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We are an important link in the chain completing
substance cycles for major
and small and medium-sized
companies of the basic substance industry and
for
galvanizers of every kind. Our international team
with specialists from
Germany, Kazakhstan, Hungary,
Poland and Finland makes us one of
Europe's most
efficient producers.
Our name obliges us to maintain a tradition:
we are RuhrZink GmbH.
Electrolysis
The neutral alkaline solution coming from the leaching plant is cooled to around 30°C, put into intermediate storage and mixed with the returning electrolyte (cell acid), which is also cooled to around between 30°C and 34°C. The solution thus produced (electrolyte) is returned to the electrolysis section. Strontium carbonate is added to the electrolyte to maintain the lead content and sodium metasilicate is also added to create smooth cathode zinc surfaces. The plaster of Paris created during the process of cooling the solution is also sold.
The zinc that has been dissolved in the electrolyte is separated as metallic zinc on cathodes in the hall of baths. The admitted fresh electrolytes contain around 45 to 55 g of zinc per litre. After running through the baths, the exiting cell acid contains around 40 g per litre. The difference is the separated zinc.
A total of 106 electrolysis cells are arranged in two rows with 85 positive (lead) anodes and 84 negative (aluminium) cathodes per cell. The separation surface on each cathode (front and rear) is 3.5 m². The cells are arranged "in-line" so that the flow of electricity is the same through all cells. With a direct current through all cells amounting up to 160,000 amperes, the equivalent of a potential drop of around 375 volts per cell, i.e. 3.5 volts, is achieved. This produces a current density of around 500 A/m² m over the entire surface of the cathodes on each cell. The hall of baths therefore possesses an electric capacity in excess of 60,000 kW. The power is supplied through three adjustable transformer-rectifier units that are able to supply the electrolysis processes with a maximum direct current of 165 kA.
Electrolysis processesThe zinc contained in the electrolytes processes a positive dual zinc ion (Zn2+). In order to be able to precipitate as neutral zinc metal, every zinc ion requires two (negatively charged) electrons, which it may "extract" from the cathode. The cathode reaction is: Zn2+ + 2e- = Zn°. This process can "actually" not work due to the fact that the hydrogen ions (H+ ) which possess a more favourable potential than zinc ions – are primarily neutralized at the cathodes, i.e. attempt to take the electrons to produce hydrogen gas (H2). However, the so-called "hydrogen overpotential", which cancels out of the hydrogen's potential advantage, makes the separation of zinc possible. Porous, soft and low adhesive zinc may be the consequence of contaminated electrolyte.
The cathodes are extracted from the basins every 24 to 48 hours and conveyed by two semi-automatic transporters to the stripping machines where the separated zinc is stripped from the cathodes and subsequently stacked for further processing. The cathodes are then brushed and washed and returned to the baths.
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