RU2078146C1 - Method of burning metal-containing sulfide-arsenic or sulfide-gold- containing ores and concentrates - Google Patents

Abstract

FIELD: mining industry. SUBSTANCE: metal-containing sulfides and arsenides are subjected to suspension burning at 600-750 C in reactor space where finely divided lime for absorbing mainly all sulfur and arsenic oxides formed under burning is homogeneously suspended all over the reaction space. Sulfur and arsenic oxide absorption is improved by maintaining minimum quantity of free oxygen in off-gas. EFFECT: enhanced efficiency of process. 6 cl, 4 dwg, 3 tbl

Description

 The invention relates to the burning of sulfides and arsenides of metals (containing metals), and more particularly, to suspension burning of metal-containing sulfides with a minimum of emission of sulfur and arsenic oxides.

 Ores of metal-containing sulphides or ore concentrates must often be fired to accelerate the subsequent metal recovery process. For example, many gold ore sediments exist in the form of oxides or sulfides.

 The oxidized fractions can be processed directly by known methods, for example, by cyanidation, but the sulfide fraction is often susceptible to this effect and must be oxidized during calcination, oxidation in an aqueous medium at elevated temperatures and pressures, or subjected to bacterial oxidation.

 Water oxidation may be uneconomical for some ores, and bacterial oxidation requires lengthy treatment accompanied by an increase in cost due to the fact that large volumes of solutions with a low content of spent sulfates are used.

 The firing of refractory gold ores is characterized on the one hand by speed, and on the other it is cost-effective, but stages should be introduced into the firing process that minimize the emission of sulfur and arsenic oxides.

 Most kilns, especially in the United States, must be equipped with acid mills or scrubbers in order to absorb sulfur dioxide before it is released to the atmosphere. Acid production apparatuses require large capital investments and may be ineffective in cases where the flue gas contains low concentrations of sulfur dioxide. In addition to capital costs and low productivity, a nearby market can have a significant effect, or rather, the needs of a nearby market for produced acid, since the cost of sulfuric acid is sensitive to the distances over which it is transported. Purification, in particular wet gas purification, creates a problem, in particular, related to where to store the semi-liquid waste generated in this process.

 The article (Taylor et al. Roasting time of refractory precious metal ores, Precious Metals, M.Jennings, Ed. TMS 1991) describes a method of roasting a mixture of a mixture of refractory gold ore and lime in a fixed layer over which oxidizing gas passes, it is reported that their process is kinetic sensitive, depends on the rate of oxidation of sulfide and on the rate of sulfation of lime. Although the process developed by Taylor et al. Is good on a laboratory scale, a continuous process is needed from a commercial point of view that can process large quantities of ore or ore concentrates in a short period of time while minimizing the emission of sulfur dioxide.

 Ground metal-containing sulfide and / or arsenides and lime are introduced into the reactor volume.

The temperature in the reactor space is maintained in the range of about 500-800 ^° C. Sulphide and / or arsenides and lime are suspended in the reactor space by passing gas through them. Free oxygen-containing gas is fed into the reactor space for the oxidation of sulfides and / or arsenides to metal oxides and sulfur and arsenic oxides. Lime is added to the reactor space in an amount substantially stoichiometrically sufficient to react with sulfur and arsenic oxides, and lime is very carefully separated so that lime is generally homogeneously suspended throughout the reactor space, which mainly reacts completely with sulfur and arsenic oxides and capture them.

 In FIG. 1 is a graph of the inverse relationship of the concentration of sulfur dioxide in the exhaust gas from the concentration of oxygen in the exhaust gas.

 On the graph for a more visual representation of the inverse relationship, the oxygen content in the exhaust gas is inverted. In FIG. 2 to 4, three types of suspension kilns are schematically presented which can be used for calcining metal-containing sulfides in accordance with the invention.

 The method corresponding to the invention will be described using firing of refractory gold ore as an example, but, as is obvious to any person skilled in the art, the present invention is not limited to this example. Minimal modifications may be needed to roast other metal-containing sulphides, but it is clear that such modifications do not go beyond the scope of the method used in practice.

 Further, the term “lime” as used herein refers to calcium oxide, limestone and hydrated lime.

 Gold is often found in ores that contain pirates, pyrrhotites, arsenopyrites, or iron-free sulfides. Gold may be present in the form of sulfides, but may also be distributed among other sulfide minerals that are present in the ore. The gold contained must first be freed from such sulfide minerals before it can be isolated in other processes, such as leaching in cyanide solutions.

 Carbonate rocks are also often associated with gold-bearing ores and influence the leaching process, prematurely adsorbing the contained gold, which is already in a dissolved state. The elimination of such carbonate rocks during the firing process, in addition, leads to a further increase in the efficiency of the subsequent hydrometallurgical process.

 The method according to the invention is based on suspension firing, providing a continuous firing process with high performance.

 Suspension roasting has an additional meaning in that the ore or ore concentrate particles are suspended in gas streams. Consequently, the gold ore must be carefully ground in order to be able to form a suspension in gas streams. Ore concentrates, for example, sulfide or arsenic minerals, concentrated by physical means, for example, by magnetic separation and / or flotation, as a rule, are already in a finely ground state, so further grinding is rarely required.

 If the ore is calcined without preliminary concentration, then it must be crushed and ground by traditional methods to create a particle size distribution corresponding to about 100% minus 10 U, S.S. mesh. predominantly approximately 80% minus 48 U.S.S. mesh. Although very finely ground ore or ore concentrations can be calcined more quickly, the further process may require that the ore or ore concentrate be somewhat coarse-grained, or that very finely ground calcined ore or ore concentrate undergo agglomeration after calcination.

 Particles of gold ore or ore concentrates and lime are placed in the heated space of the reactor, through which gas is passed at a residual speed to suspend the particles of the supplied material and to disperse the lime evenly across the reactor space. A gas containing free oxygen, for example, oxygen enriched air or hot gases containing free oxygen, is fed to oxidize mineral sulfides or arsenides to the corresponding metal oxides and sulfur or arsenic oxides, which are reacted and trapped in lime.

 According to the invention, the calcination is carried out so as to be sure that at least about 90, and preferably 95% or more, sulfur and arsenic oxides are absorbed by lime.

 An important feature of the invention is that the lime is introduced into the reactor space in an amount sufficient to stoichiometrically react with the sulfur dioxide released during the firing process, and that the lime is ground to a large extent so that it can be substantially homogeneous suspend throughout the reactor, regardless of whether the ore or ore concentrate is present as a dense fluidized bed or as a circulating fluidized bed, as will be described below. If predominantly all sulfur and arsenic oxides should be absorbed (bound) before they are released into the atmosphere, then it is obvious that a significant amount of lime must be present in the reactor space for the reaction and binding of the resulting oxides.

 In addition to the purely stoichiometric amount (minimum), additional amounts of lime may be required, depending on the particle size distribution and firing conditions, which both can affect the surface area of the lime, which is an important composite parameter of the actual mass of lime added to the reactor. Lime must be crushed to a large extent in order to be able to be distributed evenly throughout the reactor space. With a uniform distribution of lime throughout the reactor space, the number of factors affecting the interaction between sulfur and arsenic oxides and lime is maximized, resulting in an increase in the overall efficiency of removing sulfur and arsenic oxides from the exhaust gases.

 The suspension of lime throughout the reactor space ensures that the maximum surface area of the lime will be located in the gas flows, resulting in a significant increase in the possibility of interaction of sulfur oxides and arsenic contained in the gas flows with lime. This is particularly important since sulfur dioxide-lime and arsenic-lime oxides are of the gas-solid type. Uniform dispersion of lime in the reactor space maximizes the residence time of gases containing sulfur and arsenic oxides in lime, which ensures a more complete reaction.

 If lime remains only inside the dense phase of the reactor fluidized bed or at the bottom of a rotary kiln or the like. then the contact time between lime and sulfur and arsenic oxides can be half or less than the contact time achieved in the case of the distribution of lime throughout the reactor space.

 In order to guarantee a substantially uniform distribution of lime in the reactor space, the lime should have the following size distribution of the particle about 100% minus 326 U.S.S. a mesh, and preferably about 80% minus 400 U.S.S. mesh. In most cases, the average particle size of the lime should be significantly smaller than the average particle size of the metal-containing sulfides.

 It has been found that hydrated lime, due to its hydrated water content and its inherent small particle size (i.e., at least less than about 75% minus 200 U.S.S. mesh), and therefore its large surface area, provides the best results. In addition, hydrated lime has an excellent particle size and a huge surface area, fresh surfaces formed during the dehydration of hydrated lime during the firing process also lead to an increase in its reactivity.

 Moistened calcined calcium carbonate can also be used, but it must be pre-ground to such an extent that the particle size is as described above.

 When using calcined lime, better results are obtained when lime calcination is carried out at lower temperatures, since lime calcining at higher temperatures is significantly less reactive than calcining lime at lower temperatures.

Particle sulfides and finely divided lime are loaded into the reactor space either as a mixture or separately, at a reactor temperature in the range of from about 500 ^° C. to 800 ^° C., preferably at about 600,750 ^° C.

 Lower or higher firing temperatures can be used, but at lower temperatures, firing reactions proceed more slowly and with a lower yield, while at higher temperatures mechanical problems can occur, such as sticking and, as a result, the firing process may become less energy efficient.

 Depending on the sulfur content and the content of organic carbon in the feed material, firing can occur in an autogenous mode or may require exogenous heating. If exogenous heat is necessary for the process to take place, then such heat can be delivered by heating the gas being suspended, either directly or by burning fuel with the gas being suspended.

 Thermal efficiency increases when heat is taken directly from the flue gas, whether direct heating or indirect heating is used.

 To oxidize the particles of sulfide minerals, a gas containing free oxygen must be supplied to the reactor space. Oxygen enriched air or flammable gases containing free oxygen can be used. Whatever the source of the gas containing free oxygen, a sufficient amount of oxygen must be present for stoichiometric interaction with sulfides and arsenides with the formation of the corresponding oxides of metal, sulfur and arsenic. However, it has been found that it is highly desirable that large excesses of free oxygen are present in the exhaust gas in order to ensure substantially complete binding of the released sulfur dioxide.

 The amount of sulfur dioxide in the exhaust gas is inversely proportional to the oxygen content in the exhaust gas (Fig. 1).

A certain amount of excess oxygen is necessary to promote the conversion of SO ₂ to SO ₃ .

 Free oxygen also interacts and eliminates most, if not all, of any carbonate material associated with ore or ore concentrates.

 During the firing process, any arsenic component associated with ore can also be oxidized and volatilized, and volatile arsenic oxide is also bound by lime.

 In FIG. 1, the volume concentration of free oxygen is plotted in the inverse coordinate as an average variable relative to time, in the form of a dashed line, while the volume concentration of sulfur dioxide is plotted in the forward coordinate, as the average variable in relation to time, in the form of a continuous line. From figure 1 it is obvious that the oxygen content is inversely proportional to the content of sulfur dioxide in the exhaust gas. From the point of view of the relationship (Fig. 1), it is obvious that it is preferable to keep the free oxygen content in the exhaust gas at least at least about 3 by volume, and more preferably when it is at least about 8% by volume .

 The formation of calcium sulfate from calcium oxide, sulfur dioxide and oxygen at firing temperatures is fully energetic Gibbs energy formation is approximately 55 kcal / mol. During this reaction, sufficient heat is released to cause local melting of calcium sulfate, which can cause adverse effects such as a decrease in surface area during the melting process, and / or agglomeration of lime particles, both of which reduce the activity of lime.

Indeed, during testing, the formation of agglomerated growths of crystalline calcium sulfate (CaO ₄ , or anhydride) was observed. It is believed, although this assumption does not limit the invention, that having a high oxygen content in the exhaust gas can provide sufficient oxygen to oxidize sulfur dioxide, and a larger amount of free oxygen ensures a low concentration of sulfur dioxide, which minimizes any problems associated with local sulphate melting calcium.

 High productivity and completeness of firing are best realized when using a suspension type reactor (Fig. 2 4). Other types of reactors, such as a rotary kiln, can be used if measures are taken to ensure the suspension of lime throughout the reactor space. A rotary kiln equipped with a device for draining fine lime from about the top of the kiln, from where it enters the reactor space, can be used, but even approximately, it is not as effective as suspended type reactors (Fig. 2-4).

 In FIG. 2 shows a fixed or dense fluidized bed of a reactor 10 equipped with a cyclone dust collector 12. A solid material, i.e. particles of sulfides and lime are fed into the reactor 10 at the inlet 14 and left on the constricting plate 18 above the pressure chamber 16, and the calcined sulfides are removed from the reactor 10 through the hole 20.

 The suspending or fluidizing gas is introduced into the pressure chamber through the gas inlet 22. The fluidizing gas introduced into the reactor 10 through the opening 22 and the compression plate 18 transfers the solid sulfides to the fluidized bed 24, while the finer crushed lime is suspended in the reactor space 26, which is shown in the form of more oily small spots.

 The fluidizing gas containing free oxygen flows from the reactor 10 into the cyclone 12 through the pipe 28. The purified gas from the cyclone 12 can be vented to the atmosphere or passed through the heat exchanger through the outlet 30. Separated solid components, i.e. lime, sulphides and oxidized sulphides are returned to the reactor 10 through a pipe 32 or isolated, or the system is emptied through the outlet 34.

 In FIG. 3 is a diagram of a circulating fluidized bed reactor 50 equipped with a cyclone particle trap 52. Solid components, i.e. sulfides and lime in the form of particles are fed into the inlet reactor 50, and these components remain above the pressure chamber on the compression plate 58.

 The suspending or fluidizing gas is introduced into the pressure chamber 58 through the gas inlet 62. The fluidizing gas introduced into the reactor 50 through the gas inlet 62 and the narrowing / contracting plate 58 fluidizes the solid sulfides in the form of a layer 64 of suspended sulfide particles, and thinly crushed lime is suspended throughout the reactor space, it is marked by spots of lower density 66.

 The fluidizing gas containing free oxygen enters from the reactor 50 into the cyclone 52 via line 68.

 The purified gas from cyclone 52 can be vented to the atmosphere or directed to the heat sink through the outlet 70. Separated solid components, that is, lime, sulfides and oxidized sulfides, are returned to the reactor 50 via line 72 or emitted, or the system is emptied through the outlet 74 .

 In continuous operations, from about 10% to about 90%, preferably from about 20% to 80% of the separated / released components are isolated as a product. The amount of separated solid components released as a product depends on the firing conditions and the amount of sulfur that may be allowed in the firing product.

 In FIG. 2 shows a diagram of a transport reactor 100 equipped with a cyclone particle trap 102. The solid components of the reaction, i.e. sulfides and limes transferred to the particles are fed into the reactor 100 through the solids inlet 104. Suspending gas is introduced into the reactor 50 into the gas inlet 112, and it suspends and transfers solid sulfides and finely divided lime throughout the reactor space, this suspended mass is marked less greasy spots 116.

 A suspending gas containing free oxygen enters from the reactor 100 into the cyclone 102 via a conduit 118. The purified gas from the cyclone 102 can be vented to the atmosphere or sent to the heat sink through the outlet 120.

 The separated solid components, i.e., lime, sulfides and oxidized sulfides, are returned to the reactor 100 via line 122, or recovered, or the system is emptied through the outlet 124.

 In continuous operations, from about 10 to 90%, preferably from about 20 to 80% of the individual solid components are isolated as a product.

 The amount of separated solid component recovered as a product depends on the firing conditions and the amount of sulfur that may be allowed in the firing product.

 The circulating fluidized bed (FIG. 3) is particularly useful in the practice of the invention.

 Since part of the fluidized bed is intensively transferred from the reactor, the speeds of the suspending gas and the gas containing free oxygen should not be so carefully controlled so that a higher degree of freedom is achieved. For example, as noted, the binding (absorption) of sulfur dioxide is inversely proportional to the amount of oxygen in the exhaust gas, and the highest degree of freedom achieved in a circulating fluidized bed reactor allows independent supply of gas containing free oxygen to the reactor, not taking into account the moment associated with the violation of the stability of the fluidized bed.

 Another example of the advantage associated with the use of a circulating fluidized bed relates to greater freedom in choosing the feed rate of solid components into the reactor, which opens up a great opportunity for agglomeration. As noted above, even in a transport-type reactor, a certain proportion of the formed calcium sulfate is converted to agglomerate. Such agglomeration of the feed or reaction products in the fluidized bed or in another type of moving bed is a well-known source of difficulty.

 To provide the specialist with the best opportunity to familiarize themselves with the method of the invention, the following examples are illustrative.

Example 1. Ore containing gold sulfide in an amount of 4.2 ppm Au and 7% sulfur, crushed to 100% passing through a 200 mesh sieve (through a sieve with 200 holes per linear inch). It was burned in a circulating fluidized bed furnace at a rate of 20 kg / h in three different furnace campaigns. With the exception of campaign 11-d, the temperature of which was regulated at 780 ^o C, the firing was carried out at a temperature of 700 ^o C. The cinder was analyzed for sulfur content and the amount of absorbed sulfur was calculated. In the table. 1 shows the results of three campaigns.

 It should be noted that 111-s is not actually divided into sub-campaigns. Sulfur absorption data simply represents the calculated sulfur absorption (capture) value in a medium with a high, medium, and low oxygen content. These data, of course, confirm the point of view on the possibility of excellent sulfur absorption. It should be noted that campaign 111 used hydrated lime.

Example 2. Ore containing gold sulfide in an amount of 5.7 ppm. Au and 3.7% sulfur were calcined in a circulating fluidized bed furnace at a rate of 20 kg / h at a constant temperature of 700 ^o C. In addition to silicates, the ore also contained dolomite, calcium magnesium carbonate. The calcium content of the ore was 5%. Ore, containing particles of two different sizes, was tested in two different campaigns. The results of sulfur absorption, calculated on the basis of analyzes of the sulfur content in the cinder, are presented in table. 2.

Example 3. The ore obtained in example 2 was subjected to flotation to obtain a sulfide concentrate containing 36 ppm. Au and 23% sulfur. The concentrate was calcined in a circulating fluidized bed furnace at a rate of 12 kg / h, maintaining the temperature in two different campaigns of 675 ^° C, with and without lime to absorb sulfur. The particle size of the flotation concentrate was approximately 80% of the 325 mesh passage. The concentrate still contained sufficient dolomite. The results of sulfur absorption are presented in table. 3.

 Although the invention has been described in connection with preferred embodiments, it should be understood that various modifications and variations can be accommodated without changing the spirit and scope of the invention. Such modifications and variations are considered to be within the competence and within the scope of the present invention and the attached claims.

Claims (6)

1. The method of roasting metal-containing sulphide-arsenic or sulphide-gold-containing ores or concentrates, comprising supplying the starting material to the reactor, maintaining the firing temperature of 600 800 ^° C, suspending the ore or concentrate by passing an oxygen-containing gas with oxidation of the starting material to metal-containing oxides, dioxide sulfur and arsenic oxides in the presence of arsenic in the starting material to produce oxygen-containing exhaust gases containing suspended solids with their subsequent separation characterized in that the calcination is carried out with the introduction of slaked lime with a particle size of less than 75 microns, not less than 75% of the total amount of lime in an amount at least stoichiometrically sufficient for interaction with sulfur dioxide and arsenic oxides in the presence of arsenic in the starting material, the source material is mixed with slaked lime, the free oxygen content in the exhaust gases is maintained in an amount of more than 3 vol. and the sulfur dioxide content is inversely proportional to the oxygen content, the suspended particles obtained as a result of the interaction of sulfur dioxide and arsenic oxides in the presence of arsenic in the starting material with the calcined dehydration product obtained during firing are separated and particles are separated to remove part of the suspended particles as a product and returning another part for reprocessing to the reactor.  2. The method according to claim 1, characterized in that the firing is carried out with the receipt of exhaust gases containing free oxygen of more than 8 vol. 3. The method according to claim 1, characterized in that the firing is carried out while maintaining the temperature in the reactor 600 750 ^o C.  4. The method according to claim 1, characterized in that the portion of suspended particles isolated as a product is 20 to 80% of the total number of suspended particles.  5. The method according to claim 1, characterized in that the firing is carried out when creating in the reactor a circulating fluidized bed of suspended particles.  6. The method according to claim 1, characterized in that 90% of the sulfur oxides of their total amount participate in the formation of suspended particles.

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