US2978317A - Method of processing lateritic nickeliferous ores - Google Patents

Description

METHOD OF PROCESSING LATERITIC NICKELIFEROUS ORES TokuichiTakakuw-a, 4228 Minaminaya-cho,

Yokkaichi-shi, Mia-ken, Japan No Drawing. Filed Mar. 26, 1959, Ser. No. 802,035 Claims priority appli cation'Japan Aug. 29, 1958 I 12. Claims. (CI. 7521) This invention relates to a method of processing laterites, and more particularly to a method of processing nited States Patent 2,978,317 7 Patented Apr. 4, 1961 2 cobalt mineral from the laterite which may be further processed to recover the chromium and cobalt, respectively.

Another object of the invention is the provision of a new and improved means by which ferronickel alloys Table l.-Analysis of laterite of Nonoc Island, Surigao Mine, the Philippines (dry basis) Combined, Fe, Co, Ni, Cr, Mn, P, 810:, A1 0 CaO, MgO, Water, perperperperperperperperperperperpercent cent cent cent cent cent cent cent cent cent cent cent 12.4 i 48.0 109 .8 t 2.8 .7 .002 .09 1.3 6.95 .8 1.2 I

Moisture: 34.6%.

lateritic nickeliferous ores to recover the cobalt, chromium, nickel, and iron from the same. 7 o

While the laterite has been defined asair aeolianclay formed under tropical climate conditions by the weathering of igneous rocks, usually of basic composition consisting chiefly of. hydroxides-of iron and alumina, grading through increase of the latter into bauxite, the lateritic nickeliferous ores, which contain iron from to 55%, nickel from 0.5-to 2.0%, chromium from 0.5 to 3.0%, and cobalt up to 0.2 and which will hereinafter be simply referred to as the laterite, are found often in large deposits "in the Philippines, Celebes, New Caledonia, and Cuba. 7

Unfortunately most of the laterite is left untouched by iron smelters due to the. problemsmet with in smelting it. The objection made to its use by iron smelter is not only that the iron made from it is inferior in quality because of the high nickel and chromium content but also it makes a pasty slag which causes trouble in working the furnace, and in handling of the slag. Attempts at selective smelting of the laterite to produce a ferronickel alloy apparently have not been economically successful. No-attemlpt has been madetorrecover the cobalt and chromium except forincidental leaching of the cobalt involved in the nickel leaching operation,

The principal object of the present invention is the provision of a novel and improved method of processing the laterite in a most economical manner to recover the nickel and ironfby'a combination of a heneficiation procedure with selective smelting and refining processes, in which the laterite is first subjected to a simple procedure of beneficiatio'n to separate most of the cobalt and chromium, values from the crude laterite and the remainder 'containing t-he iron and nickel values is then subjected to the succeeding steps of selective smelting and refining in order to produce aiferronickel alloy free from cobalt and a steel free from chromium.

Another object of the invention is the provision of a It was found from my extensive studies on the laterite produced from various deposits that the mineralogical nature of the laterite may be summarized as follows:

(a) The iron, nickel, and alumina values occur principally in the form of aggregates of chemically fine particles. If the crude laterite is pulped with water to disintegrate it and the pH of the pulp is adjusted to over 7, the pulp liquor is easily emulsified forming a colloidal suspensionwhich may be stabilized in the presence of a protecting colloid such as starch in a small quantity without appreciable precipitation of the iron, nickel, and alumina even for several days.

(b) The chromium and cobalt values of the laterite occur principally as spinel-type crystals of chromite and cobalt ferrite which are by no means subjected to the emulsifying even though these crystals are ground to an extreme fineness.

According to the present invention, which is based on my finding as mentioned above, about of the cobalt and chromium contained in the crude laterite is separated from said emulsion as cobalt-chromium concentrate by means of, e.g., a simple gravity dressing, which is laid aside for further treatments to recover the cobalt and the chromium, while the pH of the remaining liquor of the emulsion is adjusted to lower than 7 to cause the sedimentation of the iron and nickel as iron-nickel concentrate which will be then subjected in sequence to the 1 three steps of'pro'cessing comprising a selective smelting process to recover the nickel as a ferronickel', a selective smelting process to recover the iron as a crude steel from the slag yielded as a by product of the ferronickel making and a refining process to produce a commercial steel from the crude steel.

The cobalt-chromium concentrate and the iron-nickel concentrate produced as a result of the aforesaid procedures have the ratio of about 1 to 3. This procedure of pulping and emulsifying may be regarded as a beneficiation of the crude laterite for the purpose of removing the major portion of cobalt'and satisfactory ferrouickel and steel.

chromium to produce Thus, the iron-nickel concentrate still contains small quantities of chromium and cobalt, the substantial part of which occurring as oxides and hydroxides while the remainder being as chromite, ferrite, and silicate. As regards easiness in reduction, these four metals follow each other in order of nickel, iron, cobalt, and chromium. Among these, nickel, iron, and cobalt having similar properties are rather easily separated from chromium, but nickel is somewhat more susceptible to reduction at lower temperatures.

In attempts at selective smelting of laterite to produce ferronickel 'in the presence of a suitable reducing agent in a theoretically required quantity with an electric furnace specially designed according to my invention (Japanese Patent No. 212,346), it was found that a portion of the cobalt contained in the laterite is inevitably reduced along with nickel andiron to contaminate the ferronickel produced. Also it was learned from a number of experiments that almost all of the cobalt contained in the iron-nickel concentrate enters the ferronickel produced in the case where the grade of the ferronickel is low, e.g., say, Ni, but only a trace of cobalt is detected in the higher grade ferronickel containing, e.g., 40% Ni.

It Was observed in the process of ferronickel making that chromium hardly enters the ferronickel probably 1 because of the lower reducibility of Cr O than NiO.

A feature of the present invention incorporated in the process of producing a ferronickel containing practically no cobalt from the laterite will now be described.

The crude laterite is pulped with water to separate about 80 percent of the cobalt and chromium values as a cobalt-chromium concentrate while the iron and nickel values suspended in the pulp are collected as iron-nickel concentrate by a means as has been described in the foregoing. About 70 percent out of the cobalt still contained in the iron-nickel concentrate is removed into the slag yielded as a by-product of the ferronickel produced from said concentrate, the nickel content of the ferronickel being preferably more than 30 percent. Therefore, 33 kg. of ferronickel containing 30% Ni thus produced from 1 ton of laterite containing 1.0% Ni and 0.1% Co will contain 0.06 kg. of cobalt, i.e., 0.18% Co.

Another feature of the invention with regard to the recovery of iron in good quality will be described in the following:

Should a laterite be subjected direct to the selective smelting to produce a ferronickel without resorting to the aforementioned procedure of milling comprising pulping and emulsifying and the resulting slag be smelted to recover the iron, a pig iron containing chromium as high as, say, 4 percent will be produced, as is naturally anticipated. Although it may be easy to refine this pig iron to a steel, reducing the chromium content from 4 percent to, say, about .2 percent by means of a converter, an open hearth or the like, the uses for the steel containing such high chromium are limited to a narrow range because of its high hardness. Moreover the high viscisity of the slag yielded as a by-product of the steel refining gives rise to trouble in working the furnace and handling of the slag, resulting in a poor yield of iron due to the severe loss which often exceeds 30 percent of the starting pig iron. The present invention deals with this problem as follows:

The iron-nickel concentrate obtained in the manner as has been described in the foregoing is subjected to a selective smelting to recover the nickel as a ferronickel alloy. The slag then produced is subjected to a selective smelting to recover the iron as a crude steel containing about 0.1% Cr with an electric furance having a special structure as designed according to my Japanese Patent No. 212,346. The yield of the iron is about 80 percent. The crude steel thus produced is then remelted in an electric furnace of conventional type, small amount of oxygen gas being introduced to the furnace, to obtain a 4 mild steel of good quality having a composition such as 0.05% C, 0.01% Cr, 0.01% P, and 0.03% S. An alternative of the process of refining the crude steel may be that instead of supplying oxygen gas for the decarburization and the removal of the chromium the crude steel is exposed to weathering for about, say, two to three weeks for the purpose of spontaneous oxidation and the resulting products are only molten in a furnace, thereby obtaining a mild steel containing chromium in a tolerable degree, say, 0.03 percent.

The keys to the method of processing the laterite successfully in accordance with the invention to recover the cobalt and chromium as a cobalt-chromium concentrate, the nickel as a ferronickel alloy, and the iron as a mild steel in good quality, respectively, are as follows:

(1) The laterite is pulped with water to separate the major portion of the cobalt and chromium values from the pulp liquor. When pulping the laterite, e.g., in a ball mill, with plenty of water added with a small quantity of an alkali, e.g., caustic soda, a caution is needed in disintegrating the ore lest the cobalt and chromium mineral crystals should be crushed into smaller particles. Otherwise the cobalt and chromium particles tend to suspend in the pulp liquor together with the iron and nickel values chiefly suspending in colloids and the required sedimentation of the former will be retraded.

Further, it is to be noted that to avoid crushing the hard crystals such as chromite during milling operation balls made of rubber or cast iron balls covered in rubber are preferred to conventional balls made of either cast iron or ceramics. The amount of pulp water is controlled so that the percentage by weight of the dry laterite in the pulp will be less than 30, preferably in the range from 10 to 25.- The pulp pH is then adjusted to above 7. To adjust the pH of the pulp for making a satisfactory emulsion, a basic substance which is high in electrolytic dissociation degree such as caustic soda must be employed. Instead of resorting to the gravitational sedimentation as cited in the foregoing, the separation of the solids from the colloids in the pulp may be brought about by any of known means such as Hancock jig, centrifuge, and blanket sluice. The coagulation of the iron and nickel colloids suspended in the pulp may be effected by any of such acids as hydrochloric acid, sulphuric acid, sulphurous acid, and nitric acid or any of such salts which present acidic reaction by hydrolysis, or such salts which are high in the electrolytic dissociation degree. It was still further found that since about percent of the cobalt contained in the laterite exists as cobaltferrite, the crystal particles of cobalt may be preferentially separated from the pulp as a magnetic mineral by means of a magnetic separator.

(2) All the chromium still contained in the iron-nickel concentrate in spite of the above-mentioned separation from the pulp is oxidized so as to be converted to FeO.Cr O during the course of the selective smelting of the concentrate to produce a ferronickel alloy. The FeO.Cr O thus formed in molten state grows in crystals when cooled. The purpose of the formation of is to create a considerable difficulty in the reduction of chromium during the course of the following selective smelting of the ferronickel slag to produce a crude steel.

(3) The furnace. employed for the selective smelting to produce either ferronickel alloy or crude steel may be either circular or rectangular with regard to the intenior contour provided the positioning of the electodes can be adjusted so as to form the molten metal into a bowl in shape.

Further, the electric furnace employed for the selective smelting is provided with an opening having a slidable plate to open or close the opening from which the discharge of either the slag in molten state or the metal solidified in shape of a bowl is carried out. Also the furnace is provided at the side with a. cinder 'notch for drawing the molten slag. The surfaces of the side lining of the furnace and the bottom are stamped with a pasty material consisting of crude laterite mixed with a reducing agent, e.g., coke breeze, the size of which is preferably about mesh, and the content of moisture and the combined water in the total ranging from 15 to 50 percentthe amount the laterite contains in a. natural state. As a result of this stamping .a steam curtain forms between the molten body in the furnace and the lining, and as metals are produced they solidify into a bowl in shape. Upon completion of the smelting, this stamped ore mixture containing 5 to 20% moisture is collected as the ore-melting-stock to be charged in the following batch of smelting. 7

Power voltage suitable for the selective smelting may be in a range from 10 to 200 v., depending on the iron content of the laterite and the. distance between the elec- Y trodes which will be adjusted lest any are should occur between the molten materials inside the furnace and the electrodes. P I Y The temperature inside the molten body formed in the furnace bottom in shape of a bowl must be lower than 1500 C. Metals produced by the selective smelting collect on the bottom of the furnace in a pasty lump in a semi-molten state whichis taken out of the opening in the bottom when solidified by cooling. In thecase where the slag is extremely viscous during the smelting because of the high alumina content, it is necessary to add a small quantity of fiuorspar or lime stone to the slag in order to give rise to an adequate convectioncurrent within the body of the molten materials, which is of primary importance for successfully conducting the selective smeltingaccording to the present invention. Such a convection current may be caused by supplying a high pressure steam into the furnace or by means of any suitable mechanical device which creates a stirring motion of themolten materials. As a substitute for coke breeze, :ferrosilicon or calcium silicide may serve as the reducing agent for the selective smelting.

(4) For conducting the selective smelting of the ferronickel slag to produce crude steel, the furnace bottom is stamped with a raw material mixture consisting of the ferronickel slag, coke breeze, and flux, all of which pass 6 heated to 1550 C. or above and wellag-itated in order to remove CrO as CaCrO An alternative of the process of refining the crude steel comprises a step in which the crude steel is submitted to continuous exposure to the atmosphere over a period of two through three weeks in order to oxidize the surfaces of the crude steel particles; and a step in which the steel particles are mixed with thick milk of lime and then charged into an electric furnace for melting in order to remove CrO as its CaO-compound.

In the case were the crude steel contains more than 0.1% C, the process of refining may comprise a step in which the carburization is conducted at high. temperatures by conventional method and then steam is blown into the furnace to reduce the temperature of the metal bath to lower than 1400 C., and a similar step of removing chromium as has been described in the foregoing;

In case the crude steel produced does not turn out spongy or powdered, the crude steel is remelted, and when discharged fromthe furnace compressed air or oxygen gas" is blown against thestream of the molten steelin order to render the steel to become spongy or powdered.

More specific features and advantages are apparent from the following description of a preferred embodiment of the present invention.

About 1 ton out of 100 tons of the laterite produced from Nonoc Island, Surigao mine, the Philippines, was charged in a ball mill, added with 5 kg. of caustic soda and ground therein for 2 hrs. together with water. The pulp of 4 cu. m. thus prepared was flushed into-a wooden tank, and then added with a suitable quantity of caustic soda to adjust the pH of the pulp to 9.0. After a strong agitation for about 1 hr. the pulp was left alone for 25 min. so' as to settle the solids. recovering the cobalt and chromium from the laterite as cobalt-chromium concentrate.

The remaining colloidal pulp liquor was then added witha suitable quantity of hydrochloric acid to adjust the pH to 6.0, thereby a coagulation instantly took place and sedimentation began to occur. The clear liquor was decanted, and the resulting slurry was filtered toa cake, which was dried spontaneously, the product being referred to as the iron-nickel concentrate.

vTable 2 shows the analyses of these two kinds of con centrate.

Table 2 =-Concentrate (dry basis),

Nl,. percent 00, percent 7 Cr, percent Fe, percent Weight of Total .Yield,

percent Or Yield, 7 per.- cent 7 00 Yield,

peri a cent Co-0r Concentrate Fe-Nl Concentrate through a 5 mesh screen, the moisture content of the mixture being more than 5 percent. The mixture may be used in place of refractory bricks tor lining the furnace walls as with the case of the selective smelting for making a ferronickel alloy. The smeltingis carried out at, the

' temperatures lower than 15 00 C. on the molten materials;

The metal particles produced collect together on the furnace bottom due to the boiling action of the molten body caused by the evaporation of the moisture contained in said mixture charged. This boiling action may be stimulated by an addition of powdered lime stone or fluorspar to the metal bath.

(5) For refining the crude steel, which may be spongy, powdered or granular and contains carbon less than 1.0 percent, it is kept in a semi-molten state at the temperature lower than 1400 C., added witheither oxygen. gas,

Fe O -or the like in order to oxidize the chromiumcon- About 80 percent of the cobalt and chromium containedin the crude laterite could be recovered as a cobaltchromium concentrate by means of the procedure described above, which might be treated subsequently to recover the cobalt and the chromium separately.

As a preliminary for conducting the selective smelting of the iron-nickel'concentrate to produce terronickel, 458.5 kg. of the concentrate was dried to a range of about 10 to 15% moisture, then added with 8% breeze and thoroughly mixed together. This mixture is referred to as the ore melting-stock. For the selective smelting of the iron-nickel concentrateemployed was an electric furnace so designed in accordance with my invention of Japanese Patent No. 212,346 that the meta-l as well as the slag either in molten state or semi-molten state would be easily drawn out from the bottom of the furnace. The furnace was; lined at the sides and the bottom with the tained in the crude steel to CrO, further added with fiaO, iron-nickel concentrate slurry containing about 45% moisture. The dimensions of the furnace and the particulars of the operation are shown in the following:

Outer diameter crn 150 Height cm 100 Thickness of lining:

Bottom cm 20 Sides cm Electrode (3) in 6 Voltage v 35-80 Current A 3000 In this furnace 458.5 kg. of the ore melting-stock mixed with a suitable amount of coke breeze was charged for smelting which was completed in 1% hr. at 60 v. and 2500 A.

Tables 3 and 4 show the analyses of the ferronickel alloy and the slag produced.

Table 3.Analysis of ferronickel Table 5 is to compare an example of a ferronickel, which has been produced by a. direct melting of the laterite without resorting to the previous procedure of the separation of the cobalt and chromium, with the ferronickel produced in accordance with the invention.

Table 5 .-Analyses of ferronickel produced by a conventional method 6, N1, Cr, Si, Mn, P, S, Co, (lo/Ni perperperperperperpcrper- Ratio cent cent cent cent cent cent cent cent I; .03 24.7 tr tr tr .003 .05 1.28 5.2

II .04 18.8 .01 tr tr .004 .04 1.60 8.5

It can be seen from Tables 3 and 5 that in order to produce a ferronickel of excellent quality which practically does not contain cobalt the following procedures are necessary:

(1) Cobalt should be removed as far as possible by the beneficiation such as emulsifying dressing according to the invention.

(2) The higher the grade of ferronickel the lower will be the Co-Ni ratio, but the smelting should be carried out so as to acquire at highest possible grade of ferronickel, provided the yield of the ferronickel does not become too low,

In this connection it is to be noted that any attempt to produce a ferronickel containing 60 to 70% Ni in an industrial scale should be avoided because of not only the difficulties met with in the smelting operation but also of the severe loss of the nickel into the slag.

The process of recovering the iron as a crude steel from the 339.3 kg. fer-ronickel slag will now be described.

The slag was pulverized to the particles, all of which furnace employed for the ferronickel making. The bottom of the furnace was stamped with the paste comprising the ferronickel slag kneaded with water while the side walls were lined with refractory bricks. The smelting was completed in 40 min. at 70 v, and 2500 A. on an average.

Slag amount smelted (61.25% Fe) kg 339.3

Power consumed kwh 346 Crude steel produced kg 189 The slag was drawn out from the bottom of the furnace together with the crude steel which was found in a semi-molten state on the bottom of the furnace. The analysis of the crude steel is shown in Table 6.

Table 6.Analysis of crude steel 0, Cr, 81, M P, Per- Per- Per- Per- Per- Percent cent cent cent cent cent The crude steel thus produced was remolten in an electric furnace of Heroult type having a cover for the purposes of the desulphurization with quicklime, the decarburization and the removal of chromium by means of ejection of oxygen gas for 2 min. at 2 atm.

The results were as follows:

Based on the amount of iron contained in the ferronickel slag, the yield of iron as steel represented 85.18 percent.

It is thus to be noted that starting from the material which has been got rid of the substantial part of the chromium contained in the crude ore by means of an emulsifying dressing, the nickel was recovered from said material as a ferronickel alloy by a selective smelting and then the iron was recovered from the slag yielded by said selective smelting and the refining as a steel con- 7 taining practically no chromium at more than 85% in passed through a 50-mesh screen, admixed with 16% coke breeze, and smelted in the same type of the electric yield.

To compare with this method, 2 tons of the same laterite was direct subjected to a selective smelting of nickel without resorting to beneficiation such as emulsifying dressing for removing chromium and then the resulting slag containing 32% Cr, 58% Fe, and 0.06% Ni was smelted with a conventional electric furnace lined with graphite. The results were as follows:

Yield of iron: 88%.

Table 9.-Analysis of steel On examination of the above results, it may be concluded that although the steel thus produced is usable as an ordinary steel on the ground that the chromium content is within the tolerable limit of 0.09 percent, this conventional process involves the following defects:

(1) The operation is costly because alarger amount of oxygen is required.

(2) The yield of iron is low because a larger amount of the'iron is lost in the sl-ag.

(3) More frequent discharges, of slag are required.

To save the operation hours a converter may be used in place of the electric furnace employing oxygen gas, but difiiculties will be met in the control of the temperature of the metal bath and consequently in the removal of chromium to a required extent.

All the foregoing, as well as many other highly practical advantages, attend upon the practice of the present invention. Namely, according to the present invention in a sharp contrast with the above-cited conventional method, a crude steel having a lower chromium content is first made and then this chromium in smaller quantity is removed in the following course of refining the crude steel so that a high grade of steel is manufactured from the laterites successfully in technique and economy as well.

I claim:

1. A method of processing lateritic nickeliferous ore, comprising pulping the ore to separate the cobalt and chromium values as minerals, then coagulating the iron and nickel values to separate the same as a concentrate from the pulp; subjecting the iron and nickel concentrate to a selective smelting to produce a ferronickel alloy; subjecting the slag yielded as a by-product of said selective smelting to a further selective smelting to produce a crude steel containing less than 1.0% Cr; and refining the crude steel to a commercial steel substantially free of chromium.

2. .A method of processing lateritic nickeliferous ore as claimed in claim 1, wherein the ore is pulped with water to make an emulsion in which the nickel and iron values are suspended as colloids, the emulsion then being coagulated to settle said colloids as a concentrate by adding to the emulsion at least one substance selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, nitric acid, salts presenting acidic reaction on hydrolysis, and salts high in electrolytic dissociation degree; the slag yielded as a by-product of said selective smelting being subjected to said further selective smelting to produce a crude steel containing lessthan 1.0% Cr.

3. A method of processing lateritic nickeliferous ore as claimed in claim 1, wherein the ferronickel alloy is produced in a furnace and is collected on the bottom of the furnace in a semi-molten state and is taken from the furnace in a solid state.

4. A method of processing lateritic nickeliferous ore as claimed-in claim 1, wherein the crude steel is produced in a furnace and is collected on the bottom of the furnace in a semi-molten state and then taken from the bottom of the furnace in a solid state.

5. A method of processing l-ateritic nickeliferous ore as claimed in claim 1, wherein the selective smelting is conducted at temperatures lower than 1500 C.

6. A method of processing lateritic nickeliferous ore as claimed in claim 1, wherein the crude steel produced is spongy.

7. A method processing lateritic nickeliferous ore as claimed in claim 1, wherein the crude steel produced is kept in a semi-molten state at a temperature lower than 1400 C., said process further comprising adding a suitable quantity of oxidizing agent to the crude steel to oxidize the chromium in the steel to 'CrO, further adding CaO to the steel, then heating the steel to at least about 1550 C., and stirring the same in order to remove the CrO as CaCrO 8. A method of processing lateritic nickeliferous ore as claimed in claim 1, comprising producing the crude steel in powdered form.

9. A method of processing lateritic nickeliferous ore as claimed in claim 1, comprising producing the crude steel in granular form.

10. A method of processing lateritic nickeliferous ore as claimed in claim 3, wherein the furnace in. which ferronickel alloy is produced is lined with substances containing a constituent similar to the melting stock and at least 10% moisture.

11. A method of processing lateritic nickeliferous ore as claimed in clam 4, wherein the furnace in which the crude steel is produced is lined with substances containing a constituent similar to the melting stock and 10% moisture or more.

12. A method of processing lateritic nickeliferous ore as claimed in claim 11, wherein the melting stock charged in the furnace contains from about 5 to about 20% moisture.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A METHOD OF PROCESSING LATERITIC NICKELIFEROUS ORE, COMPRISING PULPING THE ORE TO SEPARATE THE COBALT AND CHROMIUM VALUES AS MINERALS, THEN COAGULATING THE IRON AND NICKEL VALUES TO SEPARATE THE SAME AS A CONCENTRATE FROM THE PULP; SUBJECTING THE IRON AND NICKEL CONCENTRATE TO A SELECTIVE SMELTING TO PRODUCE A FERRONICKEL ALLOY; SUBJECTING THE SLAG YIELDED AS A BY-PRODUCT OF SAID SELECTIVE SMELTING TO A FURTHER SELECTIVE SMELTING TO PRODUCE A CRUDE STEEL CONTAINING LESS THAN 1.0% CR; AND REFINING THE CRUDE STEEL TO A COMMERCIAL STEEL SUBSTANTIALLY FREE OF CHROMIUM.