The method of producing chromium oxide (iii) with a low content of hexavalent chromium

 

(57) Abstract:

The invention relates to the production of chromium oxide (III) used in the paint industry and for polishing.

The method of producing chromium oxide (III) with a low content of hexavalent chromium (III) includes thermal decomposition of chromic anhydride, a hillshade from water-soluble substances resulting Cr2O3the suspension in 8 - 10% urea solution, separation from the liquid phase to a moisture content of sludge 30 - 35 wt.% and heat treated at a temperature of 200 - 280oC. 1 tab., 1 Il.

The invention relates to a process for the production of chromium oxide (III), used in the manufacture of paints, varnishes and for polishing. The method allows to obtain the oxide chromium (III) content of hexavalent chromium not more of 0.0001 wt. Cr.

The known method [1] of receipt of chromium oxide (III), based on thermal decomposition of chromium trioxide in the presence of ammonium salts, guanidine, thiourea, urea and its derivatives, taken in an amount of 1 mol CrO3not less than 0.1 mole of nitrogen-containing compounds, at a temperature in the first stage 185 220oC and on the second 700 1400oC, and way [2] continuous receipt of chromium oxide (III), based on teme is possible to reduce the content of hexavalent chromium in the chromium oxide (III) up to 0.001 wt. Cr.

Closest to the proposed invention is a method [3] of receipt of chromium oxide (III) with a low content of chromium (VI) by means of thermal recovery of chromic anhydride and subsequent supply of hot (temperature not less than 900oC) oxide chromium (III) in the reservoir layer of urea, taken in an amount of 1.5 to 2.5 wt. from Cr2O3. The disadvantages of this method include the relatively high content of hexavalent chromium in the chromium oxide (III) of 0.0005 wt. Cr.

The purpose of the proposed invention is to reduce the content of hexavalent chromium in the chromium oxide (III) to 0.0001 wt. Cr.

This goal is achieved by the proposed method of producing chromium oxide (III) with a low content of Cr (VI), which consists in termorasshirennyi chromic anhydride, hillshade from water-soluble substances resulting Cr2O3, suspendirovanie 8 10% solution of urea, separation from the liquid phase to a moisture content of sludge 30 35 wt. and additional heat treatment at a temperature of 200 to 280oC.

As a result of heating at the same temperature the decomposition of urea with simultaneous recovery of chromium (VI) by reaction

(NH2oC leads to an increase in the content of hexavalent chromium to 0.01 wt. Cr, which is associated with the possible formation of dichromate chromium. The reduction of temperature below 200oC leads to an increased content of water-soluble substances in the oxide chromium (III) due to the possible formation biureta.

The use of urea solution 8 10% concentration and separation of the liquid phase to a moisture content of sludge 30 35 wt. ensure the concentration of urea in the oxide chromium (III) 2,4 3,5 wt. which creates conditions for full recovery of hexavalent chromium. The decrease of the concentration of the urea solution below 8 wt. increases the content of hexavalent chromium (PL. the drawing), and increasing concentrations of more than 10 wt. the urea solution leads to an increase in the content of total water-soluble substances in the oxide chromium (III).

Comparative analysis of the prototype allows us to conclude that the proposed method differs in that the oxide chromium (III) derived from chromic anhydride, washed from water-soluble substances, suspendered in the urea solution with a concentration of 8 to 10 wt. is separated from the liquid phase to a moisture content of sludge 30 35 wt. and heat-treated at a temperature of 200 to 280oC.

Thus, Obama allows you to install, in similar solutions of the heat treatment in the presence of urea is subjected to a chromic anhydride or chromium oxide (III) without the prior suspension in the solution (NH2)2CO. This solution is not obvious from the level of values and technology, and allows to conclude that the criterion of "inventive step".

The invention may be used in the industry.

Example 1.

1 kg of chromium oxide obtained by termomaslyanym chromic anhydride and pre-washed from water-soluble substances, suspended in 0.005 m3an 8% aqueous urea solution, is separated by filtration from each phase to a moisture content of sludge 35 wt. Then subjected to heat treatment at a temperature of 200 220oC for 2 hours. Get the finished product with the content of hexavalent chromium 0,00004 wt.

Example 2.

1 kg of chromium oxide obtained in example 1, are suspended in 0.005 m310% -aqueous solution of urea is separated by filtration from the liquid phase to a moisture content of sludge 30 wt. Then subjected to heat treatment at a temperature of 220 260oC for 2 hours. Get the finished product with the content of hexavalent chromium 0,00003 wt.

Example 3.

1 is a formation from a liquid phase to a moisture content of sludge 30 wt. Then subjected to thermoabrasion at a temperature of 260 280oC for 1.5 hours. Get the finished product with the content of hexavalent chromium 0,00005 wt.

The method of producing chromium oxide (III) with a low content of hexavalent chromium, which includes thermal decomposition of chromic anhydride with the formation of chromium oxide (III) and the processing of the received heated oxide chromium (III) urea, characterized in that before processing the oxide chromium (III) washed from water-soluble substances, and processing is carried out by suspension of chromium oxide (III) 8 10% solution of urea, followed by the separation of the precipitate from the liquid phase to a moisture content of 30 to 35 wt. and its heat treatment at 200 - 280oC.

 

Same patents:

The invention relates to the production of chrome oxide, used for polishing
The invention relates to a method of producing chromium hydroxide from spent melt production of titanium tetrachloride, including leaching, separation of the insoluble residue from the solution, the precipitation of chromium hydroxide at pH 3,0-4,5 alkaline reagent

The invention relates to inorganic chemistry, and in particular to methods for producing metal oxide, and can be used to obtain pigments, catalysts, semiconductor materials

FIELD: industrial inorganic synthesis.

SUBSTANCE: invention relates to production of chromium oxide appropriate for use in manufacture of magnetic media as well as primers, enamels, paints, polishing pastes, abrasive material, and metallic chromium. Process comprises decomposition of sodium bichromate and ammonium sulfate, which is conducted in solution having concentration 400-450 g/L for CrO3 at 100-105°C for 45-60 min at constant stirring to form ammonium bichromate and sodium sulfate. The latter is separated from solution and ammonium bichromate-containing solution is cooled to crystallization temperature, after which ammonium bichromate crystals are submitted to thermal decomposition at 440-1400°C to form chromium oxide.

EFFECT: simplified process, improved quality of chromium oxide due to reduced content of impurities and increased content of chromium oxide, and enabled production of chromium oxide for various destinations.

FIELD: chemical industry; the thermally sprayed powders and the methods for their production.

SUBSTANCE: the invention is pertaining to the method of production of the thermally sprayed powders and may be used in production of the powders out of the chromium dioxide for the thermally sprayed wear-resistant coatings. The thermally sprayed powder contains from 45 up to 99 mass % of chromium dioxide and from 1 up to 55 mass % of alpha aluminum oxide, and less than 50 shares per one million of the alkaline-metals and the alkaline-earth metals stabilizing chromium in its hexavalent state. The powder particles have primarily the single-phase crystalline structure with the aluminum oxide share in other phases, except for the alpha phase, of no more than 10 mass % of the full contents of the aluminum oxide. The method of production of the thermally sprayed powder includes: stirring action of the aluminum oxide powder containing the impurities of the alkaline- metals and the alkaline-earth metals of no more than 120 shares per one million of each element with the chromium dioxide powder, which also has less than 120 shares per one million of the impurities of the alkaline-metals and the alkaline-earth metals stabilizing chromium in the hexavalent state; burning of the mixture at the temperature of 1300-1500°С. The invention allows to reduce formation of the toxic compounds of the hexavalent chromium during the thermal spraying of the wear-resistant powders of chromium dioxide.

EFFECT: the invention ensures the reduced formation of the toxic compounds of the hexavalent chromium during the thermal spraying of the wear-resistant powders of chromium dioxide.

6 cl, 1 dwg

FIELD: chemistry, technological processes.

SUBSTANCE: method of obtaining nanotubular structures includes mixing of oxygen-containing organic compound - oxalic acid hydrate with vanadium oxide gel or oxygen-containing compound of respective metal. As oxygen-containing compound of respective metal, peroxide molybdenum or tungsten oxides are used.

EFFECT: reduction of interlayer distance in structure of nanotubular structures of said oxides due to absence in structure of extraneous radicals of organic compounds.

2 cl, 5 dwg, 5 ex

FIELD: paint and varnish industry.

SUBSTANCE: anticorrosive pigment comprises , in mass per cents, 3.0-4.7 of calcium chromate and waterless dicalciumphosphate as the balance.

EFFECT: improved anticorrosion capabilities.

1 tbl

FIELD: chemistry.

SUBSTANCE: method of producing emerald chrome pigment involves calcination of a mixture containing chromic anhydride, boric acid and urea, subsequent washing and drying the pigment. The mixture is calcined at temperature 750-800°C for 0.5-1.0 hours to obtain a melt which is boiled with addition of boric acid in mass ratio of melt to solution equal to 1:6. The mixture has the following weight ratio of ingredients: chromic anhydride - 20 pts. wt, boric acid - 60-80 pts. wt, urea - 3-4 pts. wt.

EFFECT: obtaining green pigment with a tinge of emerald green.

1 ex

FIELD: chemistry.

SUBSTANCE: described is a method of making chromate anticorrosive pigment involving suspension of spent chrome-aluminium catalyst in aqueous solution of calcium nitrate and barium nitrate, taken in amount of 10-30% and 5-25% of the mass of catalyst respectively, in mass ratio of catalyst to the said nitrates equal to 65-70:30-35 respectively, dehydration of the obtained mixture with subsequent calcination at 800-900°C for 3-6 hours and grinding. The obtained pigment has anticorrosive effectiveness which surpasses that of the closest analogue by 6-40% and has lower cost.

EFFECT: use of pigment in ground coating improves anticorrosive properties of the coating and increases environmental friendliness.

1 cl, 1 tbl, 15 ex

FIELD: chemistry.

SUBSTANCE: chromium phosphate is obtained in a reactor by dissolving chromium trioxide in water. Orthophosphoric acid and a stabilising additive - ethanol - are then added. A strong reducing agent - aqueous hydrazine-hydrate solution - is slowly added to the obtained mixture of chromic acid, orthophosphoric acid and ethanol in an amount which enables formation and maturation of chromium phosphate particles, suspension pH of 4-7 and concentration of chromium phosphate of 50-100 g/cm. The end product is then filtered and dried. The filtrate is returned to preparation of the mixture of chromium trioxide, orthophosphoric acid and ethanol.

EFFECT: invention simplifies the technique and completely prevents formation of waste water.

1 tbl, 6 ex

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing chromium (III) oxide, comprising the following steps: a) reacting an alkali metal chromate or alkali metal bichromate with ammonia gas, particularly at 200-800°C, b) hydrolysis of the reaction product obtained at step a), wherein the pH of the hydrolysis water before hydrolysis or the pH of the alkaline mother liquor during or after hydrolysis is set at 4-11, while lowering the value with acid, c) separating the hydrolysis product precipitated at step b), d) drying the product obtained at step c) and e) calcining the hydrolysis product obtained at step d) at 700-1400°C.

EFFECT: obtained chromium (III) oxide can be used for metallurgical purposes and contains very low amounts of sulphur and alkali metals.

11 cl, 7 ex

FIELD: chemistry.

SUBSTANCE: invention relates to chemistry and can be used for production of pigment for construction materials, plastic, paint and lacquer, glass and ceramics. Sodium monochromate reacts with ammonia gas at temperature of 200-800 °C. Hydrolysis of reaction product is carried out. Water pH is reduced before hydrolysis or pH of alkaline mother liquor is reduced during or after hydrolysis to 4-11 by adding carbon dioxide. Precipitated hydrolysis product is separated at pH = 4-11. Hydrolysis product is calcined at 700-1,400 °C.

EFFECT: invention enables production of chromium (III) oxide, containing very small amount of sulphur and alkali metals and by-products.

12 cl, 3 ex

Up!