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ENGINEERING UTILIZATION TECHNOLOGY OF FLUORINE-CONTAINING GAS OF BERILLIUM PRODUCTION BY SELECTIVE SORPTION METHOD SiF4

In compound of ore concentrate of beryllium production of Ulbinskyi metallurgical works (UMW) half of it is proximately the flotation bertrandite phenacite concentrates of Ermakovskyi field with increased fluoride content (up to 10%). Utilization technology development of effluent fluorine-containing gas shall Ulbinskyi metallurgical works partly to solve problems of creating own raw material base, expand own production range on market, to improve the environment ecology.

On acid opening of Ermakovskyi concentrate the bertrandite and phenacite interaction with sulphuric acid runs according to reactions:

4ВеО.2SiO2.H2O + 4H2SO4=4BeSO4 + 2SiO2 + 5H2O (1)

2BeO.SiO2 + 2H2SO4 = 2BeSO4 + SiO2 + 2H2O (2)

Defluorination process of Ermakovskyi concentrate is based on sulphatization reaction of its fluorite component:

CaF2 + H2SO4 CaSO4 + 2HF (3)

Escaping gaseous anhydrous hydrogen fluoride interacts with beryllium minerals:

4BeO.2SiO2.H2O + 16HF = 4BeF2 + 2SiF4 + 9H2O (4)

2BeO.SiO2 + 8HF 2BeF2 + SiF4 + 4H2 (5)

BeF2 + H2SO4 BeSO4 + 2HF (6)

The major part of formed anhydrous hydrogen fluoride consumes for a silicon dioxide reaction:

SiO2 + 4HF = SiF4 + 2H2O (7)

The experiments prove that effluent fluorine-containing gases formed on thermal bertrandite phenacite concentrate sulphatization, mainly consist of tetra fluoride silicon.

As evident from reactions (4,5), escaping anhydrous hydrogen fluoride, interacting with silicon dioxide breaks the silicate structure of bertrandite phenacite concentrate crystal lattice and intensities the sulphatization of beryllium oxide.

In reaction gas of concentrate decomposition furnace, except of reaction products volatile components (3-7), shall carry the sulphuric acid in the form of smallest drops and the air, absorbed along the perimeter of furnace seal.

Fluorine-containing gas of berillium production the associated utilization gives the principal opportunity of following end products receipt:

1. Fluorosilicic acid- solution.

2. Silicone dioxide – white carbon, aerosil, silica gel and others.

3. Ammonium fluoride- solution.

4. Synthetic calcium fluoride.

5. Ammonium bifluoride.

6. Sodium silicofluoride.

7. Sodium fluoride.

8. Cryolite- sodium fluoride and aluminum.

9. Anhydrous hydrogen fluoride.

10. Other fluorine-containing compounds.

Scientific-technical and patent literature analysis testifies the realization of following fluorine-containing gas of beryllium production utilization layout.

On fluorine gas reprocessing, containing HF and SiF4, also on purification from SiF4 crude HF, by means of direct absorption with water the fluorosilicic acid might be obtained, is an end product of:

HF + SiF4 = H2SiF6 (8)

However on sulfuric acid opening of beryllium concentrates the fluorine gases mainly contains SiF4 and almost do not contain HF, therefore its direct water absorption is economically pointless because of partly silicon release in the form of silicate, blocking the absorbers:

2H2О + 3SiF4 = 2H2SiF6 + SiО2? (9)

Absorption SiF4 from fluorine gas is to carry by ammonium fluoride solution with ammonium fluosilicate solution recovery:

2NH4F + SiF4 = (NH4)2SiF6 (10)

Received ammonium fluosilicate decompose by ammonia on ammonium fluoride and amorphous silica (“white carbon”):

(NH4)2SiF6 + 4NH3 + 2H2О = 6NH4F + SiО2? (11)

The part (about 1/3) ammonium fluoride solution return for absorption SiF4, remaining solution steam for ammonium bifluoride and ammonia recovery, which return for ammonium fluosilicate decomposition:

2NH4F = NH4HF2 + NH3? (12)

Summing reaction (10-12), obtain:

2NH3 + 2H2О + SiF4 = 2NH4HF2 + SiО2? (13)

Consequently, from technological point of view the optimum is the fluorine gas reprocessing layout by means of its absorption with ammonium fluoride solution, which allows getting amorphous silica (“white carbon”) as an end product and ammonium fluorides (Fig.1).

Fluorine-containing gases obtaining with fluosilicate ammonium recovery perform in absorption packed column with residual content of released gas finishing up to sanitary standard.

Reaction gas under depression, created in technical layout with the help of vacuum pumps, stretches through the packed column, irrigated by mother solution of ammonium fluoride, which moves in cascade in backflow concerning the gas. Formed fluosilicate solution with concentration 14-16 mas.% and ammonia water enter the reactor-mixer for hydrolysis.

In the result of hydrolysis form the silica gel pulp, diluted in ammonium fluoride. The pulp is condensed in sediment box and then filtrate by pump. Solid phase (silica gel) is separated from filter and enters the reactor with mixer for flushing from ammonium fluoride containing in pores. Sediment solution condense repeatedly in sediment box, filter, cake feed to dry. Consequently, the end product is the “white carbon”.

United filtrate (ammonium fluoride solution) from the receiver feeds for postfiltration. Cooled and purified ammonium fluoride solution is divided into two parts. The third part of total quantity of obtained ammonia fluoride feed to absorption section for fluorine-containing gas recovery. Two thirds ammonium fluoride solution enter the evaporator for steam and following crystallization. It is possible to obtain fluoride fusion cake or ammonium bifluoride, it depends on selected technology. In the case of steam with ammonium bifluoride obtain, the ammonium is by-product which might be returned to technological process.

“White сarbon” is an essential product, the main consumer of which is the mechanical rubber industry, using “white carbon” as a filling compound instead of technical carbon (first of all in frost-resisting and ecologically pure “green” tyres production). As a result of ecological requirements rise is to expect the significant demand growth of “white carbon”. “White carbon” is manufactured of two types BS-100 and BS-120. Medium price on market is 1000-1300 $ USA for ton.

Ammonium bifluoride might be used in Ulbinskyi Metallurgucal Works in production of fluorite acid for fluorite concentrate purification of quartz and tiff. The purification products are ammonia and ammonium fluosilicate, which return to production cycle of ammonium bifluoride and white carbon.

Ammonium bifluoride also might be used as fluoridizer in fluoric salt production. Marketing analysis shows that from fluoric salt the most demanding is cryolite, widely used in aluminum production. As a source of sodium on cryolite production might be used the sewage of beryllium production of Ulbinskyi metallurgical works, containing the great amount of sodium. Accordingly, from the three cryolite components (sodium, aluminum and fluorine) it to buy only aluminum (in the form of alumina). The whole fluorine, utilized from effluent gas of beryllium production might be completely used for cryolite recover.

Under above-mentioned, can be made the conclusion on economic introduction practicability of fluorine-containing gases of beryllium production utilization technology of Ulbinskyi metallurgical works by selective sorption method SiF4 by ammonium fluoride solution.

Fig. 1. Fluorine-containing gases of beryllium production utilization layout