AU2008255186B2

AU2008255186B2 - Method for preventing short path in trommel

Info

Publication number: AU2008255186B2
Application number: AU2008255186A
Authority: AU
Inventors: Satoshi Matsumoto; Osamu Nakai; Keisuke Shibayama
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2008-01-22
Filing date: 2008-12-09
Publication date: 2012-12-20
Anticipated expiration: 2028-12-09
Also published as: JP2009173967A; JP5119944B2; PH12009000002A1; AU2008255186A1

Abstract

A method for preventing short path in a trommel, when a nickel oxide ore is charged into a drum washer constituted by 5 linking a drum and the trommel, and subjected to a wet grinding/classification process, in an ore processing step where a charging raw material to a smelting step is prepared from raw ore of nickel oxide ore after mined, is provided. The method is characterized by forming a projection line, 10 wherein the projection, in which the cross-section on a circumference of a cross-section perpendicular to the rotating shaft of the trommel on the inner surface of the trommel is nearly rectangular and also meets the following requirements of (1) and (2), are arranged on the same circumference, so as to meet 15 the following condition (3): (1) The width of the projection is nearly as long as the sieve opening of the trommel. (2) The height of the projection is nearly half as long as the sieve opening of the trommel. 20 (3) The pitch between projections in the projection line is nearly 4 times as long as the sieve opening of the trommel. [Figure 1] [Figure 2] (a) Side elevation view (b) Front elevation view

Description

P/00/01Il Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Method for preventing short path in trommel The following statement is a full description of this invention, including the best method of performing it known to us: lA METHOD FOR PREVENTING SHORT PATH IN TROMMEL BACKGROUND OF THE INVENTION FIELD OF THE INVENTION 5 The present invention relates to a method for preventing short path in a trommel, in more detail, to a method for preventing short path of ore in a trommel, when a nickel oxide ore is charged into a drum washer constituted by linking a drum and the trommel, and subjected to a wet grinding/classification 10 process, in an ore processing step where a charging rawmaterial to a smelting step is prepared from raw ore of nickel oxide ore after mining. Incidentally, the short path means that the nickel oxide ore, which should be essentially recovered as an undersize part in classification, is removed as an oversize part 15 in classification due to insufficient grinding of the ore lump. DESCRIPTION OF THE PRIOR ART As a smelting method for recovering nickel and cobalt from nickel oxide ore containing nickel of 1.0 to 2.0% and cobalt 20 of 0.1 to 0.5% respectively relative to the whole ore, a High Pressure Acid Leach method (may be referred to as HPAL method) using sulfuric acid, which is one of hydrometallurgy, has been lately employed. The HPAL method comprises a leaching step for obtaining 25 a leachate containing nickel and cobalt by adding sulfuric acid to, for example, an ore slurry of nickel oxide ore followed by leaching under the conditions of high temperature and high pressure; a neutralization step for adjusting the pH of the leachate containing impurity elements besides nickel and cobalt 2 to form a slurry of a neutralized deposit containing the impurity elements such as iron and a supernatant mother liquor for recovering nickel; and a sulfurization step for supplying hydrogen sulfide gas into the supernatant mother liquor for 5 recovering nickel to form a mixed sulfide of nickel/cobalt and a lean solution (for example, see Patent Document 1) . In this method, in the leaching step, 90% or more of nickel and cobalt in an ore slurry is leached. Then, after the leachate is separated, impurities in the leachate is separated and removed 10 by neutralization. In addition, the obtained mixed sulfide of nickel/cobalt has grade of nickel and cobalt in it of about 55 to 60% and 3 to 6% respectively and is used as an intermediate raw material in nickel/cobalt smelting. 15 Here, The above ore slurry of nickel oxide ore is usually prepared in an ore processing step where a charging raw material to a smelting step is prepared from raw ore of nickel oxide ore after mining. In this ore processing step for nickel oxide ore, low-grade nickel oxide ore of a nickel concentration of, for 20 example, about 1.0 to 2.0% is subjected to multi-stage classification (sieving) and grinding to form a slurry having a specified particle size and concentration for recovery, which is transferred to a subsequent leaching step. By the way, low-grade nickel oxide ore after mining has usually limonite 25 and saprolite coexisting therein and is fragile, red clay-like ore formed by weathering and contains goethite, serpentine, quartz and the like as the main mineral. It is, therefore, originally fragile and easy to be ground. When raw nickel oxide ore is piled up for storage after mining, however, the nickel 3 oxide ore lumps partly like dumpling and is necessary to be ground in order to form the ore slurry. Furthermore, because raw ore often contains contaminants other than nickel oxide ore such as gangue of peridotite etc. that does not contain valuable 5 substances such as nickel at an economical level and tree roots, which commingled in mining, it is essential to remove these contaminants in addition to classification/grinding of the nickel oxide ore, which is the primary object, in the ore processing step. 10 Incidentally, the term "grinding" used in this description means loosening a large lump of nickel oxide ore lumped like dumpling into smaller one. Consequently, an operation of "grinding" can be conducted with weaker power compared with an operation of "crushing" which usually means crushing 15 contaminants such as gangue to smaller lump. Generally, in an ore processing step for the nickel oxide ore, large lumps of nickel oxide ore and contaminants that are included in fed raw ore are separated and removed one after 20 another (hereinafter, may be referred to as rejected) through multistage grinding and classification. For example, first, after using facilities rejecting mainly the large contaminants, an undersize part is subjected to rejecting middle-sized contaminants by a wet process using water in a drum washer that 25 is constituted by linking a cylinder part called a drum and a trumpet-like screen part called a trommel so that each centerline of the circular cross sections thereof is nearly horizontal. Further, a slurry containing a grain size less than specified size is obtained through a final-stage screen in a 4 wet process using water, concentrated with a thickener and then transferred to an HPAL step. Here, because an oversize part that is rejected at the trommel of the drum washer contains many contaminants and also is too disadvantageous costwise to run 5 down with a pump, it is usually discarded. In an actual operation, however, insufficient grinding is generated in the drum of a drum washer depending on the conditions of raw ore in the ore deposit and storage conditions 10 after mining etc. In such a case, the nickel oxide ore, which is not ground and remains as a lump, is rejected as an oversize part in a trommel having a specified sieve opening. Such short path causes the efficiency of grinding and classification to be greatly lowered. Incidentally, the "sieve opening" to be 15 used here indicates a substantial size by the ore size that passed through the sieve. As this solution, it is easily thought of to increase a rotation speed of a drum washer or to put in the balls into the 20 drumof a drum washer in order to sufficiently grind nickel oxide ore. In these cases, however, contaminants in the drum, especially gangue serves as the balls in a ball mill to express a crushing effect. As the result, the gangue itself is crushed to a size below the sieve opening of the trommel, resulting in 25 increased amount of ore transferred to a subsequent screen, which may accelerate damage of the screen and its pump and piping. Another method for separating precisely and efficiently 5 excavated surplus soil to mud, gravel, coarse sand, fine sand, silt and clay has been disclosed (for example, see Patent Document 2). This method, however, is not applicable to solving the above problem of a drum washer because a lump of clay is s crushed into a size of 2 pm by a water jet. In other words, it is because the slurry formed by grinding and classification in the drum washer is expected to be adjusted to a specified grain size for suitable fluidity as described above. 10 Under the above situation, in an ore processing step for preparing a charging raw material to a smelting step from raw ore of nickel oxide ore after mining, the method for preventing short path of ore in grinding/classification of nickel oxide ore with a drum washer has been sought. 15 Patent Document 1: JP-A-2005-350766 (page 1, page 2) Patent Document 2: JP-A-09-239288 (page 1, page 2) Reference to any prior art or background information in this specification is not, and should not be taken as, 20 an acknowledgment or any form of suggestion that this prior art or background information forms part of the common general knowledge in Australia or any other jurisdiction; or that this prior art or background information could reasonably be expected to be ascertained, understood and 25 regarded as relevant by a person skilled in the art. As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not 6 intended to exclude further additives, components, integers or steps. SUMMARY OF THE INVENTION 5 Considering the above problem of conventional technologies, the object of the present invention is to provide a method for preventing short path of ore in a trommel, when a nickel oxide ore is charged into a drum washer, constituted by linking a drum and the trommel, and subjected to a wet 10 grinding/classifaction process in an ore processing step for preparing a charging raw material to a smelting step from raw ore of nickel oxide ore after mining. After having intensively studied a way to prevent short path of ore in a drum washer in order to attain the above object, 15 the present inventors have found that the short path of ore in a trommel, constituting the drum washer, can be prevented by forming a projection line comprising an arrangement of projections of a specified shape with a specified pitch at a specified position on the inner surface of the trommel. 20 That is, according to the 1st aspect of the present invention, a method for preventing short path of ore in a trommel is provided. The short path of ore in the trommel is prevented when a nickel oxide ore is charged into a drum washer constituted 25 by linking a drum and the trommel, and subjected to a wet grinding/classification process. The method is characterized by forming a projection line comprising a plurality of projections, wherein the cross-section of the projections, on a circumference 7 of a cross-section perpendicular to a rotating shaft of the trommel on the inner surface of the trommel, is nearly rectangular and also meets the following requirements of (1) and (2), as they are arranged on the circumference, so as to meet 5 the following condition (3): (1) the width of the projection is nearly as long as the sieve opening of the trommel, (2) the height of the projection is nearly half as long as the sieve opening of the trommel, and 10 (3) the pitch between projections in the projection line is nearly 4 times as long as the sieve opening of the trommel. In addition, in one or more embodiments, the sieve opening of the trommel is 25 mm, the width of the projection is 22 to 28 mm in length and the height of the projection is is 11 to 14 mm in length and that the pitch of the projections in the projection line is 88 to 112 mm in length. In one or more embodiments, the projection line is arranged at the position (a) where a slurry, composed of nickel oxide ore and water, runs down from the drum and falls 20 in the trommel. In one or more embodiments, the position (a) of the projection line is located at a position 100 to 150 mm distant from the part of a drum and the trommel toward the sieve opening of the trommel. 25 In one or more embodiments, at least one line of projections is arranged at every position distant about 3 8 times as long as the sieve opening of the trommel from the position (a) of the projection line toward the trommel outlet and that the position of projections of the arranged projection line is arranged so as to be nearly halfway between s the projections of the front line. In one or more embodiments, the sieve opening of the trommel is 25 mm and that at least one line of projections is arranged at every position 66 to 84 mm distant from the position (a) of the projection line toward the trommel outlet. 10 In one or more embodiments, there is provided a method for preventing short path in a trommel characterized in that the nickel oxide ore to be charged into the drum washer is an undersize part after passing a classification facility with a classified grain size of about 150mm. 15 The method for preventing short path in a trommel of the present invention can prevent short path of ore in a trommel, when a nickel oxide ore is charged into a drum washer constituted by linking a drum and the trommel, and subjected to a wet grinding/classification process, in an ore processing 8A step for preparing a charging raw material to a smelting step from raw ore of nickel oxide ore after mining and can suppress the amount of the nickel oxide ore removed from the ore processing process to outside of system and thus can improve a 5 recovery rate of nickel and cobalt into an ore slurry. The method, therefore, is industrially very valuable. BRIEF DESCRIPTION OF THE DRAWINGS 9 [Figure 1] Figure 1 is a schematic view illustrating one example of the structure of a drum washer. [Figure 2] Figure 2 is a schematic view illustrating one example of projection arrangement of a projection line formed 5 in the trommel used in the present invention. [Figure 3] Figure 3 is a schematic view illustrating one example of projection arrangement of a projection line formed in the trommel used in the present invention. [Figure 4] Figure 4 is a block diagram showing an ore processing 10 step for nickel oxide ore and one example of the facilities constituting the step. NOTATION 1 Drum washer 15 2 Drum 3 Trommel 4 Nickel oxide ore 5 Water 6 Feeding 20 7 Recovery blade 8 Undersize part (-25 mm) 9 Oversize part (+25 mm) 10 Projections 20 Static grizzly 25 21 Shakeout machine 22 Drum washer 23 Vibrating screen 24 Intermediate tank (Slurry tank) 25 Thickener 10 26 Nickel oxide ore 27 HPAL step 28 Water 29 +250 mm 5 30 +150 mm 31 +25 mm 32 +1.4 mm DETAILED DESCRIPTION OF THE INVENTION 10 The method for preventing short path in a trommel of the present invention is described in detail hereinafter. The method for preventing short path in a trommel of the present invention is a method for preventing short path of ore in a trommel when a nickel oxide ore is charged into a drum washer 15 constituted by linking a drum and the trommel, and subjected to a wet grinding/classification process, and the method is characterized by forming a projection line, wherein the projection, in which the cross-section on a circumference of a cross-section perpendicular to the rotating 20 shaft of the trommel on the inner surface of the trommel is nearly rectangular and also meets the following requirements of (1) and (2), are arranged on the same circumference, so as to meet the following condition (3), is provided. (1) The width of the projection is nearly as long as the sieve 25 opening of the trommel. (2) The height of the projection is nearly half as long as the sieve opening of the trommel. (3) The pitch between projections in the projection line is nearly 4 times as long as the sieve opening of the trommel.

11 In the method of the present invention, it is important to form a projection line composed of a plurality of projections of a specified shape on the inner surface of a trommel 5 constituting the drum washer in a wet grinding/classification process where nickel oxide ore is charged into the drum washer. Thereby, the above projections help that the dumpling-like lump of nickel oxide ore grinds, and by getting rid of the dumpling-like lump, short path of the dumpling-like lump of 10 nickel oxide ore run down into the trommel can be prevented. That is, the projection line works as an obstacle of the ore run down on a trommel. Here, the dumpling-like lump of nickel oxide ore is ground to an undersize part of the sieve 15 opening by collision with the projections while coming down on the substantially downward slope of the trommel, and then transferred from the trommel to a subsequent screen. The projections have also an effect to lower the speed at which the nickel oxide ore comes down. The nickel oxide ore, therefore, 20 comes down slowly on the trommel even when it does not collide directly with the projections. This increases the frequency of collision with each other of the lumps leading to grinding the nickel oxide ore to an undersize part of the sieve opening. Moreover, contaminants are not subjected to enough strength to 25 be crushed in the above any collision and are rejected from the trommel as it is. In the above method, the cross-sectional shape of the projections is nearly rectangular on the circumference of a 12 cross-section perpendicular to the rotating shaft of a trommel. Here, the nearly rectangular shape is not necessarily a rectangle having uniform width and height and includes a square, an oblong and other partly irregular shape based on these shapes 5 which are expected to serve as at least an obstacle for the ore run down on the trommel. As the size of the projections, it is essential that the width of the projection, that is, the width of the cross-section 10 of the nearly rectangular shape is nearly as long as the sieve opening of a trommel, and the height of the projection, that is, the height of the cross-section of the nearly rectangular shape is nearly half as long as the sieve opening of a trommel and that the pitch of the projections in projection line is 15 nearly 4 times as long as the sieve opening of a trommel. Incidentally, the thickness of the projection is not particularly limited and is designed so as to withstand the impact of ore and the like. Thereby, sufficient effect can be given as an obstacle to the ore run down on the trommel. 20 In the case of a sieve opening of a trommel of 25 mm, for example, it is preferable to use a projection of a width of 22 to 28 mm and a height of 11 to 14 mm, and a projection line having a pitch of 88 to 112 mm. Here, the size of projection and the 25 pitch of projection in projection line are selected as appropriate depending on the sieve opening of a trommel adjusted according to the size of nickel oxide ore and contaminants that are transferred to the trommel. However, because the size of the actual ore to be classified has a variation of at least about 13 10 to 20%, the size and pitch is adjusted based on the sieve opening of a trommel with considering the variation. Here, the relation between the sieve opening of a trommel 5 and the size of a projection is described in detail below. Firstly, the structure and function of a drum washer is explained using the figures. Figure 1 is a schematic view illustrating an example of the structure of the drum washer used in the present invention. 10 In Figure 1, the drum washer 1 is composed of a cylindrical part called a drum 2 and a trumpet-like screen called a trommel 3, which are linked so that the center lines of respective circular cross-sections are nearly horizontal. Nickel oxide ore 4 of, for example, -150 mm size and water 5 are subjected 15 to feeding 6 from the drum 2 side of the drum washer 1 and most of the ore is ground by the rotating drum washer 1 and slurried. Afterward, the ore is raked up along with the rotation of the drum 2 by a recovery blade 7 installed on the inner wall 20 of the drum 2 of the connecting part and raked out to the trommel 3. The trommel 3 has a trumpet-like shape enlarging toward the outlet and gives a downward slope when the ore is passed. Therefore, the ore transferred to the trommel 3 are classified while coming down on this slope. In the case of a sieve opening 25 of 25 mm, the undersize part 8 (-25 mm) is transferred to a subsequent screen, while the oversize part 9 (+25 mm) is rejected. In addition, the ore of -25 mmadhering on the surface of the oversize part is washed off with using water 5 in the trommel 3 and recovered in the subsequent screen.

14 Incidentally, the trommel 3 of the drum washer 1 has a diameter of about 8/10 to 9/10 of the diameter of the drum 3 at the connecting part of the drum 2 and the trommel 3 and almost 5 same diameter as that of the drum 3 at the outlet of the trommel 3 and thus has a trumpet-like shape enlarging toward the outlet of ore. In addition, the trommel 3 has a network structure of a sieve opening of 25 mm. In addition, the drum washer 1 rotates around the centerline of the circular cross-section and dips 10 water up to a depth of about 1/4 to 1/3 of the diameter of the drum. Next, the projection line formed in the trommel to be used in the present invention is explained using a figure. Figure 15 2 is a schematic view illustrating one example of the projection arrangement of the projection line formed in the trommel to be used in the present invention. Figure 2 shows the case when the projection line in trommel 3 is one line. Here, many projections 10 are usually arranged 20 at a specified pitch according to the size of the trommel 3, although the front elevation view (b) shows only 4 projections 10. Here, as shown in the side elevation view (a), the projection line is formed by arranging projections 10 of a specified size at a specified pitch in a row on the circumference 25 of a cross-section perpendicular to the rotating shaft of the trommel 3. Subsequently, the grinding function by the projection line formed in the trommel and the relation thereto between the sieve 15 opening of the trommel and the size of the projections are described. The dumpling-like lump of nickel oxide ore among the nickel oxide ore and contaminants transferred to the trommel from the 5 drum is ground to an undersize part of the sieve opening by collision with the projections while coming down on the downward slope of the trommel. In addition, the nickel oxide ore comes down more slowly in the trommel than in a conventional facilities even when it does not directly collide with the 10 projections. This increases the frequency of collision with each other of the lumps leading to grinding the nickel oxide ore to an undersize part than the sieve opening. On the other hand, contaminants are not subjected to enough strength to be crushed and are rejected from the trommel without being crushed. 15 The reason why, the width of a projection is nearly as long as the sieve opening of a trommel and its height is nearly half as long as the sieve opening of a trommel, is described. That is, a projection of which the width is shorter than 20 the sieve opening has not enough strength to hold itself on a trommel. On the other hand, a projection of which the width is longer than the sieve opening lowers the speed at which nickel oxide ore comes down on the slope resulting in clogging of the ore. The height of a projection is made nearly half as long 25 as the sieve opening in order to avoid clogging of a larger lump than the sieve opening between projections. A larger lump than a projection can easily get over the projection of which the height is nearly half as long as the sieve opening because the center of gravity of the lump is not interrupted by the 16 projection. On the other hand, a projection of which the height is less than about the half of the sieve opening does not provide a sufficient effect of preventing short path because even a smaller lump than the sieve opening easily gets over the 5 projection. Incidentally, the nickel oxide ore smaller than the sieve opening does not cause clogging even when it is interrupted by the projection, because it easily passes through the network of the trommel. 10 The pitch between projections in the projection line is made nearly 4 times as long as the sieve opening in order to avoid clogging of the lumps ground to a smaller size than sieve opening by making the pitch between projections about 3 times as long as the sieve opening. That is, because it is rare for 15 three lumps of ore to come in a row, there will be no clogging when the clearance between projections is made nearly 3 times as long as the sieve opening. Even when three lumps happen to come in a row, there will be no clogging. In contrast, when the pitch between projections is made only nearly 2 times as 20 long as the sieve opening, two lumps of ore come often in a row resulting in clogging. On the other hand, when the pitch between projections is made more than nearly 3 times as long as the sieve opening, the effect of the projections for preventing short path is reduced as much. 25 The material of the projection is not particularly limited and includes a material such as steel durable to the reaction force generated by grinding. In addition, the way for attaching a projection to the inner surface of a trommel includes a way 17 of welding or bolting, and bolting, which is easy to adjust, is preferable as demand of an actual operation. The above method enables recovery of about 40% or more 5 of the dumpling-like nickel oxide ore that would be rejected as an oversize part in a trommel when a conventional drum washer having no projection is used. In the above method, the location, at which a projection 10 line is arranged, is not particularly limited. The optimum location on the circumference of a cross-section perpendicular to the rotating shaft of a trommel on the inner surface of the trommel provides a greater effect. The position (a) which is located at 100 to 150 mm distant from the connecting part of 15 a drum and the trommel toward the trommel outlet is preferable. That is, as illustrated in Figure 1, the nickel oxide ore is raked up by the recovery blade installed on the inner wall of the connecting part of the drum and transferred to the trommel. 20 In this case, when the nickel oxide ore to be charged into the drum washer is, for example, an undersize part after passed a classifier of sieve grain size of about 150 mm, many lumps of ore having a grain size of about 25 to 50 mm are usually present accompanied partly by the lumps of a grain size of about 100 25 mm. It is observed that the nickel oxide ore of such a grain size falls on a position about 100 to 150 mm distant from the connecting part toward the trommel outlet. Consequently, when the projection line is arranged at this position, the nickel oxide ore collides with the projection at 18 falling, and thus is easily ground. Incidentally, contaminants are seldom crushed even similarly colliding with the projections at falling. This arrangement enables recovery of about 70% or more of the dumpling-like nickel oxide ore that 5 would be rejected as an oversize part in a trommel when a conventional drum washer having no projection is used. Further, 2nd projection line or more projection lines may be arranged as necessary located at a specified distance from 10 the position (a) of the above-mentioned projection line in order to obtain a greater effect. Here, it is preferable that at least one projection line is arranged at every position distant about 3 times as long as the sieve opening of the trommel from the above position (a) of the projection line toward the trommel 15 outlet and that each projection of the arranged projection line is located nearly halfway between the projections of the front line. Figure 3 is a schematic view showing one example of projection arrangement of projection line formed in the trommel used in the present invention. 20 Figure 3 shows the case of two projection lines in the trommel 3. Here, many projections 10 are usually arranged at a specified pitch according to the size of the trommel 3, although the front elevation view (b) shows only 4 projections 25 10 in each of the first and second line. Here, as shown in the side elevation view (a), the second projection line is formed by arranging the projections at a specified pitch in one line on the circumference of a cross-section perpendicular to the rotating shaft of the trommel 3 so that the position of 19 projections is located nearly halfway between the projections of the first line. Here, the first projection line which is closest to the connecting part is located at a position 100 to 150 mm distant from the connecting part, while the second line 5 is arranged at a position distant from the first line by a length of about 3 times as long as the sieve opening of the trommel. By this arrangement, an effect that the lumps having evaded the collision with the projections in the first line collide with those in the second line and an effect that the speed of coming 10 down of the lumps is reduced are added. In other words, the classification free of clogging can be conducted by making the clearance of each projections 3 times as long as the sieve opening and arranging the position of projection at nearly halfway between the projections of the front line. 15 For example, when the sieve opening of the trommel is 25 mm, at least one projection line is preferably arranged at every position 66 to 84 mm distant from the above-mentioned position (a) of the projection line toward the trommel outlet. 20 The number of the projection line to be arranged is not particularly limited. The more lines is more desirable in order to increase the chance of grinding, but 3 lines or less in total are preferable. Lines over 3 are not expected to produce as much 25 effect, and on the contrary increase trouble maintaining such as adjusting and exchanging. This arrangement of the line enables recovery of about 80% or more of the dumpling-like nickel oxide ore that would be rejected as an oversize part in a trommel when a conventional 20 drum washer having no projection is used. The ore processing step of nickel oxide ore where the above method is used is not particularly limited. It is a step for 5 preparing an ore slurry of a specified grain size and concentration as a charging raw material to a smelting step from raw ore of nickel oxide ore after mining. And it is applicable to the ore processing step where a drum washer constituted by linking a drum and a trommel is used as one stage of processing 10 facility. Thereby, when nickel oxide ore is charged into a drum washer constituted by linking a drum and a trommel and subjected to wet grinding/classification, the recovery rate of nickel and cobalt into an ore slurry can be improved by preventing short path of the ore in the trommel and suppressing discharge of 15 nickel oxide ore from the ore processing step to the outside. Figure 4 is a block diagram showing an example of the facilities constituting the ore processing step of nickel oxide ore relating to the present invention. 20 In Figure 4, large lumps of ore and contaminants contained in the charged nickel oxide ore 26 are separated and removed one after another through grinding and classification in the facilities of 4 stages. In the 1st stage, the size of +250 mm (29) is rejected by, for example, facilities called a static 25 grizzly 20 and the undersize part is transferred to, for example, facilities called a shakeout machine 21 of the 2nd stage. The size of +150 mm (30) is rejected by the shakeout machine 21 and the undersize part is transferred to facilities called a drum washer 22 of the 3rd stage. In the drum washer 22, the size 21 of +25mm (31) is rejected by charging of water 28 and transferred to facilities called a vibrating screen 23 of the 4th stage. In the vibrating screen 23, the size of +1.4 mm (32) is rejected by charging of water 28. The slurry of the undersize part than 5 those is concentrated in a thickener 25 via an intermediate tank (slurry tank) 24 and then transferred to an HPAL step 27. In the ore processing step composed of the facilities of 4 stages for grinding and classification, the role of the static 10 grizzly of the 1st stage and the shakeout machine of the 2nd stage is to prevent the subsequent facilities frombeing damaged by slurried contaminants such as gangue and large lumps. In addition, the role of the drum washer of the 3rd stage and the vibrating screen of the 4th stage is to effectively grind in 15 a wet process without increasing contaminants when making a slurry by adding water. As the result, the grain size of the ore slurry of nickel oxide ore passed through the vibrating screen of the 4th stage is usually 10% by mass or less of -1.4 to +0.1 mm and 90% by mass or more of -0.1 mm. Incidentally, 20 the obtained slurry is adjusted to have the above grain size in order to show fluidity suitable for transferring to an HPAL step after concentrating in a subsequent thickener. Here, the lumps of 150 mm or larger are rejected by the shakeout machine of the 2nd stage, while the undersize part than 25 those is fed to the drum washer of the 3rd stage. Most of contaminants are removed in the static grizzly of the 1st stage and the shakeout machine of the 2nd stage without being ground.

EXAMPLES

22 Hereinafter, the present invention is described in more detail with reference to the examples and comparative examples of the invention, however, the present invention is not limited to these examples at all. Incidentally, the method for 5 evaluating a grain size used in the examples and comparative examples was carried out by a classification method using a sieve having a sieve opening of 0.1 mm. In addition, the ore processing step and the drum washer and the operating conditions thereof used in the examples and comparative examples are as 10 follows. [Ore processing step] Raw nickel oxide ore, which limonite and saprolite coexist, was processed in the ore processing step shown in Figure 4. The classified grain size by each facilities is 250 mm for the static 15 grizzly of the 1st stage, 150 mm for the shakeout machine of the 2nd stage, 25 mm for the drum washer of the 3rd stage and 1.4 mm for the vibrating screen of the 4th stage. [Drum washer and operating conditions thereof] The drum washer is constituted by linking a drum of 6.1 20 m in length and a trommel of 1 m in length each in the direction of the rotating shaft. In addition, the drum has a diameter of 3.2 m, and the trommel has a trumpet-like shape having a diameter at the connecting part of 2.6 m and a diameter at the outlet of 2.8 m. The trommel is made of a steel net of a sieve 25 opening of 25 mm. In addition, the slurry composed of nickel oxide ore and water is present up to about 1 mm in depth in the drum part. The operating conditions of the drum washer are as follows: The charging raw material size of -150mm passed through the 23 shakeout machine of 2nd stage in the ore processing step was used and this charging raw material contains contaminants such as gangue and tree roots with nearly same ratio, wherein the nickel ore is about 90% by volume and the contaminants are about 5 10% by volume. In addition, the charging rate of nickel oxide ore is about 40 m 3 /hr (150 wet tons/hr), whereas the charging rate of water is about 100 m 3 /hr. Here, the operation was conducted in the presence and absence of the arrangement of projection line into the trommel 10 and with various shapes and pitches of projections. (Example 1) A projection line was formed in the trommel of the above drum washer. Here, the projection line was arranged by bolting 15 the projections at a pitch of 100 mm on the circumference of a cross-section perpendicular to the rotating shaft of the trommel located at the position 300 mm distant from the connecting part of the drum and the trommel toward the outlet. The projection was a plate having a width of 25 mm which was 20 nearly as long as the sieve opening of the trommel, a height of 13 mm which was nearly half as long as the sieve opening of the trommel and a thickness of 5 mm, and the plate was made of a steel plate of 5 mm in thickness. After operating the drum washer under the above operating 25 conditions for an hour, the mass fraction (fraction of short path) of the dumpling-like nickel oxide ore contained in the oversize part removed in the trommel and the grain size of the ore in the ore slurry after passed through the vibrating screen of the next stage were evaluated. The results are shown in Table 24 1. Incidentally, contaminants, which passed through the trommel and were transferred to the vibrating screen, were only small part. 5 (Example 2) The drum washer was operated similarly to in Example 1 except that a projection line was arranged on the circumference located at the position 120 mm distant from the connecting part of the drum and the trommel toward the outlet. 10 After operating the drum washer under the above operating conditions for an hour, the mass fraction (fraction of short path) of the dumpling-like nickel oxide ore contained in the oversize part removed in the trommel and the grain size of the ore in the ore slurry after passed through the vibrating screen 15 ofthenext stage were evaluated. The results are shown in Table 1. Incidentally, contaminants, which passed through the trommel and were transferred to the vibrating screen, were only small part. 20 (Example 3) The drum washer was operated similarly to in Example 1 except that the projections of a first line were arranged at the position 120 mm distant and the projections of a second line were arranged at the position 200 mm distant each from the 25 connecting part of the drum and the trommel toward the outlet and that the projections of the second line were arranged checkerwise halfway between the projections of the first line. After operating the drum washer under the above operating conditions for an hour, the mass fraction (fraction of short 25 path) of the dumpling-like nickel oxide ore contained in the oversize part removed in the trommel and the grain size of the ore in the ore slurry after passed through the vibrating screen of the next stage were evaluated. The results are shown in Table 5 1. Incidentally, contaminants, which passed through the trommel and were transferred to the vibrating screen, were only small part. (Comparative Example 1) 10 The drum washer was operated similarly to in Example 1 except that no projection line was formed in the trommel of the drum washer. After operating the drum washer under the above operating conditions for an hour, the mass fraction (fraction of short 15 path) of the dumpling-like nickel oxide ore contained in the oversize part removed in the trommel and the grain size of the ore in the ore slurry after passed through the vibrating screen of the next stage were evaluated. The results are shown in Table 1. 20 (Comparative Example 2) The drum washer was operated similarly to in Example 1 except that the width of the projection was 50 mm. After operating the drum washer under the above operating 25 conditions for an hour, the ore came down on the slope slowly and thus piled at the projection line worsening the run down situation. (Comparative Example 3) 26 The drum washer was operated similarly to in Example 1 except that the projections were arranged at a pitch of 50 mm. After operating the drum washer under the above operating conditions for an hour, the lumps of ore clogged between the 5 projections and thus piled at the projection line worsening the run down situation. (Comparative Example 4) The drum washer was operated similarly to in Example 1 10 except that the projections were arranged at a pitch of 150 mm. After operating the drum washer under the above operating conditions for an hour, the effect of suppressing short path with the projections was not obtained. 15 Table 1 Projection Position of Fraction Grain size of Width Pitch projection of short- ore in ore (mm) (mm) line pass (%) slurry (mm) Example 1 25 100 300 10 -0.1 mm: 90% by mass Example 2 25 100 120 3 -0.1 mm: 89% by mass Example 3 25 First First line: 2 -0.1 mm: 89% line: 120 by mass 100 Second ,line: 200 Comparative Non 20 -0. 1 mm: 91% Example 1 by mass It can be understood from Table 1 that because Examples 1 to 3 were conducted according to the method of the present invention where a projection line was formed on the 20 circumference of a cross-section perpendicular to the rotating 27 shaft of a trommel on the inner surface of the trommel by arranging the projections having a nearly rectangular cross-section on the circumference and a specific size, at a specified pitch, short path of nickel oxide ore in the trommel 5 was able to be suppressed when the nickel oxide ore was charged into a drum washer constituted by linking a drum and the trommel and subjected to a wet grinding/classification process in an ore processing step for preparing a charging raw material to a smelting step from raw ore of nickel oxide ore after mining. 10 With this method, an ore slurry having a grain size of the ore similar to that of a conventional method can be obtained and at the same time the contaminants transferred to a subsequent vibrating screen can be reduced. Furthermore, the nickel oxide ore that has been rejected as an oversize part in a conventional 15 method can be greatly reduced. In contrast, in Comparative Example 1, it can be understood that no projection line is formed and the above conditions are not satisfied, therefore, the short path of ore in a trommel occurs frequently resulting in insufficient performance. 20 In addition, in Comparative Examples 2 to 4, because the shape and pitch of the projections do not satisfy the above conditions, the ore piles at the projection line worsening the run down situation, or the effect of suppressing the short path by the projections can no be obtained. 25 As apparent from the above, the method for preventing short path in a trommel is effectively used as a method for preparing a charging raw material of a High Pressure Acid Leach method (HPAL method) using sulfuric acid that is used as a smelting 28 method for recovering nickel and cobalt from nickel oxide ore. Thereby, in an ore processing step for preparing a charging raw material to a smelting step from raw ore of nickel oxide ore after mining, this method can improve a recovery ratio of the 5 nickel oxide ore to an ore slurry to be used as the above charging raw material by preventing short path in a trommel.

Claims

1. A method for preventing short path in a trommel, wherein the short path of ore in said trommel is prevented when a nickel 5 oxide ore is charged into a drum washer constituted by linking a drum and the trommel, and subjected to a wet grinding/classification process, and the method is characterized by forming a projection line comprising a plurality of projections, wherein the cross 10 section of the projections, on a circumference of a cross-section perpendicular to a rotating shaft of the trommel on the inner surface of the trommel, is nearly rectangular and also meets the following requirements of (1) and (2), as they are arranged on the circumference, so as to meet the following condition (3): 15 (1) the width of the projection is nearly as long as a sieve opening of the trommel; (2) the height of the projection is nearly half as long as the sieve opening of the trommel; and (3) the pitch between projections in the projection line is 20 nearly 4 times as long as the sieve opening of the trommel.

2. The method for preventing short path in a trommel according to claim 1 characterized in that the sieve opening of the trommel is 25 mm, the width of the projection is 22 to 28 mm in length and the height of the projection is 11 to 14 25 mm in length and that the pitch of the projections in the projection line is 88 to 112 mm in length. 30

3. The method for preventing short path in a trommel according to claim 1 or 2 characterized in that the projection line is arranged at a position (a) where a slurry, composed of nickel oxide ore and water, runs down from the drum and falls in s the trommel.

4. The method for preventing short path in a trommel according to claim 3 characterized in that the position (a) of the projection line is located at position 100 to 150 mm distant 10 from the connecting part of the drum and the trommel toward the sieve opening of the trommel.

5. The method for preventing short path in a trommel according to claim 3 or 4 characterized in that at least one 15 line of projections is arranged at every position distant about 3 times as long as the sieve opening of the trommel from the position (a) of the projection line toward the trommel outlet and that the position of projections of the arranged projection line is arranged so as to be nearly halfway between the 20 projections of the front line.

6. The method for preventing short path in a trommel according to claim 5 characterized in that the sieve opening of the trommel is 25 mm and that at least one line of 25 projections is arranged at every position 66 to 84 mm distant from the position (a) of the projection line toward the trommel outlet.

7. The method for preventing short path in a trommel 31 according to any one of claims 1 to 6 characterized in that the nickel oxide ore to be charged into the drum washer is an undersized part after passing a classification facility with a classified grain size of about 150 mm. 5

8. A method for preventing short path in a trommel substantially as hereinbefore described with regard to the accompanying drawings.