CN1038497C - Purification method of ferric chloride hydrochloride solution - Google Patents

Abstract

The present invention relates to a method for purifying an aqueous hydrochloric acid solution containing iron dichloride as a dissolved main component by removing silicic acid by neutralizing, precipitating and separating the generated iron oxide. It is particularly characterized by concentrating the ferrous hydroxide slurry and advantageously returning a major part of the concentrated precipitate to the precipitation vessel.

Description

The present invention relates to a method for passivating an aqueous solution of hydrochloric acid containing iron dioxide as the main component of the solution by neutralizing, precipitating and separating the ferric hydroxide formed, which absorbs the silicic acid Most and optionally some of the other impurities, free hydrochloric acid still present in the raw solution, are preferably passivated with scrap iron, and the iron, which is present mainly in the form of divalent ferric hydroxide, is precipitated by addition of alkaline substances.

A number of methods are known, eg in AT-PS380675, for the oxidation of ferrous hydroxide to ferric hydroxide immediately after precipitation. The method is carried out according to AT-PS by direct current electrolysis or by blowing compressed air into corresponding containers. The disadvantage is that a large amount of formed precipitates leads to a corresponding loss of _FeCl2 . Yet another disadvantage is the high equipment outlay for additional electrolysis or compressed air equipment.

The present invention now overcomes these disadvantages and is characterized in that the resulting precipitate is concentrated to a maximum part consisting of a ferrous hydroxide slurry and advantageously the main part of the concentrated precipitate is returned to the settling vessel. The ferrous hydroxide is therefore preferably precipitated by known methods and the precipitated ferrous hydroxide adsorbs most of the silicic acid and if necessary some other impurities, the solubility of the impurities in these drained slurries preferably being high enough to approach saturation. Optimum utilization of the slurry adsorption effect, ie minimum slurry production and minimum precipitant consumption, can be achieved by this method. As a result, the cleaning purity can also be significantly increased. The return of the concentrated precipitate according to the invention can also increase the adsorption efficiency of the slurry and thus also achieve a higher degree of desilication or purity. This also significantly reduces the amount of slurry produced and the amount of precipitant required. The loss of _FeCl2 is reduced due to the low amount of slurry present compared to known methods.

An advantageous further development of the invention is characterized in that the return by weight ratio of concentrate to discharge is in the range from about 20:1 to about 1:1, preferably about 10:1. The adsorption efficiency of the slurry is controlled to an optimum value by returning a portion of the slurry from the concentrator, wherein the maximum value and thus the minimum separation capacity are determined by breaking up the precipitated mass. In practice the actual production point is far from this optimum for safety reasons.

A particularly suitable further development of the process according to the invention is characterized in that the precipitation is carried out with a residence time of at least 60 minutes, preferably a maximum of 90 minutes. This achieves optimum precipitation and adsorption of the impurities in the raw solution by the ferric hydroxide slurry, and also reduces the overall residence time by half to one third by omitting subsequent oxidation.

The invention is now illustrated with the aid of the accompanying drawings, in which:

Fig. 1 is the equipment flowchart of prior art;

Fig. 2 is a flow chart of equipment implementing the method of the present invention.

The stock solution containing silicic acid impurities (especially pickling) is introduced from the storage tank 1 into the scrap iron dissolving tower 4 through the pipeline 2 (pumps and heaters can also be installed if necessary). Multiple scrap iron dissolving towers can be operated in parallel. Iron filings 5 are fed into one side of the dissolution tower 4 and steam 3 is introduced into the other side. The purified solution is then introduced via line 6 (with pump if necessary) into precipitation vessel 7 with stirrer 8 . A basic solution 9, such as 25% _NH3 solution, is added to the vessel and stirred for a maximum of 60 minutes during the dwell period, in which ferrous hydroxide precipitates. An alkaline solution is fed via line 10 to an oxidation vessel 11 with a stirrer 12 . The compressed air required for oxidation is introduced via line 13. The ferric hydroxide formed is led together with the remaining solution via (overflow) line 14 into post-ripening vessel 15 with slow stirrer 16 .

After a residence period of about 20 to 60 minutes, the solution containing the ferric hydroxide precipitate formed is introduced into line 17 (to which flocculation aid is added via line 18 ) and into conduit 19 of concentrator 20 . The overflow precipitate 21 is directly passed into the storage tank 26 of the desiliconization solution or pickling solution. The precipitated ferric hydroxide slurry containing silicic acid impurities and other impurities as required is introduced into a filter press 23 through a line 22 equipped with a pump (not shown). The filtrate of the filter press 23 is also introduced via line 25 into a storage tank 26 for the desiliconization solution. The ferric hydroxide slurry containing impurities is then sent to the waste dump 24 .

A flow chart of the method of the invention is illustrated in more detail in FIG. 2 . For similar equipment the same basic notation corresponding to Figure 1 will be chosen. The difference from FIG. 1 is that the precipitation is carried out in the vessel 7 with a residence time of more than 60 minutes to preferably at most about 90 minutes, and the flocculation aid is incorporated directly via the line 18 into the weakly alkaline subhydroxide from the line 10 of the settler 7. in the iron suspension. The same type of flocculants as used in hitherto known methods can be used.

From the concentrator 20, part of the precipitate is pumped back to the precipitator 7 via line 27, wherein the precipitate mainly consists of ferrous hydroxide slurry containing part of silicic acid and other impurities. Most of the silicic acid or _SiO2 contained is adsorbed on the returning precipitate together with the freshly precipitated ferrous hydroxide. Regulate the ferrous hydroxide slurry of returning part in this way, promptly reach the limit of slurry adsorption impurity almost. In this way, the _amount of SiO in the iron oxide obtained by subsequent process steps which are known per se and are therefore not explained in more detail here, for example in the atomized iron corona roasting (sprührōst) method or similar methods, can be significantly reduced. reduction, wherein a particularly small amount of precipitating agent such as NH ₃ needs to be added and the slurry present in a particularly small amount is a particular advantage of this method.

In the following, the known method is compared with the method according to the invention using a plant with a quantity of corrosive acid of 10 m ³ /h. (see post)

Pickling solution (m ³ /h)

Passivated corrosive acid (m ³ /h)

Aqueous _NH3 solution for neutralizing free HCl (kg/h)

Aqueous NH ₃ solution for Fe(OH) ₂ precipitation (kg/h)

Slurry returned from concentrator to precipitator (m ³ /h)

Pressure filter vessel (m ³ /h)

  Filter cake for waste removal (kg/h)

FeCl ₂ lost from filter cake (kg/h)

_SiO2 (ppm max) in iron oxide known method method of the invention

10 10

10 10

62 62

123 12

… 2

2 0.2

390 39

70 7

100 60

Claims (5)

1. neutralize by contacting hydrochloric acid with scrap iron, separate and remove silicic acid to purify the method for the hydrochloric acid aqueous solution containing iron dichloride as main solute after the ferric hydroxide precipitation of generation, the ferric hydroxide adsorption of described generation is large Partial silicic acid in which the free hydrochloric acid also contained in the stock solution is neutralized with scrap iron and the iron is precipitated mainly in the form of divalent ferric hydroxide by addition of ammonia, characterized in that the precipitate constituting the main part of the ferrous hydroxide slurry The material is concentrated and a portion of the precipitate from the concentration step is returned to the settling vessel, whereby the weight ratio of return from the concentrator to drain is between 20:1 and 1:1, and settling takes place with a residence time of at least 60 minutes. 2. A method according to claim 1, characterized in that the weight ratio of return to discharge from the concentrator is 10:1. 3. The method according to claim 1 or 2, characterized in that: the concentrated ferrous hydroxide slurry drained by concentration is filtered in a pressure filter. 4. The method as claimed in claim 1 or 2, characterized in that the precipitation is carried out with a residence time of a maximum of 90 minutes. 5. The method as claimed in claim 3, characterized in that the precipitation is carried out with a residence time of a maximum of 90 minutes.

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