FREE HARMANNUS WILLEM HOMAN (NL)
TAPPEL BAS (NL)
BADLOE PARMANAND (NL)
VAN OENE JOHAN (NL)
KNIGHT CHRISTOPHER SAMUEL (US)
MANIMARAN THANIKAVELU (US)
DAUDEY PIETER JOHANNES (NL)
FREE HARMANNUS WILLEM HOMAN (NL)
TAPPEL BAS (NL)
BADLOE PARMANAND (NL)
VAN OENE JOHAN (NL)
KNIGHT CHRISTOPHER SAMUEL (US)
MANIMARAN THANIKAVELU (US)
| WO1999066085A1 | 1999-12-23 |
| US4000244A | 1976-12-28 | |||
| US4046852A | 1977-09-06 | |||
| US1923652A | 1933-08-22 | |||
| US5820844A | 1998-10-13 | |||
| US4273745A | 1981-06-16 | |||
| US4551312A | 1985-11-05 |
| CLAIMS:
1. A process for converting molybdenum technical oxide into a purified molybdenum trioxide product comprising the steps of: a. forming a reaction mass by combining molybdenum technical oxide comprising MoO 2 , MoO 3 and metal impurities with an effective amount of at least one leaching agent to leach the metal impurities and an effective amount of at least one oxidizing agent to oxidize MoO 2 to MoO 3 ; and b. separating the reaction mass into a solid purified molybdenum trioxide product and a residual impurity-containing liquid.
2. The process of claim 1, further comprising the step of recovering at least a portion of any dissolved molybdenum from the residual liquid and recycling the recovered molybdenum to the reaction mass.
3. The process of claim 2, wherein the leaching agent is sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid, or mixtures thereof.
4. The process of claim 3, wherein the oxidizing agent is chlorine, bromine, hydrogen peroxide, or mixtures thereof.
5. The process of claim 4, wherein the reaction mass is heated to a temperature in the range of about 30 the about 150 0 C.
6. The process of claim 5, wherein the reaction mass is agitated for about 15 minutes to about 24 hours.
7. The process of claim 2, wherein a single substance both leaches metal impurities and oxidizes MoO 2 to MoO 3 .
8. The process of claim 7, wherein the single substance is Caro's acid having a H 2 SO 4 to H 2 O 2 ratio ranging from about 1 :1 to 5:1.
9. The process of claim 2, wherein the addition of oxidizing agent to the reaction mass results in the in situ formation of the leaching agent.
10. The process of claim 9, wherein the oxidizing agent is chlorine, bromine or mixtures thereof.
11. The process of claim 10, wherein the reaction mass is heated to a temperature in the range of about 30 the about 150 0 C.
12. The process of claim 11, wherein the reaction mass is agitated for about 15 minutes to about 24 hours.
13. The process of claim 2, wherein the at least a portion of any dissolved molybdenum is recovered by ion exchange.
14. A solid purified molybdenum trioxide prepared in accordance with the process of claim 1. |
PURIFICATION OF MOLYBDENUM TECHNICAL OXIDE
[0001] Molybdenum is principally found in the earth's crust in the form of molybdenite (MoS 2 ) distributed as very fine veinlets in quartz which is present in an ore body comprised predominantly of altered and highly silicified granite. The concentration of the molybdenite in such ore bodies is relatively low, typically about 0.05 wt% to about 0.1 wt%. The molybdenite is present in the form of relatively soft, hexagonal, black flaky crystals which are extracted from the ore body and concentrated by any one of a variety of known processes so as to increase the molybdenum disulfide content to a level of usually greater than about 80 wt% of the concentrate. The resultant concentrate is subjected to an oxidation step, which usually is performed by a roasting operation in the presence of air, whereby the molybdenum disulfide is converted to molybdenum oxide, which is of a commercial or technical grade (technical oxide) containing various impurities including metallic contaminants present in the original ore body.
[0002] It is desirable or necessary in some instances to provide a molybdenum trioxide (MoO 3 ) product that is relatively free of metallic contaminants, as well as possessing a low concentration of molybdenum dioxide (MoO 2 ), or other molybdenum oxide species with a valency lower than +6, such as, for example, MO 4 O H 5 which, for the sake of simplicity herein, will also be referred to as MoO 2 . This high purity material may be used for the preparation of various molybdenum compounds, catalysts, chemical reagents or the like. As used herein, the term molybdenum technical oxide means any material comprising anywhere from about 1 wt% to about 99 wt% MoO2, and may optionally further comprise MoS 2 or other sulfidic molybdenum, iron, copper, or lead species. The production of high purity MOO 3 has previously been achieved by various chemical and physical refining techniques, such as the sublimation of the technical oxide at an elevated temperature, calcination of crystallized ammonium dimolybdate, or various leaching or wet chemical oxidation techniques. However, these processes may be expensive and often result in low yields and/or ineffective removal of contaminants.
[0003] One embodiment of the present invention provides a process for converting molybdenum technical oxide into a purified molybdenum trioxide product. Generally, the process comprises the steps of: combining molybdenum technical oxide with an oxidizing agent and a leaching agent in a reactor under suitable conditions to effectuate the oxidation of
residual MoS 2 , MoO 2 and other oxidizable molybdenum oxide species to MoO 3 , as well as the leaching of any metal oxide impurities; precipitating the MoO 3 species in a suitable crystal form; filtering and drying the crystallized MoO 3 product; and recovering and recycling any solubilized molybdenum. Depending on process conditions, the solid product may be precipitated as crystalline or semi-crystalline H 2 MoO 4 , H 2 MoO 4 -H 2 O, MoO 3 or other polymorphs or pseudo-polymorphs. The reaction may be performed as a batch, semi- continuous, or continuous process. Reaction conditions may be chosen to minimize the solubility of MoO 3 and to maximize the crystallization yield. Optionally, seeding with the desired crystal form may be utilized. The filtrate may be recycled to the reactor to minimize MoO 3 losses, as well as oxidizing agent and leaching agent consumption. A portion of the filtrate may be purged to a recovery process wherein various techniques may be employed, such as precipitation of molybdic acid with lime or calcium carbonate to form CaMoO 4 , precipitation as Fe 2 (MoO 4 ) 3 -xH2O and other precipitations, depending on chemical composition. Likewise, ion exchange or extraction may be employed, for example, anion exchange employing caustic soda regeneration to obtain a sodium molybdate solution that is recycled to the reaction step and crystallized to MoOs. Metal oxide impurities may also be separately treated, e.g., by ion exchange, for recovery and/or to be neutralized, filtered and discarded.
DESCRIPTION OF THE FIGURES
[0004] The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these figures in combination with the detailed description of specific embodiments presented herein.
Figure 1 shows a block flow diagram of the process of the present invention.
Figure 2 shows the dissolution of MoO 3 in HNO 3 .
Figure 3 shows the variability of leaching metal impurities with HNO 3 .
Figure 4 shows the oxidation OfMoO 2 in H 2 SO 4 (fixed) / HNO 3 (variable) solutions.
Figure 5 shows the dissolution of MoO 3 in H 2 SO 4 (fixed) / HNO 3 (variable) solutions.
Figure 6 shows the dissolution OfMoO 3 in H 2 SO 4 (variable) / HNO 3 (fixed) solutions.
Figure 7 shows the variability of leaching metal impurities with H 2 SO 4 (variable) / HNO 3 (fixed) solutions.
Figure 8 shows the oxidation OfMoO 2 in H 2 SO 4 (variable) / HNO 3 (fixed) solutions Figure 9 shows the oxidation OfMoO 2 in H 2 SO 4 / H 2 O 2 solutions.
Figure 10 shows the oxidation OfMoO 2 in H 2 SO 4 / KMnO 4 or KS 2 O 8 solutions. Figure 11 shows the oxidation OfMoO 2 in Caro's acid solutions.
DESCRIPTION OF THE INVENTION
Technical Oxide:
[0005] Technical oxides suitable for use in the present invention are available from several commercial sources. Table 1 below provides a few non-limiting examples of technical oxides suitable for use with the processes described herein. It should be noted that besides technical oxides similar to those presented, molybdenum disulfide could also be employed as a raw material. The following elemental analysis was conducted using sequential X-ray Fluorescence Spectrometry (XRP) and Inductively Coupled Plasma (ICP) Spectrometry. For the ICP analyses, samples were dissolved in aqueous ammonia wherein the MoO 3 dissolved and insolubles were filtered. The molybdenum from the ammonium dimolybdate solution is labeled as MOO 3 in the table and the molybdenum from the insolubles is denoted MoO 2 .
TABLE 1
[0006] Referring now to Figure 1, the technical oxide and/or molybdenum sulfide raw materials are introduced into a reaction vessel (100), preferably a jacketed, continuously- stirred tank reactor, but any suitable reaction vessel may be employed. The raw material is mixed in the reaction vessel (100) with a leaching agent, to dissolve metal impurities, and an oxidizing agent, to oxidize MoS 2 and MoO 2 to MoO 3 .
[0007] While any common lixiviant, or mixtures of common lixiviants, may be employed, sulfuric acid and hydrochloric acid are preferred leaching agents. Similarly, while any common oxidizing agent, or mixtures of common oxidizing agents, may be employed, including but not limited to hypochlorite, ozone, oxygen-alkali, acid permanganate, persulfate, acid-ferric chloride, nitric acid, chlorine, bromine, acid-chlorate, manganese dioxide-sulfuric acid, hydrogen peroxide, Caro's acid, or bacterial oxidation, Caro's acid and chlorine are the preferred oxidizing agents.
[0008] The leaching agent and oxidizing agent may be added in any order, or may be added together such that the leaching and oxidation occur simultaneously. In some instances, such as when using Caro's acid, leaching and oxidation occur by the action of the same reagent. In other instances, the leaching agent may be formed in situ by the addition of an oxidizing agent, for example, the addition of chlorine or bromine to the reaction mass results in the formation of hydrochloric or hydrobromic acid. The reaction mass is agitated in the reaction vessel (100) for a suitable time and under suitable process conditions to effectuate the oxidation of residual MoS 2 , MoO 2 and other oxidizable molybdenum oxide species to MoO 3 , and to leach any metal oxide impurities, say for example between about 15 minutes to about 24 hours at a temperature ranging from about 30 0 C to about 150 0 C. Depending on the particular oxidizing agent employed, the reaction pressure may range from about 1 bar to about 6 bar. Depending on the lixiviant employed, the pH of the reaction mass may range from about -1 to about 3. Whereas the lixiviant and oxidizer may act separately when dosed one after another, it has been observed that simultaneous action of lixiviant and oxidizer is beneficial for driving both the oxidation and leaching reactions to completeness.
[0009] While leaching of impurities and oxidization Of MoS 2 and MoO 2 occurs, the majority of the MoO 3 precipitates, or crystallizes, from the solution. However, a portion of the MoO 3 formed by oxidation or dissolved from MoO 3 in the starting material may remain in solution for various reasons. While not intending to be bound by theory, it is generally believed that wet-chemical oxidation in a slurry process is mechanistically explained by either oxidative
dissolution of species at the solid-liquid interface, or by dissolution, perhaps slow dissolution, of the oxidizable species followed by oxidation in the liquid phase. The most probable form of Mo 6+ species in solution, denoted as dissolved MoO 3 , is believed to be H 2 MoO 4 , but a variety of other species are also possible. It has been observed that when the oxidation is not complete, blue colored solutions with a high amount of dissolved molybdenum oxide species result, the blue color pointing at polynuclear mixed Mo 5+ / Mo 6+ oxidic species. Also, crystallization is a slow process at low temperatures, so the crystallization conditions chosen may result in a lower or higher amount of dissolved molybdenum oxide species. Thus, after the precipitated trioxide, together with hitherto undissolved MoO3 or other species from the starting technical oxide is removed by filtration (200), the filtrate can be recycled to the reaction vessel (100). Because the leached metal impurities will also be recycled to the reaction vessel (100), a slipstream of the recycled material may be drawn off and treated for removal or recovery of the metal impurities. The filter cake (MoO 3 product) may be dried (400) and packed for distribution (500).
[0010] In order to recover any molybdenum in the slipstream, it may be treated in a suitable ion-exchange bed (300). One preferred ion-exchange bed comprises a weakly basic anion exchange resin (cross-linked polystyrene backbone with N,N'-di-methyl-benzylamine functional groups), preloaded with sulfate or chloride anions, wherein molybdate ions are exchanged with sulfate or ions chloride ions during resin loading and the resin is unloaded with dilute sodium hydroxide, about 1.0 to 2.5 M. The unloaded molybdenum is recovered by recycling the dilute sodium molybdate (Na 2 MoO 4 ) stream (regenerant) to the reaction vessel (100).
[0011] Following recovery of molybdenum, the slipstream may be subsequently treated in additional ion-exchange beds (600) in order to remove additional metallic species. Any remaining metal impurities will be precipitated (700) and filtered (800) for final disposal. After these treatment steps a residual solution is obtained containing mainly dissolved salts like NaCl or Na 2 SO 4 , depending on the chemicals selected that may be purged.
EXAMPLES
[0012] It should be noted that within the following discussion several stoichiometric schemes are discussed. While not desiring to be bound by any theory, the inventors herein believe that the disclosed schemes accurately describe the discussed mechanisms.
[0013] 75 grams of technical oxide was mixed with 250 ml of various acidic solutions listed and described below. The mixtures were stirred with a Teflon coated magnetic stirrer and heated to 70 0 C for two hours. The mixtures were cooled to room temperature and filtered over a 90 mm black ribbon filter. The filter cake was washed with 20 ml of deionized water. The filtrate was brought to 250 ml volume and the filter cake was dried overnight at 120 0 C. The dried filter cake was analyzed for content, as well as metal impurities. The filtrate was analyzed for metal impurities.
Nitric Acid:
[0006] The leaching of the technical oxide (TO) and calcined technical oxide (TOC) was performed in a series of acid solutions from 0.1 to 10 N HNO 3 . Leaching and oxidation occurs by action of the single reagent. The oxidation stoichiometry can be summarized as follows:
MoO 2 + 2H + + 2(NO 3 ) " → MoO 3 + 2NO 2 (g) t + H 2 O
MoO 2 in the sample was completely converted to MoO 3 with nitric acid. A color change was also visible form dark blue (Mo 5+ ) to grass green/blue green. The solubility of MoO 3 decreases with acid concentration as shown in Figure 2. Cu and Fe dissolve readily in low concentrations of nitric acid. Some metals (Ba, Pb, Sr, and Ca) needed more the 1 N nitric acid to dissolve as shown in Figure 3 and Table 2. Brown NO 2 fumes were visible with excess FTNO 3 . The results of the leaching/oxidation of technical oxide with nitric acid are summarized in Table 2.
TABLE 2
Sulfuric Acid / Nitric Acid:
[0007] Keeping the concentration of H 2 SO 4 fixed at 4N and varying the concentration of HNO 3 from 0 to 2 N in six increments, a series of acidic solutions were prepared. Technical oxide was mixed in each of the solutions and the results of the leaching/oxidation with H 2 SQ4/HNO 3 mixtures are summarized in Table 3. Brown NO 2 fumes were visible with excess HNO 3 . The color of the solution changed from dark blue to light grass green. The oxidation was almost complete starting from 0.2 N HNO 3 . See Figure 4. The dissolution of MOO 3 in varying concentrations of the acidic solution is shown in Figure 5. Ca, Fe and Cu dissolve well, but Pb did not dissolve.
TABLE 3
EX 2A I EX 2B I EX 2C I EX 2D | EX 2E \ EX 2F | EX 2G
[0016] Keeping the concentration OfHNO 3 fixed at 0.15 N and varying the concentration Of H 2 SO 4 from 0.12 to 4 N, series of acidic solutions were prepared. Technical oxide was mixed in each of the solutions and the results of the leaching/oxidation with H 2 SO 4 /HNO 3 mixtures are summarized in Table 4. The dissolution of MoO 3 in varying concentrations of the acidic solution is shown in Figure 6. Under these conditions, Ca and K dissolved only when the concentration of H 2 SO 4 was greater than 2 N. Al required concentrations greater than 4 N to dissolve. See Figure 7. Fe and Ca dissolved readily in 0.1 N H 2 SO 4 .
TABLE 4
[0017] MoO 2 oxidized only when the concentration Of H 2 SO 4 was greater than 2 N, and the oxidation was not always complete. See Figure 8. Additional experiments were performed with 0.25 and 0.5 N HNO 3 . The results are summarized in Figure 8 and Table 4.
Sulfuric Acid / Hydrogen Peroxide:
[0018] A series of acidic solutions were prepared with an H 2 SO 4 concentration of 4 N and varying concentrations of H 2 O 2 . The quantity of water was selected such that the total volume of acid, water and hydrogen peroxide equaled 250 ml. Hydrogen peroxide was slowly dropped into the reaction mass to control the vigorous reaction. The oxidation stoichiometry can be summarized as follows:
2H 2 O 2 → O 2 (g) t + 2H 2 O
2MoO 2 + O 2 → 2MoO 3
[0019] Because oxygen is lost, oxidation proceeds with a low efficiency, thus requiring excess H 2 O 2 . See Figure 9. Addition of small amounts of nitric acid did not significantly increase oxidation efficiency. The results of the leaching/oxidation with H 2 SO 4 ZH 2 O 2 mixtures are summarized in Table 5.
[0020] Peroxide may also react directly with MoO 2 according to the following stoichiometry:
MoO 2 + H 2 O 2 → H 2 MoO 4 (dissolved) or to MoO 3 + H 2 O
followed by crystallization to H 2 MoO 4 or other MOO 3 solids. The reaction of MoO 2 with oxygen primarily occurs at autoclave conditions (temperatures above about 200 0 C).
TABLE 5
[ EX, 4A | EX. 4B |
Sulfuric Acid / Potassium Permanganate:
[0021] A series of acidic solutions were prepared with an H 2 SO 4 concentration of 4 N and varying concentrations of KMnO 4 . The oxidation stoichiometry is believed to proceed as follows:
3MoO 2 + 2MnO 4 " + 2H + → 3MoO 3 + 2MnO 2 (s) + H 2 O 2MnO 2 (s) + 2MoO 2 + 4H + → 2MoO 3 + 2Mn 2+ + 2H 2 O
With excess MnO 4
3Mn 2+ + 2MnO 4 " + 2H 2 O → 5MnO 2 (s) + 4H +
[0022] The results of the leaching/oxidation with H 2 SO 4 / KMnO 4 mixtures are summarized in Table 6 and Figure 10.
TABLE 6
Sulfuric Acid / Potassium Persulfate:
[0023] A series of acidic solutions were prepared with an H 2 SO 4 concentration of 4 N and varying concentrations of KS 2 Os. The oxidation stoichiometry is believed to proceed as follows:
MoO 2 + S 2 Og 2- + H 2 O MoO, + 2SO 4 2- + 2H
The results of the leaching/oxidation with H 2 SO 4 / BCMnO 4 mixtures are summarized in Table 6 and Figure 10.
Caro's Acid:
[0024] Caro's acid is produced from concentrated sulfuric acid (usually 96-98%) and concentrated hydrogen peroxide (usually 60-70%), and comprises peroxymonosulfuric acid. Caro's acid is an equilibrium mixture having the following relationship:
H 2 O 2 + H 2 SO 4 * → H 2 SO 5 + H 2 O The oxidation stoichiometry for MoO 2 in Caro's acid is believed to proceed as follows:
MoO 2 + H 2 SO 5 → MoO 3 + H 2 SO 4
75 grams of technical oxide was mixed with water and Caro's acid (H 2 SO 4 :H 2 O 2 = 3: 1, 2: 1, and 1:1). In some embodiments, higher ratios may also be employed, such as 4:1 and 5:1. In separate experiments, the temperature of the reaction mass was either cooled or heated to T = 25, 70 and 90 0 C for and mixed for two hours. The results of the leaching/oxidation with Caro's acid mixtures are summarized in Figure 11.
Chlorine, Chlorinated Compounds and Bromine:
[0025] A three-necked jacketed 250 mL creased flask was used as the reactor. It was fitted with a 1/8" Teflon feed tube (dip-tube) for chlorine addition, a condenser, a thermometer and a pH meter. The top of the condenser was connected with a T joint to a rubber bulb (as a pressure indicator) and to a caustic scrubber through a stop-cock and a knock-out pot. The flask was set on a magnetic stirrer. The jacket of the flask was connected to a circulating bath. Chlorine was fed from a lecture bottle set on a balance and a flow meter was used for controlling the chlorine feed. The lecture bottle was weighed before and after each experiment to determine the amount of chlorine charged.
[0026] Technical oxide (50 g) was suspended in 95g of water and/or recycled molybdenum solution from the ion-exchange step of previous experiments. Concentrated sulfuric acid was added in drops to bring the pH of the reaction mass down to 0.2 and the suspension was magnetically stirred. The suspension was heated to 60 0 C using the
circulating bath and stirred at that temperature for about 30 minutes. Chlorine was fed using a flow meter and bubbled through the suspension. The reaction was exothermic as indicated by the temperature increase to about 62 0 C. Chlorine feed was stopped when there was no more consumption of Cl 2 as indicated by an increase in pressure and drop in temperature to about 60 0 C. Stirring of the reaction mixture at 60 0 C under slight chlorine pressure was continued for an hour to ensure complete oxidation. Nitrogen or air was then bubbled for 30 minutes to strip off unreacted chlorine. A 20% solution of NaOH was carefully added in drops to bring the pH up to 0.2. After pH adjustment, the mixture was stirred at 60 0 C for an hour. It was then cooled to 30 0 C and filtered using a fritted funnel (M) under suction. The solid on the funnel was washed with 25 g of 5% sulfuric acid and then with 25 g of water. The wet cake was weighed and then dried in an oven at 95 0 C for about 15 hours. The filtrate was analyzed by ICP for molybdenum and other metals. The dried solid was analyzed by ICP for metal impurities. Some of the solid samples were also analyzed for the amount of MoO 2 and MoO 3 .
Oxidation with Chlorine:
EXAMPLE 1
[0027] A 2Og sample of the technical oxide was suspended in 6Og of water. Concentrated sulfuric acid (1Og) was added and the mixture was heated to 60 0 C. After stirring the mixture for 30 minutes at 60 0 C, chlorine (3.6g) was slowly bubbled through the mixture over a period of 40 minutes. The gray slurry became light green. The mixture was heated to 90 0 C and stirred at 90 0 C for 30 minutes. Nitrogen was bubbled through the mixture at 90 0 C for 30 minutes to strip off any unreacted chlorine. The mixture was cooled to room temperature. The slurry was then filtered under suction and washed with 20 g of 2% hydrochloric acid and 20 g of water. The wet cake (22.6 g) was dried in an oven at 90 0 C for 15 hours to yield 16.8 g of product.
Analysis of starting Tech. Oxide and Product by ICP:
EXAMPLE 2
[0028] A slurry of 50 g of the same technical oxide used in Example 1 was formed in 95 g of water was stirred at 60 0 C for 30 minutes. Chlorine (6.8 g) was bubbled through the slurry for about 40 minutes, maintaining a positive pressure of chlorine in the reactor. The slurry changed from gray to pale green. Nitrogen was bubbled for 30 minutes to strip off excess chlorine. Concentrated HNO 3 (5.0 g) was added dropwise to the mixture at 60 0 C and stirred at 60 0 C for 30 minutes after the addition. Then 20% NaOH solution was added to adjust the pH to 0.5. The mixture was cooled to 25 0 C and filtered under suction. The wet cake (62.3 g) was dried in an oven at 90 0 C for 16 hours to get 49.5 g of product. ICP analysis of the oxidized product showed that it contained 502 ppm Fe, 58 ppm Cu and 15 ppm AL
EXAMPLE 3
[0029] Concentrated HCl (8.8 g) was added to a slurry of technical oxide (from a different source as compared to Examples 1 and 2) in 15O g of water to adjust the pH of the mixture to 0.4. The mixture was heated to 60 0 C and stirred at that temperature for 30 minutes. Chlorine was slowly bubbled through the mixture till there was a positive pressure of chlorine in the reactor. It took 1.4 g of chlorine over a period of 35 minutes. The mixture was stirred at 60 0 C for 30 minutes after chlorine addition and then nitrogen was bubbled through the mixture for 30 minutes. The liquid phase of the slurry had a pH of 0.4. The slurry was then cooled to room temperature and filtered under suction. The solid was washed with 25 g of 5 wt% HCl and 25 g of water. The wet cake (55.0 g) was dried in an oven at 90 0 C for 16 hours to get 47.4 g of product.
Analysis of Starting Technical Oxide and Product by ICP:
Oxidation with Sodium Hypochlorite:
[0030] Technical oxide (20 g) was added to 45 g of water and 5 g of concentrated sulfuric acid taken in a jacketed 100 niL flask. The mixture was heated to 60 0 C and magnetically stirred at that temperature for 30 minutes. Sodium hypochlorite solution (20 g) containing 10-13% active chlorine was taken in an addition funnel and added dropwise over 30 minutes. Color of the slurry changed from gray to blue to light green indicating complete oxidation. The liquid portion of the slurry had a pH of 0 as shown by pH paper. The mixture was cooled to room temperature and filtered under suction. The solid on the funnel was washed with 20 g of 5 wt% sulfuric acid and 20 g of water. The wet product (22.4 g) was dried in an oven at 90 0 C for 16 hours to get 18.3 g of product.
ICP analysis of Tech. Oxide and Product:
Oxidation with Bromine:
[0031] A slurry of the same technical oxide from Examples 1 and 2 (40 g) in 120 g of water was taken in a 25OmL jacketed flask and stirred at 60 °C for 30 minutes. Bromine (10 g) taken in an addition funnel was slowly added in drops. Disappearance of the red color of bromine indicated reaction. Bromine addition took about 30 minutes. The mixture was heated to 90 0 C and stirred at 90 0 C for 30 minutes. Nitrogen was bubbled through the mixture at 90 0 C for 30 minutes to strip off unreacted bromine. The mixture was cooled to room temperature and filtered under suction. The solid was washed with 20 g of 2 wt% HCl
and 20 g of water. The wet cake (60.4 g) was dried at 90 0 C for 16 hours to 38.6 g of product. The oxidized product had about 5000 ppm Fe, 600 ppm Cu and 200 ppm Al.
Oxidation with Sodium Chlorate:
[0032] Technical oxide (50 g) was mixed with 80 g of water and 5 g of concentrated sulfuric acid in a 250 mL jacketed flask and stirred at 60 0 C for 30 minutes. Sodium chlorate (3 g) was dissolved in 15 g of water and the solution was taken in an addition funnel. The chlorate solution was slowly added in drops to the technical oxide slurry at 60 0 C and the addition took about 30 minutes. Change in color of the slurry to light green indicated complete oxidation. The slurry was cooled to room temperature and filtered under suction. The solid was washed with 25 g of 2 wt% sulfuric acid and 25 g of water. The wet cake (65.4 g) was dried in an oven at 90 0 C for 16 hours. Product (48.2 g) was analyzed by ICP for metallic impurities.
[0033] While the compositions and methods of this invention have been described in terms of distinct embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions, methods and/or processes and in the steps or in the sequence of steps of the methods described herein without departing from the concept and scope of the invention. More specifically, it will be apparent that certain agents, which are chemically related, may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope and concept of the invention.