About Lead Refining
1. Lead recycled from used lead acid batteries or other sources (Secondary Smelting) via the Mini Blast Furnace or Rotary Furnace route, contains lot of contamination and undesired components.
2. On the other hand, Lead required for battery manufacturing is either soft Lead with 99.97% purity or hard Lead of varying Antimony compositions.
3. In order to make quality of lead suitable for its different uses, different variations of pot melting processes are employed. These include – “Re-Melting” for removal of slag, “Refining” for attaining required purity levels and “Alloying” for producing various alloys of lead.
The equipment used are the same, the consumables and the processes, however, differ.
4. Description of Melting Pot
4A. The Melting Pot (or Refining Pot or Alloying Pot, as it is variously called), is a mechanical mixing device with a pot and a heating arrangement.
4B.The inner pot is made of heavy MS plate with dish end bottom. It is placed within a jacket of refractory bricks, which in turn, are protected by an outer cover of MS plate with reinforcements.
4C. The pot is covered at the top with opening for feeding lead ingots and is provided with an electro-mechanical mixer.
4D. At the bottom, a heating source, usually an oil fired burner, is provided to heat the pot and to melt the lead.
4E. Once lead melts, impurities are skimmed and removed and any consumables required are added. Lead is then drained from the pot through an outlet pipe and valve.
4F. Capacity of such pots depends upon the requirements of particular units. Standard pot capacities made are from 4.0 TpB to 20.0 TpB. Higher capacity pots are also manufactured as required by any particular establishment.
5. A typical 10.0 TpB Refining Pot has the following standard sizes and specifications:
6. Melting pots are installed both with and without accessories which may include Ingot Casting Machine, Ball Making Machine (where Ball Mills are installed down the line), Air Pollution Control Systems, Jib Cranes etc.
7. Production Process
7A. Melting Processes have been grouped as
7B. Re-Melting Process
This process is undertaken for value addition to the recycled lead from furnaces. Lead is melted in the pot and major impurities are skimmed from it to make it saleable in the market.
7C. Refining Process
Lead is melted in the pot, additives such as Sulphur, Wooden Powder and Coke Breeze are added and mixed gently followed by dross removal. Thereafter, Tin is added to remove Copper and temperature is increased to 550-6000C. Further, additives such as Sodium Nitrate & Caustic Soda are added to remove Antimony. This process is repeated to get the desired purity of lead.
7D. Alloying Process
Lead is melted in the pot, additives such as Sulphur, Wooden Powder & Coke Breeze are added and mixed gently followed by dross removal. Thereafter, Tin & Antimony are added to the liquid metal to get the desired grade of Lead.
8. Characteristics of Air Pollution generated in Melting Pot