SK84194A3 - Process for reduction of hexavalent chromium and device for realization of this method - Google Patents

Abstract

The present invention concerns a new process and the relative plant for reducing hexavalent chromium contained in the resultant earth after the production of chromium, in order to obtain the transformation from water-soluble compounds into insoluble compounds, the process comprising the phases of mixing the said residual products with one or more reducing agents and of indirectly heating the said mixture substantially without the presence of oxygen.

Description

A method and apparatus for reducing hexavalent chromium present in the remainder of the chromium ore treatment.

Technical field

The present invention relates to a novel method for reducing the chromium present in zinc, which is increased even after the production of chromium, to convert from 1 water-soluble apprentices to 1 water-free apprentices. They are.

The invention also relates to an apparatus for execution

BACKGROUND OF THE INVENTION

It is well known to use such a method

-t x traction e

Hexavalent chromium, in which both the chromium and the tanneries are roasted, followed by all the hexavalent chromium.

leaching, not chrome for purpose

Indeed, after leaching, a solid is obtained, generally called a leaching residue, or the resulting soil can be recovered which still contains different amounts of hexavalent chromium.

There are three very different leaching results

When they fall.

Because it is often i

t. This is a well known chromium extraction technology.

cases can be summarized very briefly as follows ^:

A)

Mixture with high content of calcium oxide (or dolomite)

B)

Mixture with low content of calcium oxide (or dolomite)

C)

Mixture even without calcium oxide (or dolomite)

The water soluble soluble chromium salt is easily solvable in water. in that way

9419 edit ŕct.va. which does not include calcium oxide, since the relative residual products do not contain partially soluble compounds due to the complexes formed between the calcium and hexavalent chromium, in which case it is appropriate to add a suitable reducing agent to the residual products, such as is ferrous sulfate.

chI or i d that is rusty, etc. , which reduced to j j;

chromium from CrOa to

C r 2 0 3, k <i c c · · p p u u n ý.

such a treatment in which there is also a vony.

this results in hexavalent chromium in a form which is difficult to dissolve in a short time, such as calcium chromate.

Thus, these derivatives cannot be leached immediately after they have been treated in their manner and remain largely free of earth.

Over time, however, this soil is subjected to clay washing, and the hexavalent chromium leaches, thus releasing and releasing that these solid residual products are serious problems and are being treated and processed. is suitable landfills according to

It should also be borne in mind that these amounts of residual products tend to be larger, sometimes relatively large; they vary from 2.8 times to 0.5 times the amount of solid alkaline dichromate produced.

various methods for carrying out the reduction of the superficial chromium present in the resulting soil.

with the help of organic and inorganic reducing agents

US Patent

I.JS č. 3,003,032 from Nippon

Deriko Co -, o p i s u is a reduction according to which the resulting wet soil of the earth with ingredients that can be carbonized

9419 (sawdust, bran, lignite, etc.) and then heated to a temperature not exceeding 700 ° C in a reducing atmosphere in an atmosphere containing no more than 2% oxygen. In doing so, it is; it is necessary to check the composition of the atmosphere in the reactor.

in order to avoid the possibility of burning the materials to which the desired formation of activated carbon could occur.

This also avoids the risk of explosion that can occur when CO is formed.

The second method, which relies on the use of sulfur as a carrier, is described in Italian patent no.

The disadvantage of this process and the other analogous to allowing the desired chromium reduction to be carried out and required in an alkaline environment requires the boiling of the aqueous dispersion of the resulting earths for the first and second steps.

The disadvantage that is common to these two processes just described is that they do not undergo a completely complete industrial process and the costs are very high.

The object of the present invention is to solve the above-mentioned problems by means of a method and a device which enables the reduction to be carried out? the hexavalent chromium compounds present in the resulting soil in an alkaline environment.

While the device is simple, economical, and the objective has been achieved by this invention, which relates to the treatment of hexavalent chromium in the products of. treatment of chrome minerals.

marked them by being in himself; includes the mixed phases of said residual products by one or more reducing agents and that indirect heating occurs

(sawdust, bran, lignite, etc.) and then heated to a temperature in the reduction system.

which does not exceed 700 ° C in an atmosphere containing not more than 2¾ oxygen. This action must be checked.

z 1 o ž. e n i c a t m o s s e r i s t e r, djy se, k to rcáii u

This also avoids the required ignition of the activated carbon.

explosion risk.

to which it may occur

Drill is calculated using sulfur as a reducing agent.

Italian patent no.

1.055.953 under the name of the applicant, who has 5 F i - A - 2

342. 347.

The disadvantage of other anaogogic effects is also possible. It is believed that allowing the desired iT.duction and the environment to be carried out in the environment requires cooking at a higher temperature, sulfur and sulfur at a certain pressure.

A disadvantage which is a common feature of the two processes just described. the main thing is. that the reaction does not go in a completely complete industrial way and the cost of the network is large and high.

P o d s tata, y yr i .1 e z u

The object of the present invention is to solve a number of problems by means of a method and an arrangement. which allow them to carry out the reduction of the hexavalent chromium compounds present in the resulting soil in an alkaline environment.

whereby the device is simple, economical and effective, the objective has been achieved by means of this invention, i. 1

The hexavalent chromium in the residual products from the treatment of chromium minerals, which is characterized by the fact that it comprises the mixed phases mentioned above. o and / or by various factors and that indirect heating occurs

9419 is essentially in the absence of oxygen.

The invention furthermore relates to an apparatus for the reduction of chromium (III) by the process according to any one of claims 1 to 11, characterized in that it comprises indirect heating of the rotary kiln and methods of sealing against gases which are collected. at the supply and discharge points of the mixture.

According to a preferred embodiment of the present invention, the reduction factor uses sulfur which is substantially lower with residual soils, being dried or then heated to a temperature at least equal to the temperature.

in which ub 1 i (445 ° C) occurs.

In another preferred embodiment by indirect heating, in a sealed rotary furnace without gas circulation.

The advantages of the invention are obvious

The use of sulfur greatly simplifies the design of the device and i? 1 is a risk of explosion; moreover, the cost of processing is reduced and ultimately a complete reduction of all the chromium present in the resulting soil is achieved, as described in

Examples that will follow.

The invention will now be described in more detail with reference to the accompanying drawing, in which: FIG. 1 shows the phasing process according to the invention. FIG. 1 shows that the residual products 1 are leached (or the resulting soils) are dried. (A) by a known treatment until they are substantially anhydrous and then mixed in 2 (Phase B) with sulfur, with compounds containing a reducing

7 In this case, it is also possible to adhere to the information below. And the role, in the praise, her.

all of them can be used.

and other types of inorganic reducing agents, for example

1.9. Sulphites, sulphides, sulfur read.

with a wound that no. ch 1ori d ο I. e; z n a t ý and tď.

Sulfur is the preferred agent and therefore references to t. This method will apply to this method without limiting it in any way.

I. o h o t. O c t i n c a n e c h a n d s e a c t a b c t a

1:00

The ratio of residual j to 100 earths with the reverberation is in the estromatic c rome, which can be reduced from one plant, in Lomné in the residual leaching products.

The anhydrous mixture thus obtained is fed into the reactor 3, which is preferably a rotary kiln with indirect heating, equipped with seals 4 and 5 located at the ends of the furnace, in any case of opening, in order to prevent or minimize the possibility of air access so it essentially took place in the absence of oxygen.

The drying, mixing and batching phases to the reactor 3 may be carried out in any time sequence, but the method described above is preferred.

The picture shows another heating system.

6, which forms a series of burners.

those which can react in this state; oxygen is removed from the compounds present in the residual products and the chromium chromium is reduced.

It is possible to assume, however, that the principle ιιί <· is quite scientifically explained that the following reaction takes place:

A Na 2 CrO 4 + 3 S> 2 Cr 2 O 3 ⁺ 3 SO 2 ⁺

To get good results in a short time it is good to maintain.

minimum temperature.

to answer

9419 the limitation of sulfur; the preferred reaction temperature is

As mentioned above.

The process is carried out without oxygen or gas purification, since a t-axis of the sulfur-containing and sulfur-containing phase is generated in a suitable manner to create the conditions.

Thus, the sulfur sulfur allows the preparation of the mixture to be carried out in the reactor at the beginning of the sulfur and evaporation. it to consume the oxygen present and obtain the necessary atmosphere composition.

At the outlet of the reactor, the treated residual determinants are not contained. in hexavalent chromium (see Examples below).

In any case, the reacted sulfur becomes bound in the material in the form of reducing salts (sulfites, sulphates, etc.) which have a certain ability. to reduce traces of hexavalent chromium which cross-link due to difficult contact, for example, due to the large granometer of residual products, cannot reduce during reaction.

The invention will be described in more detail in the following Examples. which are intended to illustrate the invention in more detail, but are not to be construed as limiting the invention in any way.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

C a rd a n d a n d e n t i n d

Chromatographic product (CrO 3, total solubility = 2.8%; hexavalent chromium extractable by cold water = 7 280 ppm; hexavalent chromium extractable by hot water = 9 880 ppm; Cr 2 O = 2.8%; CaO = 26 Pe ₂ Oa

(17.8%), the members underwent the expansion

9419 (thinning) in the laboratory (99% < 0.090 mm) and mixed with 0.75 mm and 1 mm in width.

And placed in a platinum tray in the furnace and kept at a temperature of two hours

510 ° C (ambient temperature).

and extracting the sample is carried out in a stream of nitrogen so that oxidation processes occurring in the presence of air can be avoided.

The amount of hexavalent chromium in the final product is always less than 5 ppm.

Example 2

Three parts of residual treatment products i. thunder (CrOj.

total solubility

3.7%; hexavalent chromium excited water = 4,160 ppm; hexavalent chromium

2.8%; FezO3

This way it eats with hot water

9.4%) of the laboratory mixture and the mixture to be examined

450 subject (98% <

ppm

(0.090 mm) is placed in a platinum tank into the furnace and stirred for two hours.

Na · keeps on

490 ° C (boiling point 11 ° C).

The samples were extracted in a stream of nitrogen so as to avoid oxidation processes occurring in the presence of air.

The amount of H 2 O in the final product is always less than 5 ppm.

S ection of the products from the processing industry (Cr03. Total permeability)

2.8%; hexavalent chromium

9419

2%;

F 02 l>> 3

So cold water

17,8¾)

280 ppm; hexavalent chromium

2.8%; CaO and subjected to a final lab decomposition (98% <0.090 mm) and the obtained mixture was stirred for 30 minutes at 30 m for the furnace.

680 ° C (internal temperature 1 ° C).

F d2: The insertion and extraction of the sample is carried out in a nitrogen stream so that and can be avoided.

an oxidation process that occurs in the presence of air.

The amount of nom product is always less than 5 ppm.

Twenty. kilograms of residual treatment products

i.

i: thunder (C rOj.

Extractable in laboratory by indirect cold water

%) is reported (95% <

heating.

v n ú t. The air temperature is 1 rpm

0,090

2.8%; s e s, m o c c c c 11 r ó m

280 ppm; hexavalent chromium

880 ppm; CT2 03 does not spread

C s t. g) and mixed with 0.4 kg of sulfur.

The basic dimensions are 1 edu i úcc

0.20 m, heated length 2.8 m. It is then adjusted to 510-520 ° C. the excess is removed from the furnace and these conditions are maintained for thirty rotations of the furnace maintained at 3 rpm.

After cooling, the product was removed and subjected to analysis

The amount of hexavalent chromium in the final product is always less than 5 ppm.

94.19

Example 5

Zim?

formed

100 z edited c f f Crnoc ý c bromine cx f.rahova t d * hexavalent chromium extralilatable

CC2O3 = 2.8%; CaO = 26.2%; Fez O3 ground (95% <0.090mm) and 2.0 parts residual products total solubility C = 2.8%; cold water = 7,280 ppm; hot water = 9,880 ppm;

= 17.8%), which are finely part of the ventilated sulfur being modified to turbulent at a rate of 80 kg / hour. an internal temperature of 510 to 520 ° C for 25 to 30 minutes.

continuous types? dosing after suitably according to example 4, and the work is done and these conditions are subjected to

There are no dumps 1 during the trip.

Quantity t. The chromium content is always less than 5 ppm.

n i e k o k ¾ k; h days. in the final product is

For emissive use

The importance of the hexavalent chromium reduction process and apparatus found in the chromium ore treatment residues is to improve ore processing and treatment -

Claims (3)

1. A method for reducing hexavalent chromium in residual products from the treatment of chromium ores, characterized in that it is a process for reducing chromium ore. characterized in that it comprises phases of mixing said residual products with one or more reducing agents. and heating said mixture in an indirect manner substantially in the absence of oxygen. 2. A process according to claim 1, wherein said reducing agent is sulfur or sulfur containing compounds. A method according to claim 1 or 2, characterized in that the method is as follows. characterized in that said mixture of the reducing agent with said residual products is reacted essentially under anhydrous conditions and. Λ. process by Claim 3 confesses č u it is t ý m. that said residual products s and p inland land before than before they mix with s í rou. 5. process by Claim 2 confesses č u it is t. ý m, that is said mixture zahr i eva on the temperature at least equal to the temperature at which the sulfur is sub-diminished. 6th Method according to any of claims 1. up to 5, v y z j j ú c i sa that is performs continually with the help of a rheum heating in rotating j furnace i. 7. Method according to who w e r o w o w e of claims 1 to 6, 9419 characterized in that it is carried out in the absence of gas circulating through the reactor. claim t. ii? it phases ^; introducing a predetermined amount of 1 liter into the reactor; heating said reactor until the sulfur is reacted with oxygen. present in the introduction of the reaction mixture into the reactor. using oxygen. A device for reducing hexavalent chromium by a method according to any one of claims 1 to 7, characterized in that it comprises an indirectly heated rotary kiln, gas leak-tight means, positioned so as to correspond to the entry point into the reactor. and a discharge point for the reaction mixture, and aids for introducing said reaction mixture or separate component into said furnace. 1. process PATENT you c h d s and j of the account of the c Claims for water-insoluble compounds of hexavalent chromium derivatives. o b s i h h u t h e t h o w P r o d uctoc l> From this: h a r q q m i g i n i, in that the b o c is a c r e r i n e r i n e r i n e r i s t o n o n s w a n e n e n e n e n e n e n e n e. namely, the hexavalent chromium contained in said derivatives, by mixing said derivatives with at least one reducing agent and by indirectly heating the mixture thus obtained. at least to the temperature of said reduction reaction e. > j < denominatingthe ed enr ed uk a rt the selected algae 1 edu i ucc j bought h cm ical t :: hz 1 u n i n i n e n 1 orid ž el 2; I :. wherein at least one of said f tep 1 o t. and the sublimation temperature and the ratio of said residual products containing said hexavalent chromium and sulfur derivatives in the reaction mixture i is in the range of 100 / 0.1 to 100/5: i ratio, in ppm, s. and the hexavalent chromium contained in the aforementioned starting derivatives. i e v Λ. The method of any one of:. The process of claim 1, wherein the reduction reaction products are in the form of powdered water-insoluble anhydrous chromium compounds. kd * t "" J, Spôsub podle any of the claims 1 to 4, v y z j j ú c i s a t. that the performs continual by indirect means Include evan i and in rotating j furnace i. 6th Method according to k t o r h o k o k e of the claims 1 to 5. v y z j j ú c i s a t that is performs without presence of a pollutant in the reactor. 7 ^ The method according to the invention; Claims 1 to 6; n a č u j ú c i S č j t ý m, before iMPLEMENTATION r e d u c h e r e a k c i e c der i vátov six six oc es chromium create reduction atmosphere heating at least one reduction number; initele za The method of claims 1 to 7 is characterized by an oxygen-free and substantially oxygen-deficient reduction method according to any one of claims 1 to 7, characterized in that it is disposed in a gas-tight sealing space. so that at least one of the points of entry of the reaction 1, flowing through the point of exit of the reacted means for introducing said reaction mixture or separate components into Pol: t; .