RU2228904C1 - Coarse aluminum hydroxide production process - Google Patents

Abstract

FIELD: inorganic compounds technology. SUBSTANCE: process comprises decomposition of aluminate solution, two-stage separation of hydrate slurry in centrifugal field into coarse and fine fractions, wherein, in the first stage, hydrate slurry is mixed with clarified mother solution and, in the second stage, fine fractions are levigated. EFFECT: enabled regulation of aluminum hydroxide product fineness by changing granulometric composition of starting material. 2 cl, 1 dwg, 1 tbl

Description

The invention relates to alumina production. In the known method [1], coarse-grained material is obtained from a polydisperse sludge by hydroclassification and washing in a column type apparatus, which is equipped inside a packet of gratings and concentrically arranged cones. Hydroclassification and leaching of sediment is carried out according to the principle of countercurrent in a pulsating mode. The classified suspension is fed from above into the apparatus, and the washing liquid is supplied under the lower horizontal grate of the column. Under the influence of gravitational forces, the sediment moves down, filling the entire cross section of the apparatus, and a pulsating flow of washing liquid moves up towards it. When liquid passes through the openings of the gratings, a dense layer of sediment is weighed, fine fractions of the sediment carried out upward with the solution are washed out, and larger sands washed down into the discharge cone are washed. In the described example, the pulsation frequency was 0.4 s ^-1 , the amplitude was 12-14 mm.

The disadvantages of this method of hydroclassification-washing sediment include:

- the probability of dilution of the mother liquor, which will be difficult to avoid when achieving a good washing of the precipitate;

- the need to equip the column with a reliable pulsator. When the pulsator stops for a short time on aluminum hydroxide, which is related to rapidly stratifying sediments, one cannot avoid clogging a large apparatus over its entire height.

A known method of producing aluminum hydroxide from aluminate solutions used in most alumina refineries [2], including decomposing the aluminate solution by twisting to obtain a precipitate of aluminum hydroxide of a polydisperse composition and the mother liquor, separating the hydrated suspension by size in a hydroseparator (HS), followed by separate dehydration of the upper and lower separation products. The top product - GS discharge - is sent to sedimentation of the suspension and clarification of the mother liquor in the thickener. The thickened hydroxide precipitate is filtered off on vacuum filters and then used as a seed in the decomposition of the aluminate solution. The mother liquor in some cases undergoes control clarification. The lower product of the HS is also filtered off with vacuum filters, part of the production hydroxide is taken from it and sent to the washing from the mother liquor.

In the considered method of separation of the suspension in the HS is ineffective. The low efficiency of separation of sediment by size in a gravitational field is explained by the uneven upward velocity in the cross section of the apparatus. The turbid stream of the liquid phase, rushing upward in the form of a “wandering” channel with a relatively small cross-sectional area, also captures large particles. Therefore, the size of the sediment in the sink and sand of the horizon is little different.

A known method of producing aluminum hydroxide from aluminate solutions of sintering technology [3], including decomposition of the solution to obtain a precipitate of aluminum hydroxide of a polydisperse composition and a mother liquor, separation of the hydrated suspension by size in hydrocyclones (HZ), followed by separate dehydration of the upper and lower products on vacuum filters hydroclassifications. The top product of the HC, which contains a finely dispersed precipitate, is sent first to preliminary sedimentation - thickening the suspension and clarifying the mother liquor in the thickener. The filtered precipitate is then used as seed for the decomposition of the aluminate solution. After filtration, the lower HC product is the production part of the hydroxide, which is subjected to washing from the mother liquor before calcination.

The main disadvantages of this method are the low separation efficiency in conventional HZs according to the required size class (-40 μm ≤10-12%), as well as the inability to maintain a given sludge size when changing the composition of the decomposition product. This is also due to the high content of solid separable suspension (300-500 g / l).

According to most common features, the last of the considered methods is taken as a prototype.

An object of the present invention is to increase the efficiency of hydroclassification and obtain production aluminum hydroxide of a given size with the possibility of its regulation with a change in the particle size distribution of the initial product.

The technical result is achieved by decomposing the aluminate solution, separating the hydrated suspension in a centrifugal field into coarse and fine fractions, their separate dehydration, clarification of the mother liquor. The separation of the hydrated suspension in a centrifugal field into coarse and fine fractions is carried out in two stages with mixing in the first stage of the hydrated suspension with a clarified mother liquor and elutriation of fine fractions in the second stage, as well as by the fact that the clarified mother liquor is in an amount of 0.1 -0.3 parts of the total flow rate is introduced into the hydrated suspension before feeding it to the first separation stage.

When implementing this method, increasing the separation efficiency is achieved by hydroclassification in a centrifugal field of 2 devices paired in series. The thickened coarse fractions with the remainder of the finely dispersed, which did not have time to separate in the first stage, are picked up by a stream of clarified mother liquor and are subjected to repeated centrifugal hydroclassification - elutriation. In the case of a high solid content in the initial hydrated suspension, part of the clarified mother liquor can also be brought into suspension before the 1st hydroclassification. By redistributing the flow rate of the mother liquor, the required coarseness of coarse-grained aluminum hydroxide is achieved regardless of the change in the particle size distribution of the precipitate in the initial suspension. In addition, the elutriation of fine sediment by the mother liquor does not change the concentration of the liquid phase of the suspension, which is important for the decomposition process.

To implement this method can be applied, for example, a paired vortex cyclone (CC) (drawing). With a large flow, cyclones collect in the battery [4]. A vortex cyclone consists of a vortex attachment 1 paired in series (cyclone with a reverse cone) and a conventional hydrocyclone 2, as well as 6 fittings for supplying a suspension 3 and a mother liquor 4, a connecting 5 outlet of the upper drain with a vortex attachment 6 and a hydrocyclone 7, as well as sand from under the hydrocyclone 8. The CC is paired with a thickener 9, a combined mixer 10 for receiving clarified solution and a pump 11.

Hydroclassification is carried out in two stages - in the swirl prefix 1, where the hydrated suspension from the “tail” decomposer or carbonizer (stage 1) is directed under pressure through the nozzle 3, and hydrocyclone 2 due to the supply of the clarified mother liquor under pressure through the nozzle 4 (2- I'm stage). The fine fractions that have slipped through the sands of the vortex prefix are wound off in a hydrocyclone by the flow of the mother liquor. By changing the flow rate of the hydrate stream (pressure at the inlet of the CC) and the mother liquor, the necessary degree of hydroclassification can be achieved, that is, to obtain the production hydrate in the sands of the hydrocyclone of the required size. The classified fine hydroxide fractions - the two upper discharge of the CC - are sent to the thickener to separate the seed and clarify the mother liquor.

The example below shows the experimental data on the hydroclassification of aluminum hydroxide in the experimental model CC ⌀ 150 mm and in industrial conditions on the hydrocyclone ⌀350 (GC).

Example. The hydrated suspension obtained after decomposition of the aluminate solution was subjected to separation in a centrifugal field of a vortex cyclone (CC) into coarse and fine fractions. The separation was carried out in two stages with mixing at the 1st stage in a vortex attachment of a hydrated suspension with a clarified mother liquor at various costs and elutriation of fine fractions at the 2nd stage in a hydrocyclone. The separated large and small fractions were sent for separate dehydration and clarification of the mother liquor. For comparison, the same hydrated suspension was subjected to single-stage separation in a centrifugal field of a conventional hydrocyclone. The separation results are shown in the table.

As can be seen from the above data, the efficiency of hydroclassification on the CC compared with the GC ⌀ 350 mm is obvious: 85-89 against 59.8% fr. - 45% is beaten to the top separation product.

Sources of information

1. Russian patent No. 2019296 (C1, 5 V 03 V 5/62) Classifier column, 1989.

2. A reference metallurgist on CM "Alumina Production". M .: Metallurgy, 1970, p. 108-110.

3. Liner A.I., Eremin N.I., Pevzner I.Z., Liner Yu.A. Alumina production. M .: Metallurgy, 1978, p. 191-192.

4. Tapio Keskisaari, Twin vortex cyclone improves recovery of fine material 37%. Larox news, N 1, 1990, p. 16-19.

Claims (2)

1. A method of producing coarse aluminum hydroxide, including the decomposition of an aluminate solution, the separation of the hydrated suspension in a centrifugal field into coarse and fine fractions, their separate dehydration, clarification of the mother liquor, characterized in that the separation of the hydrated suspension in a centrifugal field into coarse and fine fractions two stages with mixing in the first stage of a hydrated suspension with a clarified mother liquor and elutriation of fine fractions in the second stage. 2. The method according to claim 1, characterized in that the clarified mother liquor in an amount of 0.1-0.3 parts of the total flow rate is introduced into the hydrated suspension before feeding it to the first separation stage.