DE1215115B - Process for the production of boric acid from boron calcium minerals - Google Patents

Description

Process for the production of boric acid from boron calcium minerals Zur There are various ways of obtaining boric acid from insoluble, calcium-containing boron minerals Procedures available, e.g. B. Reaction with hydrochloric acid, sulfuric acid, sodium or ammonium bisulfite. At the moment, almost all of these methods are used Sulfuric acid processes are used, although in themselves there are still significant disadvantages has, in particular: a relatively large volume of the reaction solution; relative large heat demand; partial decomposition of the gangue accompanying the mineral as well considerable corrosion problems.

The processes that work with SO, or ammonium or alkali sulfites, on the other hand, have so far not been able to prevail over the sulfuric acid process, because they have not succeeded in solving the problem of the absorption of SO, gases from a calcium borate slurry, which is particularly difficult when heated Inadequate results are found in finding a technically economical solution or in eliminating the disadvantages resulting therefrom, namely losses of SO2 through escape, incomplete reaction, decomposition of the gangue, residues that are difficult to filter.

According to the method according to the USA: Patent 2,531,182 , a soluble alkaline earth metal salt is added to the digestion solution and the digestion reaction is carried out at a temperature of 25 to 70 ° C. and a pH range of 4.5 to 5.5. This is to ensure complete absorption of the S02. The foreign salt added to the process, preferably CaC12, has the disadvantage that the digestion solution is contaminated by Cl ions. The product must be washed abundantly in order to remove the adhering chlorine.

According to the procedure according to Swiss patent 354 760 the ore is digested in a pH range from 4.5 to 7 in the counterpart of ammonium borates acting as buffers. So much is always needed to precipitate boric acid SO2 is used so that the bisulfite stage is reached (pH about 4.5). Kick it S02 losses, especially in the second process stage, in which the boric acid is from the reaction solution is deposited on. The mother liquor is also recycled the amount of S02 absorbed is lower in each case.

Is carried out according to the procedure in Swiss Patent 354 760 started from Ulexit, the pH range is the same as that of the claimed Procedure. When using colemanite, however, this is not the case. It must it should be emphasized that the main raw material available is colemanite. In any case, colemanite is much cheaper as a raw material for the production of boric acid as ulexite, since when ulexite is used the Na 2 O supplied with this ore in each case must be removed from the process.

It has now been found that those associated with the sulphite digestion Disadvantages and difficulties can be avoided if the following new findings must be taken into account: To achieve a practically complete explanation at most a slight excess of reagent is required.

A quick and complete digestion with the formation of an easy filterable residue can be achieved in a medium that is weakly alkaline, is neutral or weakly acidic; these conditions are hereinafter referred to as "mild Digestion conditions «.

In a slurry of a calcium boron mineral in a powdered, weakly alkaline, neutral or weakly acidic solution, SO2 is also made from poor Gases and even in the warmth practically completely with decomposition of the mineral absorbed.

Boric acid can be added by introducing SO2 into the cold digestion solution at a pH of 5 to 6 precipitate in good yield, the solution not yet has disruptive S02 vapor pressure.

Taking these results into account, a new process for the production of boric acid from boron calcium minerals by means of S02 in free form and in the form of sulfite or bisulfite was developed, which is characterized in that S02 is introduced into an aqueous suspension of the mineral containing sulfite or bisulfite, the digestion solution being kept weakly alkaline, neutral or weakly acidic for the entire duration of the digestion, and that, after the digestion residue has been separated off, the boric acid is removed from a weakly acidic medium by introducing SO2 at a pH between about 5 and 6, preferably 5 , 5, "is precipitated, whereby at the same time a mother liquor suitable for the next batch is obtained." Addition of water is entered into a circulating solution, the alkali borate and alkali sulfite u nd / or bisulfite and which is saturated with boric acid, whereupon SO2 or SOZ-containing gases are introduced into the mixture, which is expediently heated to 60 to 70 ° C., for example, so that the S02 feed is approximately with the decomposition of the mineral Keeps pace; After the reaction has taken place and the digestion residue has been separated off, S02 is introduced into the cooled digestion solution to regenerate the circulating solution and to precipitate the boric acid until a weakly acidic reaction (pH value between .5 and 6) is achieved; the mother liquor from the boric acid crystallization is returned to the cycle. When the calculated amount of the calcium boron mineral is entered into the circulating solution, the sulfite-bisulfite present therein is consumed very quickly, the "mild digestion conditions" to be observed according to the invention inevitably appearing automatically.

Both! According to the invention, the ratio of the SO2 introduced with the circulating solution and that to be introduced as gas during digestion can be varied within wide limits; Experience has shown that a ratio of 3: 1 is favorable and the following reaction equations were used as a basis. -The total explanation is theoretically based on:; 4 Ca2Bs0 "+ - 6 NaHS03 -f- -2 S03 + 15 H20 $ CaS03 + 3 Na2B407 + 12 H @ B03 (1) The first stage of the digestion - conversion of the colemanite with the circulating solution - takes place after: 4. Ca2Bs0x, 1 -h 6 NaHS03 + 6 H20. D 6 CaS03 -I- Ca2Bs011 -f- 3 Na2B407 -I- 6 HaB03 The following applies to the second stage, i.e. the introduction of SO2 gas. Equation:, - (2a) Ca2BB011 + 2 S02 + 9 H20 2 CaS03 + 6 H3B03 - (2b) After the digestion residue has been separated off, S02 or S02-containing gases are passed into the solution to decompose the alkali borates, the alkali bisulfite introduced in step (2a) being regenerated and boric acid precipitating. 3 Na2B407 + 12 H @ B03 -I- 6 S02 -i- 21 H20. > 6 NaHS03 +. 24 H @ B03 (3) In order to be able to take full advantage of the new findings mentioned above, the circulatory solution always has a certain amount of undecomposed material. Alkali borate carried along, so that the method according to the invention can be formulated as follows, whereby the boric acid which is inevitably carried along in the circuit is also taken into account. - The digestion takes place according to: 4 Ca2Be0u + x Na2B407 + y H @ B03 - (- 6 N_ aHSO3 + 2 S02 -f- 15 H20 8 CaS03 -f- (3 + x) Na2B407 -f- (12 -1- y) H3B03 (4) and the regeneration of the circulatory solution after: (3 -I- x) Na2B407 -f- (12 -E- Y) H3B03 -f-- 6 S02 -E- 21 H20 - @ x Na2B407 + 6 NaHS03 -f- y H3B03 -f- 24 H3B03 - (5) weakly acidic, low = solution saturated with boric acid - blow It should be noted that both the ratio of NaHSO3 to SO2 and the amount of alkali borate circulated can be varied within wide limits, since the process according to the invention is not tied to rigid molar ratios of the compounds mentioned. However, the molar ratios are expediently chosen and the volume of the solution determined in such a way that no boron compounds precipitate from the digestion solution in the cold.

It is also expressly pointed out that in the above equations For the sake of simplicity, the tetraborate was always used for alkali borate, although It is known that in solutions that are weakly alkaline, neutral or weakly acidic are, other borates, in particular pentaborate, may also be present.

The advantages of the 'claimed process are as follows: Accompanying minerals and gait are not attacked or only to an insignificant extent, so that the Accumulation of impurities from the itri manufacturing process circulating mother liquors is largely avoided.

The digestion residue is very easy to filter and can with Wash out a little washing water completely, so that boron losses and costly evaporation be avoided.

Gases with a low SO2 content can be used; z. B. roasting gases, -use.

The exhaust gases are practically SO, -free. _ Since only with approximately neutral Solutions are worked on, no difficult corrosion problems arise.

The yield of B203 is almost 100%.

The conversion per unit of equipment and time is very favorable.

The heat requirement is low.

The process works in a closed loop.

The boric acid produced is chemically pure. Example 1 Starting the cycle 40 g of colemanite, calcined at about 550 ° C. , with a B203 content of 58%, are suspended in 200 ml of 1120, containing 10.6 g of Na2B40, -10 H20; S02 is passed in, heated to 60 to 70 ° C. and S02 continues to be passed in at this temperature with mechanical stirring until the digestion is complete. The residue is then filtered off and washed out. SO2 is introduced into the cooled filtrate, the pH of which is about 6.5, whereby boric acid precipitates. The introduction of SO2 is interrupted at a pH value of about 5.5. After some time, the boric acid is filtered off, washed with a little water and dried at 80.degree. Yield: 24.0 g of H3B03.

Example 2 Cycle operation In the 200 ml mother liquor from the previous operation, 23 g of colemanite are calcined at about 550 ° C., with a B203 content of 580/0 . The mixture is heated with stirring, then, while maintaining a temperature of about 60 to 70 ° C., S02 is introduced until the digestion is complete, the S02 supply being slowed towards the end of the reaction; after the digestion residue has been separated off and washed out, S02 is passed into the cooled filtrate until the pH has dropped to about 5.5. After some time, the precipitated boric acid is filtered off, washed and dried at 80 ° C. Yield: 23.7 g of H, B03.

Claims (3)

Claims: 1. Process for the production of boric acid from boron calcium minerals by means of S02 in free form and in the form of sulfite or bisulfite, d a u r c h characterized that S02 is in a sulfite or bisulfite-containing, aqueous suspension of the mineral introduces, which is weakly alkaline for the entire duration of the digestion, is kept neutral or weakly acidic and then the boric acid after separation of the digestion residue by further introduction of SO2 at a pH between about 5 and 6, preferably at 5.5, fails, with one for the next Approach suitable mother liquor is obtained. 2. The method according to claim 1, characterized characterized in that the digestion of the mineral is started with a mother liquor, which contains alkali sulfite and / or bisulfite, alkali borate and boric acid and through The introduction of S02 or S02-containing gases is continued. 3. Procedure according to Claim 1, characterized in that the digestion in the heat, for. B. at temperatures between 30 and 95 ° C, preferably at 60 to 70 ° C, is carried out. Into consideration Printed publications: Swiss Patent No. 354 760; U.S. Patent No. 2 531182.