DE2053334C3 - Process for the production of pure selenium from decuppered anode sludge - Google Patents

Description

z. B. Ag ₂ SO ₄ + Se -v 2 Ag + SO, + SeO ₂ (3)

The invention relates to a process for the production of pure selenium from copper-free Anode sludge, in which the anode sludge sulphates to release selenium dioxide and sulfur dioxide roasted and then by conversion of the released selenium dioxide and sulfur dioxide in dilute sulfuric acid precipitates pure selenium at a lower temperature than the roasting temperature will.

In contrast to alkaline roasting, sulfating roasting can be done with the appropriate procedure and combination with a selenium precipitation provide pure selenium in the first step. the However, this sulfating roasting was previously used due to the high level of effort involved in manual roasting Work limited to smaller amounts of anode sludge. In addition, so far with the technical Realization difficulties, partly due to the discontinuous procedure are.

Since the possibility of sulphating roasting in the first process stage is a practical one Obtaining completely pure selenium, which makes this process extremely attractive, has been sought after sought to redesign the process of sulfatizing roasting so that it is not susceptible to malfunction and became applicable for arbitrarily large throughputs.

In the known sulphating roasting process, which is more concentrated with an excess of Anode sludge mixed with sulfuric acid was brought into a roasting furnace in flat crucibles and added there Roasted at 300 to 600 ° C. During the roasting reaction, it is formed either as elemental or as selenide present selenium after

Se + 2 H ₂ SO ₄ ^ = SeO ₂ + 2 SO ₂ + 2 H ₂ O (1) or for example

Ag ₂ Se + 4H ₂ SO ₄ -y SeO ₂ + Ag "SO, + 3 SO, + 4 H..O

Selenium dioxide, which together with vaporous sulfuric acid, formed sulfur dioxide and what-The resulting SO ₂ is no longer sufficient to precipitate the selenium after reaction (1). Since the circulatory acid is enriched with sulfuric acid during the process, sulfuric acid must be released from time to time in order to maintain the optimal sulfuric acid concentration of 8 to 15 ° / »in the circuit. This usually happens at the end of the batch when the acid contains selenium dioxide. This selenium must then be used in a special process, e.g. B. can be removed by cementation with copper powder or precipitation with SO _2. In Fig. 1, SO ₂ and SeO ₂ contents of the circulatory acid are shown schematically as a function of the roasting time, the position of the passage of the curve through the time axis depending on the temperature control in the roasting oven. In practice it has been shown that shortly before and after this time the selenium is not only precipitated in the sedimentation vessel, but also in the circulation pump, which circulates the sulfuric acid, and in the connecting pipes. A layer of selenium grows on the inner walls of the pipe and in the channels of the pump impellers, which means that these units clog within a very short time towards the end of the batch, so that time-consuming cleaning work is often required and the process has to be interrupted. The invention is based on the object of creating a method of the type specified at the outset, in which such disturbances and their disadvantages are excluded and which can be carried out simply and with less effort.

This is achieved according to the invention in that by continuous or batchwise introduction appropriate amounts of the anode sludge and sulfuric acid during the process both in sulphating roasting and in the implementation of what is released during roasting Selenium dioxide and sulfur dioxide in the dilute sulfuric acid are always in excess Sulfur dioxide is maintained. Because of the aui this way throughout the process Existing permanent excess of sulfur dioxide will be disturbances by clogging avoided in the sulfuric acid cycle. The circulatory sulfuric acid only contains during de; Dissolution process dissolved selenium dioxide, so that within a few seconds all of the selenium falls is and at any point in time selenium dioxide

3 4

free sulfuric acid is released from the settling tank. The de-selenized roasted food is through a can be. This eliminates the need to discharge into lock 3 from the roasting oven. The in a special operation, the selenium dioxide to selenium roasting furnace 2 resulting gaseous reaction process to reduce. The continuous process products pass through a dust pavement heated to around 350 ° C In addition, the use is much smaller 5 settling chamber 4 and get ir, a spray chamber Apparatus with constant throughput. Wemer 5. In the spray chamber, the arrivals will remain the energy, labor and investment of the gases on the temperature of the in the spray effort greatly reduced, dilute sulfuric acid injected into the chamber

The method according to the invention is cooled by hand, as a result of which the above-mentioned reaction (1) of the drawing of an exemplary embodiment of an anio runs from right to left. Acid and reaction situation for its implementation and a numerical product flow into a settling tank 6. An example of the process itself is explained below. bubble 7 draws in non-condensable gases (SO ₂ , false

F i g. 1 shows a diagram that schematically shows the air) from the settling tank, the negative pressure SO ₂ - and SeO. 15 and the dust settling chamber 4 in the roasting furnace 2 represents a hazard; forms a slight negative pressure, which causes the leakage

F i g. 2 is a diagram that _{prevents the constant SO 2} - animal gases. A centrifugal pump 8 is used

Content of the circulatory acid according to the invention chä- to maintain the sulfuric acid cycle and against

characterizes; if necessary to promote the deposited selenium in

F i g. 3 illustrates a flow diagram of a plant 20 a filtering device.

to carry out the method according to the invention. 4 to 6 shown execution

manure; The form of the anode sludge and the acid

F i g. 4 is a longitudinal section through a schematically brought over the lock 1 into a roasting oven 2 ″,

Illustrated embodiment of a roasting oven for through which the roasted material with three shafts 10 of the

Use in the method according to the invention; 25 agitator 9 "attached claw arms 11 for

5 is the top view of the representation of the item 3 being transported. By appropriate position

according to Fig. 4, whereby the upper housing part wcggclas- lation of the Krälarmschaufeln can control the movement of the

sen is; Roasted food through the oven in the indicated in Fig. 5

Fig. 6 is a sectional view taken in the Lime AA th manner;

in Fig. 4. 30.

The characteristic of the method according to the example

As an example, the sulphating roasting of a practically constant SO ₂ content of the circulating acid, decuppered anode sludge is described, which is shown in FIG. 2. The practical implementation wa 19%> selenium (bound as selenide) contained. A roasting oven of this type, which is shown in FIG. 3 and has a useful length of 200 cm, will first be explained. The anode sludge is decupperated and has an inner diameter of 70 cm. B. used via a rotary valve 1 in the electrical to carry out the roasting reaction. Brought correspondingly heated roasting oven 2 in which a stirring device F i g. 3 the furnace was equipped with a creamer auswerk 9 for the transport and mixing of the. Partition walls a height of about reaction mixture provides. The sulfuric acid required for the roasting reaction 40 20 cm in the lower part of the roasting oven is either also distributed over a narrow dwell time. The crawler, the rotary valve 1 or a special valve consisted of an axially arranged in the roasting oven and introduced into the roasting oven 2. In order to ensure a shaft on which the flat profiles were attached in such a way that the formed SO., At least for precipitation overall, in addition to the mixing, a weakly promoting selenium was achieved according to the above-mentioned reaction (1) 45 changing function. Sufficient via a PiV system, either the copper-free anode sludge drive is driven, allows the kaleic and sulfuric acid to be continuously adjusted together, or it is simple to control the roasting time. Above zein at an almost constant speed to the filling level, there were pens in the roasting furnace that charge, or sulfuric acid or anode sludge that may have been attached to the claw arms is continuously brought into the 50 strips to crush the roasted material, while anode sludge or sulfur - contribute. The crawler shaft was placed on the furnace in batches. The reaction time of the roasting reaction must be sealed on the inside by mechanical seals, on which the time interval between two batches is small compared to external ropes by means of cooled stuffing boxes. The size is such that with the small number of individual batches prevailing in the furnace, the vacuum (about 200 mm water column) should be kept constant, with practically no air. Under observance of the last two conditions could get into the furnace interior. In all other cases, the charging of sulfuric acid and mentc and apparatus essentially corresponded to decuppered anode sludge, also discontinuously, as shown in FIG. 3 shown.

be made. The roasting reaction runs between the moist, decoppered

see 400 and 600 ° C with a sufficiently large Gc 60 anode sludge 1.5 times its weight

speed, so that one already at 400 ° C and (based on dry matter) of sulfuric acid

a reaction time of 10 hours also then practically (98 ⁰ A)) added. Before using in the roasting oven

table removed all of the selenium from the roasted food, the mixture of anode sludge and sulfur

if, as a comparatively leaky silver acid, it does not exceed itself for less than 2 hours.

selenide is present. If the reaction temperature is 6 ₅ leave. The reaction mixture was then via a

600 ° C, the de-selenization is continuous after about 2 hours with a speed of

the completed. It is assumed that the approx. 25 kg / h (based on the copper-free anode

Sulfuric acid partial pressure kept sufficiently large sludge) brought into the roasting furnace. The electric

Irritation of the furnace was in the axial direction in four divided into ions of the same size, the regulation of which enables the setting of the desired temperature profile in the Oven allows. In the case of the anode sludge present, it was found to be expedient to use the entrance zone to about 350 "C, the other zones to about 450 ° C. The speed of the Krälwerkcs was set so that the average roasting time in the oven was about 10 hours.

The gases formed during the roasting reaction were withdrawn from the oven in the manner described above and after passing through a dust settling chamber taken up in dilute sulfuric acid and brought to reaction at low temperature according to reaction equation (1) (from right to left).

After about 3 hours, calculated from the start of the process, a constant SO ₂ content of about 1.6 g SO. Per liter was reached in the dilute sulfuric acid and maintained over the operating time. The de-selenized roasting material was discharged at the end of the oven via a rotary valve. The constitution of the roasted material could be described as granules with a particle size between about 0.5 and 15 mm. Even during longer periods of operation, in contrast to the known method of operation, no significant accumulation of selenium was found in any part of the apparatus through which dilute sulfuric acid flowed, if one disregards a "selenium" thickness of about 0.1 to 0.2 mm, which, however, is not solid

ίο adhered to the walls and in no way had a disruptive effect.

Due to the constant Rösl conditions, the Degree of lintclenation, as expected, very good. The dust that accumulates in the sedimentation chamber became the Roasting process fed back. With this method of operation, the material balance resulted in a deselination · degree of 99.4 Vn.

The selenium separated from the circulating sulfuric acid in a filter press was washed with hot water in the filter press. The residue on ignition of the dry raw material was 0.045 ¹¹ O.

For this purpose 3 sheets of drawings

Claims (1)

Claim: Process for the extraction of pure beings from decuppered anode sludge, in which the Anode sludge is roasted in a sulfating manner to release selenium dioxide and sulfur dioxide and then by conversion of the released selenium dioxide and sulfur dioxide in dilute Sulfuric acid at a lower temperature than the roasting temperature the pure selenium is precipitated, characterized in that by continuous or batchwise introduction of the anode sludge and the sulfuric acid during the process process both in the sulfating roasting as well as in the implementation of the selenium dioxide released during roasting and sulfur dioxide in the dilute sulfuric acid, there is always an excess of sulfur dioxide is maintained. steam is pumped out of the roasting oven by means of an ejector will. The dilute sulfuric acid, which operates the ejector, receives the gaseous reaction products and cooled immediately to a temperature below 100 ⁰ C temperature. At this low temperature, reaction (1) runs practically instantaneously from right to left, so that elemental selenium is excreted. The precipitated selenium and the sulfuric acid get into a settling tank. In the course of a batch, the ratio of released SO., To SeO _{2 changes} in such a way that initially more SO, is formed than is necessary to reduce the SeO, according to (1), while later so much SeOo is released that the im Recirculated sulfuric acid contains selenious acid. This SeO ₂ probably comes from a slow reaction between sulfates on the one hand and selenium or selenides on the other hand: