DD155247A5 - METHOD FOR REMOVING IRON OXIDE AND SILICON DIOXIDE FROM ALUMINATE LEAVES - Google Patents

Abstract

The invention relates to a method for the removal or at least very strong reduction of Fe deep 2 O deep 3- and SiO 2 deep content of aluminate liquors, which originate from the settling system of a plant for the production of alumina. For the purpose of economic design d. Alumina production by providing an effective cleaning method will d. Aluminate solution heated to 80 to 105 ° C. 0.1 to 1.5 kg / m high 3, expediently 0.2 to 0.5 kg / m high 3, lime hydrate containing not more than 3% MgO. After a reaction time of 2, expediently for 10 minutes, the precipitate is filtered off and added in a manner known per se to the digestive bauxite-sodium hydroxide mixture and / or passed into the settling system for the aluminate liquor. According to a preferred embodiment of the process, instead of hydrated lime, the aluminate solution is admixed with a mixture of 0.1 to 1.5 kg / m 3, suitably 0.2 to 0.5 kg / m 3, at most 3% MgO-containing hydrated lime and 0, 01 to 0.10 kg / m high 3, expediently 0.01 to 0.03 kg / m high 3 Perlite added.

Description

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Process for removing iron oxide and silica from aluminate liquors

field of use the Invention:

The invention relates to a process by means of which the Fe 1 O, and SiCU content of aluminate liquor originating from a settling system can be reduced in the production of alumina by the Bayer process.

Characteristic of the known technical solutions:

The processes currently used on an industrial scale for the production of alumina have the common feature that the alumina content of the bauxites used as the starting material is dissolved, resulting in aluminate solution. The aluminate solution contains solid impurities of different particle size that are removed by settling. Oe after the efficiency of the settling process, the purified aluminate contains 10 to 30 mg / 1 · Fe ₂ O ₃ and 2 to 25 mg / 1 SiO ₂ · In order to obtain good quality alumina, these impurities must be removed if possible.

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Various procedures have been developed for this purpose, but they have not been put into practice for a number of reasons. According to DE-PS 960 811, a stirring with low efficiency is proposed for the separation of the impurities.

Methods are known according to which so-called. Nachfiltermedien be used. The post-filter medium used are various granular substances, for example natural corundum, artificial corundum or gravel beds. HU-PS 146 048 proposes filtering through coke and limestone layers. According to GB-PS 1 192 043 is filtered through a Bauxitschicht certain particle size, while according to SU-PS 468 888 filtered through a Kalkadsorptionsschicht and at the same time 0.5 to 10 g / l sodium sulfite are added as an intensifying agent.

Object of the invention:

With the invention, the deficiency of the prior art should be eliminated.

Explanation of the essence of the invention:

The invention is based on the finding that hydrated lime in warm aluminate from 80 to 100 C within 2 to 20 minutes forms a calcium aluminate precipitate, which is characterized by excellent adsorption and good filter properties. The process can be further improved if a small amount of perlite is added simultaneously with the hydrated lime. If the aluminate liquor emerging from the settling system and filtered in accordance with the invention is filtered in a known filter unit, then 60 to 100 % of its Ρβ 3 and SiO2 contents can be separated off.

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The CaO content of the precipitate may be used for digesting the bauxite-sodium hydroxide mixture as digesting agent and / or in the red mud settling and washing equipment for causticizing.

Accordingly, the invention is a process for the removal of the FSP ^ s ^"unc 'SiOP content of aluminate of Absetzsystemen for alumina production. According to the invention constitutes one of the hot aluminate of 80 to 100 ⁰ C 0/1 to 1.5 kg / m, expediently 0.2 to 0.5 kg / m, at most 3 % MgO-containing hydrated lime or a homogeneous mixture of 0.1 to 1.5 kg / m, suitably 0.2 to 0.5 kg / m, at most 3 % MgO containing hydrated lime and 0.01 to 0.10 kg / m, suitably 0.01 to 0.03 kg / m perlite to »filtered after a reaction time of about 10 minutes, the deposited precipitate in a conventional manner and sets him in already known manner to the digestive bauxite-sodium hydroxide mixture and / or passes it into the settling system for the aluminate.

Embodiments;

The invention will be explained in more detail with reference to the following examples.

example 1

In a container with a volume of 15 m is used with

¹ 3 ο

a volume velocity of 140 m / h heated to 98 C aluminate solution containing 32 mg / 1 Fe ₂ O ₃ and 14 mg / 1 SiO ₉ . Then continuously 0.3

3 kg / m lime hydrate into the container. The exiting from the container slurry is applied to a pressure filter from

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Type Kelly headed where the solids are deposited. The filtrate no longer contains Fe ₃ O ₃ and SiO ₂ in the form of suspended matter. The analysis of precipitated precipitation shows the following values:

Adherent moisture 31.6 %

Al ₂ O ₃ 17.0 %

SiO ₂ 2.2 %

Fe ₂ O ₃ 4.9 %

total * CaO 25.1%

V ₂ O ₅ . · 0.02 %

The filtrate still contains 4 mg / ^l Fe ₂ ⁰ S ^unc * ^ ' ³

The removed from the frame of the filter press CaO-containing precipitate is mixed with the digestive bauxite-sodium hydroxide mixture and used in this way in a conventional manner as a digestion aid.

Example 2

It works with the device according to Example 1 and leaves the process parameters unchanged. In the container 0.2 kg / m lime hydrate and 0.03 kg / m perlite are metered. The precipitate has the following composition:

Adherent moisture 32.4 %

Al ₂ O ₃ 17.12 %

SiO ₂ 2.92 %

Fe ₂ O ₃ . 5.30 %

ges. CaO 21.6%

V ₂ O ₅ 0.02%

The filtrate still contains 5 mg / 1 Fe ₂ O ₃ and 2 mg / 1 SiO ₂ .

The filter apparatus removed CaO-containing precipitate is placed in the settling system of the aluminate, where the CaO content of the precipitate in per se known

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Way is used for causticizing.

The method means an improvement compared to the known technologies. The calcium aluminate formed with hydrated lime gives a well adsorbing and easily filterable precipitate. The filterability and the regeneration of the filter can be improved by adding perlite. No special equipment is required to carry out the process, it can be carried out by means of the usual apparatus of clay preparation. In contrast to the previously known methods, no filter bed made of foreign material is required, and the resulting precipitate can be used in the circulation.

The majority of the CaO content of the hydrated lime is used because the precipitate is added to the digestive bauxite-sodium hydroxide mixture and / or passed into the settling system where the CaO content participates in the causticization process.

Claims (1)

invention claim A method for removing or reducing the Fe * - ^ "and SiCU content of Aluminatlaugen originating from a clay alumina settling system, characterized in that 0.1 to 1.5 kg / m heated to 80 to 105 C, 0.1 to 1.5 kg / m, appropriate 0.2 to 0.5 kg / m, at most 3 % MgO-containing hydrated lime or a homogeneous mixture of 0.1 to 1.5 mg / m, suitably 0.2 to 0.5 kg / m, at most 3 % MgO containing Hydrated lime and from 0.01 to 0.10 3 3 kg / m, suitably 0.01 to 0.03 kg / m perlite added that after a reaction time of at least Q. minutes, preferably about 10 minutes, the precipitate is filtered off in a conventional manner and that then the precipitate in an also known manner added to the digestive bauxite-sodium hydroxide mixture and / or passes into the settling system for the Aluminatlauge.