AU668313B2

AU668313B2 - A process for working up thin acid

Info

Publication number: AU668313B2
Application number: AU68938/94A
Authority: AU
Inventors: Rene De Clean; Frank Quaeyhaegens; Domien Sluyts
Original assignee: Bayer Antwerpen NV
Current assignee: Kerr-Mcgee Pigments & Co KG GmbH
Priority date: 1993-08-12
Filing date: 1994-08-05
Publication date: 1996-04-26
Anticipated expiration: 2014-08-05
Also published as: DE59409261D1; CA2130212A1; JPH082905A; EP0638515A3; FI943702A0; PL178525B1; AU6893894A; ES2146628T3; PL304612A1; NO942973D0; NO942973L; FI943702A; EP0638515B1; EP0638515A2

Description

I 1L Our Ref: 517548 668313

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT P/00/011 Regulation 3:2 9* 9 9999 99 9 9 9.

.9 9 .9 9099 9999 9 Applicant(s): Bayer Antwerpen N.V.

Haven 507 Scheldelaan 420 B-2040 ANTWERPEN

BELGIUM

DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 A process for working up thin acid Address for Service: Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 A PROCESS FOR WORKING UP THIN ACID This invention relates to a process for working up thin acid from the production of titanium dioxide by the sulfate method.

Thin acid accumulates in the production of titanium dioxide by the sulfate method and, at the present time, is recycled after concentration in several stages.

According to US 3,016,286, ammonia is added to thin acid from the production of titanium dioxide at elevated temperature up to a pH value of about 6. The solid formed (TiO(OH) 2

VO(OH)

2

AI(OH)

3 Cr(OH) 3 is filtered off. The filtrate is oxidized with air at pH 7 to 8, resulting in the formation of an iron-pigment which is also filtered off.

However, the filtrate still contains small quantities of impurities, magnesium and manganese in particular being troublesome in the concentration of the filtrate by evaporation to produce ammonium sulfate.

According to another proposal, thin acid (waste acid) is neutralized with ammonia S 15 in the presence of magnetite nuclei to precipitate iron. Residues of iron are removed after oxidation with air. The solution obtained is laden with impurities so that concentration by evaporation to form ammonium sulfate is barely possible. In addition, the ammonium sulfate would also contain numerous impurities.

According to DE 2 443 942, iron ions are removed from acidic wastewaters by a a S 20 combined oxidation and precipitation process in which a mixture of air and ammonia is delivered to the wastewater. The problems caused by other metal ions which are normally present in the thin acid are not discussed in this document.

According to DE 3 115 937, cations are removed from the thin acid by increasing the pH value in steps by addition of ammonia. The solution obtained can then be concentrated by evaporation. However, the concentration step is extremely difficult to control and the ammonium sulfate obtained contains magnesium as an impurity so that, for example, it cannot be stored.

Accordingly, the problem addressed by the present invention was to provide a process which would enable thin acid from the production of titanium 1:'AT i y PAWpDoC=EriMI75482.

dioxide to be effectively worked up, i.e. above all simply and inexpensively, the useful materials present in the thin acid being converted into a suitable useful form so that they may be put to further uses, According to the invention, this problem has been solved by a process in which the sulfate present in the thin acid is converted into technically pure ammonium sulfate which may be used as a fertilizer.

The present invention relates to a contiruous process for working up thin acid from the production of titanium dioxide by the sulfate method, characterized in that a) in a first step, the thin acid is partly neutralized with ammonia to pH values of 4 to 6 at temperatures above 50°C to the boiling point of the solution and preferably at temperatures of 70°C to 110°C, 15 b) the resulting poorly soluble compounds of the metals titanium, vanadium, chromium, aluminium and, partly, iron from a) are filtered off and the filter cake is optionally washed and further worked up, c) the filtrate and optionally the washing water from b) are neutralized with 20 ammonia to pH values of around 7 and, at the same time, oxidized with air/ oxygen, d) the resulting poorly soluble compounds of the metals iron and, partly, manganese from c) are filtered off and the filter cake is optionally washed and further worked up, e) the filtrate and optionally the washing water from d) are subjected to reactive extraction at temperatures of from 60-95°C, especially of from to remove magnesium and manganese by Le A 29 587-FC el) contacting an ammonium salt of a phosphoric acid derivative or phosphonic acid derivative in an organic solution with the filtrate in countercurrent, the ammonium ions passing into the filtrate and the magnesium and manganese ions passing into the organic solution, e2) freeing the organic solution from magnesium and manganese by addition of aqueous sulfuric acid solution to form an aqueous sulfuric acid solution containing magnesium sulfate and manganese sulfate, e3) adding ammonium hydroxide to the organic solution from e2) and .reusing the solution in el), f) after removal of magnesium and manganese, the aqueous ammonium 15 sulfate solution from e) is optionally subjected to evaporative crystallization to form solid ammonium sulfate, The process variants are schematized in Figs. 1 to 3.

The filter cake from reaction step b) is preferably further worked up by a) oxidizing the filter cake with air/oxygen, simultaneously adding sodium hydroxide and heating to temperatures above 100 0 C, the pH value being kept at >12, b) filtering off the resulting poorly soluble compounds of the metals titanium and iron from a), c) cooling the filtrate from which contains the soluble compounds of the metals aluminium, vanadium and chromium, in the presence of nuclei or neutralizing it with CO 2 to pH 7, Le A 29 587-FC d) filtering off the resulting poorly soluble compounds of aluminium from c), e) optionally adjusting the filtrate from d) with sulfuric acid to a pH value around 2, f) filtering off the resulting poorly soluble compounds of vanadium from e) and g) precipitating the chromium from the filtrate from f) by addition of sodium sulfite and sodium carbonate as chromium hydroxide at pH 5-6.

The working up of the filter cake from b) is illustrated in Fig. 4.

9 9* The aqueous magnesium- and manganese-containing sulfuric acid solution 15 accumulating in the liquid/liquid extraction is preferably cooled and the magnesium ammonium sulfate/manganese sulfate formed is separated off.

The extraction step may be principally replaced by low-temperature crystallization to remove magnesium and manganese from the filtrate and, optionally, the washing water from reaction step d) of the process according to the 20 invention, however, this low-temperature crystallization has some disadvantages less pure ammonium sulfate as product, high expense).

The invention is illustrated by the following Examples.

Examples Example 1 A. Neutralizatiov with NIH 3 and oxidation with air (invention) 1,000 kg of thin acid (for composition, see Table 1) are continuously neutralized to pH 5.0 with 99.95 kg of NIH at a temperature of 70 to 80 0 C. 19.14 kg of a precipitate are formed (36.31% TiO(OH), 2 54,37% Al(OH) 3 6.21%

VO(OH)

2 and 3,11% Cr(OH) 3 (see Table 1; solid After filtration, 1,080.81 kg Le A 29 587-F

-L

of a solution remain behind (35.92% (NH- 4 2

SO

4 4.15% FeSO 4 0.08% MnSO4, 3.25% MgSO 4 0.22% CaSO 4 and 56.37% H20), see Table 1; filtrate 1.

In a second stage, the clear liquid is oxidized with approximately 40 m 3 of air and kept at pH 7.0 during oxidation with 10.16 kg of NH- 3 Under these conditions, 22.8 kg of Fe 3 0 4 (magnetite) (Table 1; solid 2) are formed, After filtration, 1,069.74 kg of ammonium sulfate solution remain behind (39.98%

(NH

4 3.29% MgSO 4 0.08% MnSO 4 0.22% CaSO 4 and 56.43% H20), see Table 1; filtrate 2.

B1. Concentration by evaporation (prior art) When the solution accumulating in the preceding step is directly Sconcentrated by evaporation, 427.72 kg of ammonium sulfate containing Mg(NH4) 2 (S0 4 2 .6H 2 0, CaSO 4 and MnSO 4 as impurities (see Table 2) crystallize out. This solid cannot be used as a fertilizer, for example because its nitrogen 15 content (18.24%) is too low (required nitrogen content: Because of the hygroscopic character of the double salt, the product is not free-flowing and, accordingly, is difficult to handle. In addition, the solubility of Mg(NH4) 2 (SO4) 2 .6H 2 0 is highly dependent on temperature, so that caking would occur in the event of subsequent concentration of ammonium sulfate by evapora- 20 tion in crystallization towers, B2. Extraction (invention) 500 kg of a 40% solution of di-(2-ethylhexyl)-phosphoric acid in Shellsol- IK are mixed with 37 kg of a 30% NI 3 solution. The ammonium salt is formed.

1,000 kg of the ammonium sulfate solution accumulating in the preceding step (approx, 0,7% Mg; free from Ti, Al, V, Cr and Fe) are extracted with this solution in four mixer-settlers (countercurrent operation). 1,000 kg of ammonium sulfate solution containing approx. 150 ppm Mg remain behind, All other metal ions are quantitatively removed, In the re-extraction step, the organic phase is regenerated with 121 kg of 1 2

SO

4 in two additional mixer-settlers (countercurrent operation). 153 kg of Le A 29 587-FC

I

raffinate (composition: 22.6% MgSO 4 0.63% MnSO 4 and 0.44% CaSO 4 are formed.

B3. Concentration by evaporation (invention) 1,000 kg of the ammonium sulfate solution from B2. are concentrated by evaporation in stages at 50°C, 75°C and 108°C. 454.6 kg of ammonium sulfate containing 21.13% of nitrogen are formed.

C. Working up of the solid from the neutralization step (invention) Separation of the titanium: 100 kg of washed filter cake are heated beyond 100°C with 80 kg of NaOH and, at the same time, oxidized with air. 27,2 kg of NaTiO 3 remain after 0 filtration and may be reused, for example, in the titanium digestion step. The filtrate contains 65.2 kg of NaAO02, 8.6 kg of NaVO 3 and 5.6 kg of NaCrO 4 Separation of the aluminium: The aluminium can be removed in two ways: a) 100 kg of filtrate (Ti-free) are neutralized to pH 7,0 with CO 2 30 kg of A1203L3H 2 0 crystallizing out.

20 b) 100 kg of filtrate (free from Ti) are cooled to 25 0 C with recycling of hydrargillite nuclei, 25 kg of AI(OH) 3 are formed.

Separation of the vanadium: 70 kg of filtrate (free from Ti and Al) are acidified to pH 2 with 33 kg of

H

2

SO

4 at 25°C, 3,2 kg of V 2 0 5 precipitating, Separation of the chromium: 100 kg of filtrate (free from Ti, Al and V) are reduced by addition of 2 kg of NazSO 3 the solution is partly neutralized to pH 5 and 1.8 kg of Cr(OH) 3 are isolated.

Le A 29 587-FC Table 1 [all quantities in by weight]l

SQ

S S

S

S*

S S

S.

S

*5*S Thin acid Solid 1 Filtrate 1 Solid 2 Filtrate 2

H

2 S0 4 25,92 TiOSO 4 1.14 <0.0001 A1 2 (S0 4 2.28 <0,000 1

VOSO

4 0,19 <0,0001 Cr 2 (S0 4 3 0.11, <0,0001I FeSO 4 4.49 0,0010 4.15 <0.0010 MnSO 4 0.08 0.0010 0.08 2,06 0,08 MgSO 4 3,52 0,0010 3,25 3.29 CaSO4 0,24 -0.22 -0,22 H120 62.03 -56,37 -56,43 (N'-14 2 S0 4 35.92 -39.98 TiO(OH-) 2 36,31

AI(OH)

3 54.37 VO(01-I) 2 6.21 Cr(OH) 3 3.11-- Fe 3 0 4 97.94

S*

55 5 *5 5 5

*S

*SSS

S S S 55 S S

S

55.'

S

LeA 29 $87-TC, Table 2 Quantity [kg] NI

(NIJ

4 2 S0 4 427.72 86,02 18.21 MgSO 4 35,16 7,07 CaSO 4 2.38 0,48 MgSO 4 0.82 0.16 31.13 6.26 L Ttal497.21 100 *a 00 .011 6.6.

a a.

a. a a.

.a a..

a a a.

a a a a a LgLA 29, 587-FVC

Claims

1. A continuous process for working up thin acid from the production of titanium dioxide by the sulfate method characterized in that a) in a first step, the thin acid is partly neutralized with ammonia to pH values of 4 to 6 at temperatures above 50°C to the boiling point of the solution and preferably at temperatures of 70 0 C to 110°C, b) the resulting poorly soluble compounds of the metals titanium, vanadium, chromium, aluminium and, partly, iron from a) are filtered off and the filter cake is optionally washed and further worked up, c) the filtrate and optionally the washing water from b) are neutralized with 15 ammonia to pH values of around 7 and, at the same time, oxidized with air/oxygen, d) the resulting poorly soluble compounds of the metals iron and, partly, manganese from c) are filtered off and the filter cake is optionally washed 20 and further worked up, e) the filtrate and optionally the washing water from d) are subjected to reactive extraction at temperatures of from 60 0 C to 95"C; especially of from 70 0 C to 90 0 C to remove magnesium and manganese by el) contacting an ammonium salt of a phosphoric acid derivative or phosphonic acid derivative in an organic solution with the filtrate in countercurrent, the ammonium ions passing into the filtrate and the magnesium and manganese ions passing into the organic solution, 9 r:Pwroocs)EI I7.a2 _L e2) freeing the organic solution from magnesium and manganese by addition of aqueous sulfuric acid solution to form an aqueous sulfuric acid solution containing magnzsium sulfate and manganese sulfate, e3) adding ammonium, hydroxide to the organic solution from e2) and reusing the solution in el), f) after remo al of magnesium and manganese, the aqueous ammonium sulfate solution from e) is optionally subjected to evaporative crystallization to form solid ammonium sulfate.

2. A process as claimed in claim 1, characterized in that the filter cake of the resulting poorly soluble compounds of the metals titanium, vanadium, chromium, aluminium and, partly, iron from b) is further worked up by soa* a) oxidizing the filter cake with air/oxygen, simultaneously adding sodium hydroxide and heating to temperatures above 100°C, the pH value being kept at >12, 20 b) filtering off the resulting poorly soluble compounds of the metals titanium and iron from a), *9* c) cooling the filtrate from which contains the soluble compounds of the metals aluminium, vanadium and chromium, in the presence of nuclei or neutralizing it with CO2 to pH 7, d) filtering off the resulting poorly soluble compounds of aluminium from c), e) optionally adjusting the filtrate from d) with sulfuric acid to a pH- value around 2, Le A 29 587-FC f) filtering off the resulting poorly soluble compounds of vanadium from e) and g) precipitating the chromium from the filtrate from f by addition of sodium sulfite and sodium carbonate as chromium hydroxide at pH 5-6.

3. A process as claimed in claim 1, characterized in that the magnesium- and manganese-containing solution from e2) is cooled so that the magnesium ammonium sulfate/ manganese sulfate is precipitated and removed.

4. A process for working up thin acid according to Claim 1 substantially as hereinbefore described with .*0 reference to the examples. DATED this 5th day of August 1994, BAYER ANTWERPEN N.V. By Its Patent Attorney DAVIES COLLISON CAVE 0 s a 0 Le A 29 587-FC A PROCESS FOR WORKING UP THIN ACID A b s t r a c t The invention relates to a process for working up thin acid from the production of titanium dioxide by the sulfate method, S Le A 29 587-FC