CA1100283A - Removal of undesirable metal ions in the concentration of dilute sulfuric acid solutions containing iron (ii) sulfate - Google Patents
Removal of undesirable metal ions in the concentration of dilute sulfuric acid solutions containing iron (ii) sulfateInfo
- Publication number
- CA1100283A CA1100283A CA274,390A CA274390A CA1100283A CA 1100283 A CA1100283 A CA 1100283A CA 274390 A CA274390 A CA 274390A CA 1100283 A CA1100283 A CA 1100283A
- Authority
- CA
- Canada
- Prior art keywords
- sulfuric acid
- acid solution
- sulfate
- iron
- dilute
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/90—Separation; Purification
- C01B17/901—Recovery from spent acids containing metallic ions, e.g. hydrolysis acids, pickling acids
Abstract
REMOVAL OF UNDESIRABLE METAL IONS IN THE CONCENTRATION
OF DILUTE SULFURIC ACID SOLUTIONS CONTAINING IRON(II) SULFATE
ABSTRACT OF THE DISCLOSURE
A process is described for the extensive removal of undesirable metal ions, especially chromium ions, in the reconcentration of dilute iron(II) sulfate containing sulfuric acid solutions by evaporating water and separating iron(II) sulfate wherein the dilute sulfuric acid solution is evaporated up to a content of 60 to 70% by weight H2SO4.
According to the novel feature the dilute sulfuric acid solution or a preconcentrated sulfuric acid solution produced from it, without separation of metal salts, without simultaneous addition of clarified sulfuric acid or sulfuric acid solution is placed continuously into a receiver which contains a sulfuric acid metal salt suspension of which the liquid constituent contains 60 to 70% by weight H2SO4 and that at the same time so much water is evaporated that the sulfuric acid concentration in the liquid part of the metal salt suspension is maintained in the range of 60-70% by weight, and that continuously or at certain intervals a part of the sulfuric acid containing metal salt suspension is removed from the receiver and that the precipitated metal salts are separated.
These solutions are used in the manufacture of titanium dioxide pigments.
OF DILUTE SULFURIC ACID SOLUTIONS CONTAINING IRON(II) SULFATE
ABSTRACT OF THE DISCLOSURE
A process is described for the extensive removal of undesirable metal ions, especially chromium ions, in the reconcentration of dilute iron(II) sulfate containing sulfuric acid solutions by evaporating water and separating iron(II) sulfate wherein the dilute sulfuric acid solution is evaporated up to a content of 60 to 70% by weight H2SO4.
According to the novel feature the dilute sulfuric acid solution or a preconcentrated sulfuric acid solution produced from it, without separation of metal salts, without simultaneous addition of clarified sulfuric acid or sulfuric acid solution is placed continuously into a receiver which contains a sulfuric acid metal salt suspension of which the liquid constituent contains 60 to 70% by weight H2SO4 and that at the same time so much water is evaporated that the sulfuric acid concentration in the liquid part of the metal salt suspension is maintained in the range of 60-70% by weight, and that continuously or at certain intervals a part of the sulfuric acid containing metal salt suspension is removed from the receiver and that the precipitated metal salts are separated.
These solutions are used in the manufacture of titanium dioxide pigments.
Description
` 110~283 The invention is concerned with a process for the extensive removal of undesirable metal ions, especially chrom-ium ions, in the reconcentrating of dilute iron(II) sulfate containing sulfuric acid solutions by the evaporation of ` water and the separation of iron(II) sulfate, whereby the dilute sulfuric acid is evaporated down to a content of 60-70%
by weight H2S04.
During the manufacture of titanium dioxide pigments by the hydrolysis of titanium sulfate solutions, after the separation of the titanium dioxide hydrate there is obtained a large amount of filtrate which, besides 10 to 30% by weight H2S04, contains more or less considerable amounts of iron(II) sulfate and compounds of additional elements such as, for example, Ti, Al, Zn, Mg, Mn, V, ~a, Cr, Cu. This filtrate : is designated below as "waste acid".
; The problem is to reuse the waste acid profitably.
It is desired particularly to make the sulfuric acid content of the waste acid useful again by recycling within the scope ;of the titanium dioxide manufacture. For this purpose it is necessary to concentrate the waste acid to a greater or lesser extent and to separate the iron(II) sulfate precipitating in this process as well as any other metal sulfates. In this particularly those elements that form colored ions or compounds ;~ to a large extent must be removed since in the course of the process they become concentrated and lead to an impairment of the titanium dioxide pigments. Among the elements which are obnoxious even in very slight amounts and which commercially can to any great extent be removed only with difficulty belongs chromium. This problem is especially difficult to handle when ilmenite which is relatively high in chromium is to be processed, and if the waste acid obtained is to be recycled ~1¢CD283 completely in the process in order to protect the environment.
The evaporation of the dilute sulfuric acid solution i down to a concentration of 60-70% by weight H2S04 is customarily carried out according to one or more steps, essentially according to three methods: (1) Indirect heating with heat exchangers, (2) evaporation of tlle water in a vacuum and (3) direct heating with submerged burners or with hot gases in countercurrent. In most cases several of these methods are employed in succession or simultaneously. (DT-AS 11 73 074, 10 DT-AS 11 03 902, USP 2,098,056, USP 2,280,508. DT-PS 886 142, Journal: "Chem. Ing. Techn." 42 (1970) pp. 452-456; Book:
"The Manufacture of Sulfuric Acid" by W.W. Duecker and J.R.
West (Reinhold Publishing Corporation, New York 1959) pp. 300, 301, 329-337; Journal: "Wire and Wire Products" 13 (1938), p. 587). As a rule metal salts precipitate during the reconcentration process, long before a concentration of 60%
by weight H2S04 has been reached. At lower temperatures and sulfuric acid concentrations these metal salts consist mostly of iron(II) sulfate heptahydrate; at higher tempera-tures and/or sulfuric acid concentrations they consist mostly of iron(II) sulfate monohydrate. In addition, they contain other sulfates which are formed by the other elements contained in the dilute sulfuric acid solution. In multi-step procedures it is often customary to separate the metal salts precipitated in the Eirst step before the concentration process is continued. A separation of iron(II) sulfate hepta-hydrate is advantageous in that together with the metal salt large amounts of water are removed as water of crystallization so that in the reconcentration after the first st~p evaporation costs are saved.
Although it is known from USP 2,098,056 that in the customary concentration of dilute iron(II) sulfate-containing sulfuric acid solution to 65% H2S04, the precipitated iron sulfate-monohydrate carrie~ a part of the chromium along;
this part is, however, not sufficient to prevent an obnoxious concentration of the chromium during the recycling of the 60-70% sulfuric acid into the titanium dioxide manufacturing process. This is true especially if besides chromium other incidental products are present in considerable amounts.
It is, however, possible to remove chromium and other obnoxious elements to a satisfactory extent if the reconcentrated sulfuric acid is additionally concentrated to ; a highly concentrated sulfuric acid with, for example, 80-96%
by weight H2S04. This method of processing has however the definite disadvantage that it requires high investment costs and is loaded with a high energy consumption. In addition, a sulfuric acid of such high concentration is fre-quently quite unnecessary. Frequently it suffices to con-centrate the sulfuric acid to a concentration of only 60-70%
by weight H2S04 and to employ this directly if the chromium content has been reduced sufficiently in the reconcentration process.
~- The suggestion has been made in several publications that in the course of the wasteacid working up, the chromium be removed by the addition of various compounds, for example, monovalent alum forming cations (DT-AS 10 22 564), aluminum sulfate (Lakokras. Mat.*(1975), No. 2, pp. 75-76), isopropanol (Lakokras. Mat.*(1975). No. 3, pp. 23-24), acetone or isopropanol (FR-PS 2,240,183), amines and an oxidizing agent (GB-PS 1,352,306). The addition of these compounds is connec-; 30 ted with additional costs and has under certain circumstances the effect that other impurities are being carried into the *Journal "Lakokrasocnye Materialy i ich Primenenie"
~lQ6~Z83 pigment. The separation of the additions is doubtful, especial-ly if they have to be added in large amounts. Expensive additional processing steps are required in order to obtain the purified sulfuric acid of the desired quality.
It has now been found that the amount of chromium carried along depends essentially on when and in what amount the iron sulfate monohydrate precipitates out from the solution.
In this it was surprisingly found that at a sulfuric acid concentration of 55% by weight and higher the chromium is precipitated to a great extent and especially in a concen-tration between 60 and 70% by weight H2S04 the co-precipitation of the chromium takes place very effectively so that the chromium is removed from the solution to a larger extent than~
corresponds to its solubility product. Presumably it is here built into the precipitating iron sulfate monohydrate particles.
The inadequate efficiency of the prior processes is to be explained by the fact that in these cases even before the attainment of the favourable concentration range so much iron(II) sulfate has been precipitated that the amount of the precipitating iron(II) sulfate in the concentration range of 60-70% H2S04 is too small.
From DT-AS 11 19 835 a process is known in which in the reconcentration of dilute sulfuric acid solutions the process is operated in such a way that a cold, clarified, practially iron sulfate-free sulfuric acid of the concentration to be obtained in the receiver is placed in this receiver.
It is to be heated to boiling, for example, by submerged burners while the waste acid to be worked up is added contin-uously together with additional cold, clarified receiver acid, while the pre-concentrated acid is continuously drawn from the evaporating apparatus while keeping the level constant.
It is separated from the precipitating coarsely crystalline sulfate sludge and conveyed to a high concentration step.
This process is very expensive and complicated.
In order to obtain the clarifiad receiver acid expensive clarification and cooling devices are necessary; cooling and reheating of the circulating receiver acid cost much energy.
Working with submerged burners has the considerable disad-vantage that the solution or suspension is strongly overheated locally so that the sulfuric acid and the sulfates are partly thermically decomposed with S02 formation. Thus, large amounts of S02 containing waste gases are obtained which are - not permitted to be discharged into the atmosphere without purification. On the other hand, the purification to the required degree of purity is technically very complicated and very expensive.
A new process for the extensive removal of undesirable - metal ions, especially chromium ions, was found in the concen-tration process of dilute iron(II) sulfate solutions by the evaporation of water and separation of iron(II) sulfate, wherein the dilute sulfuric acid solution is evaporated to a content of 60-70% by weight H2S04.
The process is characterized in that the dilute sulfuric acid solution or a preconcentrated sulfuric acid solution produced from it without precipitation of metal salts is continuously placed into a receiver without the simultaneous addition of a clarified sulfuric acid solution. The receiver contains a sulfuric acid-containing metal salt suspension of which the liquld constituent contains 60-70% by weight H2S04 and that at the same time sufficient water is evaporated so that the sulfuric acid concentration in the liquid constituent of the metal salt suspension is maintained in the range of .
by weight H2S04.
During the manufacture of titanium dioxide pigments by the hydrolysis of titanium sulfate solutions, after the separation of the titanium dioxide hydrate there is obtained a large amount of filtrate which, besides 10 to 30% by weight H2S04, contains more or less considerable amounts of iron(II) sulfate and compounds of additional elements such as, for example, Ti, Al, Zn, Mg, Mn, V, ~a, Cr, Cu. This filtrate : is designated below as "waste acid".
; The problem is to reuse the waste acid profitably.
It is desired particularly to make the sulfuric acid content of the waste acid useful again by recycling within the scope ;of the titanium dioxide manufacture. For this purpose it is necessary to concentrate the waste acid to a greater or lesser extent and to separate the iron(II) sulfate precipitating in this process as well as any other metal sulfates. In this particularly those elements that form colored ions or compounds ;~ to a large extent must be removed since in the course of the process they become concentrated and lead to an impairment of the titanium dioxide pigments. Among the elements which are obnoxious even in very slight amounts and which commercially can to any great extent be removed only with difficulty belongs chromium. This problem is especially difficult to handle when ilmenite which is relatively high in chromium is to be processed, and if the waste acid obtained is to be recycled ~1¢CD283 completely in the process in order to protect the environment.
The evaporation of the dilute sulfuric acid solution i down to a concentration of 60-70% by weight H2S04 is customarily carried out according to one or more steps, essentially according to three methods: (1) Indirect heating with heat exchangers, (2) evaporation of tlle water in a vacuum and (3) direct heating with submerged burners or with hot gases in countercurrent. In most cases several of these methods are employed in succession or simultaneously. (DT-AS 11 73 074, 10 DT-AS 11 03 902, USP 2,098,056, USP 2,280,508. DT-PS 886 142, Journal: "Chem. Ing. Techn." 42 (1970) pp. 452-456; Book:
"The Manufacture of Sulfuric Acid" by W.W. Duecker and J.R.
West (Reinhold Publishing Corporation, New York 1959) pp. 300, 301, 329-337; Journal: "Wire and Wire Products" 13 (1938), p. 587). As a rule metal salts precipitate during the reconcentration process, long before a concentration of 60%
by weight H2S04 has been reached. At lower temperatures and sulfuric acid concentrations these metal salts consist mostly of iron(II) sulfate heptahydrate; at higher tempera-tures and/or sulfuric acid concentrations they consist mostly of iron(II) sulfate monohydrate. In addition, they contain other sulfates which are formed by the other elements contained in the dilute sulfuric acid solution. In multi-step procedures it is often customary to separate the metal salts precipitated in the Eirst step before the concentration process is continued. A separation of iron(II) sulfate hepta-hydrate is advantageous in that together with the metal salt large amounts of water are removed as water of crystallization so that in the reconcentration after the first st~p evaporation costs are saved.
Although it is known from USP 2,098,056 that in the customary concentration of dilute iron(II) sulfate-containing sulfuric acid solution to 65% H2S04, the precipitated iron sulfate-monohydrate carrie~ a part of the chromium along;
this part is, however, not sufficient to prevent an obnoxious concentration of the chromium during the recycling of the 60-70% sulfuric acid into the titanium dioxide manufacturing process. This is true especially if besides chromium other incidental products are present in considerable amounts.
It is, however, possible to remove chromium and other obnoxious elements to a satisfactory extent if the reconcentrated sulfuric acid is additionally concentrated to ; a highly concentrated sulfuric acid with, for example, 80-96%
by weight H2S04. This method of processing has however the definite disadvantage that it requires high investment costs and is loaded with a high energy consumption. In addition, a sulfuric acid of such high concentration is fre-quently quite unnecessary. Frequently it suffices to con-centrate the sulfuric acid to a concentration of only 60-70%
by weight H2S04 and to employ this directly if the chromium content has been reduced sufficiently in the reconcentration process.
~- The suggestion has been made in several publications that in the course of the wasteacid working up, the chromium be removed by the addition of various compounds, for example, monovalent alum forming cations (DT-AS 10 22 564), aluminum sulfate (Lakokras. Mat.*(1975), No. 2, pp. 75-76), isopropanol (Lakokras. Mat.*(1975). No. 3, pp. 23-24), acetone or isopropanol (FR-PS 2,240,183), amines and an oxidizing agent (GB-PS 1,352,306). The addition of these compounds is connec-; 30 ted with additional costs and has under certain circumstances the effect that other impurities are being carried into the *Journal "Lakokrasocnye Materialy i ich Primenenie"
~lQ6~Z83 pigment. The separation of the additions is doubtful, especial-ly if they have to be added in large amounts. Expensive additional processing steps are required in order to obtain the purified sulfuric acid of the desired quality.
It has now been found that the amount of chromium carried along depends essentially on when and in what amount the iron sulfate monohydrate precipitates out from the solution.
In this it was surprisingly found that at a sulfuric acid concentration of 55% by weight and higher the chromium is precipitated to a great extent and especially in a concen-tration between 60 and 70% by weight H2S04 the co-precipitation of the chromium takes place very effectively so that the chromium is removed from the solution to a larger extent than~
corresponds to its solubility product. Presumably it is here built into the precipitating iron sulfate monohydrate particles.
The inadequate efficiency of the prior processes is to be explained by the fact that in these cases even before the attainment of the favourable concentration range so much iron(II) sulfate has been precipitated that the amount of the precipitating iron(II) sulfate in the concentration range of 60-70% H2S04 is too small.
From DT-AS 11 19 835 a process is known in which in the reconcentration of dilute sulfuric acid solutions the process is operated in such a way that a cold, clarified, practially iron sulfate-free sulfuric acid of the concentration to be obtained in the receiver is placed in this receiver.
It is to be heated to boiling, for example, by submerged burners while the waste acid to be worked up is added contin-uously together with additional cold, clarified receiver acid, while the pre-concentrated acid is continuously drawn from the evaporating apparatus while keeping the level constant.
It is separated from the precipitating coarsely crystalline sulfate sludge and conveyed to a high concentration step.
This process is very expensive and complicated.
In order to obtain the clarifiad receiver acid expensive clarification and cooling devices are necessary; cooling and reheating of the circulating receiver acid cost much energy.
Working with submerged burners has the considerable disad-vantage that the solution or suspension is strongly overheated locally so that the sulfuric acid and the sulfates are partly thermically decomposed with S02 formation. Thus, large amounts of S02 containing waste gases are obtained which are - not permitted to be discharged into the atmosphere without purification. On the other hand, the purification to the required degree of purity is technically very complicated and very expensive.
A new process for the extensive removal of undesirable - metal ions, especially chromium ions, was found in the concen-tration process of dilute iron(II) sulfate solutions by the evaporation of water and separation of iron(II) sulfate, wherein the dilute sulfuric acid solution is evaporated to a content of 60-70% by weight H2S04.
The process is characterized in that the dilute sulfuric acid solution or a preconcentrated sulfuric acid solution produced from it without precipitation of metal salts is continuously placed into a receiver without the simultaneous addition of a clarified sulfuric acid solution. The receiver contains a sulfuric acid-containing metal salt suspension of which the liquld constituent contains 60-70% by weight H2S04 and that at the same time sufficient water is evaporated so that the sulfuric acid concentration in the liquid constituent of the metal salt suspension is maintained in the range of .
2~33 60-70% by weight ~12S04 and that continuously or at certain intervals a part of the sulfuric acid metal salt suspension is drawn off from the receiver and that the precipitated metal salts are separated.
~ The receiver may be a vessel that is heated indirectly - from the outside wherein the heat transfer medium is carried either outside along the wall or else is carried through heating elements which reach into the vessel. Either hot gases, water vapor or a heating liquid may serve as heat transfer medium. The heating may also be carried out in another known manner. During the energy addition, care must be taken always that no overheating with decomposition of sulfuric acid and the sulfates takes place with the formation of obnoxious gases. The receiver may also be a conventional circulatin~ evaporator. The metal salt suspension in the receiver consists of the stated sulfuric acid and precipitated metal salts which consist mainly of iron(II) sulfate mono-hydrate and contain other precipitated metal salts and the carried-along impurities, especially chromium.
The process according to the invention is carried out in such a way that the diluted or pre-concentrated sulfuric acid solution, when added to the metal salt suspension, will in a very short time reach the range of the favourable - sulfuric acid concentration. The metal salt precipitation can therefore not start in practice before this concentration is reached.
With the aid of the new process it is possible even when employing chromium and vanadium-rich ilmenites to free to such an extent, within the scope of the re-concentrating process of the waste acid, the acid of chromium and also other secondary constituents that without further high concentration , 1;1(~2 !33 , or any other purification steps the entire re-concentrated 60-70% sulfuric acid may be directly utilized within the scope of titanium dioxide manufacture and that a troublesome enrichment of the chromium and other secondary constituents in the acid cycle is reliably prevented.
A recycling of pre-concentrated or re-concentrated sulfuric acid within the concentrating process is not necessary.
The sulfuric acid solutions and the suspensions are easily handled. The waste gases produced are so pure that they may be released into the atmosphere without more ado.
The process has considerable economic advantages since the investment need is slight and the process compares favourably with prior processes by a considerably smaller consumption of energy.
The process is particularly suitable for the working up of waste acid which occurs in the manufacture of titanium dioxide according to the sulfate process from massive ilmenite with high chromium content.
The separation of chromium takes place in the re-concentration in the vacuum as well as in the re-concentration at normal pressure.
The amount of precipitated iron(II) sulfate monohydrate which is necessary for the chromium removal depends on the chromium content of the waste acid, according to the desired extent to which the chromium is to be removed as well as the type and amount of the additional trace elementsthat are present in the starting solution. These are as a rule likewise removed to a completely adequate extent in the iron(II) sulfate monohydrate precipitation.
In order to obtain with ores rich in chromium a re-concentrated acid which may be completely recycled into the llG~283 titanium dioxide process, it is usually necessary to reduce the chromium content down to 180 mg Cr/kg H2S04 or less.
The process may be carried out stepwise. It is, ~ however, more favourable to carry out the process continuously - and to separate the metal salt produced continuously or at certain intervals.
The re-concentrated sulfuric acid, freed of metal salts, may be reused in its total amount, for example, in the titanium dioxide manufacturing process. This sulfuric acid may, however, also be used, at least in part, for other purposes. In this case higher chromium contents may possibly be tolerated, in the re-concentrated sulfuric acid.
The re-concentration of the dilute sulfuric acid solution may be carried out in a one-step or a two-step procedure.
A special form of carrying out the invention consists in that the dilute iron(lI) sulfate containing sulfuric acid solution is evaporated in one step by placing the dilute sulfuric acid itself into the receiver which contains the metal salts suspension containing the 60-70% sulfuric acid.
In the case of the two-step reconcentration the dilute iron(II~ sulfate containing sulfuric acid solution is according to an additional form of the invention evaporated in two steps by preconcentrating it in a first step without separation of metal salts to a content of about 28-31% by weight H2S04 and that the preconcentrated sulfuric acid solution obtained is maintained at a temperature of at least about 50 C
and in a second step goes into the receiver and is further evaporated there.
It is essential that during the preconcentration of the dilute sulfuric acid solution and up to the reconcentration g of the preconcentrated sulfuric acid solution no metal salts separate out; this will be assured by keeping the preconcen-` trated sulfuric acid at a temperature of at least about 50 C.
The two-step mode of operation in the re-concentration of the solution has the advantage that in the large scale operation and by utilization of the water vapor condensation it is energetically more favourable than in a one-step operation.
The preconcentration may occur in any desired manner, as long as attention is paid to the fact that no metal salt precipitates out. It may, for exmaple~ take place in a heated vessel. The heating of this vessel is carried out preferably indirectly, e.g., with heating coils which surround the vessel from the outside or reach into the vessel. As heat-furnishing medium not only the water vapor obtained in thesecond concen-trating step, but also other gases or liquids may be employed.
A favourable form of operation in the two-step method of the invention consists in that in the first step the dilute sulfuric acid solution is placed continuously into a vessel which contains pre-concentrated sulfuric acid solution, and that simultaneously so much water is evaporated that the sulfuric acid concentration in this vessel remains constant and that continuously or at certain intervals a part of the preconcentrated sulfuric acid solution is drawn off from the vessel and added to the receiver of the second step.
The pre-concentration is preferably carried out in a vacuum. The reconcentration of the pre-concentrated sulfuric acid solution in the second step may be carried out either in a vacuum or at normal pressure.
It is especially favourable if the preconcentration in a vacuum is carried out in a vessel which is heated indirect-` ` ~10~283 ly by water vapor which ls obtained in the reconcentration of the preconcentrated sulfuric acid solution.
In the continuous evaporating steps of the present process it must be taken into consideration the fact that at ; a given concentration of the preconcentrated sulfuric acid solution or the li~uid part of the metal salt suspension, the boiling temperature is a function of the established pressure.
The speed of adding the dilute or preconcentrated sulfuric acid solution must be proportional to the amount of heat added which is needed for the greatest part for the evaporation of the water.
The waste acid occurring in the titanium dioxide manufacture from ilmenite contains as a rule sufficient amounts of iron(II) sulfate in order to accomplish the desired chromium removal. If, however, the iron(II) sulfate amount in the solution to be reconcentrated is not sufficient, then the iron content in the dilute sulfuric acid solution may be increased by the addition of iron(II) sulfate mono- or hepta-hydrate and dissolving it in the dilute solution. Further-more, it is possible for the purpose of increasing theamountof precipitated chromium to add solid pure iron sulfate monohydrate in several small portions to the reconcentrated solution and to separate it together with the precipitated iron(II) sulfate monohydrate.
The iron(lI) sulfate-monohydrate from an outside source is, however, not as effective as the iron(II) sulfate-monohydrate produced in the precipitation. For this reason it is necessary to add correspondingly large amounts. It is important that the added iron(II) sulfate-monohydrate be pure, that is, that it contains besides sulfuric acid less than 2% impurities of other elements. For example, an iron(II) lll~C283 sulfate monohydrate which is obtained ina known manner from the iron(II) sulfate-heptahydrate produced during the titanium dioxide manufacture prior to the hydrolysis step is suitable for this purpose. Iron(II) sulfate-monohydrate which, on the other hand, occurs in the reconcentration of the waste acid is as a rule not suitable as starting material. The presence of sulfuric acid is not troublesome.
The addition of iron(II) sulfate-monohydrate in several small portions increases materially the effect of its chromium removal.
The reconcentrated sulfuric acid obtained according to the invention may not only be recycled to the titanium dioxide manufacturing process, but may also, in a manner known as such, be employed for other purposes or worked up.
The separated iron(II) sulfate-monohydrate may, in a manner known as such, be worked up further or else utilized.
In the process according to the invention not only waste acids from the titanium dioxide manufacturing process but also other iron(II) sulfate-containing sulfuric acid solutions may be employed.
In the following examples the invention is explained in more detail.
Waste acids which are produced in the manufacture of titanium dioxide according to the sulfate process were worked up. In this the start was made with ilmenite of the following composition:
TiO2 44.3%
Fe 34.8%
Mg 2.70%
SiO2 2.72%
Mn 0.22%
~lOG2a3 Ca 0.22%
V 0.14%
Cr 0.05%
Ni 0.016%
Nb 0.006%
In this example the reconcentration of a waste acid is described as it is carried out in the known manner.
1.2 liters of waste acid with a content of 341 gpl H2S04 and 7gO mg Cr/kg H2S04 were concentrated in a rotary evaporator at a pressure of 40 mbar. Altogether 660 ml water were distilled off. In this procedure more and more iron sulfate precipitated steadily with increasing H2S04 concentration.
After separation of the precipitated iron sulfate a reconcentrated acid was obtained with 1054 gpl H2S04 (corresponding to 65.9% by weight) and 530 mg Cr/kg H2S04 Thus, only 33% of the original chromium present in the waste acid was separated out. Such an acid leads to a chromium enrichment in the titanium dioxide pigment and thus to a considerable impairment of the pigment when it is recycled B into the titanium diO~ide manufacturing process.
1 liter 65% sulfuric acid was placed into a 6-liter flask and heated to boiling at a pressure of 27 mbar (boiling point 65C). Subsequently 30 liters waste acid of the composi-tion 325 gpl H2S04 Z~33 46 gpl Fe 615 mg Cr/kg H S0 1690 mg V/kg H2S04 ' were added continuously to the boiling 65% sulfuric acid, wherein the speed of addition of the waste acid and the volume of distilled off water were correlated to each other in such a way~that the sulfuric acid concentration in the flask was fully maintained. These ratios were established at a speed of 1 liter waste acid per hour.
Practically the entire amount of dissolved iron sulfate precipitated at the moment of flowing into the 65%
sulfuric acid while carrying along considerable amount of the trace elements. The acid freed from precipitated metal salts had the following composition:
947 gpl H2S04 2.4 gpl Fe 178 mg Cr/kg H2S04 211 mg V/kg H2S04 The rate of chromium separation was 71%, referring to the amount of chromium present in the waste acid. At the same time 88% of the vanadium was separated out. The acid obtained could be returned directly into the titanium dioxide manufacturing process.
The waste acid had the following composition:
307 gpl H2S04 51 gpl Fe 684 mg Cr/kg H2S04 1760 mg V/kg H2S04 1 liter of a sulfuric acid solution with a H2S04 content of 31% was placed in a 6 liter flask and heated in a 110~
vacuum of 100 to 107 mbar to boiling (B.Pt. 54 to 57 C).
Subsequently 25 liters of waste acid were added continuously to the boiling receiver acid wherein the speed of addition of the waste acid and the amount of distilled off water are so related to one another that the sulfuric acid concentration in the flask remained the same. No metal salt precipitated.
18.7 liters preconcentrated acid were obtained. This was held at a temperature of 50C in order to avoid the crystalli-zation of iron(II) sulfate heptahydrate.
In the second reconcentration step this preconcen-trated acid was reconcentrated at normal pressure in a manner analogous to that of the waste acid in Example 2. After separating the precipitated metal salts the reconcentrated acid had the following composition:
1042 gpl H2S04 0.7 gpl Fe 146 mg Cr/kg H2S04 , 320 mg V/kg H2S04 79% of the chromium and simultaneously 82% of the vanadium had been separated out, so that the acid was suitable for return,ing to the titanium dioxide manufacturing process.
A waste acid of the following composition was worked up:
376 gpl H2S04 45 gpl Fe 585 mg Cr/kg H2S04 1700 mg V/kg H2S04 This waste acid was subjected to a two-step recon-centration as in Example 3, with the difference, however, thatthe preconcentrated acid was cooled prior to the further ilO~283 reconcentration and iron(II) sulfate heptahydrate was separated out so that the acid in an amount of 17.5 liters with a content of 413 gpl H2S04 and 23 gpl Fe was passed onto the second reconcentrating step.
By the intermediate separation of iron(II) sulfate heptahydrate the amount of precipitable iron sulfate was reduced in the second step which`led to a smaller separation of chromium and vanadium (and of additional trace elements).
The acid obtained after the second reconcentration step had the following composition:
looo gpl H2S04
~ The receiver may be a vessel that is heated indirectly - from the outside wherein the heat transfer medium is carried either outside along the wall or else is carried through heating elements which reach into the vessel. Either hot gases, water vapor or a heating liquid may serve as heat transfer medium. The heating may also be carried out in another known manner. During the energy addition, care must be taken always that no overheating with decomposition of sulfuric acid and the sulfates takes place with the formation of obnoxious gases. The receiver may also be a conventional circulatin~ evaporator. The metal salt suspension in the receiver consists of the stated sulfuric acid and precipitated metal salts which consist mainly of iron(II) sulfate mono-hydrate and contain other precipitated metal salts and the carried-along impurities, especially chromium.
The process according to the invention is carried out in such a way that the diluted or pre-concentrated sulfuric acid solution, when added to the metal salt suspension, will in a very short time reach the range of the favourable - sulfuric acid concentration. The metal salt precipitation can therefore not start in practice before this concentration is reached.
With the aid of the new process it is possible even when employing chromium and vanadium-rich ilmenites to free to such an extent, within the scope of the re-concentrating process of the waste acid, the acid of chromium and also other secondary constituents that without further high concentration , 1;1(~2 !33 , or any other purification steps the entire re-concentrated 60-70% sulfuric acid may be directly utilized within the scope of titanium dioxide manufacture and that a troublesome enrichment of the chromium and other secondary constituents in the acid cycle is reliably prevented.
A recycling of pre-concentrated or re-concentrated sulfuric acid within the concentrating process is not necessary.
The sulfuric acid solutions and the suspensions are easily handled. The waste gases produced are so pure that they may be released into the atmosphere without more ado.
The process has considerable economic advantages since the investment need is slight and the process compares favourably with prior processes by a considerably smaller consumption of energy.
The process is particularly suitable for the working up of waste acid which occurs in the manufacture of titanium dioxide according to the sulfate process from massive ilmenite with high chromium content.
The separation of chromium takes place in the re-concentration in the vacuum as well as in the re-concentration at normal pressure.
The amount of precipitated iron(II) sulfate monohydrate which is necessary for the chromium removal depends on the chromium content of the waste acid, according to the desired extent to which the chromium is to be removed as well as the type and amount of the additional trace elementsthat are present in the starting solution. These are as a rule likewise removed to a completely adequate extent in the iron(II) sulfate monohydrate precipitation.
In order to obtain with ores rich in chromium a re-concentrated acid which may be completely recycled into the llG~283 titanium dioxide process, it is usually necessary to reduce the chromium content down to 180 mg Cr/kg H2S04 or less.
The process may be carried out stepwise. It is, ~ however, more favourable to carry out the process continuously - and to separate the metal salt produced continuously or at certain intervals.
The re-concentrated sulfuric acid, freed of metal salts, may be reused in its total amount, for example, in the titanium dioxide manufacturing process. This sulfuric acid may, however, also be used, at least in part, for other purposes. In this case higher chromium contents may possibly be tolerated, in the re-concentrated sulfuric acid.
The re-concentration of the dilute sulfuric acid solution may be carried out in a one-step or a two-step procedure.
A special form of carrying out the invention consists in that the dilute iron(lI) sulfate containing sulfuric acid solution is evaporated in one step by placing the dilute sulfuric acid itself into the receiver which contains the metal salts suspension containing the 60-70% sulfuric acid.
In the case of the two-step reconcentration the dilute iron(II~ sulfate containing sulfuric acid solution is according to an additional form of the invention evaporated in two steps by preconcentrating it in a first step without separation of metal salts to a content of about 28-31% by weight H2S04 and that the preconcentrated sulfuric acid solution obtained is maintained at a temperature of at least about 50 C
and in a second step goes into the receiver and is further evaporated there.
It is essential that during the preconcentration of the dilute sulfuric acid solution and up to the reconcentration g of the preconcentrated sulfuric acid solution no metal salts separate out; this will be assured by keeping the preconcen-` trated sulfuric acid at a temperature of at least about 50 C.
The two-step mode of operation in the re-concentration of the solution has the advantage that in the large scale operation and by utilization of the water vapor condensation it is energetically more favourable than in a one-step operation.
The preconcentration may occur in any desired manner, as long as attention is paid to the fact that no metal salt precipitates out. It may, for exmaple~ take place in a heated vessel. The heating of this vessel is carried out preferably indirectly, e.g., with heating coils which surround the vessel from the outside or reach into the vessel. As heat-furnishing medium not only the water vapor obtained in thesecond concen-trating step, but also other gases or liquids may be employed.
A favourable form of operation in the two-step method of the invention consists in that in the first step the dilute sulfuric acid solution is placed continuously into a vessel which contains pre-concentrated sulfuric acid solution, and that simultaneously so much water is evaporated that the sulfuric acid concentration in this vessel remains constant and that continuously or at certain intervals a part of the preconcentrated sulfuric acid solution is drawn off from the vessel and added to the receiver of the second step.
The pre-concentration is preferably carried out in a vacuum. The reconcentration of the pre-concentrated sulfuric acid solution in the second step may be carried out either in a vacuum or at normal pressure.
It is especially favourable if the preconcentration in a vacuum is carried out in a vessel which is heated indirect-` ` ~10~283 ly by water vapor which ls obtained in the reconcentration of the preconcentrated sulfuric acid solution.
In the continuous evaporating steps of the present process it must be taken into consideration the fact that at ; a given concentration of the preconcentrated sulfuric acid solution or the li~uid part of the metal salt suspension, the boiling temperature is a function of the established pressure.
The speed of adding the dilute or preconcentrated sulfuric acid solution must be proportional to the amount of heat added which is needed for the greatest part for the evaporation of the water.
The waste acid occurring in the titanium dioxide manufacture from ilmenite contains as a rule sufficient amounts of iron(II) sulfate in order to accomplish the desired chromium removal. If, however, the iron(II) sulfate amount in the solution to be reconcentrated is not sufficient, then the iron content in the dilute sulfuric acid solution may be increased by the addition of iron(II) sulfate mono- or hepta-hydrate and dissolving it in the dilute solution. Further-more, it is possible for the purpose of increasing theamountof precipitated chromium to add solid pure iron sulfate monohydrate in several small portions to the reconcentrated solution and to separate it together with the precipitated iron(II) sulfate monohydrate.
The iron(lI) sulfate-monohydrate from an outside source is, however, not as effective as the iron(II) sulfate-monohydrate produced in the precipitation. For this reason it is necessary to add correspondingly large amounts. It is important that the added iron(II) sulfate-monohydrate be pure, that is, that it contains besides sulfuric acid less than 2% impurities of other elements. For example, an iron(II) lll~C283 sulfate monohydrate which is obtained ina known manner from the iron(II) sulfate-heptahydrate produced during the titanium dioxide manufacture prior to the hydrolysis step is suitable for this purpose. Iron(II) sulfate-monohydrate which, on the other hand, occurs in the reconcentration of the waste acid is as a rule not suitable as starting material. The presence of sulfuric acid is not troublesome.
The addition of iron(II) sulfate-monohydrate in several small portions increases materially the effect of its chromium removal.
The reconcentrated sulfuric acid obtained according to the invention may not only be recycled to the titanium dioxide manufacturing process, but may also, in a manner known as such, be employed for other purposes or worked up.
The separated iron(II) sulfate-monohydrate may, in a manner known as such, be worked up further or else utilized.
In the process according to the invention not only waste acids from the titanium dioxide manufacturing process but also other iron(II) sulfate-containing sulfuric acid solutions may be employed.
In the following examples the invention is explained in more detail.
Waste acids which are produced in the manufacture of titanium dioxide according to the sulfate process were worked up. In this the start was made with ilmenite of the following composition:
TiO2 44.3%
Fe 34.8%
Mg 2.70%
SiO2 2.72%
Mn 0.22%
~lOG2a3 Ca 0.22%
V 0.14%
Cr 0.05%
Ni 0.016%
Nb 0.006%
In this example the reconcentration of a waste acid is described as it is carried out in the known manner.
1.2 liters of waste acid with a content of 341 gpl H2S04 and 7gO mg Cr/kg H2S04 were concentrated in a rotary evaporator at a pressure of 40 mbar. Altogether 660 ml water were distilled off. In this procedure more and more iron sulfate precipitated steadily with increasing H2S04 concentration.
After separation of the precipitated iron sulfate a reconcentrated acid was obtained with 1054 gpl H2S04 (corresponding to 65.9% by weight) and 530 mg Cr/kg H2S04 Thus, only 33% of the original chromium present in the waste acid was separated out. Such an acid leads to a chromium enrichment in the titanium dioxide pigment and thus to a considerable impairment of the pigment when it is recycled B into the titanium diO~ide manufacturing process.
1 liter 65% sulfuric acid was placed into a 6-liter flask and heated to boiling at a pressure of 27 mbar (boiling point 65C). Subsequently 30 liters waste acid of the composi-tion 325 gpl H2S04 Z~33 46 gpl Fe 615 mg Cr/kg H S0 1690 mg V/kg H2S04 ' were added continuously to the boiling 65% sulfuric acid, wherein the speed of addition of the waste acid and the volume of distilled off water were correlated to each other in such a way~that the sulfuric acid concentration in the flask was fully maintained. These ratios were established at a speed of 1 liter waste acid per hour.
Practically the entire amount of dissolved iron sulfate precipitated at the moment of flowing into the 65%
sulfuric acid while carrying along considerable amount of the trace elements. The acid freed from precipitated metal salts had the following composition:
947 gpl H2S04 2.4 gpl Fe 178 mg Cr/kg H2S04 211 mg V/kg H2S04 The rate of chromium separation was 71%, referring to the amount of chromium present in the waste acid. At the same time 88% of the vanadium was separated out. The acid obtained could be returned directly into the titanium dioxide manufacturing process.
The waste acid had the following composition:
307 gpl H2S04 51 gpl Fe 684 mg Cr/kg H2S04 1760 mg V/kg H2S04 1 liter of a sulfuric acid solution with a H2S04 content of 31% was placed in a 6 liter flask and heated in a 110~
vacuum of 100 to 107 mbar to boiling (B.Pt. 54 to 57 C).
Subsequently 25 liters of waste acid were added continuously to the boiling receiver acid wherein the speed of addition of the waste acid and the amount of distilled off water are so related to one another that the sulfuric acid concentration in the flask remained the same. No metal salt precipitated.
18.7 liters preconcentrated acid were obtained. This was held at a temperature of 50C in order to avoid the crystalli-zation of iron(II) sulfate heptahydrate.
In the second reconcentration step this preconcen-trated acid was reconcentrated at normal pressure in a manner analogous to that of the waste acid in Example 2. After separating the precipitated metal salts the reconcentrated acid had the following composition:
1042 gpl H2S04 0.7 gpl Fe 146 mg Cr/kg H2S04 , 320 mg V/kg H2S04 79% of the chromium and simultaneously 82% of the vanadium had been separated out, so that the acid was suitable for return,ing to the titanium dioxide manufacturing process.
A waste acid of the following composition was worked up:
376 gpl H2S04 45 gpl Fe 585 mg Cr/kg H2S04 1700 mg V/kg H2S04 This waste acid was subjected to a two-step recon-centration as in Example 3, with the difference, however, thatthe preconcentrated acid was cooled prior to the further ilO~283 reconcentration and iron(II) sulfate heptahydrate was separated out so that the acid in an amount of 17.5 liters with a content of 413 gpl H2S04 and 23 gpl Fe was passed onto the second reconcentrating step.
By the intermediate separation of iron(II) sulfate heptahydrate the amount of precipitable iron sulfate was reduced in the second step which`led to a smaller separation of chromium and vanadium (and of additional trace elements).
The acid obtained after the second reconcentration step had the following composition:
looo gpl H2S04
3.9 gpl Fe 362 mg Cr/kg H2S04 : 542 mg V/kg H2S04 The chromium separation figure was only 38%, that of vanadium only 68%. This acid was unsuitable for the direct recycling into the titanium dioxide process.
.:
A waste acid having a sulfuric acid content of 302 gpl which contained 52.0 gpl Fe as well as 190 mg/l chromium and 520 mg/l vanadium (corresponding to 630 mg Cr/kg H2S04 and 1720 mg V/kg H2S04) was used. This waste acid was continuously reconcentrated in one step.
Herein it was pumped in a 58 liter pilot plant with the help of a centrifugal pump over a heat exchanger and a vacuum evaporating vessel. At a pressure of 67 mbar and a temperature of 92 C fresh waste acid was added contin-uously prior to the heat exchanger at an average of 20.3 liters/hr, the evaporated water was removed and, at the same time, concentrated acid taken off via an overflow.
The reconcentrated acid contained 1076 gpl H2S04, 1~0~
corresponding to 67.7% by weight, and 1.4 gpl Fe, and showed only 130 mg Cr/kg H2S04 and 120 mg V/kg H2S04. Thus, 79%
of the chromium and 93% of the vanadium had been removed.
The examples show that in the working up of waste acids originating from the processing of an ilmenite rich in chromium, according to the process of the invention 71 to 79%
of the chromium contained in the waste acids could be removed.
(Examples 2, 3 and 5). On the other hand, when operating in the known manner (Examples 1 and 4), then only 33 to 38%
of the chromium contained in the waste acids was removed.
` A comparison of Examples 3 and 4 further shows clearly that the place where the iron(II) sulfate was precipitated is important for the efficient removal of chromium. When an essential part of the iron was separated out before reaching the sulfuric acid concentration of 65%, then only 38% of the chromium could be removed (Example 4); on the other hand, by processing according to the invention 79% of the chromium could be removed (Example 3). The vanadium separation also was better in the process according to the invention (82%
compared with 68% in Example 4).
.:
A waste acid having a sulfuric acid content of 302 gpl which contained 52.0 gpl Fe as well as 190 mg/l chromium and 520 mg/l vanadium (corresponding to 630 mg Cr/kg H2S04 and 1720 mg V/kg H2S04) was used. This waste acid was continuously reconcentrated in one step.
Herein it was pumped in a 58 liter pilot plant with the help of a centrifugal pump over a heat exchanger and a vacuum evaporating vessel. At a pressure of 67 mbar and a temperature of 92 C fresh waste acid was added contin-uously prior to the heat exchanger at an average of 20.3 liters/hr, the evaporated water was removed and, at the same time, concentrated acid taken off via an overflow.
The reconcentrated acid contained 1076 gpl H2S04, 1~0~
corresponding to 67.7% by weight, and 1.4 gpl Fe, and showed only 130 mg Cr/kg H2S04 and 120 mg V/kg H2S04. Thus, 79%
of the chromium and 93% of the vanadium had been removed.
The examples show that in the working up of waste acids originating from the processing of an ilmenite rich in chromium, according to the process of the invention 71 to 79%
of the chromium contained in the waste acids could be removed.
(Examples 2, 3 and 5). On the other hand, when operating in the known manner (Examples 1 and 4), then only 33 to 38%
of the chromium contained in the waste acids was removed.
` A comparison of Examples 3 and 4 further shows clearly that the place where the iron(II) sulfate was precipitated is important for the efficient removal of chromium. When an essential part of the iron was separated out before reaching the sulfuric acid concentration of 65%, then only 38% of the chromium could be removed (Example 4); on the other hand, by processing according to the invention 79% of the chromium could be removed (Example 3). The vanadium separation also was better in the process according to the invention (82%
compared with 68% in Example 4).
Claims (5)
1. A process for the extensive removal of undesirable metal ions, especially chromium ions, in the reconcentra-tion of dilute iron(II) sulfate containing sulfuric acid solutions by evaporating water and separating iron(II) sulfate wherein the dilute sulfuric acid solution is evap-orated up to a content of 60 to 70% by weight H2SO4, characterized in that the dilute sulfuric acid solution or preconcentrated sulfuric acid solution produced from it, without separation of metal salts from solution or without formation of solid metal salts, is continuously added, without simultaneous addition of clarified sulfuric acid or sulfuric acid solution, into a receiver which contains a sulfuric acid metal salt suspension of which the liquid constitutent contains 60 to 70% by weight H2SO4 and that simultaneously sufficient water is evaporated that the sulfuric acid concentration is maintained in the range of 60-70% by weight, and that continuously or at certain intervals a part of the sulfuric acid containing metal salt suspension is removed from the receiver and that the precipitated metal salts are separated.
2. A process according to claim 1, characterized in that the diluted iron(II) sulfate containing sulfuric acid solution is concentrated in one step by placing the dilute sulfuric acid solution itself into the receiver which contains the 60-70% sulfuric acid containing metal salt suspension.
3. A process according to claim 1, characterized in that the dilute iron(II) sulfate containing sulfuric acid solution is concentrated in two steps by preconcentrating it in a first step without separation of metal salts to a content of about 28-31% by weight H2SO4, the preconcen-trated sulfuric acid solution produced maintained at a temperature of at least about 50°C and then in a second step placed into the receiver and subjected to further evaporation.
4. A process according to claim 3, characterized in that in the first step the dilute sulfuric acid solution is passed continuously into a vessel which contains precon-centrated sulfuric acid solution and that simultaneously sufficient water is evaporated that the sulfuric acid concentration in this vessel remains constant and that continuously or at certain intervals a part of the precon-centrated sulfuric acid solution is drawn off from this container and is placed in the receiver of the second step.
5. A process according to claim 4, characterized in that the preconcentration takes place in a vacuum in a vessel that is heated indirectly by the steam that is obtained in the reconcentration of the preconcentrated sulfuric acid solution.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19762618121 DE2618121A1 (en) | 1976-04-26 | 1976-04-26 | Sulphuric acid demetallisation in titanium dioxide pigment mfr. - by continuous addn. to metal salt suspension in conc. acid and evapn. |
| DEP2618121.5 | 1976-04-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1100283A true CA1100283A (en) | 1981-05-05 |
Family
ID=5976224
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA274,390A Expired CA1100283A (en) | 1976-04-26 | 1977-03-21 | Removal of undesirable metal ions in the concentration of dilute sulfuric acid solutions containing iron (ii) sulfate |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1100283A (en) |
| DE (1) | DE2618121A1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3327769A1 (en) * | 1983-08-02 | 1985-02-14 | Bayer Ag, 5090 Leverkusen | METHOD FOR THE TREATMENT OF THICK ACID |
| DE3329842A1 (en) * | 1983-08-18 | 1985-02-28 | Kronos Titan-Gesellschaft Mbh, 5090 Leverkusen | Process for substantially removing unwanted metal ions, in particular vanadium ions, when concentrating dilute iron(II) sulphate-containing sulphuric acid solutions |
| DE3513120A1 (en) * | 1985-04-12 | 1986-10-23 | Bayer Ag, 5090 Leverkusen | METHOD FOR PRODUCING TITANIUM DIOXIDE |
| FR2634751B1 (en) * | 1988-07-29 | 1991-02-08 | Metaleurop Sa | |
| DE3922105A1 (en) * | 1989-07-05 | 1991-01-17 | Bayer Ag | METHOD AND DEVICE FOR CONCENTRATING SULFURIC ACID CONTAINING METAL SULFATE |
| DE3938915C1 (en) * | 1989-11-24 | 1991-05-08 | Bayer Ag, 5090 Leverkusen, De |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1131193B (en) * | 1960-10-14 | 1962-06-14 | Bayer Ag | Process for concentrating and desalting dilute, salty sulfuric acid |
-
1976
- 1976-04-26 DE DE19762618121 patent/DE2618121A1/en not_active Withdrawn
-
1977
- 1977-03-21 CA CA274,390A patent/CA1100283A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2618121A1 (en) | 1977-11-10 |
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