FI122946B - Method of roasting nickel sulfide - Google Patents

Description

METHOD FOR ROASTING NICKEL SULFIDE FIELD OF THE INVENTION

The invention relates to a process for roasting nickel sulfide produced by precipitation into nickel oxide in a fluidized bed oven. The precipitated, very finely divided nickel sulfide precipitate is micropelleted and the micropelleted precipitate is subjected to fluidized bed treatment. The fluidized bed treatment can take place in a single fluidized bed furnace with a circulating bed or in two fluidized bed furnaces with a bubbling bed.

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BACKGROUND OF THE INVENTION

Metal sulfides have been oxidized on an industrial scale in various types of roasting ovens for decades. In sulfating roasting, sulfides are oxidized to sulfates. The formation of sulfates occurs at a temperature lower than that of the oxides. In dead roasting, the entire amount of sulfide is oxidized to the oxide under oxidizing conditions at such a high temperature that the sulfates are no longer stable. Roasting can be done in a variety of ovens, such as a multi oven, drum oven or • · ·; ··; fluidized bed incinerator. The most commonly used is the fluidized bed oven because of its efficient energy transfer • · · 20 as well as temperature control.

• • • • • • *. Roasting technology has also been used to oxidize nickel sulfide, whereby sulfide is roasted to either sulfate or oxide. The starting material is then either · · a nickel sulphide concentrate formed by flotation or a nickel stone produced by pyrometallurgical treatment. When the starting material is concentrate, the nickel content is in the range of 1 to 10%, but the nickel content is generally in the range. of the order 40-70%. Both concentrate and stone usually also contain some metals such as copper, iron, cobalt and arsenic.

• · ** 'Roasting of nickel sulphide is usually carried out in a fluidized bed, so-called. bubbling [[30 beds.

• · · • ·· • · 2

The use of fluidized bed technology is sometimes limited by excessive melt phase formation and consequent bed sintering. The oxidation of nickel sulphide to oxide occurs in principle already at a temperature of about 700 ° C, but for kinetics and other reasons, a temperature of about 900 ° C is used. According to the literature, molten phases already exist in the Ni-S system, for example at a temperature of 635 ° C. The formation of nickel sulfate is substantially reduced when the temperature rises above 700 ° C.

GB 769,267 and US 3,957,484 describe the roasting of a nickel-containing sulfide concentrate such as pyrrhotite. In the process according to GB, the concentrate is roasted to sulphate and in the process described in US to be oxidized. In the case of sulfating roasting, for example, sodium sulfate may be used as an additive and a clay-containing material as a binder. In the methods, a finely divided concentrate (80% less than 45 µm) is fed from the roof of the fluidized bed 15 furnace as slurry, whereby when dropped down, the slurry dries and agglomerates at the top of the furnace and actual oxidation occurs at the bottom. Leijup eti is composed of either those formed during roasting or. pre-fed roast particles. Pyrrhotite iron is oxidized • · ·: * ·; hematite and sulfides to sulfur dioxide. The temperature used was in the range of 1000 ° C to 20 ° C.

U.S. Patent No. 3,094,409 describes the roasting of nickel sulfide to nickel oxide in a fluidized bed. The sulfide to be treated is either a stone formed by pyrometallurgical processing or a high-nickel flotation concentrate of about 64-72%. If the material to be treated is stone, it is granulated molten to the desired grain size for roasting. The flotation concentrate is finely divided, /. it has a grain size of between 95% and 200 mesh, ie less than 0.074mm.

/ ·, *. / The flotation concentrate is agglomerated to a size of 0.25-1.3 mm (65 mesh - 0.5 in), whereby, for example, water, nickel sulfate, sulfur, * | 30 acids, lignosol, fuel oil or bentonite. According to the examples, the roasting temperature is in the range of 1050 to 1100 ° C. Dust generated by roasting is either returned to the roasting furnace or to the agglomeration.

U.S. Patent No. 1,502,986 describes the roasting of nickel-containing iron sulfide in a fluidized bed furnace for the production of ferronickel. The material to be roasted contains 5-35% nickel and is agglomerated to a grain size of 6.7 to 5.5 mm. The roasting is carried out at a temperature of 800 to 1150 ° C. The higher the roasting temperature, the lower the amount of sulfur remaining in the roast. The large pellet size allows higher temperatures to be used but requires a high gas flow for fluidization to succeed. At high temperatures, some of the material melts into a dense material and slows down diffusion. The resulting oxide roast 10 is pre-reduced and fed to an electric furnace to produce ferronickel. Because the roast is fed to the melting furnace, sand can be used as the bed material.

SE-A-346 703 discloses a roasting treatment of a sulphidic iron material 15, wherein the material to be treated contains as an impurity arsenic, antimony, tin or bismuth. In addition to iron, the sulfide material may also contain cobalt, nickel, cadmium, copper or zinc, and it has been found that these can form ferrites during roasting.

t ·· ···; The roasting is carried out in two fluidized bed reactors. In the first hover, the temperature is adjusted to be at least 800 ° C and the conditions are reduced. Under these conditions, impurities evaporate and prevent the formation of ferrites. The roasting is completed in a second fluid bed reactor at 700-800 ° C to give the product a sulfur-free magnetite material.

25 • ·

PURPOSE OF THE INVENTION

• ·. *. The roasting of nickel sulphide concentrate or nickel stone has been described in the prior art. However, the grain size of the concentrate and the nickel stone is significantly larger than the fluidized bed fluidization of the nickel sulphide formed by hydrometallurgical precipitation and therefore [[30] as such, gives great difficulty. Within the scope of this invention, attempts have been made to solve the problems associated with fluid bed bedding of fine material.

4

SUMMARY OF THE INVENTION

The invention relates to a process for oxidizing nickel sulfide to oxide in a fluidized bed furnace, wherein the finely divided 5 nickel sulphide precipitate formed by doping is treated in the following steps: a) in roads to form nickel oxide and sulfur dioxide containing gas.

According to one embodiment of the invention, the roasting of the micropelleted pellet takes place in a circulating bed furnace in one fluidized bed oven and a cyclone associated therewith, whereby the temperature of the entire cycle is adjusted to 750-150 ° C. The recirculating micropellet stream is at least 100-300% of fresh micropelleted nickel.

According to another embodiment of the invention, the micropelleted nickel sulfide precipitate is treated in at least two fluid bed furnaces in which roasting occurs in a bubbling bed, wherein the first fluid bed furnace ··· · is subjected to oxidation of the surface of the particles the temperature of the second fluidized bed furnace is adjusted to a range of 750 - ··· ·: ··: 1000 ° C for complete oxidation of the nickel sulphide to nickel oxide.

The process according to the invention is characterized in that the precipitated nickel sulphide precipitate has a grain size of the order of 5 to 20 µm.

• · • · y. According to a preferred embodiment of the invention, the size of the micropelletized nickel sulfide precipitate is of the order of 0.2 to 1 mm.

v *: **: According to an embodiment of the invention, the method uses fuel to control the temperature of the fluidized bed furnace if the heat content produced by the oxidation process is insufficient.

5

According to one embodiment of the invention, the nickel oxide formed in the fluidized bed furnace is cooled by fluidized bed cooling.

According to a preferred embodiment of the invention, the heat recovered from the exhaust gases of the fluidized bed furnace is used for drying the formed micropellets.

It is typical of the process according to the invention that the sulfur dioxide gas formed is purified, after purification, to the preparation of sulfuric acid.

LIST OF FIGURES

Figure 1 is a flow chart of a method according to the invention and Figure 2 is a flow diagram of another method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

When the nickel sulphide ore and concentrate are leached and the resulting nickel-containing solution is subjected to sulphide precipitation, ··· 20 very fine nickel sulphide precipitates with a grain size of 5 to 20 µm are obtained.

• · ·

The nickel sulphide precipitate has a nickel sulphide content of the order of 60-70% and contains only a few percent other metals as sulphides, such as iron, zinc and cobalt. Since the precipitate is hydro-metallic, it is not Due to the high content of nickel sulphide, · · 25 the material precipitated has a significantly lower melting point of about 650 ° C than that of nickel sulphide concentrate in which · · is predominantly pyrrhotite with a melting point of 1200 ° C. fines and its nickel sulphide content is very high, which means that the precipitate has a very high specific surface area. * · *** There is a problem with the oxidation of the nickel sulphide-containing material. and melting zones are • · · ** *: very close to each other and there is danger in fluidized bed oxidation The sulfide will melt and form large agglomerates that will prevent the bed from floating.

6

As is commonly known, a fluidized bed may be either a Bubbling Fluidized Bed (FB) or a Circulating Fluidized Bed (CFB). A less commonly used fluidized bed is, for example, the Annular Fluidized Bed (AFB). 5

The method according to the invention will be described in more detail with reference to the accompanying drawings. In the solution of Figure 1, the nickel sulphide is roasted on a rotary-bed basis. The fine particle size of the nickel sulphide precipitate formed by precipitation is in the order of 5 to 20 µm and is first subjected to micropelletization 1 in a suitable device. In micropelleting, the sulfated dust generated by cooling the fluidized bed exhaust gas is used as a binder. Micropelleting reduces the specific surface area of the sulphidic low melting material and thereby minimizes the formation of harmful large agglomerates and sintering. Micropelleting also minimizes the oxidation time, since diffusion takes place faster to the core than with large pellets The grain size of the pellets fed to the rotary bed is determined by the material selected. process, temperature used in the process and required residence time «t ·” *. *. Preferably, the size of the micropellets is adjusted to a range of 0.2 to 1 mm.

:: i .: 20 • · • ·. '* Γ # The dust to be recovered from the exhaust gases in the heat recovery boiler 4 and the electric filter 5 is oxidized to sulphate as it has been transported forward with sulfur dioxide gas at a temperature where sulfur dioxide and • · Oxygen forms sulfur trioxide and with metals sulfates. The sulphated dust binds the finely divided sulphide and the amount of dust fed to the pelletizer:: ··· determines the desired grain size of the micropellets. If the amount of dust is X; not enough, pelletization can be supplemented with other nickel sulfate besides dust • · ·. ···. * to bind sulfide precipitate. In addition to dust, water is fed into the sulphide precipitate • · · »« •. to provide pelletization. To strengthen pellets before. 30 fluidized bed ovens are subjected to drying. The drying of the pellets 2 is carried out preferably by steam generated in the heat recovery boiler 4.

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The circulating bed 3 of the dried micropelleted nickel sulphide article takes place in one fluidized bed furnace. In the flow diagram, the circulating bed bed 3 includes both a fluidized bed furnace and an associated cyclone. In a rotating bed, the pellets are not in such close contact with each other and therefore do not cling to each other as easily as in a bubbling bed. In a fluidized bed fluidized bed oven and the cyclone associated therewith, i.e. the entire cycle, the temperature is continuously maintained above 700 ° C, thus preventing sulfation of the nickel sulfide. However, in order to prevent sintering of pellets and formation of molten surfaces, temperatures of up to 900 ° C are employed. 10 At this temperature range nickel oxide is stable.

The flow rate of the product to be removed from the fluidized bed furnace and of the recyclable material is controlled by the cyclone lower outlet. The recyclable pellet stream is in the order of 100 to 300% of the amount of fresh micropellets fed into the furnace. The size of the pellet stream to be recycled is determined not only by the properties of the feed, such as oxidation, but also by the amount of oxidized inert material required to prevent sintering of the fresh feed. The sintering tendency, in turn, is influenced by the composition of the nickel sulphide feed and • · t: ··; grain size of micropellets. Of course, circulation is minimized by minimizing the need for energy. If oxidation • · • · V. '.' Occurs in the fluidized bed furnace. If the reaction is not sufficient to provide the required temperature, additional fuel may be • m supplied to the furnace, which may be gaseous, liquid or solid, such as elemental sulfur.

The gas exiting the fluidized bed furnace is led to a cyclone and from there to a heat recovery boiler 4 where the gas is cooled and a portion of the gas' /. the dust contained therein is recovered. As stated above, the steam generated in the boiler is directed to the drying stage of the micropellets. From the heat recovery boiler, the gas is further directed to an electric filter 5, where the final removal of dust from the gas takes place. The purified gas stream • · · ** is passed on to sulfuric acid production.

8

The hot nickel oxide material to be removed from the fluidized bed furnace is indirectly cooled by air or other oxide-containing gas. Cooling can take place, for example, as fluidized bed cooling 6. The hot oxide-containing gas produced in the cooling step is in turn fed to the fluidized bed furnace 5 as process / fluidizing gas.

The solution of Fig. 2 is otherwise similar to that of Fig. 1, but roasting is carried out in two fluidized bed furnaces 7 and 8 according to the invention. The temperature of the first fluidized bed furnace 10 is adjusted to 650-750 ° C, thereby minimizing molten phase formation. Because roasting is carried out at such a low temperature, oxidation to the oxide does not take place in the economic time to complete, leaving the first-stage product still sulfur-free. The amount of sulfur remaining in the roast is controlled by the roasting time and the oxygen factor 15. In the first step, the nickel sulfide is oxidized only to the extent that the heat generated in the reactions is sufficient to raise the temperature of the furnace to said level while producing an oxidized intermediate on its surface. At the same time, the material hardens.

The intermediate roasted in the first fluidized bed furnace is led to the moon Mana • · · · · joins the second fluidized bed furnace 8. In this second step, the temperature of the fluidized bed furnace is adjusted to the area. 750-1000 ° C because the risk of sintering is · · substantially reduced due to material hardening in the first step, · hardening, lowering of the sulfide level, and oxide layer formed on the particle in the second step, the sulfides being completely oxidized by oxygen diffusion through the first fluidized bed. If the heat generated by the oxidation of the sulfides • ·· l · / · is not sufficient to raise the temperature sufficiently, the above fuels may be used. The gas flow of both the first and second fluidized bed furnaces is directed to and from the heat recovery boiler 4. • · ** *: further through the electrostatic precipitator 5 in the manufacture of the acid gas with the entrained dust is passed mikropelletointivaiheeseen as a binder.. Some or all of the dust from the heat recovery boiler can also be returned to another fluidized bed furnace. Further treatment of the resulting nickel oxide material with cooling is carried out in the same manner as described in connection with Figure 1.

5 EXAMPLES

Example 1

The example focuses on round bed spreading.

Nickel sulphide precipitated: Ni 60%, Fe 6%, Zn 3% and S 29%.

Micropellets made of precipitated nickel sulphide are roasted in a rotary bed. The reactor is fed with 2900 Nm 3 of air per 1000 kg of fresh micropellet feed. 2700 kg of micropellets are recycled to the bed. The entire cycle temperature is maintained at 850 ° C. A cyclone is obtained from a cyclone having a sulfur content of 0.2 to 0.5%.

Example 2

The example focuses on two-stage roasting.

• ···· ·· · · · · • :: i .: 20 precipitated nickel Ni 60%, Fe 6%, 3% Zn and S 29%.

• · • ·

Micropellets of precipitated nickel sulphide are roasted in a first step in a bubbling fluidized bed. The bed is fed with 310 Nm³ of air per 1000 kg of micropellets. This causes the bed temperature to rise to 650 ° C when oxidizing some of the sulfides. The sulfur level of the material drops to about 22%.

The hot product of the first stage is conducted to the second stage, to which 2500 Nm 3 of air is introduced. The temperature of the second stage is maintained at 800 ° C. with heating or heating. This second bubbling bed also returns dust • · ♦ .I / space. The second stage gives a toast with a sulfur content of 0.3%.

• · ··· *: ··: 30 «· • · ♦ • · ♦ • ·

Claims (10)

A process for oxidizing nickel sulfide to oxide in a fluidized bed furnace, characterized in that the finely divided nickel sulphide precipitate formed by doping is treated in the following steps: 5) a) 1000 ° C under oxidizing conditions to form a nickel oxide and a sulfur dioxide containing gas 10. Process according to Claim 1, characterized in that the roasting of the micro-pelletized precipitate takes place in a circulating bed furnace in one fluidized bed oven and a cyclone associated therewith, wherein the temperature of the entire cycle 15 is set at 750-1000 ° C. A process according to claim 2, characterized in that the micropellet stream to be recycled is at least 100 to 300% of the amount of fresh micropelletized nickel sulphide precipitate fed into the furnace. 20 Method according to claim 1, characterized in that the micropelleted nickel sulphide precipitate is treated in at least two fluidized bed furnaces where roasting takes place in a bubbling bed, wherein the first fluidized bed furnace is subjected to oxidation of particle surface 25 at a temperature of 650-750 ° C and a second fluidized bed furnace. 1000 ° C for complete oxidation of nickel sulphide to nickel oxide. Process according to claim 1, characterized in that the precipitated nickel sulphide precipitate has a grain size in the order of 5 to 20 µm. Process according to Claim 1, characterized in that the size of the micropelleted nickel sulphide precipitate is of the order of 0.2 to 1 mm. Method according to one of Claims 1 to 6, characterized in that 5 fuels are used for controlling the temperature of the fluidized bed furnace. Process according to Claim 1, characterized in that the nickel oxide formed in the fluidized bed furnace is cooled by fluidized bed cooling. 10 Process according to Claim 1, characterized in that the heat recovered from the exhaust gases of the fluidized bed furnace is used for drying the formed micropellets. Process according to Claim 1, characterized in that the sulfur dioxide gas formed is purified, after purification, to the preparation of sulfuric acid. 20