DE3637270A1 - HYDROMETALLURGICAL METHOD FOR RECOVERING LEAD IN THE FORM OF A PURE METAL FROM THE FILLING SIZE OF DEPLETED BATTERIES - Google Patents

Description

According to the various known processes for desulfurization of fillings, is obtained in the treatment of the Sludge from exhausted batteries with alkali or ammonium metal carbonate Solutions a solution that is practical all of the sulfur in the form of soluble sulfate (from alkali or ammonium metal) and a mixture of insoluble Lead compounds, which after leaving the Solution and careful rinsing with water practically sulfur-free is.

This mixture can be made with coal at a relatively lower Slightly reduce the temperature (800-900 ° C), without any essential Sulfur dioxide emissions and without the occurrence of leaded hard zinc.

The pyrometallurgical reduction of this product is that is the method currently most used, and also because of advantages such as high productivity long life of the reduction furnaces and the high yield of lead.

The pyrometallurgical processing of leaded substances however requires special precautions during transportation and when loading the ovens, with smoke from the ovens and volatile dust can escape.

That is why large filtration systems are required for the corresponding systems and a dense, expensive network of monitor devices for monitoring the Pb exposure of the working environment and available to the factory environment. That's why  are the processes for recovering Pb in metal form from the filling compound extremely important that able are a real alternative to pyrometallurgical processing to offer. It is mainly about to process entirely on the hydrometallurgical Way, such as electrolytic metal recovery processes (Electrowinning).

The desulfurized filling compound has the following on average Composition:

- lead carbonate (PbCO ₃ ) 50-52% - lead sulfate (PBSO ₄ ) 2.5-4% - lead peroxide (PbO ₂ ) 14-15% - lead oxide (PbO) 11-12% - lead metal (Pb) 5-7%

As is known, the practical problem of hydrometallic processing of the filling compound of old batteries is to make all components of the mixture soluble in the solution chosen for electrolysis, in particular the PbO ₂ , which is present in considerable proportions. The caustic residue of the mixture must not correspond to an unacceptable loss of lead.

On the other hand, without a pretreatment for PbO ₂ reduction, the caustic residue of the mixture, because of the known insoluble PbO ₂ contained in the normal solutions for the electrolytic process, contains a lot of lead and must be attributed to the pyrometallic recovery.

According to the known state of the art, the resolution  the components of the filling compound in the different electrolytes accomplished in different ways.

The following patents can be cited in the sequence:
- In US Pat. No. 11 48 062, CE Tucker provides for the heating of the battery sludge in order to convert the PbO ₂ into soluble PbO and PB ₂ O.
- In US Pat. No. 1,752,356, WC Smith proposes to dissolve the PbO ₂ - starting from etching with pickling alkali - to subject the filler to heating in a reducing space to form PbO.
- In US Pat. No. 19 11 604, JH Calbeck leached out the filling mass of the battery with a sodium acetate solution. The Pb oxide and the Pb sulfate pass into a solution, while the PbO _{2 is} normally insoluble in this electrolyte. In the presence of Pb metal, however, a local moment builds up in this electrolyte, so that the PbO ₂ and an equivalent amount of metal add to a solution.
- In US-PS 41 07 007 AF Gäumann leaches the filling compound with a concentrated solution of alkali metal hydrate with the addition of molasses, raw sugar or the like. The Pb oxide and the Pb sulfate thus pass into a solution and reach electrolysis. The behavior of the PbO ₂ is not described in detail.
- In US Pat. No. 4,229,271, RD Prengman proposes two ways of removing the PbO ₂ from the filling compound and completely dissolving it in the acids customary for the electrowinning process:
a) Drying the filling compound at 100 ° C and then roasting in a reducing atmosphere at temperatures between 290 and 325 ° C
b) treatment of the aqueous suspension of the filling compound with sulfur dioxide or with alkali metal or ammonium metal sulfite or bisulfite.
- In US-PS 44 60 442 U. Ducati allows the filling mass of the battery to react in the presence of a strongly alkaline solution at 100-120 ° C in order to obtain a magnetic deposit which has the property of being in warm, concentrated solutions of fluoroboron - or completely dissolve fluorosilicic acid.
- In RI 8857, AY Lee and ER Cole des Bureau of Mines propose two methods for reducing the PbO _{2 of} the filling compound:
a) adding Pb powder during leaching with fluorosilicic acid to the mass which has already been desulfurized by reaction with ammonium carbonate.
b) adding ammonium bisulfite during the desulfurization with ammonium carbonate.

The methods proposed for the thermal reduction of PbO ₂ in a reducing atmosphere have the disadvantage that they burden processing with two additional processes: drying and reducing roasting. These processing stages require strict monitoring of the working conditions and must also be carried out in a unit (oven or roasting bed) that is equipped with a dedusting system. In addition, the transport of dry material is a source of environmental pollution, even at low temperatures.

The reduction process during the caustic attack by  Adding lead powder requires moving a portion of the lead produced to form the powder and is therefore quite expensive.

The reduction process with sulfur dioxide, sulfite or bisulfite before carbonization brings certain expenses for the reagent with it, but - more importantly - leaves desulphurization carbonate consumption increases by 25%; the corresponding costs are not insignificant. Currently the carbonate costs are the highest cost center of the whole procedure.

The invention has for its object the above mentioned Hydrometallurgical treatment problems by electrowinning the desulfurized mass of exhausted To release batteries.

To achieve this object, the invention proposes a hydrometallurgical method for recovery by extraction by the electrolytic route of lead in the form of a pure metal from the filler mass or the desulfurized mass of exhausted batteries, which consists of the following stages:
a) leaching out the filling compound with an aqueous solution of an acid selected from the acids suitable for electrolytic extraction,
b) Treatment with hydrogen peroxide of the mass leached according to point a) while the following reactions are taking place:

(1) Pb ⁴⁺ + H ₂ O ₂ → Pb ²⁺ + O ₂ + 2H⁺
(2) Pb + Pb ⁴⁺ → 2Pb ²⁺

up to the quantitative reduction of all lead dioxide contained in the filling mass,
c) Elimination of the solid residue from the resulting solution containing dissolved lead, which can be led directly to the lead extraction by electrolytic means.

The starting material for the process is that of separate components of the exhausted batteries and already the desulfurization process according to the known Filling mass subjected to technology (desulphurised mass).

This material is leached out with the aqueous solution of an acid suitable for the subsequent electrolytic extraction (preferably fluoroboric or fluorosilicic acid), to which an amount of hydrogen peroxide is added which gives the highest degree of solubility of all the lead compounds present, in particular the PbO ₂ and the Pb metal to secure.

During the caustic attack of the desulfurized mass the hydrogen peroxide triggers the following reaction:

Pb ⁴⁺ + H ₂ O ₂ → Pb ²⁺ + O ₂ + 2H⁺ (1)

so that all of PbO _{2 is} reduced to PbO and is converted into solution by the acid present.

The significant amount of O _{2 released} during reaction (1) physically activates the surface of the Pb metal particles present in the desulfurized mass so that the reaction:

Pb + Pb ⁴⁺ → 2Pb ²⁺ (2)

takes place more easily and the whole Pb metal with a suitable grain structure dissolves, whereby the hydrogen peroxide corresponding to the reducing Pb ⁴⁺ is also saved.

After acidic leaching of the desulfurized mass with addition only the organic ones remain of hydrogen peroxide Fabrics (thin separator and hard rubber splinters, fibers etc.) and that which was not converted during the desulfurization Pb sulfate undissolved.

The reacted liquid-solid mixture is filtered eliminated. The fixed filter residue does not contain more than 5% of the Pb present in the starting material and can after roasting to destroy the organic matter Desulphurization stage.

The filtered solution contains all of the Pb in ion form and usually doesn't require cleaning because of that the oxygen evolved during reaction (1) physically activated Pb powder even for the shift (also called carburizing) the foreign substances that even in small quantities during the caustic attack can ignore the solution.

The self-cleaned solution can therefore go directly to the electrolytic solution Lead extraction is promoted in normal Cells with insoluble graphite anodes and with cathodes thin lead sheets.

If you work under suitable conditions, a cathode deposit of excellent quality and purity can be obtained, the PbO ₂ deposit on the anode being avoided to the greatest extent.

The small amounts of PbO ₂ that sometimes form inevitably have to be recycled to acidic leaching with hydrogen peroxide. The cathodes melted in blocks come onto the market as electrolytic lead. The solution emerging from the electrolysis is sent back for acidic leaching of the desulfurized mass.

The features and advantages of the invention are as follows based on a non-limiting, practical embodiment described in more detail.

example

980 g of well-rinsed, desulfurized mass, which in dry Condition containing 70.5% Pb, 0.68% Sb, 0.18% S leached out in 5 l of electrowinning electrolyte, the

49 g / l Pb ⁺⁺
139 g / l HBF ₄ free

contained.

After stirring at 50% for half an hour, hydrogen peroxide became (in 35% solution) equal to 4.6% of the treated mass added and at the same temperature another half Let react for an hour.

The following were filtered:

34.2% Pb 80 g insoluble composition residue 2.4% Sb 2.2% S 181.5 g / l Pb ⁺⁺ 0.6 g / l Sb ⁺⁺ 5 l leaded electrolyte with 25.1 g / l HBF ₄ free

eliminated.  

By leaching with fluoroboric acid and hydrogen peroxide were 96.01% of the total lead content of the desulfurized Mass gained. All the sulfur was left behind.

The 5 l of electrolyte containing lead were subjected to electrowinning in a cell with graphite anodes (previously coated with PbO ₂ ) and electrolytic lead cathodes made of thin sheet metal, producing 630 g of cathode Pb and 9 g of PbO ₂ at the anode.

The cell worked at 7 A and 2.5 V for 24 hours. The cathode current density was 280 A / m ² .

The current yield was 97%. The remelted cathode lead had the following composition:
, 001 - As ≦ ωτ 0.001 - Sn ≦ ωτ 0.001 - Bi ≦ ωτ 0.002 - Cu = 0.0003 - Ag ≦ ωτ 0.0005. The exhausted electrolyte, which is due to the attack of new desulfurized mass, contained:
53 g / l Pb ⁺⁺ and 131 g / l HBF ₄ free.

The attached drawing shows the block diagram of an example the inventive method.

In general, it can be said that the hydrogen peroxide offers the following advantages over the other agents proposed by the known technique for reducing the PbO ₂ :
- it is non-toxic,
it does not bring any foreign ions to the solution to be supplied for electrolysis, which has to be constantly returned,
- it is a commercially available and not too expensive reagent,
- It can be precisely dosed and is therefore not wasted because the end of the PbO ₂ reduction is indicated by a clear color change in the suspension from brown red to brown gray. This change can easily be determined by a visual inspection,
- With a consumption of 4-5% H ₂ O ₂ (in 35% solution, a Pb yield is obtained which is not less than 95%.

Claims (5)

1. Hydrometallurgical process for the recovery by extraction by the electrolytic way of lead in the form of a pure metal from the filling mass or the desulfurized mass of exhausted batteries, characterized in that it consists of the following stages:
a) leaching out the filling compound with an aqueous solution of an acid selected from the acids suitable for electrolytic extraction,
b) Treatment with hydrogen peroxide of the mass leached according to point a), with the following reactions taking place simultaneously: (1) Pb ⁴⁺ + H ₂ O ₂ → Pb ²⁺ + O ₂ + 2H +
(2) Pb + Pb ⁴⁺ → 2Pb ²⁺ up to the quantitative reduction of all lead dioxide contained in the filling compound,
c) Elimination of the solid residue from the resulting solution containing dissolved lead, which can be led directly to the lead extraction by electrolytic means. 2. The method according to claim 1, characterized in that the reaction (2) according to point b) through which in the reaction (1) Oxygen evolving according to point b) becomes. 3. The method according to claim 2, characterized in that, together with the reactions (1) and (2), carburization of the foreign substances present takes place, this effect on the Pb physically activated by the O ₂ developing during the reaction (1). Metal. 4. The method according to claim 1, characterized in that it additionally comprises the following stages:
d) treatment of the solution containing lead dissolved according to point c) by extraction by the electrolytic route with formation of lead metal cathodes,
e) Return of the exhausted electrolyte formed in stage d) to stage a) (leaching). 5. The method according to claim 1, characterized in that it the acid according to point a) is fluoroboric or fluorosisilicic acid acts.