CA1077176A - Process for neutralizing waste sulfuric acids - Google Patents
Process for neutralizing waste sulfuric acidsInfo
- Publication number
- CA1077176A CA1077176A CA275,436A CA275436A CA1077176A CA 1077176 A CA1077176 A CA 1077176A CA 275436 A CA275436 A CA 275436A CA 1077176 A CA1077176 A CA 1077176A
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- CA
- Canada
- Prior art keywords
- slurry
- asbestos tailings
- magnesium sulfate
- filtrate
- sulfate
- Prior art date
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- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
- A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
- A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
- A62D3/36—Detoxification by using acid or alkaline reagents
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/40—Magnesium sulfates
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
- C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical processes
-
- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
- A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
- A62D2101/40—Inorganic substances
- A62D2101/41—Inorganic fibres, e.g. asbestos
-
- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
- A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
- A62D2101/40—Inorganic substances
- A62D2101/47—Inorganic substances containing oxygen, sulfur, selenium or tellurium, i.e. chalcogen
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Geology (AREA)
- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- General Health & Medical Sciences (AREA)
- Business, Economics & Management (AREA)
- Emergency Management (AREA)
- Environmental & Geological Engineering (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Toxicology (AREA)
- Inorganic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Removal Of Specific Substances (AREA)
Abstract
There is provided a novel process for the neutralization of waste industrial sulfuric acids which comprises partially neutralizing waste industrial sulfuric acids with asbestos tailings, thereby forming a slurry containing magnesium sulfate and subjecting said slurry to a further neutralization step under oxidizing conditions by the addition of asbestos tailings which may be followed by the addition of magnesium hydroxide until the pH of the slurry is about 7.0 and recovering the filtrate containing the magnesium sulfate thus formed.
Description
1~77176 The present invention relates to a novel process for disposing of industrial waste sulfuric acid. More particular-ly, it relates to a novel process for disposing of industrial waste sulfuric acid by reacting same with industrial material products containing magnesium oxide and particularly asbestos tailings.
BACKGROUND OF THE INVENTION
Almost one third of the world asbestos production comes from the Province of Quebec, where more than nine tenths of mined asbestos ores become wastes or tailings after extraction of the fiber fractions therein. Thus, colossal tonnages of the asbestos tailings have accumulated in Quebec as solid waste hills, and the tonnage is steadily increasing. The -average asbestos tailings comprise about 40% MgO by weight, an attractive magnesia source.
Some titanium dioxide manufacturers situated in Quebec dump a large quantity of waste sulfuric acid and various sulfates into the St-Lawrence river as liquid effluents. No processing to recover the waste acid or to reduce the water pollution has currently been practised through lack of an economical method.
As for recovery of magnesium values from serpentine ores or asbestos tailings, U.S. patent No. 3,338,667 issued Aug. 29, 1967 to Pundsack describes a process wherein serpen-tine ores are treated with ammonium bisulfate to solubilize magnesium values therein and recover same as magnesia through magnesium basic carbonate. Japanese patent No. 71-16,245 issued May 4, 1971 to Takeuchi claims a process wherein serpen-tine ores are made to react with concentrated sulfuric acid in solid state to obtain magnesium sulfate. Another Japanese patent No. 71-26,096 issued July 28, 1971 to Kikuchi et al _l _ ~
1~77176 discloses a process wherein serpentine ores are roasted at about 600C, followed by ammonium sulfate leaching to obtain magnesia through magnesium carbonate. Rumanian patent No.
52,988 issued Jan. 7, 1972 to Socolescu et al describes a process wherein waste pickling acids are treated with ground serpentine ores, the solidified mixtures being dried at 250C, then calcined at 800C, leached with dilute sulfuric acid and spray-dried at 800C to obtain magnesia and sulfur.
In contrast, it is the object of the instant invention to provide a process primarily for the production of pure magnesium sulfate from waste sulfuric acids and asbestos tailings by a wet method.
The instant invention provides an economical process for reducing water pollution by employing asbestos tailings to neutralize waste sulfuric acid such as is obtained from titanium dioxide plants or picking sulfuric acid solutions obtained from steel mills.
THE INVENTION
In accordance with the present invention, there is now provided a novel process for the neutralization of waste industrial sulfuric acids which comprises partially neutral-izing waste industrial sulfuric acids with asbestos tailings, thereby forming a slurry containing magnesium sulfate and subjecting said slurry to a further neutralization step under oxidizing conditions by the addition of asbestos tailings which may be followed by the addition of magnesium hydroxide until the pH of the slurry is about 7.0 and recovering the filtrate containing the magnesium sulfate thus formed. A crude residue of magnesium sulfate may be recovered from the filtrate by evaporation or substantially pure magnesium sulfate may be obtained by adding magnesia to the filtrate thereby precipi-10771~76 tating undesired impurities and recovering a filtrate contain-ing substantially pure magnesium sulfate.
The first neutralization step of the industrial waste sulfuric acids is carried out with asbestos tailings containing an important amount of magnesium oxide to neutralize a major portion of the free sulfate anions originally present in the industrial waste sulfuric acids, thus forming an initial slurry containing a substantial amount of magnesium sulfate.
The second neutralization step carried out under oxidizing conditions on the magnesium sulfate slurry is done to liberate further sulfate anions from any soluble metal sulfates present in the slurry obtained from the first neutralization step while the pH of the slurry rises to about 7. At the end -of the second neutralization step, as the pH of the slurry is increased to more than 7 any heavy metal cations will precipi-tate out as hydroxides and will be eliminated along with any unreacted asbestos tailings by filtration, thus yielding a filtrate which is a neutral solution of magnesium sulfate which can be used for the preparation of crude or purified magnesium sulfate or other magnesium compounds such as magnesium hydroxide, magnesium carbonate or magnesium salts such as ammonium-magnesium sulfate and others.
The waste industrial sulfuric acids to be neutralized are those produced by titanium dioxide manufacturers or pickling sulfuric acid solutions from steel mills and the like.
Essentially such waste sulfuric acids contain soluble salts of iron, aluminum, vanadium, titanium and other metals as well as free sulfuric acid. Those industrial sulfuric acid wastes containing from about 30 to about 300 grams S04 per liter are economical to use with 100 to 300 grams S04 per liter being preferred. If a more concentrated waste acid solution is 1~77176 available it can be readily diluted to fall within the above range, while a waste acid having a S04 concentration lower than the above range can be concentrated by evaporation to the desired concentration, but obviously a weak S04 containing acid should not be used if too much energy has to be used to concen-` trate it to the desired S04 content or by adding the necessary amount of concentrated sulfuric acid to raise the S04 concen-tration to the required range. It should also be noted that if a waste acid having a S04 content substantially higher than 300 grams/liter is used there will be obtained a solution of mag-nesium sulfate which will be too concentrated thus resulting in difficulties in the purification of this solution or in the elimination of manganese and chromium.
When operating with any waste industrial sulfuric acid solution containing sulfate anions in the form of free sulfuric acid and soluble metal sulfates practically all these sulfate anions will be reacted with magnesium from the asbestos tailings by the time the slurry reaches pH 7Ø
The amount of asbestos tailings used in accordance with the present invention can be minimized with the use of finely ground asbestos tailings.
For optimum results, asbestos tailings having a parti-` cle size of smaller than 20 mesh but preferably from about 60to about 200 mesh should be used. When a particle size bigger than 20 mesh is used larger quantities of asbestos tailings will be required because less magnesium oxide will be available for neutralizing the sulfate anions, thus resulting in a less efficient process. On the other hand, a particle size smaller than 200 mesh can be used, but if the particle size of asbestos tailings is smaller than 325 mesh, difficulties in filteringwill be encountered in the later stages of the process of the ~0771~6 present invention.
To exemplify the first neutralization step when 1.0 liter of waste acid containing 100 grams S04 per liter is made to react with 200 grams of ground asbestos tailings with a granulometry of -100 mesh, the pH of the slurry will reach about 3.0 in one hour provided the slurry is agitated moder-ately at 95C. More generally, when the pH of the slurry reaches a value of 2.5 to 3.5, the initial neutralization step can be terminated.
The initial neutralization step is conducted at temperatures of from 15 to 100C with the range of about 70 to about 100C being preferred. It should also be appreciated that a very sudden addition of asbestos tailings to hot waste sulfuric acid may cause a violent exothermic reaction accompa-nied by gas evolution. On the other hand, a slow or gradual addition tends to generate some viscous silicic acid leading to a slow filtration in later stages. The formation of the viscous silicic acid can be minimized when about twice more asbestos tailings than the stoichiometric equivalence to S04 anions present in the waste acid is admixed with a given amount of hot waste acid at a time. The stoichiometric equivalence hereinabove refers to the magnesium sulfate (MgS04). The amount of asbestos tailings used should be in excess of the stoichiometric amount required for neutralizing the sulfuric acid. Accordingly the excess of asbestos tailings should be from 25 to 600%. The neutralization step can be carried out either batchwise or continuously in countercurrent with the use of a number of neutralization tanks.
The neutralization reaction may be illustrated as follows:
(3MgO-2S~02-2H20) + H2S04 >
MgS04 t (2MgO-2SiO2 2H20) ~ H20 where the formula (3MgO-2SiO2 2H20) refers to asbestos tailings and (2MgO 2SiO2 2H20) represents partially reacted asbestos tailings. The partial dissolution of the magnesium oxide from the asbestos tailings is done intentionally in the preferred practice of the present invention in order not to dissolve the silica and magnetite contained in the asbestos tailings.
The end of the initial neutralization step is observed when the pH of the magnesium sulfate slurry is within the range of from 2.5 to 3.5, preferably 3.0, and the slurry is then subjected to the second neutralization step under oxidizing conditions. The magnesium sulfate slurry is oxidized ` so that most of the ferrous ions present in the slurry are converted to ferric ions whereby further sulfate anions become available for reaction with the magnesium oxide in the tailings. The oxidation step may be economically carried out by bubbling air through the slurry. Obviously, if cost is not a consideration other oxidizing agents such as hydrogen per-oxide may also be used.
While the oxidation is being carried out, further amounts of asbestos tailings are added thereby resulting in further neutralization of the slurry which is observed by an increase in the pH while low valence cations are oxidized and precipitated out as hydroxides. The progress of the oxidizing neutralization is marked by color change in the slurry from ; grey to dark brown thus indicating particularly the formation of ferric ions. The pH of the slurry can, if desired, be increased to a value higher than 8.0 by the further gradual addition of asbestos tailings. However, when the pH of a well oxidized slurry is higher than about 6.5, the filtrate is 1077~76 practically free of most heavy metal cations which have by then precipitated out as hydroxides.
The dissolution efficiency of magnesia from asbestos tailings continuously decreases after the pH has reached 3.0 and progresses higher. It is possible to then use as auxiliary some low quality magnesia or calcined magnesite in slurry form in the neutralization after pH 5Ø Notwithstanding, the average utilization efficiency of magnesia from asbestos tailings can be maintained above 10% during the neutralization when the pH ranges from 3 to 7, insofar as sufficient stirring and temperature are provided. Decision as to whether or not auxiliary magnesia slurry should be employed in said neutrali-zation is dependent upon the local economic factors. In general, the use of said magnesia slurry becomes more economi-cal with deteriorating dissolution efficiency of magnesia from asbestos tailings. Auxiliary neutralizers should in principle be limited to magnesia or magnesia-containing materials so as to maintain magnesium content in the end product as high as possible and impurity content therein as low as possible. The . 20 pH of the slurry resulting from the first neutralization can be increased from 3.0 to 5.0 by the gradual addition of asbestos tailings under stirring with aeration.
At this point there are two choices: one is to keep on using asbestos tailings in neutralizing the slurry, and the other is to start using the aforementioned auxiliary such as slurry of a low grade magnesia. In the latter case, even if the magnesia herein used contains some appreciable amount of iron, aluminium and other heavy metals, there is no serious contamination of the product when the contents of manganese and chromium therein are sufficiently low. In both procedures of neutralization, the amorphous silicic acid which may have ~077176 formed in the first neutralization stage is by this time coprecipitated together with ferrous and ferric hydroxides and causes little or no problem in the subsequent filtering operation. Either before or while the slurry is allowed to settle or thicken there can be recovered from the slurry by means of magnetic separator an iron-rich concentrate which may represent as much as 7% of the total weight of the asbestos tailings used in the first and second neutralizing steps. This magnetic concentrate has a commercial value as an iron ore which contains nickel and chromium. Chemical reactions during the oxidizing neutralization may be represented as follows.
Firstly, for the oxidation:
2FeS04 + 1 2 ~ 5H20 > 2Fe(OH)3 ~ 2H2S4 Similar reactions may be postulated for sulfates of the other -~ metals having low and high valences. The sulfuric acid thus produced reacts with added asbestos tailings:
H2S04 + (3M90-2SiO2-2H20) >
(2M90-2SiO2 2H20) + MgS04 + H20 When the pH of the slurry becomes higher than about 6.5, most of the other heavy metal cations can be separated out as the hydroxide precipitates:
(3M90-2SiO2.2H20) + MeS04 + H20 Me(OH)2 + MgS04 + (2MgO-2SiO2 2H20) It is observed that most of the manganese and chromium as well as the majority of the iron, aluminum, silicon, titanium, vanadium, nickel, copper and cobalt could be eliminated as their hydroxide precipitates. Further elimination of the manganese and chromium is an object of the purification oper-ation. It is noteworthy that the oxidation of ferrous to ferric ions does not have to be completed inasmuch as the pH of the slurry is higher than about 7, where most of both ferric 1~)'77176 and ferrous ions precipitate out together with the afore-mentioned heavy metal cations as mixed hydroxides. However, when a filtrate resulting from the insufficient oxidation is yellowish or nontransparent, additional aeration should be applied thereto in the presence of a small amount of asbestos tailings or low grade magnesia. This supplementary aeration takes a far shorter time than that required for a slurry having a high concentration of solids. In the oxidizing-neutrali-zation the aeration may be partially or totally replaced by bubbling oxygen or oxidation with hydrogen peroxide. When hydrogen peroxide is employed the elimination of manganese and - chromium tends to deteriorate unless the peroxide is added in dilute solution and as long as an excess is not used. Halogens which may be present in waste acids or water to be used cannot be eliminated in the present process, and tend to increase -calcium content in the filtrate resulting from the oxidizing-neutralization.
Abundant use of asbestos tailings in the herein described neutralization, despite rather low extraction yield , 20 of magnesium values therefrom, constitutes one of the important characteristics of the instant invention, differing greatly from other processes where efforts are made toward a total utilization of the serpentine ores including recoveries of silica and iron. The preferred practice of the instant invention is in line particularly with the local conditions around Quebec where the ground asbestos tailings are available in abundance.
When the filtration following the oxidizing-neutrali-zation is done on slurries having a pH higher than 7.0, the filtrates resulting therefrom will comprise very small amounts of impurities. The filtrates may therefore be evaporated to g _ :,, 1~77176 produce hydrated magnesium sulfate crystals which readily meet quality standards required for some commercial products such as magnesium sulfate fertilizer.
The solution can also be processed further for the production of refractory grade magnesia via magnesium hydroxide with the use of ammonia gas or ammonium hydroxide solution.
Halogens in the raw materials of the present process go practi-cally all in the filtrate as halides of alkali metals as well as those of magnesium and calcium. When excessive calcium salts are present in the raw materials, the majority of the salts may be eliminated as solid waste of insoluble calcium sulfate. If the filtrate is saturated with calcium sulfate the concentration thereof in the filtrate can reach as high as 2 grams CaS04 per liter as compared to a typical MgS04 concen-tration of 200 grams per liter. The presence of a small amount of calcium salts in magnesium compounds, however, does not cause major problems in most of usages.
The ratios of Ti/Mg, V/Mg, Cr/Mg, and Fe/Mg are consistently lower than 1/1,000 in the resultant solution of magnesium sulfate having a pH higher than 7. The only heavy metal cation that may surpass the foregoing ratio is manganese, the ratio thereof being in some cases as high as 3/1,000. The magnesium sulfate, magnesium hydroxide and magnesia derived from said filtrate comprising these levels of impurities are often pure enough to meet criteria for certain usages. How-ever, in need of higher purity magnesium compounds, said magnesium sulfate solution can be further purified economically by adding fine magnesia slurry thereto in a small quantity, followed by the filtration thereof. Addition of the magnesia slurry should be made under stirring and heating so as to dis-solve in the solution as much of magnesium hydroxide as possible. The amount of magnesia slurry to be added depends upon the impurity levels in the solution and also on the aimed levels in the end products. The magnesia slurry herein not only displaces impurity cations but also coprecipitates some cations and anions as well. A period of digestion time is needed, and while the solution is kept at a pH higher than about 8.5, most of the manganese and chromium, and also some important fraction of calcium can be precipitated out therefrom as hydroxide mixture. The solution treated with magnesia slurry is then cooled and then filtered after standing. A
solution of high purity magnesium sulfate results therefrom.
The resulting precipitates rich in magnesium hydroxide may be recycled, only if low in impurities, for the use as neutralizer during the oxidizing-neutralization. When said hydroxide precipitate is rich in manganese or other useful or harmless elements, the hydroxide may be used as an additive to fertil-izers. A more concentrated solution of magnesium sulfate is less amenable to this purification method, so that the method should be applied, if possible, to solutions while dilute in magnesium sulfate, preferably below 200 grams MgS04 per liter.
For example, 1.0 liter of a filtrate solution com-prising 125 grams MgS04, 400 milligrams Ca, 40 milligrams Mn, and 10 milligrams Fe can be purified by adding magnesium hydroxide slurry containing 1.5 gram MgO, whereby the pH of the solution is increased up to 8.5. Filtration thereof yields 1.0 liter of a clear solution, comprising 125 grams MgS04, 150 milligrams Ca, 4 milligrams Mn, and 2 milligrams Fe. The pH of this alkaline filtrate can be adjusted to 7, if desired, by adding thereto pure sulfuric acid. Evaporation of the solution yields a high purity magnesium sulfate crystal, MgS04 7H20.
The use of magnesium hydroxide slurry mentioned hereinabove can be partly replaced with a minimal use of sodium hydroxide solution.
If the solution comprises those impurities which can be eliminated as hydroxide under reducing conditions, a small amount of ferrous sulfate may be added to once boiled or degassed neutral solution. The ferrous sulfate is then slightly oxidized by aeration, followed by the neutralization with magnesium hydroxide slurry to precipitate out iron as mixed ferrous and ferric hydroxides, wherein the impurities are precipitated or coprecipitated. Addition of ferric sulfate to the neutral solution, followed by the neutralization with magnesium hydroxide slurry, is also effective in eliminating some impurities mainly through coprecipitation or adsorption.
The magnesium sulfate prepared in accordance with the present invention may be usedto prepare other magnesium com-pounds such as magnesium hydroxide, magnesium oxide, magnesium basic carbonate, lactate and oxalate by procedures which are well known to those skilled in the art.
The following examples are presented in order to further illustrate the preferred and typical means of prac-ticing the instant invention and the advantages thereof, but it is distinctly understood that these examples are illustra-tive only and in no way limitative.
EXAMPLE I
1.0 liter or 1,300 grams of waste sulfuric acid from a manufacturerof titanium dioxide pigment having the following chemical composition:
1~)771'76 Free H2S04320 9./l.
Total S04 404 9-/1-Fe 28 g./l.
Ti 5 9./l.
Al 4 9./l.
V 1.0 9./1. , '-Cr 0.5 9./l.
Ca 0.3 9./l.
Mn 0.1 9./l.
was diluted with 3.0 liters of water to a total volume of about 4.0 liters and then heated to 95C. 800 grams of asbestos tailings ground to -75 mesh having the following chemical composition:
MgO 39.7%
SiO2 37-3%
Fe203 7.1%
A1203 0.6%
H20 13.0%
Cr 600 ppm Mn 500 ppm Ni 400 ppm Co 50 ppm Na 50 ppm Pb 20 ppm K 10 ppm Zn 10 ppm Ca 4 ppm was added to the waste acid while stirring. The slurry was continuously heated and stirred at 95C for 30 minutes. The slurry then indicated a pH of 2.9. Aeration of the slurry was then started at a rate of 10 liters at 20C per minute and 50 ~'/7176 grams of the ground asbestos tailings were added every 5 minutes while agitating the slurry at 85C. In 80 minutes when the total addition of asbestos tailings amounted to 800 grams, the pH of the slurry reached 7.3. In other words, the total of 1,600 grams of the ground asbestos tailings was required together with 800 liters of air at 20C to neutralize 1.0 liter of the aforementioned waste acid solution. The slurry was then subjected to thickening, during early stages of which a magnet was moved through the bottom solids to collect magnetic fraction thereof. A magnetic concentrate weighing 80 grams and containing 53% Fe, 1.10% Cr and 0.83% Ni was recovered there-from. Filtration of the slurry coupled with washing of the separated solids with 1.0 liter of water yielded about 5.0 liters of a clear filtrate and a solid waste weighing 1,450 grams (air-dried basis). Chemical analyses of the filtrate indicated the following composition:
Mg 20.0 9./l.
S04 79 9./1.
Fe 8 mg./l.
; 20 Tibelow 1 mg./l.
Al 4 mg./l.
Vbelow 1 mg./l.
Crbelow 1 mg./l.
Ca 300 mg./l.
Mn 30 mg./l.
Recovery of the sulfate anions from the waste acid was 98%.
In carrying out a further purification, the filtrate was heated almost to boil and a magnesium hydroxide slurry comprising 4.0 grams of MgO was added thereto while agitating. The solution was continuously heated and stirred for 100 minutes and then cooled to room temperature, and the solution was allowed to .
stand for a few hours prior to filtration thereof. Most of the magnesium in the added magnesium hydroxide slurry was recovered after filtration as yellowish magnesium hydroxide, which con-tained too much impurities to be returned to the oxidizing neutralization stage. The purified filtrate still having a volume of about 5.0 liters indicated a pH of 8.5, and chemical analysis thereof revealed the following composition:
Mg 20.0 9./1.
Febelow 1 mg./l.
Tibelow 1 mg./l.
Albelow 1 mg./l.
Vbelow 1 mg./l.
Crbelow 1 mg./l.
Ca100 mg./l.
Mn 3 mg./l.
This solution could be treated by the aforesaid pH adjusting method with sulfuric acid, followed by evaporation thereof to produce hydrated magnesium sulfate crystals.
EXAMPLE II
The waste sulfuric acid and asbestos tailings used hereinbelow were the same as in the preceding Example I. 1.0 liter of the waste acid was diluted with 3.0 liters of water to 4.0 liters in total and then heated to 95C. The acid was then ; admixed with 800 grams of the finely ground asbestos tailings.
The pH of the slurry after 60 minutes neutralization indicated 3Ø Aeration was then started at a rate of 10 litersat 20C
per minute as the asbestos tailings was added to the slurry at a rate of 10 grams per minute while heating and stirring the slurry at 85C. When the addition of the asbestos tailings amounted to 400 grams and the volume of the injected air to 500 ~ .
.
' . . - . ~ , .
~77176 liters (20C), the pH of the slurry indicated 5.0, and then while the aeration was temporarily ceased about 70 grams of an iron-rich magnetic concentrate was collected therefrom with a magnet. Aeration was restarted, and neutralization thereafter was carried out using low grade magnesium hydroxide in slurry form. The slurry comprising 10 grams of magnesium hydroxide comprising 35% Mg was added thereto every 5 minutes while aerating. 200 liters of air was bubbled thereinto during 20 minutes as 40 grams of the magnesium hydroxide was added thereto, and the pH then indicated 6.6. Filtration of the slurry yielded 5.0 liters of slightly yellowish filtrate. 10 grams magnesium hydroxide in slurry form was then added to the filtrate while aerating with 100 liters of air. The slurry was then cooled to room temperature and filtered. 5.0 liters of a clear solution was obtained therefrom, the pH of which indi-cated 8.1. Chemical analysis thereof yielded the following composition:
Mg20.0 9./l.
so479 9./1.
Fe2 mg./l.
Al2 mg./l.
Tibelow 1 mg./l.
Vbelow 1 mg./l.
Crbelow 1 mg./l.
; Ca250 mg./l.
Mn20 mg./l.
EXAMPLE III
The waste sulfuric acid and asbestos tailings used hereinbelow were the same as in the preceding Example I. 1.0 liter of the waste acid was diluted with 3.0 liters of water to 4.0 liters and then heated to 95C. The acid was then admixed .. . .
. .
-~77176 .
with 800 grams of the finely ground asbestos tailings. pH of the slurry after 60 minutes leaching indicated 3Ø Aeration was then started at a rate of 10 liters per minute and 50 grams of the asbestos tailings was added to the slurry every 5 minutes while heating and stirring the slurry at 85C. When the additional asbestos tailings amounted to 800 grams, the slurry indicated a pH of 7.3. Filtration of the slurry yielded ` 5.0 liters of slightly yellowish filtrate, comprising 16 ppm Mn and 4 ppm Fe. 1.0 gram FeS04 in solution form was added to the filtrate. 4.0 grams of MgO in fine slurry form was then added thereto while heating and stirring the slurry. Filtration of the cooled slurry yielded a filtrate containing 1.5 ppm Mn and 1 ppm Fe. Evaporation and crystallization of the filtrate yielded a high pur;ty magnesium sulfate crystal.
' .
~' :
.
BACKGROUND OF THE INVENTION
Almost one third of the world asbestos production comes from the Province of Quebec, where more than nine tenths of mined asbestos ores become wastes or tailings after extraction of the fiber fractions therein. Thus, colossal tonnages of the asbestos tailings have accumulated in Quebec as solid waste hills, and the tonnage is steadily increasing. The -average asbestos tailings comprise about 40% MgO by weight, an attractive magnesia source.
Some titanium dioxide manufacturers situated in Quebec dump a large quantity of waste sulfuric acid and various sulfates into the St-Lawrence river as liquid effluents. No processing to recover the waste acid or to reduce the water pollution has currently been practised through lack of an economical method.
As for recovery of magnesium values from serpentine ores or asbestos tailings, U.S. patent No. 3,338,667 issued Aug. 29, 1967 to Pundsack describes a process wherein serpen-tine ores are treated with ammonium bisulfate to solubilize magnesium values therein and recover same as magnesia through magnesium basic carbonate. Japanese patent No. 71-16,245 issued May 4, 1971 to Takeuchi claims a process wherein serpen-tine ores are made to react with concentrated sulfuric acid in solid state to obtain magnesium sulfate. Another Japanese patent No. 71-26,096 issued July 28, 1971 to Kikuchi et al _l _ ~
1~77176 discloses a process wherein serpentine ores are roasted at about 600C, followed by ammonium sulfate leaching to obtain magnesia through magnesium carbonate. Rumanian patent No.
52,988 issued Jan. 7, 1972 to Socolescu et al describes a process wherein waste pickling acids are treated with ground serpentine ores, the solidified mixtures being dried at 250C, then calcined at 800C, leached with dilute sulfuric acid and spray-dried at 800C to obtain magnesia and sulfur.
In contrast, it is the object of the instant invention to provide a process primarily for the production of pure magnesium sulfate from waste sulfuric acids and asbestos tailings by a wet method.
The instant invention provides an economical process for reducing water pollution by employing asbestos tailings to neutralize waste sulfuric acid such as is obtained from titanium dioxide plants or picking sulfuric acid solutions obtained from steel mills.
THE INVENTION
In accordance with the present invention, there is now provided a novel process for the neutralization of waste industrial sulfuric acids which comprises partially neutral-izing waste industrial sulfuric acids with asbestos tailings, thereby forming a slurry containing magnesium sulfate and subjecting said slurry to a further neutralization step under oxidizing conditions by the addition of asbestos tailings which may be followed by the addition of magnesium hydroxide until the pH of the slurry is about 7.0 and recovering the filtrate containing the magnesium sulfate thus formed. A crude residue of magnesium sulfate may be recovered from the filtrate by evaporation or substantially pure magnesium sulfate may be obtained by adding magnesia to the filtrate thereby precipi-10771~76 tating undesired impurities and recovering a filtrate contain-ing substantially pure magnesium sulfate.
The first neutralization step of the industrial waste sulfuric acids is carried out with asbestos tailings containing an important amount of magnesium oxide to neutralize a major portion of the free sulfate anions originally present in the industrial waste sulfuric acids, thus forming an initial slurry containing a substantial amount of magnesium sulfate.
The second neutralization step carried out under oxidizing conditions on the magnesium sulfate slurry is done to liberate further sulfate anions from any soluble metal sulfates present in the slurry obtained from the first neutralization step while the pH of the slurry rises to about 7. At the end -of the second neutralization step, as the pH of the slurry is increased to more than 7 any heavy metal cations will precipi-tate out as hydroxides and will be eliminated along with any unreacted asbestos tailings by filtration, thus yielding a filtrate which is a neutral solution of magnesium sulfate which can be used for the preparation of crude or purified magnesium sulfate or other magnesium compounds such as magnesium hydroxide, magnesium carbonate or magnesium salts such as ammonium-magnesium sulfate and others.
The waste industrial sulfuric acids to be neutralized are those produced by titanium dioxide manufacturers or pickling sulfuric acid solutions from steel mills and the like.
Essentially such waste sulfuric acids contain soluble salts of iron, aluminum, vanadium, titanium and other metals as well as free sulfuric acid. Those industrial sulfuric acid wastes containing from about 30 to about 300 grams S04 per liter are economical to use with 100 to 300 grams S04 per liter being preferred. If a more concentrated waste acid solution is 1~77176 available it can be readily diluted to fall within the above range, while a waste acid having a S04 concentration lower than the above range can be concentrated by evaporation to the desired concentration, but obviously a weak S04 containing acid should not be used if too much energy has to be used to concen-` trate it to the desired S04 content or by adding the necessary amount of concentrated sulfuric acid to raise the S04 concen-tration to the required range. It should also be noted that if a waste acid having a S04 content substantially higher than 300 grams/liter is used there will be obtained a solution of mag-nesium sulfate which will be too concentrated thus resulting in difficulties in the purification of this solution or in the elimination of manganese and chromium.
When operating with any waste industrial sulfuric acid solution containing sulfate anions in the form of free sulfuric acid and soluble metal sulfates practically all these sulfate anions will be reacted with magnesium from the asbestos tailings by the time the slurry reaches pH 7Ø
The amount of asbestos tailings used in accordance with the present invention can be minimized with the use of finely ground asbestos tailings.
For optimum results, asbestos tailings having a parti-` cle size of smaller than 20 mesh but preferably from about 60to about 200 mesh should be used. When a particle size bigger than 20 mesh is used larger quantities of asbestos tailings will be required because less magnesium oxide will be available for neutralizing the sulfate anions, thus resulting in a less efficient process. On the other hand, a particle size smaller than 200 mesh can be used, but if the particle size of asbestos tailings is smaller than 325 mesh, difficulties in filteringwill be encountered in the later stages of the process of the ~0771~6 present invention.
To exemplify the first neutralization step when 1.0 liter of waste acid containing 100 grams S04 per liter is made to react with 200 grams of ground asbestos tailings with a granulometry of -100 mesh, the pH of the slurry will reach about 3.0 in one hour provided the slurry is agitated moder-ately at 95C. More generally, when the pH of the slurry reaches a value of 2.5 to 3.5, the initial neutralization step can be terminated.
The initial neutralization step is conducted at temperatures of from 15 to 100C with the range of about 70 to about 100C being preferred. It should also be appreciated that a very sudden addition of asbestos tailings to hot waste sulfuric acid may cause a violent exothermic reaction accompa-nied by gas evolution. On the other hand, a slow or gradual addition tends to generate some viscous silicic acid leading to a slow filtration in later stages. The formation of the viscous silicic acid can be minimized when about twice more asbestos tailings than the stoichiometric equivalence to S04 anions present in the waste acid is admixed with a given amount of hot waste acid at a time. The stoichiometric equivalence hereinabove refers to the magnesium sulfate (MgS04). The amount of asbestos tailings used should be in excess of the stoichiometric amount required for neutralizing the sulfuric acid. Accordingly the excess of asbestos tailings should be from 25 to 600%. The neutralization step can be carried out either batchwise or continuously in countercurrent with the use of a number of neutralization tanks.
The neutralization reaction may be illustrated as follows:
(3MgO-2S~02-2H20) + H2S04 >
MgS04 t (2MgO-2SiO2 2H20) ~ H20 where the formula (3MgO-2SiO2 2H20) refers to asbestos tailings and (2MgO 2SiO2 2H20) represents partially reacted asbestos tailings. The partial dissolution of the magnesium oxide from the asbestos tailings is done intentionally in the preferred practice of the present invention in order not to dissolve the silica and magnetite contained in the asbestos tailings.
The end of the initial neutralization step is observed when the pH of the magnesium sulfate slurry is within the range of from 2.5 to 3.5, preferably 3.0, and the slurry is then subjected to the second neutralization step under oxidizing conditions. The magnesium sulfate slurry is oxidized ` so that most of the ferrous ions present in the slurry are converted to ferric ions whereby further sulfate anions become available for reaction with the magnesium oxide in the tailings. The oxidation step may be economically carried out by bubbling air through the slurry. Obviously, if cost is not a consideration other oxidizing agents such as hydrogen per-oxide may also be used.
While the oxidation is being carried out, further amounts of asbestos tailings are added thereby resulting in further neutralization of the slurry which is observed by an increase in the pH while low valence cations are oxidized and precipitated out as hydroxides. The progress of the oxidizing neutralization is marked by color change in the slurry from ; grey to dark brown thus indicating particularly the formation of ferric ions. The pH of the slurry can, if desired, be increased to a value higher than 8.0 by the further gradual addition of asbestos tailings. However, when the pH of a well oxidized slurry is higher than about 6.5, the filtrate is 1077~76 practically free of most heavy metal cations which have by then precipitated out as hydroxides.
The dissolution efficiency of magnesia from asbestos tailings continuously decreases after the pH has reached 3.0 and progresses higher. It is possible to then use as auxiliary some low quality magnesia or calcined magnesite in slurry form in the neutralization after pH 5Ø Notwithstanding, the average utilization efficiency of magnesia from asbestos tailings can be maintained above 10% during the neutralization when the pH ranges from 3 to 7, insofar as sufficient stirring and temperature are provided. Decision as to whether or not auxiliary magnesia slurry should be employed in said neutrali-zation is dependent upon the local economic factors. In general, the use of said magnesia slurry becomes more economi-cal with deteriorating dissolution efficiency of magnesia from asbestos tailings. Auxiliary neutralizers should in principle be limited to magnesia or magnesia-containing materials so as to maintain magnesium content in the end product as high as possible and impurity content therein as low as possible. The . 20 pH of the slurry resulting from the first neutralization can be increased from 3.0 to 5.0 by the gradual addition of asbestos tailings under stirring with aeration.
At this point there are two choices: one is to keep on using asbestos tailings in neutralizing the slurry, and the other is to start using the aforementioned auxiliary such as slurry of a low grade magnesia. In the latter case, even if the magnesia herein used contains some appreciable amount of iron, aluminium and other heavy metals, there is no serious contamination of the product when the contents of manganese and chromium therein are sufficiently low. In both procedures of neutralization, the amorphous silicic acid which may have ~077176 formed in the first neutralization stage is by this time coprecipitated together with ferrous and ferric hydroxides and causes little or no problem in the subsequent filtering operation. Either before or while the slurry is allowed to settle or thicken there can be recovered from the slurry by means of magnetic separator an iron-rich concentrate which may represent as much as 7% of the total weight of the asbestos tailings used in the first and second neutralizing steps. This magnetic concentrate has a commercial value as an iron ore which contains nickel and chromium. Chemical reactions during the oxidizing neutralization may be represented as follows.
Firstly, for the oxidation:
2FeS04 + 1 2 ~ 5H20 > 2Fe(OH)3 ~ 2H2S4 Similar reactions may be postulated for sulfates of the other -~ metals having low and high valences. The sulfuric acid thus produced reacts with added asbestos tailings:
H2S04 + (3M90-2SiO2-2H20) >
(2M90-2SiO2 2H20) + MgS04 + H20 When the pH of the slurry becomes higher than about 6.5, most of the other heavy metal cations can be separated out as the hydroxide precipitates:
(3M90-2SiO2.2H20) + MeS04 + H20 Me(OH)2 + MgS04 + (2MgO-2SiO2 2H20) It is observed that most of the manganese and chromium as well as the majority of the iron, aluminum, silicon, titanium, vanadium, nickel, copper and cobalt could be eliminated as their hydroxide precipitates. Further elimination of the manganese and chromium is an object of the purification oper-ation. It is noteworthy that the oxidation of ferrous to ferric ions does not have to be completed inasmuch as the pH of the slurry is higher than about 7, where most of both ferric 1~)'77176 and ferrous ions precipitate out together with the afore-mentioned heavy metal cations as mixed hydroxides. However, when a filtrate resulting from the insufficient oxidation is yellowish or nontransparent, additional aeration should be applied thereto in the presence of a small amount of asbestos tailings or low grade magnesia. This supplementary aeration takes a far shorter time than that required for a slurry having a high concentration of solids. In the oxidizing-neutrali-zation the aeration may be partially or totally replaced by bubbling oxygen or oxidation with hydrogen peroxide. When hydrogen peroxide is employed the elimination of manganese and - chromium tends to deteriorate unless the peroxide is added in dilute solution and as long as an excess is not used. Halogens which may be present in waste acids or water to be used cannot be eliminated in the present process, and tend to increase -calcium content in the filtrate resulting from the oxidizing-neutralization.
Abundant use of asbestos tailings in the herein described neutralization, despite rather low extraction yield , 20 of magnesium values therefrom, constitutes one of the important characteristics of the instant invention, differing greatly from other processes where efforts are made toward a total utilization of the serpentine ores including recoveries of silica and iron. The preferred practice of the instant invention is in line particularly with the local conditions around Quebec where the ground asbestos tailings are available in abundance.
When the filtration following the oxidizing-neutrali-zation is done on slurries having a pH higher than 7.0, the filtrates resulting therefrom will comprise very small amounts of impurities. The filtrates may therefore be evaporated to g _ :,, 1~77176 produce hydrated magnesium sulfate crystals which readily meet quality standards required for some commercial products such as magnesium sulfate fertilizer.
The solution can also be processed further for the production of refractory grade magnesia via magnesium hydroxide with the use of ammonia gas or ammonium hydroxide solution.
Halogens in the raw materials of the present process go practi-cally all in the filtrate as halides of alkali metals as well as those of magnesium and calcium. When excessive calcium salts are present in the raw materials, the majority of the salts may be eliminated as solid waste of insoluble calcium sulfate. If the filtrate is saturated with calcium sulfate the concentration thereof in the filtrate can reach as high as 2 grams CaS04 per liter as compared to a typical MgS04 concen-tration of 200 grams per liter. The presence of a small amount of calcium salts in magnesium compounds, however, does not cause major problems in most of usages.
The ratios of Ti/Mg, V/Mg, Cr/Mg, and Fe/Mg are consistently lower than 1/1,000 in the resultant solution of magnesium sulfate having a pH higher than 7. The only heavy metal cation that may surpass the foregoing ratio is manganese, the ratio thereof being in some cases as high as 3/1,000. The magnesium sulfate, magnesium hydroxide and magnesia derived from said filtrate comprising these levels of impurities are often pure enough to meet criteria for certain usages. How-ever, in need of higher purity magnesium compounds, said magnesium sulfate solution can be further purified economically by adding fine magnesia slurry thereto in a small quantity, followed by the filtration thereof. Addition of the magnesia slurry should be made under stirring and heating so as to dis-solve in the solution as much of magnesium hydroxide as possible. The amount of magnesia slurry to be added depends upon the impurity levels in the solution and also on the aimed levels in the end products. The magnesia slurry herein not only displaces impurity cations but also coprecipitates some cations and anions as well. A period of digestion time is needed, and while the solution is kept at a pH higher than about 8.5, most of the manganese and chromium, and also some important fraction of calcium can be precipitated out therefrom as hydroxide mixture. The solution treated with magnesia slurry is then cooled and then filtered after standing. A
solution of high purity magnesium sulfate results therefrom.
The resulting precipitates rich in magnesium hydroxide may be recycled, only if low in impurities, for the use as neutralizer during the oxidizing-neutralization. When said hydroxide precipitate is rich in manganese or other useful or harmless elements, the hydroxide may be used as an additive to fertil-izers. A more concentrated solution of magnesium sulfate is less amenable to this purification method, so that the method should be applied, if possible, to solutions while dilute in magnesium sulfate, preferably below 200 grams MgS04 per liter.
For example, 1.0 liter of a filtrate solution com-prising 125 grams MgS04, 400 milligrams Ca, 40 milligrams Mn, and 10 milligrams Fe can be purified by adding magnesium hydroxide slurry containing 1.5 gram MgO, whereby the pH of the solution is increased up to 8.5. Filtration thereof yields 1.0 liter of a clear solution, comprising 125 grams MgS04, 150 milligrams Ca, 4 milligrams Mn, and 2 milligrams Fe. The pH of this alkaline filtrate can be adjusted to 7, if desired, by adding thereto pure sulfuric acid. Evaporation of the solution yields a high purity magnesium sulfate crystal, MgS04 7H20.
The use of magnesium hydroxide slurry mentioned hereinabove can be partly replaced with a minimal use of sodium hydroxide solution.
If the solution comprises those impurities which can be eliminated as hydroxide under reducing conditions, a small amount of ferrous sulfate may be added to once boiled or degassed neutral solution. The ferrous sulfate is then slightly oxidized by aeration, followed by the neutralization with magnesium hydroxide slurry to precipitate out iron as mixed ferrous and ferric hydroxides, wherein the impurities are precipitated or coprecipitated. Addition of ferric sulfate to the neutral solution, followed by the neutralization with magnesium hydroxide slurry, is also effective in eliminating some impurities mainly through coprecipitation or adsorption.
The magnesium sulfate prepared in accordance with the present invention may be usedto prepare other magnesium com-pounds such as magnesium hydroxide, magnesium oxide, magnesium basic carbonate, lactate and oxalate by procedures which are well known to those skilled in the art.
The following examples are presented in order to further illustrate the preferred and typical means of prac-ticing the instant invention and the advantages thereof, but it is distinctly understood that these examples are illustra-tive only and in no way limitative.
EXAMPLE I
1.0 liter or 1,300 grams of waste sulfuric acid from a manufacturerof titanium dioxide pigment having the following chemical composition:
1~)771'76 Free H2S04320 9./l.
Total S04 404 9-/1-Fe 28 g./l.
Ti 5 9./l.
Al 4 9./l.
V 1.0 9./1. , '-Cr 0.5 9./l.
Ca 0.3 9./l.
Mn 0.1 9./l.
was diluted with 3.0 liters of water to a total volume of about 4.0 liters and then heated to 95C. 800 grams of asbestos tailings ground to -75 mesh having the following chemical composition:
MgO 39.7%
SiO2 37-3%
Fe203 7.1%
A1203 0.6%
H20 13.0%
Cr 600 ppm Mn 500 ppm Ni 400 ppm Co 50 ppm Na 50 ppm Pb 20 ppm K 10 ppm Zn 10 ppm Ca 4 ppm was added to the waste acid while stirring. The slurry was continuously heated and stirred at 95C for 30 minutes. The slurry then indicated a pH of 2.9. Aeration of the slurry was then started at a rate of 10 liters at 20C per minute and 50 ~'/7176 grams of the ground asbestos tailings were added every 5 minutes while agitating the slurry at 85C. In 80 minutes when the total addition of asbestos tailings amounted to 800 grams, the pH of the slurry reached 7.3. In other words, the total of 1,600 grams of the ground asbestos tailings was required together with 800 liters of air at 20C to neutralize 1.0 liter of the aforementioned waste acid solution. The slurry was then subjected to thickening, during early stages of which a magnet was moved through the bottom solids to collect magnetic fraction thereof. A magnetic concentrate weighing 80 grams and containing 53% Fe, 1.10% Cr and 0.83% Ni was recovered there-from. Filtration of the slurry coupled with washing of the separated solids with 1.0 liter of water yielded about 5.0 liters of a clear filtrate and a solid waste weighing 1,450 grams (air-dried basis). Chemical analyses of the filtrate indicated the following composition:
Mg 20.0 9./l.
S04 79 9./1.
Fe 8 mg./l.
; 20 Tibelow 1 mg./l.
Al 4 mg./l.
Vbelow 1 mg./l.
Crbelow 1 mg./l.
Ca 300 mg./l.
Mn 30 mg./l.
Recovery of the sulfate anions from the waste acid was 98%.
In carrying out a further purification, the filtrate was heated almost to boil and a magnesium hydroxide slurry comprising 4.0 grams of MgO was added thereto while agitating. The solution was continuously heated and stirred for 100 minutes and then cooled to room temperature, and the solution was allowed to .
stand for a few hours prior to filtration thereof. Most of the magnesium in the added magnesium hydroxide slurry was recovered after filtration as yellowish magnesium hydroxide, which con-tained too much impurities to be returned to the oxidizing neutralization stage. The purified filtrate still having a volume of about 5.0 liters indicated a pH of 8.5, and chemical analysis thereof revealed the following composition:
Mg 20.0 9./1.
Febelow 1 mg./l.
Tibelow 1 mg./l.
Albelow 1 mg./l.
Vbelow 1 mg./l.
Crbelow 1 mg./l.
Ca100 mg./l.
Mn 3 mg./l.
This solution could be treated by the aforesaid pH adjusting method with sulfuric acid, followed by evaporation thereof to produce hydrated magnesium sulfate crystals.
EXAMPLE II
The waste sulfuric acid and asbestos tailings used hereinbelow were the same as in the preceding Example I. 1.0 liter of the waste acid was diluted with 3.0 liters of water to 4.0 liters in total and then heated to 95C. The acid was then ; admixed with 800 grams of the finely ground asbestos tailings.
The pH of the slurry after 60 minutes neutralization indicated 3Ø Aeration was then started at a rate of 10 litersat 20C
per minute as the asbestos tailings was added to the slurry at a rate of 10 grams per minute while heating and stirring the slurry at 85C. When the addition of the asbestos tailings amounted to 400 grams and the volume of the injected air to 500 ~ .
.
' . . - . ~ , .
~77176 liters (20C), the pH of the slurry indicated 5.0, and then while the aeration was temporarily ceased about 70 grams of an iron-rich magnetic concentrate was collected therefrom with a magnet. Aeration was restarted, and neutralization thereafter was carried out using low grade magnesium hydroxide in slurry form. The slurry comprising 10 grams of magnesium hydroxide comprising 35% Mg was added thereto every 5 minutes while aerating. 200 liters of air was bubbled thereinto during 20 minutes as 40 grams of the magnesium hydroxide was added thereto, and the pH then indicated 6.6. Filtration of the slurry yielded 5.0 liters of slightly yellowish filtrate. 10 grams magnesium hydroxide in slurry form was then added to the filtrate while aerating with 100 liters of air. The slurry was then cooled to room temperature and filtered. 5.0 liters of a clear solution was obtained therefrom, the pH of which indi-cated 8.1. Chemical analysis thereof yielded the following composition:
Mg20.0 9./l.
so479 9./1.
Fe2 mg./l.
Al2 mg./l.
Tibelow 1 mg./l.
Vbelow 1 mg./l.
Crbelow 1 mg./l.
; Ca250 mg./l.
Mn20 mg./l.
EXAMPLE III
The waste sulfuric acid and asbestos tailings used hereinbelow were the same as in the preceding Example I. 1.0 liter of the waste acid was diluted with 3.0 liters of water to 4.0 liters and then heated to 95C. The acid was then admixed .. . .
. .
-~77176 .
with 800 grams of the finely ground asbestos tailings. pH of the slurry after 60 minutes leaching indicated 3Ø Aeration was then started at a rate of 10 liters per minute and 50 grams of the asbestos tailings was added to the slurry every 5 minutes while heating and stirring the slurry at 85C. When the additional asbestos tailings amounted to 800 grams, the slurry indicated a pH of 7.3. Filtration of the slurry yielded ` 5.0 liters of slightly yellowish filtrate, comprising 16 ppm Mn and 4 ppm Fe. 1.0 gram FeS04 in solution form was added to the filtrate. 4.0 grams of MgO in fine slurry form was then added thereto while heating and stirring the slurry. Filtration of the cooled slurry yielded a filtrate containing 1.5 ppm Mn and 1 ppm Fe. Evaporation and crystallization of the filtrate yielded a high pur;ty magnesium sulfate crystal.
' .
~' :
.
Claims (11)
1. A process for the neutralization of waste industrial sulfuric acids which comprises:
a) partially neutralizing a waste sulfuric acid solution by adding asbestos tailings until the pH of the slurry thus formed is between 2.5 to 3.5 and thereby forming a slurry containing magnesium sulfate;
b) continuing the neutralization of said magnesium sulfate containing slurry under oxidizing conditions by i) adding a further amount of asbestos tailings until the pH of the slurry is at least 6.5, or ii) adding a further amount of asbestos tailings until the pH of the slurry is about 5.0 followed by the addition of a magnesia-containing slurry until the pH is at least 6.5; and c) filtering the neutralized solution thus obtained and recovering the filtrate containing the magnesium sulfate thus formed.
a) partially neutralizing a waste sulfuric acid solution by adding asbestos tailings until the pH of the slurry thus formed is between 2.5 to 3.5 and thereby forming a slurry containing magnesium sulfate;
b) continuing the neutralization of said magnesium sulfate containing slurry under oxidizing conditions by i) adding a further amount of asbestos tailings until the pH of the slurry is at least 6.5, or ii) adding a further amount of asbestos tailings until the pH of the slurry is about 5.0 followed by the addition of a magnesia-containing slurry until the pH is at least 6.5; and c) filtering the neutralized solution thus obtained and recovering the filtrate containing the magnesium sulfate thus formed.
2. The process of Claim 1, wherein the particle size of the asbestos tailings is smaller than 20 mesh.
3. The process of Claim 1, wherein the particle size of the asbestos tailings is from 60 to 200 mesh.
4. The process of Claim 1, wherein the concentration of the S04 anions in the starting waste sulfuric acid solution is between 30 to 300 grams/liter.
5. The process of Claim 1, wherein the concentration of the S04 anions in the starting waste sulfuric acid solution is between 100 to 300 grams/liter.
6. The process of Claim 1, wherein both neutrali-zation steps are carried out at a temperature of from 15 to 100°C.
7. The process of Claim 1, wherein both neutrali-zation steps are carried out at a temperature of from 70 to 100°C.
8. The process of Claim 1, wherein the asbestos tailings is used in an amount which exceeds the stoichiometric amount for neutralizing the sulfate anions by from 25 to 600%.
9. The process of Claim 1, wherein ferrous and/or ferric sulfate is added to the filtrate containing the mag-nesium sulfate to precipitate heavy metal cations and recover-ing a purified filtrate containing magnesium sulfate.
10. The process of Claim 1, wherein the slurry is treated with a magnetic separator to recover from the slurry a concentrate rich in iron, nickel and chromium.
11. The process of Claim 1, wherein the pH of filtrate containing the magnesium sulfate is raised to at least 8.0 by treatment with a magnesia-containing slurry followed by filtration to recover a filtrate containing substantially pure magnesium sulfate, and adjusting the pH of said filtrate to about 7.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA275,436A CA1077176A (en) | 1977-04-04 | 1977-04-04 | Process for neutralizing waste sulfuric acids |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA275,436A CA1077176A (en) | 1977-04-04 | 1977-04-04 | Process for neutralizing waste sulfuric acids |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1077176A true CA1077176A (en) | 1980-05-06 |
Family
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA275,436A Expired CA1077176A (en) | 1977-04-04 | 1977-04-04 | Process for neutralizing waste sulfuric acids |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0348502A1 (en) * | 1988-01-07 | 1990-01-03 | Chou Song Tien | Asbestos decomposition. |
| WO2013037649A1 (en) * | 2011-09-13 | 2013-03-21 | Tioxide Europe Sas | Magnesium sulphate |
| EP3473738A1 (en) * | 2017-10-20 | 2019-04-24 | CrisolteQ Ltd | Process for recovering components from pickling acid residue |
| CN110408794A (en) * | 2019-08-14 | 2019-11-05 | 白鹰 | Asbestos deposit process for cleanly preparing |
| EP3839100A1 (en) | 2019-12-19 | 2021-06-23 | CrisolteQ Ltd | Method for treating pickling acid residue |
| CN113620688A (en) * | 2021-09-07 | 2021-11-09 | 中科镁基（北京）科技有限公司 | Method for preparing building material by using asbestos tailings |
-
1977
- 1977-04-04 CA CA275,436A patent/CA1077176A/en not_active Expired
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0348502A1 (en) * | 1988-01-07 | 1990-01-03 | Chou Song Tien | Asbestos decomposition. |
| EP0348502A4 (en) * | 1988-01-07 | 1990-05-14 | Song-Tien Chou | Asbestos decomposition. |
| WO2013037649A1 (en) * | 2011-09-13 | 2013-03-21 | Tioxide Europe Sas | Magnesium sulphate |
| JP2014530160A (en) * | 2011-09-13 | 2014-11-17 | チオキシド・ユーロプ・エスエイエス | Magnesium sulfate |
| US9073797B2 (en) | 2011-09-13 | 2015-07-07 | Tioxide Europe Sas | Magnesium sulphate |
| EP3473738A1 (en) * | 2017-10-20 | 2019-04-24 | CrisolteQ Ltd | Process for recovering components from pickling acid residue |
| CN109850928A (en) * | 2017-10-20 | 2019-06-07 | 克里硕泰丘有限公司 | The method of component is recycled from pickling residue |
| US10526684B2 (en) | 2017-10-20 | 2020-01-07 | Crisolteq Ltd | Process for recovering components from pickling acid residue |
| CN110408794A (en) * | 2019-08-14 | 2019-11-05 | 白鹰 | Asbestos deposit process for cleanly preparing |
| EP3839100A1 (en) | 2019-12-19 | 2021-06-23 | CrisolteQ Ltd | Method for treating pickling acid residue |
| US11254585B2 (en) | 2019-12-19 | 2022-02-22 | Crisolteq Ltd | Method for treating pickling acid residue |
| CN113620688A (en) * | 2021-09-07 | 2021-11-09 | 中科镁基（北京）科技有限公司 | Method for preparing building material by using asbestos tailings |
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