CN104726705B - A kind of chromite leaches the method for carrying chromium - Google Patents

Abstract

The present invention relates to the method that chromite pressure leaching carries chromium, comprise the following steps：Chromite and/or pretreated chromite are mixed to prepare original slurry with potassium hydroxide aqueous solution, wet chemical, the potassium metaaluminate aqueous solution；Obtained original slurry is added in autoclave, is passed through oxidizing gas, carries out pressure leaching oxidation reaction, obtains reacting disposed slurry；Through separation of solid and liquid, iron-rich tailings and the solution containing potassium chromate, potassium hydroxide, potassium carbonate, potassium aluminate and other water-solubility impurity components are respectively obtained.Of the invention to put forward chromium method, reaction temperature is greatly lowered, and energy consumption is small, effectively reduces production cost, and chromium recovery rate reaches as high as more than 97%；Additionally, autoclave volume used can be 200L, reaction medium is identical with industrial cycle feed liquid proportioning so that this process is with industrial process closely, it is easy to accomplish industrialization.

Description

A kind of method for extracting chromium by chromite ore leaching

technical field

The invention belongs to the fields of chromite hydrometallurgy and chromium chemical industry, and in particular relates to a method for extracting chromium by pressurized leaching of chromite in a mixed solution of potassium hydroxide, potassium carbonate and potassium aluminate.

Background technique

Chromite, a mineral in the spinel configuration, is the only chromium ore currently available for mining. The main components of chromite are oxides of iron, magnesium and chromium, and the general formula can be expressed as (Fe,Mg)Cr ₂ O ₄ . Chromium salt is one of the important inorganic chemical products and the basic raw material of important chemical industry-light industry-advanced alloy materials. About 10% of industrial products in China's national economy are related to chromium salt.

At present, the methods for producing chromium salt products from chromite mainly include calcium roasting method and calcium-free roasting method. The current production technology of my country's chromium chemical industry is backward. At present, most enterprises adopt the traditional calcium-sodium roasting process. Existence in the form of calcium. Serious pollution of water, soil and air, threatening personal safety and health, has become the focus of widespread concern in society and has attracted great attention from the state. Chromium slag pollution is a long-standing environmental protection problem. The calcium-free roasting technology that optimizes the traditional process has a high chromium leaching rate and less slag discharge, but the investment in equipment is large, and the furnace body is seriously ringed during the roasting process, making it difficult to implement industrialization.

CN1418823A, CN102275992A, CN85102681, CN1579947, CN101066779, CN102643977A, CN85100396, etc. respectively optimize and improve the roasting process with calcium or without calcification, which improves the conversion rate of chromium to a certain extent and reduces the discharge of chromium slag, but the roasting principle and operation of the above process The process and operating temperature are basically the same as the traditional process, the reaction temperature is still high, the energy consumption is high, and the problem of chromium slag pollution can only be partially reduced rather than essentially solved.

In recent years, the Institute of Process Engineering, Chinese Academy of Sciences has done a lot of research on the liquid-phase clean production process of chromium salts, and developed a series of clean production processes for chromium salts by sub-molten salt method and molten salt method. US7968066B2 uses KOH molten salt liquid phase oxidation to decompose chromite, with high conversion rate, small amount of slag discharge, and reaction temperature at 250-400°C. At present, this process has been built into a 10,000-ton demonstration project. However, the lye circulation evaporation and concentration process consumes a lot of energy.

Also CN101659444 and CN101481144 propose to add potassium chromate under the effect of adding catalyst in the system, chromite reacts with oxidizing gas in NaOH-NaNO ₃ -H ₂ O or KOH-KNO ₃ -H ₂ O medium, nitric acid As a catalytic medium, the root is not consumed in the reaction; after the reaction, a mixed reaction product of lye, sodium chromate (potassium) and iron slag is obtained. After leaching of mixed reaction products, liquid-solid separation, evaporation cooling and crystallization to obtain sodium (potassium) chromate, after leaching and drying, the qualified sodium (potassium) chromate product is finally obtained; crystallization mother liquor and lye are circulated together . The chromium conversion rate of the method is greater than 99%, and the chromium content in the slag is less than 0.5%. However, this method introduces NaNO ₃ into the system, which complicates the subsequent separation.

CN101817561A discloses a method for the clean production of sodium chromate by pressurized leaching of chromite. The method is that chromite is heated and oxidized with oxidizing gas in NaOH solution; the liquid after the reaction is diluted and separated from solid and liquid, and calcium oxide is added to the liquid to remove impurities, and the obtained impurity removal solution is evaporated and crystallized to obtain chromic acid Sodium crystals and crystallization mother liquor, after solid-liquid separation, sodium chromate crystals are rinsed with saturated sodium chromate solution, and qualified sodium chromate products can be obtained after drying. The composition of the reaction system of this method is simple, and no difficult-to-separate phase is introduced into the system, which is beneficial to the efficient separation of sodium chromate. However, the pressure of this method is high and the investment in equipment is large.

Contents of the invention

The object of the present invention is to provide a method for extracting chromium by pressurized leaching of chromite according to the properties of the sub-molten salt and the mineral properties of the chromite. The method has low cost, high extraction rate and mild conditions.

The principle of the present invention is that chromite reacts with oxidizing gas at 200°C to 300°C in a mixed solution of potassium hydroxide, potassium carbonate, and potassium metaaluminate at a certain concentration in a 200L autoclave, so that trivalent chromium is Oxidation to hexavalent chromium to form potassium chromate enters the solution, and the reactions involved are:

FeO·Cr ₂ O ₃ +4KOH+7/2O ₂ →1/2Fe ₂ O ₃ +2K ₂ CrO ₄ +2H ₂ O

MgO·Cr ₂ O ₃ +4KOH+3/2O ₂ →MgO+2K ₂ CrO ₄ +2H ₂ O

Cr ₂ O ₃ +4KOH+3/2O ₂ →2K ₂ CrO ₄ +2H ₂ O

For reaching above-mentioned object, the present invention adopts following technical scheme:

A method for extracting chromium by pressurized leaching of chromite, comprising the steps of:

(1) mixing chromite and/or pretreated chromite with potassium hydroxide aqueous solution, potassium carbonate aqueous solution and potassium metaaluminate aqueous solution to obtain original slurry;

(2) adding the original slurry prepared in step (1) into an autoclave, feeding an oxidizing gas, and carrying out a pressurized leaching oxidation reaction to obtain a post-reaction slurry;

(3) Separating the reacted slurry obtained in step (2) through solid-liquid separation to obtain iron-rich tailings and solutions containing potassium chromate, potassium hydroxide, potassium carbonate, potassium aluminate and other water-soluble impurity components .

Among them, the mixed solution of potassium hydroxide, potassium carbonate and potassium aluminate used in the present invention has the same ratio as the circulating liquid after the factory reaction, so the circulating liquid can be directly used without impurity removal, which makes the present invention easy to realize industrialization; in addition, adding carbonic acid Potassium and potassium aluminate can increase the boiling point of the reaction liquid, can greatly reduce the reaction operating pressure, and reduce equipment investment.

In the method of the present invention, the pretreatment in step (1) is mechanical activation and/or roasting activation.

In the method of the present invention, the mechanical activation is one or a combination of roller ball milling, planetary ball milling or stirring ball milling.

In the method of the present invention, in the step (1), the potassium hydroxide aqueous solution concentration is 40%wt～70wt%, for example is 42wt%, 46wt%, 55wt%, 62wt%, 68wt% etc., potassium carbonate aqueous solution concentration is 1 %wt~15%wt, such as 2wt%, 5wt%, 9wt%, 13wt%, etc., the concentration of potassium metaaluminate aqueous solution is 1%wt~10%wt, such as 2wt%, 5wt%, 7wt%, 9wt% Wait.

In the method of the present invention, the mass ratio of potassium hydroxide and chromite in step (1) is 2.5:1～8:1, such as 2.7:1, 3.8:1, 5.5:1, 6.5:1, 7:1 etc., preferably 3:1-5:1, more preferably 3.3:1-4:1.

In the method of the present invention, the oxidizing gas in step (2) is one or a mixture of two or more of air, oxygen, oxygen-enriched air or ozone gas; preferably oxygen and/or air.

In the method of the present invention, the oxidation reaction temperature in step (2) is 200-300°C, such as 205°C, 215°C, 222°C, 250°C, 260°C, 280°C, 295°C, etc., preferably 230~260°C; the reaction time is 2~8h, preferably 4~6h, for example, 4.1h, 4.8h, 5.2h, 5.7h, 5.9h, etc.

In the method of the present invention, after the oxidizing gas is introduced in step (2), the total pressure of the oxidizing gas and the steam in the kettle is 0.1MPa to 2MPa, such as 0.3MPa, 0.8MPa, 1.2MPa, 1.6MPa, 1.9MPa etc., preferably 0.5 MPa to 1 MPa.

In the method of the present invention, the solid-liquid separation described in step (3) is first diluted with clear water, and then solid-liquid separation; preferably diluted to the concentration of potassium hydroxide in the slurry is 100-500g/L, For example, 110g/L, 140g/L, 180g/L, 250g/L, 310g/L, 390g/L, 420g/L, 460g/L, 480g/L, etc., more preferably 300g/L.

Preferably, the temperature during the solid-liquid separation is 60-130°C, such as 65°C, 88°C, 102°C, 110°C, 116°C, 124°C, etc., and separation by filtration or centrifugation is used.

As a preferred technical solution, the method of the present invention comprises the following steps:

(1) Mixing chromite with potassium hydroxide, potassium carbonate and potassium aluminate to prepare raw material slurry, and preheating to 200-300°C;

Among them, the mass ratio of potassium hydroxide to chromite is 2.5:1~8:1, the concentration of potassium hydroxide aqueous solution is 40%wt~70%wt, the concentration of potassium carbonate aqueous solution is 1%wt~15%wt, potassium metaaluminate The concentration of the aqueous solution is 1%wt~10%wt;

(2) When the raw material slurry obtained in step (1) reaches a predetermined temperature, an oxidizing gas is introduced, and mechanical stirring is applied, and the oxidation is carried out at 200-300° C. for 2-8 hours, and the reaction slurry is obtained after the reaction is completed;

(3) Dilute the reaction slurry obtained in step (2) with clear water until the potassium hydroxide concentration in the slurry is 100-500g/L to obtain iron-rich tailings, potassium chromate, potassium hydroxide, carbonic acid Solid-liquid mixed slurry of potassium, potassium metaaluminate and other water-soluble impurity components; then the obtained solid-liquid mixed slurry is filtered or centrifuged at 60-130°C to obtain iron-rich tailings and Chromium solution.

Compared with the prior art, the present invention has obvious advantages:

The chromium content in the tailings obtained by the method is low, the conversion rate of chromium in chromite ore can reach more than 97%, and the tailings discharge is small, the hexavalent chromium content in the tailings is low, the environmental pollution is small, and the tailings are easy to realize Comprehensive utilization.

From the perspective of reaction conditions, compared with the traditional process, the reaction temperature is greatly reduced, the energy consumption is low, and the production cost of potassium chromate can be effectively reduced.

Compared with CN101817561A, after adding potassium carbonate and potassium aluminate, the boiling point of the solution is greatly increased under the same alkali concentration, which can greatly reduce the reaction operating pressure and equipment investment.

From the perspective of reaction scale, the effective volume of the autoclave is 200L, and the proportion of the reaction medium is the same as that of the circulating liquid after the industrial reaction, so this process is very close to the industrial process, and it is easy to realize industrialization.

Description of drawings

Fig. 1 is a schematic flow chart of the method of the present invention.

detailed description

In order to facilitate understanding of the present invention, the present invention enumerates the following examples. Those skilled in the art should understand that the examples are only used to help understand the present invention, and should not be regarded as specific limitations on the present invention.

Example 1

Add 13Kg of chromite with particle size below 200 mesh and 140L mixed solution containing 45%wt KOH, 10%wt K ₂ CO ₃ , 8%wt KAlO ₂ into a 200L autoclave, the ratio of alkali to mineral is 8:1, and heat to 250°C, then feed oxygen into the solution and stir evenly to fully mix the chromite and oxygen, control the total pressure of the system to 1.5MPa, and react for 6 hours to fully react the chromite and oxygen. Finally, a solid-liquid mixed slurry containing iron-rich tailings, potassium chromate, potassium hydroxide, potassium carbonate, potassium metaaluminate and other water-soluble impurity components is obtained, the temperature is lowered, the sample is diluted, and diluted into the reaction slurry for hydrogenation The potassium concentration is 300g/L, and the mixed slurry is filtered and separated at about 80°C to obtain iron-rich tailings and chromium-containing lye respectively. After repeated washing and drying of the tailings, the chromium content is measured by titration, and the chromite ore is calculated. The conversion rate of medium chromium is over 97%. Example 2

Add 22Kg of chromite with particle size below 200 mesh and 140L mixed solution containing 50%wt KOH, 10%wt K ₂ CO ₃ , 10%wt KAlO ₂ into a 200L autoclave, the ratio of alkali to mineral is 5:1, and heat to 280°C, then feed oxygen into the solution and stir evenly to fully mix the chromite and oxygen, control the total pressure of the system to 1MPa, and react for 4 hours to fully react the chromite and oxygen. Finally, a solid-liquid mixed slurry containing iron-rich tailings, potassium chromate, potassium hydroxide, potassium carbonate, potassium metaaluminate and other water-soluble impurity components is obtained, the temperature is lowered, the sample is diluted, and diluted into the reaction slurry for hydrogenation The potassium concentration is 300g/L, and the mixed slurry is filtered and separated at about 80°C to obtain iron-rich tailings and chromium-containing lye respectively. After repeated washing and drying of the tailings, the chromium content is measured by titration, and the chromite ore is calculated. The conversion rate of medium chromium is above 88%. Example 3

Add 36Kg of chromite with particle size below 200 mesh and 140L mixed solution containing 55%wt KOH, 15%wt K ₂ CO ₃ , 5%wt KAlO ₂ into a 200L autoclave, the ratio of alkali to mineral is 3:1, and heat to 260°C, then feed oxygen into the solution and stir evenly to fully mix the chromite and oxygen, control the total pressure of the system to 0.2MPa, and react for 7 hours to fully react the chromite and oxygen. Finally, a solid-liquid mixed slurry containing iron-rich tailings, potassium chromate, potassium hydroxide, potassium carbonate, potassium metaaluminate and other water-soluble impurity components is obtained, the temperature is lowered, the sample is diluted, and diluted into the reaction slurry for hydrogenation The potassium concentration is 300g/L, and the mixed slurry is filtered and separated at about 80°C to obtain iron-rich tailings and chromium-containing lye respectively. After repeated washing and drying of the tailings, the chromium content is measured by titration, and the chromite ore is calculated. The conversion rate of medium chromium is over 97%. Example 4

Add 33Kg of chromite with particle size below 200 mesh and 145L mixed solution containing 60%wt KOH, 10%wt K ₂ CO ₃ , 6%wt KAlO ₂ into a 200L autoclave, the ratio of alkali to mineral is 3.3:1, heat to 210°C, then feed oxygen into the solution and stir evenly to fully mix the chromite and oxygen, control the total pressure of the system to 2MPa, and react for 6 hours to fully react the chromite and oxygen. Finally, a solid-liquid mixed slurry containing iron-rich tailings, potassium chromate, potassium hydroxide, potassium carbonate, potassium metaaluminate and other water-soluble impurity components is obtained, the temperature is lowered, the sample is diluted, and diluted into the reaction slurry for hydrogenation The potassium concentration is 120g/L, and the mixed slurry is filtered and separated at about 100°C to obtain iron-rich tailings and chromium-containing lye respectively. After repeated washing and drying of the tailings, the chromium content is measured by titration, and the chromite ore is calculated. The conversion rate of medium chromium is over 96%.

Example 5

Add 22Kg of chromite with particle size below 200 mesh and 140L mixed solution containing 65%wt KOH, 5%wt K ₂ CO ₃ , 8%wt KAlO ₂ into a 200L autoclave, the ratio of alkali to mineral is 5:1, and heat to 290°C, then pass compressed air into the solution and stir evenly to fully mix the chromite and gas, control the total pressure of the system to 2MPa, and react for 5 hours to fully react the chromite and oxygen. Finally, a solid-liquid mixed slurry containing iron-rich tailings, potassium chromate, potassium hydroxide, potassium carbonate, potassium metaaluminate and other water-soluble impurity components is obtained, the temperature is lowered, the sample is diluted, and diluted into the reaction slurry for hydrogenation The potassium concentration is 500g/L, and the mixed slurry is filtered and separated at about 130°C to obtain iron-rich tailings and chromium-containing lye respectively. After repeated washing and drying of the tailings, the chromium content is measured by titration, and the chromite ore is calculated. The conversion rate of medium chromium is over 98%.

Example 6

Add 36Kg of chromite with particle size below 200 mesh and 140L mixed solution containing 52%wt KOH, 15%wt K ₂ CO ₃ , 8%wt KAlO ₂ into a 200L autoclave, the ratio of alkali to mineral is 3:1, and heat to 240°C, then pass compressed air into the solution and stir evenly to fully mix the chromite and gas, control the total pressure of the system to 0.8MPa, and react for 8 hours to fully react the chromite and oxygen. Finally, a solid-liquid mixed slurry containing iron-rich tailings, potassium chromate, potassium hydroxide, potassium carbonate, potassium metaaluminate and other water-soluble impurity components is obtained, the temperature is lowered, the sample is diluted, and diluted into the reaction slurry for hydrogenation The potassium concentration is 400g/L, and the mixed slurry is filtered and separated at about 60°C to obtain iron-rich tailings and chromium-containing lye, respectively. After repeated washing and drying of the tailings, the chromium content is measured by titration, and the chromite ore is calculated. The conversion rate of medium chromium is above 99%.

The applicant declares that the present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned examples, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow process can be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (3)

1. a kind of method that chromite pressure leaching carries chromium, comprises the following steps：

(1) chromite is obtained into raw material slurry with the mixed liquor mixed preparing of potassium hydroxide, potassium carbonate, potassium metaaluminate, and is preheated To 200~300 DEG C；

Wherein potassium hydroxide and chromite mass ratio is 2.5:1~8:1, potassium hydroxide aqueous solution concentration is 40%wt~70% Wt, wet chemical concentration is 1%wt~15%wt, and potassium metaaluminate concentration of aqueous solution is 1%wt~10%wt；

(2) treat that raw slurry that step (1) obtains, to predetermined temperature, is passed through oxidizing gas, and apply mechanical agitation, be maintained at 2~8h of oxidation is carried out at 200~300 DEG C, reaction paste is obtained after completion of the reaction；

(3) step (2) gained reaction paste is diluted with clear water, the concentration of potassium hydroxide being diluted in slurry is 100- 500g/L, obtains consolidating containing iron-rich tailings, potassium chromate, potassium hydroxide, potassium carbonate, potassium metaaluminate and other water-solubility impurity components Liquid mixed slurry；Then at 60~130 DEG C, resulting solid-liquid mixed slurry is separated by filtration or centrifugation, point Iron-rich tailings and chromium aqueous slkali are not obtained.

2. method according to claim 1, it is characterised in that step (2) described oxidizing gas are air, oxygen, richness One kind or two or more mixing in oxygen air or ozone gas.

3. the method for claim 1, step (2) described oxidizing gas are oxygen and/or air.