RO108787B1 - Integral using of chrome residues and noxious removing working process - Google Patents

Description

The present invention relates to a processing process for the complete removal and recovery of chromic residues.

It is known that a large amount of chromic residue is eliminated during the production of chromates, through the chromium ore calcination. Statistics show that for the production of one tonne of sodium dichromate, 2.5 ... 3 t of harmful chromic residues are eliminated, containing 3 ... 7% residual Cr2O3, 8 ... 11% Fe2O3 and 0.5 ... 1.5% Cr ⁶⁺ soluble in water, the latter being toxic to both humans and animals. Throwing away these metal oxides is not only a waste of resources, but also a source of environmental pollution.

Various methods of elimination of chromic residues are known which can be grouped into two categories. One category is based on reduction, that is, hexavalent chromium of residues is reduced to bivalent, after which, the reduced residues are removed, by burial at great depth, discarding, storage. In US Patent Nos. 975580 and CN 85105628, processes are described according to which the chromic residues are first processed with hydrochloric acid and then the addition of a reducing agent. In the patent CN 90103420, a process for reducing the chromic residues in high temperature and vacuum conditions is described. Either of the abatement processes listed raises the problem of switching bivalent chromium back to its hexavalent form, which is due in particular to the existence of calcium, magnesium and other metals in chromic residues.

The second category consists in the full use of chromic residues as industrial raw material, which ensures both the consumption of these residues and the obtaining of economic benefits. In the Chinese magazine Wujiyen Gongye Nr. 2 of 1987 and in CN patent 85105628, the use of chromic residues for the coloring of the glass, for the production of colored cement, in the indus2 sorting of bricks and as chemical fertilizers based on calcium / magnesium / phosphorus, as well as in steel, as an auxiliary material for melting is described. iron. However, the methodology cannot be applied on an industrial scale, due to the complexity of the technological processes and the high costs.

More recently, a technology has been developed, according to which the chromic residues were reduced to high temperatures for detoxification, with the addition of auxiliary materials, which made their full use possible. Thus, in CN patent 88104766, it is described the reduction of chromic residues, by high temperature calcination in a suitable furnace, with the addition of auxiliary materials of potassium carbonate and calcium oxide, for the formation of the slags used in the cement industry, chemical fertilizers. with potassium carbonate and chromium-containing cast iron. It should be noted that the direct melting of the chromium residues in the presence of 7 ... 10% sodium, leads to formation in the furnace of agglomerations that affect its operation and shortens its operating life.

The process according to the invention removes the disadvantages presented by the fact that it provides the mixing - chromic residues: chromium ore powder: sodium carbonate: coke powder, at a weight ratio of 1: (0.1 ... 0.25 ) :( 0,1 ... 0,25) :( 0 ... 0,16), which is homogenized with the addition of water, is pre-dried, crushed at the granulation of passage through the sieve with 12,4. 15.5 mesh / cm ^z and calcined at 1000-1200 ° C, predetermined time The product obtained by calcination is treated with water for the solubilization separation of the sodium chromate resulting by calcination from the insoluble residue which is premixed. with iron ores and is processed pyrometallurgically to obtain a synthesized iron of a low chromium content and, finally, a slab without toxicity. The above-mentioned sodium chromate solution is further processed under predetermined conditions for passage to other chromium salts.

The process according to the invention has the following advantages:

- using the calcination process according to the conditions of the invention, the chromium trioxide contained in different types of chromic residues, some of which are difficult to extract by direct extraction, can be converted into sodium chromate, so that the chromium trioxide can be used effectively, and respectively the completely denosured chromic residues;

- by the calcination treatment according to the conditions according to the invention, 50 ... 60% Cr2O3 of the chromic residues can be reused, 60 ... 70% Cr · ⁺ soluble in water, it is removed from these residues and different usable salts can be obtained in the industry, so that a complete use of the chromic residues is realized in their entirety, obtaining benefits, both from the environmental and economic point of view.

In the following, the process according to the invention will be presented in detail with reference to the figure, which represents the flow diagram of the technological flow.

The process according to the invention comprises the following steps:

1). Calcination of chemical residues

The chromic residues are dried, they are crushed to the granulation through the sieve with 12.4 ... 15.5 mesh / cm ² , and from them the mixture is prepared comprising in weight reports - chromic residues: chromium ore powder: carbonate Sodium: Coconut powder = 1: (0.1 ... 0.25) :( 0.1 ... 0.25) :( 0 ... 0.16). In this mixture water is introduced and it is homogenized, after which it is introduced in a usual calcination furnace. The temperature in the oven is gradually increased to 1000 ... 1200 ° C, and the calcination can be carried out, for 30 ... 60 minutes, to obtain a chipboard. The calcination can also be carried out for 2 hours at the same temperature in a rotary oven. In the calcination phase of the chromic residues the main reactions that take place are the following:

4 (FeO.Cr2O3) + 8Na2CO3 + 702 -> 8Na2CrO4 + 2Fe2O3 + 8CO2;

4 (MgO + Cr2O3) + 8Na2CO3 + 6O2 - ^ 8Na2CiO4 + 4MgO + 8CO2.

2). extraction

The calcined agglomerate is treated with water in a high extractor to remove the sodium chromate content. The solution obtained by aqueous extraction with the sodium chromate content can be further treated to obtain other chromium compounds - chromium oxide, basic sulphate. of chromium, yellow of medium chromium and so on, and the residues resulting after aqueous extraction, can also be further processed, resulting in sintered iron or low chromium content and finally a non-toxic slag.

3). Complete treatment of the extracted aqueous solution

- a) Production of chromium oxide or basic chromium sulfate.

The aqueous solution of sodium chromate, resulting from extraction, is pumped into a precipitation vessel, sodium sulfide or sulfide is introduced and the reaction medium is heated with steam to 100 ° C, to pass Na2CiO4 from the solution into Cr (OH). )3. The reactions are as follows:

4Na2CrO4 + 6S + 7H2O 4Cr (OH) 3l + 3 Na2S2O3 + 2NaOH;

8Na2CiO4 + 6Na2S + 23H2O -► 8Cr (OH) 3l + 3Na2S2O3 + 22NaOH

The resulting precipitates are filtered and washed with water, then calcined in the oven, at 1200 ° C, for passage into Cr2O ₃ :

1200 ^ 0

2 (4 (011) 3 ^ 0203 + 3H2O

The basic chromium sulphate is formed by treating the chromium hydroxide obtained as above with sulfuric acid or sodium acid sulfate:

CR (OH) 3 + H2SO4 - * Cr (OH) SO4 + H2O;

Cr (OH) 3 + 2NaHSO4 -> Cr (OH) SO4 '+ Na2SO4 + 2H2O

Sulfuric acid or sodium sulfate is introduced into the solution only after the separation of chromium hydroxide, for the recovery of sodium sulfate or in the reaction medium, sulfur dioxide is fed to obtain sodium thiosulphate, a very important chemical reagent.

- b) Production of basic chromium sulphate and sodium sulphate:

Sodium sulfate residues, toxic and highly corrosive (H2SO435 ... 40%, Na2SO4 45 ... 50% and Na2Cr2O7 .2H2O 2 ... 3%), resulting from the manufacture of Cr2O3, are used for obtaining the solution of NaHSO4 by dissolving in water, sedimentation and removal of acid mud impurities. The aqueous solution containing sodium chromate is passed into a neutralization vessel, in which the above sodium acid sulfate solution is introduced, to bring the pH to

6 ... 7, the reaction medium is filtered under pressure, resulting in a neutral solution of sodium chromate, which is then acidified into an acidification vessel by a further addition of NaHSO4.

2Na2CrO4 + 2NaHSO4 —-Na2CnO7 + 2Na2SO4 + H2O.

Sucrose or formaldehyde is introduced into the acidified solution, which is then heated to 100 ° C, to obtain basic chromium sulfate and sodium sulfate, respectively:

8Na2CrzO7 + 48NaHSO4 + C12H22O11 --- *> 16Cr (OH) SO ₄ + 8Na2SO4 + 12002f + 2H ₂ O or

2Na2Cr2O7 + 12NaHSO4 + 3HCHO - * 4Cr (OH) SO ₄ + 8Na2SO4 + 3CO2Î + 7H2O

When the reaction is complete, the solution is cooled to 21-24 ° C, and the crystals of sodium sulfate decahydrate are isolated, after the sodium sulfate decahydrate is separated by centrifugation and a basic chromium sulfate - standardized product is obtained.

- c). Production of medium chromium yellow chromium.

The aqueous solution of sodium chromate is neutralized with nitric acid up to Ia = 6.0 ... 8.0; a solution of lead nitrate or lead acetate is then added to obtain the lead chromate, respectively:

Na2CiO4 + Pb (NO3) 2 -> PbCrO ₄ | + 2NaNO3 or

Na2CyO4 + Pb (CH3COO) ₂ -► PbCrO ₄ | + 2CH3COONa

The lead chromate is separated, washed, filtered under pressure and after drying at 70 ... 100 ° C and grinding, the average chromium yellow of the desired granulation is obtained.

4). Treatment of separate residues after aqueous extraction of CrOqNa2

The mixture is made, comprising the following weight ratios: residues: iron ore (with granulation below 6 mm and iron content of 38 ... 55%): coke = 1: (1.0 ... 2.4): (0.10 ... 0.28). The mixture is placed in a furnace under slag with continuous air inlet or circulation, after ignition and the temperature rises up to 1300 ... 1500 ° C, to obtain a massive self-melted sintered iron and in which Cr ⁺ is reduced to one stable trivalent chromic compound. The main reactions are:

2Na2CrO4 + 3CO -> Cr2O3 + 2NaO + 3CO ₂

2CaCiO ₄ + 3CO --Cr2O3 + 2CaO + 3CO2

Due to the initial presence of a large amount of S1O2 in the chromic residues, the following reactions take place, in addition:

Cr2O3 + Na2O + 2SiO2 2NaCrSiO ₄

Cr2O3 + 3CaO + 3SiO2 Ca ₃ Cr2 (SiO4) 3

A new mixture is made in the following weight reports: self-melting sintered iron (with a grain size between 5 and 80 mm): iron residue (with a grain size below 6 mm and an iron content between 48 and 65%): coke: calcium caxrbonate = 1: (0.5 ... 2.6) :( 0.1 ... 1.5) :( 0.15

8

... 0.22). The mixture is melted in a casting oven at 1350 ... 1500 ° C, after which it is reduced for removal, and stratified, resulting in a low chromium content and a non-toxic slag. The main reactions are:

C12O3 + 3CO - ^ 2Cr + 3CO2; Cr2O3 + 3H2 - »* 2Cr + 3H2O; Cr2O3 + 3C --2Cr + 3CO; FeO.Cr2O3 4- C Fe + Cr2O3 +

CO;

Cr2O3 + 2Fe + 3C - 2Cr.Fe + 3CO S1O2 + + Fe + 2C - Fe.Si + 2CO and

Cr2O3 + 2Fe.Si + 3C - 2Fe.Si.Cr + 3CO.

The following are three examples of embodiments of the invention.

Example 1. Networks 10 were subjected to the following treatment:

constituent Cr2O3 Soluble Cr ⁶⁺ Fe2O3 As a MgO S1O2 Al2O3 % by weight 5.43 0.49 9.02 29.67 25.90 6.38 6.79

These residues were dried and crushed to granulation through the sieve

12.4 ... 15.5 stitches / cm. From the residues thus prepared, 120 kg (dry base) are taken and 16.6 kg of chrome ore powder (Cr2O3 - 48.13%), 21 kg of sodium carbonate and 10 kg of coke dust are added. This mixture is homogenized with water in an air mixture and calcined in a disc oven for one hour at 1000 ... 1200 ° C and pressure 4900 ... 6230 Pa (with air circulation), resulting 174 kg calcined mixture containing 11.26% total chromium and 6.58% Cr ⁺ soluble in water (both based on Cr2O3), Cr203 conversion being 58.44%. The mixture is treated with water in an extractor, yielding 0.161 rn of extraction solution, with a Na 2 CrC content> 4 151.4 g / 1. This solution is introduced into a precipitation reactor, in which 7.32 kg of sulfur dust is introduced, and is heated directly to steam at 100 ° C. After the reaction is complete, the precipitate is filtered, separated and washed, resulting in 23.5 kg of chromium hydroxide, which is then dried and calcined at 1200 ° C, resulting in 10.7 kg of chromium-Cr 2 O 3 92.4%.

Example 2. The same powder of chromium residue - 100 kg, in the dry state and powder of chromium ore kg, as in example 1, to which 22.5 kg of sodium carbonate and 9 15 kg of coke are added. This mixture is homogenized with water and calcined in a calcining furnace for 35 minutes under the same temperature and pressure conditions with air circulation as in Example 1, in order to obtain 114 kg of calcined mixture with a content of 12 , 3% total chromium and 7.57% Cr ^{6 +} water soluble (both based on Cr2O3), Cr2O3 conversion being 61.52%. The calcined mixture is treated with water in an extractor, yielding 0.108 rn in an extraction solution containing 16.5 kg Na2CrC> 4 (152.5 g / 1). The basic extraction solution of Na2CrO4 is introduced into a neutralization vessel, in which sodium sulphate, strong acid (specific weight 1,41 ... 1,45, obtained by dissolving the chromic anhydride waste in water, is added, sedimentation and removal of acid sludge impurities), for 35 a neutralization to pH = 6.5 and a neutral solution of sodium chromate. This is introduced into an acidification vessel, and the sodium acid sulfate specified above is added again, 40 to bring the pH to 1.5 ... 2.0, when Na2CrO4 passes into Na2Cr4O7. Next, 2.181 kg of sucrose crystals are added with vigorous stirring to obtain the basic chromium sulphate. The presence of Cr was not detected, which, in 108787, shows that the reduction reaction was complete. After a predetermined time of maintenance, a cooling flap was introduced into the vessel casing to lower the temperature to 22 ° C, at which Na2SO4 in 5 solution passes into decahydrated sodium sulfate which is isolated. The crystals are finally separated by centrifugation, remaining in. 63.4 kg basic chromium sulphate solution. The results of the analysis showed that the basic chromium sulphate 10 thus obtained contains

11.83% Cr2O3, with a basicity 40.22%, which corresponds to the requirements of such products. For this example 0.069 m ³ solution of NaHSO4 was produced, using 69 kg of toxic, strongly acidic chromic anhydride waste.

Example 3. The composition of chromic residues and chromic ores used in this example are shown in the table below.

% Cr2O ₃ Cr ⁶⁺ . soluble Fe2O3 As a MgO SiO2 Al2O3 Chromic residues 7.00 2.14 10.16 31,68 23.80 5.40 9.96 Chromium ore 25.69 - 11.68 1.20 27.24 15.50 11.04

a) Based on Cr2O3

The chromic residues are dried and minced at the granulation through the sieve with 12.4 ... 15.5 mesh / cm ² and 100 parts are taken and mixed with 25 parts chrome ore and 18 parts sodium carbonate. This mixture is homogenized in a mixer and calcined in a rotary oven of φ = 1800 x 28 m, for 2 h, at 1050 ° C. Five tests were performed and the results of these tests are presented in the table below.

Nr. books. Chromic residues, kg Chromium ores, kg Sodium carbonate, kg Result mixture, kg Total chrome, % Cr ^{6 +} soluble,% conversion % 1 7410 1800 1134 9485 9.26 8.7 93.95 2 16800 4200 2646 12820 13.53 10.6 78.34 3 12000 3000 1890 10783 13.30 9.23 69.40 4 14400 3600 2268 10110 10.47 9.81 93.70 5 14400 3600 2268 9830 11.69 9.59 81.99 Total 65010 16200 10206 52 983 11.65 9.58 82.28

All the mixtures resulted in the 20 five tests were treated with water, obtaining 80.96 m ³ of extraction solution, containing 9299.7 kg Na2CiO4 (300.37 g / l), which was converted to 8555, 4 kg Na2Cr2O7.2H2O, with a 25% extraction rate of 85%. All the basic extraction solutions were transferred to the sodium dichromate process step. In this example 65010 kg of chromic residues were treated in total and resulted in 52983 kg of mixture, with a conversion rate of 82.28% in the calcination phase, and with an extraction rate of 85%. After water extraction, the chromic residues contain 3.56% total chromium (Cr2.O3), 0.75% Cr ⁺ soluble in water (based on Cr2O3), 11.85% Fe2O3, 26.21% CaO, 25, 25% MgO, 6.61% SiO2 and 10.96% AI2O3. Compared with the original residues, it is found that 49.14% of the total chromium was extracted, recovered efficiently and used as hexavalent or trivalent chromium, while the chromic residues were completely dissociated.

Claims (11)

claims 1. Processing process for the complete removal and recovery of chromic residues, by calcination reduces all mixed with sodium carbonate, water treatment for extraction of soluble sodium chromate, which is further processed for passage to other predetermined chromium salts and processing of the insoluble reduction for removal and recovery of the useful elements contained in it, characterized in that the mixture is made of chromic residues: chromium ore powder: sodium carbonate: coke powder, at a weight ratio of 1: (0,1. .. 0,25) :( 0,1 ... 0,25) :( 0 ... 0,16), which is homogenized with an addition of water, is dried preliminary, is crushed at the granulation of passage through the sieve with 12.4 ... 15.5 mesh / cm ^z and calcined at 1000 ... 1200 ° C, a predetermined time, after which the calcined product is treated with water, for the solubilization separation of the sodium chromate resulting by calcination , of the insoluble residue which, if it is premixed with iron ore and is pyrometallurgically processed to obtain a sintered iron or a low chromium content and, finally, a non-toxic slag, and the aqueous sodium chromate solution is further processed under predetermined conditions. Process according to Claim 1, characterized in that the initial mixture can be calcined for 30 to 60 minutes in a suitable oven, usually, to obtain a calcined agglomerate. 3. The method according to claim 1, characterized in that the initial mixture may be calcined for 2 hours in a rotary oven to obtain the pre-calcined mixture Process according to Claim 1, characterized in that the solution containing sodium chromate may be treated with sulfur powder or sodium sulphide and steam heated to 100 ° C to precipitate chromium hydroxide, which it is separated and can be subjected to calcination at 1200 ° C to obtain chromium oxide. 5. Process according to claims 1 and 4, characterized in that, after separation, the chromium hydroxide can be brought into contact with sulfuric acid or sodium acid sulfate, to obtain the basic chromium sulfate. 6. Process according to claims 1 and 4, characterized in that, after the separation of the chromium hydroxide, sulfuric acid or sodium acid sulfate may be added to the mother solution to finally obtain sodium sulfate. Process according to Claims 1 and 4, characterized in that, after the separation of chromium hydroxide, sulfur dioxide may be added to the mother's solution, in order finally to obtain sodium thiosulphate. 8. Process according to claim 1, characterized in that the solution containing sodium chromate may be treated with sodium acid sulfate, to bring the pH to 6-7 and the neutral solution of sodium chromate is acidify again, after which, sucrose or formaldehyde is added, the reaction mixture is heated to above 100 ° C, to obtain basic chromium sulfate and sodium sulfate, which is separated after cooling to 21 ... 24 ° C, when crystallized sodium sulfate decahydrate which can be separated from the usual chromium sulphate solution. 9. Process according to Claim 1, characterized in that the solution containing sodium chromate may be neutralized at pile = 6 ... 8, with nitric acid, followed by the addition of nitrate or lead acetate. , to obtain the lead chromate, from which, after filtration, drying at 70 - 100 ° C and grinding, the pigment - yellow chromium medium. The process according to claim 1, characterized in that, the residue 5 separated after the solubilization of the sodium chromate, is mixed with iron ore with the granulation below 6 mm and iron content, of 38 ... 55%, and with coke, at a weight ratio respectively from 1: (1,0 ... 2,4): 10 (0,10 ... 0,28) and is subjected to calcination in a suitable oven at 1300 ... 1500 ° C, in order to obtain a massive sintered iron, wherein hexavalent chromium is reduced to trivalent chromium 15 Process according to the claims 1 and 10, characterized in that the sintered iron, resulting in the first phase of pyrometallurgical processing, having the granulation of 5 ... 80 mm, is further mixed with iron ore with granulation below 6 mm and an iron content of 48. .. 65%, with coke and calcium carbonate, at a weight ratio of 1: (0.5 ... 2.4) :( 0.1 ... 1.5) :( 0.15 ... 0,22) and the resulting mixture is melted in a suitable oven, in the temperature range of 1300 ... 1500 ° C, finally, a cast iron having a low chromium content and a slag separating respectively. non-toxic.