US1631170A - Process for the manufacture of chromium compounds - Google Patents

Description

Patented June 7, 1927.

PAUL wmsn, or wmsnoar, NEAR ooLoen -oN-rnE-anmn GERMANY, ASSIGNOR Eve I. G. FARBENINDUSTRIE AKTIENGESELLSGHAFT, OF FRANKFORT-ON-THE-HAIN GERMANY- PROCESS FOR THE MANUFACTURE OF CHROMIUM COMPOUNDS.

'No Drawing. Application flied March 6, 1926, Seria111'o. 92,837, and in Germany August 24, 1925.

The processes for the manufacture of chromium compounds from chrome ore emplo ed in industry up to the present time sufl er fromthe disadvantage that the in:

volve losses of ore which are very di cult to recover. According to most of such processes a diluent is added to the mixture ofchrome ore and alkali, as for example chalk, dolomite, iron oxide, etc., these substances being only recoverable in exceptional cases. In most cases they are completely lost with the unattacked ore, thus causing av considerable increase in the cost of the process. Proposals have already been made for usingas diluents such materials as can be recovered in a form available for further use. Thus the German Patent No. 166,767 suggests the 'use of finely crushedv chrome ore but theprocess according to this patent is restricted to the joint use of ahand fed furnace. In order to obtain a satisfactory attack, when working with mechanical furnaces and with ;mixtures of finely crushed. chrome ore and alkali metal carbonates or hydroxides, very large amounts 'of ore in proportion to the material used for attacking the ore must be emplo ved, as for example six times the quantity o finely crushed ore. This is due to the fact that a certain amount. of diluent material must be present in order to render the melt sutficiently porous that the air-oxygen required to bring about the attack can pene trate into the interior of the charge and of the clinker produced.

According to the present invention satisfactory working can be achieved \with a much smaller quantity of ore acting as the diluent material and to prevent caking if ore of a definite grain size is employed. In this manner only the most finely crushed portions of the'ore are preponderantly attacked while the coarser portions remain practically unaltered and serve as diluent material thus preventin the otherwise unavoidable caking togeter of the charge. The application of my invention increases the pro uctive capacity of the wliole. process I concerned.

The method of working is as follows The moist or dr mixture of an ore which leaves a residue of 1530% on a sieve of 70 mesh per cm. with so much of the 'decomposition agent that the content of the same amounts to 28 32% are heated in an oxidizing atmosphere to the reaction temperature of over 1100 C. The sintered melt is leached with Water, advantageously in the presence of a small amount of acid in order to decompose the aluminate. The chromate which then passes into' solution is separated from the residue and 'worked up in the customary manner.

-The residue after the leaching operation consists of unattacked chrome ore; alumina, magnesium and iron oxide. For the recovery of the unattacked chrome ore mechanical methods may be employed, as for example sedimentation or sorting processes.

However it has been discovered that the most advantageous means is not the mechanical but the chemicaLmethod, according -to which it is possible by treatment of the residue with dilute acid to recover a chrome ore almost completelyfree from admixed substances. It is essential in this connection,

however, that the concentration of the acid should'not be too hi h, as'otherwise the final liquors obtained are iflicult to filter. Particularlyfavourable are acids of about B. Sulfuric acid of from 5 B. to 30 B. may be used. It is likewise advantageous to moderately heat the acid although it is advisable not to allow the temperature to rise above C. In general temperatures ranging from atmospheric temperature, 15C., up.to

60 C. may be employed. If these conditions are taken into account a residue is obtained which can ,be filtered ofi quite easily.

, The amourit of acid employed may vary Within wide limits, either the theoretical amount, an insuflicient amount, or an excess, may be employed. C I

. When using the theoretical quantity of acid the final liquors obtained are diflicult to filter and this method is therefore only selected in special cases.

I When an insuiiicient quantity of acid is" employed the recovered chrome ore still contains corresponding quantities of iron and magnesium oxide s. A proportionate quantity of acidmay be added in order to maintain the content of these impurities the same or by varying the acid the amounts of the impurities may be allowed to increase. In the latter case the possibility arises that the ,melt may become so enriched in iron and magnesium oxides that the decomposition agents added to the charge'may just succeed in, attacking the whole of the available chrome ore. The resulting, residue is then practically free from chromium and may be thrown away.

By the application of an excess of acid pure ore is invariably recovered.

When using either an insuflicient quantity of acid or an excess of acid the liquors obtained can be filtered with ease. The velocity of reaction is very great in all cases.

Therecovered ore, with or without the addition of fresh ore, is brought to the desired grain size by means of suitable appli times and returned to the charge.

The following examples will serve to illustrate my invention:-

Ewa mple parts of ground chrome ore of any composition and leaving a residue of 25% on a sieve'of 70 mesh per cm. are'intimately mixed with 30 parts of sodium carbonate. According to the construction of the revolving furnace and the feeding arrangement, .the mixture may be introduced into the furnace either moist or dry and there heated in the customary manner to.

above 1100 C.- The resultin melt is quenched in water, allowed to soak and the chromium liquor leached and separated from the water-insoluble portion. For the purpose of recovering the unattached chrome ore this water-insoluble portion is treated with so much sulphuric acid of 15 B. at 50 C. that not all the iron and magnesium oxides are dissolved; the weakly basic liquor is separated off and the residue dried. This residue is mixed with a fresh supply ofore of the required grain size and with sodium carbonate and returned to the furnace. The amount of sulphuric acid required as the process proceeds should be always adjusted so that the basicity ,of the liquor remains always the same. The yield of chromate obtainedis about 90% calculated on the amount of-sodium carbonate used.

.Ewample. 2.The Water-insoluble portion as obtained in example 1,'after the separation of the chromate liquor is treated with suflicient sulphuric acid of about 20 B. in the cold that after the dissolution of all the undesirable impurities a slightly acid solucial heating. The recovered ore can be em-i ployed in a fresh charge without further treatment.

Example 3.-The water-insoluble portion obtained according to Example 1, is treated with sulphuric acid according to the counter-current principle. Thereby the almost extracted ore comes into contact with fresh acid, and thus the acid may be selected of any desired strength. As the process of extraction proceeds further, the most suitable dilution can be easily adjusted by the addition of water.

Iclaim: 1. In processes for the manufacture of chromium compounds involving the use of mechanical furnaces, the steps which consist essentially in forming a mixture of an alkali with chrome ore of such a grain size that a residue of from 15% to 30% remains on a sieve of 70 mesh per 0. m., heating the mixture to a reacting temperature above 1100 C., leaching the furnaccd mixture, treating the undissolved residue of the leaching step with acid, and using the residue of the acid treatment with fresh chrome ore as the starting material in a subsequent operation.

2. Process for the manufacture of chromium compounds as defined in claim 1, in which dilute acid is used for treating the undissolved residue of the leaching step, and the residue of the acid treatment is separated from the dilute acid by filtering at the temperature of the greatest filtering velocity.

3. Process for the manufacture of chromium compounds as defined in claim 1, in which a quantity of acid insufiicient to dissolve the impurities present in the undissolved residue of the leaching step is employed in treating said undissolved residue.

1L Process for the manufacture of chromium compounds as defined in claim 1, in which sulfuric acid of from 5 to 30 B. is used in treating, the undissolved residue of the leaching step and the acid treatment is carried out at a temperature of from about, atmospheric temperature to not exceeding 60"? i In testimony whereof I have hereunto set my hand. 1

PAUL WEISE.