JPH07204411A - Method for decontaminating hydrochloric acid aqueous solution containing ferric chloride as main solute - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to decontamination of an aqueous hydrochloric acid solution containing ferric hydroxide as a main solute, and removal of silicic acid by neutralization, precipitation and separation of iron hydroxide formed thereby. The purpose is to provide a method of doing. The main feature of the present invention is that ferric hydroxide sludge is concentrated and a part, preferably a large part, of the deposit of the concentrator is recycled to the precipitation vessel.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for decontaminating an aqueous hydrochloric acid solution containing ferric chloride as a main solute.
A method of removing silicic acid by neutralizing, precipitating and separating iron hydroxide formed thereby, which has absorbed most of the silicic acid and other contaminants if applicable. It relates to a decontamination method in which the free hydrochloric acid still present in the solution is preferably neutralized with scrap and the iron is predominantly precipitated in the form of divalent iron hydroxide by the addition of alkaline substances.

[0002]

2. Description of the Related Art Several methods are known, for example AT-SP3.
Known from 80,675, these processes oxidize ferric hydroxide to ferric hydroxide following precipitation. This may be done by galvanic electrolysis according to this Austrian patent specification or by blowing compressed air into a suitable container. The drawback is that it produces a large amount of sludge and, as a result, the corresponding F
This is the loss of eCl ₂ . This further entails high equipment costs for additional electrolysis or compressed air plants.

[0003]

The object of the present invention is to eliminate these disadvantages of the prior art.

[0004]

SUMMARY OF THE INVENTION The features of the present invention include concentrating a precipitated deposit, which is composed primarily of ferric hydroxide sludge, and returning the deposit resulting from the enrichment process to a precipitation vessel. is there. In this context, the ferric hydroxide is preferably precipitated in a manner known per se, the precipitated ferric hydroxide absorbing most of the silicic acid and, if applicable, some of the other contaminants. However, sludge that is highly absorbent of these contaminants and is preferably almost saturated is removed. This procedure maximizes the sludge absorptive effect, resulting in minimal sludge output and precipitant consumption. Furthermore, the purity of the spent pickling liquor can be essentially increased. By recycling the condensor deposits in accordance with the present invention, the sludge absorptive effect can be further enhanced, thus providing a higher degree of desiliconization or decontamination. Moreover, the sludge yield as well as the amount of precipitant required is substantially reduced. Furthermore, compared to known methods, FeCl ₂ losses are substantially reduced due to the smaller amount of sludge dumped.

An advantageous further development of the inventive idea is that the weight ratio of recycled material discharged from the concentrator is in the range of about 20: 1 to about 1: 1 and preferably about 10: 1. : 1. This recycling ratio of sludge from the concentrator makes it possible to optimize the absorption effect of the sludge, the maximum absorption effect being dictated by the destruction of the sludge mass and the resulting reduction of the separating power. In practice, for safety reasons, the actual operating point is slightly offset from the optimum point. Another particularly advantageous embodiment of the process according to the invention is characterized in that the precipitation is carried out for a residence time of at least 60 minutes, preferably up to 90 minutes. In this way, the impurities in the starting solution are optimally precipitated and absorbed on the iron hydroxide sludge,
Nevertheless, due to the omission of the subsequent oxidation, the total residence time is 2
It is reduced by a factor of 1 to 3.

The present invention will be further described by way of examples with reference to the accompanying drawings. FIG. 1 is a flow chart of a plant according to the prior art, and FIG. 2 is a flow chart of a plant for carrying out the method of the present invention.

The starting solution contaminated with silicic acid, in particular the used pickling solution, is led from the storage tank 1 to the scrap dissolution tower 4 via a duct 2 (where a pump and heater can be optionally installed). It is also possible to operate a plurality of scrap melting towers in parallel. The melting tower 4 is preferably supplied with scrap iron 5 on the one hand and steam 3 on the other hand. The neutralized solution is then introduced via duct 6 (optionally equipped with a pump) into a precipitation vessel 7 with a stirrer 8. To this vessel is added an alkaline solution such as a 25% NH3 solution and stirring is carried out for a residence time of up to 60 minutes to precipitate ferric hydroxide. This alkaline solution is introduced into an oxidation container 11 having a stirrer 12 via a duct 10 (first
The compressed air required for oxidation is introduced via duct 13. The formed ferric hydroxide is passed through the (overflow) duct 14 together with the residual solution, and the post-curing container 15
(With a slowly operating stirrer 16).

After a residence time of about 20 to 60 minutes, the solution, together with the ferric hydroxide formed, is led via the duct 17 to the feed pipe 19 of the concentrator 20 and to the feed pipe 19 through the duct 18. A coagulation aid is then metered in. Overflow 21
Is led directly to a storage tank 26 of desiliconized solution or used pickling solution. The precipitated ferric hydroxide sludge containing contaminants consisting of silicic acid and other contaminants,
It is led to a filter press 23 via a duct 22 equipped with a pump (not shown). Filter press 23
Similarly, the filtrate is led to the storage tank 26 of the desiliconized solution via the duct 25. The ferric hydroxide sludge containing contaminants is then directed to dump 24.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 2, there is shown a flow diagram of the method of the present invention. The same reference numerals as in FIG. 1 have been used for equal parts of the device. As can be seen from FIG. 1, the precipitation takes place in the vessel 7 for a residence time of more than 60 minutes, preferably up to about 90 minutes, and the precipitation vessel 7 to the duct 10
A slightly alkaline suspension of ferric hydroxide passing through
The duct 18 mixes directly with the flocculation aid. The same type of flocculant as in conventional methods can be used.

Essentially second with silicic acid and other contaminants
The part of the deposit consisting of iron hydroxide sludge is in duct 2
It is pumped into the precipitation container 7 via 7. With the newly precipitated ferric hydroxide, most of the silicic acid or SiO ₂ contained therein is absorbed on the recycled deposits. The recycled portion of ferric hydroxide is adjusted to approximately reach the sludge absorption limit for pollutants. Therefore, S in iron oxide obtained in a later known step (hence not described in detail), for example, a spray culture step
The amount of iO ₂ can be significantly reduced, in which respect the amount of precipitating agent to be added, for example NH ₃ , and the amount of sludge to be dumped, constitutes a particular advantage of the process according to the invention. is doing.

[0011]

The method according to the invention is compared with the known method with reference to a plant having a treatment capacity of a pickling solution of 10 m ³ / hour. Known method Method of the invention Consumed pickling solution (m ³ / h) 10 10 Neutralized pickling solution (m ³ / h) 10 10 NH ₃ aqueous solution for neutralization of free HCl (Kg / 62) 62 62 Aqueous solution of NH ₃ for Fe (OH) ₂ precipitation (Kg / h) 123 12 Sludge recycled from the concentrator to the precipitation vessel (m ³ / h) −2 Volume of filter press (m ³ / h) 2 0.2 Filter cake for disposal (Kg / h) 390 39 Loss of FeCl ₂ by filter cake (Kg / h) 70 7 SiO _{2 in} iron oxide (max, ppm) 100 60

[Brief description of drawings]

FIG. 1 is a flow diagram of a conventional plant.

FIG. 2 is a flow diagram of a plant for carrying out the method of the present invention.

[Explanation of symbols]

 1 ... Storage tank 2 ... Duct 3 ... Steam 4 ... Scrap melting tower 5 ... Scrap iron 6 ... Duct 7 ... Precipitation vessel 8 ... Stirrer 9 ... Alkali Solution 10 ... Duct 18 ... Duct 19 ... Supply pipe 20 ... Concentrator 21 ... Overflow 26 ... Storage tank 25 ... Duct 23 ... Filter press 24 ... dump

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Brigitta Wasserwauer Austria, A-1230 Vienna, Lehomathhauser Gasse 18-24 / House 5 (72) Inventor Dietfried Gamsligler Austria, A-2700 Wiener Neustadt, Parse Fargasse 10

Claims (4)

[Claims] 1. A method for decontamination of an aqueous hydrochloric acid solution containing ferric chloride as the main solute, formed thereby to absorb most of the silicic acid and other contaminants when applicable. A method of removing silicic acid by neutralizing, precipitating and separating iron hydroxide, wherein free hydrochloric acid still present in the starting solution is neutralized, preferably with scrap, by addition of an alkaline substance. In a method for precipitating iron in the form of predominantly divalent iron hydroxide, the precipitated deposit, which is composed mainly of ferric hydroxide sludge, is concentrated and the majority of the deposit resulting from the enrichment process To the precipitation vessel, and a method for decontaminating an aqueous hydrochloric acid solution containing ferric chloride as a main solute. 2. The weight ratio of recycled material discharged from the concentrator is in the range of about 20: 1 to about 1: 1 and is preferably 10: 1. The method for decontaminating an aqueous hydrochloric acid solution according to 1. 3. The concentrated ferric hydroxide sludge obtained from the effluent of the enrichment step is preferably filtered.
The method for decontaminating a hydrochloric acid aqueous solution according to claim 1 or 2, wherein the method is carried out by filtering in a press. 4. The method for decontaminating an aqueous hydrochloric acid solution according to any one of claims 1 to 3, wherein the precipitation is carried out for a residence time of at least 60 minutes, preferably 90 minutes at the maximum.