GB2279081A

GB2279081A - Electrolytic recovery of tin from gaseous tin compounds

Info

Publication number: GB2279081A
Application number: GB9312532A
Authority: GB
Inventors: Echevarria Rodolfo Solozabal; Iraola Juan Carlos Mugica; Mugica Patricio Aguirre; Astobiza Juan Iturriondobeitia
Original assignee: Vidrala SA
Current assignee: Vidrala SA
Priority date: 1992-10-16
Filing date: 1993-06-17
Publication date: 1994-12-21
Anticipated expiration: 2013-06-17
Also published as: AU4171893A; FR2706490A1; ES2049185A1; ES2049185B1; GB9312532D0; DE4322740A1; GB2279081B

Description

--A- 2279081 Process for obtaining tin metal from tin compounds RSn in

gaseous form The invention relates to a process for obtaining tin metal starting from a cloud which is formed by generating a stream of air which entrains the tin compound.

In the hollow glassware industry (principally bottles and jars), metal (principally tin) is deposited onto the surface of the glass with the aim of improving the mechanical strength of the container by sealing the microfissures which are produced during moulding. This deposition is performed at elevated temperature in a tunnel in which there is created an atmosphere rich in tin compounds arising from the total or partial decomposition of some compounds of the said metal. Not all the tin which was produced in the gaseous mixture prepared to be passed through the tunnel is consumed during deposition of the metal onto the surface of the glass. This amount must be drawn off through a flue, bringing about a dilution of the tin salt vapour.

In the conventional process, the tin vapour exits to the atmosphere, causing the emission of the said gases which may be observed by their striking white colour.

The present invention proposes a process for obtaining tin metal from tin compounds in gaseous form, which process is characterised in that:

a) b) c) the tin compound RSn is hydrolysed forming a solution of tin dioxide Sn02 in an acid medium RH, a neutralising compound RtOH is added to the acid medium RH, producing a salt RRI, the solution is circulated around a tin recovery circuit comprising an electrolytic recovery unit in which the tin Sn is retrieved by electrolysis of the tin dioxide Sn02.

2 Figure 1 is a diagram of the process/plant provided by the invention.

Figure 2 is a diagram of a different embodiment of the process/plant provided by the invention.

A tin salt RSn (17) is introduced in vapour form into the tunnels (1), through which the bottles (2) travel, wherein R may be a metalloid, for example a halogen, a complex inorganic radical, an organic radical etc., which acts to block any possible microfissures arising during production of the bottles (2).

The tin salt RSn is preferably hydrolysable.

The remainder of the tin salt (17) not used in the bottles is extracted from the tunnels (1) by means of a plurality of flues (3) which transport the tin salt vapour to an absorption tower (4) in which the dissolving medium will normally be acid due to the hydrolysis or reaction with a liquid solvent and, particularly in those cases in which the tin salt (17) originates from anions arising from strong acids, for example Cl-, hydrolysis of the salt will be acidic.

The following reaction occurs in the hydrolysis (unadjusted):

H20 + RSn RH + Sn02 which clearly indicates that the medium is acidified and becomes enriched with tin.

The solvent to be used, normally water, depends on the tin salt used and must be capable of capturing the tin ion from the salt to form a soluble and electrolysable tin compound.

3 It will be appreciated that the longer the treatment lasts, for example in a closed circuit, acidification of the medium will convert it into a toxic effluent.

In the lower part of the absorption tower (4) will be seen the inlet (18) for an absorbent to neutralise the acid medium, for example, an alkali RFOH, for example potassium hydroxide, forming a scrubbing circuit (6) in which, by means of a spray arrangement, the liquid (9), which collects in the base (10) of the tower (4) and principally consists of the neutralising absorbent, is caused to fall over the tin vapour (7) transported by the flues (3). From the chemical reactions occurring in the process, there appear in the base (10) of the tower (4) inter alla the following products: a salt which is dependent upon the tin salt RSn used and on the alkaline absorbent RfOH, thus a salt RRI, and an electrolysable tin compound, for example Sn02.

Since, during acid neutralisation, a precipitate is formed when the concentration of the salt RRI formed exceeds the maximum (threshold) solubility index at a particular temperature, this precipitate must conveniently be removed from the circuit so that its presence does not interfere with the process according to the present invention.

If the salt used were SnC14. the liquid solvent H20 and the neutralising agent KOH, the following reactions would occur (adjusted):

2H20 + SnCl4 # HC1 + KOH 4-1-1 4HCl + Sn02 (electrolysable) KCl (decantable) + H20 A decanting or filtration circuit (11) to circulate the liquid (9) from the base of the tank (10) is provided via a decanter (12) or conventional means in which the salt RRf, for example 4 KCl, which is a reusable product, remains deposited, normally as crystals.

A tin recovery (metallisation) circuit (13) is also provided through which the liquid (9) from the base of the tank (10) is circulated via an electrolytic recovery unit (14) in which the tin is retrieved from the liquid material by electrolysis of the electrolysable compound.

Once purified, the gases (15) are discharged into the atmosphere through a conventional chimney (16).

The system maintains the concentration of tin within determined ranges, for example 1 - 100 g/1, preferably 20 - 40 g/1, such that the speed of tin neutralisation is equal to the absorption of tin by the liquid solvent.

In addition to this systemi pH is monitored and controlled by means of the pH sensor (19) and by addition of the neutralising agent controlled by the electrovalve (20).

Figure 2 shows a variant to improve the anti-pollution process. A second absorption tower (42) has been provided into which water H20 (21) is introduced as golvent. The liquid (92) from the base of the second absorption tower (42) passes through an overflow (22) to the first tower (41) and to this end it is arranged that the level (U2) of the liquid in the second tower (42) is higher than the level (U,) of the liquid in the first tower (41).

In both towers (41), (42)f the liquids (91), (92) from the base of the respective tanks (101) g, (102) are pumped to establish the corresponding scrubbing circuits (61), (62) in which the corresponding liquid (91) j (92) is caused to fall through spray arrangements (81) j (82) causing hydrolysis of the tin salt:

1 H20 + RSn # RH + Sn02 which clearly indicates that the medium is acidified and becomes enriched with tin.

An initial scrubbing occurs and the remaining gas (151) is introduced into the second tower (42) f or a second scrubbing.

After the second scrubbing in the second absorption tower (42). the exiting gases (152) fulf il the strictest pollution standards and are discharged into the atmosphere via the chimney (16).

The liquid (9,) from the first tower (41) passes through an overflow (23) to a neutralising tank (24) into which is supplied the neutralising agent for the acid medium, for example NaOH, from an absorbent tank (25), there appearing in the tank (24) a salt which is dependent upon the tin salt RSn used and the alkaline absorbent R10H, thus a salt RRI, and an electrolysable tin compound, for example Sn02.

A decanting or filtration circuit (111) to circulate the liquid (26) from the neutralising tank (24) is provided via a decanter (121) or conventional means in which the salt RRI, for example NaCl, which is a reusable product, remains deposited, normally as crystals.

A tin recovery (metallisation) circuit (131) is also provided through which the liquid (26) from the neutralising tank (24) is circulated via an electrolytic recovery unit (141) in which the tin is retrieved from the liquid material by electrolysis of the electrolysable compound.

In order to maintain the pH level in the neutralising tank (24), a pH sensor (19,) is provided which controls the pump or 6 electrovalve (201) supplying neutralising agent froin the tank (25).

A stirrer (27) for the liquid (26) is also provided 1 7

Claims

Process for obtaining tin metal from tin compounds RSn in gaseous form, characterised in that a) the tin compound RSn is hydrolysed to form a solution of tin dioxide Sn02 in an acid medium RH, b) a neutralising compound R10H is added to the acid medium RH, producing a salt RRI, the solution is circulated around a tin recovery circuit comprising an electrolytic recovery unit in which the tin Sn is retrieved by electrolysis of the tin dioxide Sn02.
2.

Process for obtaining tin metal from tin compounds Rsn in gaseous form according to the preceding claim, characterised in that the solution is circulated through a decanting/filtration circuit comprising a decanter/filter in which the solid of the salt RRI is deposited.
3. Process for obtaining tin metal from tin compounds RSn in gaseous form according to claim 1, characterised in that a pH sensor for the solution is provided which actuates an electrovalve which controls the supply of neutralising compound RfOH.
4. Process for obtaining tin metal from tin compounds RSn in gaseous form according to claim 1, characterised in that the tin compound RSn is introduced into an absorption tower having a scrubbing circuit for its hydrolysis and in which the solution formed at its base is circulated and caused to fall via a spray arrangement over the tin compound RSn, the remaining gases being discharged to the exterior.

8
5. Process for obtaining tin metal from tin compounds RSn in gaseous form according to claim 4, characterised in that at least two absorption towers are arranged in series, the gases leaving the first tower being introduced for scrubbing into the second tower and the solution formed in the second tower being introduced into the first tower.
6. Process for obtaining tin metal from tin compounds Rsn in gaseous form according to the preceding claim, characterised in that the solution formed in the first tower passes into a neutralising tank to which is supplied a neutralising agent for the acid medium from an absorbent tank.
Process for obtaining tin metal from tin compounds Rsn in gaseous form according to claim 6, characterised in that the tin recovery circuit circulates the solution formed in the neutralising tank.
8. Process for obtaining tin metal from tin compounds RSn in gaseous form according to claim 5, characterised in that the water of hydrolysis is introduced into the second tower.
9. Process for obtaining tin metal from tin compounds RSn in gaseous form according to claim 6, characterised in that the decanting/filtration circuit circulates the solution formed in the neutralising tank.
10. Process for obtaining tin metal from tin compounds RSn in gaseous form according to claim 4, characterised in that neutralising of the acid medium is performed in the absorption tower and the tin recovery circuit circulates the solution from/to the absorption tower.