Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B13/00—Obtaining lead
  • C22B13/02—Obtaining lead by dry processes
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B13/00—Obtaining lead
  • C22B13/06—Refining

Definitions

• metallic lead is normally produced from sulphidic lead raw-materials, such as concentrates, it is also produced from metallic, oxidic and sulphatic lead raw-materials, such as dust, ashes and slags.
• the most common furnace for smelting and reducing lead is the shaft furnace, which is charged with lead raw-materials which may have been pre-sintered or roasted to oxidize the sulphidic sulphur with atmospheric oxygen to a content of less than 2% sulphidic sulphur.
• This smelting and reduction of lead raw-material can also be effected to advantage in a rotary, inclined furnace, such as a furnace of the Kaldo-type as described in Swedish Patent specifications 7317217-3 and 7317219-9, which illustrate processes for producing crude lead from sulphidic and from oxidic and sulphatic lead raw materials.
• crude lead is meant here, generally, a lead product which must be subjected to further purifying or refining stages, in order to be retailed as a normal market product.
• the lead When producing crude lead from different raw materials the lead will thus practically always contain impurities undesirable in the finished lead. Examples of such impurities include copper, arsenic and antimony.
• the crude lead will normally also contain gold and silver.
• crude lead must always be refined in order to obtain a sufficiently pure lead, commercially known as a so-called refined lead.
• the lead is refined in various chambers or pots specifically designed for such refining work.
• the copper, and above all the arsenic, present in the crude lead create a particular problem when refining said lead, since these impurities may reach to 15% or, in certain cases,even higher, which give very large quantities of more or less solid powderous, products, normally called dross, on the surface of the metal bath, thereby rendering handling difficult.
• the arsenic represents a direct threat to the environment, since a significant amount thereof is fumed-off from the pots or chambers during the refining process.
• the present invention substantially eliminates the aforedescribed problems. Moreover, the method according to the invention enables extremely rapid reaction sequences to be obtained whilst requiring a relatively low energy input, which are important and decisive factors in respect of the economy of the process.
• the lead raw-material may be of the metallic, sulphidic, oxidic or sulphatic type, and may comprise, for example,various dust- products and powderous-products obtained from non-ferrous metallurgical processes.
• the lead raw-material is melted in a furnace , in which turbulence of the content can be created, in the presence of a slag former, whereafter the slag is drawn-off, said method being characterized by the fact that subsequent to drawing-off the slag , there is charged to the furnace at a temperature of 850-1200°C under strong agitation, iron in a metallic , finely-divided form, or iron is caused to be formed in situ, whereafter the insoluble liquid iron speiss formed in the lead melt is.separated therefrom in immediate conjunction with a gravitational separation of speiss and crude lead.
• iron in a finely-divided form is meant metallic iron in a form such as to present a relatively high specific surface area to the lead melt and such that the iron can be charged to the lead melt in a simple manner.
• the lead raw-material is charged to the furnace prior to or . during the smelting process,together uith a slag former.
• the crude lead is reduced chemically in a known manner and the resultant lead-containing slag is chemically reduced , suitably with coke for example, until the lead content of the slag is sufficiently lou , for example less than 2%.
• the slag purified from lead, is then tapped off. In order to fill the furnace to the extent desired, further lead raw-material can then be charged to the furnace and the slag reduced to a lead content of less than 2% and the slag tapped-off,in a repeated number of operations.
• a "speiss” is a compound of arsenic and/or antimony with iron metals and/or copper, i.e. a “speiss” may comprise arsenides and/or antimonides of one or more of the metals copper,iron, nickel and cobalt.
• Formed iron- arsenic-speiss is practically insoluble in a lead melt, and hence it readily separates , floats to the surface and lies above the lead melt and can be poured therefrom in a liquid state at a temperature of 800-1150 C.
• a temperature range of 950-1000°C is preferred,due to the viscosity of the speiss, which enables rapid separation and tapping.
• the iron charged to the furnace may conveniently comprise an iron alloy containing more than about 60% iron.
• any copper impurities present are then suitably segregated or frozen out from the lead melt whilst agitating the same in said furnace;by adding a coolant to the melt,to cool the same suitably to a temperature of between 400 and 600°C, whereafter crude lead is tapped off , said lead being free from copper and arsenic.
• the coolant may conveniently have the form of an oxidic or sulphatic lead raw-material or a crushed iron-silicate slag.
• a rapid and effective cooling effect is obtained when the coolant is water, which is injected directly into the furnace in a liquid , finely-divided form.
• it may also be suitable for the coolant to comprise a slag former intended for a subsequent smelting operation.
• minor quantities of copper it is possible to leave the copper-segregation step until several charges of lead raw-materials have been smelted and treated with iron.
• Copper can also be removed from the crude-lead melt as a copper speiss.
• a copper speiss is formed when the temperature ⁇ is lowered to less than 1100°C.
• the mole ratio between copper and free arsenic must be between 1.17 and 4.43.
• iron is suitably added to form an iron speiss in order to raise the mole ratio,to enable segregation of a copper speiss when cooling. Further arsenic can then be removed,by charging more iron to the furnace.
• the melt also contains recoverable quantities of tin
• iron is suitably charged in an amount which will ensure that sufficient arsenic remains in the melt to form copper speiss, for example Cu 3 As.
• copper speiss for example Cu 3 As.
• the tin content will exist in a metallic solution in the lead melt, which can be retailed in the form of tin-containing lead , which can demand a higher price on the market.
• iron can be caused to form in situ in the melt , preferably by adding silicon, silicides, carbon, carbides or ferro-.alloys containing carbon and silicon in such quantities that iron present in the slag is reducad out in metallic form prior to removing the slag.
• the melting capacity of the furnace can be utilized to the maximum , since the formation of speiss in a charge of about 30-40 tons is obtained already after 30 minutes and , when cooling , the heat content of the lead can be recovered by , as aforementioned , using as the coolant a quantity of slag former intended for a subsequent process, said slag former thus being preheated in readiness for said subsequent process. If so desired, the melt of lead raw-material can also be cooled by charging a part of a subsequent charge of lead raw-material.
• the melting process and also the formation of speiss and the segregation of copper, are effected in a furnace in which the melt can be treated whilst being strongly agitated.
• a furnace in which the melt can be treated whilst being strongly agitated.
• One suitable furnace in this respect is a top-blown rotary converter, known as a TBRC converter or a Kaldo furnace.
• a TBRC converter or a Kaldo furnace can be rotated at a speed of from 10 to 60 r.p.m., the choice of suitable rotary speed being controlled by the diameter of the furnace.
• a suitable turbulence or agitation can be obtained when the inside of the furnace moves at a peripheral speed of 0.5 - 7 m/s, preferably 2-5 m/s, which enables the melt to accompany the rotating inner surface of the furnace and fall down onto the surface of the bath in droplet form, which results in extremely good contact between solid phase, liquid phase and gas phase. Good contact is a prerequisite of rapid chemical and physical sequences, such as reduction sequence, cooling and separation.
• the formation of dust is avoided to a surprisingly high degree, owing to the fact that the showerof droplets falling down onto said surface drive down that dust which would otherwise leave the furnace with the reaction gases.
• the slag and the crude-lead bath were chemically reduced with 1.3 tons of coke until the lead content of the slag was about 1.5 % at a temperature of about 1000 C, whereafter the slag was tapped off. 3.0 tons of iron filings were then charged to the furnace , the arsenic content of the melt during rotation of the converter at a speed of about 30 r.p.m. falling from 7.3% to less than 0.01 %.
• it is extremely important that the speiss formation is effected with good contact between the iron and lead phase and with an iron surplus of at least 20% above the stoichometric value.
• the temperature during the formation of speiss was in excess of 1000°C.
• the formed and segregated speiss phase was tapped-off immediately the converter stopped rotating, since in a stationary crude-lead bath some arsenic will re-dissolve in the crude-lead melt from the speiss.
• Example 1 30 tons of oxidic-sulphatic pellets of the kind and composition recited in Example 1 were melted in a manner similar to that described in Example 1, with 9 tons of fayalite slag and 2.25 tons of limestone in a Kaldo converter,whilst burning oil with oxygen. Subsequent to melting the pellets, the slag and crude lead were chemically reduced at a temperature of 1000°C with 1.3 tons of coke,until the lead content of the slag was about 1.5 %, whereafter about 70% of the slag was tapped-off from the converter. About 1.5 tons of silicon iron , FeSi, were then charged to the converter, to reduce the remainder of the slag and to form a speiss.
• the converter was rotated at a speed of about 25 r.p.m., whereupon the arsenic content fell from an original 5%, firstly to about 1.3 % and then , during the rotation of the converter for about one hour and subsequent to the charge of silicon iron, to about 0.4%.
• Oxidic-sulphatic pellets mixed with pellets of metallic and sulphidic type were melted with fayalite slag and limestone in a manner similar to that described in Example 1, resulting in a crude-lead melt of about 15 tons'having the following composition: lead 84.4%, copper 2.7 %, arsenic 5.5% and tin 1.4%.
• the melt was rolled at 1100°C and 1200 kg of iron filings were added and rolling of the melt continued at 30 r.p.m for some minutes, an iron speiss being formed.
• the speiss was tapped-off and the resultant lead melt had the following composition: lead 86.1 %, copper 2.4%, arsenic 1.1%, tin 1.3%.
• the mole ratio of copper to arsenic was 2.6.
• the melt was then cooled to 450 0 C by injecting water thereinto whilst the furnace was rotating, a copper-speiss-copper- dross segregating out.
• the resultant lead melt had the following composition: lead 96.3%, copper 0.1%, arsenic 0.01% and tin 1.3 %.
• Example 3 It will be evident from Example 3 that by limiting the iron charge in a manner such as to obtain in the crude-lead melt a copper/arsenic mole ratio of 2.6,it is possible to avoid losing the tin content to speiss phases in the form of copper-tin-compounds from which tin is not readily recoverable. A lead which contains tin has a very high commercial value.

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• Chemical & Material Sciences (AREA)
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• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Manufacturing & Machinery (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Saccharide Compounds (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• Steroid Compounds (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
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Cited By (6)

Citations (5)

• 1978
  • 1978-06-29 SE SE7807357A patent/SE412766B/sv not_active IP Right Cessation
• 1979
  • 1979-06-15 EP EP79850058A patent/EP0007890B1/de not_active Expired
  • 1979-06-15 AT AT79850058T patent/ATE1752T1/de not_active IP Right Cessation
  • 1979-06-15 DE DE7979850058T patent/DE2963968D1/de not_active Expired
  • 1979-06-26 PL PL1979216607A patent/PL117462B1/pl unknown
  • 1979-06-27 DK DK271379A patent/DK148810C/da not_active IP Right Cessation
  • 1979-06-28 NO NO792174A patent/NO152516C/no unknown
  • 1979-06-29 FI FI792060A patent/FI68265C/fi not_active IP Right Cessation

Patent Citations (5)

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