DD160611A1 - PROCESS FOR PRODUCTION V. SPECIAL TONER FOR OXID CERAMICS - Google Patents

Abstract

The invention relates to a process for the production of alumina with increased chemical purity and specific physical characteristics for the production of high quality oxide ceramic on AL deep 2 O deep 3-base. The aim of the invention is, starting from the aluminate liquor obtained during the bauxite digestion, to produce in a direct way pure ceramic clay with defined physical characteristics. According to the invention, this is achieved by adding the aluminate liquor obtained as an intermediate in conventional bauxite processing with an aqueous suspension of alkaline earth metal hydroxides, in particular calcium hydroxide or magnesium hydroxide or a mixture thereof, and at temperatures between 70 and 95 degrees C is depressurized, this suspension after about 4 to 6 hours Aluminiumspaene usual Huettenqualitaet be added after their dissolution and removal of all suspended solids by ultrafine filtration, the so purified aluminate a special decomposition process to set the desired Primaerkorngroessenbereiches in the produced alumina hydrate, which is the precursor for each particular Tonerdequalitaet is subjected.

Description

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Process for the production of special clay for oxide ceramics

Application of the invention

The invention relates to a process for the production of alumina with increased chemical purity and specific physical characteristics for the production of high-quality oxide ceramics

Well-known technical solutions

As a starting material for the production of special clay is generally used in the classical Bauxite processing according to the BAYER technology to normal clay as an intermediate product Tonerdefeuchthydrat.

Previously known method proposals assume that this material alkaline or acid dissolve again or to use aluminum metal for this purpose and to further process the Al salt solutions thus prepared.

WP 37 495 describes a process according to which technical alumina hydrate is dissolved in alkali liquors with simultaneous addition of zinc compounds and salts of calcium or magnesium which form sparingly soluble hydroxides or carbonates.

Dissolved zinc must then react with sulphidic sulfur again

L · L ·

precipitated and separated by serving as a filter aid hydroxides or carbonates of Ca or Mg in a further process stage. The method only deals with the removal of ferrous metal contaminants and does not include the necessary SiO 2 absorption ».

French Patent Specification 155 45 86 also relates to pure clay based on normal alumina hydrate which is dissolved in sulfuric acid. From this solution is precipitated by the introduction of HCl gas Aluminiumchloridsulfathydrat whose thermal decomposition leads to pure clay, while the decomposition gas HCl, S0 _? , SO, H "0 are recycled. According to DBP 1 O63 589 HUttenalurainium average quality, z. B. 99.5 % Al, reacted with an alcohol to Aluminiumalkoholat. After separation of the impurities and hydrolysis of the alcoholates practically pure alumina is obtained.

All of these processes are inherent in that they start from alumina hydrate or cottage aluminum as refined precursors.

Object of the invention

The aim of the invention is to start directly from the alkaline bauxite digestion after separation of the digestion residue red mud incurred aluminate liquors while avoiding the other, for the preparation of the mentioned in the cited patents precursors Tonerdehydrat or HUttenaluminium required process steps and directly involving already made other context of known process steps to arrive at pure ceramic earth with defined physical characteristics.

Essence of the invention

The invention has for its object to provide a process for the production of special clay for the oxide ceramic. According to the invention the object is achieved, ind-em in the usual Bauxitverarbeitung after the BAYER process as an intermediate product aluminate with the purpose of increasing their purity

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an aqueous suspension of alkaline earth metal hydroxides, in particular calcium hydroxide or magnesium hydroxide or their mixture, and stirred at temperatures between 70 and 95 C without pressure, this suspension after about 4 to 6 hours of aluminum shavings usual HUttenquälitat be added after their dissolution and removal of all By ultrafine filtration, the so purified aluminate liquor is subjected to a special decomposition process for setting the respective desired primary grain size range in the produced alumina hydrate, which is the precursor for the particular special clay soil quality.

Ceramic clays differ from normal clays by z. T. much higher purity requirements regarding the main impurities Na _? 0, Fe _? 0_ and SiO- and defined physical parameters, in particular the primary crystal size, a high Oi -Al "O -, - content (* 95 %) , a high purity (* 3.94 g / cm) and a minimum secondary grain content, which Fine grinding (super grinding) - but without damaging the primary grain - can be achieved.

With the exception of a Spezialtonerdequalität for the production of transparent ceramic, which is characterized by highest purity, all other ceramic earth metals can be produced by appropriate variation of the production parameters by erfindungsgeraäßen method, starting from conventional aluminate from alkaline bauxite pulping.

For depletion of SiO ₂ and Fe ₂ O- entering the process ^with 95-98 ⁰ C in the process initially with an aqueous suspension of hydrated lime or magnesium hydroxide, preferably a ratio of 1: 1 produced mixture of both alkaline earth metal hydroxides, about 200 g contains pesticides, mixed in a proportion of 10 to 15 g of pesticide / l aluminate and stirred at temperatures of 70 - 90 ⁰ C, preferably 8o ⁰ C for about 5 hours so that the pesticide is kept in suspension. By the feindis

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pers alkaline earth hydroxides, in particular by the high adsorption of Magnesiurohydroxides contained in the aluminate finely dispersed red mud particles, iron oxide hydrates and Nachentkieselungsprodukte be reliably bound. At the same time, chemical decomposition of the alkaline earth metal hydroxides leads to a depletion of the dissolved silicic acid fraction in the aluminate liquor due to the formation of insoluble complex Ca MgAl hydrosilicates, which causes the SiO _? Content is lowered so far that SiCl is only deposited in traces during the subsequent toner alumina precipitation. After the said reaction time, the proportion of 1 to 5 g Al chips / l added to the thus pretreated aluminate liquor is added at the same temperature, and the cooling rate is increased until the formation of a light trump.

Up to 5 mg Fe _? O, / l can be present in aluminate liquors of conventional concentration in real solution as hydroxoferrit anions and in the Tonerdehydratabscheidung z. T. init are incorporated into the hydrate grid. The resulting in the implementation of the added Al shavings with the alkali metal hydrogen in statu nascendi a short-term reduction effect is achieved, wherein Fe _? O_. nH _? O including higher-value heavy metals in teilreduzierter form finely dispersed and adsorbed by the alkaline earth metal hydroxides.

In a subsequent stage, the thus purified Alurainatlauge is removed by ultrafine filtration (polishing filtration) of all the pesticides to the optical purity, the Erdalkalihydroxidsuspension serves in a third property as a filter aid.

The so of heavy metals and SiO _? Substantially liberated aluminate liquor is now subjected to a special decomposition process which has a defined primary crystal formation and is characterized by the following stages:

- cooling the aluminate to normal temperature;

- Periodic ultrasound treatment until turbidity by crystal formation;

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- Heating the aluminate to 50 to 70 ⁰ C in order to reduce the AlpO ^ supersaturation

- Cooling and increased agitation until exhaustion of the aluminate lye.

The decomposition process is characterized by an initial strong supersaturation with the aim of rapid and intense crystal formation and a subsequent phase of reduced supersaturation on AlpO_, in which the targeted growth of hydrate crystals formed in the foreground and as possible no further crystal remodeling occurs.

Increased agitation in the second phase pursues the goal of promoting primary crystal growth and suppressing the formation of secondary crystal aggregates.

The decomposition process is completed when the molar ratio Na_O / AIpO- has increased from initially 1.6-1, "B to approximately 3.0-3.5.

The resulting alumina trihydrate is separated from the mother liquor by wash filtration and fed to the thermal dehydration process step. At 350 to 400 ⁰ C is carried out preferably in a vortex unit, a partial elimination of water, corresponding to a dry matter based on loss of about 35 % to about 15 #. The hot fluidized material is then vermäischt in pure water in the Pest-Plüssig ratio of preferably 0.5 to 1: 1 and subjected to a new wash filtration. This process stage serves to deplete the alkali content in the alumina hydrate.

After re-washing filtration resulting partially dehydrated Tonerdehydrat is after admixing the respective required mineralizer, eg. B. 0.25% -BpO, - based on the AIpO -, - content - directly the Hochtemperaturkalzinierung at 1200 'to 1400 ⁰ C supplied.

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In a subsequent grinding process - preferably in a closed system with a Feinstkorn sifter - the Aufmahlung of crystal aggregations and associated with the exposure of Primärkornea.

Calcination, separation and milling devices are preferably lined with pure corundum stones.

As a result of the described process design, based on the inventively designed process stages special toners for Al _? 0_ ceramic obtained, which are characterized by the following chemical purities and physical properties:

- Na 0 :. iS 0.01 %

- Pe ₂ O-: Äs 0.01 %

: S & 0.02 </> : S £ 0.02 % : SS 0.005 %

: 0.5 to 10 - depending on the direction of the decomposition process in connection with the Hochtemperaturkalzination

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:> 3.95 g / cm ³ ,

J 0.5 - 10 in / g depending on primary grain size and grain form factor.

- CaO

- primary grain size

-Al ₂ O ₃ content

- true density

- specific surface

The process of the invention will be explained in more detail by the following examples:

example 1

From the operational bauxite digestion the following aluminate liquor is available after separation of the red mud:

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Al ₂ O 110 g / l

^Na 2 ° caust. ¹¹²

MV 1,675

226.5

'gea, Iß, O rag / l

ßiO «226.5 mg / 1

1 m of this liquor 10 kg of a mixture of 5 kg of magnesium hydroxide and 5 kg of calcium hydroxide are added pumped suspended in water. At 80 ^° C., this suspension is stirred gently for 5 hours. Subsequently, the addition of 1.5 kg of coarse aluminum chips of 99.5 % Al is carried out. With increased stirring, the reaction is complete after 20 min.

After separation of the pesticides, a liquor with the following impurity contents is obtained:

SiO ₂ 71.5 mg / l

Pe ₂ O ₃ 2.8 mg / 1.

After the alkali has been cooled to normal temperature, a rod-shaped ultrasonic donor with an operating frequency of 50 kHz is periodically put into operation in a stirred vessel whose structural design permits high reflection.

Depending on the degree of supersaturation, optical purity and Al "0_ concentration of the aluminate and intensity of the ultrasound exposure, however, a spontaneous primary crystal formation takes place at the latest after 24 h, which leads to a strong turbidity of the solution. After this time, the pulp is heated according to the example to 70 ° C and cooled within 72 to 96 hours at 50 ⁰ C with moderate stirring.

The deposited alumina hydrate is filtered off, thermally dehydrated, washed alkali-free, mixed with 0.5 % AIP- and annealed at 1400 ⁰ C for 1 h. ,

After grinding in a corundum ball mill, a special clay with the following quality characteristics is obtained:

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Na ₂ O 0.009 %

SiO ₂ 0.015 %

Fe ₂ O- 0.007 %

CaO 0.015 %

TiQ ₂ 0.003 %

Primary grain size 6.5 / Cd ₅ value to Fisher)

2 Specific surface area 0.5 m / g

Pure density 3.98 g / cm

Corundum content 5Τ 95 % ^ -Al-O-

Weight 1100 g / dm ³

Example 2

The cleaned according to Example 1 and placed at normal temperature for the deposition of Hydratprimärkristallen aluminate is heated to 55 ⁰ C and in a period of 4Θ to. 72 hours with increased agitation to 40 ⁰ C cooled. The alumina hydrate thus obtained and then dealkalized is also calcined at 1400 ° C. after addition of 0.5 % B ₃ O ₃ and ground in accordance with Example 1.

The following special clay soil is obtained:

Na ₂ O 0.010 %

SiO ₂ 0.017%

Fe ₂ O 0.006 %

CaO 0.016 %

TiO ₂ 0.003 %

Primary grain size 1.5 / μm (d, - _n value according to Fisher)

Specific surface 5.5 m ² / g

Pure density 3.96 g / cm ³

Corundum content -2Γ 95 % oC -Al _? 0_

Bulk density 650 g / dm ³

Claims (4)

2287 1 9 2 Claim for invention 1. Process Herstellungην production of special clay for the oxide ceramic gekanr ^ ^ Ql ^ that in the usual Baincityerarbeitung after the BAYER process as gwischenpr-oäukt accruing Aluminatlauge to increase their purity with an aqueous suspension of alkaline earth metal hydroxides, in particular calcium hydroxide or magnesium hydroxide or whose mixture is added and stirred at temperatures between 70 and 95 ⁰ C without pressure, this suspension after about 4 to 6 hours of aluminum shavings usual hut quality are added, after their dissolution and removal of all suspended pesticides by ultrafine filtration, the so purified aluminate a special decomposition process for setting the respectively desired primary grain size range in the produced alumina hydrate, which is the precursor for the particular special clay soil quality, is subjected. 2. The method according to item 1 characterized in that the decomposition process by cooling the Aluminatiauge first with the goal of intensive primary crystal formation in the highly supersaturated Al ₂ 0_ Konzentrierung3bereich runs and in a second phase after renewed heating and concomitant reduction of supersaturation mainly crystal growth according to the desired Priraärkristallgröße takes place. , 3. The method according to item 1 to 2, characterized in that the process of primary crystal formation in the supersaturated solution by the use of ultrasound can be significantly accelerated. , 4. The method according to item 1 to 3 characterized gek ennzeichnet characterized in that the process of Kristallwachstume is accompanied by an intense stirring of the system mother liquor - pesticide. See page drawing " 19 ti 1 * 0 ^ 905. * Π Jf 1 O Λ / 7/770 / SfAv ^ <y .///// # // # /? JZ