HU203853B - Process for producing sodium- and potassium-aluminate from aluminium-silicate withhydrochemical treating - Google Patents

Abstract

Raw material is crushed, mixed with an alkaline soln. - of 90-110 g/l R2O, where R = Na(+) or K(+), followed by adjusting the mol. ratio 5 Na2O:7.5-8.4 Al2O3, heating to 900-100 deg.C for up to 24 hrs., adjusting the ratio of 2 liq. pts.:1 solid pt., settling and filtering off the prod. The alkaline filtrate is returned to the start of the process. - (-pp (-pp Dwg.No. 0/0)

Description

The present invention relates to a process for the preparation of sodium and potassium aluminate from a raw material containing aluminum silicate by a hydrochemical process.

A method of making alumina from bauxite is known, which allows for the reduction of deposits on the walls of the devices. According to this process (Japanese Patent Laid-Open No. 54-22,198), the starting ore is suspended in an alkaline solution, the Na ₂ O: Al ₁₀ O molar ratio is adjusted to less than one, preferably between 0.3 and 0.8, and the suspension is brought to heat up, on which deposits no longer form. The thus preheated slurry is introduced into the digestion reactor, to which the separately heated digestion liquor is added simultaneously. The digestion is carried out at a temperature of 200-230 ° C.

A process is known from French Patent No. 2,286,199, which divides the recycled alkali (by which the ore is broken down) into primary and secondary alkali. The secondary alkali is mixed in a tank with bauxite to form a slurry having a NajCkA ^ Clj molar ratio = 1. The slurry is then introduced into the preheater through the silica desiccant tank (into which the alkali is added). After preheating, the suspension enters the extractor, where the aluminum hydroxide is recovered.

There is also a known process for the hydrochemical processing of aluminum silicate (Hittner HT: Anorthosite of Hydrothermal Alkaliine Process to Extract Aluminum, Trav. Com. Ind. Bauxites, Alumine, Alum., 1981, N16, pp. 13-21). the raw material is crushed, mixed with lime, the returlum is heated, the raw material is digested at a temperature of at least 230 ° C, the sludge is separated and sodium aluminate and / or calcium aluminate is prepared from the alumina base.

The above procedure has two significant disadvantages:

1. The aluminum silicate-containing raw material contains potassium and is enriched in the recycled alkali. When the K ₂ O concentration in the returlug reaches 381%, the yield of Na ₂ Al _{2 is} abruptly decreased because of the formation of stable potassium aluminum silicate under autoclave digestion conditions (Pevzner IZ, Rajzman V.L. "Autoclave Processes"). in alumina production, M. Metallurgy 1983, p. 60). Potassium is sought to be removed from the system by carbonization to potassium carbonate by the introduction of CO ₂ , but of course the reaction is non-selective and carbonic acid in large quantities is also carbonated. Sodium carbonate. This loss has to be compensated with fresh caustic soda, which increases the cost of raw materials for the process

2. Raw material and limestone are not pre-heated prior to digestion because deposits of heat in such a mixture occur in heat exchangers.

The aim of the invention was to reduce the above process, thermal energy and material expenses so as to seek opportunities for the slurry preheating without buildup of deposits, eliminate the use of fresh caustic soda and ensure removal of potassium even solid before detection phase calcium hydroxide added ² rogranat design.

It has been found that the above object can be achieved if a process comprising crushing the raw material, mixing it with limestone, heating the retort liquor, digestion at a temperature of at least 230 ° C, separating the sludge and preparing the sodium and potassium aluminate from the alumina is carried out as follows: for the crushing of the raw material, a solution of 90110 R 10 g / l (R ₂ O - content of caustic alkali oxides, meaning K or Na) and a molar ratio of Na ₂ O / Al ₂ O _{3 to} 5.75 are used. Adjusted to -8.4 and the slurry heated at 90-100 ° C for 10-24 hours and then sedimented (to form a thick slurry and a supernatant lye phase containing a solid to a liquid ratio of 1: 2.1-2.2) the sedimented slurry is heated to the digestion temperature and the alkaline solution is recycled to the crude material for shredding.

Studies have shown that alkali can be recovered from aluminum silicates, including nepheline ores, under autoclave conditions. The starting materials used were Kola Peninsula, nepheline concentrate ground to a particle size of less than 50 microns, calcium oxide (98% CaO) and NaOH solution. The CaO: SiO ₂ molar ratio was kept at 1-1.1: 1. It was found that the highest alkali yield (40%) was achieved when the Na ₂ O: Al ₁₀ O molar ratio was 5.75-8.4: 1, preheating at 90-110 ° C, and initial alkali concentration of 90%. -110 g Na ₂ O. Heat retention can vary from 10 to 24 hours, at which time the alkaline yield increases from 37% to 40%. Virtually all the alkaline solution in nepheline is dissolved in solution (20-30% by weight of K ₂ O in the amount of Na ₂ O + K ₂ O in the cola nepheline concentrate). The solid backbone is composed primarily of calcium hydrogranate and an undamaged nepheline residue. Calcium hydrogranate (3 CaO.Al ₂ O ₃ jcH ₂ O. Y SiO ₂ ) is a stable compound with decomposition starting at 150 ° C (Rajzman VL: Thermodynamic analysis of the interaction between calcium hydrogranate and NaOH solution. Him, 1986, 59, Vol. 1, p. 234). Under industrial conditions, the slurry remains in the heat exchanger tubes for up to 2-3 minutes, during which time the disintegration of calcium hydrogranate and the formation of deposits are excluded. This allows parallel heating of the lime-nepheline mixture and the returicus prior to zautoclastic digestion, and also allows the returic acid preheating temperature to be reduced in a fly mode. The Na ₂ O / Al ₂ O ₃ molar ratio and accordingly the solid-liquid ratio (in the sludge) can be increased without deterioration of the process parameters. The effect of this change in the molar ratio on the sedimentation rate and the Sz: F ratio of the sludge was investigated. In the above molar ratio (5.75-8.5), satisfactory sedimentation parameters were achieved (overflow volume velocity 0.23 m ³ / h, weight ratio of sedimented sludge: solid: liquid): 1: 2.8 -2.9).

If the Na ₂ O / Al ₂ O ₃ molar ratio is less than 5.75, the alkali cannot be completely recovered and the formation of calcium hydrogranate is incomplete, the alkali solution and

EN 203 853 Β the proportion of alumina in the raw material changes, so the heat exchangers are clogged and need to be replaced with fresh caustic soda

If said molar ratio is greater than 8.4, the calcium hydrogranate begins to decompose, with the associated disadvantages stated above.

It can be calculated that the most suitable concentration of the recycle liquor, 450 g / l, Na ₂ O - can be achieved by the concentration of 350 g / l Na ₂ O in the digestion circle, with a ratio of Sz: F to 1: 2.1 in the sedimented sludge. Must be -2.2. Therefore, a portion of the slurry is born and the filter cake is added to the sludge in the settler to adjust the Sz: F ratio. If the weight ratio Sz: F is greater than 1 l, the viscosity of the slurry increases, the formation of calcium hydrogranate slows down, and the alkali yield is reduced; this leads to known phenomena: the heat exchanger surfaces are clogged and the alkaline losses have to be replaced with fresh caustic soda. If the ratio by weight of Sz: F is less than 1: 2.2, less than 350 g / l of NajO, the concentration in the digestion loop is reduced, thereby accelerating the decomposition of the calcium hydrogranate; the negative effects mentioned above.

If the concentration of the alkali solution is less than 90 g / l R ₂ O (R: K or Na) or the slurry is kept for less than 10 25 hours and the temperature of the slurry is above 100 ° C, calcium -hydrogranate decomposes, yield of R ₂ O decreases, heat exchangers become clogged and alkali losses occur. Concentrations of 100 g / l R ₂ O in the alkaline solution and heat storage for longer than 24 hours have similar consequences.

The results obtained under laboratory conditions have also been confirmed by semi-industrial experiments on the hydrochemical processing of various red sludges (Medvedev VV, Rajzman VL, Malc N. Sz., Tihonov NN: 35 " GR 0183.0026611, VAMI 1986). It has been proven that 40 times the limestone is passivated during the continuous mixing of the slurry due to the formation of aluminum-calcium hydrogranate. During the semi-industrial studies, no significant deposits were observed when the raw material and the alkaline solution were heated separately, although these are common under the conditions of processing the bauxite in an autoclave.

In the process of the invention, the heat exchangers did not have to be replaced due to deposition during five test cycles. A further advantage of the process is that fresh caustic soda is not used to compensate for alkali losses due to the removal of potassium from the system prior to digestion.

The crushing of the raw material in alkaline solution is known in hydrochemical processes (Szazsin V. Sz.

"New Hydrochemical Processes for Aluminum Production," Kiev, 55 Nauk. Dumka 1979,208. and Bayer alumina production (Malc, N., "Autoclave Exploration of Bauxites" - M. Metallurgy, 1980, 80).

The process according to the invention differs from the known processes in that the R ₂ O concentration is 60

90-110 g / l (R is K or Na), as opposed to 200-300 g / l used in the Bayer process and 300-350 g / l used in the hydrochemical process. This allows the hydrogranate to form and dissolve all the alkalis. Another difference is the Na ₂ O: Al ₂ O ₃ molar ratio which is 5.65-8.4-1 in the process according to the invention (1.5-1.7: 1 in the Bayer process and 10-14: 1 in the hydrochemical process). A new element is the sedimentation of the slurry before digestion and the adjustment of the moisture content of the slurry to a weight ratio of Sz: F to 1: 2.1-2.2. The heat retention of the slurry to be explored is also a new feature.

example

100 kg of Nephrine is subjected to the following hydrochemical treatment:

^ SiO Crowd% 43.8 A1 ₂ O ₃ 27.9 r ₂ o 16.3 CaO 1

(16.31% R ₂ 0: 12.91% Na ₂ O and 5.11% K ₂ O).

The following calculation parameters are introduced for numerical comparison:

The Caustic Module of the Retro-Alkaline <\ = 30 for the Aluminum Alloy 0 ^ = 11 (the Caustic-Module Number can be determined as follows:

NajOug / dm ³ x 1.645)

A1 ₂ O ₃ g / dm ³

CaO / SiO ₂ molar ratio: 1.07

Na ₂ O / SiO ₂ molar ratio (in sludge, after digestion): 0.5 concentration of caustic alkali (in digestion loop):

n = 350 g / l R ₂ O (calculated as Na ₂ O); efficiency of dissolution of A1 ₂ O ₃ : 90%, active CaO content of calcined lime: 1001%,

Digestion temperature: 230 'C.

Processing by the Known Method The nephelite is ground in a retooled alkali, the resulting alkaline nepheline slurry is mixed with the lime, and the slurry is fed without preheating to an autoclave or tubular reactor for digestion. Also, potassium lye in solution during digestion promotes the carbonation of the alumina, which is undesirable because it causes a loss of maize broth according to the following equation:

Na ₂ O (K ₂ O) ₂ + CO -> Na 2 CO ₃ (K ₂ CO ₃₎

If the molar ratio K ₂ O: Na ₂ O is 1: 1 and the K ₂ O content of nepheline is 5.11%, the amount of caustic soda used to compensate for the loss of alkali is 8.5 kg per 100 kg of nepheline.

Processing according to the invention The lime is inoculated with an alkaline solution of 90-110 g / l R ₂ O. The amount of lime used is 42.8 kg. Calculate the amount of alkali solution required (so that the Na ₂ O: Al ₂ O ₃ molar ratio is between 5.75 and 8.4) as follows:

HU 203 853 Β

27.9 (5.75 + 8.4) -12,9.0,2

V = 1.59 + 2.58 m ³ + 100 (0.2 = Na ₂ O dissolution coefficient when K ₂ O is obtained at 100%). The resulting calcareous slurry was ground with 100 kg of nepheline and the resulting slurry was kept at 100 ° C for 10 hours, during which time the alkaline yield was 37%.

In the alkaline phase, the molar ratio of Na 2 O 4 to O 8 is 5.75, and the weight ratio of liquid to dry matter in the sedimented slurry is 2.9: 1. A portion of the sediment was filtered and the resulting 0.104 m ³ filtrate (alkaline solution) was removed from the system. By mixing the filter cake and the sedimented slurry, 156.54 kg of material with a liquid to dry weight ratio of 2.1: 1 are obtained.

The caustic potash basically passes completely into the effluent from the settler and into the filtrate, and from there it can be recovered and sold as alkali.

Working similarly to the above, but changing the parameters within the required range, the results of Table 1 were compiled.

Table 1

Influence of the parameters set according to the invention on the fresh NaOH consumption per 100 kg of nepheline and on the antifouling life of the heat exchangers

Parameter Capacity of heat exchangers (days) Fresh NaOH consumption (kg) per 100 kg nepheline O ₂ concentration in g / l 80 15 5.1 90 30 no 100 '30 no 110 30 no 120 4 no Na ^ OA ^ Og molar ratio 5.5 12 4.9 5.75 30 no 7 30 no 8.4 30 no 9 30 no Heating time (hours) 5 13 3.6 10 30 1.2 15 30 1.0 20 30 0.7 24 30 no 28 30 no

Parameter Capacity of heat exchangers (days) Fresh NaOH consumption (kg) per 100 kg nepheline The temperature ('C) 80 20 8.0 90 30 no 95 30 no 100 30 no 110 4 no Slurry liquid to solid ratio (weight) 2.0 30 - no 2.1 30 no 2.15 30 no 2.2 30 no 2.3 30 no

By comparison, the heat exchangers, according to the known procedure, are full of deposits within 3 days and the fresh NaOH consumption per 100 kg of nepheline reaches 8.5 kg.

It can be seen from the table that the parameters highlighted according to the invention strongly influence the fresh NaOH utilization, and more particularly the deposition of heat exchangers. The life of the heat exchangers increases from 3 days to more than 30 days.

Compared to the known process, the useful result for producing 1 tonne of alumina is to reduce the energy requirement by 10% by saving 0.045 tonnes of caustic soda and preheating the slurry.

Claims (1)

³⁵ PATENT CLAIMS A process for the preparation of sodium and potassium aluminates by hydrochemical processing of aluminum silicate-containing raw materials by crushing the raw material, mixing with lime, digesting at a temperature of at least 230 ° C, separating the sludge, and sodium or potassium aluminate. recovering the warmed returlúgot, with plate with reference to the crushing of the raw material R ₂ O 90-110 g / 1 concentration is used lú45 goldatot-R is sodium or potassium atom -, alkali solution of Na ^ / A ^ Og molar ratio of 5.75 to 8 Is set to 4, and the slurry is kept at 90100C for 10-24 hours, then sedimented if the sedimented slurry is a solid The weight ratio of 50 is different from 2.1-2.2: 1, the weight ratio is adjusted to 2.1-2 / 2: 1 by filtration, the sedimented slurry is heated to the digestion temperature and the alkaline solution is recycled to crude crushing.