DE66592C - Process for the electrodeposition of zinc - Google Patents

Description

In the electrolysis of the zinc from the prepared according to any method sulfuric acid zinc solutions formation indicates the so-called zinc sponge, that is, a gray fine powder, which consists essentially ¹ of zinc, but läfst difficult to melt, and partly on account of the loose condition, makes the use of electrolysis practically impossible, partly because of the difficulty in melting it. The cause of this sponge formation, which occurs in both neutral and weakly acidic solutions, has not yet been precisely identified; However, a large number of phenomena support the assumption that the zinc hydrogen Zn H _2, which appears in traces in the electrolysis of zinc, together with the nasal hydrogen which occurs at the same time in small quantities, causes a molecular change in the zinc to be deposited, which is expressed in the spongy aggregate .

The subject of the present invention now forms a method by which the formation of zinc sponges is completely prevented during the electrolysis. The process itself is based on the idea that hydrogen zinc (Zn H ₂ ) , which is the probable cause of the formation of sponges, and the nascent hydrogen that also arises through the addition of free halogens or halogen compounds, which bind the hydrogen with the formation of the hydrogen halides in question, are based on the idea remove.

In practicing this electrolysis of zinc on the basis of the present new procedure is operated as follows:

The one after some kind of technical investigation procedure neutral or weakly acidic zinc vitriol liquor obtained from ores • added before electrolysis:

a) with weak chlorine, bromine or iodine solution; ■

b) with a weak solution of free hypochlorous or hypobromous acid;

or _{oversaturated:}

c) with chlorine or bromine gas, whereby, as can be seen from the formulas below, hypochlorous acid can arise; or offset:

d) organic bodies with such water-soluble chlorine and bromine substitution products, which their chlorine or bromine with reduction to lower compounds of nascent hydrogen like the halogen-substituted, water-soluble chlorohydrins of glycerine and other glycols;

or it will be:

e) Additions from combinations of the bodies listed under a), b), c) and d) are used.

Because the amounts of the interfering with the electrolysis and to be removed zinc hydrogen and nascent hydrogen is small, so do the quantity of halogens and halogen compounds which are needed added to the bath, so that the action of the free chlorine is negligible and so on, the cathode mass during the passage of current is out of the question. The beneficial effect is therefore not impaired.

In this process it is only necessary that the liquor to be electrolyzed during the During operation, there is always a clear reaction of the free halogen or the active halogen oxygen bodies show.

The zinc deposited on the cathode after this process has in contrast to

Claims (1)

the one initially resulting from other methods gray. Zinc a light silver color and a clear crystalline structure, and from the moment the power cut off. The chemical processes at the cathode in the process described above can be clearly overlooked by the following equations, which are assumed to be the removal or suppression of zinc hydrogen (Zrc H ₂ ) or nascent hydrogen (H) as the disturbing cause of sponge formation . If according to a). In the sulfuric acid lye around the cathode there is a halogen, e.g. B. free chlorine is present, the same acts on ZnH ₁₁ and nascent H in the sense of the equations: I. «) Zn H ₂ + CL = Zn +2 H Cl,
ß) H + Cl = HCl, the hydrochloric acid being due to the great dilution does not dissolve the cathode. According to a) and ß) - resulting small amounts H Cl act on the hypochlorous acid (HOCl), which in case of Schufs of chlorine in Zinkvitriollösung always according to the equation: 2 Zn SO ₄ + 2 H ₂ O + 2 Ci ₂
= Zn Cl ₂ + Zn (H SOJ ₂ + 2 HO Cl
arises, forming chlorine again according to the equation: HCl + HO Cl = H ₂ O + Cl ₂ . If, according to b), there is free hypochlorous or hypobromous acid in the cathode liquor, then this takes place the chemical process according to: II. ZnH ₂ + HOCl = Zn + H ₂ O + HCl; H ₁ + HOCl = H ₂ O + HCl. If, according to c), the lye is oversaturated with chlorine gas, the result is according to the equation: III. "2 Zn SO ₄ + 2 H ₂ O + 2 Cl ₂ - Zn Cl ₂ + Zn (H SOJ ₂ + '2 HO Cl
hypochlorous acid (HO Cl), which acts in the sense of II. on the hydrogen products. That too. resulting HCl acts on. excess HO Cl after I. again with the formation of free chlorine, which on zinc vitriol again after III. reacts with the formation of hypochlorous acid. From III. It can be seen that at the beginning, in addition to the other bodies, Zn Cl _{2 is also} present, that is, a part of the chlorine introduced is bound to zinc. However, this chlorine is not lost for the process, but occurs again as free chlorine or. free hydrochloric acid as soon as the lye has become weakly sulfuric acid due to acid diffused from the anode. The weak sulfuric acid reacts to Zn Cl ₂ as follows: Zn Cl ₂ + H ₂ SO ₄ = Zn SO ₄ + 2 H Cl, thus forming hydrochloric acid, which in turn gives free chlorine with free hypochlorous acid (HO Cl). Is after d) a chlorine-releasing organic compound, such as monochlorohydrin of glycerine, if nascent hydrogen is present, the Reaction in terms of the following chemical equation: Monochlorohydrin and · Propylcnslyk ol C Hn Cl C Hn C HO H + 2 H = HCl + CHOH CH ₂ OH CH ₂ OH (The next lowest glycol is generally formed here). If, according to c), mixtures of the bodies mentioned are used as additives, then either the effects of free chlorine, like those of the loosely bound oxygen in case II. run next to each other. In general the effect of the additives can be summarized as the free Halogen combines with the hydrogen of the hydrogen products of the electrolysis and Hydrochloric acid forms, which in turn acts on the existing hypochlorous acid to form chlorine, which the latter again from new in the sense of the above equations in reaction, so that one therefore with one initial slight excess of chlorine in the presence of hypochlorous acid as soon as the electrodeposited hydrogen with chlorine to form hydrochloric acid in Effect occurs, again and again chlorine to the greatest extent Part can regenerate. The process can be illustrated briefly in the following formulas: a) H + Cl = H Cl,. ß) HO Cl + HCl-H ₂ O + Cl ₂ , which acts again on Zn SO ₄ with formation of HO Cl: ' Zn Cl ₂ + H ₂ SO ₄ = Zn SO ₄ + HCl, which reacts after β). Ψ ατent claim: Process for the electrolytic deposition of zinc from neutral or weakly acidic ones Zinc sulphate solutions, consisting in using the latter to prevent the formation of sponges free halogens or such inorganic or organic compounds (hypochlorous or hypobromous acid, chlorohydrins of the glycols, etc.), which under reduction give up their halogen to nascent hydrogen. . ν