FI75192C - Process for the enrichment of chromite ores. - Google Patents

Description

1 75192

Method for the enrichment of chromite ores

The invention relates to a process for the enrichment of chromite ores by directly reducing part of their iron oxide content to iron sponge using solid carbonaceous reducing agents, oxidatively dissolving the reduced material to convert the metallic iron it contains to iron oxides and separating the iron oxides from the rest.

The chromium to iron ratio (CrMFe) of pure chromite spinel (FeO.C 2 Cl 2) is 2: 1. In the naturally occurring Chromite spinel, the chromium-iron ratio, on the other hand, is greater than 2 because Mg or Ai dominates the iron sites in the chromite lattice. The desired ratio for metallurgical purposes is 3: 1 15 or higher. Because of the high use of natural chromium ores with a chromium-to-iron ratio of more than 2, the ratio needs to be raised in poorer deposits. There are large deposits of chromite with a chromium to iron ratio of much less than 2: 1.

20 GB patent publication 980 864 and U.S. patent publication 2 339 793, which deal in detail with the enrichment of ilmenite ores, make it known that iron oxide-containing ores containing Mn, Cu, Al, Cr, V, Ti or Au, enriched by first reducing the ore directly in a rotary kiln by adding a solid carbonaceous substance, whereby at least a portion of the amount of iron oxide it contains is reduced to iron sponge. The reduced material is then subjected to an oxidative treatment in a water-30 solution. In this case, the metallic iron oxidizes and dissolves from the lattice. The oxidized iron can then be separated from the rest of the substance, for example by decantation, whereby the content of the non-ferrous metals contained in the latter is increased. The reduced material is soaked in cations such as ammonium, alkali metal, copper or - - 1.

2,751,922 in aqueous solutions containing cobalt ions, and anions such as chloride, sulfate, nitrate or fluoride ions. In addition, small amounts of acids are added to adjust the pH to approximately 4-7. The excess solid-reducing agent can be separated before starting the soaking. In order to accelerate the oxidation of the metallic iron, air is blown into the suspension formed by the aqueous solution and the reduced material and / or the suspension is stirred.

U.S. Patent No. 2,339,793 discloses a reduction temperature of about 1000 ° C. GB 980 864 discloses a temperature of 950 ° C for gold ores and 1000 ° C and 1150 ° C for ilmenite, where the enrichment of TiO 2 is worse at a higher temperature than at a lower temperature. Applying these values to the enrichment of chromite ores results in very poor chromium enrichment.

The invention is based on the need to significantly increase the chromium content of iron oxide-containing Kro-20 mite ores in an economical manner.

This is carried out according to the invention in such a way that the particle size of the chromite ore to be directly reduced is less than 3 mm, the ratio C 1 to R 2 is set higher than 1 and the temperature in this direct reduction is set above 2500 ° C. The direct reduction is preferably carried out in a rotary kiln by feeding a fixed charge and a gas atmosphere upstream. As solid carbonaceous reducing agents, mainly highly reactive non-agglomerated carbon grades, such as lignite grades, are mainly used. The ratio Cfix: Fe is calculated in the input.

When a rotary tube furnace is used, some of the carbon can be blown in from the outlet end and distributed to the charge in the reduction zone. The ratio of C These range from about 0.3 to 0.6. Ratio means weight ratio. Temperature refers to the temperature of the charge. The upper temperature limit is determined by the temperature at which sintering of the batch components takes place. The ore particle size of 3 mms refers to the largest particle size, i.e., the ore may contain significant amounts of finer fractions. The reduced material is preferably separated from the excess carbon 10 and then dissolved in a known manner. The metal lipid content is adjusted to the value required for the desired enrichment.

The preferred embodiment is that the direct reduction is performed on chromite ore with a particle size of less than 2 mm. Using this upper particle size limit gives particularly good results.

In a preferred embodiment, the temperature in the direct reduction is adjusted above 1150 ° C. Thus, enrichment is further enhanced.

In a preferred embodiment, the ratio C £. : Fe weather

f IX

set to a value of more than one to two. Adherence to these limits achieves good results and avoids unnecessarily large amounts of carbon.

A preferred embodiment is that alkali metal compounds are added in connection with direct reduction.

By adding alkali metal compounds, especially Na 2 CO 2 and / or K 2 CO 3, the reduction temperature can be lowered while maintaining the same results, the result can be improved by keeping the temperature the same and a good result can be obtained by using less reactive carbon grades. Similar results can be obtained by adding a highly reactive carbon, for example lignite or reactive recovery carbon, to the less reactive reducing agent.

4,751 92

In a preferred embodiment, the oxidative soaking of the reduced material is carried out so that the ratio of the amount of solids to the amount of water in the suspension is 1: 2 to 1: 5. Thus, good oxidation of the metallic iron is achieved in a relatively short time.

The preferred embodiment is that the oxidative soaking of the reduced material takes place in a solution to which NH 2 Cl has been added. This addition accelerates oxidation and does not cause any effluent problems.

The invention is further illustrated by the following examples.

Example 1 A 1000 g sample of chromite ore concentrate (particle size less than 2 mm) with a C 2 O 2 content of 44% and a chromium iron ratio (Cr: Fe) of 1.55: 1 was reduced with ki-15 coal in a rotary tube furnace at 1100 ° At C for 4 hours.

The Cfix: Fe ratio was 2. After reduction, the product was cooled under a nitrogen atmosphere. The reduced chromium ore concentrate was separated from the excess carbon using magnetic separation. The reduced concentrate (930 g) was stirred in 1860 ml of NH 4 Cl-containing hot water (temperature about 80 ° C). The concentration of NH 4 Cl in the solution was 15 g / l H 2 O, and the ratio of the amount of reduced concentrate to the amount of water was 1: 2. The initial pH was 5.9. During the stir-soaking step, air was introduced into the suspension at a rate of about 25 l / min. The temperature of the suspension was adjusted to 80 ° C with a water bath.

Immediately after the reduced concentrate was added to NH 4 Cl-containing water, the suspension turned black, which turned brown over time. The reaction mechanism of the stir-30 soak was monitored by redox potential measurements. The initial value of the redox potential was -545 mV. After 1 hour (the suspension had turned brown) the redox potential was -250 mV. After 21/2 hours, the redox potential was -0 mV. After 4 hours, the 35 (redox potential + 55 mV) experiments were stopped.

Il * 5 75192

The oxidized iron was separated from the chromite concentrate in a vertical plexiglass tube using an ascending flow. Iron oxide was removed from the top end, while chromite accumulated at the bottom of the tube. 798 g of enriched chromite were obtained. The chromium to iron ratio improved from 1.55: 1 to 2.8: 1.

Example 2

The chromite ore concentrate (1000 g; similar starting material as in Example 1) was reduced in a rotary kiln at 1000 ° C for 4 hours. Relationship C-. : Fe X ΧΛ was 2. The separation and stir-soaking took place in the same manner as in Example 1. The chromium-iron ratio increased from 1.55: 1 to 1.7: 1.

Example 3 1000 g of chromite ore concentrate were reduced at 1100 ° C according to Example 1. The ratio of C 20 to Fe was 0.5 in the reduction. The chromium to iron ratio rose from 1.55: 1 to 1.75: 1.

Example 4 1000 g of chromite ore concentrate were reduced at 1100 ° C according to Example 1. The ratio C. ^ x: Fe in the reduction was 1.2. The chromium to iron ratio improved from 1.55: 1 to 2.1: 1.

Example 5 1000 g of chromite ore concentrate were reduced at 1150 ° C according to Example 1. The ratio C ^ x: Fe in the reduction was 2.0. The chromium to iron ratio rose from 1.55: 1 to 3.4: 1.

Example 6 1000 g of chromite ore concentrate were reduced at 1100 ° C according to Example 1. The ratio of Cfix: Fe in the reduction was 2.0. ^ 200 ^ was added to the carbon. The chromium to iron ratio increased from 1.55: 1 to 3.3: 1.

6,751,922

Example 7 1000 g of chromite ore concentrate with a particle size of more than 3.5 mm and a chromium-iron ratio of 1.63: 1 were treated according to Example 1 (reduction-5 temperature 1100 ° C, Cf ^ x: Fe s 2.0). The chromium to iron ratio rose from 1.63: 1 to 1.69: 1.

Example 8 1000 g of chromite ore concentrate with a chromium iron ratio of 2.28: 1 were treated according to Example 1. The reduction temperature was 1150 ° C and the ratio C ^ x: Fe was 2.0. The chromium to iron ratio rose from 2.28: 1 to 5.1: 1.

The advantage of the invention is that a very strong increase in the chromium content of ferrous chromite ores in an economical manner is possible.

Claims (7)

751 92 A process for enriching chromite ores by directly reducing a portion of the amount of iron oxide they contain to iron sponge using solid carbon dioxide reducing agents, oxidatively extracting the reduced material to convert the metallic iron it contains to iron oxides and separating the iron oxides from other material, characterized in that mm, and that the ratio C ^. : The Fe J fix is set higher than 1 in the batch and the temperature in direct reduction is set above 1100 ° C. Method according to Claim 1, characterized in that the particle size of the chromite ore to be directly reduced is less than 2 mm. Process according to Claim 1 or 2, characterized in that the temperature in the direct reduction is adjusted above 1150 ° C. Method according to one of Claims 1 to 3, characterized in that the ratio C ^ x: Fe is adjusted to a value of more than 1-2. Process according to one of Claims 1 to 4, characterized in that alkali metal compounds are added in connection with the direct reduction. Process according to one of Claims 1 to 5, characterized in that the oxidative extraction of the reduced material is carried out in a suspension in which the solids ratio is between 1: 2 and 1: 5. Process according to one of Claims 1 to 6, characterized in that the oxidative extraction of the reduced material is carried out by adding NH 4 Cl.