceiver R.

ably be capable of extracting or selectively removing the alkali cyanidfrom the other solid reaction residues.

I make no claim herein to the discovery of this preferred solvent, per 86, and in general do not desire to be limited to the solvent specified. v

I also do not desire to be limited in any way to the mode of initially producing the cyanogen compound sought, the present invention being concerned more especially with an improved method of handling a solvent of the character in question whereby, in one aspect of my invention, to expeditiously extract alkali cyanid from substances from which it otherwise is diflicultly separated.

Referring now to Fig. 1, let it be assumed that the extractor or lixiviator, L, has been charged with cyanid bearing material, such as the briquets aforesaid. This receptacle is in connection through pipes 1 and 2 with a This latter may initially be charged with the solvent in its liquid phase, and a valve a controls the flow of the liquid from said receiver to the extractor.

The receiver is connected with a suitable condenser C, bymeans of a pipe 3 in which is a valve 7), and a by-pass at containing suitable purging apparatus Q, hereinafter re ferred to, connects the sections of pipe 33 disposed upon opposite sides of valve b. It is also preferable to provide a valve 0 in the by-pass 4. The condenser has connected thereto a pipe 5, preferably of somewhat larger size, in which pipe there is also preferably disposed a valve (1, the pipe 5 in turn being connected to a riser or pipe 6. A suitable pump or compressor P, may have one end thereof connected as at 7 with the riser aforesaid, while a connection or pipe 8 at the other end of said compressor connects with the pipe 5 adjacent to the condenser.

Pipe 6, shown inFig. 1 as an extended riser, although it obviously may be otherwise, disposed, preferably as therein a i valve e,'and for convenience of description the section of the riser below valve 6 has been designated 6.

In the figure it Wlll be observed that a connection 9 is provided between the upper end of the-extractor and the lower end of the pipe 6, and in this connection there is located a valve 7. The pipe 1, previously referred to, may conveniently be extended up to the bottom of the releaching tank L, and, in order to vent the gas from this tank when the latter is being filled, a connection 10 is provided between the upper side of said. tank and the riser 6.

Extending down from the opposite side of the tank L, is a pipe 11 from which. laterally extends a pipe 12 at the end of which 'tion designated 15.

is located a vacuum pump P. A P p connects'the'lower end of the lixiviator with pipe12; pipe 13 having therein a valveg, and the pipe 12 having avalve- 71. therein, between pump P and pipe 13.

Immediately belowthe connection of the pipe 14 with pipe 11, and in the latter, I have shown a valve j, and the lower end of pipe 11 is in connection with a pipe see- From this latter extends up a pipe 16, which is disposed at .the right hand. end of the evaporator, as.

shown in Fig. 1; pipe 16 being connected to said end of the evaporator via pipe 17.

A valve is is located in pipe 17 and the upper end of the pipe 16 is in connection with a pipe 18 which extends between the lixiviator. and a heating coil or superheater S. To the left of the connection of pipe 16 with pipe 18 is valve], and the left hand end of pipe 18, adjacent the lixiviator, has connected thereto a pipe or conduit 19, which in turn connects with the riser section 6. In connection 19 there is preferably located a valve m. The super-heater S is connected at its lower extremity by a pipe 20 with a. pipe 2121, which extends up from the right hand end of pipe 15 to the pipe 2 aforesaid, as shown. A connection 22 opposite the pipe 20 places pipe 21 in connection with a gas tank or reservoir T, and the latter is in turn connected with acompression pump P, by a pipe 23.

The compression pump is in connection with a part of the condenser, as shown in Fig. 5; a pipe 24 being provided for this purpose. In the upper end of the pipe '21 I preferably locate a valve 'n, which, .as hereinafter described, controls the flow of gas from the tank T direct to the evaporator. A valve 0, preferably at the upper end of pipe 21, similarly controls. the flow of said gas into the pipe 2.

I also prefer to provide a valve 10 in pipe 1 above the connection of pipe 2 with the latter and a valve (1 in the pipe 11 leading down from the re-leaching tank, below the connection of pipe 12 with said pipe 11. In pipe 24 is a valve T which may be closed when the purging apparatus 0 is in use, on account of the backing up of liquid in the condenser coils at such time.

Ammonia may be introduced into the system, either in liquid form directly into the receiver, by removing the plu 27 of the latter,or, in gaseous form through the same pipe, 28, through which nitrogen may be supplied; valve 8 controlling the flow of gas through this pipe.

My invention also referably involves the provision of a suitab e agitating or stirring device 29 in the evaporator; this device becomplete volatilization of solvent from the cyanid crystallizing out in the evaporator, when the steam jacket of the latter, or its equivalent, is in operation,and, also, in manner hereinafter referred to, to :t'avor the formation of fine crystals'ot' said cyanid. Indeed, if the apparatus. be not rovided with an agitatin device, the cyanid, when operating on aarge scale, will frequently solidify into a massive block'or cake which can only be removed or handled with-{lifticulty.

When, the product is in the form of tine crystals or relatively small masses, it can be removed from the evaporator through a suitable opening; the latter normally being plugged as at 30.

The openings through which the preferably briqueted charge is introduced into and discharged from the lixiviator are correspondingly plugged as at 31 and 32.

A few details of the apparatus will now be considered before discussing the operation of the system as a whole.

T he lixiviator, as shown in some detail in Fig. 2, preferably comprises a cylindrical container 33, which is provided with a steam jacket 3%; live steam being introduced into the latter, as desired, through a pipe 35, and

the exhaust steam passing out by way of a I pipe 36.

it may be here noted that all of the vari- ()Us receptacles, their plugs or closures, and connections should be adapted to withstand reasonably high )ressures; pressures of 150 pounds to the inch, or more, being frequently attained in the lixiviator and other parts of the system. Thus, the plug above referred to, is preferably, as shown in detail in Fig. 25. received into a close fitting aperture in the head 37 ot the lixiviator, suitable provisions being made, as shown, for insuring a gas-tight closure; the plug being retained iirmly in position by backing out its screw 38 against a hookor retaining-plate 39. to place the bolts 40' of the latter under tension.

When the screw 38 is reversely turned, or slackcned, plate 39 may be rotated arrowwise, as viewed in Fig. 4, to permit the plug 32 and its screw to be withdrawn.

The head 37 is provided with a filter block 4&0 through which the cyanid containing solvent passes, toirec it from any pulverulent material in the charge being leached; and. for conveniem'e, this block may be secured in position by pouring molten lead or the like thcrearound, as at 41; a sleeve 42 being driven into a suitable recess in the head to provide an inner wall for the i retaining material.

of the recessin the head in which said block is located, so as to provide. below the filter block a series of channels 44. As shown in Fig. 3, the channels 44 are in connection with each other and with the pipe 13, which may be tapped into the head.

t the upper end of the liniviator is a head a5, similar to that just described, except that it is not provided with the cylindrical extension 37', since, obviously, no filter block is needed therein.

The heads 37 and 45 are held by bolts 4(5, firmly in engagement with annular flanges 47, secured as at 4-7 to the respective ends of the casing 33 and gas-tight connections are made between these rings and their heads by gaskets 4:8. I

It may be well at this point to consider a further detail, before discussing the mode of operation of the apparatus, and the steps of the process which may be carried out by means of such apparatus.

As shown in Fig. 5 the condenser C may comprise a coil 49, preferably although-not necessarily of somewhat flattened tubing to allow the condensed ammonia to How down therethrough, while leaving a space thereabove in the tubing, to permit of gases in this space being drawn of!" through the pipe 24, as shown. Suitable referigerating fluid 52 may be circulated through the condenser as by means of pipes 53 and 54 and the liquid ammonia passes off from the condenser through the pipe 3 as above described.

The operation of the system is as follows:

r..HSlHllt that the lixiviator is cold and has been charged with alkali metal cyanid bearing material; that the receiver contains the solvent to be employed, in liquid form, 0. (1., liquid ammonia; and that the various valves in the system have all been closed with the exception of valves 9, 7', r and i.

The vacuum pump 1 is nowstarted, to exhaust the air from the lixiviator, evapora tor and, it the rcleaching tank be provided, as is to be preferred, it also, together with the various connections thereto, will be corrcspondingly exhausted.

if desired, in order to make the removal of atmospheric oxygen more complete, the valve 0 may be opened, admitting compressed nitrogen gas, or mixed nitrogen and gaseous ammonia, from the gas tank 'l, which passes up through the pipe 21, to the pipe 2, and thence into the releaching tank, extractor and evaporator. Valve 0 may then be closed and the nitrogen removed from these several receptacles .by the vacuum pump; any gaseous ammonia present in this nitrogen being absorbed in the absorber or scrubber A.

valve a is opened to admit liquid ammonia,

via pipes 2 and 1, to lixiviator," r tter the latter has been filled, valve 0. is closed, and valves 9 and 0 maybe opened, so that compressed gas flows into the top of the lixiiviator and drives the liquid ammonia through; pipes 13 and 12, and up through pipe 11, to the releaching tank.

. Valves g and 0 are now closed and valve p 'is opened to permit the solvent (partially saturated with alkali cyanid) in tank L, to flow down by gravity, into the lixiviator, whereby to more nearly complete the removal of alkali metal cyanid, cyanamid, or

vthe like, from the lixiviator. Valves f and (1 may be cracked to relieve the gas pressure the solvent up through the pipe 11 to the releaching tank, in the manner described, the latter may be exhausted, by operating the compressor P, or even the 1 smaller compressor P for a short time.

Assuming now that the evaporator has been properly charged with quite well saturated solution; the problem then arises how best tospeedily eliminate the liquid ammonia, or the like, occluded in the pores and interstices of the mass in the lixiviator. This occluded liquid. is considerable in quantity and evaporates but slowly, even though steam' be turned into the jacket of the lixiviator, on account of the poor heat-conductive qualities of the mass in the latter. It has hitherto, therefore, proven to be a serious problemhow to shorten the time required for the removal of this occluded liquid, and the solution of this problem is one of the ob ects of the present invention.

Another object of the invention concerns the proper andyet reasonably rapid evaporation of liquid in the evaporator. On account of the fact that the mass being treated, at least initially, in this receptacle, is wholly liquid, it would not except for the-difliculty hereinbelow pointed out, involve a serious problem to speedilyevaporate such liquid bymeans of steam supplied to the evaporator steam jacket. The difficulty is, however, that this heat is largely supplied to the bottom and sides of the liquid mass, which is of course a readily volatilizable one, and the vapor formed rises in the form of bubbles to the surface of the liquid, where it bursts through, entraining the cyanid or the like, and carrying the latter along through the conduit through which the vapor escapes, until it causes considerable trouble in the piping and especially at the valves, by reason of its accumulation at such points. It is for this. reason that I prefer to provide an extended riser, such as that disignated 6, through which the generated gas may escape. This difiiculty may, however, be further and come by not starting the steam jacket of the evaporator into operation until much of the liquid in said evaporator has been driven off by the passage of warm gas over the liquid surface. 1

This gas may be any suitable one which will not injure the product or solvent, and the inert gas nitrogen, being entirely innocuous, lends itself readily to the purpose.

I do not however desire to be limited to this, since various gases may be employed. or even mixtures of gases.

Thus, as ammonia gas evaporator, it, obviously, is available for use as a heat medium; and indeed,.as will be pointed out hereinafter, when, for example, nitrogen gas is thus used in the system, it becomes intermingled with the gas evolved upon the evaporation of the solvent.

Referring again to Fig. 1, therefore, the superheater S, as it may for convenience be termed, is started into operation, and, all other valves being closed, the below mentioned valves will be opened:

Gas will pass from the tank T through the connections 22 and 20 to the superheaterv and thence via pipes 18 and 16 to pipe 17, and also to pipe 15, the lower end of pipe 11, and connection 14, to the respective ends of the evaporator, the valves is, j and 2' being open at such time.

By proper adjustment of valves j, i and k, the flow of warm gas into the opposite ends ofthe evaporator, may be adjusted, so that a substantially equal flow may be obtained; said gas, together with the vaporous ammonia or the like, given off at the surface of the body of liquid in the evaporator, passing up through the riser 6, and as it is usually preferred to direct this warm gas through the lixiviator to hasten the evaporation of occluded. liquid therein, the valve 6 may be closed, or nearly closed, as desired, and the valves m and f are opened. The expression warm. gas, above mentioned, is intended to be used as a relative term which contemplates that the temperature of the gas in question is rather materially above that at which the solvent copiously volatilizes.

Normally during the just described operation, the valve d may be open, compressor being idle, this will prevent the flow of gas through connections 7 and 8.

and, the,

more nearly completely overis evolved in the I 4 However, thepressure of gas generated by the evaporation of liquid from the receptacles L and E, will normally be sufiicient to enable the condensation of said gas in the condenser; whence the liouid solvent, now free from cyanid, may pass directly down into the receptacle R.

By the procedure above set forth, not only is the volatilization of liquid in the evaporator hastened, but there is a markedly less tendency for the carrying over or up of cy'anid. Also the evaporation of the occluded liquid solvent in the llXlVlfi-tOl" is greatly expedited.

If at any time the rate of volatilization in the evaporator becomes excessive, either the heat imparted by the superheater may be reduced, or the valvewz may be opened and relatively ,cool' gas admitted to the streams of warm gas entering the evaporator; this cool gas passing down through pipe 21 and entering pipes 15 and 16.

When the liquid in the receptacle L has been completely removed, as by this procedure it Will be in a comparatively short time, the valve 6 may be opened and valves f and m closed, so that the gas leaving the evaporator will pass directly up through the riser section 6 Without entering the lixiviator.

If for any reason, as on account of the nature of the charge introduced into the lixiviator, difiiculty should be encountered in removing the occluded liquid from said charge Within a reasonable time, evaporation thereof can be speeded up by opening valve Z, and closing the valve m, whereby to admit Warmer gas directly to the'lixiviator; this, together with the heat at such time supplied by means of the steam jacketof the l ixiviator, very speedily evaporating the residual occluded liquid.

After evaporation has been so far reduced that the pressure generated in the condenser is not sutlicient to effectively enable this apparatus to perform its function, the valve 03, if desired, may be closed and the compressor P started. "lhis exhausts the gases "from the extractor and evaporator, and it will frequently be necessary to gain access to the former sooner than'the latter, the valves m, c and q (and if desired ;0 andvg) may be closed for a short time, to enable the compressor to exert its full effect upon the gas in the lixiviator, to produce a reasonably high vacuum therein After this has been accomplished the valve 7 may be closed and the valve 6 opened to allow the compressor to act Wholly upon the evaporator, in like fashion.-

When all of the occluded liquid in the lixiviator as been removed from the charge therein, all valved connections thereto should be closed, and the plug 32 in'the head ma be Withdrawn, to remove the charge. At su time the said charge, if the operation has been properlyconducted, will be perfectly dry, and have at most therein but substantially a trace of cyanid.

The gas present in the space 50, above the condensed fluid flowing down through the condenser, may be tapped ofi' continuously or intermittently as desired through the pipe 24, through the operation of the com.- pression pump P which delivers said gas under pressure to the gas tank T.

Thus, if nitrogen be initially supplied from tank T to the system, this nitrogen Will be returned to said tank, and unless some special apparatus be provided for removing the ammonia gas mixed therewith, some of this latter gas also will pass through the pump P into the gas tan Under a system such as I have described however there is he objection to this, and in so far as the system is concerned, it may be operated substantially as well with ammonia gas alone. a

On account of the fact however that, vas above noted, such a relatively inexpensive gas as nitrogen, permits of its use for the purpose of sweeping out traces of atmospheric'oxygen or the like, and as it is not only cheaper than ammonia, but also equally harmless to the process, I. prefer to use it, in manner aforesaid. After the system has been in operation for some time, the gas thus used for sweeping out purposes, will comprise a mixture of nitrogen and ammonia, and to prevent loss of this latter, the.

absorber A is connected to the delivery end of the vacuum pump P" As various impurities are, during the course of an extended operation of apparatus of this description, apt to accumulate in the solvent employed, it is desirable to provide means to remove such impurities from time to time. To this end, the purging apparatus 0 is disposedin the bypass 4;, so that the liquid passing from the condenser to the receiver, instead of passing directly to the latter through pipe 3, may, by the closing of valve 6 and opening of valve 0, be forced to pass through said purging apparatus. At such time, With the arrangement shown, it is preferable not to operate the pumpP', on account of the rise in level of liquid Within condenser coil.

Iparticularly desire to emphasize the importance of using a suitable gaseous medium as a means for conveying heat to the interior of the mass in the lixiviator, as a means for efi'ectively removing occluded liquid therefrom. The importance of thus speeding up this phase of the operation Will he did appreciated upon consideration of the fact liquid from said mass, the apparatus can in any given period of time handle the output of a very much larger cyanizing unit; so that a marked economy is effected, not only in time, but in the cost of installation, space occupied by the plant, and other costly items.

In like fashion, the speeding up of the. rate of evaporation of liquid in the evaporator through the practical overcoming of the diiiiculty above noted, similarly efi'ects worth-while economies of operation.

I also desire to direct attention to the utilization, in the preferred mode of effectuating my process, of the still relatively w-arm gases passing off from the evaporator, as a means for hastening the volatilizati-on of occluded liquid in the lixiviator.

The system as a whole, moreover, is a very flexible one and adapts itself to varying conditions; and while all of the features shown therein are by no means essential "thereto, in so far as the broadest aspects of my invention are concerned, they nevertheless add to the efliciency of the system as a whole. Thus,while I am aware that it isnot necessary to provide '"a releaching tank in order to with ease nearly completely saturate the solvent with its solute; still the combination of this tank with the lixiviator and associated parts, permits of the solvent being exceedingly well circulated or flushed through the charge to be leached, and this Without loss of the solvent, and with very appreciable gain in recovering cyanid from all parts of the leached mass. The importance of this will be seen when it is pointed out that if one merely allows liquid ammonia, for example, to run into the, lixiviator, and even though it be allowed to stand in this receptacle for 20 or 30 minutes, when it has been drawn off, and the briquets or the like are analyzed to ascertain the cyanid content remaining therein, it will be found usually that there is a very much larger percentage of cyanid in the briquets at the top of the charge than in those in the center; and that for some reason, the briquets in the lower part of the charge are richer in cyanid than those in the center, although not normally so rich as those at the top.

The combination of the jets or currents of warm gasover the surface of the liquid inthe evaporator, with the means for applying heat superficially to this receptacle, 6. 9., the steam jacket, is also of importance, in that a large part of the liquid may be first removed, working from the surface of the liquid down, so to speak, and after much of this liquid has thus been evaporated, the bringing into play of the steam jacket or the like, accelerates the last portion of this operation, which otherwise is quite slow.

The effect of the superficial heating of the charge in the evaporator, when much of the liquid in the latter has been driven ed and the mass is approaching its crystalline con dition, has ,animportant bearing upon the tilizing solvent, there is a tendency for this mass, especially as itbecomes thick with crystals, to cake or solidify in portions thereof and thereby to resist the action of the agitator. This calls for expenditure of more work in driving the latter, .and the product is apt not to be asv finely divided as might be'desired. On the other hand the flow of warm gas over. the surface of the charge at such time, supplements the heat imparted to the charge by the walls of the receptacle and tends to maintain the temperature of the chargeas a whole, more nearly'uniform; with the result that the product is improved and the expenditure of energy in turning the agitating'paddles is reduced.

Finally, the evaporation of solvent in the above described manner, coupled with the part of the time during which the condenser is idle, results in great fuel economy, for.

the following reason: With this method the energy for forcing the ammonia from the evaporator to the condenser coils, and for producing the pressure at which the ammonia will condense in the coils, has its source in the superheater' and in the heat of the steam in the steam jacket or jackets,

and all of this heat is used to produce the desired results.

As above noted, when, substantially all of the liquid ammonia is vaporized,-the evaporator is left full of gaseous ammonia,.which must be withdrawn and since it must be deliver-ed to the condenser coils under high pressure, a compressor is required; but in this case it need be but a relatively small one. Indeed, it is even possible to omit the compressor P, relatively small though it. is, and rely upon the pump P to remove this residual gas; it being understood, however, that in such case this remaining-gas will not he condensed but will "be delivered to the tank T under ressure read for return to the system through the .superheater, or

otherwise, as desired.

If the gas delivered to the tank T be not allowed to cool, it will normally be quite warm, in most cases, after being compressed.

The above described'system hasv the further advantage that if liquid ammonia be the solvent used, as it, to be preferred,- only anhydrous ammonia need be used as is to be desired where substantially pure cyanid is the product sought. I

Having thus described my invention, what I claim is:

1. A system for recovering-alkali cyanid from material bearing the same, which comprises a lixiviator in which said material is leached, an evaporator to receive the cyanid-containing solution produced in said lixiviator, means to impart heat to said solution to volatilize the solvent thereof, and connections co-acting with said lixiviator to conduct warm gas from said evaporator through the leached material, to volatilize the occluded solvent in the pores of the latter.

2. A system for recovering alkali cyanid from material bearing the same, which comprises a lixiviator in which said material is leached, an evaporator to receive the cyanid-con'taining solution produced in said lixiviator, means to impart heat to said evaporator to volatilize the solvent therein, heating means for said lixiviator, and connections co-acting with said lixiviator to conduct warm gas through the leached material, to volatilize the occluded solvent in the pores of the latter. I

3. Asystem for recovering alkali cyanid from material bearing the same, which comprises a lixiviator in which said material is leached, means for removing solvent from and returning such removed solvent to said lixiviator, an evaporator to receive the cya-' hid-containing solution produced in said lixiviator, and means to promote rapld vola tilization of the solvent in said evaporator and also of that occluded in the pores of the from porous material bearing the same, which comprises a lixiviator in which said material is leached, an evaporator to receive the cyanid containing solution producedin said lixiviator, and means for supplying a gaseous heating medium successively to the evaporator, when the latter is charged, and to the lixiviator, when said solution has been discharged therefrom, to volatilize solvent in the evaporator and residual solvent occluded in the pores of the leached material.

6. A system for recovering alkali cyanid from porous material bearing the same, which comprises a lixiviator in which said material is leached, means to receive liquid drawn off from said lixiviator, and means to volatilize residual occluded solvent from the pores of said material by the passage of warm gas through said pores, said means including connections for supplying the gas to said lixiviator and means for elevating the temperature and pressure of said gas previous to its introduction into said lixiviator.

7. A system for recovering alkali cyanid from porous material. bearing the same, which comprises a lixiviator in which said material is leached, means to receive liquid drawn off from said lixiviator, and means to volatilize residual occluded solvent from the pores of said material by the passage of warm gas through said pores, said means including connections for supplying an innocuous gas to said lixiviator and means for elevating the temperature of said gas.

8. A system for recovering alkali cyauid from porous material bearing the same, which comprises a lixiviator in which said material is leached, means to receive liquid drawn off from said lixiviator, and means to volatilize residual occluded solvent from the pores of said material by the passage ofwarm gas through said pores, said means including connections for supplying an innocuous gas to said lixiviator and means to compress the gas passing oft from said lixiviator preparatory to the return of a portion at least of such gas to said supplying connections.

9. A system for recovering alkali cyanid from porous material bearing the same, which comprises a lixiviator in which said material is leached, means to receive the sol vent drawn ofi' from said lixiviator, heating means to volatilize the solvent so drawn oii, means to collect substantially all and condense a part of the volatilized solvent, and means for deliveringapart of said volatilized solvent, while Warm, again to said lixiviator to evaporate residual solvent occluded in the pores of the leached material.

10. A system for recovering alkali cyanid from porous material bearing the same, which comprises a lixiviator in which said material is leached, means to receive the solvent drawn oii from said lixiviator, heating means to volatilize the solvent so drawn ofi', means to collect and compress substantially all of the volatilized solventgmcans to condeliver an uncondensed part of said solvent under pressure and while warm, again to both said lixiviator, to evaporate residual dense a part of said solvent, and means too solvent occluded in the pores of the leached. material, and to said evaporator, to supplement the action of said heating means.

11.- A systemfor recovering alkali cyanid from material bearing the same, which comprises means for leaching said material with liquid ammonia to form a solution of cyanid in said ammonia, means to Supply hot gas to the upper surface of said solution to there evaporate said ammonia, and means to collect andcondense a part of the gaseous material leaving said surface, said last mentioned means having a portion thereof connected to said gas supplying means to permit the fiow of apart of the gaseous 1 signature, in the presence of two witnesses. 2

EDWARD E. ARNOLD. Witnesses:

HAROLD vE. TRUE HOWARD C. RIPLEY.

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