Method for shortening operation shutdown time of high pressure acid leach equipment in a hydrometallurgical process

Abstract

This invention provides a method for shortening operation shutdown time of high pressure acid leach equipment in a hydrometallurgical process, wherein the high pressure acid leach equipment comprises (i) means to transfer an ore slurry into the high pressure acid leach equipment;(ii) means to increase temperature and pressure of an ore slurry before leaching; (iii) means to add sulfuric acid into the high pressure acid leach equipment and to leach the ore slurry to obtain a leached slurry at high temperature under high pressure; (iv) means to adjust the pressure of the leached slurry; and (v) means to discharge the leached from the high pressure acid leach equipment; wherein, upon operation shutdown of the high pressure acid leach equipment, the leached slurry is subjected to self-circulation inside the high pressure acid leach equipment.

Claims

1. A method for shortening operation shutdown time of high pressure acid leach equipment in a hydrometallurgical process, wherein the high pressure acid leach equipment comprises (i) a first piping, wherein the first piping is used to transfer an ore slurry into the high pressure acid leach equipment; (ii) a multistage heater, wherein the multistage heater is used stepwise to increase temperature and pressure of the ore slurry before leaching or a leached slurry; (iii) an autoclave, wherein the autoclave is used to add sulfuric acid to the ore slurry with temperature and pressure increased by the multistage heater (ii) and to leach the ore slurry to obtain a leached slurry at high temperature under high pressure; (iv) a multistage flash tank to adjust the pressure of the leached slurry; (v) a second piping, wherein the second piping is used to discharge the leached slurry from the high pressure acid leach equipment; and (vi) a piping for self-circulation, wherein the piping for self-circulation is used to discharge the leached slurry from the multistage flash tank (iv) to transfer the leached slurry to the multistage heater (ii); wherein, in case of operation shutdown of the high pressure acid leach equipment, the leached slurry is subjected to self-circulation inside the high pressure acid leach equipment by transferring the leached slurry from the autoclave (iii) through the multistage flash tank (iv) and the piping for self-circulation (vi) to the multistage heater (ii), so that the high temperature and high pressure atmosphere of the autoclave (iii) is held.

2. The method according to claim 1, wherein the self-circulation of the leach slurry is achieved by: shutdown of the transfer of the ore slurry through the first piping (i), shutdown of the addition of sulfuric acid autoclave (iii), and shutdown of the discharge of the leached slurry in the second piping (v); and discharging the leached slurry from the multistage flash tank (iv) to transfer the leached slurry through the piping for self-circulation (vi) to the multistage heater (ii).

3. The method according to claim 1, wherein the pH of the leached slurry inside the high pressure acid leach equipment is adjusted at 3.0 to 5.0.

4. The method according to claim 1, wherein the temperature of the autoclave (iii) is 200 to 260° C.

5. The method according to claim 1, wherein the operation shutdown time is within 12 hours.

6. The method according to claim 2, wherein the pH of the leached slurry inside the high pressure acid leach equipment is adjusted at 3.0 to 5.0.

7. The method according to claim 2, wherein the operation shutdown time is within 12 hours.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a process chart representing an example of one embodiment of a hydrometallurgical Process for a nickel oxide ore, in a normal state, according to a High Pressure Acid Leach.

NOTATION

(2) 1 ore slurry preparation step 2 leaching step 3 solid-liquid separation step 4 neutralization step 5 sulfurization step 6 nickel oxide ore 7 ore slurry 8 leached slurry 9 leach solution 10 leaching residue 11 neutralized precipitate slurry 12 pregnant solution for nickel recovery 13 sulfide 14 barren solution

DETAILED DESCRIPTION OF THE INVENTION

(3) Explanation will be given below in detail on the hydrometallurgical Process for a nickel oxide ore, of the present invention.

(4) The hydrometallurgical Process for a nickel oxide ore of the present invention is a hydrometallurgical Process for a nickel oxide ore using a High Pressure Acid Leach including: a preparation step of ore slurry for making a slurry of a nickel oxide ore; a leaching step for obtaining leached slurry by transferring of the ore slurry to a High Pressure Acid Leach equipment equipped with the following means (a) to (c), for leaching nickel and cobalt; and a solid-liquid separation step of the leached slurry; and is characterized in that, in a trouble of the steps other than the above leaching step, the leached slurry, discharged from the means (c), which is used in the above High Pressure Acid Leach equipment, is subjected to self-circulation inside the High Pressure Acid Leach equipment, by shutdown of transfer to the above solid-liquid separation step, and transferring to the means (a), which is used in the above High Pressure Acid Leach equipment, as well as by shutdown of receiving the above ore slurry and the addition of sulfuric acid, in the above leaching step: means (a) to preliminarily increase temperature and pressure of the ore slurry; means (b) to form the leached slurry, by the addition of sulfuric acid to the ore slurry with preliminarily increased temperature and pressure, and leaching under blow of high-pressure steam and high-pressure air; means (c) to adjust a pressurized state of the leached slurry formed.

(5) In the hydrometallurgical Process for a nickel oxide ore of the present invention, it is important that, in a trouble of the steps other than the above leaching step, the above leached slurry is subjected to self-circulation inside the High Pressure Acid Leach equipment. In order to attain this, in the above leaching step, the leached slurry, discharged from the means (c), which is used in the above High Pressure Acid Leach equipment, is transferring to the means (a), which is used in the above High Pressure Acid Leach equipment, by shutdown of transfer to the above solid-liquid separation step, as well as by shutdown of receiving the above ore slurry and the addition of sulfuric acid. That is, by self-circulation of the above leached slurry inside the above High Pressure Acid Leach equipment, high-temperature and high-pressure conditions near a normal operation can be held inside the High Pressure Acid Leach equipment, in particular, in the means (b), therefore, operation can be started-up by switching to the ore slurry soon, if necessary, and high operation efficiency can be maintained. In addition, different from a conventional shutdown, switching to industrial water is not necessary, and thus discharged water is not generated, which contribute to enhancement of operation efficiency.

(6) The hydrometallurgical Process for a nickel oxide ore using the High Pressure Acid Leach relevant to the hydrometallurgical Process for of the present invention, is one including a preparation step of ore slurry by making a slurry of a nickel oxide ore; a leaching step for obtaining leached slurry by transferring of the ore slurry to the High Pressure Acid Leach equipment equipped with the following means (a) to (c), for leaching nickel and cobalt; and a solid-liquid separation step of the leached slurry, and the total process steps are those shown, for example, in FIG. 1.

(7) FIG. 1 is a process chart representing one example of an embodiment of a hydrometallurgical Process for a nickel oxide ore, in a normal state, according to a High Pressure Acid Leach.

(8) In FIG. 1, a nickel oxide ore 6 is firstly subjected to an ore slurry preparation step 1, to prepare ore slurry 7 including predetermined ore particle size and slurry concentration, and subsequently, in a leaching step 2, subjected to High Pressure Acid Leach using sulfuric acid to form a leached slurry 8. Next, the leached slurry 8 is subjected to the solid-liquid separation step 3, and after multistage washings, is separated to a leach solution 9 containing nickel and cobalt, and a leaching residue 10. The leach solution 9 is subjected to a neutralization step 4 to form a neutralized precipitate slurry 11 containing trivalent iron hydroxide and a pregnant solution for nickel recovery 12. Lastly, the pregnant solution for nickel recovery 12 is subjected to a sulfurization step 5, and is separated to a sulfide 13 containing nickel and cobalt and a barren solution 14 removed the nickel or the like. Here, the neutralized precipitate slurry 11 and the barren solution 14 are circulated to the solid-liquid separation step 3, if necessary. Still more, prior to the solid-liquid separation step 3, a step for preliminary neutralization of free sulfuric acid in the leached slurry 8 (a preliminary neutralization step), not shown in the drawing, may be provided with.

(9) Here, in a trouble of the steps other than the above leaching step 2 (for example, the ore slurry preparation step 1, the solid-liquid separation step 3, the neutralization step 4, the sulfurization step 5 or the preliminary neutralization step), the leached slurry 8 discharged from an apparatus at the exit side of the High Pressure Acid Leach equipment, which configures the leaching step 2, is subjected to self-circulation inside the High Pressure Acid Leach equipment, by shutdown of transfer to the solid-liquid separation step 3 or the preliminary neutralization step, and transferring to an apparatus at the entrance side of the High Pressure Acid Leach equipment, as well as by shutdown of receiving the above ore slurry 7 and the addition of sulfuric acid, in the leaching step 2.

(10) The above nickel oxide ore is not specially limited one but so-called a lateritic ore such as mainly limonite and saprolite. Nickel content in the above lateritic ore is usually 0.8 to 2.5% by weight, and nickel is contained as a hydroxide or a silicic bittern (magnesium silicate) mineral. In addition, iron content is 10 to 50% by weight, and iron is contained mainly as a trivalent hydroxide (goethite) form, however, divalent iron is partially contained in the silicic bittern mineral.

(11) The leaching step for obtaining the above leached slurry, that is, a leaching reaction in a normal state of the leaching step, for example, is performed by the leach reaction represented by the following formulae (1) to (3), and the high-temperature hydrolysis represented by the following formulae (4) and (5).

(12) [Leach Reaction]

(13) Formula (1):
MO+H.sub.2SO.sub.4.fwdarw.MSO.sub.4+H.sub.2O  (1)
(wherein M represents Ni, Co, Fe, Zn, Cu, Mg, Cr, Mn or the like.)
Formula (2):
2Fe(OH).sub.3+3H.sub.2SO.sub.4.fwdarw.Fe.sub.2(SO.sub.4).sub.3+6H.sub.2O  (2)
Formula (3):
FeO+H.sub.2SO.sub.4.fwdarw.FeSO.sub.4+H.sub.2O  (3)
[High-Temperature Thermal Hydrolysis]
Formula (4):
2FeSO.sub.4+H.sub.2SO.sub.4+½O.sub.2.fwdarw.Fe.sub.2(SO.sub.4).sub.3+H.sub.2O  (4)
Formula (5):
Fe.sub.2(SO.sub.4).sub.3+3H.sub.2O.fwdarw.Fe.sub.2O.sub.3+3H.sub.2SO.sub.4  (5)

(14) Temperature in the above leaching step, in a normal state, is 220 to 280° C., and preferably 240 to 270° C. That is, iron is fixed as hematite mostly, by performance of the reaction in this temperature range. In the temperature below 220° C., iron dissolves and remains in the reaction solution, due to low rate of the high-temperature thermal hydrolysis, resulting in increase in the solution purification load for removing the iron, which makes it very difficult to separate the iron from nickel. On the other hand, the temperature over 280° C. is not suitable, because not only selection of a material of a reactor to be used for High Pressure Acid Leach is difficult but also steam cost for raising temperature increases, although the high-temperature thermal hydrolysis itself is promoted.

(15) Slurry concentration in the above leaching step, in a normal state, is not especially limited, however, it is preferable that slurry concentration of the leached slurry is adjusted at about 30 to 45% by mass. That is, the leached slurry concentration lower than 30% by mass requires a large equipment to obtain the same residence time in leaching, and also the addition amount of an acid increases to adjust the residual acid concentration. In addition, the resulting leach solution has lower nickel concentration. On the other hand, the slurry concentration over 45% by mass raises a problem of difficult transfer (frequent pipe clogging, high energy requirement etc.) of high concentration slurry, although it allows smaller facility scale.

(16) The addition amount of sulfuric acid in the above leaching step, in a normal state, is not especially limited, and an excess amount is used so as to leach iron in a nickel oxide ore, for example, the amount of 250 to 400 kg per ton of the ore. The addition amount of sulfuric acid over 400 kg, per one ton of the ore, is not preferable, due to increased cost of the sulfuric acid.

(17) The High Pressure Acid Leach equipment to be used in the hydrometallurgical Process for of the present invention, is composed of means of the above (a) to (c), and means of the above (a) to (c) are not especially limited, however, it is preferable to use the following apparatus, respectively: means of (a): a multistage heater for increasing temperature and pressure of the ore slurry stepwise, means of (b): an autoclave for leaching the ore slurry at high temperature under high pressure, and forming the leached slurry with high temperature and high pressure, and means of (c): a multistage flash tank for decreasing temperature and pressure of the leached slurry stepwise. Here, self-circulation of the leached slurry inside the High Pressure Acid Leach equipment is performed by utilization of a valve on a pipeline to connect the flash tank and the preliminary neutralization step or the solid-liquid separation step, and by installment of a pipeline for self-circulation to connect the valve and the above heater.

(18) In the hydrometallurgical Process for of the present invention, pH of the relevant leached slurry, in self-circulation of the leached slurry inside the High Pressure Acid Leach equipment, is not especially limited, however, it is preferable to be adjusted at 3.0 to 5.0, and more preferably 4.0 to 5.0. That is, the pH below 3.0 provides low suppression effect of corrosion of the apparatus. On the other hand, the pH over 5.0 is not preferable due to increase in use amount of industrial water, that is, also discharged water amount.

(19) In the hydrometallurgical Process for of the present invention, temperature of the means (b), which composes the relevant High Pressure Acid Leach equipment, in self-circulation of the leached slurry inside the High Pressure Acid Leach equipment, is preferably set at 200 to 260° C., and more preferably 220 to 240° C. That is, it is most desirable to maintain temperature of the above normal state, however, the temperature below 200° C. decreases shortening effect of heat-up time in re-startup. On the other hand, the temperature over 260° C. may require temperature decrease, and thus provides useless consumption of high-pressure steam. It should be noted that it is enough to continuously supply and adjust steam to the autoclave in order to maintain and control temperature.

(20) The hydrometallurgical Process for of the present invention can be applied in a trouble of the steps other than the above leaching step for obtaining the above leached slurry, however, it is preferable to determine in what a state the High Pressure Acid Leach equipment shall wait, by judgment of which method is most suitable in view of operation efficiency, among a countermeasure method for self-circulation of the leached slurry of the present invention in the High Pressure Acid Leach equipment, corresponding to decision of estimated shutdown time in the leaching step accompanying with the relevant trouble; or a conventional method, that is a method for cooling by supplying industrial water instead of the ore slurry, in a connected state of each of the apparatuses; or a countermeasure method for cooling individually by separation of each of the apparatuses. In this way, in a practical operation, in the case of trouble generation in the above other steps, countermeasure is possible, based on judgment standards, for example, shown in Table 1, corresponding to estimated shutdown time of the above leaching step, based on restoration time of each of the troubles in normal operation.

(21) TABLE-US-00001 TABLE 1 Estimated Countermeasure Basis of judgment shutdown time method standards* The case Self-circulation Cooling time: 2 to 3 hours within of the present Heating time: 12 hours invention 1 to 2 hours Generated waste solution (volume): ≦600 m.sup.3 The case over Conventional Cooling time: 6 to 8 hours 12 hours method Heating time: 4 to 6 hours Generated waste solution (volume): ≧2000 m.sup.3 *Required values for each of the countermeasure methods.

(22) In Table 1, the above estimated shutdown time as a judgment standard of a countermeasure, is 12 hours. That is, a method for self-circulation of the leached slurry of the present invention in the High Pressure Acid Leach equipment is applicable preferably in the case where the above estimated shutdown time is within 12 hours. Here, reason for setting the above estimated shutdown time, as a standard, to be within 12 hours is because it requires usually about 6 to 8 hours to decrease temperature down to 150 to 180° C., and about 4 to 6 hours to increase temperature again, that is about 12 hours in total, in average, in the case where the High Pressure Acid Leach equipment is shutdown and temperature is decreased by separation of each of the apparatuses, and then temperature is increased again. That is, in the case where restoration time of troubles is over 12 hours, it is sufficient to respond to them by a conventional method. It should be noted that, in the case where restoration time of troubles is over 24 hours, a countermeasure by further decreasing temperature may be taken, in consideration of cost of steam to be consumed in warming the autoclave.

(23) It should be noted that 12 hours is taken as a guideline, in the judgment standard in Table 1, however, this is based on a time required from shutdown to start-up by a conventional countermeasure method, and thus in the case where this required time varies, the standard time may be adjusted and varied, as appropriate.

EXAMPLES

(24) Explanation will be given below in further detail on the present invention with reference to Example and Comparative Example of the present invention, however, the present invention should not be limited to these Examples.

Example 1

(25) In the hydrometallurgical Process for a nickel oxide ore using the High Pressure Acid Leach, which process is shown in FIG. 1, countermeasures was prepared to take that, in the case of generation of a trouble of the steps other than the above leaching step, the leached slurry discharged from a three-stage flash tank, which configures the above High Pressure Acid Leach equipment of the leaching step, is subjected to self-circulation inside the High Pressure Acid Leach equipment, by transferring to the entrance side of a three-stage heater, which configures the above High Pressure Acid Leach equipment, as well as by shutdown of receiving the ore slurry and the addition of sulfuric acid to the autoclave, in the above leaching step. It should be noted that pH of the leached slurry to be self-circulated was controlled at 3.7, and temperature inside the autoclave at 220° C.

(26) After one-year of operation performance (from January to December, 2007), the number of troubles generated during the relevant period was 6 times, however, a trouble giving estimated shutdown time of the High Pressure Acid Leach equipment over 12 hours was only once. As a result, shutdown of the High Pressure Acid Leach equipment was also only once (8 hours). Results are shown in Table 2.

(27) It should be noted that troubles caused by corrosion of a supply pump to the heater, mechanical seal apparatus and the like, were not observed.

Comparative Example 1

(28) In the hydrometallurgical Process for a nickel oxide ore using the High Pressure Acid Leach, which process is shown in FIG. 1, in the case of generation of a trouble of the steps other than the above leaching step, countermeasure was taken by either of a method for cooling, by supplying industrial water instead of the ore slurry, while each of the apparatuses are connected; or a method for cooling individually, by separation of each of the apparatuses.

(29) After one-year of operation performance (from January to December, 2006), the number of troubles generated during the relevant period was 7 times, and the High Pressure Acid Leach equipment was shutdown each time. Results are shown in Table 2.

(30) TABLE-US-00002 TABLE 2 Generated waste Shutdown Shutdown solution frequency time (volume) Example 1 once/y  8 hours/y 500 m.sup.3/y Com. 7 times/y 336 hours/y about 15,000 m.sup.3/y Example 1

(31) From Table 2, it is understood that, in Example 1, because countermeasures was taken, according to a method of the present invention, by self-circulation of the leached slurry inside the High Pressure Acid Leach equipment, in trouble generation, and for a trouble which estimated shutdown time of the High Pressure Acid Leach equipment is within 12 hours, shutdown time of the High Pressure Acid Leach equipment for one year, and discharged water amount generated are improved to a large extent, as compared with Comparative Example 1 representing a conventional method. That is, in Example 1, shutdown time of the High Pressure Acid Leach equipment for one year becomes equal to 1/40 or lower, as well as discharged water amount generated becomes about 1/30, showing that high operation efficiency can be maintained as a whole operation basis.

(32) As is clear from the above, the hydrometallurgical Process for a nickel oxide ore of the present invention, is suitable as a method for maintaining operation efficiency in trouble generation, in a hydrometallurgical Process for a nickel oxide ore using a High Pressure Acid Leach, because it is capable of preventing inevitable operation shutdown of the above leaching step, and maintaining high operation efficiency as a whole process basis, in a trouble of the steps other than the leaching step.