FI60381B - FRAMEWORK FOR FRAMSTATING AV AND JAERNFRI KROM (III) FOERENING - Google Patents

Description

RHr ^ I Γβΐ (m ANNOUNCEMENT £ (\ Ύ0Α mA lBJ (11> UTLÄGGNINGSSKMFT OU0ö1 C .... Patent granted li 01 1982 '* Patent meddelat (51) Kv.lk?/lnt,CI.3 Q Q1 G 37 / 00 FINLAND —FINLAND (21) Ptwnttlh »k * mu« - Pit * nund) knlnj 790391 (22) HakvmitpUvi - An * ekoln | sdag 06.02.79 ^ '(23) Alkuptlvi - Glltlghetsdag 06.02.79 (41) Tullut Julklsakal - Bllvlt offancllg 07 · 08.80

National Board of Patents and Registration .... M .....

(44) Date of issue of the contract

Patent and registration authorities; Amekan utla «i och uti. * KrHtan pubiicand 30.09-81 (32) (33) (31) Pyydetty atuolkeu * —EUglrd priority (71) Outokumpu Oy, Outokumpu, FI; Töölönkatu * +, 00100 Helsinki 10, Finland-Finland (FI) (72) Seppo Olavi Heimala, Pori, Stig-Erik Hultholm, Pori, Frans Heikki Tuovinen, Ulvila, Finland-Finland (Fl) (7 * 0 Berggren Oy Ab ( The present invention relates to a process for precipitating a substantially iron-free chromium (III) compound at elevated temperature and pressure from an acidic aqueous solution containing iron and chromium.

Chromium chemicals are now manufactured industrially from Chromite or ferrochrome alone by oxidative annealing. The alkali chromate is separated from the annealed product by dissolving it in water, and after many purification and washing steps, dichromate conversion is performed with sodium bisulfate, sulfuric acid, carbon dioxide or the like from the production of chromium trioxide. Other chromium salts, such as potassium, ammonium, zinc and lead chromates, chromium trioxide, Cl 2 OH, Cr 2 chromium.

The previously known methods are both complex and expensive, due to the toxic nature of hexavalent chromium, these previously known methods have always been associated with environmental and health protection disadvantages.

60381 2

It is an object of the present invention to obviate the above drawbacks and to provide a process for precipitating a substantially iron-free chromium (III) compound at elevated temperature and pressure from an acidic aqueous solution containing iron and chromium without the precipitation of iron. Chromium-poor or chromium-rich chromite, ferrochrome, chromium-containing waste, etc. can be used as a raw material in the process according to the invention.

The main features of the invention appear from the appended claim 1.

In the process according to the invention, co-precipitation of iron is prevented by carrying out precipitation from a solution in which at least 2 g / l, preferably about 5-15 g / l of divalent chromium is present. The pH of the solution is preferably at least 0.5 and most preferably 1.5-2.2 and the temperature is about 110-300 ° C, preferably 180-250 ° C. Acids can be used quite a lot. Of course, the most technically interesting are mainly H2SO4 and / or HCl.

Depending on the raw material used, the beginning of the process can be quite different. For example, SiO 2, calcium, sulfate, sulfite, divalent nickel, trivalent aluminum, etc. can be separated in the pretreatment steps. The use of so-called low-valence processes has been hindered by the fact that the separation of iron and chromium in particular has been very difficult. This difficulty has now been overcome by the method of the present invention and without the use of any external reagent. This is achieved by carrying out precipitation from a solution in which at least 2 g / l of divalent chromium is present and which preferably contains at least about 70-90 g / l of trivalent chromium.

In this way, chromium has been successfully precipitated as chromium oxyhydrate and / or basic sulphate without co-precipitating iron into the final product. At the same time, the chromium-bound acid can be regenerated and returned to the beginning of the process. The iron content of the circulating solution is considered suitable, for example between about 40 and 70 g / l of iron, by crystallization of ferrous sulphate from the solution or by hydrolysis of the solution at elevated temperature. The precipitation temperature of CrOOH depends on the hydrochloric acid content of the solution. The temperature limit for pure sulfate is 250 ° C, but if hydrochloric acid is present, this temperature limit is higher.

3 60381 The upper temperature limit is due to the fact that the precipitating iron compound is no longer water-soluble above this temperature. It is also clear that the treatment temperature must not be too low, as this will result in the loss of acid regeneration advantage, not to mention a reduction in product intake.

The iron and chromium-containing solution used in the process of the invention can be prepared from chromite. In the production of metallic chromium or chromium oxide for color purposes, the starting solution may also contain aluminum, since the precipitated jarosite-type aluminum minisulphate decomposes in calcination. In this way, the color tone of the obtained chromium oxide can be adjusted. When producing metallic chromium aluminothermically, a small amount of alumina in chromium oxide is still not a disadvantage.

Divalent chromium is best obtained directly from the dissolution of ferrochrome, but some other reducing agent or electrolysis can also be used. This, of course, also applies if the starting material is a substance other than an alloy-like substance, e.g. chromite. In this case, in addition to the reduction function, an alloy such as ferrochrome can also act as a neutralizer of the acid remaining in the leaching of chromite, for example. Since Cr is operated in an imbalance system E ° (Cr ^ -— ^ Cr ^ +) - -410 mV compared to the hydrogen electrode, it is self-evident that it is not advisable to delay between dissolution and precipitation of the pure Cr compound.

If the starting material does not contain e.g. Si, or Si-containing ^ -Fe is separated off even magnetically, it is possible to carry out the dissolution and precipitation in the same state and even simultaneously. This gives full benefit to the dissolution mechanism of metal-like phases, in which 2+ are first formed in Cr. In simultaneous dissolution and precipitation, the emphasis is on e.g. requirement for the existence of adequate CrOOH nuclei. In this case, lower temperatures can also be used, up to 100-130 ° C if a pure anion-containing Cr compound is satisfied and 180-200 ° C if pure CrOOH is desired. The lower limit of the temperature is then formed, in particular, determined by the filterability of the Cr compound 2+ and the active (-> Cr) dissolution of the Cr mixture.

4 6038 1

Still, in the industrial application of the process, it is often expedient, for example, to separate the leach residue or, due to the temperature control, to carry out the leaching and the precipitation of the pure Cr compound separately.

The precipitation is preferably carried out from a solution having a pH of at least 0.5, but the pH of the starting solution must not rise to the precipitation range of basic trivalent chromium (pH above 3) unless the dissolution and precipitation are carried out simultaneously, in which case the upper limit of pH is determined e.g. on the basis of precipitation and is of the order of 3.5-4.0.

It will be apparent to those skilled in the art that the iron-free chromium (III) compound can be precipitated from an iron and chromium-containing solution according to the present invention at pH above 0.5 and at elevated temperature and pressure using a variety of raw materials such as chromium-containing scrap and waste, chromite and carbon ferrochrome. By the process and calcination according to the invention, pure or doped aqueous chromium oxyhydrate, calcined chromium oxyhydrate, chromium oxide and chromium of these metals can be prepared.

The invention will be described in more detail below with reference to the accompanying drawings, in which Figures 1-3 show three alternative flow diagrams for carrying out the method according to the invention.

In the embodiment of Figure 1, precipitation of chromium oxyhydrate is performed according to the present invention, and then the chromium oxyhydrate or the basic salt of chromium is separated from the solution, which is passed to crystallization. Sulphates of nickel, cobalt and iron with a chromium content of 0,5% are then separated from a solution of 10 to 15 g / l of divalent iron, about 40 g / l of trivalent chromium and more than 100 g / l of sulfuric acid. The chromium-containing mixture is dissolved in this solution and possibly further electrolysed to increase the concentration of divalent chromium in the solution, to the level required for the subsequent precipitation of chromium oxyhydrate, if the starting material has a difficult 2+

Cr oxidation catalysts.

In the embodiment of Figure 2, the solution from the chromium oxyhydrate precipitation is subjected to the separation of iron in an autoclave in the presence of oxygen. Filtration gives trivalent iron hydroxysulphate with a chromium content of 4-10%. To a solution of 60381 5 of about 20 g / l of trivalent iron is added sulfuric acid so that the sulfuric acid content is more than 100 g / l, after which the solution is introduced to dissolve the chromium-containing raw material to

In the embodiment of Figure 3, all or part of the solution from the crystallization and separation is passed to dissolve the chromite, after which it and any by-product are subjected to electrolysis or ferrochrome is dissolved in it to raise the divalent chromium content to the desired level.

Figure 4 below shows the percentage of iron in the chromium oxyhydrate precipitate obtained as a function of the divalent chromium content (g / l). It can be seen from Figure 4 that the concentration of iron in the precipitate decreases very sharply as the concentration of divalent chromium in the solution increases. The shape of the curve shown in Figure 4 remains the same even if the precipitation conditions change. However, the curve may move within the limits indicated by the dashed lines in the figure, depending on the crystal nuclei and other substances present in the solution or whether dissolution and precipitation are performed simultaneously.

The invention is described in more detail below with reference to the following examples.

Example 1

The ferrochrome was dissolved in sulfuric acid to directly give a solution of 70 g / l of trivalent chromium, 40 g / l of divalent iron and 5 g / l of divalent chromium. The pH of the solution was then 2.0. The solution was sealed in a pressure vessel at 235 ° C for 30 minutes (nitrogen atmosphere). The resulting chromium oxyhydrate precipitate was washed with water and dried. The iron content of the precipitate was 0.15%. The chromium yield of the precipitate was 65%.

Example 2

The solution of Example 1 was oxidized so that its divalent chromium content decreased to 2 g / l, followed by precipitation at 235 ° C for 30 minutes. The iron content of the precipitate was then 0.5%. The product was mixed with 1% carbon and kept at 1000 ° C for 30 minutes in a stream of chlorine gas. The resulting chromium oxide had an iron content of less than 0.1%.

60381 6

Example 3

The divalent chromium content of the solution of Example 1 was reduced to 0.5 g / l and the solution was kept at 235 ° C for 30 minutes. The product obtained contained 4.3% iron.

Example 4

Ferrochrome was dissolved in a mixture of sulfuric acid and hydrochloric acid. A solution with a pH of 2.0, a total chromium content of 100 g / l, an iron content of 63 g / l and a chloride content of 50 g / l was obtained. Heating the solution at 230 ° C for 60 minutes gave chromium oxyhydrate in 40% yield when the initial divalent chromium content of the solution was 6.7 g / l. The iron content of the product was 0.08%.

Example 5

The divalent chromium content of the solution of Example 4 was increased by additional dissolution to 8.9 g / l and the pH was raised to 2.1 and 2 g / l of chromium oxyhydrate cores were added. The solution was heated at 230 ° C for 60 minutes, during which time 48% of the chromium precipitated from the solution as chromium oxyhydrate. The iron content of the product was 0.03%.

Example 6

The pH of the solution of Example 4 was lowered to 1.5 with sulfuric acid and the concentration of divalent chromium was reduced to 3.4 g / l at the same time. The solution was heated at 230 ° C for 60 minutes with a chromium oxyhydrate yield of 35%.

Example 7

Chromite was dissolved in sulfuric acid. A part of divalent iron, divalent magnesium, trivalent aluminum was removed from the resulting solution by crystallization. To the resulting solution was added ferrochrome to increase the content of divalent chromium to give a solution with a total chromium content of 92 g / l, a content of divalent chromium of 5.2 g / l, a content of divalent iron of 43 g / l, an aluminum content of 1 g / l, a magnesium content of 1 , 5 g / l and pH 2.2. The solution was kept at 240 ° C for 30 minutes to give chromium oxyhydrate with an iron content of 0.15%, an aluminum content of 1.8%, a magnesium content of 0.04% and a chromium content of 53%.

Claims (5)

60381 7 Example 8 A solution of divalent iron 43 g / l, trivalent chromium 70 g / l and divalent chromium 3 g / l and pH 2 was maintained at 200 ° C. a) for one hour with a chromium oxyhydrate yield of 10% and an iron content of 0.4%, b) for 16 minutes with a chromium oxyhydrate yield of 6.5% and an iron content of 0.2% in the precipitate. Example 9 A solution of divalent iron 71 g / l, trivalent chromium 90 g / l and divalent chromium 5 g / l and having a pH of 2 was maintained at 250 ° C for 30 minutes with a chromium oxyhydrate yield of 74 g / l. % and iron content 4.5%. Example 10 A solution of 43 g / l of divalent iron, 70 g / l of trivalent chromium, 15 g / l of divalent chromium, 10 g / l of magnesium, and pH 2 was treated for one hour at 235 ° C, to give a chromium oxyhydrate precipitate with an iron content of 0.03%. Example 11 Fine fine Si-poor ferrochrome was sealed with H 2 SO 4, N 2 and CrOOH cores in a pressure vessel with good mixing. The pressure was adjusted by draining the gas. The temperature was allowed to rise to 210 ° C. At best, about 1/4 of the chromium was in the Cr2 + form. After 4 hours, the solution and precipitate were removed and filtered. The pH of the FeSO 4 solution was 1.4 and the Fe content was 83 g / l. After gentle grinding, magnetic separation, acid washing and drying, the Fe content of the CrOOH product was 0.18%. A process for precipitating a substantially iron-free chromium (III) compound at elevated temperature and pressure from an acidic aqueous solution containing iron and chromium, characterized in that precipitation is carried out from a solution in which at least 2 g / l of divalent chromium is present to prevent co-precipitation of iron. Process according to Claim 1, characterized in that the precipitation is carried out from a solution in the presence of 5415 g / l of divalent chromium. Process according to Claim 1 or 2, characterized in that the precipitation is carried out from a solution having a pH of at least 0.5, preferably 1.5-2.2 and a temperature of about 110-300, e.g. 180-250 ° C, preferably 200 -250 ° C. Process according to one of the preceding claims, characterized in that the precipitation is carried out from a solution of at least about 70 g / l of trivalent chromium and at least about 40 g / l of iron. Process according to one of the preceding claims, characterized in that the acidic aqueous solution is obtained by dissolving an iron-containing chromium raw material such as ferrochrome or chromite in an acid such as sulfuric acid or hydrochloric acid and / or chromium (III) in a regenerated circulating acid solution. , and to which divalent chromium is added to the acidic aqueous solution, if necessary, or divalent chromium is generated by reducing the trivalent chromium already present therein.