Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G37/00—Compounds of chromium
  • C01G37/14—Chromates; Bichromates

Definitions

• This invention relates to the manufacture'of chromates and dichromates.
• Chromates are in general manufactured by roasting chromium ores in the presence of alkali in a furnace at a high temperature.
• Such a process is usually effected by heating the finest ground chromium ore in admixture with sodium carbonate and lime in a stream of air to about 1000 C. and converting the extracted monochromate with sulphuric acid into dichromate.
• Another method consists in roasting the ore with a larger quantity of lime at 1200-1300 C. in a cement furnace and treating the calcium chromatelime mixture with sodium bisulphate.
• alkali chromate can be obtained by treating ferrochrome with fused caustic alkali.
• ferrochrome in the presence of alkali carbonate is converted into chromate by heating above 1000 C.
• the oxidation of metallic chromium, its alloys or mixtures containing chromium is effected in a very simple and economic manner.
• the process of the invention is by subjecting these substances to wet alkaline opening up treatment with oxidizing agents in particular oxidizing gases under pressure, whereby according to the quantity of alkali introduced either monochromate or dichromate or a mixture of monochrome and dichromate can be obtained as required. Since in the oxidation to dichromate, monochromate is first formed, it is clear that instead of alkalies also monochromates can be employed all of which are referred to herein as alkaline agents.
• alkaline agent may accordingly, for the purpose of positive definition, state that the term alkaline agent is used herein to designate a substance which behaves with relation to an acid as a base, and may include oxides, hydroxides, carbonates, and dicarbonates, of both alkali metals and alkaline earths as well as monochromates and other substances.
• chromium metal or its alloys or mixtures behave apparently as equivalents provided that they are applied in a suitably finely divided condition which is certainly also necessary in the case of chromium ore.
• chromium ore As a matter of fact it is the cheapest iron chromium alloys i. e. the most rich in carbon, which are easiest pulverized.
• the carbon advantageously the chemically combined carbon, is likewise taken up in the oxidizing process and appears in the form of carbon dioxide. It may therefore be recommended to remove the latter during the process or to bind it chemically in order not to increase the pressure in the apparatus unnecessarily.
• alkaline agents can be employed caustic alkalies, alkali carbonates, bicarbonates, monochromates and also alkaline earth and alkali metal oxides, hydroxides, carbonates, dicarbonates and monochromates or mixtures in which connection it may be remarked that the alkaline earths are less suited to the formation of dichromate.
• alkaline earths are less suited to the formation of dichromate.
• they are employed in aqueous solution or suspension.
• oxygen As oxidizing agents are advantageously employed oxygen, and oxygen containing or oxidizing gases.
• aqueous alkaline chromium suspension For the execution of the process it is suflicient to heat the aqueous alkaline chromium suspension to a suitable temperature and pressure and to force in the oxidizing gas before or during the working process.
• Example 2 kg. of ferrochrome of 68.2% Cr, 8-l0% C are well pulverized and heated in the presence of 100 kg. of caustic soda lye 40% and 900 kg. of water in a stirring autoclave for about 6 hours to 250-300 C. and oxygen or air passed through. After cooling the dichromate lye is separated from residue by filtration and worked up in the known manner.
• Example 3 54.5 parts of chromium powder 95-96% Cr content are heated with 210-220 parts of caustic soda lye 40% and about 200 parts of water in a stirring autoclave with oxygen or air for 4-6 hours under pressure to 150-250 C. After cooling the chromate lye is filtered from the residue of graphite or other impurities and worked up in the customary manner. The yield is practically quantitative.
• Example 4 7.170 kg. of ferrochrome of 72.5% Cr and 6.8% C. are well pulverized and heated with 100 litres of normal caustic soda lye in a stirring autoclave for 4-6 hours at 200-280 C. under pressure with oxygen or air. After cooling the dilute dichromate lye is separated from the residue and worked up.
• Example 5 152.5 parts of ferrochrome of 68.2% Cr and 8.10% C, well pulverized, are heated with 125 parts of calcium oxide (95-98%) or better with an equivalent quantity of slaked lime and about 400 parts of water for about 5-6 hours in the presence of oxygen to 150-250 C. After cooling, together with some chromate in solution, the majority of the chromate is found in the residue together with iron oxide and some graphite.
• the carbon dioxide formed in the oxidation can be removed in a suitable manner. This operation is to be recommended in particular in working with alkali carbonates.
• oxidizing agents which act in the presence of alkalies can be employed for the oxidation in the aqueous phase, as, for example, hydrogen peroxide, ozonized oxygen or air, halogens and the like, ferricyanides and the like, although oxygen or air are more economic.
• Process for the manufacture of monochromates and dichromates which comprises oxidizing a substance containing chromium in the presence of water and an alkaline agent by means of an oxidizing gas under pressure.
• Process for the manufacture of mono-chromates and dichromates which comprises oxidizing ferro-chromium in the presence of water and a monochromate of an alkali metal by means of an oxidizing gas under pressure.
• Process for the manufacture of mono-chromates and dichromates which comprises oxidizing a substance containing chromium in the presence of water and an alkaline agent by means of oxygen under pressure.
• Process for the manufacture of mono-chromates and dichromates which comprises oxidizing a substance containing chromium in the presence of water and an alkaline agent by means of oxygen under pressure and removing the carbon dioxide produced.
• Process for the manufacture of mono-chromates and dichromates which comprises oxidizing ferro-chromium in the presence of water and an alkaline agent by means of an oxidizing gas under pressure and removing the carbon dioxide produced.
• Process for the manufacture of mono-chromates and dichromates which comprises oxidizing a substance containing chromium in the presence of water and an alkaline agent by means of oxygen under pressure and binding chemically the carbon dioxide produced.
• Process for the manufacture of mono-chromates and dichromates which comprises oxidizing ferro-chromium in the presence of water and an alkaline agent by means of oxidizing gas under pressure and binding chemically the carbon dioxide produced.
• Process for the manufacture of mono-chromates and dichromates which comprises oxidizing ferro-chromium in the presence of water and an alkaline agent by means of oxygen under pressure and binding chemically the carbon dioxide produced.
• Process for the manufacture of mono-chromates and dichromates which comprises oxidizing ferro-chromium in the presence of water and an alkaline agent by means of oxygen. under pressure and removing the carbon dioxide produced.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Compounds Of Iron (AREA)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (5)

Cited By (9)

• 1930
  • 1930-05-09 FR FR710771D patent/FR710771A/fr not_active Expired
  • 1930-05-29 DE DE1930547422D patent/DE547422C/de not_active Expired
• 1931
  • 1931-01-23 GB GB2343/31A patent/GB364361A/en not_active Expired
  • 1931-01-30 US US512506A patent/US1955326A/en not_active Expired - Lifetime
  • 1931-03-06 CH CH156745D patent/CH156745A/fr unknown

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