136
5 Recovery of Metals from Electronic Waste
– Plastic components of the e-waste cannot be easily recovered, as there are a
mixture of flame-retardants, pigments and different types of plastics. However,
the plastics could partially replace coke as a source of energy during the smelting
process and hence help to reduce the energy usage.
– Fe and Al cannot be easily recovered as they are transferred to the slag phase as
oxides.
– Some e-waste components such as silicon chips or bare fiberglass boards cannot
be recovered.
– Smelting of the halogenated flame retardants and Polyvinyl Chloride (PVC)
components of e-waste could produce dioxins, requiring special emission control
measures to minimize environmental pollution.
– The pyrometallurgical processes are normally followed by a hydrometallurgical
and electrochemical processing to fully separate the precious metals.
– Installation of integrated e-waste recycling facilities with the maximum recovery
of precious metals requires high investment.
– The fine dusts of the non-metallic components of e-waste may burn instantly
before reaching the metal bath, a potential fire hazard risk. Agglomeration of fine
dusts might be required to mitigate this risk.
– The volume of the produced slag increased by the presence of ceramic components
in e-waste feedstock, which could result in losing precious metals during the
recovery process.
– The smelting/refining processes are difficult to handle due to the complex
compositions of the feeding materials.
– The pyrometallurgical processes have high energy demand and costs.
5.8.1.1 Smelting in Furnaces
E-waste is usually treated by physical methods (sorting, dismantling, size reduction
and separation of metals and plastics) before it is fed into a smelting process. Smelting
is performed in furnaces at high temperatures to liberate the valuable metals. The
precious metals are then separated by dissolving to form a solution metal phase
(copper or lead) and an oxides slag phase [21]. The general procedure for the recovery
of metals through smelting is shown in Fig. 5.2.
The smelting routes for two main metals, i.e., lead and copper, are detailed below:
– Lead smelting route
In this process, sulfide ores are treated with e-waste to extract the lead and precious
metals. In the first stage of sintering, the sulfur content of the feed material is reduced
in blast furnaces by using coke and the plastic fraction of the e-waste as the reducing
agents. The resulted molten lead has a purity of about 85%. The lead dross is then
refined by skimming off the copper dross. The copper dross is then transferred to a
reverberatory furnace. The lead dross is treated with wood chips, fine coke and sulfur
and the produced sulfur dross are transferred to the reverberatory furnace. During
the refining stage, the lead bullion, copper matte (a solution of copper sulfide and a
5 Recovery of Metals from Electronic Waste
– Plastic components of the e-waste cannot be easily recovered, as there are a
mixture of flame-retardants, pigments and different types of plastics. However,
the plastics could partially replace coke as a source of energy during the smelting
process and hence help to reduce the energy usage.
– Fe and Al cannot be easily recovered as they are transferred to the slag phase as
oxides.
– Some e-waste components such as silicon chips or bare fiberglass boards cannot
be recovered.
– Smelting of the halogenated flame retardants and Polyvinyl Chloride (PVC)
components of e-waste could produce dioxins, requiring special emission control
measures to minimize environmental pollution.
– The pyrometallurgical processes are normally followed by a hydrometallurgical
and electrochemical processing to fully separate the precious metals.
– Installation of integrated e-waste recycling facilities with the maximum recovery
of precious metals requires high investment.
– The fine dusts of the non-metallic components of e-waste may burn instantly
before reaching the metal bath, a potential fire hazard risk. Agglomeration of fine
dusts might be required to mitigate this risk.
– The volume of the produced slag increased by the presence of ceramic components
in e-waste feedstock, which could result in losing precious metals during the
recovery process.
– The smelting/refining processes are difficult to handle due to the complex
compositions of the feeding materials.
– The pyrometallurgical processes have high energy demand and costs.
5.8.1.1 Smelting in Furnaces
E-waste is usually treated by physical methods (sorting, dismantling, size reduction
and separation of metals and plastics) before it is fed into a smelting process. Smelting
is performed in furnaces at high temperatures to liberate the valuable metals. The
precious metals are then separated by dissolving to form a solution metal phase
(copper or lead) and an oxides slag phase [21]. The general procedure for the recovery
of metals through smelting is shown in Fig. 5.2.
The smelting routes for two main metals, i.e., lead and copper, are detailed below:
– Lead smelting route
In this process, sulfide ores are treated with e-waste to extract the lead and precious
metals. In the first stage of sintering, the sulfur content of the feed material is reduced
in blast furnaces by using coke and the plastic fraction of the e-waste as the reducing
agents. The resulted molten lead has a purity of about 85%. The lead dross is then
refined by skimming off the copper dross. The copper dross is then transferred to a
reverberatory furnace. The lead dross is treated with wood chips, fine coke and sulfur
and the produced sulfur dross are transferred to the reverberatory furnace. During
the refining stage, the lead bullion, copper matte (a solution of copper sulfide and a