0a. 15,1946.- A. w. sADDlNG-roN MANUFACTURE OF SODIUM SULPHIDES Filed oct. 9, '1945, l 2,409,392 Patented Oct. 15, 1946 »_ 2,409,392 UNITED STATES PATENT -OFFICE 2,409,392 MANUFACTURE OF SODIUM SULFIDES Arthur W. Saddington, Syracuse, N. Y., assign or to The Solvay Process Company, New York, N. Y., a corporation of New York Application October 9, 1943, Serial No. 505,596 10 Claims. (Cl. ,2S-_134) l 2 This invention relates to the manufacture of soda as the source of sodium, coagulation and sodium hydrosulfide (NaHS) or sodium sulfide precipitation of metallic impurities are not ob- ' (NazS) or mixtures of both. tained consistently even when pure Hes gas is used and even though the liquor has been gassed with a large excess of H25. Thus, while the prior art indications are that coagulation and pre - It is known that sodium hydroxide may be reacted with HzS to form NazS which may be treated with more I-IzS to convert Nass to NaHS, and it has been proposed to make sodium hydro sulflde by gassing an NazS-NaHS liquor with cipitation of metallic impurities may be had by _ gassing the liquor to such an extent that the liq pure hydrogen sulfide. . ' uor contains no NazS and then using an excess of In processes of the type to which the inven 10 HzS, I ñnd these conditions are not controlling tion relates, the source of >sodium is commercial in all circumstances, and have discovered that caustic soda which contains appreciable quanti ties of impurities, such as iron, copper, nickel, manganese and silicon. These impurities do not , discolor caustic soda to any great extent, and 15 NazS contents. While not identified with cer hence their presence in commercial caustic is un tainty, indications are that the carbonate of so coagulation and precipitation of impurities are dependent upon the composition of the NaI-IS liquor with respect to carbonate of sodium and objectionable. However, during HzS gassing of commercial caustic liquor, such impurities pass dium present in the system is in the form'of NazCOa and for convenience will be referred to thru the process and are carried into the re as such in this specification. sulting NaI-IS liquor. Such impurities may be 20 It will be understood that good grades of com present in the NaHS liquor as soluble salts or mercial caustic soda contain appreciable suspended in finely divided condition. While amounts, sometimes as much as O16-0.20%, of probably largely sulfides, exact compositions of NazCOa. Further, synthetic I-IzS gas also con the impurities are not known, and whatever tains appreciable quantity of CO2 as an impurity, their nature, these substances are referred to 25 while the more common hydrogen sulñde gases, herein as metallic impurities. The presence of such as those formed in oil refining operations, even small amounts of these impurities in NazS or NaHS solutions results in products of very poor appearance because of the highly colored often contain as much as 10-25% CO2 by volume. A principal object of this invention lies in pro Vision of a process for making sodium hydrosul nature of the impurities after having been'sub 30 ñde or sodium sulfide, of purity acceptable to the jected to H2S gassing. Accordingly, a major trade, from commercial raw materials which con problem presented in manufacture of relatively stitute a source of metallic impurities and sodium pure sodium hydrosulñde has been the elimina carbonate in the NaHS liquor resulting from HzS tion of such impurities. ‘ gassing. The invention also aims to provide a Commercially available hydrogen sulñde gases 35 process which permits use of an HzS gas contain contain appreciable amounts of carbon dioxide ing substantial amount of CO2. Further objects as an impurity. The discoveries constituting this are provision of a process by which it is possible to avoid troublesome solid sodium sulfide phase invention arose out of attempts to manufacture, in accordance with known procedure, relatively during the NaHS producing reaction, to operate pure sodium hydrosulñde from commercial 40 such reaction continuously and at relatively low caustic soda and hydrogen sulfide gases contain temperature, and if desired to provide for quan titative utilization of hydrogen sulñde. ing carbon dioxide. The prior art indicates that The process of the invention comprises gener ally three major stages: first, formation of a I-I2S sufiicient to convert all of the NazS content of the liquor to NaHS and gassing is continued 45 suitable NazS-NaHS starting liquor utilizing com utilizing a substantial excess of I-IzS, the metallic mercial NaOH as a raw material; second, a re impurities in the liquor coagulate and precipitate action stage in which the NazS-NaI-IS liquor is contacted with hydrogen sulfide gas to convert in a ñlterable form. _ I noted that, in no instance, are coagulation and precipitation of metallic im NazS to NaHS; and third, a purification stage in purities effected where the sodium hydrosulfide which the NaHS liquor'discharged fromthe re-` when an NazS-NaHS liquor is gassed with pure liquor has been produced from I-I2S gas contain ing CO2, even if all the NazSy has been converted to NaHS and a further large excess of H2S has been employed. This observation- led to a fur action stage is treated in accordance with certain principles of the invention to effect (a) reduc tion of the amount of available sodium carbonate present in the liquor, and (U) control of the com ther ñnding that when using commercial caustic 65 position of such liquor with respect to NazS con 2,409,392 3 4 tent, whereby to bring about elimination from the system of metallic impurities brought into tinuous operation, and accordingly absorbing liquor is fed continuously from make-up tank H the process as impurities in the initial caustic soda. The nature of the invention is such that a major advantage is that H28 gas containing a substantial amount of CO2 may be employed. Hence, a preferred embodiment, using H2S con taining COz, is described below in connection with into the top of a tower I4 providing a reaction zone I5 in which the absorbing liquor is contact ed preferably counter-current with I-IzS gas from an inlet pipe I6, which gas, in accordance with the invention, may permissibly contain substan tial amounts` of carbon dioxide. I have found that any carbon dioxide contained the accompanying drawing diagrammatically 10 in the hydrogen sulfide gas reacts substantially quantitatively with NazS to form a reaction prod showing suitable apparatus. In usual practice of the invention, the NazS-NaHS absorbing liquor in tank II is made by treating a portion of NaI-IS product liquor of a previous run with commercial sodium hydroxide which may contain say 0.l-0.2% or more by weight of NazCOs. However, to start the process an aqueous solution of sodium hydroxide of any suitable concentration, e. g. 50-'70% NaOI-I, may uct which appears and is herein considered for purposes of illustration to be sodium carbonate. I further observe that most of this sodium car bonate immediately precipitates as a solid read ily filterable form. Since the H28 gas used may contain substantial amount of carbon dioxide the quantity of solid sodium carbonate produced may be correspondingly substantial. When the proc be gassed with hydrogen sulfide, preferably pure, 20 ess is carried out as a batch procedure, solid so dium carbonate readily settles to the bottom of to such an extent as to form a liquor containing NazS and a substantial amount of NaHS. In the reaction vessel and causes no particular op this preliminary step, the liquor mass should be erating difficulty. However, to provide for con tinuous operation throughout, I nnd that be kept at any suitable temperature, e. g. 70° C. or upwards depending upon the sodium sulñde con 25 cause of formation of solid sodium carbonate it is not feasible to carry out the NaHS produc centration of the liquor, needed to maintain all ing reaction in the more or less usual type of of the sodium sulñdes in the liquid phase. Pre packed. liquor-gas contacting tower. An open liminary starting liquor, as to composition and spray tower, containing no packing and provid temperature, should be similar in all respects to the absorbing liquor formed during the usual 30 ed at the top with a spray head for introduction of NazS-NaI-IS absorbing liquor and at the bot practice of the process which is preferably con tom an inlet for the HzS gas, may be employed. tinuous. Contact towers containing bailles 20 such as in When the process is under way, a portion of the dicated on the drawing may be used, although sodium hydrosulñde liquor discharged from the I-IzS gassing zone is run continuously thru line 35 in such instance baille arrangement should be such as to afford good contact of gas and liquor Iß .into NazS-NaHS absorbing liquor make-up but at the same time permit downiiow of a rela tank I I Iwhich may be steam jacketed to keep tem tively light slurry and discharge of all of the perature high enough to hold all sodium sulfide slurry from the bottom of the tower. The type in liquid phase. While HzS gassing zone efliuent liquor may contain a limited amount of Nats, 40 of liquor-gas contacting tower suitable for use in practice of the continuous basis may be de such liquor is preferably an aqueous solution of sodium hydrosulfide containing substantially no fined as an unobstructed reaction chamber, but it should be understood that the term unob NazS. A strong solution of NaOH from tank I2 structed is used in the sense that while the re is likewise continuously fed into make-up tank I I. Although an absorbing liquor containing any 45 action chamber rnay contain mixing baffles, con~ struction of these baffles is such as not to cause suitable relative proportions of NazS and NaHS plugging but permits retarded but steady down may be employed, it is more desirable to regulate flow of liquor containing some solids in Isuspen feed of NaI-IS liquor and sodium hydroxide solu tion to tank II in such a way as to maintain sion. therein an absorbing liquor of certain composi Hence in the preferred continuous operation, tion with respect to Na2S and NaHS, purpose of absorbing liquor of the type described is run into this feature being to provide an absorbing liquor the top of a contact tower of suitable design, a of such composition as to make possible ready stream of I-IzS gas which may contain carbon maintenance of sodium sulfide in the liquid phase dioxide is fed into the bottom, unused and inert both in tank II and in the subsequent reaction 55 gases leave the top of the tower thru pipe 2I, stage in which NazS of the absorbing liquor is and reacted liquor is discharged from the bottom converted to NaHS, and further to facilitate into pipe 22 provided with valve 23. Hydrogen carrying out the HzS contacting operation at 'sulfide and carbon dioxide react with NazS of relatively low temperatures. To afford accom the absorbing liquor to form NaHS and sodium plishment of these ends, feed of sodium hydro 60 carbonate, and any NazCOs impurity contained sulñde liquor from line l0 and of NaOH solution in the initial commercial NaOH passes thru from tank I2 to the make-up tank is regulated to the contacting Zone unchanged. As a whole, re provide therein an absorbing liquor desirably con actions eiiected in the contacting zone are exo thermic and some heat is developed. Broadly, taining not more than 15% by weight of NazS. Especially where it is desired to supply absorbing 65 the absorbing operation may be carried out at any temperature high enough to keep all so-dium liquor to the HzS reaction zone at a relatively low suliide's in the liquor phase under the prevailing temperature, e. g. 'l0-80° C., and at the same time conditions of operation. However, temperatures avoid any solid phase formation either in the in the reaction zone above about 90° C. are not absorbing liquor make-up tank or in the reaction zone, it is preferred to control formation of the 70 desirable because of greatly accelerated corro sion of equipment. I find that by regulating the absorbing liquor in such a Way that the liquor composition of the NazS-NaHS absorbing liquor contains not more than 10% by weight of NazS and at least 25% by weight of NaHS. as in the above indicated preferred conditions, it is possible to feed the absorbing liquor to the re While the entire process may be practiced batchwise, one of the advantages afforded is con 75 action zone at a low temperature, e. g. 'l0-80° C., 2,409,392 . 5 v6 Y tial' amount of NazS. The preferred condition of operation is to bring about substantially com plete removal `of available carbonate of sodium. The second factor critical as to effecting coagula phase but does not exceed the indicated maxi-' mum temperature and does not require extra Ul tion and precipitation of metallic impurities is the NazS content 0f the NaHS liquor. I have found neous cooling. . While the carbon dioxide content of the I-IzS that,`in conjunction With the maximum carbon in which case the heat developed in the reaction zone automatically maintains a temperature high enough> to keep all> sodium sulñdes in the liquid gas fed to the reaction Zone may vary consider ably and may be usually about 10% by volume, ate of sodium tolerance noted above, the NaHSA liquor should contain not more than 5% by Weight ordinarily it is preferred thatl such gas contain a 10 of NazS, and preferably substantially noNazS at predominating amount of I-IzS and not more than all. The preferred conditions of substantial ab sence of available carbonate of sodium and of about 25% CO2 by volume. « . In practice of the emb-odiment being described, substantial absence of NazS, cause the most thorough and rapid coagulation and precipitation design of the gas-liquor contacting tower` and rates of feed thereto of absorbing liquor and HzS 15 of metallic impurities. Other permissible condi tions, as to available carbonate of sodium and gas, whether the process is carried out batchwise, Na2S contents, Within the limits stated bring countercurrent, or co-current, are vregulated so about an ultimately satisfactory coagulation and that during the contacting operation reaction precipitation of metallic impurities, the overall of the NazS content of the absorbing liquor-,fed to the contacting zone is effected to such an ex 20 difference being that as the available carbonate of sodium and NazS contents increase to the maxi tent that the reaction zone eñluent NaHS liquor mum values noted, rates of coagulation and pre contains not more than 5% by Weight of NazS, cipitation of metallic impurities correspondingly and preferably substantially no NazS at all. `Rea decrease. Hence, briefly, theinvention involves son for such conversions of the Naas content of NaI-IS will subsequently appear. 25 formation of sodium hydrosulñde liquor contain ing Vcertain metallic impurities and also an In usual operation, employing an I-I2S gas amount of carbonate of sodium equivalent to more containing substantial amount of CO2, the NaI-IS than 0.06% by Weight of CO3 radical, and com liquor discharged from the bottom of tower i4 prises the steps of reducing the available car contains a substantial amount of suspended solid sodium carbonate which is readily separable and 30 bonate of sodium content of the liquor to` an amount equivalent to not more than 0.06% by is removed by ñlter 25. The ñltrate in pipe 26 weight of CO3 radical, and controlling the com contains in solution the metallic impurities such position of the resulting liquor so that such liquor as iron, brought into the process as impurities in contains not more than 5% by Weight of sodium the commercial sodium hydroxide or picked up from the liquor make-up or gassing apparatus, sulfide. and if any NaHS or NazS product Were recovered In the more usual practice of the invention process, i. e. where the HzS gas contains substan tial amount cf CO2 and the reaction zone liquor eflluent contains a comparable substantial amount directly from the filtrate, such products would be badly discolored and contain these impurities in amounts in excess of trade specifications. ‘ As above stated, prior literature indicates that 40 of solid sodium carbonate, the clear liquor filtrate in line 26 contains soluble sodium carbonate to when an NazS-NaHS liquor is gassed with enough the point of saturation and may Well contain in H2S tc convert all NazS to NaHS, plus a substan . tial excess of HzS, the metallic impurities in the liquor coagulate and precipitate out in a ñlter able form. I have found, with respect to con sistently securing- coagulation and precipitation of metallic impurities, that the controlling fac tors are the amounts of carbonate of sodium and NazS present in the NaHS liquor, and that the use of an excess of I-I2S is not critical. For ex solution say 0.2-0.5% or more by Weight sodium carbonate. In the modification being described, à valve 2l in pipe 28 is closed and valve 29 is open. A portion of the filtrate runs into recycle line l0, and by suitable adjustment of valves 30 and 3l, a portion of the filtrate corresponding with the “make” of one cycle of the process is run thru 5 O valve 3| into a tank 32 in which the NaHS liquor ample, in one operation, in which a substantial excess of HzS was employed, and the resulting is treated in any suitable way to bring the sodium carbonate content down to the conditions stated. liquor contained 46% by weight of NaI-IS, no NazS, and carbonate of sodium in amount equiv alent to 0.08% by weight of CO3 radical, the liquor Carbonate remained dark brown and there was no coagula tion and precipitation of metallic impurities. I have found that if sodium hydrosulflde liquor reduction or elimination may be effected by treating the filtrate with a compound of an alkaline earth metal, e. g. calcium com pound capable of reacting with the soluble sodium carbonate to precipitate the combined CO3 as calcium carbonate. The amount of treating ma terial used should be at least sufficient to reduce an amount of available (i. e. in solution or both 6 O soluble sodium carbonate content of the NaHS liquor to an amount equivalent to not more than in solution and in solid form) carbonate of so is saturated with carbonate of sodium, or contains dium equivalent to more than 0.06% by Weight 0.06% by Weight of CO3 radical. Preferably, the quantity of treating agent employed is that which of CO3 radical, metallic impurities do not co is theoretically required to react with all of the agulate or precipitate even though the liquor con tains no NazS and has been treated with a large 65 soluble sodium carbonate. The preferred treatñ ing materialis calcium hydrosulñde, and in this excess of HzS, and regardless of Whether the instance sodium carbonate is converted in accord~ liquor has been made by gassing With purel HzS or ance with the equation with I-IzS containing carbon dioxide. I ñnd that if available carbonate of sodium is substantially completely removed from an NaI-IS liquor, or re moved to an extent such that the liquor does not Ca (HS) z-l-NazCOsèCaCOa-i-ZNaHS 70 calcium carbonate being precipitated and the sodium of the NazCOa being converted to NaHS, the desired product. The calcium hydrosulfide dium equivalent to more than 0.06% by weight treatment does not bring about any increase in of CO3 radical, metallic impurities coagulate and the Na2S content of the treated liquor. In this precipitate even if the liquor contains a substan 75 instance, the control of the treated liquor com contain an amount of available carbonate of so 2,409,392 8 position, with respect to NazS content, is had by principles of the invention apply to puriñcation of regulating the I-I2S gassing in tower I'll so that the NaI-IS liquor fed to the treating tank con tains not more than 5% by weight of Naas> or any lesser amount that may be desired in that particu Cn NaHS liquors containng an amount of available lar operation. The foregoing procedure creates conditions which cause coagulation and precipita tion of the metallic impurities in. readily filterable form. The treated liquor is then filtered in ñlter 34 to remove the calcium carbonate and the carbonate of sodium equivalent to more than 0.06% by weight of CO3 radical, no matter how such liquors are produced. It will be understood that if the final product desired is VNaHS, gassing in the reaction Zone, and in tank 32 if needed, is carried out to an ex material such as Ca(OH)2 may be employed. In this instance Ca(OI-I) 2 reacts with NazC‘Oa to form CaCOa and NaOH ywhich in turn reacts with NaHS to form NazS, thus increasing the NazS content tent surlìcient to convert all the NazS to NaHS. On the other hand if an NazS product is desired, except as indicated, complete conversion of NazS to Nal-IS is unnecessary, since the liquor eil‘luent of ñlter 34 may be treated with NaOl-I to cut back the product to NazS. If desired, the NaI-IS or NazS may be converted to solid form by evapo ration of the liquors and solidiiication by known of the NaI-IS liquor Iundergoing methods. metallic impurity precipitates. In place of calcium hydrosuliide, other treating treatment. I claim: Should the quantity of Ca(OI-l) 2 used be suñicient to raise the NazS content of the treated liquor to 1. The method for producing puriñed sodium above the maximum permissible Naas value for 20 hydrosulñde from a sodium hydrosuli'lde liquor that particular operation, after the Ca(OI-I)2 containing (a) at least one metallic impurity of treatment, the liquor in tank 32 may be gassed the group consisting of iron, copper, nickel, man with enough H28, preferably pure, to lower the ganese and silicon, and (b) an amount of avail Nags content to the desired amount. In this able carbonate of sodium equivalent to more than mode of operation, control of the NazS content of 0.06% by weight of CO3 radical, which method Ca(OH)2 treated liquid is had partly by gassing in tower I4 and partly by gassing in tank 32. comprises treating said liquor with an alkaline earth compound so as to react with available It will be noted that even when Ca(HS) 2 is used carbonate of sodium to precipitate combined CO3 as a treating agent, it is not critically important thereof as alkaline earth carbonate, the amount that the NaHS liquor fed into tank 32 contain not 30 of said alkaline earth compound being at least more than the permissible Nazs maximum for sufficient to reduce the available carbonate of that operation. For example, an Nazs liquor con sodium content of said liquor to an amount equiv taining say 6% by weight of NazS may be fed alent to not more than 0.06% by weight of CO3 into tank 32, treated with Ca(I-IS)2, and there radical, controlling the composition of the result after gassed with enough H25, preferably pure, ing liquor so that such liquor contains not more to reduce the Na2S content to the point desired. than 5% by weight of sodium sulfide, thereby Hence, it will be understood that control of the effecting coagulation and precipitation of metal composition, with respect to Naz-S content, of the lic impurities, and separating said metallic im treated liquor may be elîected either before or purities from such liquor. ' after, or partly before and partly after treatment 2. The method for producing purified sodium with the sodium carbonate content reducing hydrosuli'lde from a sodium hydrosulñde liquor agent, and unless speciñcally stated to be con containing (a) metallic impurities of the type trary, the appended claims are to be so con present in commercial sodium hydroxide, and strued. (b) an amount of available carbonate of sodium In some modiñcations the reaction zone ef- f equivalent to more than 0.06% by Weight of CO3 fluent may contain only a relatively small amount radical, which method comprises treating said of solid sodium carbonate, e. g. where the HzS liquor with an alkaline earth compound so as to gas contains no or only a small amount of CO2. react with available carbonate of sodium to pre In these instances, Valve 21 may be opened, valves cipitate combined CO3 thereof as alkaline earth 23 and 29 closed, ñlter 25 by-passed, and filtration carbonate, the amount of said alkaline earth of the reaction eiiluent may be omitted. However, compound being at least sufficient to reduce the in such circumstances the amount of treating available carbonate of sodium content of said agent used in tank 32 should be sufficient to react liquor to an amount equivalent to not more than with all available sodium carbonate (i. e. both 0.06% by weight of CO3 radical, controlling the solid and soluble) present at the time of addition composition of the resulting liquor so that such of the calcium compound to an extent such that liquor contains not more than 5% by weight of the treated liquor does not contain more available sodium suliide, thereby effecting coagulation and carbonate of sodium than is equivalent to 0.06% precipitation of metallic impurities, and separat by weight of CO3 radical. Otherwise, procedure is ing said metallic impurities from such liquor. the same. 3. The method of producing puriñed sodium In practice of the invention, when treating hydrosulñde which comprises forming an NazS NaHS liquors, containing as high as L1.2% by NaHS liquor containing metallic impurities of weight of NazS, in such a way as to reduce the the type present in commercial sodium hydroxide, available carbonate of sodium content substan contacting Said liquor with an HzS gas under tially to zero, straw yellow product liquors have been obtained containing as little as 0.0002% FezOa and 0.045% SiO2 by weight. temperature conditions high enough to maintain sodium sulñde in liquid phase, continuing contact of the liquor and HzS gas for an interval sufûcient to elîect conversion of at least a major portion in connection with use of an H28 gas containing of the NazS content of said liquor to Nal-IS CO2, it is noted that the invention is not thus 70 thereby forming an NaI-IS liquor containing, as restricted. It will be understood that many grades a result of presence of oxide of carbon impurities of commercial caustic contain sufficient Na2CO3 in the system, an amount of available carbonate as an impurity to result in formation of an NaI-IS of sodium equivalent to more than 0.06% by liquoi` containing more than the indicated toleraweight of CO3 radical, reducing the available car While the invention has been described chie-fly ble maximum of carbonate of sodi-um. The bonate of sodium content of said NaHS liquor to 2,409,392 ' 9 an amount equivalent to not more than v0.06% by Weight of CO3 radical, controlling ‘the composi tion of the resulting NaHS liquor so that such ing >in solution an amount of carbonate of sodium equivalent to more than 0.06% by weight of CO3 radical,- treating recovered NaHS liquor with a liquor contains not more than 5% by weight of calcium compound'so as to react With soluble car sodium sulfide, thereby effecting coagulation and bonate of sodium to precipitate combined CO3 precipitation of metallic impurities, and separat thereof as calcium carbonate, the amount of said ing said metallic impurities from such liquor. calcium compound being at least sufficient to re 4. The method of producing purified sodium duce the soluble carbonate of sodium content of hydrosulñde which comprises forming an NazS said recovered NaHS liquor to an amount equiva NaI-IS liquor containing metallic impurities of the 10 lent to not more than 0.06% by Weight of` CO3 radical, controlling the composition o_f the. result-` type present in commercial sodium hydroxide, ing NaHS liquor so that such liquor contains sub contacting said liquor with an H25 gas containing stantially no sodium sulfide, thereby eiîecting CO2 as an impurity under temperature conditions coagulation and precipitation of metallic impuri high enough to maintain sodium sulfide in liquid phase, continuing contact of the liquor and HZS 15 ties, and separating said metallic impurities from gas for an interval sufficient to effect conversion the NaHS liquor. ì 7. The method of producing puriiied sodium of at least a major portion of the NazS content hydrosuliide which comprises forming an NazS of said liquor to NaHS thereby forming an Nal-IS NaHS liquor containing metallic impurities of the liquor containing an amount of available car bonate of sodium equivalent to substantially more 20 type present in commercial sodium hydroxide, continuously introducing said liquor into a rela than 0.06% by weight of CO3 radical, reducing . tively unobstructed reaction zone and counter the available carbonate of sodium content of said currently contacting said liquor therein with a NaHS liquor to an amount equivalent to not more gas containing predominantly H2S and a substan than 0.06% by weight of CO3 radical, controlling tial amount but not more than 25% by volume the composition of the resulting Nal-IS liquor so of CO2 as an impurity under temperature con that such liquor contains not more than 5% by Weight of sodium sulñde, thereby effecting coagu lation and precipitation of metallic impurities, and separating said metallic impurities from such liquor. ‘ y ‘ 5. The method of producing purified sodium hydrosulñde which comprises forming an NazS NaHS liquor containing metallic impurities of the type present in commercial sodium hydroxide, contacting said liquor with a gas containing pre dominantly H2S and a substantial amount of CO2 as an impurity under temperature conditions ditions high enough to maintain sodium sulñde in liquid phase, regulating contacting of liquor and HzS gas in said zone for an interval suf? 30 cient to effect conversion of NaeS and NaI-IS to such an extent that the resulting NaHS liquor contains substantially no NazS, said NaHS liquor containing carbonate of sodium in solution and as a solid precipitate, continuously withdrawing 'such NaI-IS liquor and’suspended solid from the reaction zone, separating solids from said NaI-IS liquor thereby recovering NaHS liquor contain high enough to maintain sodium sulfide in liquid phase, continuing contact of liquor and HzS gas ing in solution an amount of carbonate of sodium NaI-IS liquor contains not more than 5% by Weight of NazS, said NaHS liquor containing carbonate alent to that needed to precipitate soluble com bined CO3 as calcium carbonate, thereby effect equivalent to more than 0.06% by Weight of CO3 'for an interval sufficient to effect conversion of 40 radical, treating recovered NaHS liquor with cal cium hydrosuliide in amount substantially equiv NazS to NaHS to such an extent that the resulting of sodium in solution and as a solid precipitate, separating solids from said NaHS liquor thereby ing coagulation and precipitation of metallic im purities, and separating said metallic impurities recovering NaI-IS liquorcontaining in solution an amount of carbonate of sodium equivalent to from said recovered NaI-IS liquor. in said zone for an interval suilicient to effect conversion of Naas and NaHS to such an extent ganese and silicon, and (b) an amount of avail able carbonate of sodium equivalent to more than 8. The method of producing puriiied sodium hydrosulñde from a sodium hydrosuliide liquor more than 0.06% by weight of CO3 radical, treat containing (a) atleast one metallic impurity of ing said recovered NaHS liquor with calcium hydrosulñde in amount substantially equivalent " the group consisting of iron, copper, nickel, man ganese and silicon, and (b) an amount of avail to that needed to precipitate soluble combined able carbonate of sodium equivalent to more than C03 as calcium carbonate, thereby eiîecting co agulation and precipitation of metallic impurities, , 0.06% by weight of CO3 radical, which method comprises reducing the available carbonate of and separating said metallic impurities from said 55 sodium content of said liquor to an amount recovered NaHS liquor. equivalent to not more than 0.06% by weight of 6. The method of producing puriñed sodium CO3 radical, controlling the composition of the hydrosuliide which comprises forming an NazS resulting liquor so that such liquor contains not . NaHS liquor containing metallic impurities of the more than 5% by weight of sodium sulfide, there type present in commercial sodium hydroxide, continuously introducing said liquor into a rela 60 by effecting coagulation and precipitation of metallic impurities, and separating said metallic tively unobstructed reaction zone and contacting impurities from such liquor. said liquor therein with a gas containing pre 9. The method of producing purified sodium dominantly H25 and a substantial amount of CO2 as an impurity under temperature conditions high 65 hydrosulíide from a sodium hydrosulñde liquor containing (a) at least one metallic impurity of enough to maintain sodium sulfide in liquid the group consisting of iron, copper, nickel, man phase, regulating contacting of liquor and HzS gas 0.06% by weight of CO3 radical, which method that the NaI-IS liquor formed contains not more than 5% by .weight of NazS, said NaHS `liquor 70 comprises treating said liquor with calcium hy drosulflde in amount substantially equivalent to containing carbonate of sodium in solution and that needed to react with available carbonate of ` as a solid precipitate, continuously withdrawing such NaI-IS liquor and suspended solids from the sodium to precipitate combined CO3 thereof _as calcium carbonate, controlling the compositlon reaction zone, separating solids from said Nal-IS liquor thereby recovering NaHS liquor contain.1 75 of the resulting liquor so that such liquor con 2,409,392 12 tains not more than 5% by weight of sodium sulñde, thereby effecting coagulation and precipi tation of metallic impurities, and separating said metallic impurities from such liquor. l0. The method of producing purified sodium hydrosulñde `from a sodium hydrosulñde liquor containing (a) metallic impurities of the type present in commercial sodium hydroxide, and (b) an amount of available carbonate of sodium available carbonate of sodium content of said sodium hydrosulñde liquor to an amount equiva lent to not more than 0.06% by Weight of CO3 radical, controlling the composition of the result ing liquor so that such liquor contains not more than 5% by Weight of sodium sulñde, thereby effecting coagulation and precipitation of metallic impurities, and separating said metallic impuri ties from such liquor. equivalent to more than 0.06% by weight of CO3 10 radical, which method comprises reducing the ARTHUR W. SADDINGTON.