DE852844C - Process for working up a sodium vanadate, sodium arsenate, sodium phosphate salt mixture - Google Patents

Description

Process for processing a sodium vanadate, sodium arsenate, Sodium phosphate salt mixture Those used as raw materials for aluminum production It is well known that alumina-containing minerals always contain small amounts of vanadium, Phosphorus and arsenic compounds, which are formed after the alkaline digestion of bauxites in less than sodium vanadate, sodium phosphate and sodium arsenate in the Find aluminate liquors again. Since these salts are in the lye cycle over time enrich, they must be removed from this regularly if it is not too significant Operational disruptions should come. These malfunctions can z. B. given thereby be that as a result of oversaturation of the aluminate liquor with the salts mentioned These deposit in pipelines and evaporation vessels and give rise to crust formation there give. The separation of these foreign salts takes place in a simple way by cooling the more or less largely thickened lye, with some of the dissolved Salts in the form of a trisodium vanadate, trisodium phosphate, trisodium arsenate salt mixture crystallized out. Leaches containing sulphates and carbonates separate when they cool down sulfate- and carbonate-containing salt mixture.

The composition of the salt mixtures obtained in this way varies naturally within wide limits. For example, determine the vanadium and phosphorus content of the processed bauxite and the conditions of the digestion in the lyes and the ratio V2 0S: P2 O5 present in the salts. For their worthwhile use are especially their vanadate and phosphate content of gecleutung. For example, the salt mixture has contents of 6 to 1% vanadic anhydride (V205) and 14 to 6% phosphoric anhydride (P205).

This salt mixture has so far been worked up in such a way that the Vanadium from the ammoniacal, sulfuric acid solution of the salt mixture precipitated as ammonium metavanadate and calcined to vanadic anhydride. at This procedure, however, the phosphate was lost because the work-up of the filtrate is uneconomical.

The present invention is now. a procedure that extensive separation of the vanadate or arsenate present in the salt mixture permitted by its other components.

Since the dod'ekahydrates present in the salt mixture crystallize isomorphically, a Na3V04- i 2H20 crystal is known to continue to grow in a phosphate solution, succeeds a simple separation of vanadate and phosphate by fractional crystallization not. When the salt is dissolved in water or dilute sodium hydroxide solution hence a separation of the vanadate from the other components of the salt mixture not achieved. However, both the alumina manufacturer and convenient to the buyer of the salt for various reasons. First of all, there is in view on the extraction of the most valuable component, vanadic acid, on the one hand I wish the salt to be transported cheaply, i.e. rich in vanadate, to the processing plants to feed. On the other hand, the vanadic acid becomes via the intermediate stage of the ammonium metavanadate all the more pure in terms of chemical consumption and the container space required The more economically isolated, the lower in phosphate and richer in vanadate that is for processing coming salt is.

Surprisingly, it has now been found that the salt mixture in can be easily split by hot concentrated sodium hydroxide solution. Useful Results can already be achieved with 35%, but it is preferable to work with it 4 and higher percent caustic soda. The temperature of the liquor is preferably chosen between 9o and 100 °. The vanadate present dissolves in such a lye V2O5 completely, the As present as arsenate. 0, almost completely, that as However, only 15 to 25% of P205 present in phosphate; the remaining residue contains 75 to 85% of the P2 05 in the form of Nag P04 and practically all of the Na2S04 and Na2C03. After the residue has been separated off from the hot solution, it crystallizes on cooling a high percentage of arsenate-containing sodium vanadate vtnm; very easy to filter the end; the mother liquor itself can be used for further cleavage. From the residue can contain the main amount of the salt mixture that is being worked up Sodium phosphates can be obtained in a manner known per se ..

The method according to the invention therefore makes it possible from the in operation accruing crude salts an end product that is moist with suction filter and enriched in V205 to produce, which easily loses its water of crystallization at io5 ° and thus for the Shipping can be made more suitable. According to the method according to the invention can thus also the residue resulting from the treatment with sodium hydroxide solution without difficulty processed into sodium phosphate, which, as already mentioned above, with the known Procedure is not possible.

So while the alumina manufacturer often endeavored to keep the deposition of the vanadate-containing crude salt from aluminate liquors by suitable choice of the deposition conditions to be managed in such a way that the highest possible percentage of salt that is easy to sell is obtained and at the same time, to the disadvantage of the cleaning of its alkalis, the simultaneous crystallization Avoid sodium carbonate and sodium sulfate whenever possible the inventive method in a simple manner, subsequent work-up vanadium salts and thus makes the above unhealthy objectives superfluous.

The method according to the invention is based on the following exemplary embodiment iooo kg of crude salt with 7.0% V2 05, 7.3% P2 05, 0.7% Ase Ob, 4.6% Na2 S04, 3.0% A12 03, 23.4% Nag O (bound to V20.1 P2051 C02), 44.2% H20, Remainder: C02, loss on ignition are in 140o to 2000 1 40%, 90 to 100 ° hot, at a previous decomposition of crude salt (40% NaOH) accumulating mother liquor entered. After stirring for one hour at 90 ° to 100 °, the solution is separated from the residue at 90 °, the residue covered with 100 m3 of hot, 40% sodium hydroxide solution or mother liquor and vacuumed dry.

This gives 400 kg of residual salt with 0.4 to 0.6 0/0 V2 O5, 15.0 0/0 P205, 11.2% Na2 S04, 34 0/0 Na2 0 (bound to P205, V205, C02), Remainder: bound and adhering water, C02. The small amounts of V205 can be explained by the fact that a quantitative separation of residue and solution is difficult in practical operation.

On cooling, the filtrate yields 46o kg of vanadate which crystallizes well with 4.7% V205, 3.0 0/0 P2053 i, 5% Ase O5, 29.0% Na2 O.49, o% H20- Used for the Decomposition mother liquor used from previous use already with Phosphate and vanadate are saturated, a V2 0 yield is easily achieved of 95% and more.

The salt is dispatched in a dried state. Even if if the subsequent drying is disregarded, this means the preparation of the one containing water of crystallization Salt in. In the present case, a V.05 enrichment of around 100%. Strong sulfate and salts containing carbonate are lower in vanadate and provide the same end product; these salts are therefore enriched by an even higher amount.

Claims (1)

PATENT CLAIM: A method for processing a sodium vanadate, sodium arsenate, sodium phosphate salt mixture which is in particular precipitated from aluminate liquors and which is in pure form or other salts such as accompanying components. B. sodium carbonate and sodium sulfate, characterized in that the salt mixture is treated with hot, preferably a temperature of 9o to ioo ° exhibiting, concentrated, preferably 40 to 45o / o, sodium vanadate and sodium arsenate by letting the solution cool Solution in the form of a low-phosphate, arsenate-containing sodium vanadate is made to crystallize and the main amount of the sodium phosphate contained in the salt mixture is obtained in a manner known per se from the residue.