US2784074A - Method of treating iron ores containing chromium - Google Patents

Description

March 5, 1957 KIYOTO MATSUZUKA 2,784,074

METHOD OF TREATING IRON ORES CONTAINING CHROMIUM Filed Nov. 5, 1953 3 Sheets-Sheet l Lateriie Edge runne ----Soda ash 8: .Lime

Pug mill Roastin {urnace Leaching tank Leached Solution Pel let Precipitation & Separation of Aluminium Hydroxide Precipitation 5: Separation 0\ Sodium Dichromate JNVEN TOR.

Ki/a To MHTSl/l u A March 5, 1957 KIYOTO MATSUZUKA METHOD OF TREATING IRON ORES CONTAINING CHROMIUM Filed NOV. 5, 1953 3 Sheets-Sheet 3 ON 9 0 +1 N O m 0 3 w ows zifiQwoqm Q2 w RON 5 mvq ou z KI BY United States atento METHOD OF TREATING IRON ORES CONTAINING CHROMIUNI Kiyoto .Matsuzuka, Kumamoto-ken, Japan, 'assignor to Yawata'lron & Steel Co., Ltd.,'Tokyo, Japan Application November 5, 1953,, SerialNo. 390,,376 Claims-priority, application Japan February 14, 1953 9 Claims. ,(Cl. 75-3) This invention relates to a method of removingchromium from iron ores containing chromiumand particularly to a method of recovering chromium from l-ateritic ore and of making .said ores especially suitable as raw materials for producing iron.

Laterite is representative of iron ores containing chro' mium and it is as such representative thatit .is dealt with in the following. laterite as .known is an -air-slaked product of serpentine and the amount of its deposits is said to be inexhaustible. It .is produced in quantitiesin every country of the world. Laterite, .for example, produced in the Philippines contains 47.7 to 51.4% Fe, 2.10 .to 2.74% Cr, 4.50 to 7.52% A1203, 1.90 to 3.33% SiOzand small amounts of Ni, Co and Mn. The main constituent of this ore is ferric oxide. The result :of analysis by heat shows that this ore has 5.5% water of crystallization at 200 to 250 C. It can be presumed from theamount of dehydration that all F6203 exists in ,the .form of FezOs-HzO (needle iron ore). Needless tosa-y, zit is judged from the constitution of said me that some gelled iron oxide containing water and F62O3'3Ha0 also exist. Alumina seems to exist as Alz'Oa'3H2O or rAlzOs-H2O. Silicic acid exists as silica, gelled silicic .acid andsilicate. Chromium exists mostly as chromite .(FeO-CrzOs) and partly as chromate. The chromiteis so 'britt'le in nature that it'can be easilycrushed by finger tips. Its grains are so fine as to he muddy. The fine grains of-limonite-are adsorbed by chromite or envelop chromite; this state continues the same all through to thefinegrains of chromite. When both of these minerals are crushed for physical separation, chromite will be readily finely .ground, will become colloidal and will be very difficult to.separate by gravity or any other method. This is the maincause of the difiiculty of dressing this ore. Asregards ithematter of removing chromium for the sake of utilizing .laterite, various methods have been tested and reported in the United States on ores produced in Cuba, and in Japan on ores -produced in the Philippines and Japan proper. These respective methods and the results of laboratory tests are discussed in the following.

(1') DRESSING BY GRAVITY This is to utilize the diiference of specific gravity between iron ore and chromite. In "U. S. Patent No. 2,363,315 aiming at separating nickel and chromium from Cuban laterite, Mr. John .D. Grothe purports to achieve separation by utilizing vthe difierence nf'specific gravity between magnetite 1(551 specific :garvity) produced by reduction and roasting and chromite 01:4 specific gravity); in the case iof.removing-chromium'this method being especially .named flotation. .However, it:1is :found in the light of the theory in dressing Jthat'rsu'ch ".fine fgrains cannot :be .well separated -by the .-':specific gravity difference of 0.7. .As the .assignee of patentee, ;Dnrr Company, confesses, this method dustrialized.

2 ,2 DISPERSION When :laterite is lthrownintowater and stirred, itwill readily collapse and will sink down :after .:a while. Howeve1:,;if 2a :small amount of *a dispersing agent :such as :for example, alkali is added thereto and the mixture:is:stirred and :left alone, the fine grains of ilimonite will .be "dispersed and floated. The deposit contains comparatively much chromium. Itris intended to attain the .o'bject 'of :dressing by separating the .floating substance and the \deposit by an adequate method. The results of testsma'de by using NaOH as .a -dispersing agent on an Omonhon specimen (containing 2.74% chromium) are now listed in the following:

-. Raw Dispcrsing Dispersed Substance No. .Material Water Agent,20% Weight Chromium in g. in l. 'NaOH in inPercent inPercent :300 6; -20i 4b LL33 As seen'from the above results of experiments, in'this method, .the percentage of the removal of chromium is low (below 50%) and the percentage of collection of can diardly he reliably :iu- I iron ores is below 50%, being out of the question.

This method was named emulsion dressing by the Heavy Metal Research Laboratory established in Japan during "World War II. n is found in the light of the reports of experiments made by this method on various kinds of laterite produced in various producing places as published 'in Reports of the Heavy Metal Research Ins'titue, 1st edition, December 1944, that, though some favorable results have been shown in some producing places, the percentage of the removal of chromium and the percentage of collection of iron ores are not favorable and the drying-operation after separation is difiicult. 'In view of such results, this method is-never'suited to treatment of large quantities.

(3) ADDITION OF SODA ASH fE-his AIS like the method of the present invention to be described later and is a method wherein chromium is extracted as sodiumchromate by merely adding soda ash to the rawm'aterial and heating the mixture as in manntfacturing usual sodium .c'nromate without any combination with pelletizing. Mr. McCormack applied this :method :to :Cuban iores as easly :as 1926 but "the result showed-that the extraction of chromium was quite insutfi- .cient .-(-E. -Erary: The Aluminum industry, p. 142). .I, the present inventor, have first experimented Omonhon ores byrthis method. The percentages of extraction' were 57.7,, 5.9.0, .-63. 6-and 87.2% against the amounts of addi- :tion ,of .soda ash :of 5, 10, 20 and 30%, respectively,- at .the heating temperature of 700 C. for 30 minutes. .These .resultsare not favorable as compared with those of the method .of this invention, partly due to the low temperature. .After extraction, reheating :at a high tern;

perature .is necessary to obtain powdered ziron ores and This method-is covered by S. Patent No. 2,584,700 "011 a :method not treating iron ores containing nickel and chromium invented by Mr. C. R. Hayward. This patent .is owned hy FBethlehem Steel Company. This -=method is alsoitoztreat Mayaricores producedfinictiba assumrnarized rin'tthe tfollowing'. al'iirst of tall, I laterite' 'is trea'ted stilphuric acid. Insoluble chromite and silicic acid are removed. Parts of iron, nickel, aluminum and chromium are then replaced by iron powder thrown in and are precipitated. The remaining iron solution is evaporated, dried and solidified as iron oxide. Sulphur dioxide produced then is utilized for solution. However, the operation in this method is complicated and cannot help being uneconomical, being not a method suited to treatment of large quantities.

An object of this invention is to provide an improved industrial method of extracting chromium from iron ores containing chromium and particularly from laterite.

Another object of this invention is to provide a method of making iron ores containing chromium and particularly laterite raw materials suitable for producing iron.

Further objects of this invention will become clear from the following description. 1

According to the method of this invention, soda as and/or lime are/is added to laterite and the mixture is ground and mixed. The mixture is molded into pellets and is roasted in an oxidizing atmosphere in a furnace to convert chromium contained in the laterite ore into sodium chromate. Then, by immersing the roasted products in water or a solvent, the sodium chromate content is dissolved out and the solid part is separated. Chromium is recovered from the solution. The remaining solid part has very low chromium content and is very suitable as a raw material for producing iron.

Figure 1 of the drawings is a flow sheet showing a mode of working the method of this invention.

Figure 2 shows the precentages of extraction of Cr, Na, Al and SiOz when 15% NazCOa and various percentages of Ca(OH)2 were added to laterite and the mixture was treated by the method of this invention.

Figure 3 shows the constitution of pellets obtained by adding 15% NazCOs and various percentages of Ca(OH)z to laterite as in the case of Figure 2 and by treating the mixture by the method of this invention.

Figure 4 shows the percentages of extraction of Cr and Al when various amounts of Ca(OI-I)z were added to 12.5, 15, 20 and 25% NazCOs and the mixtures were treated by the method of this invention.

Figure 5 shows the weight in percentage of Cr remaining in the pellet obtained by treatment under the same condition as in Figure 4.

In the present invention, laterite alone or with the addition of an adequate amount of iron ores or any other raw material for producing iron is first finely ground by means of a grinder. The grinder to be used may be an edge mill or any other known grinder. The size of a ground grain is preferably such as will pass through a 200 mesh screen.

Soda ash or a mixture of soda ash and quick lime in a powdered state in an amount adequate depending on the chromium content is added to the ground iron ores containing chromium and is intimately mixed together. Slaked lime may be used in place of the above quick lime. In mixing them, an adequate amount of water is added for convenience in pelletizing. This water may be fed by adding said soda ash or mixture of soda ash and lime as a solution or suspension. This mixture is then molded into pellets of an adequate size and shape which are preferably of a column 20 to 30 millimeters in diameter and to millimeters long. If the pellet is made a holed pellet by making one or several through-extending holes in the central part thereof, the below mentioned percentage of extraction will be improved, because, in the below mentioned roasting, oxygen will come into contact with the interior of the pellet and, in extracting, the entry of water into the interior will be madeeasier. When the molded mixture is enclosed in a furnace such as a roasting furnace and is heated at a temperature of 900 to 1200" C. or preferably 1000 to 1100 C. in an oxidizing atmosphere, roasted-pellets can be. produced. By this heating, the

chromium content in the pellets will be converted to sodium chromate by the following reaction:

In case sodium carbonate NazCOs only is used, sodium chromate will be obtained by the following formula:

The sodium chromate thus obtained is very easily soluble in hot water. Therefore, if the roasted pellets while at a high temperature are thrown into and immersed in water which is preferably warm, the greater part of the sodium chromate will be extracted as dissolved. It is preferable to stir the solution in the above immersion. In the above roasting of the pellets the roasted pellets become porous due to the volatilization, of water of crystallization of limonite. Therefore, in extracting sodium chromate, water can readily penetrate into the interior of the pellet and sodium chromate can be further dissolved out. Such solvent as, for example, sodium sulphateor calcium carbonate solution may be used instead of the above water. The effects of adding the above soda are as follows:

(1) The iron content is at first limonite but, when heated, becomes hematite. The surface temporarily becomes ferrite due to soda but decomposes and again becomes hematite. A part remains as ferrite but, when made to act with water, becomes hematite and caustic soda. This caustic soda helps the growth of sodium chromate.

(2) Alumina existing as bauxite loses water of crystallization and combines with soda at 550 to 600 C. and leaches out as sodium aluminate, improving the quality of the iron content. The production of alumina as a byproduct from ores containing a large amount of alumina and a small amount of silicic acid can be considered.

(3) Silicic acid existing as silica or silica gel combines with soda, becomes sodium silicate and is leached out by water, also serving to improve the quality of the iron content.

The effects of adding lime are as follows:

(1) Lime with the addition of either CaO or Ca(OH)2 combines with CO2 obtained by the production of sodium chromate, sodium aluminate or sodium silicate and becomes CaCOs, serving to increase the strength of the pellets.

(2) Soda is prevented from acting with alumina or silica and the loss of soda ash is prevented. (In the case of producing alumina as a by-product or of requiring high quality pellets as mentioned above, the amount to be used is limited.)

If the chromium content of the extract obtained by the treatment as mentioned above is concentrated after impurities are removed and is then treated with concentrated sulphuric acid, sodium chromate will become sodium dichromate. It can likewise be made potassium dichromate or chromate by a known method. On the other hand, the pellets from which chromium content has been removed can be used as they are as raw materials for producing iron.

Examples of this invention are shown in the following to help it to be understood. However, this invention is not to be limited to these examples.

Example 1 PELLETIZING OF IRON ORES CONTAINING CHROMIUM AND ALUMINUM (AN EXPERIMENT BY THE EXTRU- SIVE METHOD) The specimen used in the experiment was Philippine Omonhon laterite and its chemical composition was 50.1% Fe, 2.1% Cr, 7.5% A1203, 1.9% SiOz, 10.6% combined water and small amounts of Ni, CO, Mn, etc.

This specimen was first ground to grains finer than 200 mesh by meansof an edge runner as shown in Fig. I. Soda ash (sodium carbonate) and slaked lime in a state of solation or suspension were added to the above specimen and the mixture was well mixed by means of :a mixer. Then the mixture was extruded into the shape-of a column .by means of an Auger type pug mill and 'was cut into pellets each 20 millimeters in dimeter and millimeters long.

These pellets were put into a roasting furnace, were heated for an hour at 1 100" C. to 1200 C. in an oxidizingatmosp'here, were -then'thrown while still at a high temperature (about 500 G.) into an extracting tank provided with :an agitator and were subjected to extractionfor l to 2 hours with the water temperature kept at'70 to 80" C. The greater parts of chromium and aluminum "were extracted during .the first hour and al- Example 3 Pellets were .made in the same way as .in Example 1. except that they were cylindricalpelle'ts each '20 millimeters in diameter and 20 millimeters 'long with a 'hole 5 millimeters india'meter made through the ceriter 'the're-.

. y g u of. The "amounts of addition in percent of Na2COs most .Dflhem were extracted i t two Hours and Ca('OH')2 and the 'perce'ntagesof "extraction of Cr 5222a? Hated and was treated with Concentrated sulphuric acid pellet without a hole being also shown for information. to ."produce sodium 'c'lichromate. Ihetpercentages of the above extraction were as shown .in Fig. 2. As more than 1', Percentages 'offExtraetion 15% Na evaporated in roasting, it could be separately Naooa recovered and utilized. .As .seen .in'the figure, the .perg centageof extraction of Cr and Al was .the best at 2 I rigggg am:

to 4% of added Ca(OH)2. The percentage of extractinn *of ;SiO z;.was lower. The percentages by weight of Percent Percent Pmem I .Pmem

the compositions of the pellet produced by the above- 10 12 72 2 .00 mentioned method were .as shown in Fig. 3. They decreased a little with the increase of Ca(OH)2 at 60% iron content. With the addition of 3% Ca(OH)2, Fe

was 59.0%,Na20 was lQ.4:-%,.Al203 was 2.1% and S102 As in the above. the ipercentege extraction of was 2.0%. The'compressive strength of this pellet was Chr mium Cmlld be increased by 6 to 12% by making 10 kg. and its specific gravity was 3.45. a hole in ithepellet. Almost the same results were ob- Theipercentages of extraction in case the amount of mined in sp aluminum CaIOH): was van'ed against *the'amounts of 12.5, 15, 20 Example 4 and '25% NazCOs are shown in Fig. -4. As seen from said figure, Cr-showed the maximum'value of 85% at Pellets for Producing Iron could-be made Y Yemctvmg 17.55% Naz'COs and more than 90% at both 15 and Cr and by Ihe Same e hod as in the abovefrom a 20% N co A '1 5%, h i 1 f C O product from which Ni and Co have been removed by was 2 to 4% but, at 20%, it was 6 to 8%. The perthe wet or dry Process. Ni-and 9 were e e y the centage of extractiqn at 25% NazCOs was lower than 40 Wet Q f Q Q P 111 the I pp and at 20%. It was found that the increase of the amount cfiiltamlng 54-08% Fe, 03% 232% of extraction of Al in proportion to the amount of ad- 192% A1203 and 2 5102- sodajmd 4%11me dition of Na2CO3 was more remarkable than that of Cr. M H) were added to the abeve resldues and the Fi 5 shows th h i contents of h ll mixture was heated for an hour at 1100 C. and was subdu d against th a t f dditi of jected to extraction for two hours. Thus the percentage NMCOaCMOHh of extraction of Cr of 85% was obtained. shown in Fig. 3. The minima of Cr against 12.5, 15, Examples 540 20 and 25% NasCOs were 0.42, 0.24, 0.19 and 0.18%, Laterite ores containing d chromium. respectively. Especially, with the increase of Naacos, respectively, were ground t grains finer than 200 m hthe strength of the pellet decreased. The compressive Powd re soda ash nd q lck lime were added to said strength of 10 kg. of the pellet at 15% NazCOs and 3% ground laterite and the mixture was well mixed to be a Ca(OH)s lowered to that of 7 and 3 kg., respectively raw material for pelletizing by a balling mill. The condiat the same percentage of Ca(OH)2 but at 20 and 25% tions and results were as listed below.

Chromium Chromium Amounts of Percentage Examples content in Additives Tempera- Time (hours) Remaining Extraction 0i Extraction the ore in Percent; tures, O. inPellets in of Chromium oi Chromium Percent in Percent 205 13 soda ash. 1.000 0.5 0. 40 1.66 80.0 2.05 -do 1.000 1.0 0.28 1.77 20.0 2.05 do 1.000 2.0 0.23 1.83 89.2 2. 2 10 soda ash, 1. 000 0. 5 0. 36 1. s4 s2. 7

71irne. 2.2 do 1.000 1.0 0.20 1.04 88.2 2.2 do 1.000 2.0 0.18 2.03 02.3

NazCOa. Therefore, the decrease of strength could be In case the heating temperature was 1100 to 1200 C., compensated by increasing the amount of addition of the heating time could be further reduced and yet the Ca(OH)z. Generally, the most favorable amount of same results could be obtained. addition of Ca(OH)2 is A to /3 the amount of addition The pellets from which chromium was thus removed of NaCOa. However, the absolute values of the amounts contained 57% iron, were good in both strength and reof addition of NazCOa and C8.(OH)2 vary depending on duction rate and could be made raw materials for prothe composition of the raw material to be used or parducing iron as they were. ticularly on the contents of Cr and Al to be extracted Now the features of the method of this invention are and on whether Cr only is to be removed as a lay-product 75 enumerated as follows:

or both Cr and A1 are to be removed.

(1) If water is added to laterite in the wet treatment,

it will take a long time for precipitation and drying, such method being unecouomical. The method of this invention wherein the dry treatment is utilized is advantageous.

(2) In this method, the characteristics of laterite are ingeniously utilized and the property which would be very troublesome in the ordinary method proves all the more advantageous.

For example, (i) chromite which is brittle in nature and is apt to be powdered is all the more favorable in completely acting with soda ash. (ii) It is almost impossible to ideally separate limonite adsorbed around chromite. However, in this method wherein the material is finely ground from the first,,the above disadvantage has no effect whatsoever. (iii) Iron oxide and alumina have water of crystallization (8.5% at 200 to 250 C.). When the pellet is heated, said water of crystallization will volatilize and the pellet will become porous. This will facilitate the circulation of air, promote the growth of sodium chromate and also facilitate leaching with water, increasing the percentage of removal of chromium.

While this invention has been described in the above chiefiy'with respect to laterite, it will be easily understood that the same can be applied to any other iron ores containing chromium.

What I claim is:

i. A method of producing pellets containing substantially no chromium, said pellets being suitable as raw material for the production of iron, which method comprises grinding an iron-bearing material comprising chromium and aluminum, adding to the ground material (a) a suflicient quantity of soda ash to convert at least the chromium into a sodium salt thereof and (b) lime in an amount of at least about A the quantity of added soda ash, intimately admixing said materials, adding to the resultant mixture sufiicient water to enable the mixture to be molded, molding the aqueous mixture into pellet form, heating the thus-obtained pellets to 900- 1200 C. in an oxidizing atmosphere, extracting the thustreated pellets with an aqueous liquid, whereby at least substantially all the chromium is extracted therefrom.

2. A method according to claim 1, and recovering sodium salt of chromium from the aqueous extract.

3. A method of producing pellets containing sub: stantially no chromium, said pellets being suitable asraw material for the production of iron, which method comprises grinding an iron-bearing material comprising chromium and aluminum, adding to the ground material (a) a sufiicient quantity of soda ash to convert at least the chromium and aluminum into sodium salts thereof and (b) lime in an amount of at least about $4 the quan: tity of added soda ash, intimately admixing said materials, adding to the resultant mixture suificient water to enable the mixture to be molded, molding the aqueous mixture into pellet form, heating the thus-obtained pellets to 900-1200 C. in an oxidizing atmosphere, extracting the. thus-treated pellets with an aqueous liquid, whereby at least substantially all the chromium and aluminum are extracted therefrom.

4. A method according to claim 1, wherein the heating or the pellets is carried out at 1000 to 1100 C.

5. A method according to claim 1, wherein the iron. bearing material is laterite ore.

6. A method according to claim 1, wherein the pellets are extruded into hollow pellet form.

7. A method according to claim 1, wherein the aqueous liquid is warm water. 8. A method according to claim I, wherein the moldinginto pellet form is effected by extrusion. I 9. A method according to claim 1, wherein the molding into pellet form is eifected in a balling mill.

References Cited in the are of this patent UNITED STATES PATENTS Great Britain May 5, 1927

Claims (1)

1. A METHOD OF PRODUCING PELLETS CONTAINING SUBSTANTIALLY NO CHROMIUM, SAID PELLETS BEING SUITABLE AS RAW MATERIAL FOR THE PRODUCTION OF IRON, WHICH METHOD COMPRISES GRINDING AN IRON-BEARING MATERIAL COMPRISING CHROMIUM AND ALUMINUM, ADDING TO THE GROUND MATERIAL (A) A SUFFICIENT QUANTITY OF SODA ASH TO CONVERT AT LEAST THE CHROMIUM INTO A SODIUM SALT THEREOF AND (B) LIME IN AN AMOUNT OF AT LEAST ABOUT 1/4 THE QUANTITY OF ADDED SODA ASH, INTIMATELY ADMIXING SAID MATERIALS, ADDING TO THE RESULTANT MIXTURE SUFFICIENT WATER TO ENABLE THE MIXTURE TO BE MOLDED, MOLDING THE AQUEOUS MIXTURE INTO PELLET FORM, HEATING THE THUS-OBTAINED PELLETS TO 9001200*C. IN AN OXIDIZING ATMOSPHERE, EXTRACTING THE THUSTREATED PELLETS WITH AN AQUEOUS LIQUID, WHEREBY AT LEAST SUBSTANTIALLY ALL THE CHROMIUM IS EXTRACTED THEREFROM.

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