WO2020132752A1 - Modern plant for producing trioxides of antimony and arsenic, and metal lead - Google Patents

Abstract

The present application relates to a modern plant that includes a method for obtaining commercial antimony trioxide (Sb2O3), arsenic trioxide (As2O3) and metal lead (Pb) from a mineral containing predominantly antimonite. The first step begins with a process of oxidative roasting of the sulfide mineral in rotary ovens at a controlled temperature of 480-520°C, to oxidise antimony trioxide and arsenic trioxide and consequently volatilise same. In this step of the method, the air is regulated to ensure the adequate oxidation of antimony and arsenic until the trioxides thereof are formed, preventing the formation of cervantite (Sb2O4). The second step of the in-plant method is carried out in a fixed double-chamber oven, to cause the volatilisation of the products of interest, antimony trioxide and arsenic trioxide, which separate according to their different condensation temperatures. The temperature of the gases reduces from 450°C to 350°C, separating the antimony trioxide first, while the arsenic trioxide remains volatile and subsequently solidifies at a gas temperature of 300°C to 90°C. Given the condition that lead oxide does not volatilise at the temperature of the initial process, this compound remains solid inside the oven, being recovered as liquid lead, following reduction with carbon.

Description

Modern plant for the production of Antimony Trioxides, Arsenic, and Metal Lead "

DESCRIPTIVE MEMORY

FIELD OF THE INVENTION

The present application considers a Plant for the Obtaining of Antimony Trioxide, Arsenic Trioxide and metallic Lead from a mineral, predominant in Antimonite or Stibine (Sb2S3) and of other sulfided minerals of Arsenic (As) and Lead (Pb) contained in the mineral, which chemically contain on average 30% Antimony, 4% Arsenic and 10% Lead. The designed plant has a mineral treatment capacity to produce 300 t / month of Antimony Trioxide (Sb ₂ 0 ₃ ), 44 t / month of Arsenic Trioxide (AS2O3) and 89.7 t / month of Lead (Pb) metallic, considering a global metallurgical recovery of 90%, as well as being environmentally sustainable from the gaseous and solid waste generated point of view.

BACKGROUND OF THE INVENTION

The processes for obtaining Antimony Trioxide from metallic sulphide minerals are based on the ease of oxidation between the elements present, arsenic, tin, antimony and lead, which decreases in the following order:

Arsenic (As)> Tin (Sn)> Antimony (Sb)> Lead (Pb).

Antimony is partially oxidized as long as the concentrate or mineral contains arsenic and tin, and only when these two elements are oxidized, the oxidation of the antimony increases, while the oxidation of lead does not begin until all the antimony is oxidized. In this way, the significant presence of Arsenic (As) and Tin (Sn) in the mineral rich in antimonite, must be kept in mind before generating the complete oxidation of antimony (Sb). In the case of Arsenic (As), its trioxide sublimes at 465 ° C, which facilitates its separation in melting or roasting pyrometallurgical processes. It should be borne in mind in the selection of the process for obtaining antimony trioxide (Sb) that the melting point of antimony (Sb) is 630 ° C and its trioxide

656 ° C and Antimonite 525 ° C, whereby the oxidation of molten metallic antimony (Sb) is feasible by direct oxidation of the liquid bath or in suspended drops, in an oxidizing atmosphere in a cyclone furnace melting process .

There are known pyrometallurgical processes for obtaining trioxide from sulfuric mineral Antimony (Sb) or its concentrate, the most traditional method being that of fusion with metallic iron, to cause reduction to metallic antimony (Sb); as well as treating said low antimony (Sb) minerals by roasting volatilization with the subsequent carbothermal reduction of the oxide produced.

Sometimes native stibine (Sb2S3) is roasted in an oxidizing atmosphere with preheated air to remove sulfur and generate white oxide (trioxide), which can then be reduced with carbon (coke), to obtain metallic antimony (Sb). Roasting is done to transform sulfides into oxides, which are easier to reduce. Oxidation requires a temperature high enough to produce the necessary affinity between oxygen and the compound to be oxidized. The lowest temperature used in the process is 600 ° C. Normally, the temperature varies, depending on the type of raw material and the furnace, from 750 to 950 ° C. For the oxidation to be carried out uniformly, it is necessary to have an abundance of air, in contact with the matter to be oxidized. The need for air abundance is due to the fact that its oxidizing power decreases when mixed with the gaseous products of oxidation, reducing it by up to 50% of its value. The roasting speed is accelerated, increasing the speed of release of the gaseous products and their replacement by pure air. The speed and also the finish of the roasting are influenced by the size of the raw material. The roasting speed has a maximum point, from the economic point of view, since when exceeding it, the losses of the material in the form of dust that carry the exhaust gases, do not compensate the increase in speed, since the recovery of these powders is expensive. The factors that control roasting are: temperature and time. The heat necessary to carry out the oxidative roasting is produced by the combustion of a fuel, either alone or mixed with the load, or using the heat caused by the exothermic reactions between the mineral and the oxygen in the air.

By roasting the antimony sulfide, antimony oxide (lli and IV), Sb ₂ 0 ₃ and Sb ₂ 04 respectively, is obtained, according to the reactions: 2Sb ₂ S ₃ + 9O2 2Sb ₂ Ü ₃ + 6SO2 1 Sb ₂ S ₃ ⁺ 50å— Sb ₂ 0 ₄ + 3SO2 †

From the oxide obtained by the previous oxidative roasting operation to which the ore has been subjected, heating is carried out at high temperature with reducing reagents (coke) to originate a molten metal or an alloy or other product, but always in the state molten. (9.2. Pyrometallurgical extraction. Antimony Metallurgy Course, Antonio Ros Moreno, 2009).

From this background it can be clearly deduced the need to use high temperatures, above 600 ° C to obtain antimony trioxide and also the importance of also supplying an important input of oxygen in the system, to increase and improve the production of antimony when we are in the presence of Lead and Arsenic in the minerals considered as raw material of the process. It is desirable to have a controlled, low-cost (energy) process that allows obtaining commercial antimony trioxide (Sb).

Antimony trioxide is obtained from the antimonite mineral by roasting it in conventional ovens. Rotary roasting ovens are the most commonly used today. The antimonite beneficiation process mainly depends on the content of antimony and other minerals present. The antimony trioxide is obtained by roasting the antimony sulfide, antimonite (Sb2S3), in conventional roasting ovens. Sulfur roasting is a Gas-Solid reaction process in a (special) furnace in which large amounts of air, sometimes enriched with oxygen, are brought into contact with the sulphide ore concentrates. Antimony sulfide is oxidized to antimony (III) oxide (volatile in roasting) or to antimony (IV) oxide (nonvolatile). Control of the furnace in the production of non-volatile antimony (IV) oxide is relatively simple, however the oxide does not separate from the residue, to the detriment of the trioxide obtaining efficiency. Roasting has the advantage that SÓ203 volatiles are selectively produced in 98% yield and separated from the gangue, which contains the precious metals in a recoverable form. However, it is difficult to control the oven and temperature. The oxide forms between 290 and 340 ° C in an oxidizing atmosphere, and the reaction rate peaks at 500 ° C, at which antimony (IV) oxide begins to form. The impurities that come to Present in the products are carried away by the gases of sulfur dioxide (SO2) or Antimony Trioxide (Sb ₂ 03), as the case may be. The basic reaction is:

2 Sb ₂ S ₃ + 9 0 ₂ 2Sb ₂ C> ₃ + 6 S0 ₂ If there is too much oxygen, antimony (IV) oxide forms:

Sb ₂ S ₃ + 5 0 ₂ - Sb ₂ 0 ₄ + 3 S0 ₂

Above 560 ° C, the reaction rate decreases considerably. During roasting, antimony (IV) oxide can react with antimony (III) sulfide and fresh Cervantine, resulting in antimony (III) oxide when the reaction is gestated with low presence of Oxygen (0 ₂ )

Sb ₂ S ₃ + 9 Sb ₂ 0 ₄ 10 Sb ₂ Ü ₃ + 3 S0 ₂

Therefore, the process should be designed so that antimony (III) oxide (Sb ₂ 0 ₃ ) is formed quickly and preferably. The temperature must be high enough to guarantee adequate volatilization and the oxygen supply must be kept low to inhibit the formation of antimony (IV) oxide. When the temperature is too high, part of the charge melts on other sulphide grains, and prevents optimal oxidation. During condensation of antimony (III) oxide, the oxygen content in the gas phase must be kept low enough to prevent the formation of antimony (IV) oxide. The temperature level is governed by the sulfur content in the mineral. Low grade antimony sulfide minerals (Sb ₂ S3) can be roasted between 850 and 1000 ° C. If minerals rich in antimony sulfide (Sb ₂ S3) are roasted, the upper limit is the sulfide melting point (546 ° C); in practice, the temperature should not exceed 400 ° C. The degree of oxidation is controlled by charcoal or coke powder, combined with the charge, admitting only the amount of air necessary to form carbon monoxide and antimony (III) oxide. Carbon monoxide inhibits oxidation to antimony (IV) oxide. Regardless, the formation of antimony (IV) oxide cannot be completely suppressed. In the first condensation, antimony (IV) oxide, lead (II) oxide and smoke powders are obtained. Antimony (III) oxide condenses second, and volatile arsenic (III) oxide last. If the oxygen concentration in the furnace is too low, partial oxidation can occur and give a mixture of oxide and molten sulfide at 485 ° C. If the oxygen concentration is too high, it can form arsenates and antimoniates of lead, copper and others. metals that pass into the slag. If the antimony oxide consists of very fine crystals, which adhere firmly to the fingers and do not agglomerate, it is considered to be of good quality. The oxide must be white, a reddish tint indicates the presence of antimony (III) sulfide. The yellowish tone is due to selenium and lead (II) oxides. The arsenic content should be in the order of 0.1%. (Study of the behavior of antimonite during roasting at Sb2C> 3 (antimony trioxide) in electric resistance and microwave ovens, TJ Ornelas, HJA Hernández, MM Márquez, and MA ortiz Dept. of Mining Exploitation and Metallurgy of the Faculty of Engineering Universidad Nacional Autónoma de México Cd. Universitaria, 2012.)

From this background, it is possible to clearly deduce the need to control oxygen and temperature to obtain antimony trioxide and also avoid the formation of Antimony Oxide IV (Sb204). Achieving a controlled process in oxygen quantity and adequate temperatures is desirable to obtain commercial grade antimony trioxide (Sb) at a low cost.

The reduction of antimonite (SÓ2S3) with carbon in the presence of calcium oxide was investigated in the temperature range of 700 to 850 ° C. The experimental tests were carried out on a laboratory scale in a thermogravimetric apparatus to determine the technical feasibility of the reduction process and study its kinetics. This paper provides relevant background information for the present study, such as the description of current processes for the production of metallic antimony in South American countries:

The production of antimony, according to the requirement of fluxes such as hematite, limestone and charcoal, these materials are fed into hoppers with the purpose of mixing in defined proportions. This mixture subsequently feeds a cyclone oven 81 cm in diameter and 130 cm high, where the antimony volatilization process begins with preheated air to obtain an intermediate product called impure antimony trioxide and whose antimony trioxide laws reach content. maximum 80% antimony (III) oxide Sb2C> 3. The powders are recovered in bag filters and electrostatic filters, this material is pelletized with fluxes such as sodium carbonate (Na2CC> 3) and charcoal which is reduced in short drum rotary kilns, to obtain 99 metal antimony. to 99.2%. Subsequently, the metal is refined in stationary type furnaces (reverberatory furnace), until purities of 99.5 or 99.6% are achieved, eliminating mainly arsenic and iron. The oxidation of metallic antimony (regulus) depends on the market for antimony trioxide, which is carried out in an electric furnace to produce trioxide. high purity antimony (Sb ₂ C> 3) (99.5% Sb ₂ C> 3). This study shows the arrangement of the cyclone kiln and electric kiln of an antimony plant that treat antimony concentrates shown in the process described above, to produce antimony by oxidation / reduction, considering the grade of the mineral shown, 498 kg S0 are produced ₂ / t mineral (174 m ³ S0 ₂ / t mineral). Taking into account the previous criterion, the small metallurgical plants that produce antimony cannot implement the required process for the care of the environment because their facilities do not have units that allow the recovery or mitigation of polluting gases with Sulfurous Anhydride (S0 ₂ ) and mainly they cannot access this technology due to economic infeasibility, therefore, they continue to resort to conventional processes such as roasting of antimony minerals and reduction in rotary kilns, achieving low recoveries of metal antimony and with an incidence on environmental contamination with Sulfurous Anhydride (S02). (CARBOTHERMAL REDUCTION OF ANTIMONY SULFIDE IN THE PRESENCE OF CALCIUM OXIDE (Master's Thesis in Metallurgical Engineering, U of C), 2011)

From this background it can be clearly deduced that many plants generate metallic antimony, by roasting processes that include Oxido-reduction processes, but do not consider polluting gases as Sulfurous Anhydride (S0 ₂ ) producing a negative environmental impact. It is therefore desirable to have a plant that is fully concerned with the process, finally eliminating gases that are not harmful to the population and their environment.

Roasting is a preparatory operation for pyrometallurgical-type minerals. In its oxidizing form, it is used to transform metallic mineral sulphides into oxides and / or sulfates, by reaction with oxygen in the air at temperatures between 500 and 900 ° C, facilitating extraction by both methods. The corresponding chemical-physical system is composed of: metal, sulfur and oxygen (Me-SO), and supports a maximum of five phases in equilibrium. When operating at constant temperature they are reduced to four. Three are combinations of the metal, its sulphide, its oxide and its sulfate, and the fourth is made up of a mixture of gases subjected to an external pressure of 1atm. When only two condensed phases coexist with the gas, the system, under isothermal conditions, has a degree of freedom and the equilibrium lines are representable in the two-dimensional coordinate plane. The graphic study of the equilibrium of these ternary systems with a restriction is carried out using the Kellogg- isothermal diagram. Ingraham. The industrial operation is carried out in the presence of atmospheric air and at temperatures between 500 and 900 ° C, which, being higher than that of ignition or self-priming of the reaction, do not exceed the softening point of the load. The reactions are exothermic, using part of the heat generated to preheat the charge and the air, recovering the surplus outside the reactor, normally in steam generation. Gases rich in sulfur dioxide (SO2) are used in the production of sulfuric acid. The most important is the balance MeS-MeO and also MeS-MeS0 ₄ , for which, taking as a function of balance the partial pressure of: sulfur dioxide (SO2), and as a variable the partial pressure of oxygen (O2).

Roasting consists of changing the chemical composition of a metallic mineral by reaction at high temperature, but without changing its solid state, with the gaseous substances in the furnace's atmosphere. Roasting, like calcination, is an operation of a chemical nature but, unlike this, it is not intended to eliminate inert matter but only to transform it, its effects on the metallic concentration of ores are few. Roasting is a preparation applicable to both pyrometallurgical and hydrometallurgical extraction, since its purposes are diverse depending on the nature of the mineral: oxides, sulfides, etc., and the gaseous reagent used: oxygen, carbon oxide, chlorides, being able to distinguish, depending on the latter, in three basic types: oxidizing, reducing, and chlorinating, of which the most characteristic is the first, carried out on sulphides in the presence of air, which corresponds to the strict concept of the term. The oxidizing roasting can be carried out under the modality of death, or complete, and partial, and the latter can be sulfating or non-sulfating. In roasting to death, the sulfide is completely oxidized to facilitate its subsequent reduction by carbon. In the non-sulphating partial, the sulfur content is decreased to later be able to form a molten phase of sulphides or matte that concentrates the metal; in the sulfant, a part of the sulfur remains as sulfate, to make it soluble in aqueous media.

Chemical-physical model of oxidative roasting. The oxidative roasting pattern of a metal sulfide, at the temperature: T (K), can be expressed by the following physical chemical reaction:

MeS (s) + 3/20 ₂ (g) = MeO (s) + S0 ₂ (g); DH (T); AG (T)

As in the cases previously studied, the enthalpy variation of this reaction at temperature T can be made by adding the formation heats in standard conditions of oxide and sulfide, the sensible heat of the system between 298 ° K and T (K), given by its equivalent specific heat: (Cp), according to the equation:

DH = DH ° + í ^T ₂₉₈ (Cp) S dT and if we call: K to the quotient: PS0 ₂ / P0 ₂ ^3/2 , it is verified:

AG (T) = RT InK / Keq Keq being the equilibrium constant for temperature: T (K).

The above expression gives us the roasting potential of the reactor at temperature T and any partial pressure P0 ₂ and PS0 ₂ . The analysis of the oxidative roasting conditions is carried out with the help of the isothermal diagram of areas of stability, Kellog-Ingraham system (Me-SO). To toast to death without forming sulfates, work must be done so that the equilibrium line between MeO and MeS0, which moves parallel to itself away from the origin of coordinates with increasing temperature, does not cross the line of composition of the gas at atmospheric pressure . Non-sulfating partial oxidative roasting is controlled by regulating the amount of access air to the reactor and the residence time of the charge in it.

Technological model of roasting.

Unlike drying and calcination, roasting is an exothermic operation that requires, for its autogenous development, that the charge reaches the ignition temperature in its reaction zone. The operation proceeds in countercurrent of mineral and gases in such a way that the metallic sulphide: MeS, accompanied by a gangue of other sulphides, generally pyrite and various silicates, gradually heats up as it moves through the reactor from its entrance through the upper part of the rear cylinder head and makes contact with the combustion and roasting gases that in the opposite direction run through the furnace from the front cylinder head to the rear cylinder, in this way the reaction zone until reaching the ignition point is reached at an intermediate point of the reactor , which causes the toasted ore (gangue) to move away from the reaction zone, cooling with the air that enters from the outside, through the discharge opening of this material.

The temperature: T’f, outlet of the solids, and Tf, of the gases are different.

DH (MeS MeO) = AH (MeO + G) (298 Tf) + AHS0 ₂ (298 T'f) + q The start or priming of the operation requires external input of heat, providing the reactor with the necessary elements for this purpose. The temperatures are regulated so that they do not excessively exceed the ignition temperature or fall below it, graduating the air supply or recycling or extracting sensible heat. The heat balance: q, of the operation varies with the nature of the sulfide, the richness of the ore, and its pyritic content, being able to recover to produce high pressure steam in the reactor itself or outside it. In the diagram of the thermal balance (Sankey) shown below, it can be seen from the operation that the useful heat or roasting enthalpy appears here as input given the exothermicity of the operation. From a thermal point of view, the reactor works as a heat generator used in the production of steam.

Energy Energy Lost Sensitive Heat Energy Lost

Chemistry transferred to _j_ Termicas -) - de Gases

due to fuel inefficiencies * "^ the Combustion Charge

Thermal

Kinetics of oxidative roasting.

The sulfides with the highest degree of sulfidation, such as pyrite: FeS2, are calcined, losing a sulfur atom that is released as steam from inside the grains, and the stable sulfur atom is removed by countercurrent diffusion of sulfur (S ) and oxygen (O), the first towards the exterior and the second towards the interior of the particle; the mechanism can be explained considering that both atoms, of similar physical characteristics, substitute each other in the crystal lattice, according to the reaction: MeS + O = MeO + S (Kelloogg-Ingrahamk-1 Roasting Diagrams. José María Palacios de Liñán. 11 / October 2011).

This background clearly reinforces the importance of very well controlling the process temperature and the oxygen contributions to the mineral roasting chamber.

Lead Concentrate Foundry. The currently most used method is the reduction of the sinter of lead oxide, which in turn is produced by sintering roasting of lead concentrates (galena), mixed with fine recycled sinter and lead sulfate, among others, in sintering. The purpose of this stage is to remove the sulfur from the concentrate as Sulphurous Anhydride (SO2) and to form an appropriate solid mass to load in the reduction furnace. Sintering of lead concentrate in sinter machines (machines

Dwight-Lloyd) proceeds at 800-850 ° C and the main reaction is the oxidation of the galena to Lead Oxide (PbO) with generation of Sulphurous anhydride (S0 ₂ ) according to:

The reaction is maintained at 800-850 ° C by diluting the charge with recirculated sinter fines since the melting point of Oxide and Lead (PbO) is 886 ° C and the

Lead Sulfide (PbS) at 1119 ° C.

The sinter contains 40-50% Pb, 1-10% Zn, 1-2% S, 8-10% Si02, 5-8% CaO and 12-15% Fe203. This is crushed and harneanea to have a load of -37 + 1/4 "for the next stage of reduction with coal.

The reduction of lead oxide II (PbO) with carbon (coke) is a thermodynamically very simple process and can be carried out even at temperatures between 400-450 ° C. However, due to the significant presence of zinc (Zn) and other components (CaO, S1O2 and Fe203), it is necessary to have a fluid slag, which requires operating at 1000 ° C. Due to the problems that zinc presents, a more universal process was developed for these concentrates (Imperial Smelting Process, ISP) which allows the production of both lead and zinc. (Lead Metallurgy, Seba Rivano Villagra .Scribd, March 19, 2013)

From this background it follows that in order to obtain Lead Oxide (PbO) from sulfur derivatives, it is necessary to work at temperatures above 800 ° C and for the process of obtaining metallic lead, much higher temperatures must be used, close to 1000 ° C .depending on the components of the slag that accompany the product to be reduced.

A patent published in 1985 describes a method of producing metallic lead, from lead-containing starting materials, by melting the starting materials under oxidation conditions and reducing the resulting oxidized melt, characterized by reducing the melt with agent reducing solid carbonaceous in the melt and ensuring that the carbonate-containing solid material is present in the melt along with the reducing agent. (ES8602957, 11-16-1985, Prodn. Of metallic lead from lead-contg starting materials, BOLIDEN AB).

Basically this background describes an optimized process to obtain Lead, by oxidation of the mineral and then reduction with the help of carbonates, which must be added to the molten material. In a patent published in 1995, a process for obtaining arsenic trioxide, of more than 98% purity, is described. The theoretical basis of this invention is based on the lower constant of the solubility product of antimony trioxide (Sb ₂ C> 3 ₎ with respect to Arsenic trioxide (AS2O3), as well as the adequate adjustment of the solid-liquid ratio and the acidity of the medium; aspects that preferably favor the hydrolysis of the antimony oxychlorinated complexes, which causes their separation from the solution, the arsenic remaining in it.

The leaching of arsenic wastes with NaOH solution makes it possible to concentrate the precious metals in the solid residue and originates a new residual: an alkaline solution rich in arsenic and antimony, from which the antimony is separated by preferentially favoring the displacement of the equilibria of antimony (III) trioxide formation, obtaining in this way a solution with a high ratio of Arsenic (As): Antimony (Sb) from which Arsenic trioxide (AS ₂ 0 ₃ ) crystallizes

The procedure object of the patent consists of diluting the alkaline solution, which contains arsenic and antimony, with acid with HCI of concentration 4.5 to 5.5 mol / L, until causing the separation of more than 94 % of the latter element, by filtration, this solid constituting an antimony concentrate. By evaporating the water from the filtrate, the antimony trioxide crystals (Sb ₂ C> 3) are obtained. (CU22289, 31-01-1995, Procedure for obtaining arsenic trioxide from alkaline liquors with a high antimony-content, UNIV LA HABANA, Bustely Sánchez María de la Libertad)

From this background it is clear how difficult it is to separate antimony trioxide (Sb ₂ 03) from arsenic trioxide (As ₂ Ü3), even with leaching of the minerals that contain them. Therefore, it is relevant to have a procedure that allows to obtain Antimony Trioxide (Sb ₂ 0 ₃ ) and Arsenic Trioxide (As ₂ 0 ₃ ) of Commercial quality.

DESCRIPTION OF THE INVENTION

A more detailed description of the industrial plant (Fig. 1) is presented below, which will basically consist of the following two phases of a series of equipment that account for pyrometallurgical processes: First phase: Equipment and processes involved in the volatilization and formation of the Solid Mixture of Products of Interest.

This first phase consists of equipment for a controlled oxidizing roasting process, of sulphided minerals at temperatures between 480 and 520 ° C, in rotary kilns inclined longitudinally (between the rear and front cylinder heads of them) and lined internally with refractories , and lifters installed between the rear cylinder head and half its length, which allow the load to be lifted to the highest point of the furnace and so that it spreads in its vertical fall on the gas stream. The supply of the mineral to the furnaces is continuous entering them through the upper part of the rear cylinder head of these, against the current of the combustion gases and the induced air that enter through the front cylinder head of these. it must be regulated to ensure the adequate oxidation of Antimony (Sb) and Arsenic (As) until the formation of its trioxides, and the consequent volatilization thereof, as well as to ensure the direct volatilization of the fed Galena (PbS) and avoid the formation de Cervantina (Sb ₂ 0 ₄ ). These volatile products will evacuate from the furnace together with the combustion gases and the sulfur dioxide (SO2) formed from the oxidation of the Antimony (Sb) and Arsenic (As) sulfides, together with the mineral gangue particles carried by the gas stream.

The heat required to reach the process operating temperature, between 480 and 520 ° C, in the kiln exhaust gases, is generated with a natural gas burner installed in the center of the front cylinder head of the kiln inserted in the Corresponding combustion chamber, allowing a quantity of heat that makes it possible to generate a temperature greater than 500 ° C at the entrance of the furnace, overheating the outgoing calcined material and ensuring the exit temperature of the furnace with the volatilized products of interest. The mineral material that does not volatilize will remain inside the furnace, which is mainly made up of a mineral gangue and that will be continuously evacuated by the discharge of the furnace located in the lower area of its previous cylinder head, and whose runoff is generated as a result of the vertical inclination that the furnace presents between its rear cylinder head and the previous one. The calcined gangue leaving the furnace is transported to cooling wells, three in total, in which the material is deposited for its subsequent cooling and removal to its final destination, dump or return to the place of origin, the deposit. The three wells will rotate, fulfilling a specific function, either of reception, cooling or removal of the material. Mineralogical composition of the mineral to be processed, the analysis of the characteristics of minerals that are generally processed to obtain antimony trioxide in South America has been taken into account, for this purpose, the antecedents published by various mining companies have been studied:

The mineral generally has the following generic composition:

• Antimonite> 50%

• Galena (PbS) <0.15%

• Arsenopyrite <2%

• Silica (S1O2) is mainly the gangue

• Traces of mercury

From specific studies, there is an initial history of the characteristics of the mineral.

DETAILED DESCRIPTION OF THE INVENTION

The received mineral will be treated in three identical lines of operation (Plant), as detailed in the flow diagram that is part of the drawings in Fig. 1.

First Phase: Equipment for the Volatilization and formation of the Mix of the Products of Interest.

This first phase consists of equipment for a controlled oxidizing roasting process of sulphided minerals at temperatures between 480 and 520 ° C, in rotary kilns (2) inclined longitudinally (between the rear and front cylinder heads of them) and lined internally with refractories, and lifters installed between the rear cylinder head and half its length, which allow the load to be lifted to the highest point of the furnace, so that it spreads in its vertical fall on the gas stream.

Once the combustion gases, sulfur dioxide and volatile gases leave the furnace at temperatures between 480 and 520 ° C, they enter an Expansion Chamber (3) or Gas Sedimentation whose function is to reduce the initial velocity of the entrained particles by the gas stream, eliminating the larger particles (> 50 pm) and abrasives, as well as lowering the temperature of the outgoing gases. This chamber has a lower section of sloping walls that converge to a drag chain, which recovers the dust particles settled in it. The chamber is designed to cause a temperature drop of 100 ° C. Based on the separation criteria, for the collection of particles, the gravitational force is used as the principle of operation, allowing sedimentation of particulate material in sizes from 20 to 50 pm or larger.

The sizing of equipment that enables this objective is closely linked to the knowledge of the nature of the movement of a particle that moves within a fluid. The accepted model is the one proposed by Stokes known as Stokes' law

In essence, a sedimentation chamber is a container with an inlet on one side and an outlet located on the opposite side frontally or on top of it, generally of rectangular geometry its central part, where a gas stream is allowed to expand in such a way In this way, the velocity of the gas within it decreases considerably, allowing the action of gravity to settle the particles it carries. The cross section of the equipment is much greater than that of the pipeline that approaches it so that the gas can expand and consequently slow down. Hoppers are used that collect the separated solid in the lower part of the same, from where it is removed by means of a drag chain to be sent to its next destination. It should be noted that the dust collection system is completely well sealed to prevent air from entering through it, which can increase turbulence in the equipment and consequently re-incorporate the removed particles back into the stream. There are two fundamental types of construction models: that of baffle plates or Howard's model and that of expansion chambers.

In essence, a sedimentation chamber is a container with an inlet on one side and an outlet located on the opposite side frontally or on top of it, generally of rectangular geometry its central part, where a gas stream is allowed to expand in such a way In this way, the velocity of the gas within it decreases considerably, allowing the action of gravity to settle the particles it carries. The cross section of the equipment is much greater than that of the pipeline that approaches it so that the gas can expand and consequently slow down. Hoppers are used that collect the solid separated at the bottom of it, from where it is removed by means of a drag chain to be sent to its next destination. There are two types of construction models: that of baffle plates or Howard's model and that of expansion chambers.

The operation of the cyclone in this process is applied to those mineral particles that remain in the gas stream (preferably gangue) and that were not recovered in the previous process, with an approximate diameter of less than 20pm.

The cyclone is essentially a sedimentation chamber in which gravitational acceleration is replaced by centrifugal acceleration. Cyclones are one of the least expensive means of dust collection, both from an operational and investment point of view. These are basically simple constructions that do not have moving parts, which facilitates maintenance operations; They can be made from a wide range of materials and can be designed for high temperatures (up to 1,000 ° C) and operating pressures. Cyclones are suitable for separating particles with diameters greater than 5 pm; although much smaller particles, in certain cases, can be separated. Cyclones have higher efficiencies than the gravitational sedimentation chamber, and lower efficiencies than pan filters, scrubbers, and electrostatic precipitators. The centrifugal force generated by the gyrations of the gas within the cyclone can be much greater than the gravitational force, since the centrifugal force varies in magnitude depending on the speed of the gas's rotation and the radius of gyration. Theoretically, increasing the speed of entry to the cyclone would imply an increase in the centrifugal force and, therefore, an increase in efficiency; however, very high input speeds generate the resuspension of particulate material from the internal walls of the cyclone, which decreases the efficiency of the cyclone; Additionally, increasing the input speed implies higher energy consumption.

According to the selection of the cyclone (High efficiency), it is expected to achieve full recovery of solid particles still present at the entrance of this equipment, thus it is expected that the outgoing gases from the cyclone at 350 ° C are clean of solid particles bargain of the first stage.

Given the temperature reached in the gases at the cyclone outlet, 350 ° C, they will enter a radiative cooling system (4) similar to a coil consisting of vertical columns joined to each other, through which the gas circulates dissipating its latent heat by contacting the walls of the equipment, a system that cools releasing into the surrounding atmosphere a significant amount of heat by radiation and convection. The duct that constitutes the radiative cooling system must be dimensioned for high conduction velocity in order to avoid sedimentation of particles inside, which will be generated by solidification of the volatile products upon reaching their dew point due to the fact that their length a decrease in gas temperature of at least 250 ° C will be caused, a range in which the volatile compounds present (AS ₂ O ₃ , Sb ₂ 0 ₃ and PbO) condense. The high speed required and downstream pressure drop in the gas handling system is compensated by the inclusion of a Booster extractor at the inlet of the radiative cooler. To ensure that the volatilized Galena oxidizes and solidifies as Lead Oxide (PbO) in the following steps, air will be induced through a controlled opening valve installed at the inlet of the radiative cooling system. The outgoing gases of the Radiative Cooler containing the condensed particles of the oxides of Arsenic (As), Antimony (Sb) and Lead (Pb) volatilized in the roasting, enter a Bag Filter (5) where they will be recovered when trapped by the filter fabrics installed inside, fabrics that only allow the gases to be treated to pass and evacuate from the plant. The mixture of solid particles of the interesting products, Antimony Trioxide (Sb ₂ 0 ₃ ), Trapped Arsenic Trioxide (AS ₂ O ₃ ) and Oxidized Lead (PbO), are removed from the sleeves by an intermittent vibration mechanism, as well as by the emission of pressurized air pulses, which cause them to come off. The obtained product mixture is pneumatically transported to the feeding system of the next phase of the process.

In the bag filter (5), the dust present in the gases is separated by passing this gaseous current through filtering tissues, which retain the solid particles present. The operation basically consists of forcing the passage of the gas stream through the filter medium (tissue), whose mission is to retain the dust transported by the gas, accumulating on it and generating a layer that favors the efficiency of the filtration of the smaller particles. As the filter is loaded with particles externally, the pressure drop of the gas through it increases. Therefore, there comes a time when it is necessary to detach the accumulated dust layer to recover the functionality of the equipment, this action being carried out by means of pressurized air pulses in the opposite direction to the passage of gas. Filter surfaces are bag-shaped or sleeves inserted into cells or filter compartments neatly in a number of 10 or more units. The filter is made up of several cells in operation or sealed. It is a device that has high purification yields, even for very fine particles, whose usual yield values are from 99% to 99.9%, for sizes in the sub-micron range up to several hundred microns. Bearing in mind that they cannot operate in humid environments or near the dew point of the gas stream, such as treating adhesive or binder powders, since there is a risk of clogging of the fabric as the wet dust adheres to them after cleaning. Regarding its design, the most important data is the gas flow to be treated, marking the size of the equipment and, consequently, the investment cost. The main design variable of the bag filter is the A / C ratio (actual gas flow and the collection surface) or filtration speed expressed in m / s, and the other important operating parameter is the total pressure drop in the equipment, which determines the energy need to supply gas through the equipment. To deliver clean flue gases to the environment, outgoing gases from the bag filter containing sulfur dioxide (SO2) will enter a packed Gas Cleaning Tower (7) (Gas Washers) where counter current spraying of lime milk 10% dilution on the gas that rises through the packaging material neutralizes S02, generating Plaster (CaS0 ₃ ) diluted in water, which is removed from the system for final disposal. The clean gas leaving the tower is propelled by the effect of an extractor to the Chimney (8) for gas evacuation from the Plant.

Gas scrubbers are gas-liquid contact equipment, in which the liquid acts as a collector of polluting compounds in the gas stream. With the proper design, removal efficiencies of 99% are achieved.

These teams are based on the phenomenon of gas absorption in the liquid, so its operation depends on achieving intimate contact between the two. To achieve such contact, the exposure surfaces of the gas and / or liquid must be maximized, which in packed towers occurs by dividing the liquid into an infinity of thin films of the same, at low speed, through the packaging.

The clean gas outgoing from the washing tower, consisting mainly of combustion gases and water vapor, is transported and driven by the action of the Extractor that shares and supports the handling of gases from the operational cooling system to their evacuation through the Chimney. . The unique chimney of the plant has the function of evacuating the clean gases from the process and that are emitted at the height that the establish environmental regulations, ensuring the minimum environmental impact on the environment and the surrounding community.

Second Phase: Equipment for the Separation of Commercial Products (Fig. 1)

This Second Phase of the process is carried out in several teams, starting in a double chamber fixed furnace (reverberation type) with burners (Figs. 2 and 3), one for each chamber inclined towards the floor of the crucibles to avoid dragging of Fine powder (10) that characterizes the mixture of Antimony (Sb), Arsenic (As) and Lead (Pb) oxides, recovered in the Sleeve Filter (5) of the previous stage. As in the previous stage, the temperature of the process in the oven is between 480 and 520 ° C, in order to generate volatilization of the products of interest, Antimony Trioxide (Sb ₂ 0 ₃ ) and Arsenic Trioxide ( AS ₂ O ₃ ) that are separated according to their different solidification temperatures in equipment other than the Gas Management system, as shown in Fig. 1 below, where Sb ₂ C> ₃ is recovered in a Radiative Cooling (CER) (12) that operates at the 350 ° C level and the AS ₂ O ₃ at the end of the system in the Sleeve Filter (FM) (14) at a temperature below 100 ° C. Given the condition that Lead oxide (PbO) does not volatilize at the indicated process temperature, this compound remains solid inside the furnace. For the recovery of lead (Pb) as a commercial product from inside the furnace, a reduction process must be carried out with coal coke that transforms it into liquid metallic Pb at the process temperature, between 480 and 520 ° C.

For these reasons and different atmosphere conditions required for products for commercial recovery, this 2nd phase is performed in a dual - chamber furnace (Fig.2 and 3) in two sub-stages, which in Fig 1 are described, and we can detail it as follows:

Sub-Stage of Volatilization of Sb and As Trioxides and accumulation of PbO inside the furnace, with a controlled atmosphere to maintain the chemical characteristics of the Sb ₂ 0 ₃ and A _S2 O ₃ volatilized and ensure its recovery in terms of quality in the CER and FM respectively. Once the optimal volume of PbO that is compatible with the capacity of the furnace is completed, the next sub-stage is carried out.

Sub-Stage of PbO Reduction and Obtaining Liquid Pb, reducing the accumulated PbO in the previous sub-stage in the corresponding furnace chamber, with a reducer, carbon coke, which is added to the crucible to produce the reduction of the oxide to metallic Pb, which between 480 and 520 ° C liquefies and can be extracted from the furnace, towards its ingot generation molding system marketable.

In the formation of equipment for the gas handling system in this phase, a Radiative Expansion Chamber (12) (Fig. 3 and 4) is used, whose function is to recover the Condensed Antimony Trioxide from the gas flow.

Process mass balance

In this particular case, the content of the mineral fed to the process has been conditioned to carry out the balance, complying with the following characteristics:

• Antimony, 30%.

• Lead, 10%.

• Arsenic, 4%.

• Mineral humidity, 7%.

Starting from a mineral with these characteristics, 300 dry metric tons (TMS) of antimony trioxide are generated monthly, with an efficiency in each of the process stages of 95%. Conciling the characteristics of the region's antimony minerals and the conditions of mineralogy and trioxide production, the feeder mineral of the process would be composed according to what is shown in Table 1, where the mass of each component is expressed in dry Kg per hour. In this way, taking one hour of production as the basis for calculation, the roaster is fed 1,309.2 kg / h of ore, with 7% humidity. It is considered that 100% of the gangue present in the mineral corresponds to silica (S1O2)

Table 1: Composition of the feeder mineral of the process, by elements and mineralogical species.

Fig. 1 shows the diagrams of the process and equipment (Plant) for obtaining antimony trioxide, divided into two phases. In the first one, the volatilization of oxides, cooling and cleaning of oxidation gases are carried out. The second phase divided into two sub-stages per production batch, corresponds to the separation of antimony, arsenic and lead oxides, reduction of the latter liquid lead oxide (Pb) and cleaning of reduction gases. The final products of the process are, arsenic trioxide, Pb in ingots and antimony trioxide, as the main product. The chemical reactions of interest that are carried out in the first phase of the process are:

2Sb ₂ S ₂ +90 ₂ 2Sb ₂ 0 ₂ + 6S0 ₂ (1)

9Sb ₂ 0 ₄ + Sb ₂ S ₂ b ₂ 0 ₂ + 3S0 ₂ (2)

Sb ₂₂ Pb ₉ S ₄₂ +630 ₂ ^ ^ Sb ₂ 0 _^ + 9Pb0 + 42S0 ₂ (3)

2PbS + 30 ₂ 2Pb0 + 2S0 ₂ (4)

2FeAsS + 50 ₂ Fe ₂ 0 ₂ + As ₂ 0 ₂ + 2S0 ₂ (5)

2As ₂ S ₂ +90 ₂ 2As ₂ 0z + eS0 ₂ (6)

2As ₂ S ₂ +90 ₂ -> AS ₄ 0Q + 6S0 ₂ (7)

AS ₄ S ₄ +10 ₂ -> 2AS ₂ 0 ₂ + 4S0 ₂ (8)

AS4S ₄ ⁺ 70 ₂ ®AS ₄ 0 _I ¡+ 4S0 ₂ (9)

As in any process involving chemical reactions, the probability of each one occurring is conditioned by various factors, such as: temperature and pressure, among others. However, to perform the mass balance, the reactions listed above are mainly considered. The mass balance of the process is carried out in the main equipment, where the aforementioned chemical reactions are carried out and the energy balance is carried out in the same way. Mass balance in the toaster. As mentioned above, the feed to the toaster corresponds to 5,219.6 kg / hr of ore that is brought to a temperature between 480 and 520 ° C, by means of a natural gas or diesel oil burner, depending on the facilities of the region where the technology in question is installed. Heat losses in the main equipment are considered close to 10% and the efficiency of the fuel used is assumed to be close to 98%.

Table 2 shows the mass of the main roaster output products, considering the three roasting lines as one. The oxidation of the galena (PbS) is carried out by blowing the necessary air downstream of the toaster, to guarantee its oxidation outside this equipment, thus avoiding losses of this oxide in the expansion chamber and in the cyclone.

Table 2: Toaster output products.

The detail of other inlets and outlets of the roaster flows are specified in the corresponding global balance of the process. To calculate the flow of volatile substances that leave the expansion chamber, it is considered that iron oxide y (Fe ₂ 03) and arsenic oxide (As ₄ C> ₆ ), will be dragged with the gangue and sent to the cooling wells.

Adding the masses of the galena and the antimony and arsenic oxides, and assuming that this total mass behaves like Sulfur Dioxide (SO ₂ ), the outflow towards the expansion chamber is calculated, under normal conditions. In this way, the sum of volatile gases and dusts leaving towards the expansion chamber, would be a total of 4587.3 Nm ³ / h. Table 3 shows the detail of the flows at the entrance to the expansion chamber.

Table 3 Gas and volatiles flow to the expansion chamber.

The fuel flow required for roasting (diesel oil) is 278.8 l / h and the air required for combustion is 2,755.8 Nm ³ / h. On the other hand, the air for oxidation of the mineral in the roaster is 865.0 Nm ³ / h. To calculate the flow of trioxides Arsenic and Antimony and Galena volatilized in this stage, they are assimilated to Air, in terms of the volume occupied. In this case, the mass to volatilize is 608 kg / h. Volatile flux is calculated under normal conditions. Galena oxidation, as specified above, galena oxidation is performed outside the roaster as indicated in Fig. 1 and the chemical reactions associated with such oxidation are numbers (3) and (4), listed previously. The corresponding material balance indicates that the air flow required for this purpose is 123.1 Nm ³ / h.

Mass balance in the washing tower Gas cleaning

The gases resulting from the first stage of the process, reaction and combustion gases, are directed to a washing tower, in which 10% w / w lime milk is contacted, to generate conditioned gases to comply with the corresponding regulations. and be eliminated into the environment through a fireplace. Table 4 shows the flow of gases sent to the washing tower, generated in the first stage of the process. Abatement of Sulfur Dioxide (SO2) in the washing tower The chemical reaction corresponding to the abatement of Sulfur Dioxide (SO2) in the washing tower is as follows:

S0 ₂ (g) + Ca (0H) ₂ (s) ®CaS0 _z * MH ₂ 0s +12 H ₂ 0 (l) (10)

To knock down the 252.9 Nm ³ / h of sulfur dioxide entering the tower, 834.1 kg / h of Cal will be required and 1,454 kg / h of CaSO _z * \ 2H ₂ Oy 101, 4kg / h of liquid water.

Table 4: Flow of inlet gases to the Washing Tower.

Mass balance in the second phase

As mentioned above, the second phase of the process is carried out in two cycled sub-phases for each charge introduced into one of the furnace chambers, where it will accumulate, the sufficient amount of PbO that generates the adequate volume of Pb metallic to be continuously molded. Given the dimensions of the crucibles of the double chamber furnace, the time required in the first sub phase is estimated at two days to start the second sub phase. The first of these, which is carried out at a temperature between 480 and 520 ° C, in a fixed reverberatory type furnace with burners in the vault, corresponds to the volatilization of the Arsenic and Antimony trioxides that made up the mixture of oxides together with PbO and recovered in the first stage bag filters. Lead oxide, which does not volatilize, remains in the reactor and accumulates to be reduced with coke in the second mineral charge sub-stage. Sb ₂ 0 ₃ , one of the final products of the process, is captured in a Radiative Cooling Chamber because its condensation occurs between 350 and 400 ° C, and reaches 418.0 kg / hr, which corresponds to a monthly production of 300 tons.

AS2O3, 61, 1 kg / h, passes to the bag filter, where it is captured, because its condensation occurs below 280 ° C. The monthly production of this product is 44 tons. The required fuel, diesel oil, to raise the temperature to 500 ° C, is 287.8 Nm ³ / hr and the air required for this purpose is 2,840.6 NrrvVh. The exhaust gases, product of the combustion of natural gas in the reactor are summarized in Table 5.

Table 5: Exit gases from the first ore-charging sub-phase reactor.

To calculate the flow of volatilized trioxides in this sub-phase, it is considered that lead oxide is retained inside the reactor and that both antimony trioxide and arsenic trioxide behave as Air in terms of the volume occupied . In this case, the mass to volatilize is 479.1 kg / h. Volatile flux is calculated under normal conditions. In this way, the volatile powders leaving the reactor reach 372.8 Nm ³ / h and the sum of gases and volatile powders leaving the first mineral charge sub-phase will total 454.5 Nm ³ / h.

Lead oxide reduction

The lead oxide retained in the reactor is reduced with Coke Coal, according to the following chemical reactions.

2Pb0 + C 2Pb + C0 ₂ (11)

PbO + C Pb + CO (12)

Pb0 + C0 Pb + C0 ₂ (13)

Thus, to reduce 124.6 kg / h of PbO, the amount of coke required is 3.4 kg / h.

The Pb product of said reduction is 115.7 kg / h, so it will be necessary to accumulate the metal inside the oven, to achieve an adequate bleeding height. It is estimated that after 2 days of accumulation, the optimal height of approximately 40.8 cm is generated, considering that the dimensions of each crucible in the furnace is 1.2 m ² (0.6 x 2.0 m ² ) of basal area and that the density of Pb is 11, 35 gr / cm ³ . The gases generated in the Lead oxide reduction process are negligible compared to those required to maintain the furnace temperature between 480 and 520 ° C and the Lead oxide that accumulates inside, along with carrying out the volatilization of Antimony and Arsenic trioxides, even more so if the only contribution of gas is due to the formation of carbon dioxide (CO2), at a rate of 6.36 Nm / h during this process, representing 0.2% of the total gas outgoing from the oven. The background found supports that the recommended process and furnace for the transformation of antimonite to Sb Trioxide is an oxidative but controlled roasting in rotary kilns, so that they only ensure the generation of volatile Sb and As trioxides at the process temperature. (between 480 and 520 ° C) and that the non-oxidized Galena (PbS) volatilizes and incorporates into the gases leaving the furnace, products of combustion and sulphurous anhydride (SO2) resulting from the oxidation of Antimony sulphides ( Sb) and Arsenic (As).

The volatile gas mixture generated in the roasting process (in a First Phase of the Obtaining process) undergoes different cooling processes to obtain a solidified mixture of it at the end of the gas handling system (Sb203, AS2O3 and PbO) .

The oxidation of Lead Sulfide (PbS) to Lead Oxide (PbO) is induced by injecting air into the gas handling system, through a controlled valve installed at the inlet of one of the components of the cooling system.

In this way, the condensed mixture at the end of this system is made up of Antimony Trioxides (Sb) and Arsenic (As) and Lead oxide (Pb) and is recovered in a Bag Filter that operates below 100 ° C.

To deliver clean flue gases to the environment, the outgoing gases from the bag filter containing sulfur dioxide (SO2) enter a packed gas scrubber where by countercurrent spraying of 10% dilution lime milk onto the Gas that rises through the packaging material neutralizes the sulfur dioxide (SO2) generating Plaster (CaS04) diluted in water, which is removed from the system for final disposal.

The non-volatile material of the mineral, the calcined mineral gangue is removed from the furnace, it is transported, together with the powders dragged by the outgoing gases from said equipment and recovered from the gas handling system, to cooling wells, three in total in that the material is deposited for its subsequent cooling and removal to its final destination, dump or return to the place of origin, the deposit. The three wells will rotate, fulfilling a specific function of receiving, cooling or removing the material once it has cooled.

In accordance with the aforementioned background and oriented to lead metallurgy, it is supported that in order to carry out the separation in commercial products (trioxides of WO 2020/132752 PCT / CL20, *, 000045

Antimony and Arsenic) and generation of metallic Lead, the solidified mixture of oxides obtained at the end of the first phase of the process, undergoes a second phase with a fixed double chamber oven similar to a reverberation, which inhibit dust entrainment and maintain the oven temperature between 480 and 520 ° C, where by taking advantage of the physical properties inherent in the products to be obtained, they are separated and obtained as commercial products. To do this, the process at this stage is subdivided into two production batch operations, as follows:

Volatilization of Antimony (Sb) and Arsenic (As) Trioxides and separate condensation of them, in the gas handling system, given their different solidification temperature, first removing the Antimony Trioxide (Sb203) in the Radiative Cooling Chamber , which operates between 350 and 300 ° C and subsequently the Arsenic Trioxide ^' (As203) in a Bag Filter below 100 ° C, meanwhile the Oxidized Lead (PbO) accumulates inside the furnace for its subsequent treatment in the Next Production Lot. Reduction of the Lead Oxide (PbO) accumulated at the end of each charge cycle introduced into one of the furnace chambers, for this, coking coal or other similar fuel is added on this material in order to induce its transformation to metallic Lead (Pb) , liquid at the process temperature (between 480 and 520 ° C), a fact that once the liquid Lead (Pb) obtained is specified, it is extracted from the oven for molding.

Fig. 1 shows with a block diagram the Plant for obtaining antimony trioxide, arsenic trioxide and metallic lead.

First phase of Volatilization and Formation of Oxide Mixture (1-9).

1. Antimonite mineral feeding system, which is characterized by being made up of sulfur minerals predominantly Antimony, Arsenic and Lead, whose average contents fluctuate between 20-30% Antimony (Sb), 2-4% Arsenic ( As) and 5-10% of Lead (Pb), which is fed from the storage field to the feed hoppers of the Toasters through a transport circuit consisting of three conveyor belts, to raise the mineral load from the level from the storage field to the horizontal belt feeding mailbox that distributes the mineral to the feeding hoppers to each Toaster, from where it is continuously extracted by means of a channel-type endless screw being transferred to a second screw perpendicular to the previous one, tubular that deposits the load inside the toaster adequately away from its rear end and on the refractory lining and the lifters inside the Toaster.

Regulated oxidizing roasting in Rotary Homo (Toaster), at a controlled temperature between 480 and 520 ° C of the sulphided mineral, in order to generate trioxides of Antimony and Arsenic and consequently its volatilization together with the present galena (PbS). The calcined material that does not volatilize mostly mineral gangue, is removed from the process so it must drain out of the Toaster, which is why this equipment has a longitudinal inclination of 2%, from the rear head to the previous one, instead where the combustion burner is installed, which generates the gases that allow maintaining the temperature between 480 and 520 ° C inside the Toaster, and that circulate against the movement of the fed mineral. In order to transfer the heat from the gases to the mineral and facilitate the volatilization of the products of interest in the rotary kiln, it has load lifters inserted in the first third of the length of the kiln from the rear end where the mineral enters , elements that allow the material to be removed and lifted to a high interior point, falling from there and spreading over the gas stream. The air to generate the oxidation of Antimony and Arsenic is induced by the draft exerted by an induced draft fan, located upstream in the Gas Management system (between the Bag Filter and the Gas Washing Tower) towards the interior of the toaster, which is why the burner head wall (above) will consist of an adequate number and size of holes, distributed symmetrically in relation to its horizontal axis, each one having a controlled valve for the regulation of the quantity of air to infiltrate in benefit of the adequate oxidation of trioxides in formation.

Once the combustion gases, sulfur dioxide and volatiles (Trioxides of

Arsenic and Antimony, and Galena) leave the Toaster at a temperature between 480 and 520 ° C, enter an Expansion or Sedimentation Chamber for gases whose function is to reduce the initial velocity of gases (less than 3 m / s) and recovering most of the particles carried by the gas stream, eliminating the largest ones (greater than 20 pm), as well as reducing the temperature of the outgoing gases. Said chamber consists of a lower section of inclined walls that discharge the recovered material to a channel-type endless screw, which collects the gangue dust particles decanted in said chamber and which also collects the gangue particles. separated from the gas flow in the cyclone that precedes it. Due to its shape and design, the Expansion Chamber allows a moderate decrease in the temperature of the gases. The dimensioning of such equipment is closely linked to the knowledge of the nature of the motion of a particle that moves within a fluid, which conforms to the model proposed by Stokes known as Stokes' law.

To ensure maximum recovery of entrained gangue dust particles, the outgoing gases flow from the Expansion Chamber goes to a second cleaning operation in a Cyclone, equipment that removes the particulate material still present in the gas stream, based on the principle of inertial impaction, as the gaseous flow loaded with particles enters tangentially into the upper cylindrical zone, taking advantage of the increased speed in its circulation and the centrifugal force generated by the rotation of gases and solid particles, the latter, due to their The heavier the weight, they will come out through the Cyclone underflow and the particle-free gases through the overflow. Given the high speed reached by the gases in the process, greater than 20 m / s, the effect of heat losses due to radiation is low, which is why it is estimated that the temperature of the gases when leaving this equipment does not present large variations .

As detailed in the previous paragraphs, the Expansion Chamber and Cyclone assembly generates a temperature decrease of around 150 ° C. Considering that the products of interest are Arsenic Trioxide (AS2O3), Antimony Trioxide (Sb2C> 3) already formed and volatilized in roasting and Lead (Pb) in the form of PbS, and that are present in the outgoing gases at 350 ° C of stage 3, said gases will be subjected to a Radiative Cooling process, which is described below. However, due to the conception of the process for obtaining metallic lead in the 2nd stage, this Galena gases must be oxidized and condensed as lead oxide (PbO), for which the air required for oxidation is induced by the action of the Induced Draft Fan through a controlled opening valve installed at the inlet of this cooling system.

Said cooling system is made up of parallel coils made up of a series of inverted U's joined together (each one constituting a branch of the system). The gas entering the equipment circulates inside it to cool down from 350 ° to less than 100 ° C, dissipating the latent heat of the gases through the walls of the coils that make up the equipment, releasing this heat through convection phenomena and mainly radiation, into the atmospheric air that surrounds it and circulates around it.

On the other hand, the duct that constitutes this cooling system must be dimensioned for a high conduction speed in order to avoid the sedimentation of particles that condense as the temperature decrease advances and the solidification of the volatile products of interest. The heat dissipation capacity according to the pipe size that according to the coil defines the length required for the decrease in the temperature of the gases pursued, which in this case is around 250 ° C.

5. Product of the temperature decrease (less than 100 ° C) generated in the gases in the previous process (Radiative Cooling), the Antimony and Arsenic Trioxides and Lead Oxide have been solidified in very fine size (powders with 95% below 3pm), which are transported together with the gases to a Sleeve Filter (FM), where they can be separated from the gas stream. The separation of the powders is generated by passing the gaseous current through filtering fabrics, called sleeves, which retain the solid particles present and the particle-free gas continues in its cleaning process, for its later evacuation through the chimney of the plant. The mixture of solid products consisting of Antimony Trioxides (Sb20 ₃ ) and Arsenic (AS2O3) powders and Pb oxide (PbO), is removed from the FM by means of a rotary valve, which discharges onto a conveyor chain (harrow) to feeding the material hopper the pneumatic transport system that moves the oxide mixture to the feed hopper 2 ^to Phase (Separation of Commercial Products).

6. induced draft fan (VTI), equipment causing the movement of the generated gases in the processes that make up the 1st phase, ie from the Rotary Kiln (Toaster) to the outlet of the baghouse and subsequently boost the outgoing gases from this equipment to a single Gas Cleaning Tower (TL) and cause the evacuation of the pollutant-free gases to the single chimney of the plant. For each line of operation processes 1 ^to required phase, it must have its respective (VTI) which should be able to generate suction (negative pressure) necessary for the transfer of the gases generated in the toaster, to finish its processing in the Bag Filter, overcoming the load losses generated by its transfer. 7. The gases generated by the formation and oxidation of the products of interest contain Sulphurous Anhydride (SO2), which must be neutralized and removed from the gas stream, an operation that is carried out in a Washing Tower, in which apply lime milk as a neutralizer, allowing the transformation of SO2 to Hydrated Gypsum (CaS0 ₄ ^* 2H ₂ 0), a compound that is collected in the liquid retention tank of said Tower. By a counter current spraying system, the 10% dilution lime slurry descends on the gas that rises through the packaging material, thus causing the neutralization of the S0 ₂ contained in it. These teams are based on the phenomenon of gas absorption in liquid, for which their operation depends on achieving intimate contact between them. To achieve such contact, the gas and / or liquid exposure surfaces must be maximized, which in packed towers occurs by dividing the liquid into an infinity of thin films of the same, low speed, through the type of packaging, in this case one inch (1 ”) Rasching rings.

8. The clean gas outgoing from the washing tower, consisting mainly of combustion gases and water vapor, is driven by the action of a VTI towards its evacuation through the single chimney that will emit the total of clean gases generated by the process, both of its Phase 1 and Phase 2 ^through at the level that establishes environmental regulations in force, ensuring minimal environmental impact on the environment and the surrounding community.

9. Like all high-temperature processes (between 480 and 520 ° C), the part of the mineral that does not volatilize, as detailed in 2, is transferred from the posterior head to the previous head of the Toaster, constituting a mineral gangue that is extracted continuously by the discharge of the Furnace located in the lower area of its previous head. Said calcined gangue together with the powders recovered from the gases in 3 (Expansion Chamber and Cyclone) will be transported to cooling wells and removal to their final destination.

Second Phase of Separation of Commercial Products (10-18)

10. A double reaction chamber fixed oven (Fig. 2 and 3) receives the mixture of solid products from its feed hopper, in which it is carried out at a temperature between 480 and 520 ° C, volatilization of Antimony trioxide (Sb ₂ 0 ₃₎ and arsenic (As ₂ 0 ₃₎ constituting the mixture of oxides generated in the 1 Phase (Sleeve Filter) and retention of the Pb oxide (PbO) that does not volatilize in it, in order to separate the volatilized products according to their different condensation temperatures in different equipment upstream in the Gas Management system of this Phase 2. The mixture of solid products transferred from the 1st ^{to the} Phase are fed into the Fixed Furnace (reverberation type) whose crucible has been divided into two equal chambers separated by an interior longitudinal wall, being joined together at the gas phase level, which they take advantage of the heat generated by two burners installed on their rear walls, from each chamber, which with an inclination of 20% and a flame of adequate length, point towards the floor of the corresponding crucible, countercurrent to the flow of gases leaving the furnace, a condition that counteract the possible drag of fine dust that characterizes the fed solids mixture. With the same intention, a vertical deflector plate is installed inside the oven, installed at a suitable distance from the oven's gas evacuation opening.

You due to different conditions required by the products for commercial recovery, this 2nd phase must be performed in cyclized form dividing operation the oven into two sub-stages, as described below:

Sub-Stage of Volatilization of Antimony (Sb) and Arsenic (As) Trioxides and accumulation of Lead Oxide (PbO) inside the furnace, with controlled atmosphere, free of oxygen to maintain the chemical characteristics of Antimony Trioxide (Sb203) and volatilized Arsenic Trioxide (AS2O3) - and ensure their recovery in terms of quality respectively. Once the optimal volume of Lead Oxide (PbO) that is compatible with the capacity of the furnace is completed, the next sub-stage is carried out.

Sub-Stage of Reduction of Lead Oxide (PbO) and molding of Liquid Lead (PbO), reducing the Lead Oxide (PbO) accumulated in the previous sub-stage, with a reducer that will be added to the furnace to produce the transformation of the oxide a lead (Pb) metal, which temperature between 480 and 520 ° C lic _ú ay can be extracted from the furnace to a molding system for forming ingots marketable.

However, bearing in mind that it is more practical and efficient to have a continuous process in the same equipment, with the characteristics indicated above, it is possible to carry out the consecutive sub-stages of the process, in a same unit and at the same time. In this way, the formation of the furnace allows the volatilization process of Antimony and Arsenic Trioxides to be carried out in one of the chambers and the process of reducing oxide to Lead (PbO) and extraction of the Metal Lead in the adjacent chamber. , bearing in mind that the sub-stage of reduction of oxide to Lead (PbO) is carried out with the direct application of the solid reducer on the PbO and the Lead generated and accumulated in the respective chamber, while in the other chamber it is developed in a The volatilization process simultaneously requires the availability of a controlled atmosphere in oxygen, a condition that is compatible with the requirement of the reducing chamber. Once the mixture of Arsenic and Antimony Oxides is volatilized in the furnace, the gases are sent to a Cyclone in order to recover the presence of particles that could have been carried away by the generated gases. The powders recovered in this equipment are reincorporated into the furnace through a transport system consisting of a refrigerated conveyor screw, which discharges into a hoist elevator which lifts the recycled load to be deposited in a second conveyor screw, which transfers the material to recycle to the oven feed hopper. The gases containing the Antimony and Arsenic trioxides are sent to the following process. Considering that the solidification of Antimony Trioxide (Sb ₂ 03) is imminent in the range of 400 to 300 ° C, the set of Radiative Expansion Chamber with baffle plates (Howard Model) and a second Cyclone is used, since said set complies with the objectives of generating a decrease in the temperature of gases between 450 and 300 ° C, by presenting the Radiative Cooling Chamber (CER) inside a greater path for the gas, and therefore greater efficiency in the recovery of solid particles of Antimony Trioxide (Sb ₂ 0 ₃ ) that solidify inside, said chamber having deflector plates uniformly distributed that make it difficult for the gas and particles to travel, resulting in a lower travel speed and consequently a greater residence time, supporting said function with the presence of a second Cyclone for optimal recovery of Antimony Trioxide (Sb203). Given the possible presence of particles that were not recovered in the first cyclone, the section 1 ^to the expansion chamber Radiative (1 of 4) (Fig.3 and 4) is used for recovering these particles, which are incorporated to the recirculation system of powders extracted from the first Cyclone, to be reincorporated into the Kiln. The next three remaining sections of the Radiative Expansion Chamber are used for the recovery of the solidified Antimony Trioxide (Sb ₂ 0 ₃ ), which is one of the marketable products of the plant, bearing in mind that the temperature in the gases has already decreased. under the 370 ° C to enter the section 2, temperature from which the antimony trioxide (Sb ₂ 0 ₃₎ and solidify begins to condense into very fine particles (powders). In order to maximize the recovery of the product, a cyclone is added to the Radiation Expansion Chamber, which allows the recovery of the solids of the product not captured in the Radiation Expansion Chamber.

The product recovered by the Radiative Expansion Chamber and the Second Cyclone are discharged onto a refrigerated transport screw, which reduces the temperature of the material to an approximate temperature of 60 ° C, and which in turn discharges the Antimony Trioxide (Sb ₂ 0 ₃ ) commercial to the packaging plant of said product. The non-condensed gases in this process are transferred to the following process (Radiative Cooling), to be subsequently recovered. The gases that leave the Second Cyclone at 300 ° C enter a

Radiative Cooler similar to that described in 4 (from 1st ^to Phase) to reduce the temperature to less than 100 ° C, and induce solidification of Arsenic Trioxide (AS ₂ 0 ₃ ) as a marketable product. Said cooling system is made up of parallel coils made up of inverted U strings, joined together (each constituting a branch of the system). The gas entering the equipment circulates inside it to cool from 300 ° C to less than 100 ° C, dissipating the latent heat of the gases through the walls of the coils that make up the equipment, releasing this heat through convection phenomena and mainly radiation, into the atmospheric air that surrounds it and circulates around it. On the other hand, the duct that constitutes this cooling system must be dimensioned for a high conduction speed in order to avoid the sedimentation of condensing particles as the temperature decreases and the solidification of Antimony Trioxide (As ₂ is generated. 0 ₃ ). The heat dissipation capacity according to the pipe size that the coil will define the length required for the decrease in the temperature of the gases pursued, which in this case is around 200 ° C.

14. The outgoing gases of the Radiative Cooler, equipment in which the Arsenic Trioxides to be generated as a commercial product have been solidified in a very fine size, powders with 95% under 3pm, are transported to a Bag Filter, to generate the separation of the tradable product (AS2O3) from process gases. This is accomplished by passing the gas stream through filter tissues, called sleeves, which retain the solid particles present and the particle-free gas continues in its process to be evacuated by the Chimney. The solid discharge of the Bag Filter, marketable Arsenic Trioxide (As ₂ 0 ₃ ), is emptied by a rotary valve on a conveyor screw to discharge the commercial AS2O3 to the packaging plant of said product.

15. The clean outgoing gases from the hose filter are propelled by the gas extractor (EG) towards the chimney for its evacuation into the atmosphere. The extractor in this stage must be able to generate the suction (negative pressure) necessary for the transfer of the gases generated in the Fixed Oven, until finishing its processing in the Bag Filter, overcoming the pressure losses that occur in its transfer Through the process, both upstream and downstream to the location of the Gas Extractor (EG) in the operation line.

16. Molding system for the formation of marketable Metal Lead ingots.

17. Antimony T dioxide packaging system.

18. Arsenic Thioxide packaging system.

Figs. 2 and 3 correspond to an elevation view of the Double Chamber Oven, a cross section and a plan view of the double chamber oven, in section, respectively.

1 and 2. Component chambers of the fixed furnace, in which the volatilization of the products of interest is generated, Antimony Trioxide (Sb20 ₃ ) and Arsenic Trioxide (AS2O3) between 480 and 520 ° C, which are separated according at its different condensation temperatures in equipment other than the Gas Management system, downstream of said Furnace. However, the PbO entered the oven that does not volatilize, accumulates inside for subsequent recovery as a commercial product (metallic Pb). Each one of the chambers operates consecutively carrying out the following two sub-stages, each sub-stage can be performed simultaneously and out of phase in each chamber: a) Sub-Stage of Volatilization of Trioxides of Sb and As and accumulation of PbO at inside the furnace, with a controlled oxygen-free atmosphere to maintain the chemical characteristics of Sb ₂ 03 and As ₂ 0 ₃ volatilized and to ensure its recovery in terms of quality respectively. Once the optimum volume of PbO that is compatible with the capacity of the furnace is completed, the next sub-stage is developed. b) Sub-Stage of Reduction of PbO and molding of Liquid Pb, effecting the reduction of the accumulated PbO inside the corresponding chamber in the previous sub-stage, with a reducer, coking coal crushed under Y · ”, which is added to the furnace to produce the reduction of oxide to metallic Pb, material that between 480 and 520 ° C liquefies and can be extracted from the furnace to a molding system with the formation of marketable ingots.

The described conceptualization allows conceiving the consecutive realization of the two productive load sub-stages, in a single furnace unit with divided crucible chambers and shared gas chamber, a fact that contributes to reducing the process in question to a line of operation and consequently to reduce fuel consumption and maintenance costs.

3. Gas outlet duct (0.73 · 0.73 m ² ) generated in the Furnace between 480 and 520 ° C.

4. Vertical baffle plate, 1.4 m wide and 0.73 m high and 1 ”thick, installed at a convenient distance from the furnace gas evacuation opening, whose objective is to counteract the drag of fine dust that It characterizes the mixture fed with oxides of Sb, As and Pb, products of interest to be generated separately on a commercial basis. 5. Two burners installed in its rear wall of the Kiln, in each chamber, inclined towards the floor of the chrysolene by 20%, whose 2.5 m long flame develops countercurrent to the flow of outgoing gases.

6. Longitudinal dividing wall of the furnace crucible, 0.75 m high and 15 ”thick, which divides the Furnace crucible into two equal chambers. These chambers are linked by the gas phase, to take advantage of the heat generated by the burners installed on its rear wall.

7. 0.381 m high furnace crucible floor, built in straight brick refractory material, 15 ”x6” x3 ”, high Alumina type HA 45 ISO 10081-1.

8. Side walls (8), front and rear (11), vertical above the floor and up to the height of the crucible (0.75m high), made of refractory material of straight brick, 12 "x 4-1 / 2" 3 ”, Of high Alumina type HA 45 ISO 10081-1.

9. Side walls (9), front and rear (12), vertical of 0.75m above the walls 8 above, built in refractory material of straight brick, 9 "x 4-1 / 2" 3 ", of high Alumina type HA 45 ISO 10081-1.

10. Suspended vault, built in refractory material of straight brick, 12 "x 6" x 3 ", of high Alumina type HA 45 ISO 10081-1.

Figs. 4 and 5 correspond to a schematic and cross-sectional view of the Radiative Expansion Chamber (CER), respectively.

1.The outgoing gases of the Double Chamber Furnace, between 480 and 520 ° C, which possibly contain dusts entrained from the product mixture fed to it, enter firstly to a Cyclone of high efficiency in dust recovery, action that is reinforced by the first section of the

CER, where those particles that are not captured in the Cyclone. The powders thus recovered, in the cyclone 1 and 1 ^to section CER discharged into a common screw conveyor cooled, allowing reincorporating said material to said furnace. , 3 and 4 Sections 2, 3 and 4 of the CER are aimed at generating the condensation and recovery in solid form of Antimony Trioxide (Sb ₂ 0 ₃ ), bearing in mind that the temperature of the gases has dropped below 370 ° C, temperature from which Sb20 ₃ begins to condense and solidify into fine particles (powders). The Cyclone (CL2) has the function of supporting and maximizing the recovery of the commercial product (Sb ₂ 0 ₃ ) already solidified in the corresponding sections of the CER (in the range of 370 and 300 ° C). The product recovered in the 3 final sections of the CER and in the CL2 is discharged onto a refrigerated stainless steel conveyor screw that reduces the temperature of the recovered material from around 330 to 60 ° C, which in turn feeds said commercial product. to the corresponding packaging plant. 5.Inlet pipeline for gases from Cyclone 1 to the CER.

6. Exit duct for gases from the CER to Cyclone 2.

7, 8 and 9. Deflector plates (Howard Model), which make it difficult for the gas and particles to travel, causing a lower displacement speed and, therefore, a longer residence time for gases and solid particles inside. .

10. Space released for transfer of gas between 1 and 2 ^to the CER section located from the bottom of the first baffle plate (7) and the top of the transverse partition structure (13) physically separates the leg download end of sections 1 ^a and 2 ^a .

11. Space released for transfer of gases between 2 and 3 ^to the CER section, located on top of the second baffle plate (8) and the roof of the CER.

12. Space released for transfer of gas between 3 and 4 ^to the CER section located from the bottom of the third baffle plate (9) and the discharge screw conveyor cooled 13. transversal partition structure between the discharges of 2 ^to 1 and CER section, gathering in differentially powders entrained by the gases (section 1) and the product from 2 ^to section hereinafter.

14. Inspection door (manhole) for maintenance interventions.

15. discharge opening powders recovered in section 1 and the commercial product in sections 2, 3 and 4.

REFERENCES

1. Antimony Metallurgy Course, Antonio Ros Moreno, 2009.

2. Study of the behavior of antimonite during its roasting to sb2o3 (antimony trioxide) in electric resistance and microwave ovens, T.J. Ornelas, H.J.A. Hernández, M.M. Márquez, and M.A. Ortiz Dept. of Mining Exploitation and Metallurgy of the Faculty of Engineering Universidad Nacional Autónoma de México Cd. Universitaria, 2012.

3. CARBOTHERMAL REDUCTION OF ANTIMONY SULFIDE IN

PRESENCE OF CALCIUM OXIDE (Master's Degree Thesis in Metallurgical Engineering, UdeC), 2011

4. Kelloogg-Ingraham Roasting Diagrams (k-1. José María Palacios de Liñán.

11 / October 2011.

5. Lead Metallurgy, Seba RivanoVillagra .Scribd, March 19, 2013.

6. ES8602957, 11-16-1985, Prodn. of metallic lead from lead-contg starting materials, BOLIDEN AB

7. CU22289, 01-31-1995, Procedure for obtaining arsenic trioxide from alkaline

liquors with a high antimony-content., UNIV LA HABANA, Bustamente Sánchez María de la Libertad.

Claims

1. Modern plant to obtain Antimony Trioxide (Sb ₂ 0 ₃ ), Arsenic Trioxide (As ₂ 0 ₃ ) and Lead (Pb) metallic, from a predominant mineral in Antimonite, CHARACTERIZED by teams prepared for a method divided into two phases: a. Controlled oxidative roasting phase, in ovens where the gases undergo different cooling processes to finally obtain a solidified mixture formed by Antimony Trioxide (Sb ₂ 0 ₃ ), Arsenic trioxide (As ₂ 0 ₃ ) and Lead oxide (PbO). b. Phase of separation of the solid mixture in a fixed double chamber furnace by volatilization and recovery at different solidification temperatures and subsequent obtaining of metallic Lead by reduction of Lead oxide.

2. The plant for obtaining the Oxides according to claim 1, CHARACTERIZED because the first phase (a) of controlled oxidative roasting is carried out in rotary kilns with an induced draft fan to generate the oxidation of Antimony and Arsenic to a temperature between 480 and 520 ° C

3. The plant for obtaining Lead Oxide according to claim 1, CHARACTERIZED because in the first phase (a) the oxidation of Lead Sulfide (PbS) to Lead oxide (PbO) is induced by the injection of air to the gas handling system at the entrance of one of the Radiation Cooling system equipment.

4. The plant for obtaining according to claim 1, CHARACTERIZED because in the first phase (a) the mixture of interest is condensed at the end of the cooling system of the first phase and consists of Antimony Trioxide, Arsenic Trioxide and Lead oxide that is recovered in a Sleeve Filter that operates below 100 ° C.

5. The plant for obtaining according to claim 1, CHARACTERIZED because the second phase (b) of volatilization and separation of the mixture is carried out in fixed furnaces that work at a temperature between 480 and 520 ° C, whose crucibles have two equal reaction chambers separated by a wall and joined together at the gas phase level.

6. The plant for obtaining according to claim 1, CHARACTERIZED because in the second phase (b) the Antimony trioxide (Sb ₂ 0 ₃ ) is recovered in a Radiative Cooling Chamber that operates at temperatures close to 350 ° C.

7. The plant for obtaining according to claim 1, CHARACTERIZED because in the second phase (b) the Arsenic trioxide (AS2O3) is recovered at the end of the system in a Bag Filter (FM) at temperatures below 100 ° C.

8. The plant for obtaining according to claim 1, CHARACTERIZED because in the second phase (b) the lead (Pb) is recovered as a commercial product from the interior of the double chamber furnace, by a process of reduction with coking coal. that transforms Lead Oxide (PbO) to Liquid metallic Lead at the process temperature, between 480 and 520 ° C.

9. The plant for obtaining according to claims 1 to 4, CHARACTERIZED because in the first phase the Anhydrous sulphurous gases (SO2) are eliminated, clean combustion gases are delivered to the environment, the outgoing gases from the bag filter enter They are cleaned in a gas scrubbing tower and by counter-current spraying with 10% dilution of Calcium Hydroxide.