The process manufacturing plants use to create lead is referred to as lead smelting. Lead smelting companies were once prevalent throughout the United States and other countries in the world, and lead is still required in a number of day-to-day tasks.
The Process of Smelting
Producing lead first begins with sintering. This is when lead ore gets put inside a sintering machine along with a number of other substances, which can include:
- Soda ash
- Limestone fluxes
- Pollution control particulates
These reducing substances fuse with oxidizing elements. This frees up the metal, and then reduction takes place. The material is put inside a reducing environment, which often consists of an air-starved furnace filled with carbon monoxide. Reduction involves the raw material being stripped of its last oxygen atoms to produce the final element.
Key Pieces of Equipment in Smelting
A crucial component in creating lead is the blast furnace. The furnace is a giant steel stack that typically gets lined with refractory bricks. Its purpose is to create liquid iron from chemically transforming iron oxides. Limestone, coke and iron ore are also thrown into the blast furnace. Once all these components are put inside the furnace, it generally takes between six and eight hours for everything to reach the bottom of the furnace. This material forming at the bottom is referred to as liquid slag. This liquid slag will be drained from the blast furnace. An interesting aspect of this furnace is that runs continuously, and most run for between four and ten years. It may just need to be stopped periodically so that workers can maintain it.
Another important item in this process is lead bullion, which is an impure form of lead that contains silver and gold. This material is drawn from the blast furnace, and it has to go through a drossing process. Professionals put the bullion inside a kettle to cool it down to between 700 and 800 degrees. Drossing produces two different materials: dross and molten lead. Dross is a material that consists of antimony, copper, lead oxides and possibly other elements in the concoction. Professionals obtain the dross because it moves toward the top of the lead mixture. It is skimmed off the top, and dross is sent to another furnace, this one referred to as a dross furnace. The reason for this is that non-lead minerals can be drawn from it and sent to other metal manufacturers.
The Parkes Process
This concept was first created in 1850 and patented by Alexander Parkes, hence the name. Initially, the process was not utilized in the United States. The reason for this is that it ultimately resulted in a low production of lead. However, updates to the process throughout the late 19th century resulted in the being implemented widely in 1923.
The Parkes Process uses liquid-liquid extraction to separate lead from silver. Liquid-liquid extraction consists of removing one liquid substance from another liquid item. This process is also occasionally used to remove gold from lead if it is also located in the material.
History of Lead Smelting
The process of creating lead can be traced back to 6500 B.C. Lead was created by dumping lead ore inside a furnace along with charcoal. However, it seems as though the lead was not used that often in the ancient past. The main problem was that it is too soft to be used to create a structure or forge weapons. However, it seems as though it had a number of beneficial purposes, including water storage and piping.
Lead Production in the United States
At one point, there were as many as 400 lead smelting companies throughout the United States. These plants primarily operated between 1930 and 1960. However, at this point in time, many of them have been abandoned.
Other Processes Necessary to Create Lead
To adequately produce pure lead, other processes are necessary. One is the Betterton-Kroll process. Similarly to how the Parkes Process removes silver from lead, the Betterton-Kroll process removes bismuth from the lead. It was first developed in the 1920s but was later refined in the 1930s. This is when a substance contains both lead and bismuth. It requires professionals to add magnesium and calcium to the concoction. This separates the bismuth from the lead, and the bismuth can be removed similarly to dross.
Additionally, there is the Betts electrolytic process. This process purifies lead. For numerous lead materials, it is acceptable if the lead contains impurities. However, there are times where the lead needs to be pure. This process was first developed in 1901 by Anson Gardner Betts. The process can be incredibly expensive, which is why it is typically only utilized when a high-quality lead is absolutely mandatory.
Number of Lead Smelting Plants Left
Lead smelting plants and mines can still be found around the world. Several are still located in North America. There are others located in Europe, Asia, Australia, Africa and South America. Some of these do not necessarily produce lead. Instead, they produce other precious metals, such as copper.
Lead smelting has a long, rich history, and while it is not commonly used in today’s world, people and businesses still require lead for a number of reasons. In fact, there are some companies that are trying to improve the process to make it more efficient. With the advent of new technologies combined with tried and true methods, lead smelting companies may be looking at a resurgence throughout the world.