The process of purification of any substance is called refining. Lead refining is no different, except that while refining we do a lot of value addition to the crude ore.
In our process of refining we use a Pyrometallurgical process for producing Lead with a purity level of 99.97%. We supply refining Kettle- furnaces of various capacities ranging from 5 – 100 tons per batch, accompanied by high efficiency natural gas burners/ furnace oil burners, equipped with pre-heating arrangements. Emissions are controlled by a flexible kettle hand, venting into a venture type wet- scrubber, attached to an Induced Draft Fan along with a chimney/ stack arrangement.
Pyrometallurgical Refining is performed in the liquid state, meaning thereby that the crude Lead needs to be melted at temperatures between 327°C (Fusion point of Lead) to 650°C. As a general rule, the process is performed in batches of 20-200 tons depending on the capacity of the plant. The chemical concept behind this refining process is the addition of specific reagents to the molten lead at appropriate temperatures. These reagents help remove the unwanted metals in a specific order, according to the process for which they are added.
We also provide additional equipment for the automatic removal of ‘dross’. On demand, we supply a range of special fluxes designed to reduce the formation of dross and increase the efficiency of the process. The refining unit complement is completed by the automatic Lead- Ingot Casting machine (with Lead pump) having the capacity of upto 25 tons/ hour. Our refining unit package is optimally configured for high output with excellent emission control.
The impurities present in crude Lead are – S, Cu, N, As, Sb, Br, Ag, Au, etc. The refining process, as mentioned earlier, is done in several steps in kettles with the addition of specific reagents. Alternatively smaller quantities can be produced via electrolytic refining. If the smelting plant stops in the fusion reduction phase what we’ll get is hard or Antimonical Lead. If the plant is meant to produce soft lead, the crude Lead obviously needs to be refined. The basic objective of refining is to remove almost all traces of Copper (Cu), Antimony (Sb), Arsenic (As), and Tin (Sn) since, as per specifications, Soft Lead cannot have more than 10 gms per ton of these impurities.
Copper (Cu) is the first element to be removed along with Sulphur (S)in a two-phased procedure. At the first stage almost all of Copper is removed as Copper Sulphide (CuS) when elementary Sulphur is added at a temperature of 450°C. The next step is to remove the remaining residual Copper by adding small amounts of elementary Sulphur at 330°C until the reaction stops.Tin (Sn) is the next to be removed through oxidation by Chlorine or Ammonium Chloride (NH4Cl). The addition of Chlorine to the molten lead at 550°C produces Tin Chloride (SnCl2) which can be mechanically removed. Simultaneously small amounts of Antimony (Sb) and Arsenic (As) are also removed by oxidation.