Dec. 31, 1946. A. J. PHILLIPS ETAL 2,413,374 PROCESS FOR PRODUCING ELEMENTAL SELENIUM 2 Sheets-Shee't 1 Filed March 15, 1944 < um A“ u BY I f?it’li/IS Yam 63 [Made/f James A’. franda/Z' W6; Dec. 31, 1946. A. J. PHILLIPS EI'AL 2,413,374 PROCESS FOR PRODUCING ELEMENTAL SELEILIIUMI ‘Filed March 15, 1944 2 Sheets-Sheet 2 B1 2,413,374 Patented Dec. 31, 1946 UNITED STATES PATENT OFFICE 2,413,374 PROCESS FOR gRODUCING ELEMENTAL ELE Albert J. Phillips, Plain?cld, and Yurii E. Lebedeif and James R.. Crandall, Metuchen, N. J., assignors to American smelting and Re ?ning Company, New York, N. Y., a corpora tion of New Jersey Application March 15, 1944, Serial No. 526,630 8 Claims. (Cl. 23-209) 1 This invention relates to a process for treating selenium bearing material to recover selenium as 2 release the selenium. The receptacle containing the charge is then placed in a closed retort and elemental selenium. The invention has been utilized advantageously in the treatment of ?ue or baghouse dust containing selenium collected during the roasting and doré furnace processing heated to react and drive off the selenium as gas eous selenium and selenium dioxide. The closed retort is provided at one end with a compartment or section which, during operation, is ?lled with of copper re?nery slimes. However, the inven tion is not limited to the treatment of baghouse ducing reagent. A condenser is connected to this section of the retort to condense the reduced 10 metal vapors. Volatilized SeOz and Se vapors dust but may be employed in the processing of raw sludges, slimes and the like material con taining selenium. In treating copper re?nery slimes which con tain gold, silver, copper, selenium and tellurium, it has been the general practice in most re?neries to subject the slimes to an oxidizing roast to as sist in the subsequent removal of copper by leach ing with acid. During roasting some of the se heated coke, charcoal or like carbonaceous re which are released from the roasted charge are drawn through or over this heated coke whereby the SeOz vapor is reduced to selenium metal va por. The latter is recovered as liquid selenium by passing the vapors into a suitable condenser. Moisture and excess H2804 vapor which are in termiXed with the selenium vapor are not con densed and pass from the selenium vapor con denser into an outer condenser where these va lenium and tellurium present is oxidized and passes into the ?ue system where it is collected in the baghouse along with other metal values. 20 pors of sulphuric acid and steam are condensed and collected, the waste gases, largely carbon Most of the selenium, however, is not volatilized dioxide, being discharged therefrom through a and remains in the slimes possibly as doré metal water sealed exit. ' selenides and tellurides. In the conventional In carrying out the process no preliminary di practice, selenium is separated from the roasted gesting of the selenium bearing material is re slimes as sodium selenite by establishing 2. mol quired and the amount of H2804 added usually ten bath of the slimes and adding sodium car is only about 5% by weight of the charge depend bonate and nitre in suflicient amounts to react ing, of course, on the content of selenium in the with the gold and silver selenides present to slag off the selenium in the form of sodium selenite. 30 material being treated. Preferably the required amount of sulphuric acid is vmixed with the This sodium selenium slag is subsequently leached charge before it is placed in the retort and no with water and neutralized to precipitate tellu rabbling or stirring of the charge during roast rium which is recovered as tellurium oxide. After ing is necessary as the preliminary mixing is suf ?ltering the solution the selenium is then pre ?cient to adequately disperse the acid throughout cipitated from the ?ltrate by acidifying the solu tion and treating it with sulphur dioxide gas in I'‘~. . til the charge whereby the selenium is caused to react with the acid and is driven off as either the conventional manner whereby the selenium oxide or elemental Se vapor when heated in the is recovered as red amorphous selenium. retort. By utilizing the novel heating and re The present invention provides a relatively ducing arrangement of our invention the digest simple process which permits the selective recov ery of selenium from selenium bearing baghouse 40 ing and roasting of the charge to release the selenium as gaseous S802 and the reduction of dust without involving the treatment of aqueous this gaseous selenium dioxide to Se prior to con- , solutions of selenium dioxide and acid. The pro densing is carried out concurrently and in a single cess of this invention results in the direct re retort. The apparatus is easy to operate and the covery of elemental selenium from selenium bear ing material by a single pyrometallurgical opera process results in high recoveries of selenium with tion and eliminates the necessity of employing a minimum loss of values. solution handling means, centrifuges, stills, and Although the novel features which are believed _ ?lter press equipment, which is expensive, in or to be characteristic of this invention will be par der to recover selenium in a commercially valua ble form. - According to our process selenium bearing ma terial which may contain 1% or more moisture ticularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which it may be carried out, may be better understood by refer ring to the following description in connection is placed in a receptacle and su?icient sulphuric acid is added in excess of that required to react With the accompanying drawings forming a part with the selenium compounds in the charge and 55 2,413,374 3 thereof in which a typical commercial installa tion embodying our invention is illustrated. Fig. 1 is a plan view of one type of apparatus for practicing our invention, the arrangement showing a battery of retorts connected to a con denser, the retorts being shown partly broken 4 An over?ow spout 4| is provided near the top of the receptacle 40 whereby condensate collected in the receptacle 4!] over?ows into a receiving vessel 42. Liquid condensate in the receptacle 40 provides a liquid seal for the condenser 36 and is arranged to maintain the entire furnace at away and in section to more clearly illustrate the a pressure of about one inch of water during the construction; operation. Fig. 2 is a vertical sectional view of’ the appa~ ratus shown in Fig. 1 and taken substantially on line 2-—2 of Fig. 1 and looking in the direc tion of the arrows; Fig. 3 is a sectional view in elevation taken substantially on the line 3-3 of Fig.‘ 1.. i . Referring to the drawings in detail In desig nates a retort in which the charge is roasted. A number of these retorts forming a battery'may' be used, as shown in Fig. 1, where the. quantity .The retorts H] are preferably made of cast iron inasmuch as it is resistant to attack. For our commercial installation we have used a - standard 10" cast iron pipe 8' and 6" long with ?anged end portions 45 and 46. The charging end of‘ the retort: is?tted with a removable plate 15 48 which ‘is machined so that it can be bolted tightly in place. The opposite end of the re tort is. ?tted. to.the condenser pipe or tube I2 at its ?anged end 5|, the contacting surfaces be of material to be treated warrants such an in ing machined so as tov ?t closely together to stallation. The retorts are each connected to a 20 provide a sealed connection as illustrated in Fig. condenser l2 which in turn is connected to a 2. Inasmuch as we have found that cast iron common condenser and storage receptacle I3 is more. resistant to- attack‘ by selenium than from which liquid selenium is tapped as indi ordinary iron or steel we prefer to make the re~ cated at I4. The condenser I2, as illustrated in tort l0 and forepart' of the selenium condenser Fig. 2, is arranged to slope downwardly from 25 t2 of‘ cast iron. The remaining portion of the the retort to the storage condenser receptacle l3 so that as the selenium condenses on the walls of the condenser l2 it will flow away from the condenser l2‘ and larger condenser receptacle 13 may be made of ordinary iron or steel since these parts are subjected to lower temperatures retort end and into the large condenser recep than the: retort and forepart of the condenser l2‘. tacle l3. For‘ retaining the charge during roasting 30 For convenience in making‘ a tightly sealed boats 55 are utilized. These boats, which may joint between the retort and condenser the re be made of iron, are of suitable length- and size tort i0’ is also arranged to slope downwardly so that they can be ?lled with selenium bearing from the front to the rear in conformity with material and inserted inside the retort ID as the'slope-of the attached'condenser l2. To pro illustrated in Figs. 2-- and‘ 3- The boats may be vide for controlled heating of the retort and con made by'slitting a length of 8“ pipe and spread denser arrangement they are disposed in tem ing it' so asv to fit the 10" diameter retort and perature regulated'compartments of a furnace welding en'ds onto the‘ pipe sections. The size of as illustrated in Fig. 2; To accomplish this‘ the the boats are preferably such as can be readily retort‘ H1‘ is suitably mounted over the‘ furnace 40 loaded and manually" handled. combustionv chamber l5 by supporting it at its Using our process in the treatment of ?ue opposite ends in. the furnace walls’ Hi and H. dust, the. boats are loaded with selenium bear A ba?le wall l8 extends along beneath the retort ing baghouse dust mixed with approximately 5% and is. provided with ?ue openings I'S- near the by weight of the dry chargeof 60° Bé. sulphuric rear wall I‘! of. the furnace‘. 45 acid. The boats containing this mixture are Hot gasesof combustion produced by the burn placed in the retort which. has been. previously er 2]‘ pass upwardly through the ?ue openings heatedto about1350'° F. Each boat ordinarily l9, as. indicated by arrows in Figs. 2' and 3, and contains. approximately 70- pounds of material circulate about." the retort'throughout its length and is operated. on a twelve hour cycle.‘ That is, heating it uniformly, the waste gases being ? 50 the. complete cycle for each retort, including nally discharged .into the. stack opening 22; at charging and unloading, is 12 hours. When the the front‘of the; furnace- Each retort is'con retort is heatedto the proper temperature, ordi tained in a separate compartment 23 utilizing nary lump charcoal or coke isplaced in the rear common: partitioning walls 24; A wall or pier most section of: the retort as illustrated-at 80 in 25 extends upward from the ground?ll 26 beneath 55 Fig. 2. before: the charge boats 55 are inserted. the resort chamber providing a ?rm" support for Sufficient charcoal is- introduced to reduce all the retort and furnace structure as illustrated the S602 vapor given off by the charge to Se in Fig. 3. ' vapor before it passes tov the condenser I2. In order to maintain the chambers 30 and. 3| In carrying out the process the temperature of of'thefurnaoe in which the condensers I2 and I 3 60 the retort and. charcoal is kept above the boiling are mounted at the temperature required for point of selenium (1272° F.) , otherwise selenium proper operation, auxiliary burners 32. may be may condense in the‘ charge or retort before it utilized. Similar auxiliary burners, not shown, maybe utilized to raise. the, temperature of the reaches the selenium condenser l2. This, of course, should‘ be avoided. The temperature in the! furnace combustion chamber I5 is prefer ably maintained‘ at about 1350°'F. which is some what. above-theb'oiling point of selenium and as chamber‘. 30 where necessary. for. proper opera tion of the condenser [2‘. Waste combustion gases. from these burners‘ may be discharged through a separate stack opening not’ shown. sures a. temperature ofatleast 1-272° F. in the Steam and sulphuric acid vapors which are not center ofjthe charge- In view of the very low allowed to condense in the condenser l3- are 70 thermal conductivity of selenium bearing’ bag passed out through the discharge conduit 35 and house. dusta longer. timeand higher roasting’ tem~ into the air cooled~ condenser 3.6. This latter perature isirequired than: Would'otherwise‘b'e the condenser is closed at the top while the lower case toremove: the selenium; from the‘dust par. end is sealed by water and condensate 38‘ re‘~ ticles forming thev charge. , tained in the receptacle 40 as shown in Fig. 2. The chamber around: the. selenium condenser 2,413,374. 5 l2 and condenser storage [3 is maintained at about 450° F. At this temperature liquid selenium collects on the inside of the condenser pipe 52 and ?ows by gravity down into the larger condenser tlal charge contained about ‘ 7.44 pounds ‘of selenium of which 6.5 pounds or 87.5% was re covered as'vitreous selenium. A small amount of selenium, usually less than 1% under optimum Hi. In order to cause the liquid selenium to 5 conditions, escapes to the outer condenser and is found in the condensate along with sulphuric readily flow out of the tap hole [4 the condenser acid and water. This selenim, however, is not l3 should be kept at a temperature of about lost being returned for treatment with the next 450° F. Should it fall below this temperature the charge. auxiliary burners 32 are operated to raise the In the speci?c method described selenium‘ is temperature so that the selenium ?ows freely 10 recovered as liquid selenium which we refer to from the condenser 13 which is tapped inter as elemental selenium. When this liquid ele mittently. After tapping the selenium from the mental selenium is tapped from the condenser and condenser IS the auxiliary burners may be turned cooled quickly, as by casting in shallow or water off. Where the selenium bearing .material contains 15 chilled molds, a vitreous form of selenium is pro— duced. Where the more stable so-‘called metallic too much moisture it may be subjected to a pre form vis desired the liquid selenium is cooled slowly liminary de-watering and drying treatment prior or the vitreous modi?cation is heated for some to adding sulphuric acid and roasting. The time above about 180° F. to cause it to pass over selenium bearing dust which we have treated as described ordinarily contains upwards of 1% 20 into the metallic form. The several allotropic forms of selenium are well known and it will be moisture. This moisture is driven off as water obvious that the method of this invention may vapor along with excess sulphuric acid during the be utilized to recover selenium in any desired process and is recovered as condensate in the con form. Such changes as required to produce the denser 36. The recovered sulphuric acid may if desired be used over again in a new charge. In 25 desired form of Se is contemplated to come within addition to the sulphuric acid and water vapor the scope of this inventionas de?ned by the collected in the condenser 36 a small amount, appended claims. ' It will be apparent from the foregoing descrip usually less than 1%, of colloidal red selenium tion that the method of this invention may be escapes from condenser I3 and is deposited on the walls of the outer condenser. This is, how- . modi?ed to suit the varying conditions incident to using the invention, and while certain novel features of the invention have been disclosedand ever, not lost as it is recharged into the retort and recycled. The residue remaining in the roasted charge at the end of the heating cycle contains about 0.5% selenium. are pointed out in the annexed claims it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit and scope of the invention. As a typical example of how our process is car ried out, the following is illustrative: To a charge comprising selenium baghouse dust What is claimed is: l. A process for treating selenium bearing ma pounds of 60° Bé. H2SO4 was added and after thoroughly intermixing the acid with the dust at 40 terial to recover selenium as elemental selenium which comprises intermixing said selenium bear ordinary room temperature conditions the mix ing material with sulphuric acid and subjecting ture, which was relatively dry, was placed in an the mixture to a roasting temperature of approx iron boat and inserted into the cast-iron retort imately 1350° F. while shielded from contact with of the furnace. The retort was tightly sealed and heated to 1350° F. Roasting of the charge " air to react the acid with said material and drive o? substantially all the selenium as volatile se was conducted for approximately eight hours. lenium and selenium dioxide, passing said vola At a temperature of 600° F. SeOz was volatilized tile vapors through heated carbonaceous mate and around 1300° F. Se was vaporized. Both rial to cause the reduction of the selenium dioxide S602 and Se vapors were passed through the heated charcoal, the temperature of the charcoal 50 to selenium vapor, and condensing the selenium vapor to recover the selenium as elemental se- ' being maintained at around 1300° F. whereby all lenium substantially free from sulphuric acid and SeOz was reduced to Se while in the vapor phase. weighing 40 pounds and assaying 18.6% Se, 2.2 moisture. The selenium vapor was passed into the con~ 2. A process for treating selenium bearing ma denser I2 which was kept at a temperature such that the Sc vapor condensed and flowed into the 55 terial to recover selenium as elemental selenium which comprises intermixing said selenium bear large condenser and storage receptacle [3 con ing material with sulphuric acid, said acid being nected thereto as shown in the drawings. Mois introduced in an amount up to about 5% by ture and excess I-I2S04 vapor was carried through weight of the charge, heating the mixture sub the selenium condenser to the outer condenser 60 stantially out of contact with air to a tempera where it was condensed and collected. ture above the boiling point of selenium and se Liquid selenium tapped from the condenser lenium dioxide to react the charge with said acid weighed 6.5 pounds. This liquid selenium was and bring about volatilization of substantially cooled quickly in a mold forming vitreous selenium having a black glassy appearance but when viewed _ all the selenium in said material, conducting the through relatively thin sheets appeared dark red. G” selenium vapors over a bed of hot carbonaceous material to cause the reduction of selenium diox Selenium in the amount of about 1% collected ide vapor to selenium vapor, and then condensing in the condensate along with excess H2804 and was returned to the retort with a new charge. After roasting for eight hours the residue was re moved and charged into a cupel furnace for re— said selenium vapors to recover selenium as ele TU covery of remaining metal values. The residue taken from the retort was found to contain 0.8% selenium. This material was charged into a cupel furnace for treatment to recover other values. In the example it will be observed that the ini 75 mental selenium. 3. A process for treating selenium bearing ma terial to recover selenium as elemental selenium which comprises intermixing said selenium bear ing material with sulphuric acid, said acid being introduced in an amount up to about 5% by weight of the charge, heating the mixture while 2,418,374 7 excluding air therefrom to a temperature above the boiling point of selenium and selenium diox ide to react the chargev with said acid and bring about volatilization of substantially all the se lenium in said material, conducting the vapors 8 phuric acid to approximately 1350° F. with sub stantial exclusion of air and‘ for a time sui?cient to cause the selenium compounds to react with the acid and the selenium to be released as SeOz 4 and Se vapors, conducting said SeOz and Se va evolved during heating over a bed of hot car bonaceous material to cause the reduction of se pors along with excess sulphuric acid vapor and water vapor through heated carbonaceous mate lenium dioxide vapor to selenium vapor, then rial whereby all the SeOz vapor is reduced to Sc cooling the vapors which comprise selenium va vapor, selectively condensing the ‘Sc vapor from por, sulphuric acid and water vapor to a tem 10 the mixture of sulphuric acid vapor and water va perature which will cause the selenium vapor to Dor to recover said selenium as elemental sele condense but above that at which sulphuric acid nium, and condensing the mixture of sulphuric and water vapor condense whereby elemental se lenium is recovered, and thereafter condensing the sulphuric'acid and water vapor. 4. A process for treating selenium bearing bag~ house dust recovered from metallurgical furnace operations which comprises intermixing a charge of said selenium bearing material with sulphuric acid in excess of the amount required to react with the selenium compounds present in said charge, heating said charge substantially out of acid and Water vapors which has been substan tially depleted of selenium whereby said excess sulphuric acid and water vapors are collected as a condensate for recycling. 7. A process for treating selenium bearing bag~ house dust recovered from metallurgical furnace operations which comprises intermixing sulphuric acid therewith in excess of the amount required to react with the selenium compounds present in the resulting charge, heating said charge sub contact with air to react the acid with the se stantially out of contact with air toreact the acid lenium of the charge whereby the selenium of with the selenium of the charge whereby the sele the‘ charge is volatilized as SeOz and Se vapors, nium of the charge is released as S802 and Se subjecting said vapors: to a reducing action to vapors, passing said vapors through a reducing bring about the reduction of S602 to Se while in atmosphere to bring about the reduction of SeOz the vapor phase, and conducting the resulting to Se while in the vapor phase, conducting the stream of selenium vapors, water vapor and sul selenium vapors along with water vapor and sul phuric acid vapor along a course while cooling it 30 phuric acid vapor into a condenser and condens to selectively condense the Se vapor in the form ing the Se vapor in the form of elemental sele of elemental selenium without condensing the nium without condensing the sulphuric acid and sulphuric acid and water vapor present. water vapors present, maintaining the condensed 5. A process for recovering selenium as e1e~ selenium heated to a temperature su?icient to mental selenium from selenium bearing baghouse maintain the condensed selenium vapor in a liq dust comprising preparing a charge by intermix uid state, drawing 01? said liquid selenium into ing approximately 5% by weight of sulphuric acid a receptacle and quickly cooling the liquid sele with a portion of said selenium. bearing material, nium to form vitreous selenium. the quantity of acid introducedrbeing based on 8. A process for treating selenium bearing ma the amount .of seleniumpresent in the portion terial such as slimes from copper re?neries to making up the charge, heating the resultant mix recover selenium which comprises intermixing ture of selenium bearing material and sulphuric the selenium bearing material with sulphuric acid to approximately 1350° F. while precluding acid, roasting the mixture substantially out of any substantial access of- air to the mixture,hold contact with air to react the selenium bearing ing said charge at this temperature fora time material and sulphuric acid and cause the sele su?icient to cause the selenium compounds to nium to be released as gaseous selenium dioxide react with the acid and the selenium to be re and selenium metal vapor, the selenium contain leased as S802 and Se vapors, conducting said ing vapors being intermixed with evolved sul SeOs and Se vapors along with excess sulphuric phuric acid and water vapor, subjecting the gase acid vapor and Water vapor through a reducing 50 ous mixture to reducing conditions whereby the _ atmosphere comprising heated carbonaceous ma gaseous selenium dioxide present is converted to terial whereby all the SeOz is reduced toSe vapor, selenium meta-l vapor, cooling the resultant gase and selectively condensing the Se vapors from ous mixture of selenium metal vapor, sulphuric said gaseous mixture of sulphuric acid vapor and acid and water vapor to selectively condense the water vapor to recover said selenium as elemental selenium metal vapor to liquid selenium, the cool selenium.v ing temperature to which the vapor mixture is 6. A process for recovering selenium as ele subjected being controlled to cause the selenium mental selenium from selenium Ibearing bag metal vapor to condense to liquid elemental sele house dust comprising preparing a charge by in nium while preventing the condensation of sul termixing approximately 5% by weight of sul 60 phuric acid and water vapor, and withdrawing phuric acid with a portion of said selenium bear~ the resulting liquid elemental selenium. ing material, the quantity of acid introduced be ing based .on the amount of selenium present in the portion making up the charge,_heating ‘said mixture of selenium bearing material and sul-' 65 ALBERT J. PHILLIPS. YURII E. LEBEDEFR. JAMES R. CRANDALL.