Show lea lead d zinc separation volatilization A full resume of its practical possibilities by G L 1 the various districts in the united states where complex lead zinc ores occur are too well known to require description there being hardly a mining state with any large amount of ores of either metal that is free from this problem this paper briefly presents developments in the volatilization process as applied to the treatment of such ores since the data in bureau of mines bulletin 21 2112 12 were published in that bulletin among the many types of ore treated examples are afe given of the treatment of lead zinc ores by the chloride volatilization process for the separation of lead an outline of the general process with views views of the rotary kiln ore feeder firing system these three features resemble closely those of cement kiln practice dust chambers and a cottrell precipitator to remove the fume from the gas are also shown shown in that bulletin to which the reader is referred for the results obtained and for practical details of operation the small initial cost of a volatilization plant and its adaptability for use in isolated districts were emphasized in general it was found that when an intensely oxidizing atmosphere was maintained in the furnace a good lead zinc separation could be made therefore a heavy sulphide ore would have to be pre roasted and enough air would have to be admitted to obtain complete combustion of whatever fuel might be used the work done by private companies and the bureau since the data for bulletin were obtained indicates that the ores ost lost immediately amenable to treatment by volatilization are of two types the first is an oxidized lead silver ore whose variable lime content makes it impractical to the ore ia for acidulated brine leaching and whose base metal content diakes treatment by unfeasible the second type is ls the lead zinc ore mentioned ped above and is thi the e one on which bata ata are available for n at present this article shows what ores of this latter type are amenable to treatment by volatilization by giving briefly some of the more important physical ca and chemical properties an ore should preferably possess several examples examples are give from both laboratory experimental work wk and from practice in the field showing various phases of 01 the volatilization process constituents of ores affecting volatilization of lead the fundamental facts upon which may be based the pos sivility biety lity of separating tha the lead from the zinc minerals of an ore might be listed as follows 1 lead oxide is very much more II bureau of mines department of the interior intermountain experiment station salt lake city utah of fay thomas and others the chloride volatilization process or 0 r e treatment bull 11 ll I bureau of mines 1923 0 o volatile than zinc oxide when it is desired to volatilize zinc zinc as from the retort or the wetherill grate a reducing agent 6 is added and the zinc is volatilized as the metal which b burns urns in the air to zinc oxide if air be permitted to enter after distillation of the zinc 2 from experience with other ores it would appear although the boiling point of zinc chloride is lower than that of lead chloride that if a stif sufficiently oxidizing atmosphere be maintained the lead will vola volatilize utilize while the zinc will remain as zinc oxide not only is lead oxide much more volatile than zinc oxide at say or but the chloride of lead is probably much more difficulty than the chloride of zinc in an oxidizing atmosphere mo sphere lead oxide is appreciably volatile at and at C the volatilization is quite rapid 3 theoretically should take place more rapidly in a fused mass than in an open porous bed of ore but for the volatilization itself fusion should be prevented as far as possible the ore charge should itself be moved and its surface subjected to a rapid gas circulation in order to evaporate and remove quickly the volatile oxides and chlorides many lead compounds fuse with great ease as do also the ordinary slag forming materials the subject of lead zinc separation resolves itself quite largely into a study of the fusibility of the constituents of which an ore may be composed factors affecting Fusi libity of ores a sulphides Sulp hides the fusion points of some of the more common sulphides sulp hides are given below see van strands No chemical annual by olsen it must be remembered that some of these fusion points were obtained in an atmosphere of nitrogen all are for pure minerals a mixture of sulphides sulp hides bides will of course melt at a lower temperature it is known for instance that fes fess in conjunction with other sulphides sulp hides in a sulphide ore say of copper if heated rapidly at a much lower temperature in a rotating cylinder will cause balling and ringing bringing this is particularly true if the free atom of s sulphur is not permitted to burn off slowly this balling action may be made so strong t as to form the basis for a process whose aim is to fort form nodules so that a flotation concentrate ma may y be handled by a blast furnace sulphide fusion point sulphide fusion point degrees decreed C degrees 0 1049 pbs 1120 ans I 1 fes 1197 1100 fesa 1171 b lead compounds As the assayer knows the addition of f enough will flux almost any difficultly fusible ore the majority oi of the fusion p points eints following were taken from hofman above quoted H 0 the metallurgy of af lead 4 compound fusion point REMARKS degrees C paso 1100 but in contact with air starts to form the oxide around X 1030 abo 2 pbs I 1 lowest fusion point of compounds 3 j A iDt oUi v abo 82 sn 0 u o lowest fusion point eutectic of lowest pelting melting point contains 87 per cent abo for any other chlorides desired see van nostrand etc the point about a mixture being more fusible than a pure salt is also to be remembered c silicate flags for the fusibility of flags it might be said that the silicates formed with lime magnesia and require a high temperature to make them plastic hofman general metallurgy gives 1350 cC for the compound of lowest fusion point As workers with sponge iron have learned under reducing conditions that is with large amounts of ferrous oxide present if a large amount of iron oxide be present it will unite with silica to form easily fusible flags A of iron with a melting point of has been given while with the addition of a small amount of lime a compound with a melting point of has been formed with the replacement of cao by zno or mno the fusion point for any silicate raises with the partial replacement of cao by bao a silicate melting at has been obtained for chloride volatilization with the use of salt melting point it may be noted that sodium silicate NaSi Oi fuses at the sodium radical of salt un unites ites with silica when chlorine is liberated in case there is no SO present d lead silicates it has been noted that lead oxide combines at a much lower temperature with silica to form a fusible silicate than does lead sulphate and also that this latter itself is more fusible than lead oxide according to hofman metallurgy of lead p 38 at 1000 C no lead oxide will volatilize from a silicate containing less lead than shown by the proportion abo sio only a few ores will remain much above this temperature if an ore were extremely infusible other than in lead silicate it might be possible to heat the ore still higher with beneficial results the lead may be blown from a matte with air in converter practice but even the smelter using this process takes off all the lead possible before adding siliceous flux the abo sio ratio is then of very great importance for oxide volatilization of the lead for as shown the higher the abo the more fusible the silicate and it is difficult to decompose a silicate once it is formed carbon is helpful to assist the volatilization of the lead from a silicate but it causes volatilization liza tion of zinc lime or other gangue matter mentioned might assist mechanically to prevent fusion but is not always available nor is it at times permissible to dilute the ore from 1 the fusion point of the sulphides sulp hides and silicates noted above 2 the melting points of various lead compounds 3 the temperature required to commercially volatilize lead as the chloride or oxide say and 4 the fact that air circulation through a fused mass can be obtained only with some difficulty the effect of the fusion of the ore on volatilization may be readily seen air might be blown through the fused mass in some apparatus as in a converter the ore just before formation of the lead silicates takes place might also be showered down a hot shaft or fed directly into the gas flame in order that each particle of lead oxide might have a chance to itself from the ore bea before ore it was fused it is clear however that if an ore becomes plastic at the temperature required for volatilization and it is impractical to add infusible substances doubts are immediately cast on its amend ability to treatment by this method and a fairly a accurate forecast might be made of the types of ores with which the process might be successful |